Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://jet.sao.ru/hq/skai/article/0802.3982v1.pdf Äàòà èçìåíåíèÿ: Wed Feb 24 17:52:06 2010 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 01:00:09 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: sculptor galaxy

Mon. Not. R. Astron. Soc. 000, 000­000 (0000)

Printed 27 February 2008

A (MN L TEX style file v2.2)

FIGGS: Faint Irregular Galaxies GMRT Survey - Overview, observations and first results

arXiv:0802.3982v1 [astro-ph] 27 Feb 2008

Ayesha Begum1 , Jayaram N. Chengalur2, I. D. Karachentsev3, M. E. Sharina3 and S. S. Kaisin3
1 2 3

Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK National Centre for Radio Astrophysics, Post Bag 3, Ganeshkhind, Pune 411 007, India Special Astrophysical Observatory, Nizhnii Arkhys 369167, Russia

ABSTRACT

The Faint Irregular Galaxies GMRT Survey (FIGGS) is a Giant Metrewave Radio Telescope (GMRT) based HI imaging survey of a systematically selected sample of extremely faint nearby dwarf irregular galaxies. The primary goal of FIGGS is to provide a comprehensive and statistically robust characterization of the neutral inter-stellar medium properties of faint, gas rich dwarf galaxies. The FIGGS galaxies represent the extremely low-mass end of the dwarf irregular galaxies population, with a median MB -13.0 and median HI mass of 3 â 107 M , extending the baseline in mass and luminosity space for a comparative study of galaxy properties. The HI data is supplemented with observations at other wavelengths. In addition, distances accurate to 10% are available for most of the sample galaxies. This paper gives an introduction to FIGGS, describe the GMRT observations and presents the first results from the HI observations. From the FIGGS data we confirm the trend of increasing HI to optical diameter ratio with decreasing optical luminosity; the median ratio of DHI /DHo for the FIGGS sample is 2.4. Further, on comparing our data with aperture synthesis surveys of bright spirals, we find at best marginal evidence for a decrease in average surface density with decreasing HI mass. To a good approximation the disks of gas rich galaxies, ranging over 3 orders of magnitude in HI mass, can be described as being drawn from a family with constant HI surface density. Key words: galaxies: dwarf ­ galaxies: kinematics and dynamics ­ radio lines: galaxies

1 INTRODUCTION HI 21cm aperture synthesis observations of nearby spiral galaxies is a mature field with over three decades of history ­ probably something of the order of a thousand galaxies have already been imaged. However observers have tended to focus on bright ( L ) galaxies with HI masses 109 M . HI observations of faint dwarf galaxies (MB -17) generally require comparatively long integration times, and such galaxies have hence not been studied in similar numbers. While there have been some systematic HI surveys of dwarf galaxies (Swaters 1999; Stil & Israel 2002), these e have generally been restricted to the brighter (MB < - 14) dwarfs. In hierarchical models of galaxy formation, nearby dwarf galaxies would, in some ways, be analogs of the primordial building blocks of large galaxies. A systematic HI survey of the faintest dwarf galaxies could provide data that would be useful for a di-

verse range of studies, ranging from, for example, testing the predictions of cold dark matter models (e.g Simon & Geha (2007); Blanton et al. (2007)), checking if such systems could be the host population of quasar absorption line systems (e.g. Zwaan et al. (2005); Kanekar & Chengalur (2005)) etc. As the most chemically unevolved systems in the present-day galaxy population, the faintest dwarfs provide unique laboratories for understanding star formation and galaxy evolution in extreme environments, i.e. low metallicity, low dust content, low pressure, low shear, and low escape velocity (e.g. Ekta et al. (2006)). In this paper we describe and present the first results from a Giant Meterwave Radio Telescope (GMRT) based HI imaging study of faint dwarf galaxies - the Faint Irregular Galaxies GMRT Survey (FIGGS). The primary goal of FIGGS is to obtain high quality observations of the atomic ISM for a large, systematically selected sample of faint, gas rich, dwarf irregular (dIrr) galaxies. Our GMRT HI images are supplemented by single dish HI observations, HST V and I band images and ground based H images



E-mail:ayesha@ast.cam.ac.uk


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The FIGGS sample has a median MB -13 and a median HI mass 3 â 107 M , while spanning range of more than 100 in stellar light, gas mass and dynamical mass, and more than 4 in gas fraction. It can also be clearly seen that by focusing on fainter, lower mass galaxies than those observed in previous HI imaging studies, FIGGS bridges the transition to rotation dominated low mass spirals and provides a substantially extended baseline in mass and luminosity space for a comparative study of galaxy properties.

from the 6-m BTA telescope. Additionally, the HII region abundances and H rotation curves are being obtained on the William Herschel Telescope (WHT), Isaac Newton Telescope (INT) telescopes on La Palma and 6-m Russian BTA telescope, respectively. This paper is organised as follows. In Section 2 we describe the design and the properties of the galaxy sample. The main science drivers for FIGGS are described in Section.3. The GMRT observations are described in Section 4 and the results of the survey are presented and discussed in Section 5.

3 SCIENCE DRIVERS FOR FIGGS 2 FIGGS: SAMPLE DEFINITION AND PROPERTIES The Faint Irregular Galaxies GMRT Survey - FIGGS, is a large observing program aimed at providing a comprehensive and statistically robust characterisation of the neutral ISM properties of faint, gas rich, dwarf irregular galaxies using the Giant Metrewave Radio Telescope (GMRT). The FIGGS sample forms a subsample of the Karachentsev et al.(2004) catalog of galaxies within 10 Mpc. Specifically, the FIGGS sample consists of 65 faint dwarf irregular (dIrr)galaxies with: e (i) absolute blue magnitude, MB > - 14.5, (ii) HI flux integral > 1 Jy kms-1 e (iii) optical B band major axis > 1.0 arcmin. The sample choice was dictated by a balance between achieving the scientific goals described in Section.3 and the practical limitations of the observing time. We note that the above mentioned criterion on the optical B band major axis was not strictly followed in few cases. Some unusual, very faint dwarf galaxies, with optical B band major axis < 1 arcmin were still included in our sample, as they are interesting cases to study in detail in HI. Further, for some of the galaxies in the FIGGS sample, fresh estimates of the distance (obtained after our observations were complete) imply absolute magnitudes slightly larger than the cut off above. These galaxies have however been retained in the sample. Some properties (mainly derived from optical observations) of galaxies in the FIGGS sample are listed in Table 1. The columns are as follows: Column(1) the galaxy name, Column(2)&(3) the equatorial coordinates (J2000), Column(4) the absolute blue magnitude (corrected for galactic extinction), Column(5) the Holmberg diameter in arcmin, Column(6) the (B-V) colour, Column(7) the distance in Mpc, Column(8) the method used to measure the distance - from the tip of the red giant branch (rgb), from membership in a group with known distance (grp), from the Tully-Fisher relation (tf), and from the Hubble flow (h). Column(9) gives the group membership of the galaxy, Column(10) the inclination determined from optical photometry (and assuming an intrinsic thickness, qo =0.2) and Column(11) the reference for the (B-V) colour, and/or revised distance. The data presented in the Table 1 (except for the colour) is taken from Karachentsev et al. (2004) catalog, except that revised distances have been adopted, if available. As can be seen from the Table 1, tip of the red giant branch (rgb) distances (which are generally accurate to 10%) are available for most of the galaxies in our sample. Figure 1 shows the histogram of the absolute blue magnitude (MB ), distance, HI mass, and HI mass to light ratio (MHI /LB ) for the FIGGS sample, while Figure 2 compares the distributions of gas fraction, luminosity and dynamical mass of the FIGGS galaxies with that of existing samples of galaxies with HI aperture synthesis observations. The gas fraction and the dynamical masses for the FIGGS sample have been derived from the GMRT observations. The aim of FIGGS is to provide a large multi-wavelength database for a systematically selected sample of extremely faint dwarf irregular galaxies. As mentioned in Section 1, such a database could be used to address a diverse range of astrophysical questions. Rather than attempting to enumerate all of these, in this section, we describe in some detail a couple of key science drivers for the FIGGS survey. 3.1 Star formation and feedback in small galaxies One of the main goals of FIGGS is to use the HI interferometric images in conjunction with the optical data to study the interplay between the neutral ISM and star formation in the faintest, lowest mass, gas rich dIrr galaxies. The gravitational binding energy for very faint dwarf irregular galaxies is not much larger than the energy output from a few supernovae; consequently star formation in such galaxies could have a profound effect on the morphology and kinematics of the ISM of these systems. The FIGGS data will enable us to study the ISM of most of our sample galaxies at a linear resolution of 15 - 300 pc - i.e. comparable to the scales at which energy is injected into the ISM through supernova and stellar winds. FIGGS thus provide a unique opportunity to study the effects of feedback from star formation in low mass, gas rich galaxies, which in turn will allow us to understand the processes driving the evolution of these galaxies. For example, it has been suggested that star formation in dwarf galaxies occurs only above a constant threshold HI column density of NHI 1021 cm-2 (e.g. Skillman 1987; Taylor 1994). Such a threshold could be a consequence of disk dynamics (e.g. related to Toomre's instability criterion; Kennicutt (1989)) or a consequence of some other physical process, e.g. self shielding or thermo-gravitational instability (Schaye (2004)). A preliminary study of a small subsample of FIGGS (Begum et al. (2006)) suggested that unlike brighter dwarfs, the faintest dwarf galaxies do not show well defined threshold density. A detailed comparison of H and UV images with HI column density maps for the FIGGS sample will allow us to definitively answer the issue of the existence of a threshold density in the faintest galaxies and also to check whether the recipes for star formation derived from larger galaxies (Kennicutt (1989)) continue to be valid at this mass regime. These are critical issues in hierarchical galaxy formation models. 3.2 Dark and visible matter in small galaxies The second major aim of this survey is to study the relation between dark and baryonic matter in the smallest known star forming galaxies. According to several models of galaxy formation and evolution, the first burst of star formation in dwarf galaxies below a critical halo circular velocity (100 kms-1 ) could lead to the loss of a significant fraction of baryons (e.g. Efstathiou 2000;


FIGGS: Faint Irregular Galaxies GMRT Survey
Table 1. The FIGGS sample

3

Galaxy

(J2000) (h m s) 00 00 00 00 01 01 01 02 02 04 04 04 05 06 07 07 07 07 07 08 08 08 09 09 10 10 11 11 11 11 11 11 11 12 12 12 12 12 12 12 12 12 12 12 13 13 13 13 13 13 13 13 13 13 13 14 14 14 16 20 36 42 43 49 07 34 44 24 27 25 32 53 59 37 00 13 28 42 57 32 34 52 42 45 07 21 05 28 33 36 47 50 54 13 13 14 15 16 25 25 27 28 56 58 08 13 21 24 30 36 39 39 40 50 54 07 15 28 13 03 38. 32. 03. 49. 22. 51. 42. 35. 27. 15. 00. 06. 41. 56. 29. 51. 17. 31. 01. 56. 06. 50. 59. 04. 19. 25. 35. 00. 29. 06. 11. 53. 43. 22. 49. 07. 46. 28. 17. 27. 41. 39. 04. 40. 03. 22. 08. 36. 44. 30. 19. 53. 18. 51. 48. 10. 56. 03. 47. 57. 00 30 80 30 30 60 70 00 00 60 30 90 20 60 30 80 20 20 80 00 50 70 80 20 70 20 00 60 10 40 20 00 00 70 60 40 70 60 90 90 80 00 00 40 60 80 20 00 40 80 40 80 10 10 70 70 50 70 60 40

(J2000) ( ) - 32 34 28 +40 34 19 -22 15 01 -21 00 58 +16 41 02 +52 5 30 +27 17 16 +56 0 42 +57 29 16 +72 48 21 +63 36 50 +67 05 57 +73 25 39 -25 59 59 -04 12 30 +10 31 19 +40 46 13 +16 33 40 +14 23 27 +71 01 46 +66 10 45 +33 47 52 +33 15 52 +32 14 18 +10 21 44 +71 06 58 -01 51 49 +78 59 29 +49 14 17 +45 17 7 +43 40 19 +38 52 50 -33 33 29 +29 55 18 -38 13 53 +66 05 32 +52 23 15 +52 13 38 +26 42 53 +28 28 57 +43 29 38 +35 43 05 +03 48 41 +14 13 03 +46 49 41 +46 19 11 -31 31 45 -30 58 20 +54 54 36 -29 14 11 +24 46 33 +40 44 21 -28 53 40 +38 01 16 +35 50 15 +35 03 37 +23 03 19 -46 18 06 +54 22 16 -31 40 54

MB (mag) -8.39 -12.23 -14.17 -12.5 -14.31 -12.42 -12.13 -13.35 -13.03 -14.06 -15.65 -11.85 -12.30 -14.46 -12.6 -14.90 -14.75 -14.29 -14.27 -11.49 -13.37 -12.76 -12.98 -13.15 -15.08 -11.83 -13.14 -14.03 -13.71 -13.13 -9.73 -13.52 -12.31 -15.30 -12.70 -14.06 -13.25 -12.27 -15.55 -12.59 -14.16 -13.53 -15.49 -12.11 -12.26 -12.70 -11.76 -11.96 -12.98 -13.3 -13.68 -13.03 -13.90 -13.17 -12.42 -9.55 -12.51 -11.83 -9.96 -13.69

DH o ( ) 0.6 1.1 3.2 2.1 2.2 0.9 1.6 1.7 2.2 2.6 2.0 1.4 1.0 2.0 2.0 1.8 1.8 0.9 1.5 1.3 1.6 2.0 1.3 0.9 1.9 1.5 1.7 1.5 1.6 1.7 0.6 3.5 1.1 1.0 1.4 1.9 1.8 1.1 1.0 1.5 4.2 2.2 1.4 2.2 1.0 1.6 1.3 1.3 2.0 1.2 1.2 1.6 1.6 1.7 1.3 1.7 2.28 2.4 1.2 1.3

B-V (mag) - 0.47 0.4 0.32 0.52 0.43 0.42 - - 0.63 1.1 0.58 0.4 0.51 - 0.55 0.31 0.54 0.47 0.24 0.45 - 0.49 0.56 0.33 - - 0.38 0.41 0.37 0.36 0.38 0.23 0.4 0.41 0.4 0.4 0.29 0.45 0.4 0.59 0.41 0.24 0.32 0.38 0.32 - 0.4 0.45 0.49 0.51 0.46 - 0.31 0.42 0.4 0.28 - - 0.58

Dist (Mpc) 1.66 6.3 4.9 3.34 4.5 3.73 7.2 3.0 3.0 3.9 3.01 3.34 4.6 4.2 1.69 6.96 7.8 7.62 7.5 3.55 3.56 7.7 6.9 6.7 5.6 3.96 7.4 4.3 3.9 3.0 4.5 2.6 5.2 13.0 3.2 5.4 4.9 4.21 12.8 6.3 2.5 4.43 17.4 2.1 4.5 4.2 5.22 4.6 2.6 5.25 4.27 3.1 4.4 3.24 3.2 1.9 2.5 3.6 1.86 7.83

D estm

Group

iopt (deg) 57 41 72 69 46 55 71 59 78 57 62 62 58 42 55 55 48 58 58 24 30 42 83 17 62 55 64 60 57 58 49 71 44 69 67 68 77 58 84 74 58 44 40 25 47 58 65 53 55 68 49 57 52 75 28 35 42 71 55 68

Ref

SC 24 And IV DDO 226 DDO 6 UGC 685 KKH 6 KK 14 KKH 11 KKH 12 KK 41 UGCA 92 KK 44 KKH 34 E490-17 HIZSS003 UGC 3755 DDO 43 KK 65 UGC 4115 KDG 52 UGC 4459 KK 69 UGC 5186 UGC 5209 UGC 5456 HS 117 UGC 6145 UGC 6456 UGC 6541 NGC 3741 KK 109 DDO 99 E379-07 KK 127 E321-014 UGC 7242 CGCG 269-049 UGC 7298 UGC 7505 KK 144 DDO 125 UGC 7605 UGC 8055 GR 8 UGC 8215 DDO 167 KK 195 KK 200 UGC 8508 E444-78 UGC 8638 DDO 181 I4316 DDO 183 UGC 8833 KK 230 DDO 187 P51659 KKR 25 KK 246

Sculptor grp(?) rgb rgb rgb rgb rgb N672 grp Mafeii grp Maffei grp rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb N2683 grp h h rgb rgb h rgb rgb rgb rgb rgb rgb ComaI grp rgb rgb rgb rgb tf h rgb rgb tf rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb rgb

distant Irr Field Sculptor Sculptor Field IC 342/Maffei N672 IC 342/Maffei IC 342/Maffei IC 342 IC 342/Maffei IC432 M81 Field Field Field Field Field Field M81 M81 N2638 Field Field Field Field Field M81 CVn I CVn I CVn I CVn I Cen A ComaI Cen A M81 CVn I CVn I ComaI CVn I CVn I CVn I Field Field CVn I CVn I M83 M83 CVn I M83 CVn I CVn I M83 CVn I CVn I Field Field Cen A Field Field

18,19 1 1 1 13,17 13

2 3, 17 4 13 5 6,15 7 8 13 4 4 13 8 9

11 10 7 13 13 13 17 13 13,17 16 4 6 13 6 13 9 4 12, 17 12 13 6 13 13, 17 13 9 13 4 1

13, 17

*: Optical diameter measured at 25.0 mag arcsec-2 .


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Table 1. (continued) The FIGGS sample

Galaxy

(J2000) (h m s) 20 20 20 23 23 30 30 46 26 45 15. 32. 53. 27. 34. 30 60 00 50 00

(J2000) ( ) +60 +60 -12 -32 +38 26 25 21 13 50 57 23 26 43 4

MB (mag) - - - - - 14. 13. 11. 12. 10. 54 72 09 94 78

DH o ( ) 1. 1. 3. 2. 1. 8 6 6 4 1

B-V (mag) 0. 0. 0. 0. 0. 91 37 24 42 21

Dist (Mpc) 5. 5. 1. 2. 2. 6 6 0 2 5

D estm

Group

iopt (deg) 62 66 62 38 58

Ref

KK 250, UGC11583 KK 251 DDO 210 UGCA 438 KKH 98

N6946 grp N6946 grp rgb rgb rgb

N6946 N6946 Field Sculptor Field

14 14 4 13 13

References: 1-van Zee (2000) 2-Karachentsev et al. (1999) 3-Karachentsev et al. (1996) 4-Begum et al. (2006) 5-Parodi (2002) 6-Makarova (1999) 7-Taylor et al. (2005) 8-Makarova et al. (2002) 9-Hunter & Elmegreen (2006) 10-Bremnes et al. (2000) 11-Hopp & Schulte-Ladbeck (1995) 12-Bremnes et al. (1999) 13-Sharina et al. 2008 (in preparation) 14-Begum & Chengalur (2004b) 15-Tully et al. (2006) 16-Corbin et al. (2008) 17-Karachentsev et al. (2006) 18-Ferguson et al. (2000) 19-Chengalur et al. 2008 (in preparation)

[A]

[B]

[C]

[D]

Figure 1. The histogram of MB (panel [A]), distance (panel [B]), logarithm of the HI mass (panel [C]) and the HI mass to light ratio, MHI /LB (panel [D]) for the FIGGS sample.

Dekel & Woo 2003). In fact, expulsion of gas because of energy input from supernovae has been postulated as a possible mechanism to produce dwarf elliptical galaxies from gas rich progenitors (e.g. Miralda-Escude & Rees (1997)). Although a complete expulsion of the ISM from galaxies has not been observed so far, expansive outward motions of the neutral gas in dwarf galaxies has been observed in at least two galaxies (viz. GR8, Begum & Chengalur 2003; NGC 625, Cannon et al. 2004). To test these models, high spatial resolution interferometric observations are crucial. The Tully-Fisher (TF) relation demonstrates the existence of a tight relation between dark and luminous matter in bright spiral galaxies. Mcgaugh et al. (2000) (see also McGaugh (2005)) showed that dwarf galaxies deviate from the TF relation defined by bright spirals, but that the relationship is restored if one works with the total baryonic mass instead of the luminosity, i.e. a "Baryonic Tully Fisher" (BTF) relation. The FIGGS sample, both because it extends well beyond the region of rotation dominated dwarfs and because accurate distances are known for a large subsample, forms a very interesting dataset for studying TF and BTF relations. Most of the past studies have been done using the HI global velocity widths from the single dish observations (Geha et al. 2006; Mcgaugh et al. 2000). While for the brighter galaxies W20 (the velocity width at 20% emission, after correction for random motions and instrumental broadening), is a good measure of the rotational velocity of the galaxy (Verheijen & Sancisi 2001); it is unclear if this would remain true in the case of faint dwarf galaxies, where random motions could be comparable to the peak rotational velocities (e.g. Begum et al. 2003; Begum & Chengalur 2004a). For such galaxies, it is important to accurately correct for the pressure support ("asymmetric drift" correction) for which one needs to know

both the rotation curve as well as the distribution of the HI gas, both of which can only be obtained by interferometric observations such as in FIGGS. The FIGGS sample would thus allow us to concretely answer this question using actual observational data. The HI kinematics of FIGGS galaxies, in conjunction with the H rotation curves can be used to accurately determine the density distribution of the dark matter halos of faint galaxies. Since stars generally make a minor contribution to the total mass in the FIGGS galaxies, accurate kinematical studies can provide direct information on the density profiles of their dark matter halos with less uncertainties arising from the unknown stellar mass to light ratio. Cosmological simulations of hierarchical galaxy formation predict a "universal" cusped density core for the dark matter halos of galaxies (e.g. Navarro et al. 2004). On the other hand, observations of dIrr galaxies indicate a constant density core for their dark matter halos (e.g. Weldrake et al. 2003; de Blok et al. 2003); however this comparison remains controversial (e.g. van den Bosch & Swaters 2001; de Blok 2005). FIGGS would not only provide a large sample for such a comparison, but would also provide a data set that is less subject to uncertainties due to the unknown stellar mass to light ratio or large scale non circular motions due to bars or spiral arms.

4 HI OBSERVATIONS AND DATA ANALYSIS For all the GMRT HI observations, the observing bandwidth of 1 MHz was divided into 128 spectral channels, yielding a spectral resolution of 7.81 kHz (velocity resolution of 1.65 km s-1 ). It is worth noting that this velocity resolution is 4 times bet-


FIGGS: Faint Irregular Galaxies GMRT Survey

5

[A]

[B]

Figure 2. The gas fraction of FIGGS galaxies (circles) plotted as a function of the absolute blue magnitude (left) and dynamical mass (right). FIGGS galaxies with TRGB distances are shown as solid circles, whereas the remaining FIGGS galaxies are shown as empty circles. The same quantity is also plotted for the galaxies in literature with interferometric HI maps. The gas fraction (fgas ) is defined as fgas = Mgas /(Mgas +M ). Mgas , is computed by scaling the HI mass by 1.33 to account for the primordial He fraction. No correction is made for the molecular gas. To compute the stellar mass, M , the stellar mass to light ratio in the B band ( ) was derived from the observed (B-V) colour , using from the galaxy evolution models of Bell et al.(2003) and assuming a "diet" Salpeter IMF. Solid triangles are from McGaugh(2005), solid squares from Verheijen(2001), crosses from Swaters (1999) and empty triangles from Cote et al.(2000). ^´ Note how the GMRT FIGGS sample extends the coverage of all three galaxy properties.

0.0

0.5

1.0

1.5

0

200

400

600

0

50

100

40 50

49

[A]
DECLINATION (J2000)

40 49

[B]
DECLINATION (J2000)

40 48 00

[C]

47 30
48

48
DECLINATION (J2000)

00
47

47

46 30

46

46

00

45

45 30

45

44
44

00

43

44 30
43

42 07 28 35

30

25

20 15 10 RIGHT ASCENSION (J2000)

05

00

27 55

00
07 28 30 25 20 15 10 RIGHT ASCENSION (J2000) 05 00

07 28 25

20 15 RIGHT ASCENSION (J2000)

10

Figure 3. The figure shows the integrated HI emission from one of the galaxy in FIGGS sample, DDO 43 at various resolutions viz. 46 â 42 (panel [A]), 32 â 21 (panel [B]) and 15 â 12 (panel [C]). The first contour level and contour separation for these resolutions are (1.3,12.2), (2.5,18.1) and (4.0,26.2), respectively, in units of 1019 cm-2 .

ter than most earlier interferometric studies of such faint dwarf galaxies (e.g.Lo et al. (1993)). This high velocity resolution is crucial to detect large scale velocity gradients in the faintest dwarf galaxies (e.g. Begum et al. (2003); Begum & Chengalur (2004a)). For each observing run, absolute flux and bandpass calibration was done by observing one of the standard flux calibrators 3C48, 3C286

and 3C147, at the start and end of the observations. For the sample galaxies with low LSR velocities, particular care was taken to choose a bandpass calibrator which does not have any absorption feature in the relevant velocity range. The phase calibration was done once every 30 min by observing a nearby VLA phase calibrator source.


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Table 2. Parameters of the GMRT observations

Galaxy

Date of Observations

Velocity Coverage (km s-1 ) 257 - 469 189 - 401 51 - 263 -45 - 166 317 - 529 205 - 415 - 36- 176 -205 - 7 -152 - 60 -5 - 216 404 - 616 209 - 421 248 - 460 173 - 385 235 - 447 357 - 569 445 - 657 432 - 644 438 - 650 -143 - 69 634 - 846 -208 - 3 144 - 356 106 - 318 136 - 348 534 - 746 46.0 - 258 507 - 719 -37 - 174 210 - 422 377 - 589 89 - 301 204 - 416 512 - 724 112 - 324 57 - 269 460 - 672 381 - 593 -44 - 167 475 - 686 168 - 380 96 - 308 474 - 686 86 - 298 121 - 333 47 - 259 285 - 497 255 - 469 -243 - -32

Time on Source (hours) 3. 5. 3. 4. 5. 3. 3. 2. 3. 4. 3. 5. 3. 5. 4. 4. 5. 4. 3. 3. 5. 3. 5. 4. 3. 4. 3. 3. 6. 3. 4. 4. 7. 6. 6. 3. 4. 5. 7. 2. 2. 5. 2. 6. 3. 2. 3. 2. 6. 5 0 5 0 0 0 7 1 0 5 5 0 5 0 0 0 0 5 0 0 0 5 0 0 5 5 5 5 5 0 5 0 0 0 0 5 5 0 0 5 5 5 7 5 5 5 0 5 0

synthesised Beam (arcsec2 ) 52â 50â 42â 41â 41â 46â 47â 42â 53â 53â 49â 42â 46â 41â 42â 56â 41â 41â 41â 42â 53â 42â 49â 45â 54â 51â 45â 45â 41â 45â 43â 40â 46â 51â 62â 48â 42â 48â 44â 50â 48â 42â 41â 46â 48â 61â 42â 46, 45, 40, 33, 38, 36, 37, 40, 52, 50, 46, 40, 42, 37, 41, 51, 37, 37, 36, 37, 39, 33, 41, 37, 47, 45, 37, 39, 40, 36, 38, 37, 39, 38, 54, 47, 38, 47, 36, 41, 46, 38, 39, 37, 41, 39, 41, 26â 26â 36â 30â 28â 21â 32â 26â 31â 34â 35â 28â 32â 27â 34â 42â 27â 27â 34â 46â 34â 23â 28â 27â 28â 33â 49â 28â 27â 28â 28â 31â 29â 27â 28â 29â 30â 32â 32â 26â 25â 26â 26â 31â 30â 30â 26â 36â 32â 21, 21, 25, 20, 24, 14, 26, 21, 22, 27, 25, 25, 21, 25, 26, 35, 24, 24, 25, 42 27, 20, 23, 21, 23, 24, 44 18, 23, 27, 24, 22, 24, 25, 22, 23, 24, 23, 24, 21, 17, 21, 20, 24, 25, 25, 20, 21, 28, 19â 16â 27â 16â 16â 13â 16â 16â 20â 22â 24â 18â 15â 19â 18â 28â 15â 18â 22â 20â 16â 21â 18â 19â 19â 15â 18â 24â 19â 20â 16â 19â 17â 19â 18â 21â 18â 18â 16â 17â 15â 17â 21â 19â 15â 15â 15â 17 12 19 11 13 10 11 14 16 18 14 16 12 17 14 24 13 15 20 14 15 15 13 16 18 10 15 18 14 14 12 17 14 16 16 17 15 11 11 14 11 13 18 13 14 11 14 3. 3. 4. 3. 3. 3. 1. 5. 1. 4. 6. 3. 3. 3. 3. 4. 3. 3. 4. 2. 5. 3. 4. 3. 3. 3. 2. 4. 4. 4. 2. 3. 3. 6. 3. 2. 2. 6. 4. 5. 3. 2. 3. 5. 3. 4. 3.

Noise (mJy) 2, 4, 0, 0, 0, 0, 6, 5, 9, 0, 0, 8, 2, 0, 4, 0, 0, 2, 0, 4, 0, 8, 8, 8, 0, 9, 2, 0, 0, 2, 3, 3, 6, 0, 9, 9, 6, 0, 0, 2, 6, 7, 7, 0, 4, 2, 2, 2. 1. 3. 2. 2. 2. 1. 4. 1. 2. 5. 3. 2. 2. 3. 3. 2. 2. 3. 3. 2. 3. 3. 3. 3. 2. 3. 2. 1. 3. 3. 3. 2. 2. 2. 4. 2. 2. 2. 4. 2. 3. 2. 2. 2. 4. 2. 3. 2. 4, 7, 5, 6, 5, 1, 3, 2, 3, 8, 8, 0, 6, 3, 2, 0, 2, 6, 2, 8 0, 4, 0, 5, 0, 0, 0 7, 9, 2, 2, 8, 0, 7, 7, 7, 7, 1, 2, 0, 6, 4, 8, 0, 8, 1, 6, 5, 7, 2. 1. 3. 2. 2. 1. 1. 3. 1. 2. 4. 2. 2. 1. 2. 2. 1. 2. 2. 1. 3. 2. 2. 2. 1. 2. 1. 2. 2. 3. 1. 2. 2. 4. 2. 1. 1. 3. 2. 2. 2. 1. 2. 3. 2. 2. 2. 1 4 1 2 1 8 0 5 1 4 0 6 2 9 7 5 6 1 6 8 0 4 7 7 7 3 6 8 7 0 7 4 4 1 1 8 8 5 0 7 3 7 3 4 2 9 4

Phase Cal

Cont Noise (mJy) 1. 1. 1. 1. 1. 1. 1. 2. 1. 1. 2. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 2. 2. 2. 2. 1. 1. 1. 1. 1. 1. 1. 1. 2. 2. 2. 2. 1. 1. 2. 1. 2. 1. 1. 2. 2. 1. 2. 2. 5, 3, 9, 3, 6, 9, 6, 9, 3, 7, 4, 9, 6, 7, 8, 9, 5, 6, 9, 8, 4, 0, 2, 3, 0, 8, 7, 8, 4, 6, 8, 8, 5, 0, 1, 5, 2, 8, 5, 3, 7, 1, 9, 5, 0, 4, 9, 2, 1, 0. 0. 1. 0. 0. 0. 0. 1. 0. 0. 1. 1. 1. 0. 1. 1. 0. 0. 1. 1. 1. 1. 1. 1. 1. 1. 1. 0. 0. 1. 1. 1. 0. 1. 1. 1. 1. 0. 0. 1. 1. 1. 1. 0. 1. 1. 1. 1. 1. 9 8 0 8 8 9 8 8 8 9 2 0 0 9 1 3 8 9 2 1 0 2 0 2 1 1 1 9 8 1 0 2 9 2 2 3 1 9 8 6 0 2 0 9 5 5 1 2 2

DDO 226 DDO 6 UGC 685 KKH 6 KK 14 KKH 11 KKH 12 UGCA 92 KK 41 KKH 34 E490-17 UGC 3755 DDO 43 KK 65 UGC 4115 KK 69 UGC 5186 UGC 5209 UGC 5456 HS 117 UGC 6145 UGC 6456 UGC 6541 KK 109 DDO 99 E379-07 KK 127 E321-014 UGC 7242 UGC 7505 KK 144 DDO 125 UGC 7605 UGC 8055 UGC 8215 DDO 167 KK 195 KK 200 UGC 8508 E444-78 UGC 8638 DDO 181 I4316 DDO 183 UGC 8833 DDO 187 P51659 KK 246 KKH 98

8 July 2004 1 Feb 2004 18 June 2004 9 July 2004 19 June 2004 25 Nov 2004 16 July 2004 6 June 2005 8 July 2004 9 June 2004 17 June 2004 11 Jan 2004 16 Jan 2005 25 Nov 2004 10 July 2004 3 Jan 2005 26 Nov 2004 15 Jan 2005 9 July 2004 8 Aug 2005 11 Feb 2005 19 June 2004 29 Nov 2004 6 June 2005 30 June 2005 19 Jan 2005 9 July 2004 7 Oct 2005 3 Feb 2004 28 Nov 2004 12 July 2004 6 June 2005 1 Feb 2004 13 June 2005 29 Nov 2004 10 July 2004 4 Jan 2005 26 Nov 2004 31 Jan 2004 20 June 2004 9 July 2004 6 June 2005 7 Aug 2005 31 Jan 2004 16 June 2004 16 June 2004 14 Jan 2005 16 June 2004 10 July 2004

0025-260 0116-208 0204+152 0136+473 3C48 0110+565 0110+565 0410+769 0410+769 0410+769 0608-223 0745+101 0713+438 0738+177 0745+101 0741+312 0958+324 0958+324 1008+075 1035+564 1150-003 1435+760 1035+564 1227+365 1227+365 1154-350 1227+365 1154-350 1313+675 1227+365 1221+282 1227+365 1227+365 1254+116 1227+365 1227+365 1018-317 1316-336 1400+621 1316-336 1330+251 3C286 1316-336 1331+305 3C286 3C286 1316-336 1923-210 0029+349

The GMRT data were reduced in the usual way using the standard tasks in classic AIPS. For each run, bad visibility points were edited out, after which the data were calibrated. The GMRT does not do online doppler tracking ­ any required doppler shifts have to be applied during the offline analysis. However, for all of the sample galaxies, the differential doppler shift over our observing interval was much less than the channel width, hence, there was no need to apply any offline correction. The GMRT has a hybrid configuration (Swarup et al. 1991) with 14 of its 30 antennas located

in a central compact array with size 1 km ( 5 k at 21cm) and the remaining antennas distributed in a roughly "Y" shaped configuration, giving a maximum baseline length of 25 km ( 120 k at 21 cm). The baselines obtained from antennas in the central compact array are similar in length to those of the "D" array of the VLA, while the baselines between the arm antennas are comparable in length to the "B" array of the VLA. A single observation with the GMRT hence yields information on both large and small angular scales. Data cubes at a range of angular resolutions were made


FIGGS: Faint Irregular Galaxies GMRT Survey

7

80

60

40

Kilo Wavlngth

20

0

-20

-40

-60

-80

-80

-60

-40

-20

0 20 Kilo Wavlngth

40

60

80

Figure 4. The figure shows the (u,v) coverage for UA 92, the sample galaxy with the shortest on source integration time (viz. 2.1 hours)

using appropriate (u,v) ranges and tapers. In this paper we present only the low resolution HI images, i.e. made using (u,v) ranges of 0-5 k, 0-10 k and 0-20 k. Higher resolution observations of the FIGGS sample will be presented in the companion paper. To obtain the low resolution HI images for the sample galaxies, the uv-taper at each (u,v) range was adjusted to achieve as close as possible to a circular synthesized beam. A low resolution data cube was generated for each galaxy, using the AIPS task IMAGR, and the individual channels were inspected using the task TVMOVIE to identify the channels with HI emission. Emission was detected from all of the galaxies in our sample, except for SC 24, HS 117, KK 127 and KKR 25. Apart from HS 117, all of these galaxies were previously claimed to be detected by single dish observations. The GMRT data suggest that the previous flux measurements were spurious, probably as a result of confusion with galactic emission. The galaxies KK 127 and SC 24 are likely to be distant dwarf irregular galaxies whereas KKR 25 is a normal dwarf spheroidal galaxy (Begum & Chengalur (2005); Karachentsev et al. (2006)). In the case of HS 117, single dish observations did not detect this galaxy (Huchtmeier & Skillman (1998)). The HI data given in Karachentsev et al. (2002) is a result of misidentifying galactic HI emission as emission from HS 117. For the rest of the galaxies in the sample, frequency channels with emission were identified and the continuum maps were made at both low (26 â 22 ) and high (5 â 5 ) resolutions using the average of the remaining line free channels. No extended or compact emission was detected from the disk of any of our sample galaxies. All other continuum sources lying with the field of view were subtracted using the task UVSUB. After continuum subtraction, deconvolved data cubes of the line emission were made at a range of resolutions using the AIPS task IMAGR. HI images at both high and low spatial resolutions are crucial for a complete understanding of the properties of the atomic ISM of faint dwarf galaxies. As an example, Figure 3 shows the integrated HI column distribution at various resolutions for one of the FIGGS galaxies DDO 43. This galaxy shows a faint, extended HI envelope which is only seen clearly in the lowest resolution HI maps. On the other hand, DDO 43 also has a large hole in the center (see also the

VLA observations in Simpson, Hunter, & Nordgren (2005)), which is seen in the high resolution HI map. However this hole in the HI distribution is not at all obvious in the low resolution HI maps due to the beam smearing. The setup and observational results for 49 galaxies from the FIGGS sample are given in Table 2. For the remaining 15 sample galaxies, the details of the observations and data analysis can be found in Begum et al. 2003; Begum & Chengalur 2003, 2004a,b; Begum et al. 2005; Begum & Chengalur 2005; Begum et al. 2005, 2006 and Chengalur et al. 2008 (in preparation). In the case of UGCA 438, most of the short baselines were missing because of the non availability of some of the GMRT antennas during the observing run, thus missing the diffuse, extended emission from the galaxy. Future observations of this galaxy are planned. We have not considered this galaxy for the analysis in this paper. The columns in Table 2 are as follows: Column(1) the galaxy name, Column(2) the date of observations, Column(3) the velocity coverage of the observation, Column(4) the total integration time on source, Column(5) the synthesized beam sizes of the data cubes, Column(6) the rms noise per channel for the different resolution data cubes, Column(7) the phase calibrator used, Column(8) the 3 limits on continuum emission from the galaxy at resolutions of (26 â 22 ) and (5 â 5 ) respectively. We note that although for some of the sample galaxies the on-source integration time is short ( 2 - 2.5 hours), the hybrid configuration of the GMRT leads to a reasonable sampling of the (u,v) plane. As an example, Figure 4 shows the (u,v) coverage for UA 92, the sample galaxy with the shortest on source integration time (viz. 2.1 hours). We examined the line profiles at various locations in the galaxy and found that they were (to zeroth order) symmetric and single peaked. For some galaxies, in the very high column density regions, a double gaussian and/or a gauss-hermite fit does provide a somewhat better description of the data, but even in these regions, the mean velocity produced by the moment method agrees within the errors with the peak velocity of the profile. Since we are interested here mainly in the systematic velocities, moment maps provide an adequate description of the data. Moment maps (i.e. maps of the total integrated flux (moment 0), the flux weighted velocity (moment 1) and the flux weighted velocity dispersion (moment 2)) were made from the data cubes using the AIPS task MOMNT. To obtain the moment maps, lines of sight with a low signal to noise ratio were excluded by applying a cutoff at the 2 level, ( being the rms noise level in a line free channel), after smoothing in velocity (using boxcar smoothing three channels wide) and position (using a gaussian with full width at half maximum (FWHM) 2 times that of the synthesized beam). Maps of the velocity field were also made in GIPSY using single gaussian fits to the individual profiles. The velocities produced by MOMNT in AIPS are in reasonable agreement with those obtained using a single gaussian fit. Note that the AIPS moment 2 map systematically underestimates the velocity dispersion (as obtained from gaussian fitting) particularly near the edges where the signal to noise ratio is low. This can be understood as the effect of the thresholding algorithm used by the MOMNT task to identify the regions with signal.

5 RESULTS AND DISCUSSION A detailed analysis of FIGGS data papers. Here we restrict ourselves global HI and optical properties of The global HI profiles for our will be presented in companion to a preliminary analysis of the the FIGGS sample. sample galaxies, obtained from


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Table 3. Results from the GMRT observations Galaxy FIGMRT (Jy kms-1 ) 19.5 ± 4.8 ± 2.6 ± 11.8 ± 3.0 ± 1.8 ± 25.0 ± 5.5 ± 18.8 ± 70.0 ± 4.6 ± 2.1 ± 7.3 ± 6.5 ± 14.2 ± 2.52 ± 21.6 ± 3.8 ± 21.5 ± 3.0 ± 1.4 ± 2.0 ± 8.0 ± 2.1 ± 10.1 ± 2.7 ± 74.7 ± 0.76 ± 33.0 ± 5.0 ± 1.3 ± 7.2 ± 4.7 ± 5.2 ± 11.5 ± 8.7 ± 21.7 ± 4.93 ± 11.0 ± 9.0 ± 4.5 ± 3.7 ± 4.8 ± 1.6 ± 18.3 ± 2.3 ± 3.5 ± 12.2 ± 2.2 ± 10.5 ± 6.3 ± 2.2 ± 11.1 ± 17.4 ± 4.4 ± 16.4 ± 10.6 ± 12.1 ± 4.4 ± 2.0 0.5 0.3 1.2 0.3 0.2 2.5 0.6 1.9 7.1 0.4 0.2 0.7 0.7 1.4 0.3 2.2 0.4 2.2 0.3 0.1 0.2 0.8 0.2 1.0 0.3 7.5 0.08 3.3 0.5 0.1 0.7 0.5 0.5 1.2 0.9 2.2 0.5 1.1 0.9 0.5 0.4 0.5 0.2 1.8 0.2 0.4 1.2 0.2 1.1 0.6 0.2 1.1 1.7 0.4 1.6 1.0 1.2 0.4 Vsys (kms-1 ) 237.0 358.57 291.83 156.29 59.92 420.11 295.71 70.0 -54.2 -94.58 77.5 106.29 505.17 310.81 352.63 281.45 342.78 116.0 19.2 462.04 546.08 535.19 526.75 753.0 -93.69 249.36 228.8 210.67 251.22 644.04 609.39 66.05 159.0 174.0 316.0 479.54 206.25 309.95 609.05 217.0 224.15 150.24 571.91 493.69 56.17 577.0 275.9 213.6 576.34 188.37 221.03 63.31 159.95 391.48 434.71 126.0 130.3 -139.5 -132.26 V50 (kms-1 ) 90.0 37.0 19.2 64.4 28.0 27.7 84.4 48.4 38.5 56.2 21.4 21.7 39.2 34.5 36.5 33.3 78.0 20.6 29.6 13.1 34.0 31.6 62.4 41.1 37.4 25.5 83.4 18.2 33.7 28.5 19.0 66.5 26.6 21.4 125.1 37.5 27.4 25.8 85.6 26.0 24.6 18.6 24.0 17.4 45.8 30.6 30.8 39.1 21.5 28.7 27.8 17.0 30.6 46.4 52.2 95.5 51.7 19.1 20.7 DH ()
I

MHI (106 M ) 205.19 25.95 6.82 56.15 10.18 21.93 52.88 11.63 67.20 156.05 12.2 10.44 30.26 41.30 203.02 34.38 285.53 10.8 64.2 41.89 15.66 21.10 58.96 27.02 43.89 9.65 130.0 3.62 52.42 31.77 3.13 45.75 26.4 21.6 442.78 81.15 31.87 22.29 782.64 10.38 21.41 14.51 30.50 7.96 29.07 14.62 13.76 27.55 10.01 25.90 15.16 1.90 16.30 52.99 84.50 121.0 78.0 2.8 6.46

MHI LB

DH I DH o

FIGMRT FISD

iHI (deg) 55.0 ± 55.0 ± - 36.0 ± 30.0 ± 45.0 ± 66.0 ± 60.0 ± 30.0 ± 56.0 ± 61.0 ± 45.0 ± - 46.0 ± 30.0 ± 47.0 ± 50.0 ± 23.0 ± 30.0 ± 35.0 ± - - 60.0 ± 55.0 ± 65.0 ± - 68.0 ± - - 31.0 - - 58.0 ± 42.0 ± 28.0 ± 70.0 ± 57.0 ± - 40.0 ± 45.0 ± 27.0 ± 45.0 ± - 52.0 - - 53.0 ± 42.0 - - 53.0 ± - 67.0 ± 26.0 ± 50.0 ± 37.0 ± 68.0 ± 56.0 ± 73.0 ± 59.0 ± 26.0 ± 46.0 ± 5.0 5.0 4. 3. 3. 3. 3. 4. 3. 5. 3. 4. 5. 4. 7. 4. 4. 3. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Ref

And IV DDO 226 DDO 6 UGC 685 KKH 6 KK 14 KKH 11 KKH 12 KK 41 UGCA 92 KK 44 KKH 34 E490-17 UGC 3755 DDO 43 KK 65 UGC 4115 KDG 52 UGC 4459 KK 69 UGC 5186 UGC 5209 UGC 5456 UGC 6145 UGC 6456 UGC 6541 NGC 3741 KK 109 DDO 99 E379-07 E321-014 UGC 7242 CGCG 269-049 UGC 7298 UGC 7505 KK 144 DDO 125 UGC 7605 UGC 8055 GR 8 UGC 8215 DDO 167 KK 195 KK 200 UGC 8508 E444-78 UGC 8638 DDO 181 I4316 DDO 183 UGC 8833 KK 230 DDO 187 P51659 KK 246 KK 250 KK 251 DDO 210 KKH 98

7.6 3.5 3.3 3.6 2.6 2.4 7.2 4.6 8.7 9.0 3.2 2.6 3.0 3.0 5.0 2.1 6.0 3.5 4.5 4.0 1.6 1.9 2.8 2.7 3.7 2.1 14.6 1.4 9.6 3.6 2.1 4.0 2.6 3.5 5.3 4.7 7.0 3.3 4.2 4.3 3.5 2.0 5.0 1.4 6.6 0.9 1.2 5.2 2.8 4.6 3.0 3.0 3.4 6.5 3.5 5.8 4.2 4.8 3.8

16.9 0.36 0.44 0.68 0.71 1.98 1.56 0.46 1.03 0.55 1.4 0.81 0.32 0.29 1.64 0.43 3.59 1.8 1.4 2.11 0.65 0.75 0.35 0.96 0.69 0.20 4.7 2.98 1.32 2.43 0.17 0.70 0.9 1.7 1.72 4.80 0.44 0.55 3.20 1.02 1.72 0.78 3.88 0.84 1.21 0.45 0.30 1.08 0.18 0.90 1.05 1.9 1.04 6.31 1.36 1.2 1.6 1.0 2.02

6.9 1.09 1.57 1.64 2.90 1.50 4.23 2.10 3.35 4.50 2.3 2.60 1.50 1.67 2.78 2.33 4.00 2.7 2.8 2.0 1.00 2.11 1.50 1.59 2.47 1.29 8.80 1.00 2.74 3.27 1.49 2.11 2.3 3.1 5.30 3.13 1.67 1.50 3.00 2.3 3.50 1.25 3.85 1.00 3.30 1.67 1.00 3.25 1.00 2.71 2.31 3.3 1.36 2.71 2.69 3.2 2.6 1.3 3.45

0. 0. 0. 0.

87 ± 0.11 79 ± 0.10 77 ± 0.10 99 ± 0.11 0.72 0.89 ± 0.10 1.09 ± 0.12 0.34 0.42 0.70 1.02 ± 0.11 0.89 ± 0.1 1.11 ± 0.13 0.96 ± 0.11 1.20 ± 0.15 0.97 ± 0.11 1.00 ± 0.11 0.85 ± 0.11 1.01 ± 0.11 1.07 ± 0.12 0.96 ± 0.11 1.21 ± 0.13 1.16 ± 0.14 1.00± 0.11 0.72 0.90 ± 0.10 - 1.08 ± 0.12 1.04 ± 0.12 0.93 ± 0.10 0.46 ± 0.05 1.02 ± 0.11 0.91 ± 0.10 1.06 ± 0.11 0.92 ± 0.10 1.01 ± 0.11 1.00 ± 0.11 0.87 ± 0.10 1.34 ± 0.32 1.03 ± 0.11 1.05 ± 0.11 0.88 ± 0.10 0.91 ± 0.11 0.94 ± 0.11 1.21 ± 0.14 0.83 ± 0.12 0.90 ± 0.10 1.07 ± 0.12 1.05 ± 0.12 1.07 ± 0.12 1.05 ± 0.11 0.86 ± 0.11 0.93 ±0.10 1.03 ± 0.11 0.53 0.82 ± 0.11 0.73 ±0.11 1.05 ± 0.11 1.07 ± 0.12

5.0 5.0 3.0 4.0

6.0 3. 4. 3. 4. 4. 5. 3. 4. 4. 0 0 0 0 0 0 0 0 0

4.0 4.0 3.0 3.0 3. 3. 4. 4. 4. 3. 4. 5. 7. 5. 0 0 0 0 0 0 0 0 0 0

14 1 2 3 2 6 2 2 2 5 11 2 2 2 2 2 2 11 11 2 2 7 3 5 2 2 10 2 5 8 5 5 11,12 11 5 2 5 2 3 11 2 4 5 2 4 9 2 2 5 2 2 11 2 5 5 13 13 11 2

References: 1-Cote et al. (1997) 2-Huchtmeier et al. (2003) 3-Hoffman et al. (1996) 4-Huchtmeier & Richter (1986) 5-Karachentsev et al. (2004) 6-Giovanelli et al. (2005) 7-Springob et al. (2005) 8-Matthews et al. (1995) 9-Bouchard et al. (2007) 10-Begum et al. (2008) 11-Begum et al. (2006) 12-Pustilnik & Martin (2007) 13-Begum & Chengalur (2004b) 14- Chengalur et al. 2008 (in preparation)


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Figure 5. The global HI profiles of the sample galaxies obtained from the lowest resolution data cubes (see Table 2).

the coarsest resolution data cubes (see Table 2) are shown in Figure 5. The parameters derived from the global HI profiles for the whole FIGGS sample are listed in Table 3. The columns are as follows: (1) the galaxy name, (2) the integrated HI flux along with the errorbars, (3) the central heliocentric velocity (Vsys ), (4) the velocity width at 50% of the peak (V50 ), (5) the HI diameter (in arcmin) at a column density of 1019 atoms cm-2 (DHI ), (6) the

derived HI mass (MHI ), (7) the HI mass-to-light ratio (MHI /LB ), (8) the ratio of the HI diameter to the Holmberg diameter. (9) the ratio of the GMRT flux to the single dish flux (FI/FISD ), (10) the inclination as measured from the HI moment 0 maps (iHI ), and (11) the reference for the single dish fluxes. As seen in Column(9) in Table 3, the HI flux measured from the GMRT HI profiles for most FIGGS galaxies, in general, agree


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Figure 5. (continued)The global HI profiles of the sample galaxies obtained from the lowest resolution data cubes (see Table 2).

(within the errorbars) with the values obtained from the single dish observations. The average ratio of GMRT flux to single dish flux is 0.98. This indicates that in general no flux was missed because of the missing short spacings in our interferometric observations. However, for some galaxies the integrated flux derived from the GMRT observations is significantly smaller than the single dish values. The GMRT fluxes could be lower than those obtained from

single dish measurements either because of (i) a calibration error or (ii) a large fraction of HI being in an extended distribution that is resolved out, or (iii) the single dish flux is erroneous, possibly because of confusion with galactic emission. However, the flux of the point sources seen in the GMRT images are in good agreement with those listed in NVSS, indicating that our calibration is not at fault. We note that in the case of KKH 12, KKH 6, UGC 6456, UGCA 92


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Figure 5. (continued)The global HI profiles of the sample galaxies obtained from the lowest resolution data cubes (see Table 2).

and KK 41 there is a strong local HI emission at velocities very close to the systemic velocities, making it likely that the single dish integrated flux measurements for these galaxies were contaminated by blending of their HI emission with that of the galactic emission. In the case of KK 246, its HI spectrum was near the edge of the GMRT observing band, hence the flux could not be reliably estimated. The GMRT integrated HI emission of the sample galaxies, obtained from the coarsest resolution data cubes (see Table 2), overlayed on the optical Digitized Sky Survey (DSS) images are shown in Figure 6. The HI morphological inclinations (iHI ) for our sample galaxies were estimated from the integrated HI maps by fitting elliptical annuli to the HI images at various resolutions. For sample galaxies which have HI disks less extended than 2 synthesised beams (across the diameter of the galaxy) at the lowest HI resolution, could in principle be derived from the higher resolution HI maps. However, for most sample galaxies ellipse fitting to the high resolution HI maps is not reliable because of clumpiness in the central high column density regions. The derived inclination (without applying any correction for the intrinsic thickness of the HI disk) is given in Column(10) in Table 3. Figure 7 shows a comparison between the morphological inclination derived from the optical and HI isophotes of the galaxy. No correction has been applied for the intrinsic thickness of the disk in both cases. The solid line shows a case when both inclinations are the same. We find that for 6 galaxies the HI inclination is significantly greater than the optical inclination (viz. KKH 11, UGC 6456, NGC 3741, UGC 8055, KK 230, KK 250). On the other hand, for many galaxies the optical inclination is found to be systematically higher than the inclination derived from the HI morphology. This result, if interpreted literally, suggest that the HI disks of these galaxies are thicker than the disks of their optical counterparts. However, we caution that a proper analysis using deconvolved angular sizes of the the HI disks needs to be done before a firm conclusion can be drawn. The diameter of the HI disk at a column density of

NHI 1019 atoms cm-2 (except for UGCA 92 where the HI diameter is measured at NHI 1020 atoms cm-2 ) estimated from the lowest resolution integrated HI emission maps is given in Column(7) of Table 3. The ratio of the HI diameter to the optical (Holmberg) diameter for the sample is also given in Column(9) of the same table. Figure 8 shows the histogram of the derived HI extent of FIGGS at NHI 1019 cm-2 , normalised to the Holmberg diameter of the galaxy. The median HI extent of the FIGGS sample (normalised to Holmberg diameter of the galaxy) is 2.4. For a comparison, Hunter (1997) using the data compiled from the literature for comparatively bright Im galaxies found that the ratio of DHI /DHo is somewhat smaller, viz. 1.5-2. The extreme outliers in Figure 8 is NGC 3741, our FIGGS data show it to have an HI extent of 8.3 times DHo (Holmberg diameter). Followup WSRT+DRAO+GMRT observations resulted in HI being detected out to 8.8 DHo - NGC 3741 has the most extended HI disk known. For NGC 3741 the rotation curve could be derived out a record of 44 times the disk scale length and from the last measured point of the rotation curve we estimate the dynamical mass to light ratio, MD /LB 149 - which makes it one of the "darkest" irregular galaxies known (Begum et al. 2005, 2008). Figure 9 shows a tight correlation between HI mass and the HI diameter, measured at NHI of 1 â 1019 cm-2 for FIGGS sample. The galaxies in FIGGS sample with accurate distances are shown as solid points, whereas the remaining galaxies are shown as open circle. The best fit to the whole FIGGS sample shown as a solid line gives log(MHI ) = (1.99 ± 0.11)log(DHI ) + (6.08 ± 0.06) (1)

The best fit relation was also derived using only the galaxies with TRGB distances, however no significant difference was found between the best fit parameters derived in this case and that derived using the whole sample. Eqn.(1) implies that the HI disks of the FIGGS sample are well described as having an constant average surface mass density 1.5 M pc-2 . A tight correlation between HI mass and the size of the HI disk has been noted


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Figure 6. The GMRT integrated HI column density distribution (contours) overlayed on the optical DSS images (grey scales) of FIGGS galaxies from the lowest resolution data cubes (see Table 2). The contours are uniformly spaced. The first contour level and the contour separation are printed below the galaxy name in units of 1019 cm-2 .


FIGGS: Faint Irregular Galaxies GMRT Survey

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Figure 6. (continued) The GMRT integrated HI column density distribution (contours) overlayed on the optical DSS images (grey scales) of FIGGS galaxies from the lowest resolution data cubes (see Table 2).The first contour level and the contour separation are printed below the galaxy name in units of 1019 cm-2 .


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Figure 6. (continued) The GMRT integrated HI column density distribution (contours) overlayed on the optical DSS images (grey scales) of FIGGS galaxies from the lowest resolution data cubes (see Table 2). The first contour level and the contour separation are printed below the galaxy name in units of 1019 cm-2 .

earlier for spiral galaxies (e.g. Broeils & Rhees (1997)) and for brighter dwarf galaxies (Swaters 1999). For these samples the HI diameter was measured at a slightly higher column density, viz. 1 M pc-2 . For the FIGGS galaxies, the relationship between the HI mass and the HI diameter measured at 1 M pc-2 is log(MHI ) = (1.96 ± 0.10)log(DHI ) + (6.37 ± 0.07), for comparison, Broeils & Rhees (1997) measure log(MHI ) = (1.96 ± 0.04)log(DHI ) + (6.52 ± 0.06). The fit coefficients overlap within the error bars. Hence from the FIGGS data we find that there is at best marginal evidence for a decrease in average HI surface density with decreasing HI mass; to a good approximation, the disks of gas rich galaxies, ranging over 3 orders of magnitudes in HI mass, can be described as being drawn from a family with constant HI surface density. The HI mass also correlates with the optical (Holmberg) diameter (shown in Fig. 10), although with a larger scatter. A linear fit with a slope and intercept of 1.74±0.22 and 6.93±0.18, respectively is shown as a solid line. The larger scatter in the relation between MHI and the optical diameter, also seen in sample of brighter dwarfs (e.g. Swaters (1999)), is probably indicative of a looser coupling between the gas and star formation in dwarfs, compared to that in spiral galaxies. Figure 11 shows the HI mass to light ratio for the FIGGS sample plotted as a function of the HI extent, DHI /DHo . A trend of an increase in the MHI /LB with an increase in the HI extent of the galaxies is clearly seen. The best fit to the FIGGS sample shown as a solid line gives log( MHI DHI ) = (1.31 ± 0.18)log( ) + (-0.43 ± 0.08) LB DHo (2)

Figure 7. A comparison of the morphological optical and HI inclination of the FIGGS sample. The solid lines shows the case when the two inclinations are the same.

van Zee et al.(1995) from a HI mapping of a sample of low luminosity galaxies also found an evidence of an extended HI extent for high MHI /LB galaxies. Figure 12 shows MHI /LB for the FIGGS sample as a function

of MB . The same quantity for several other spiral and dwarf galaxies, spanning a range in absolute B magnitude from MB -23 to MB -9 is also plotted. The sample from which these galaxies have been drawn are listed in the figure caption. The galaxies in FIGGS sample with TRGB distances are shown as solid circles, whereas the remaining FIGGS galaxies are shown as open circles. The solid line shows an empirically determined upper envelope for MHI /LB as a function of a MB from Warren et al. (2007). This upper envelope can be interpreted as a minimum fraction of the total


FIGGS: Faint Irregular Galaxies GMRT Survey

15

Figure 8. The histogram of the extent of the HI disk (measured at NH I = 1 â 1019 cm-2 ), normalised to the Holmberg diameter for the FIGGS sample.

Figure 10. The HI mass for the FIGGS sample versus the Holmberg diameter. The solid line represents the fit to the data points. Galaxies in FIGGS sample with TRGB distances are shown as solid points, while the remaining galaxies in the sample are shown as open circles.

E215-G009

DDO154 UA292

Figure 9. The HI mass for the FIGGS sample versus the HI diameter (measured at NHI 1019 cm-2 ). The solid line represents the fit to the data points. Galaxies in FIGGS sample with TRGB distances are shown as solid points, while the remaining galaxies in the sample are shown as open circles.

Figure 11. The log of HI mass to B band light ratio for the FIGGS sample plotted as a function of the extent of the HI disk (measured at NHI 1 â 1019 cm-2 ) normalised to the Holmberg diameter. Crosses show three additional galaxies from the literature with high MHI /LB and extended HI disks, UA292 (Young et al. 2003), ESO215-G?009 (Warren et al. 2004) and DDO 154 ( Carignan & Purton 1998).

baryonic mass which needs to be converted into stars in order for a galaxy of a given baryonic mass to remain gravothermally stable (Warren et al. (2007)). It is interesting to note that except for And IV, all FIGGS galaxies lie much below this upper envelope. This implies that these galaxies have converted much more baryons into stars than the minimum required for remaining stable. In this context, it is interesting to note that the average gas fraction for the FIGGS sample is 0.7. Thus, for the majority of the dwarf galaxies in our sample, the baryonic mass is dominated by gas, rather than stars.

In order to investigate the environmental dependence of the HI content for FIGGS galaxies, we plot MHI /LB for FIGGS sample as a function of tidal index (TI) (Figure 13). Some additional gas rich galaxies with known HI extent are also plotted in the figure. TI is taken from Karachentsev et al. (2004) and it represents the local mass density around a given galaxy, estimated using a large sample of galaxies within 10 Mpc of the Milky Way. A negative value of TI for a galaxy indicates that the galaxy is isolated, whereas a pos-


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DDO154 E215-G009

Figure 12. The log of HI mass to light ratio vs. B band absolute magnitude. Galaxies from FIGGS sample with TRGB distances are shown as solid points whereas the remaining FIGGS galaxies are shown as open circles. Crosses are galaxies from Warren et al.(2007) and solid triangles from Verheijen (2001). The solid line marks the locus of an upper envelope for the H I mass-to-light ratio at a given luminosity from Warren et al.(2007).

Figure 14. The HI berg radius) plotted Additional galaxies 154 and ESO215-G

extent of the FIGGS sam as a function of the tidal from literature with very ?009 and are also marked

ple (normalised to the Holmindex for the FIGGS sample. extended HI disks viz. DDO in the plot.

E215-G009

DDO154 UA292

Faint Irregular Galaxies GMRT Survey (FIGGS). FIGGS is a large imaging program aimed at providing a comprehensive and statistically robust characterisation of the neutral ISM properties of extremely faint, nearby, gas rich, dIrr galaxies using the GMRT. The GMRT HI data is supplemented with observations at other wavelengths. The HI images in conjunction with the optical data will be used to investigate a variety of scientific questions including the star formation feedback on the neutral ISM, threshold for star formation, baryonic TF relation and dark matter distribution in low mass galaxies. The optical properties of the FIGGS sample, GMRT observations and the main science drivers for the survey are described. The GMRT integrated HI column density maps and the HI spectra for the sample galaxies are presented. The global HI properties of the FIGGS sample, derived from the GMRT observations, and their comparison with the optical properties of the sample galaxies are also presented. A detailed comparison of the gas distribution, kinematics and star formation in the sample galaxies will be presented in the companion papers.

ACKNOWLEDGMENTS
Figure 13. The log of HI mass to light ratio as a function of the tidal index for the FIGGS sample. Additional galaxies from literature with high MHI /LB are also marked in the plot.

The observations presented in this paper were made with the Giant Metrewave Radio Telescope (GMRT). The GMRT is operated by the National Center for Radio Astrophysics of the Tata Institute of Fundamental Research. Partial support for this work was provided by ILTP grant B-3.13.

itive number indicates that the galaxy is in a dense environment. Figure 13. shows that most of the FIGGS galaxies are in less dense e environments, and that all the galaxies with high MHI /LB (i.e > 2.5) have negative tidal index i.e are isolated. Figure 14 shows the HI extent of the FIGGS sample, normalised to the optical (Holmberg) radius, plotted as a function of TI. As seen in the figure, the galaxies with very extended HI disks (DHI /DHo > 5.0) are isolated. To summarize, we have presented the first results from the

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