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Mon. Not. R. Astron. Soc. 419, 3505­3520 (2012)

doi:10.1111/j.1365-2966.2011.19993.x

The Herschel Virgo Cluster Survey ­ VIII. The Bright Galaxy Sample
J. I. Davies,1 S. Bianchi,2 L. Cortese,3 R. Auld,1 M. Baes,4 G. J. Bendo,5 A. Boselli, L. Ciesla,6 M. Clemens,7 E. Corbelli,2 I. De Looze,4 S. di Serego Alighieri,2 J. Fritz,4 G. Gavazzi,8 C. Pappalardo,2 M. Grossi,9 L. K. Hunt,2 S. Madden,10 L. Magrini,2 M. Pohlen,1 M. W. L. Smith,1 J. Verstappen4 and C. Vlahakis11
1 2

6

School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA INAF-Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy 3 European Southern Observatory, Karl-Schwarzschild Strasse 2, 85748 Garching bei Muenchen, Germany 4 Sterrenkundig Observatorium, Universiteit Gent, KrijgslAAn 281 S9, B-9000 Gent, Belgium 5 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL 6 Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS, 38 rue F. Joliot-Curie, F-13388 Marseille, France 7 INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy 8 Universita' di Milano-Bicocca, piazza della Scienza 3, 20100 Milano, Italy 9 CAAUL, Observatorio Astronomico de Lisboa, Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal ´ ´ 10 Laboratoire AIM, CEA/DSM - CNRS - Universite Paris Diderot, Irfu/Service, Paris, France ´ 11 Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile

Accepted 2011 October 11. Received 2011 September 30; in original form 2011 May 19

ABSTRACT

We describe the Herschel Virgo Cluster Survey and the first data that cover the complete survey area (four 4 â 4 deg2 regions). We use these data to measure and compare the global far-infrared properties of 78 optically bright galaxies that are selected at 500 µm and detected in all five far-infrared bands. We show that our measurements and calibration are broadly consistent with previous data obtained by the IRAS, ISO, Spitzer and Planck. We use SPIRE and PACS photometry data to produce 100-, 160-, 250-, 350- and 500-µm cluster luminosity distributions. These luminosity distributions are not power laws, but `peaked', with small numbers of both faint and bright galaxies. We measure a cluster 100­500 µm far-infrared luminosity density of 1.6(7.0) ± 0.2 â 109 L Mpc-3 . This compares to a cluster 0.4­2.5 µm optical luminosity density of 5.0(20.0) â 109 L Mpc-3 , some 3.2(2.9) times larger than the far-infrared. A `typical' photon originates from an optical depth of 0.4 ± 0.1. Most of our sample galaxies are well fitted by a single modified blackbody ( = 2), leading to a mean dust mass of log MDust = 7.31 M and temperature of 20.0 K. We also derive both stellar and atomic hydrogen masses from which we calculate mean values for the star-to-gas (atomic) and gas (atomic)-to-dust mass ratios of 15.1 and 58.2, respectively. Using our derived dust, atomic gas and stellar masses, we estimate cluster mass densities of 8.6(27.8) â 106 , 4.6(13.9) â 108 and 7.8(29.7) â 109 M Mpc-3 for dust, atomic gas and stars, respectively. These values are higher than those derived for field galaxies by factors of 39(126), 6(18) and 34(129), respectively. In the above, the luminosity/mass densities are given using the whole sample with the values in brackets using just those galaxies that lie between 17 and 23 Mpc. We provide a data table of flux densities in all the Herschel bands for all 78 bright Virgo Cluster galaxies. Key words: galaxies: clusters: individual: Virgo ­ galaxies: general ­ galaxies: ISM.

1 I NTR O DUCTION
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. E-mail: jid@astro.cf.ac.uk
C 2011 The Authors Monthly Notices of the Royal Astronomical Society

The spectacular number of large diffuse nebulae in the constellation of Virgo has attracted the attention of astronomers for centuries. We now know the nebulae to be galaxies and that they reside in the largest nearby galaxy cluster. The cluster consists of many

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nearby galaxies at wavelengths at or just beyond that observed by the IRAS (out to about 200 µm) with the Spitzer Infrared Nearby Galaxy Survey sample being of particular importance in helping us understand the far-infrared properties of galaxies (Kennicutt et al. 2003). Both the ISO and Spitzer have been somewhat limited in what can be inferred about the cold dust issue for three reasons. The first is that the wavelength coverage is not in the critical wavelength region where we expect to detect the signature of cold dust (200­600 µm). The second is that these were not survey telescopes and so they did not provide objectively selected large samples of galaxies for comparative study at the wavelengths of interest. Thirdly, because small quantities of warm dust can swamp the signal from cold dust, it is important to have sufficient spatial resolution to identify regions in the galaxy where cold dust emission is dominant. Although SCUBA observations at 850 µm (Alton et al. 1998b; Bianchi et al. 2000b; Dunne et al. 2000; Vlahakis et al. 2005) have also attempted to address the above issues, with the advent of the Herschel Space Telescope, these problems we hope can be solved conclusively. The observations of Virgo Cluster galaxies described below make use of the unique imaging qualities and sensitivity of Herschel at five wavelengths from 100 to 500 µm. With a 3.5-m mirror, the spatial resolution of Herschel at these wavelengths ranges from 7 to 35 arcsec, enabling spatially resolved observations of many of the bright galaxies at the distance of Virgo. The Herschel Virgo Cluster Survey (HeViCS) is an approved ESA Herschel Space Telescope (Pilbratt et al. 2010) Open Time Key Project. The project has been awarded 286 hours of observing time in parallel mode using tle PACS (Poglitsch et al. 2010) at 100 and 160 µm, and SPIRE (Griffin et al. 2010) at 250, 350 and 500 µm. Eventually, we will map four 4â4 deg2 regions of the cluster down to the confusion limit in the SPIRE bands. Pre-Herschel comparable surveys describing the farinfrared properties of nearby bright galaxies have been described by Soifer et al. (1987), Doyon & Joseph (1989) (IRAS), Tuffs et al. (2002) (ISO) and Draine et al. (2007) (Spitzer). In this paper, we describe results from an initial data release that covers the entire HeViCS area but using only a quarter of the scans that will constitute the final data set. For this reason, this paper concentrates on the properties of the bright galaxies because these are still detected at high signal-to-noise ratio (S/N) even in these as yet incomplete data. The primary HeViCS science goals using the full depth data include the detection of dust in the intergalactic medium, the extent of cold dust in the outskirts of galaxies, far-infrared luminosity functions, the complete spectral energy distributions (SEDs) of galaxies, the dust content of dwarf ellipticals and irregulars, and a detailed analysis of the dust content of early-type galaxies (for further details, visit http://www.hevics.org). This paper is an extension of a previous paper (Paper I, Davies et al. 2010), of this series of papers, that considered the properties of the bright galaxies in a single central 4 â 4 deg2 HeViCS field. In the other six papers (of this series) on this central field, we have discussed how the cluster environment truncates the dust discs of spiral galaxies (Paper II, Cortese et al. 2010), the dust lifetime in early-type galaxies (Paper III, Clemens et al. 2010), the spiral galaxy dust surface density and temperature distribution (Paper IV, Smith et al. 2010), the properties of metal-poor star-forming dwarf galaxies (Paper V, Grossi et al. 2010), the lack of thermal emission from the elliptical galaxy M87 (Paper VI, Baes et al. 2010), and the far-infrared detection of dwarf elliptical galaxies (Paper VII, De Looze et al. 2010). Another paper (Boselli et al. 2010) discusses the SEDs of HeViCS galaxies together with others observed as part of the Herschel Reference Survey (HRS).
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thousands of galaxies both physically large and small, and because of its proximity (v 1094 km s-1 , Binggeli, Tammann & Sandage 1987; d 17 Mpc, Gavazzi et al. 1999; d 16.5 Mpc, Mei et al. 2007) the largest galaxies subtend some of the biggest angular sizes (10 arcmin) in the sky. These big bright galaxies occupy a relatively small area (100 deg2 ) and so, over the years, the whole region has been subject to extensive `survey' observations. Recent surveys range from the X-ray (Boehringer et al. 1994), ultraviolet (Boselli et al. 2011), optical (Virgo Cluster Catalogue, hereinafter VCC, Binggeli, Sandage & Tammann 1985; SDSS, Abazajian et al. 2009; VGVS, Mei et al. 2010), near-infrared (Two-Micron All-Sky Survey, hereinafter 2MASS, Skrutskie et al. 2006; UKIDSS, Warren et al. 2007), far-infrared (IRAS, Neugebauer et al. 1984) and 21 cm (ALFALFA, Giovanelli et al. 2005; VIVA, Chung et al. 2009; AGES, Taylor 2010). These extensive large data sets provide us with a unique opportunity to study in detail a large number of galaxies at high spatial resolution. However, the properties of cluster galaxies may not be typical of galaxies in general. The environment of a galaxy cluster is very different from that of other less densely populated `field' regions of the Universe. The proximity of other galaxies and the existence of an intergalactic medium means that Virgo Cluster galaxies probably evolve in ways that are in detail quite different from that of field galaxies. For example, in the cluster, the morphological mix of galaxies is quite different from that in the field and many galaxies are observed to be relatively deficient in atomic gas (Haynes & Giovanelli 1984). This deficiency in gas is probably responsible for the observed lower star formation rates (Lewis et al. 2002; Gomez et al. 2003) and the truncation of star-forming discs (Boselli & Gavazzi 2006) seen in cluster galaxies. An understanding of the prime physical processes that influence how a galaxy changes and evolves with time is a primary motivation for the study of galaxies in the nearby Universe, particularly the identification of processes unique to the cluster environment. Given that the very essence of what a galaxy does is to form stars, and hence convert primordial gas into heavy elements (metals), the fractional mass of these elements compared to the gas is a primary indicator of how far a galaxy has proceeded along its evolutionary path. A major depository of these metals is in the interstellar dust, and an important and outstanding legacy from the hugely successful IRAS survey of the 1980s has been the question of determining the total quantity of dust in galaxies. The issue has been outstanding because the IRAS with a maximum wavelength of 100 µm measured warm dust in galaxies (generally T 30+ K), leading to gas-todust mass ratios higher by about a factor of 10 than that observed in our Galaxy (measured by other means, i.e. stellar extinction). They are also much higher than expected using chemical evolution models that predict the fractional mass of dust produced in each generation of stars (Dwek 1998; Edmunds & Eales 1998). The open question since then has been just how much cold dust (T 20 K) remains undetected in galaxies and whether this can reconcile our local observations of the Milky Way and the dust-production models. There have, of course, been other far-infrared space missions since the IRAS that have to some extent addressed the cold dust issue. In particular, Tuffs et al. (2002) and Popescu et al. (2002) discuss this, amongst other issues, using bright Virgo Cluster galaxies observed by the Infra-red Space Observatory (ISO). Other ISO observations of individual galaxies which specifically address the cold dust issue have been described by Alton et al. (1998a), Davies et al. (1999), Trewhella et al. (2000), Bendo et al. (2002) and Bendo et al. (2003). The Spitzer Space Telescope has also made observations of


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Figure 1. The Virgo Cluster. On the left-hand side is shown the area (100 deg2 ) observed as part of the Binggeli et al. (1987) survey which led to the VCC of some 2000 galaxies. Each VCC galaxy is marked as a circle. The area (64 deg2 ) covered by the HeViCS is indicated by the red boxes. X-ray contours as observed by the ROSAT are shown in blue (Boehringer et al., 1994). On the right-hand side are the four fields as observed by Herschel (SPIRE) at 250 µm. Bright galaxies can be seen as white dots. Prominent on the frames is the emission from the Galactic cirrus.

2 O BSER VATIONS, D AT A REDUCTION, OBJECT SELECTION AND CALIBRATION CHECKS We have obtained 64 deg2 of data over four fields covering a large part of the Virgo Cluster using the SPIRE/PACS parallel scanmap mode (Fig. 1). We use nominal detector settings and a fast scan rate of 60 arcsec s-1 over two orthogonal cross-linked scan directions. Here we discuss combined data from two scans per field (the complete survey will comprise eight scans). PACS data reduction was carried out with the standard pipeline for both the 100- and the 160-µm channels. Dead and saturated pixels were masked. Deglitching was performed in two steps, using the standard multiwavelength median transform deglitcher and another based on sigma-clipping. Bright sources were masked before a highpass filter was used to reduce 1/f noise. Finally, the two orthogonal scans were combined and maps made using the naive map-maker. Overall, the HeViCS PACS data reduction strategy is similar to the approach used for the Herschel-ATLAS key programme (Eales et al. 2010), as explained in detail in Ibar et al. (2010). After combining orthogonal scans, the full width at half-maximum (FWHM) beam sizes are approximately 9 and 13 arcsec with pixel sizes of 3.2 and 6.4 arcsec for the 100- and 160-µm channels, respectively. The SPIRE photometer (Griffin et al. 2010) data were processed up to Level 1 (to the level where the pointed photometer time-lines have been derived) with a custom-driven pipeline script adapted
C 2011 The Authors, MNRAS 419, 3505­3520 Monthly Notices of the Royal Astronomical Society

from the official pipeline (POF5_pipeline.py, dated 2010 June 8) as provided by the SPIRE Instrument Control Centre (ICC).1 This JYTHON script was run in the Herschel Interactive Processing Environment (Ott 2010). Our data reduction up to Level 1 is very similar to the Herschel Common Science System/Standard Product Generation v5 with a calibration based on Neptune data. Specific differences from the standard pipeline were that we used sigmaKappaDeglitcher instead of the ICC-default waveletDeglitcher. Furthermore, we did not run the default temperatureDriftCorrection and the residual, median baseline subtraction. Instead we use a custom method called BriGAdE (Smith et al., in preparation) to remove the temperature drift and bring all bolometers to the same level (equivalent to baseline removal). We have found this method improves the baseline subtraction significantly, especially in cases where there are strong temperature variations during the observation. Both scans were then combined to make our final maps using the naive mapper provided in the standard pipeline. The FWHMs of the SPIRE beams are 18.1, 25.2 and 36.9 arcsec with pixel sizes of 6, 10 and 14 arcsec at 250, 350 and 500 µm, respectively. The final data products have a mean 1 noise, determined from the whole of

1

See `The SPIRE Analogue Signal Chain and Photometer Detector Data Processing Pipeline' (Griffin et al. 2009 or Dowell et al. 2010) for a more detailed description of the pipeline and a list of the individual modules.

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centroiding the 500-µm data, and the velocities and distances have been taken from GOLDMINE (Gavazzi et al. 2003). The fluxes in Table 1 do not include colour corrections (see Section 5). For both PACS and SPIRE data, we can make some comparisons of our results with those obtained by others. Where available (73 galaxies) we have taken IRAS 100-µm fluxes from the GOLDMINE data base (Gavazzi et al. 2003) and show their comparison with the PACS in Fig. 2. UGC 7557 stands out as being the only obvious anomalous result, as we measure a barely detected value of 0.13 Jy, while the IRAS value is 0.73 Jy. A linear least-squares fit to the data gives the relationship F (PACS) = 1.16(±0.02)F (IR AS ) - 0.69(±0.47). Using the ISO, Tuffs et al. (2002) also measured 100-µm fluxes for 12 of our galaxies (see Fig. 2). The linear least-squares fit to these data gives the relationship F (PACS) = 2.52(±0.16)F (ISO) - 3.51(±1.71). This is the least good of our comparison calibrations with an indication that the largest fluxes correspond less well. NGC 4567 has a PACS 100-µm flux a factor of 2.6 larger than that measured by the ISO (76.3 compared with 29.3 Jy; Fig. 2), but it is very close to NGC 4568 and will be difficult to separate it from NGC 4568 in the lower resolution ISO data. Spitzer 160-µm data exist for 44 out of the 78 galaxies in our sample (Bendo, in preparation; see Fig. 3). A linear least-squares fit to the data gives F (PACS) = 0.97(±0.02)F (MIPS) + 1.16(±0.56). There appears to be just a small calibration of-set (PACS fluxes are higher) between the PACS and MIPS. There are 14 galaxies from the ISOPHOT 170-µm Serendipity Survey (Stickel et al. 2004) that are in common with our survey, and we compare these fluxes with ours in Fig. 3. Comparing these 14 galaxies with our 160-µm data, we obtain F (PACS) = 0.60(±0.05)F (ISO) + 2.4(±1.12). Here there is a larger discrepancy between the two data sets which appears to be entirely due to NGC 4192 with the ISO measurement almost twice that of the PACS (66.6 compared to 37.7 Jy). Removing NGC 4192 from the sample gives F (PACS) = 0.94(±0.05)F (ISO) + 0.16(±0.48). There are also 12 galaxies measured at 170 µm in the ISO survey of Tuffs et al. (2002) (see Fig. 3). A linear least-squares fit to these data gives F (PACS) = 0.93(±0.05)F (ISO) + 2.11(±1.47). Finally, the Planck Consortium have released a point source catalogue of bright sources which, at 350 µm, contains 17 of the galaxies in our list. In Fig. 2, we compare these 350-µm flux densities (we use the flux within an aperture of radius = FWHM) with our SPIRE data, obtaining the relationship F (SPIRE) = 0.98(±0.05)F (Pl a nck ) - 0.37(±0.45); only NGC 4260 stands out as being an anomaly with regard to the SPIRE and Planck.

each image, of 2.6, 4.5, 0.9, 1.1 and 1.3 mJy pixel-1 at 100, 160, 250, 350 and 500 µm, respectively. To obtain a bright far-infrared selected sample, we carried out our initial object selection at 500 µm. This is because it is the least explored part of the spectrum, it has the lowest resolution, and most galaxies will produce their lowest flux in this band, guaranteeing a detection in all five bands. To produce an objectively selected sample, we used the automatic image detection algorithm SEXTRACTOR (Bertin & Arnouts 1996). To minimize background contamination by faint sources, each object was required to have more than 30 connected pixels at 1.5500 or above. The result is a 500 µm flux density limit of 0.1 Jy for sources with a diameter larger than 1.4 arcmin. Each object was then checked for correspondence with a known Virgo Cluster galaxy. The final sample consists of 78 Virgo Cluster objects, which is 12 per cent of the 629 VCC galaxies in our fields that are listed by GOLDMINE as confirmed cluster members (Gavazzi et al. 2003). Discarded objects are either associated with extended galactic cirrus emission or objects in the background of Virgo. In this paper, our intention is to concentrate on these bright galaxies detected at high S/N. The faintest galaxy in the final sample (see below) being detected with a S/N of 15. Before carrying out aperture photometry on the selected galaxies, the data at other wavelengths were smoothed and re-gridded to the 500-µm resolution and pixel scale. Elliptical apertures were initially chosen by eye using the 500-µm data, with the sky defined by a concentric annulus. These same annuli were then used on the smoothed and re-gridded data at other wavelengths. Independent measurements were carried out on the maps at the original resolution, defining for each galaxy a polygonal aperture that included all pixels with S/N 2 at 250 µm (the deepest band), and a nearby sky aperture that avoided pixels contaminated by bright background sources. Our results from these two approaches are significantly affected by the apertures chosen and after careful analysis we estimate errors of 17, 10, 8, 8 and 10 per cent at 100, 160, 250, 350 and 500 µm, respectively, due to the choices made. Independently as part of the HRS data analysis, Ciesla et al. (in preparation) have compared our SPIRE aperture photometry with that derived using apertures set at 1.4 times the galaxy's optical radius and a 60 arcsec width annulus for the background. Mean values of the flux density ratios between these HRS values and those given here are 0.98 ± 0.06, 0.96 ± 0.08 and 0.96 ± 0.09 for 250, 350 and 500 µm, respectively. The scatter between the Ciesla et al. values and those quoted here is 6, 8 and 10 per cent, respectively, that is, very close to the SPIRE aperture uncertainty we estimated above. As shown in Fig. 1, the four separate 4 â 4 deg2 fields have a small overlap region. A few of our galaxies fall within these overlap regions and so have been observed independently twice. Also, two of the fields have already been observed with more than two scans. Using the same apertures on these independent measurements leads to an uncertainty in flux values due to noise in the data recording and processing of 20, 10, 2, 3 and 5 per cent at 100, 160, 250, 350 and 500 µm, respectively. The absolute calibration of the data is thought to be uncertain to 15, 15, 7, 7 and 7 per cent at 100, 160, 250, 350 and 500 µm, respectively (Ibar et al. 2010; Swinyard et al. 2010). Taking the above three uncertainties to be independent, we estimate total uncertainties in our flux values of 30 20, 10, 10 and 15 per cent at 100, 160, 250, 350 and 500 µm, respectively. In Table 1, we list all 78 Virgo bright galaxies with their names, coordinates, velocities, distances and flux values in each band. The coordinates are obtained from

3 L UMINOSITY F UNCTIONS AND DISTRIB U TIONS Cosmic dust contributes only a small fraction of the total baryonic mass of galaxies, but although small in mass, it plays a prominent role in how galaxies evolve with time. For example, dust is thought to be the major site for the formation of molecular hydrogen. Radiative cooling by dust grains allows this molecular gas to collapse to form stars and the residual dust is probably a major contributor to the material that forms protoplanetary discs and eventually planets. The link between dust and the formation of stars is confirmed by the close correlation of far-infrared emission at shorter wavelengths (<100 µm) and the star formation rate measured by other means (e.g. Calzetti et al. 2010). Longer wavelength dust emission is probably associated with more extensive colder material distributed throughout galaxies (Bendo et al. 2010, 2011). The comparative
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Herschel Virgo Cluster Survey ­ VIII
Table 1. The HeViCS Bright Galaxy Sample. Column (1): name; columns (2) and (3): position; column (4): velocity; column (5): distance; and column (6): far-infrared flux density. Note that NGC 4567 and 4568 are very close together and so it is difficult to separate the measurements of one from the other. (1) Name (2) RA (J2000) 12:12:12.6 12:12:32.6 12:13:47.8 12:13:48.4 12:13:53.7 12:14:38.8 12:15:04.6 12:15:17.1 12:15:39.0 12:15:54.9 12:16:22.5 12:17:09.2 12:17:11.5 12:17:25.6 12:18:00.1 12:18:31.6 12:18:49.7 12:19:21.2 12:19:42.7 12:19:56.1 12:20:17.8 12:21:02.9 12:21:17.8 12:21:33.3 12:21:40.7 12:21:42.4 12:21:55.1 12:22:05.7 12:22:12.1 12:22:27.6 12:22:31.3 12:22:38.4 12:22:38.7 12:22:42.0 12:22:54.9 12:23:06.6 12:23:17.2 12:23:38.3 12:23:43.7 12:23:47.3 12:24:01.5 12:24:07.7 12:25:03.7 12:25:18.4 12:25:18.5 12:25:22.0 12:25:42.8 12:25:47.5 12:25:51.5 12:25:54.1 12:26:07.4 12:26:29.6 12:26:32.3 12:26:36.5 12:26:46.8 12:26:47.6 12:27:09.8 12:27:10.4 12:27:11.3 (3) Dec. (J2000) 13:14:40.0 12:07:22.1 13:25:32.1 14:54:00.5 13:10:22.0 05:48:23.0 14:01:42.9 13:01:28.4 13:54:08.7 13:08:52.7 13:18:20.9 03:40:51.1 15:19:26.6 06:41:19.6 06:39:00.2 05:33:53.6 14:25:10.8 06:06:03.2 05:32:18.6 05:20:36.3 04:12:04.8 03:43:24.7 11:30:37.8 14:36:15.2 11:30:02.6 14:35:50.4 04:28:27.8 09:02:29.0 07:08:43.9 04:33:49.3 15:32:19.0 11:48:01.5 06:40:37.3 09:20:00.0 15:49:24.8 05:15:03.8 11:22:02.0 06:57:20.6 12:28:40.7 07:11:23.8 12:12:17.4 06:36:22.9 12:52:55.4 05:44:30.1 04:55:23.4 10:01:06.3 07:13:01.3 12:39:44.7 10:27:33.3 07:33:19.5 13:06:44.7 08:52:19.8 12:36:38.2 03:57:55.6 07:55:06.8 08:52:54.2 05:52:56.5 07:15:58.7 09:25:14.5 (4) v (km s-1 ) 1862 2209 2114 -139 2470 2062 2316 704 -88 139 229 2031 865 2239 732 864 2404 1935 1617 2379 1732 2541 355 1136 232 1150 1566 1035 1071 1278 148 1442 2362 1250 1575 1668 1563 1013 -430 1420 2316 727 910 1138 2557 963 993 2515 1101 1202 230 1278 103 2289 1390 1272 1120 932 437 (5) D (Mpc) 32.0 32.0 32.0 17.0 32.0 32.0 17.0 17.0 17.0 17.0 17.0 32.0 17.0 32.0 23.0 32.0 17.0 23.0 32.0 32.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 23.0 23.0 17.0 17.0 17.0 23.0 23.0 17.0 17.0 17.0 23.0 17.0 23.0 17.0 23.0 17.0 23.0 17.0 23.0 23.0 17.0 23.0 23.0 17.0 23.0 17.0 17.0 17.0 23.0 23.0 23.0 23.0 (6) F250 (Jy) 0.81 1.81 6.91 27.75 3.51 3.37 1.56 3.56 12.96 21.10 3.35 2.11 7.38 1.17 1.03 0.35 65.45 0.88 1.30 10.45 0.94 2.29 4.16 11.89 2.41 18.67 54.57 4.58 1.10 0.81 4.19 4.11 0.90 4.91 68.31 1.94 3.54 3.60 0.72 1.06 1.41 0.79 0.27 1.06 3.36 4.91 4.91 8.64 1.89 1.85 14.50 1.11 2.50 2.77 2.39 2.25 0.99 1.14 2.47

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F500 (Jy) 0.15 0.40 0.99 5.07 0.68 0.67 0.32 1.08 1.85 3.93 0.86 0.31 1.01 0.23 0.32 0.12 8.79 0.16 0.17 1.47 0.19 0.48 0.89 1.66 0.46 2.89 8.08 0.72 0.22 0.17 0.55 0.62 0.20 0.84 9.98 0.36 0.74 0.58 0.17 0.22 0.26 0.17 0.13 0.23 0.56 0.76 1.02 1.25 0.40 0.36 2.08 0.26 0.44 0.36 0.40 0.56 0.30 0.36 0.32

F350 (Jy) 0.38 0.96 2.88 12.87 1.68 1.68 0.77 2.20 5.33 9.99 1.95 0.93 3.00 0.59 0.62 0.24 26.29 0.44 0.53 4.20 0.48 1.22 2.06 4.94 1.16 8.24 22.55 2.06 0.55 0.45 1.66 1.81 0.46 2.16 28.54 0.95 1.80 1.59 0.40 0.53 0.68 0.41 0.15 0.54 1.85 2.23 2.45 3.50 0.94 0.91 6.08 0.60 1.16 1.11 1.08 1.24 0.59 0.73 0.96

F160 (Jy) 1.19 3.04 12.26 37.65 6.93 6.37 2.35 4.69 26.77 31.89 4.19 4.80 15.16 1.86 1.25 0.55 130.99 1.33 2.63 24.31 1.52 3.14 7.27 21.95 4.75 30.44 114.90 7.75 2.03 1.44 8.62 8.23 1.40 9.12 109.45 2.71 5.19 6.70 1.37 1.37 2.65 1.50 0.86 2.76 1.10 6.17 8.35 20.68 2.85 2.99 28.15 1.58 4.36 6.60 4.79 2.62 1.93 0.74 5.52

F100 (Jy) 0.61 0.99 11.34 24.24 2.62 6.32 1.68 2.35 21.78 16.47 4.02 4.73 10.81 0.44 0.38 0.61 114.25 0.68 1.64 26.01 0.87 2.31 5.78 15.62 4.83 18.73 102.95 4.71 1.70 1.52 7.33 4.73 0.81 5.92 76.34 1.69 2.42 5.53 0.80 0.95 1.41 1.77 1.14 1.60 1.00 3.04 5.87 21.41 1.61 2.67 21.15 0.94 1.94 6.88 2.93 1.08 1.15 0.13 6.21

NGC 4165 IC 00769 NGC 4189 NGC 4192 NGC 4193 NGC 4197 IC 03061 NGC 4206 NGC 4212 NGC 4216 NGC 4222 NGC 4234 NGC 4237 NGC 4241 IC 03115 NGC 4252 NGC 4254 NGC 4260 NGC 4266 NGC 4273 UGC 7387 NGC 4289 NGC 4294 NGC 4298 NGC 4299 NGC 4302 NGC 4303 NGC 4307 NGC 4309 NGC 4301 NGC 4312 NGC 4313 IC 03225 NGC 4316 NGC 4321 NGC 4324 NGC 4330 NGC 4343 IC 03258 IC 03259 NGC 4351 IC 03268 NGC 4374 NGC 4376 NGC 4378 NGC 4380 UGC 7513 NGC 4388 NGC 4390 IC 03322 NGC 4402 UGC7537 NGC 4413 NGC 4412 NGC 4416 UGC 7546 NGC 4423 UGC 7557 NGC 4424

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Table 1 ­ continued (1) Name (2) RA (J2000) 12:27:40.3 12:27:44.7 12:28:15.9 12:28:40.6 12:29:00.1 12:29:28.1 12:29:29.9 12:29:37.9 12:30:49.2 12:30:59.6 12:32:40.9 12:33:30.5 12:33:39.7 12:34:03.1 12:34:16.0 12:34:20.1 12:34:39.3 12:36:32.4 12:36:33.9 (3) Dec. (J2000) 13:04:43.9 13:00:25.5 09:26:10.4 09:15:40.7 13:58:46.0 08:44:58.7 07:41:43.1 07:49:26.9 12:23:24.8 08:04:35.2 14:02:52.3 08:39:17.6 09:10:32.4 07:41:57.3 13:04:32.2 08:11:53.5 07:09:43.2 11:15:27.0 11:14:35.1 (4) v (km s-1 ) 775 104 328 858 1210 508 759 2341 1292 1777 -170 1216 2329 448 195 1964 593 2277 2255 (5) D (Mpc) 17.0 17.0 23.0 23.0 17.0 23.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 (6) F250 (Jy) 1.87 7.62 1.39 2.21 1.63 2.05 0.83 2.44 0.67 1.37 2.19 5.06 3.56 7.90 1.44 34.43 1.48 12.64 30.89

F500 (Jy) 0.21 1.07 0.20 0.30 0.19 0.25 0.19 0.36 1.28 0.22 0.43 1.03 0.65 0.96 0.22 5.81 0.18 1.68 4.12

F350 (Jy) 0.68 3.23 0.59 0.87 0.61 0.84 0.40 1.04 0.92 0.65 1.09 2.47 1.68 3.02 0.63 15.63 0.60 5.01 12.33

F160 (Jy) 4.31 15.54 2.44 5.24 4.26 4.02 1.13 5.84 0.92 2.39 3.34 9.44 6.29 17.59 2.59 49.42 2.93 26.49 64.45

F100 (Jy) 4.77 11.40 1.73 4.90 5.20 3.80 1.10 5.26 0.53 1.07 3.41 6.48 5.12 17.33 1.15 21.89 2.36 20.76 55.58

NGC 4435 NGC 4438 NGC 4445 NGC 4451 NGC 4459 NGC 4469 NGC 4466 NGC 4470 NGC 4486 NGC 4492 IC 03476 NGC 4519 NGC 4522 NGC 4526 NGC 4531 NGC 4535 IC 03521 NGC 4567 NGC 4568

Figure 2. A comparison of IRAS (blue) and ISO (black) fluxes with the PACS 100-µm fluxes along with the Planck/SPIRE 350-µm (red) fluxes. Linear least-squares fit parameters are given at the top left-hand side of the figure. The black dashed line is the one-to-one relationship.

Figure 3. A comparison of the Spitzer (MIPS) 160-µm (blue), the Stickel et al. ISO 170-µm (red) and the Tuffs et al. ISO 170-µm (black) fluxes with the PACS 160-µm fluxes. Linear least-squares fit parameters are given at the top left-hand side of the figure. The black dashed line is the one-to-one relationship.

luminosity of a galaxy at different far-infrared wavelengths is thus a measure of the relative importance of the dust associated with star formation and that which is cold and diffusely distributed throughout the interstellar medium. The Virgo bright galaxy luminosity function/distributions (total numbers of galaxies within each luminosity interval) for each Herschel wavelength are shown in Fig. 4.2 The shape of these luminosity distributions can be used in comparison with those obtained for galaxies in other environments to assess the influence of that particular environment (field or varying richness of group or cluster) and at different redshifts to assess evolution over cosmic time. Given the proximity of Virgo, and hence the detail and depth of

2

We use the term luminosity function to refer to the 500-µm data because the data are selected at this wavelength. We use the term luminosity distribution for data at other wavelengths.

the observations, we expect this bright galaxy sample to act as a benchmark for future studies. The far-infrared luminosity function/distributions we obtain are quite different from those derived in the optical. At optical wavelengths, large numbers of low-luminosity galaxies are found in the cluster that give rise to a reasonably good Schechter function fit with the faint-end slope of the order of -1.3 to -1.6 (Sabatini et al. 2003). All of our far-infrared luminosity function/distributions turn over at faint luminosities. All galaxy samples, no matter how selected, are subject to selection effects primarily related to the sensitivity of the observations compared to the surface brightness of the objects. Given that this is an isophotal size selected sample, there may be galaxies that have large enough luminosities to appear in Fig. 4, but are not included in our sample because they are too small at the isophote of choice.
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Figure 4. The luminosity distributions derived from the data listed in Table 1. The dot­dashed line indicates a slope of -1 as found by Rowan-Robinson, Helou & Walker (1987) using IRAS 100-µm data. The vertical black dashed lines indicate the minimum luminosity at 17 and 32 Mpc for a minimum 500-µm flux density of 0.1 Jy. The yellow dashed line indicates the shape of the 500-µm luminosity distribution, if known star-forming dwarf galaxies, beyond our detection limit, are included.

Future studies will investigate this further, so here we just discuss some relevant issues which indicate that our 500-µm luminosity function and derived luminosity distributions may not be too awry. (i) Even the lowest luminosity galaxies in the sample are detected at a minimum S/N of 15, that is, the last point of the 500-µm luminosity function is not adversely affected by being close to a limit set by S/N. (ii) In Davies et al. (2010), we show that the luminosity function/distributions are peaked independent of the wavelength (e.g. 160 µm) used for selection. (iii) At optical wavelengths, Sandage, Binggeli & Tammann (1985) found that the luminosity distributions of Virgo Cluster bright spiral and elliptical galaxies (analogous to our sample) were Gaussian and only became power laws (Schechter) when the dwarf galaxies were included. These dwarf galaxies are predominantly metal-poor dE galaxies and we have previously shown that these are not detected at 500 µm in our current data (De Looze et al. 2010). (iv) Confirmed Virgo Cluster galaxies fainter than our 500-µm selection limit have been detected in the HeViCS data, but they are too small to be included in our sample (Grossi et al. 2010). Grossi (private communication) has identified 24 out of 139 late-type dwarf galaxies listed in the VCC that have a measurable 500-µm flux. Six of these lie, according to GOLDMINE, in the most distant structure at 32 Mpc. We have added these 24 galaxies to the 500-µm data shown in Fig. 4 (yellow dashed line) and as can be seen they do not alter our conclusion about a `peaked' luminosity function. We have an ongoing programme to try to detect as many VCC galaxies as possible in the HeViCS data. For this programme to seriously change our conclusions, we would need to find a population of far-infrared bright objects that have very low optical luminosities.
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There is of course always the possibility of far-infrared sources with no optical counterparts, but we would have to show conclusively that they were cluster members and not associated with faint optical sources in the background. If confirmed, the `peaked' nature of the far-infrared luminosity function/distributions is similar to the Virgo Cluster H I mass function, where there is also an apparent turnover at low masses (Davies et al. 2004; Taylor 2010). This is also quite different from the low-mass power-law slope of the global H I mass function (Martin et al. 2010; Davies et al. 2011). The straightforward explanation of the different H I mass function shapes is that gasstripping processes (Doyon & Joseph 1989) in the cluster are more dramatic for low-mass galaxies. Thus, the form of the luminosity function/distributions suggests that this may now also apply to the removal of cosmic dust. Although a number of tidal gas (21-cm) streams (Kent et al. 2007) have been identified in the cluster environment, the identification of intergalactic dust has been a little more controversial and would benefit from additional confirmation (see Stickel et al. 1998, for an example of a detection). The fate of stripped galactic dust is still unclear. At the current time, the availability of comparison luminosity distributions derived at the wavelengths of interest here is somewhat limited (see Davies et al. 2010). Many of the luminosity distributions derived using IRAS data used the 60-µm fluxes as their longest wavelength (see e.g. Soifer et al. 1987; Saunders et al. 1990). With a few exceptions (see Takeuchi et al. 2006, and references therein), the ISO also concentrated on shorter wavelengths than those considered here. The same is true of Spitzer (Babbedge et al. 2006; Rodighiero et al. 2010). The most informative comparison is with the IRAS 100-µm luminosity function derived by Rowan-Robinson et al. (1987). In a similar way to us, they constructed a far-infrared sample from

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L Mpc-3 again for a sample occupying various environments. Our value for the Virgo Cluster is [5.1(15.9) ± 0.6] â 108 L Mpc-3 , a factor of 14(44) higher. A value of H0 = 72 km s-1 Mpc-1 has been assumed to adjust the literature luminosity densities. Simply multiplying the luminosity densities given in Table 2 by the bandwidths (assuming non-overlapping bands, see below), we obtain a Virgo 100­500 µm far-infrared luminosity density of 100­500 = [2.2(9.6) ± 0.3] â 10-32 W m-3 or [1.6(7.0) ± 0.2] â 109 L Mpc-3 using a solar luminosity of 3.9 â 1026 W. 4 F AR-INFRARED AND OPTICAL LUMINOSITY The luminosity density (100­500 ) given above was calculated using non-overlapping bands corresponding to each Herschel wavelength (not necessarily centred on the nominal wavelength because of the uneven band spacing). This also provides a means of calculating a far-infrared luminosity for each galaxy. We define the Herschel far-infrared luminosity as L100­
500 2 = 3.1 â 104 dMpc [(f100 f 100

Table 2. The mean luminosity and luminosity density in each band for the Virgo Bright Galaxy Sample. The luminosity density using just the galaxies with distances of 17­23 Mpc are given in brackets. The temperatures are those that produce modified blackbody curves that peak in each band ( = 2). Band (µm) 100 160 250 350 500 Mean luminosity â1022 (W Hz-1 sr-1 ) 3 4 2 1 0 . . . . . 4 4 4 0 4 ± ± ± ± ± 0 0 0 0 0 . . . . . 6 8 4 2 1 Luminosity density â10-45 (W m-3 Hz-1 ) 6.5(19.7) ± 8.3(25.9) ± 4.6(14.8) ± 1.9(6.3) ± 0.7(2.3) ± 0.6 0.6 0.2 0.2 0.2 Temperature (K) 20.2 12.6 8.1 5.8 4.0

optically identified galaxies with an available redshift. This is roughly comparable with our Virgo sample in the sense that all the galaxies have to have an optical identification and a distance, but their sample is drawn from a wide range of environments. The Rowan-Robinson et al. luminosity function follows a power-law slope of about -1 from 1024 to 4 â 1021 WHz-1 sr-1 . Although the luminosity function/distribution normalization is arbitrary when comparing with our data (Fig. 4), it is clear that the Rowan-Robinson et al. luminosity function predicts 103 more galaxies at the faint end than at the bright end ­ even with the small numbers in our sample, this is difficult to reconcile with our Virgo data, unless subsequent investigation reveals large numbers of small faint cluster far-infrared sources. The Rowan-Robinson et al. data also include galaxies that are one order of magnitude brighter than the brightest galaxies found in the Virgo Cluster ­ it has previously been noted that clusters in general do not have the very bright far-infrared sources seen in the field (Bicay & Giovanelli 1987). Given the apparent shape of the Virgo Cluster luminosity function/distributions, it is currently more informative to simply characterize them by their mean values rather than a poorly fitted and parametrized Schechter function. These mean values are given in Table 2. It is clear that the majority of the far-infrared energy of the cluster is being produced at the shortest of these wavelengths. Using Wien's law for the predicted temperature of a modified black142.9 body curve with emissitvity , that is, Td (514 )max , leads to the + temperatures given in Table 2 for each wavelength (band) max and emissivity = 2. Clearly, we expect from this dust temperatures of the order of 13­20 K (see below). As the luminosity distributions apparently turn over at both the faint and luminous ends, we can make an estimate of the luminosity density in each band. Listed Virgo members in GOLDMINE extend from 17 to 32 Mpc, which is a large distance compared to what is normally assumed for the size of a cluster. So, all densities quoted below will be calculated using both the whole sample and just using those with distances between 23 and 17 Mpc (given in brackets). The volume we sample over 64 deg2 of sky is 181.3 Mpc3 for galaxies between 17 and 32 Mpc, and 47.2 Mpc3 for the reduced sample with distance between 17 and 23 Mpc (68 galaxies). Values for the luminosity density in each band are given in Table 2. It is difficult to make comparisons with previous work because this is a newly explored part of the electromagnetic spectrum. Saunders et al. (1990) using IRAS data give a luminosity density of (4.0 ± 0.4) â 107 L Mpc-3 for emission in the range 42.5­122.5 µm from galaxies in all environments. Using this bandpass and our 100-µm luminosity density gives a value of [1.1(3.3) ± 0.1] â 109 L Mpc-3 for this Virgo Cluster sample, a factor of 28(83) higher. At 160 µm, Takeuchi et al. (2006) use ISO data to obtain a value of 3.7 â 107

) + (f160 f

160

) )] L ,

+ (f250 f

250

) + (f350 f

350

) + (f500 f

500

where f100 , f160 , f250 , f350 and f500 , and f100 = 18.0, f160 = 8.9, f250 = 4.6, f350 = 3.1 and f500 = 1.8 are the flux density (Jy) and bandwidth (1011 Hz) in each band, respectively, and we have again taken the solar luminosity to be 3.9 â 1026 W. For this particular analysis, we prefer this method of calculating the luminosity because it does not depend on any particular fit to the SED, that is, it is valid for galaxies well fitted by a single modified blackbody with any value of emissivity power index ( ), those that require two components or more and those that do not have a thermal spectrum. To check the consistency of our determination of the far-infrared luminosity, we have compared it with that predicted analytically for a galaxy that is well fitted by a modified blackbody (see the next section). For NGC 4254, the analytical value derived from the fit gives log (LFIR ) = 10.59, while the above method gives log (L100­500 ) = 10.51. Far-infrared luminosities (L100­500 ) for each galaxy are listed in Table 3. Comparing the average far-infrared SEDs of the galaxies in the sample, we find the highest flux density (38 per cent) in the 160-µm band. We can use a similar approach for the apparent stellar luminosity of each galaxy. We define the apparent stellar luminosity as L0.4­
2.5 2 = 3.1 â 107 dMpc [(fg fg ) + (fr fr ) + (fi fi )

+ (fJ fJ ) + (fH fH + (fK fK ))] L ,
Table 3. Colour corrections for a = 2 modified blackbody of temperature T . Pipeline fluxes (i.e. calibrated assuming F = constant) should be multiplied by the above factors to retrieve the corrected fluxes. For the SPIRE bands, the values without brackets are for extended sources, while those within brackets are for point sources. T (K) 15 20 25 100 µm 0.96 1.03 1.03 160 µm 1.06 1.03 0.99 250 µm 1.00 (0.98) 0.99 (0.96) 0.08 (0.94) 350 µm 0.99 (0.96) 0.98 (0.94) 0.97 (0.93) 500 µm 0.99 (0.92) 0.98 (0.90) 0.97 (0.88)

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where fg , fr , fi , fJ , fH and fK , and fg = 1.9, fr = 1.1, fi = 1.6, fJ = 0.9, fH = 0.3 and fK = 0.5 are the flux (Jy) and bandwidth (1014 Hz) in each band, respectively. The g -, r - and i -band data (g = 0.48 µm, r = 0.62 µm, i = 0.76 µm) are taken from the Sloan Digital Sky Survey (SDSS). Automated magnitude derivations from within the SDSS data base are notoriously inaccurate for extended sources, so for 54 sources where the data are available we have used SDSS magnitudes derived from our own surface photometry as described in Cortese et al. (2011). For the additional 24 galaxies, we have used SDSS data from the NASA Extragalactic Database (NED). For most of these galaxies, the magnitudes are plausibly consistent with those given in the nearinfrared. For two galaxies (UGC 7557 and NGC 4451), there are no consistent SDSS magnitudes and we have set their apparent luminosities in these bands to zero. As we will see below, this does not greatly affect our calculations because by far the largest fraction of the apparent stellar luminosity is emitted in the near-infrared. The SDSS AB magnitudes are converted to Jy using a zero-point of KSDSS = 8.9. In the near-infrared, we have used the 2MASS which lists J -, H - and K -band (total) magnitudes for all of our galaxies (J = 1.25 µm, H = 1.65 µm, K = 2.17 µm). The 2MASS website gives the following zero-points for the conversion of magnitudes to Jy: KJ = 8.01, KH = 7.53, KK = 7.06. Considering the average SED of all the galaxies in the sample, but this time in the optical, the highest flux density is produced in the H band (28 per cent of the total), while in the J and K bands it is 23 and 22 per cent, respectively, thus justifying our statement made above that by far the largest fraction of the escaping starlight is emitted in the near-infrared bands. Summing the contribution from all the galaxies leads to an optical luminosity density of 0.4­2.5 = 5.0(20.0) â 109 L Mpc-3 , some 3.1(2.9) times larger than the far-infrared value given in the previous section. For their ISO sample of Virgo galaxies, Popescu et al. (2002) obtain values of 5.7 and 2.3 for the ratio of optical to far-infrared luminosity in early- and late-type galaxies, respectively, consistent with our global value. There are of course some very optically luminous galaxies like NGC 4486 (M87) and NGC 4374 (M84) that emit little in the far-infrared. The range of both optical and far-infrared luminosities for the galaxies in this sample is shown in Fig. 5.

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We can use the optical and far-infrared luminosities to make a crude estimate of the `typical' optical depth ( ) experienced by a photon as it leaves a galaxy, based on a simple screen of dust model: = ln 1.0 + L100­ L0.4­
500 2.5

.

Values of are also listed in Table 4. The mean value for galaxies in this sample is mean = 0.4 ± 0.1, so on average the optical energy emerging from regions of intermediate optical depth is neither totally optically thin nor totally optically thick. This mean value may be high when compared to galaxies in general because this is a far-infrared-selected sample. Values of range from 0.04 to 2.76. The two `optically-thick' galaxies with greater than unity are both late-type spirals ­ NGC 4234 (Sc) and NGC 4299 (Scd). As galactic dust is typically confined to a relatively thin disc, the value of should be dependent on the inclination of each galaxy to the line of sight. It is therefore surprising that both NGC 4234 and 4299 are relatively face-on galaxies with inclinations of approximately 40 and 20 , respectively. In the optical, both galaxies show signs of possible disturbance and so maybe the dust has been `stirred up' in these two galaxies. Given the complexities of the relative distributions of stars and dust, a full understanding of the radiative processes that give rise to dust emission will only come about by carrying out detailed radiative transfer modelling (e.g. Bianchi, Davies & Alton 2000a; Baes & Dejonghe 2001; Bianchi 2008). The above value of mean is very close to the value given in Saunders et al. (1990), derived in a similar way using IRAS data ( IRAS = 0.3 ± 0.1). The mean value we find implies that on average 33 ± 7 per cent of the stellar radiation of a galaxy is absorbed by dust. The value is in agreement with that found by Popescu & Tuffs (2002) using a sample of late-type Virgo galaxies observed with the ISO. After removing a contribution of hotter dust using data at 60 µm, they fitted the 100- and 170-µm fluxes with a single-temperature modified blackbody with = 2 and extrapolated to longer wavelength. Using the Herschel data up to 500 µm, we will show in the next section that indeed this simple model can describe very well the dusty thermal SED in most of our sample. 5 DUST , GAS AND STELLAR M ASS In order to derive the dust temperature and masses, we fitted the SED for each galaxy, as defined by the Herschel flux densities in Table 1, with a single-temperature modified blackbody. We followed the same procedure as adopted in Smith et al. (2010), Bendo et al. (2010) and Magrini et al. (2011) (see the later work for a discussion of the uncertainties when using a single-temperature model). We adopted a power-law dust emissivity = 0 (0 /) , with spectral index = 2 and emissivity 0 = 0.192 m2 kg-1 at 0 = 350 µm. These values reproduce the behaviour of models of Milky Way dust in the far-infrared­submillimetre, which were also found to reproduce the dust emission SED in several other galaxies (Draine 2003; Draine et al. 2007). The fit was obtained with a standard 2 minimization technique. The monocromatic flux densities measured from the images, and reported in Table 1, come from the pipeline calibration. They have been derived from the passband-weighted flux density (measured by the instruments), applying a colour correction for a flat energy spectrum (F -1 ). We retrieved the passband-weighted flux density by removing this correction (for the SPIRE, this is equivalent to dividing the pipeline flux densities by the K4 factor for point sources; SPIRE Observers' Manual 2010) and then fitted to the data the average of the model over the spectral response function for each of the bands. We used the

Figure 5. A comparison of the range of optical luminosity in solar units from 0.4 to 2.5 µm (blue) with that in the far-infrared from 100 to 500 µm (red).
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Table 4. The Herschel Virgo Cluster Survey Bright Galaxy Sample. Column (1): name; column (2): absolute B magnitude; column (3): stellar mass; column (4): H I mass; column (5): dust mass; column (6): dust temperature; column (7): stellar luminosity from 0.4 to 2.5 µm; column (8): far-infrared luminosity from 100 to 500 µm; column (9): mean optical depth; column (10): stellar-to-atomic gas mass ratio; and column (11): atomic gas-to-dust mass ratio. The B -, V - and H -band magnitudes, used to calculate stellar mass, are taken from the GOLDMINE data base. The mean fractional dust mass and temperature errors are approximately 19 and 6 per cent, respectively. Seven galaxies have no detected atomic hydrogen. Two galaxies have no dust mass and temperatures listed because their SEDs are not well fitted by a thermal spectrum. Stellar luminosities were calculated using SDSS and 2MASS data. Far-infrared luminosities were calculated using the data from this paper. (1) Name (2) MB -17.99 -19.13 -19.84 -20.42 -19.24 -19.15 -16.77 -18.15 -19.33 -20.31 -17.20 -19.05 -18.49 -19.55 -17.96 -17.74 -20.70 -19.22 -19.04 -20.04 -16.11 -16.56 -18.47 -19.20 -18.16 -18.84 -20.85 -19.03 -18.01 -17.51 -18.69 -18.65 -17.32 -18.12 -21.13 -18.58 -18.01 -18.61 -17.31 -17.45 -18.16 -18.01 -20.97 -17.98 -18.63 -19.38 -18.04 -19.28 -18.39 -17.58 -18.51 -18.17 -18.21 -18.06 -17.89 (3) log(Mstars ) (M ) 9.77 9.98 10.39 10.88 10.29 9.91 9.23 9.72 10.27 10.94 9.57 9.61 10.01 10.28 9.35 9.25 10.67 10.38 10.24 10.33 9.05 9.52 9.59 10.12 8.98 10.32 10.71 10.12 9.80 8.99 9.94 10.12 9.16 10.03 10.90 10.15 9.71 10.16 8.95 9.40 9.29 9.27 10.99 9.35 10.16 10.40 9.91 10.24 9.51 9.57 10.11 9.36 9.60 9.59 9.50 (4) log(MH I ) (M ) 8.39 9.48 9.40 9.63 9.24 9.71 8.79 9.38 8.91 9.25 9.03 8.88 8.32 8.45 9.03 9.00 9.65 ­ ­ 9.54 8.39 9.02 9.22 8.94 9.04 9.24 9.68 8.15 7.64 9.08 8.08 8.02 8.81 9.01 9.44 8.73 8.61 8.78 8.45 8.40 8.52 8.89 8.96 8.83 8.84 8.47 9.45 8.65 8.90 8.71 8.66 9.23 8.29 8.33 8.41 (5) log(MDust ) (M ) 6.97 7.44 7.65 7.93 7.60 7.46 6.69 7.31 7.35 7.83 7.20 7.08 7.11 7.28 7.11 6.88 8.02 6.73 6.93 7.71 6.49 6.92 7.06 7.36 6.72 7.66 7.96 7.31 6.72 6.37 6.82 6.96 6.76 7.32 8.17 6.80 7.13 7.13 6.39 6.84 6.60 6.56 6.69 7.45 7.42 7.08 7.08 6.96 7.43 6.91 6.87 6.56 6.74 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ­ ± ­ ± ± ± ± ± ± ± ± ± ± 0.07 0.07 0.07 0.07 0.07 0.08 0.08 0.08 0.07 0.07 0.09 0.08 0.07 0.06 0.07 0.11 0.07 0.07 0.07 0.08 0.07 0.08 0.08 0.07 0.08 0.07 0.08 0.07 0.08 0.09 0.07 0.07 0.08 0.00 0.07 0.07 0.07 0.08 0.08 0.08 0.07 0.09 0.08 0.07 0.08 0.08 0.07 0.08 0.07 0.08 0.07 0.08 0.07 (6) Td (K) 18.2 17.0 21.8 18.4 18.4 20.6 18.7 16.1 22.4 18.3 16.8 23.3 22.0 16.3 15.1 16.0 22.7 18.2 21.5 24.4 18.5 17.9 19.5 21.3 21.2 19.7 22.7 19.8 20.1 19.6 22.9 20.6 18.1 20.3 20.3 18.3 17.5 21.2 18.6 17.9 19.3 20.4 20.5 18.0 19.2 24.4 18.1 19.6 21.6 17.5 18.7 24.8 20.5 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ­ ± ­ ± ± ± ± ± ± ± ± ± ± 0.9 0.8 1.3 0.9 0.9 1.3 1.0 0.8 1.3 0.9 1.0 1.5 1.2 0.6 0.6 1.1 1.3 0.9 1.1 1.6 0.9 0.9 1.1 1.1 1.4 1.0 1.4 1.0 1.2 1.3 1.4 1.1 0.9 0.0 1.0 0.9 0.8 1.2 1.0 0.9 1.0 1.4 1.2 0.8 1.1 1.6 0.9 1.1 1.2 0.9 0.9 1.6 1.1 (7) log(L0.4­ (L ) 9.67 9.71 10.08 10.56 10.11 9.80 9.08 9.63 10.04 10.66 9.25 9.36 9.89 10.21 9.14 9.26 10.59 10.09 9.81 10.19 8.96 9.25 9.59 10.00 7.94 10.08 10.66 10.09 9.65 9.09 9.85 9.93 9.02 9.81 10.77 9.94 9.55 9.96 7.49 9.23 9.40 9.35 10.90 9.32 9.96 10.25 9.66 10.14 9.58 9.44 9.90 9.15 9.59 9.51 9.36 (8) log(L100­ (L ) 8.93 9.26 10.05 9.93 9.62 9.79 8.74 8.99 9.80 9.81 9.07 9.65 9.53 9.01 8.62 8.77 10.51 8.69 9.29 10.38 8.50 8.88 9.24 9.69 9.11 9.81 10.46 9.48 8.96 8.61 9.32 9.22 9.06 9.55 10.39 8.78 9.01 9.47 8.45 8.77 8.72 8.92 8.43 9.00 8.65 9.36 9.54 9.75 9.04 9.15 9.81 8.80 8.90 9.25 9.00 (9) (10) Mstars /MH (11) MH I /MDust

2.5

)

500

)

I

NGC 4165 IC 00769 NGC 4189 NGC 4192 NGC 4193 NGC 4197 IC 03061 NGC 4206 NGC 4212 NGC 4216 NGC 4222 NGC 4234 NGC 4237 NGC 4241 IC 03115 NGC 4252 NGC 4254 NGC 4260 NGC 4266 NGC 4273 UGC 7387 NGC 4289 NGC 4294 NGC 4298 NGC 4299 NGC 4302 NGC 4303 NGC 4307 NGC 4309 NGC 4301 NGC 4312 NGC 4313 IC 03225 NGC 4316 NGC 4321 NGC 4324 NGC 4330 NGC 4343 IC 03258 IC 03259 NGC 4351 IC 03268 NGC 4374 NGC 4376 NGC 4378 NGC 4380 UGC 7513 NGC 4388 NGC 4390 IC 03322 NGC 4402 UGC 7537 NGC 4413 NGC 4412 NGC 4416

0.17 0.30 0.66 0.21 0.28 0.68 0.37 0.21 0.45 0.13 0.51 1.09 0.36 0.06 0.26 0.28 0.60 0.04 0.26 0.93 0.30 0.35 0.37 0.40 2.76 0.43 0.49 0.22 0.19 0.28 0.26 0.18 0.74 0.44 0.35 0.07 0.25 0.28 2.32 0.30 0.19 0.31 ­ 0.39 0.05 0.12 0.57 0.34 0.25 0.42 0.60 0.37 0.19 0.44 0.36

24.0 3.2 9.8 17.8 11.2 1.6 2.8 2.2 22.9 49.0 3.5 5.4 49.0 67.6 2.1 1.8 10.5 ­ ­ 6.2 4.6 3.2 2.3 15.1 0.9 12.0 10.7 93.3 144.5 0.8 72.4 125.9 2.2 10.5 28.8 26.3 12.6 24.0 3.2 10.0 5.9 2.4 107.2 3.3 20.9 85.1 2.9 38.9 4.1 7.2 28.2 1.3 20.4 18.2 12.3

26.3 109.6 56.2 50.1 43.7 177.8 125.9 117.5 36.3 26.3 67.6 63.1 16.2 14.8 83.2 131.8 42.7 ­ ­ 67.6 79.4 125.9 144.5 38.0 208.9 38.0 52.5 6.9 8.3 512.9 18.2 11.5 134.9 49.0 18.6 85.1 30.2 44.7 114.8 33.1 83.2 213.8 ­ 138.0 ­ 10.5 107.2 37.2 66.1 56.2 17.0 208.9 26.3 58.9 46.8

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Table 4 ­ continued (1) Name (2) MB -18.75 -17.92 -18.54 -19.48 -19.35 -20.03 -18.12 -18.37 -19.63 -19.62 -16.55 -17.97 -21.32 -18.02 -17.80 -18.69 -18.18 -20.35 -18.68 -20.42 -17.23 -19.24 -19.93 (3) log(Mstars ) (M ) 9.57 9.23 9.24 10.18 10.44 10.70 9.86 9.79 10.60 10.57 8.98 9.43 11.13 9.79 9.18 9.63 9.57 10.95 9.99 10.63 9.27 10.01 10.49 (4) log(MH I ) (M ) 9.34 9.20 9.43 8.59 ­ 8.68 8.06 8.50 ­ ­ 8.16 8.63 ­ 7.94 8.39 9.43 8.63 9.33 ­ 9.59 7.94 8.69 8.99 (5) log(MDust ) (M ) 7.34 6.85 7.42 6.77 6.32 7.14 6.72 6.75 6.22 6.75 6.43 6.58 6.60 6.79 7.14 6.94 7.01 6.57 8.04 6.37 7.31 7.68 ± ± ± ± ± ± ± ± ± ± ± ± ­ ± ± ± ± ± ± ± ± ± ± 0.07 0.09 0.07 0.07 0.08 0.02 0.07 0.08 0.08 0.07 0.08 0.08 0.07 0.08 0.08 0.08 0.07 0.07 0.07 0.07 0.07 0.07 (6) Td (K) 16.0 18.0 12.8 24.8 25.9 21.9 20.8 24.2 27.2 23.2 18.4 23.5 18.8 19.4 19.7 20.2 24.5 19.2 18.0 22.7 22.7 23.0 ± ± ± ± ± ± ± ± ± ± ± ± ­ ± ± ± ± ± ± ± ± ± ± 0.7 1.1 0.4 1.5 1.7 0.3 1.1 1.5 2.0 1.4 1.1 1.5 0.9 1.2 1.1 1.2 1.5 0.9 0.8 1.3 1.3 1.4 (7) log(L0.4­ (L ) 9.60 9.39 8.83 10.12 10.33 10.27 9.69 9.34 10.45 10.38 8.86 9.44 11.05 9.81 9.07 9.65 9.53 10.72 9.77 10.48 9.17 10.01 10.25 (8) log(L100­ (L ) 8.98 8.87 8.45 9.46 9.08 9.54 9.00 9.39 9.10 9.28 8.50 9.16 8.37 8.64 8.97 9.32 9.18 9.66 8.67 9.97 8.84 9.79 10.20 (9) (10) Mstars /MH

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2.5

)

500

)

I

(11) MH I /MDust

UGC 7546 NGC 4423 UGC 7557 NGC 4424 NGC 4435 NGC 4438 NGC 4445 NGC 4451 NGC 4459 NGC 4469 NGC 4466 NGC 4470 NGC 4486 NGC 4492 IC 03476 NGC 4519 NGC 4522 NGC 4526 NGC 4531 NGC 4535 IC 03521 NGC 4567 NGC 4568

0.22 0.26 0.35 0.20 0.06 0.17 0.19 0.75 0.04 0.08 0.36 0.42 ­ 0.07 0.59 0.39 0.37 0.08 0.08 0.27 0.39 0.47 0.63

1.7 1.1 0.6 38.9 ­ 104.7 63.1 19.5 ­ ­ 6.6 6.3 ­ 70.8 6.2 1.6 8.7 41.7 ­ 11.0 21.4 20.9 31.6

100.0 223.9 102.3 66.1 ­ 34.7 21.9 56.2 ­ ­ 53.7 112.2 ­ 21.9 39.8 195.0 49.0 208.9 ­ 35.5 37.2 24.0 20.4

appropriate response functions for the PACS and SPIRE bands. The above procedure is equivalent to applying colour corrections to the pipeline monochromatic fluxes, if a SED model is known a priori. The colour corrections are given in Table 3. Given the nature of most of our sources, we used the SPIRE spectral response functions for extended emission. Since these corrections are much smaller than the assumed errors in each band, the fluxes given in Table 1 have not been colour corrected. In a few of our galaxies, the SPIRE fluxes might be dominated by point source emission and thus need a larger colour correction (see Table 3). Even in this case, the colour corrections are of the order of or less than the errors derived above. Remarkably, plotting the data given in Table 1 shows that the majority of galaxies are well fitted by this single-temperature (modified) blackbody curve with fixed emissivity index; the fits are illustrated in Fig. 6 (ordered by 2 value). There are three notable exceptions to this. The early-type galaxies NGC 4486 (M87) and NGC 4374 (M84) show departures from a thermal spectrum (Boselli et al. 2010), particularly at longer wavelengths. As discussed in Baes et al. (2010), specifically for NGC 4486, both these galaxies require modelling of the synchrotron component and its removal before the thermal dust spectrum can be analysed. The third galaxy, NGC 4378, is an early-type spiral with a Seyfert nucleus. Its SED does not appear to be contaminated by a non-thermal contribution, but rather dominated by a colder dust component, because its 160-µm flux is lower than expected when compared to the other values. NGC 4378 requires more detailed radiative transfer modelling and probably a multicomponent dust model before a substantial cold dust component is confirmed. Further modelling of these galaxies with peculiar SEDs is deferred to future papers. Here we concentrate on dust emission and those galaxies that can be fitted by a thermal spectrum. A few galaxies do not fit a thermal spectrum as well as others, though they do not show any clear evidence of a non-thermal component. For example, NGC 4423 and 4252 have a reduced chi-squared
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of 2 > 2, and NGC 4241, 4301, 4206, 4466, 4376, 4222 and IC 3268 have 1 < 2 < 2 where 2 is derived from the best model fit to the data. We nevertheless use the best single-temperature fitting parameters for these galaxies and defer more complicated fits to later papers. Derived dust masses and temperatures (75 galaxies) within these 500-µm determined apertures are in the range 106.22 ­108.17 M and 12.8­27.2 K, with mean values of 107.31 M and 20.0 K, respectively (Table 4). This illustrates the potential sensitivity of the full-depth survey to low dust masses (<106 M ) and the existence of a significant cold dust component (T < 20 K). Prior to the availability of observations at wavelengths longer than about 100 µm, calculated galaxy dust masses and temperatures from surveys similar to the HeViCS were typically 106.6 M and 30­50 K, respectively (taken from Soifer et al. 1987 where they have 31 galaxies in common with the HeViCS, see also Devereux & Young 1990). The typical dust mass is now almost an order of magnitude higher and the temperature almost 20 K colder (see also Tuffs et al. 2002). Interestingly, the coldest galaxy in the sample (12.8 K) is UGC 7557, the galaxy with the most discrepant IRAS 100-µm flux (Fig. 6). It is barely detected in the PACS 100-µm data, but is relatively strongly detected in the other bands. The data provide a reasonably good fit to a modified blackbody curve with a calculated dust mass of 107.42 M . UGC 7557 is classified as an Scd galaxy and appears to be of rather low surface brightness in the optical. Compared to the other galaxies in this sample, it is also little underluminous in the optical with a B -band absolute magnitude of -18.5. If it is very cold dust, then its origin is unclear; being apparently of low surface brightness, the dust may just be farther away from the stars. Alternately, the dust in this low-luminosity galaxy may have a different emissivity and/or size distribution. We will be investigating this further, once the full-depth HeViCS data become available. The complete distribution of dust temperatures is shown in Fig. 7.

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Figure 6. The SEDs of the Bright Galaxy Sample and modified blackbody fits ordered by reduced 2 value (given in parentheses). Three galaxies that are not well fitted by a modified blackbody are shown by the dashed line.

We have calculated the stellar masses (Mstar ) for each galaxy (Table 4) using the prescription given in Bell et al. (2003), that is, log M = -0.359 + 0.21(B - V ) + log LH . L

star

LH has been calculated using an H -band absolute magnitude for the Sun of MH = 3.32, and (B - V ) values have been taken from the GOLDMINE data base (Gavazzi et al. 2003). Where available (71 out of the 78 galaxies), we have also taken atomic hydrogen gas masses (MH I ) for each galaxy from the GOLDMINE data base; these are also given in Table 4 along with the dust
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Figure 6 ­ continued

masses. In Fig. 8, we show the distribution of mass in each of the three components, dust, gas and stars. In Fig. 9, we show the mass ratio of stars to atomic gas and atomic gas to dust; these have mean values of 15.1 and 58.2, respectively. We suggest that a factor of 2.9 (see below) can be used to convert atomic gas to total gas
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(H I + H2 ) in which case the mean values of the mass ratios are 5 and 170, respectively. The local value of the gas-to-dust ratio for the Milky Way is 143 (Draine et al. 2007). By very simply dividing the total mass in each component by the volume sampled [181.1(47.2) Mpc3 ], we can calculate the cluster

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Figure 7. The distribution of dust temperature.

Figure 9. The star-to-atomic gas mass ratio (red) and atomic gas-to-dust mass ratio (blue). Numbers quoted are the mean of the individual values for each galaxy.

Figure 8. The distribution of stellar mass, atomic gas mass and dust mass. All 78 galaxies have measured stellar masses, 71 have measured atomic gas masses and 76 have measured dust masses.

mass densities. Provided the luminosity distributions in each farinfrared band are peaked, the total cluster dust mass should be well constrained by our sample galaxies, unless there is a significant dust component in the intergalactic medium (Stickel et al. 1998). From the dust in our sample galaxies, we derive a cluster dust mass density of [8.6(27.8) ± 1.6] â 106 M Mpc-3 . This compares with a recent determination of the local dust mass density for galaxies in all environments of (2.2 ± 0.4) â 105 M Mpc-3 (Dunne et al. 2011), that is, the Virgo Cluster is overdense in dust by about a factor of 39(126). The Virgo Cluster H I mass function is also peaked (Davies et al. 2004; Taylor 2010), so again the H I gas in these galaxies should provide a good estimate of the cluster total. From our sample of 71 galaxies, we derive an H I mass density of 4.6(13.9) â 108 M Mpc-3 . The error on this is uncertain because the H I masses come from a wide variety of sources. Recently, Davies et al. (2011) measured a local `field' H I mass density of (7.9 ± 1.2) â 107 M Mpc-3 (see also Martin et al. 2010). Thus, the Virgo Cluster is overdense in H I by a factor of only about 6(18). Using the Davies et al. and Dunne et al. values for the global H I and dust mass densities gives a local `field' atomic gas-to-dust ratio of 359, while the same ratio in the cluster is only 54(50) (total atomic gas mass divided by total dust mass). At face value, these relative overdensities in dust and gas indicate that the cluster galaxies have

either processed more gas through stars, and hence created more metals, or they have lost gas and not dust when compared to the general population of galaxies. H I complexes within the cluster, but external to previously identified galaxies, have been found by Kent et al. (2007), but they only represent a small fraction of the cluster atomic gas. Comparing stellar mass functions is not quite so straightforward because of uncertainties in the faint-end slope of the Virgo Cluster luminosity distribution, that is, the numbers of faint dwarf galaxies (see Sabatini et al. 2003, and references therein). We obtain from the stars in our sample galaxies a value of 7.8(29.7) â 109 M Mpc-3 for the stellar density. Baldry, Glazebrook & Driver (2008) recently derived the local galaxy stellar mass function and from it a stellar mass density of (2.3 ± 1.2) â 108 M Mpc-3 . This is 34(129) times smaller than our value for Virgo. Interestingly, the stars and dust are in rough agreement as to the value of the overdensity that Virgo represents, while the atomic gas does not concur. Where required in the above derivations, we have used H0 = 72 km s-1 , m = 0.27, = 0.73.

6 C ONCLUSIONS The HeViCS is providing unprecedented high-resolution data, at farinfrared wavelengths, on some of the largest angular sized galaxies in the sky. In this paper, we have described some of the global properties of these galaxies. The Virgo bright galaxy sample discussed here consists of 78 galaxies selected at 500 µm each with a confirmed Virgo Cluster optical counterpart. Each galaxy is detected in each of the five (100­500 µm) far-infrared bands. We have carried out aperture photometry on each galaxy and compared, where possible, our data with that previously produced by the IRAS, ISO, Spitzer and Planck. Table 1 gives a complete list of the galaxies in the sample and their flux densities in each far-infrared band. These flux densities enable us to make a measurement of the luminosity function/distribution in each band. These luminosity function/distributions are not power laws but `peaked' functions. If subsequent measurements of the luminosity distributions in more wide-ranging environments have the more common power-law form (Schechter), then this is a clear indication of environmental processes in the cluster affecting the far-infrared properties of galaxies.
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We define and measure for each galaxy a 100­500 µm far-infrared and an optical 0.4­2.5 µm luminosity (L100­500 and L0.4­2.5 , respectively). Assuming a simple screen model of dust, these luminosities can be used to calculate a `typical' optical depth ( ) for photons emerging from a galaxy. Values of range from zero to an optically thick 2.8. With a mean value of mean = 0.4, most cluster (stellar) photons are emerging from reasonably optically-thin optical depths. We also use the values of L100­500 and L0.4­2.5 for each galaxy to calculate far-infrared and optical luminosity densities of [1.6(7.0) ± 0.2] â 109 L Mpc-3 and 5.0(20.0) â 109 L Mpc-3 , respectively. The optical luminosity density is some 3.2(2.9) times larger than the far-infrared one. The derived flux densities in each band are also used to calculate a dust mass and temperature for each galaxy, assuming a single-component modified blackbody with = 2. The mean (typical) dust mass and temperature for the galaxies in this sample are log (MDust ) = 7.31 and TD = 20.0 K, respectively. We have also used data from the literature to calculate both stellar and atomic gas masses for each galaxy; these have mean values of log (Mstars ) = 10.26 and log (MH I ) = 9.08, respectively. The total masses in each of these baryonic components are used to calculate mass densities of 8.6(27.8) â 106 , 4.6(13.9) â 108 and 7.8(29.7) â 109 M Mpc-3 for cluster dust, atomic gas and stars, respectively. These values are higher than that derived using galaxies in the general field by factors of 39(126), 6(18) and 34(129), respectively. Atomic gas appears to have been lost or consumed more effectively than is typical in field galaxies. The above information on the properties of Virgo Cluster galaxies and on the properties of the cluster as a whole will hopefully be useful when compared with the global properties of galaxies throughout the local Universe and also with studies of other galaxy clusters both near and far.

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This research has made use of the NED which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the US Department of Energy, NASA, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS website is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max Planck Institute for Astronomy (MPIA), the Max Planck Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory and the University of Washington. This publication makes use of data products from the 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by NASA and the National Science Foundation. SB, LM, CP, LKH, SdiSA, EC and GG acknowledge the financial support by the ASI through the ASI-INAF grant `HeViCS: the Herschel Virgo Cluster Survey' I/009/10/0. This work received support from the ALMA-CONICYT Fund for the Development of Chilean Astronomy (Project 31090013) and from the Center for Excellence in Astrophysics and Associated Technologies (PBF 06).

A C KNO W LEDGMENTS The Herschel spacecraft was designed, built, tested and launched under a contract to the ESA managed by the Herschel/Planck Project team by an industrial consortium under the overall responsibility of the prime contractor Thales Alenia Space (Cannes), and including Astrium (Friedrichshafen) responsible for the payload module and for system testing at spacecraft level, Thales Alenia Space (Turin) responsible for the service module, and Astrium (Toulouse) responsible for the telescope, within excess of a hundred subcontractors. The PACS has been developed by a consortium of institutes led by the MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF-IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); and IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy) and CICYT/MCYT (Spain). The SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including University of Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, University of Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, University of Sussex (UK); and Caltech, JPL, NHSC, University of Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC (UK); and NASA (USA).
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A This paper has been typeset from a TEX/L TEX file prepared by the author.

C 2011 The Authors, MNRAS 419, 3505­3520 Monthly Notices of the Royal Astronomical Society C 2011 RAS