Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/people/Ray.Norris/papers/n274.pdf Дата изменения: Fri Apr 15 03:35:37 2011 Дата индексирования: Fri Feb 28 08:13:29 2014 Кодировка: Поисковые слова: galaxy cluster

J. Astrophys. Astr. (0000) 00, 000­000

ATLAS, and Wide-Angle Tail Galaxies in ATLAS Minnie Y. Mao1,2,3, Rob Sharp2, D. J. Saikia Ray P. Norris3, Melanie Johnston-Hollitt6, Enno Middelberg7 and Jim E. J. Lovell1
1 2 3 4 5 6 7

3 ,4 ,5

,

University of Tasmania, Hobart, 7001, Australia AAO, Epping, NSW, 1710, Australia CSIRO ATNF, Epping, NSW, 1710, Australia NCRA, TIFR, Pune 411 007, India ICRAR, University of Western Australia, Craw ley, WA 6009, Australia Victoria University of Wel lington, Wel lington, New Zealand Ruhr-UniversitЁt Bochum, 44801 Bochum, Germany a

2011 April 14

Abstract. Using the Australia Telescop e Compact Array (ATCA), ATLAS (Australia Telescop e Large Area Survey) is imaging two fields totalling 7 square degrees down to 10 µJy b eam-1 at 1.4 GHz. We have found 6 wide-angle tail galaxies (WATs), 4 of which have sufficient data to identify associated galaxy overdensities. The largest WAT, at a redshift of 0.22, app ears to b e associated with an overdensity of galaxies that is spread over an unusually large extent of 12 Mp c, with a velocity range of 4500 km s-1 . Here we present the WATs in ATLAS and discuss the implications of these observations for future largescale radio surveys such as ASKAP-EMU. Key words: galaxies: clusters: general ­ galaxies: active ­ galaxies: general ­ radio continuum: galaxies ­ galaxies: distances and redshifts

1.

Intro duction

The formation and evolution of galaxies over cosmic time remains one of the most p erplexing issues in modern astronomy. Radio-loud galaxies can b e seen to arbitrality high redshifts, consequently deep radio surveys can b e used to help understand galaxy formation and evolution. ATLAS is imaging


e-mail: mymao@utas.edu.au

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Mao et al.

7 square degrees down to 10 µJy b eam-1 at 1.4 GHz using ATCA (Data Release 1: Norris et al. 2006, Middelb erg et al. 2008). To mitigate the effects of cosmic variance, ATLAS is split over two fields; Chandra Deep Field South (CDFS) and Europ ean Large Area ISO Survey - South 1 (ELAISS1). The ATLAS fields were chosen to coincide with the Spitzer Wide-Area InfraRed Extragalactic (SWIRE) survey program (Lonsdale et al. 2003) so that corresp onding optical and infrared photometric data are available. ATLAS's first data release has an rms of 30 µJy b eam-1 and contains 2004 radio sources. The final data release (Banfield et al. 2011) will have an rms of 10 µJy b eam-1 and we exp ect the detection of 16000 radio sources. The data presented in this pap er are from data release one. The resolution of ATLAS (10 ) allows us to classify morphologically many of the extended radio sources including wide-angle tail galaxies (WATs) and radio relics. WATs are radio galaxies whose radio jets app ear to b end in a common direction. They are usually associated with dominant cluster galaxies (Owen & Rudnick 1976), are generally detected in unrelaxed clusters (Burns 2008) and have b een used as prob es for clusters (e.g. Blanton et al 2000, 2001). In ATLAS we have found six WATs and also a putative radio relic (Middelb erg et al. 2008, Mao et al. 2010).

2.

WATs in ATLAS

We identified six WATs in ATLAS by visually examining ATLAS images. Figure 1 show the ATLAS radio contours overlaid on DSS red images. The WATs range in redshift from 0.15 to 0.38, and their prop erties are summarized in Table 1. The WATs all have radio luminosities consistent with FRI typ e galaxies. The optical sp ectra of the host galaxies are all typical of early-typ e galaxies that host luminous radio sources. Four of the WATs have sufficient optical data in their immediate vicinity to allow us to prob e for overdensities, and all four showed evidence for overdensities (Mao et al. 2010). S1189, the largest WAT in our sample, app ears to b e associated with an overdensity that spans a linear extent of 12 Mp c. The overdensity has a velocity range of 4500 km s-1 , which is similar to typical rich clusters in the local Universe undergoing mergers. There also app ears to b e a radio relic in the immediate vicinity (10 arcmin) of S1189. In Mao et al. (2010) we discuss the p ossibility that the large substructure surrounding S1189 represents an unrelaxed system with different sub-structures interacting or merging with one another.


ATLAS & WATs in ATLAS S132 S483 S1189

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S1192

S031

S409

Figure 1. Radio contours of the six WATs in ATLAS overlaid on DSS red images. The radio contours start from 100 µJy beam -1 (3 в rms) and increase by factors of 2.

Table 1. The WATs in ATLAS. All except for S132 where we have listed from SWIRE is not available. All the observations with the exception of S4 et al. (2001).

of the R-band magnitudes are from SWIRE, the value from superCOSMOS since a value WAT redshifts were obtained from our AAT 09 whose redshift was determined by Colless

ATLAS ELAIS S132 S483 S1189 S1192 CDFS S031 S409

SWIRE Counterpart

z

Robs (mag) 18.1 18.28 17.12 18.92 16.63 16.35

Power1.4 (1024 W/Hz) 2.58 2.16 6.25 4.82 5.81 2.41

S S S S

WI WI WI WI

R R R R

E E E E

4 4 4 4

J J J J

003236.18-44210 003311.21-43551 003427.54-43022 003320.68-43020

1.1 2.3 2.5 3.6

0.3762 0.3164 0.2193 0.3690 0.2183 0.1469

SWIRE3 J032639.11-280801.5 SWIRE3 J033210.74-272635.5


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3.

Implications for EMU and beyond

We have found six WATs in ATLAS. Using deep er, higher resolution radio data, Dehghan et al. (2011) have identified 10 more WATs in CDFS. In the near future EMU, the Evolutionary Map of the Universe (Norris et al. 2011a, Norris et al. 2011b), will image 75% of the sky down to an rms of 10 µJy b eam-1 at 1.4 GHz at a resolution similar to that of ATLAS. EMU exp ects to detect 70 million radio sources. Extrap olating the six WATs out of 2004 sources in ATLAS suggests EMU might exp ect to detect 200000 WATs. Alternatively, extrap olating the six WATs in 7 deg2 of ATLAS suggests EMU might exp ect to detect 26000 in its 30000 deg2 . The difference b etween these figures is caused by the difference in sensitivity b etween EMU and the ATLAS data release 1, and these two numb ers therefore represent upp er and lower b ounds resp ectively. All we can say at present is that EMU will detect b etween 26000 and 200000 WATs. To narrow this numb er down we need to know the local luminosity function for WATs, the redshift distribution of WATs, and how the luminosity function evolves with cosmic time, and our knowledge of each of these is limited by the small numb er of known WATs. The detection of tens of thousands of WATs in the Universe will b e significant. Given that each WAT is associated with a cluster, EMU will b e exceptional for detecting clusters and exploring their prop erties, particularly since the luminosity of the WATs makes them detectable out to high redshifts. The detection of high-redshift clusters will contribute significantly to understanding the formation and evolution of large-scale structure and clusters.

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