The ATLAS3D project – XIII. Mass and morphology of H i in early-type galaxies as a function of environment

Mon. Not. R. Astron. Soc. 422, 1835–1862 (2012) doi:10.1111/j.1365-2966.2012.20219.x The ATLAS3D project – XIII. Mass and morphology of H I in early-type galaxies as a function of environment Paolo Serra,1 Tom Oosterloo,1,2 Raffaella Morganti,1,2 Katherine Alatalo,3 Leo Blitz,3 Maxime Bois,4,5 Frédéric Bournaud,6 Martin Bureau,7 Michele Cappellari,7 Alison F. Crocker,7,8 Roger L. Davies,7 Timothy A. Davis,7 P. T. de Zeeuw,4,9 Pierre-Alain Duc,6 Eric Emsellem,4,5 Sadegh Khochfar,10 Davor Krajnović,4 Harald Kuntschner,11 Pierre-Yves Lablanche,4,5 Richard M. McDermid,12 Thorsten Naab,13 Marc Sarzi,14 Nicholas Scott,7 Scott C. Trager,2 Anne-Marie Weijmans15 † and Lisa M. Young16 1 Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, the Netherlands 3 Department of Astronomy, Campbell Hall, University of California, Berkeley, CA 94720, USA 4 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany 5 Université Lyon 1, Observatoire de Lyon, Centre de Recherche Astrophysique de Lyon and Ecole Normale Supérieure de Lyon, 9 avenue Charles André, F-69230 Saint-Genis Laval, France 6 Laboratoire AIM Paris-Saclay, CEA/IRFU/SAp – CNRS – Université Paris Diderot, 91191 Gif-sur-Yvette Cedex, France 7 Sub-Department of Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH 8 Department of Astrophysics, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003, USA 9 Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, the Netherlands 10 Max-Planck Institut für extraterrestrische Physik, PO Box 1312, D-85478 Garching, Germany 11 Space Telescope European Coordinating Facility, European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany 12 Gemini Observatory, Northern Operations Centre, 670 N. A‘ohoku Place, Hilo, HI 96720, USA 13 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany 14 Centre for Astrophysics Research, University of Hertfordshire, Hatfield, Herts AL1 9AB 15 Dunlap Institute for Astronomy & Astrophysics, University of Toronto, 50 St George Street, Toronto, ON M5S 3H4, Canada 16 Physics Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA Accepted 2011 November 15. Received 2011 October 3 ABSTRACT We present the ATLAS3D H I survey of a volume-limited, complete sample of 166 nearby early-type galaxies (ETGs) brighter than M K = −21.5. The survey is mostly based on data taken with the Westerbork Synthesis Radio Telescope, which enables us to detect H I down to 5 × 106 –5 × 107 M within the survey volume. We detect ∼40 per cent of all ETGs outside the Virgo galaxy cluster and ∼10 per cent of all ETGs inside it. This demonstrates that it is common for non-cluster ETGs to host H I. The morphology of the detected gas varies in a continuous way from regular, settled H I discs and rings to unsettled gas distributions (including tidal or accretion tails) and systems of clouds scattered around the galaxy. The majority of the detections consist of H I discs or rings (1/4 of all ETGs outside Virgo) so that if H I is detected in an ETG it is most likely distributed on a settled configuration. These systems come in two main types: small discs [M(H I) < 108 M ], which are confined within the stellar body and share the same kinematics of the stars; and large discs/rings [M(H I) up to 5 × 109 M ], which extend to tens of kpc from the host galaxy and are in half of the cases kinematically decoupled from the stars.  E-mail: †Dunlap Fellow.  C 2012 The Authors C 2012 RAS Monthly Notices of the Royal Astronomical Society  2 Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, the Netherlands 1836 P. Serra et al. Key words: galaxies: elliptical and lenticular, cD – galaxies: evolution – galaxies: ISM – radio lines: galaxies. 1 I N T RO D U C T I O N In the classification scheme proposed by Hubble (1936) galaxies are arranged in a sequence going from ellipticals to lenticulars and, from these, to spirals of progressively later type (Sa to Sc). Ellipticals are dominated by a stellar bulge while the spiral sequence is essentially one of decreasing bulge-to-disc ratio. The intermediate position of lenticular galaxies in this scheme has led to the common idea that all early-type galaxies (ETGs; ellipticals and lenticulars) have higher bulge-to-disc ratio than spirals. The other difference between ETGs and spirals is that the former lack the blue spiral arms typical of the latter (Hubble 1926). It was early recognized that this corresponds to a lack of star formation in ETGs, leading to the simplified picture that their stellar populations are uniformly old. In contrast with this traditional view, ETGs exhibit a large variety of shapes and some authors suggest that their bulge-to-disc ratio can in fact be as low as that of Sc, disc-dominated spirals (Spitzer & Baade 1951; Sandage, Freeman & Stokes 1970; van den Bergh 1976). Furthermore, following early insights by Gunn, Stryker & Tinsley (1981) and Rabin (1982), it is now established that a large fraction of ETGs are forming small amounts of stars or have done so in their recent past (e.g. González 1993; Trager et al. 2000; Yi et al. 2005; Kaviraj et al. 2007; Thomas et al. 2010). Support to these ideas comes from recent studies of nearby ETGs using integral-field spectroscopy (de Zeeuw et al. 2002). These show that most ETGs host a rotating, kinematically cold component (Krajnović et al. 2008) whose stars are usually younger and more metal-rich than those in the bulge (Kuntschner et al. 2010). These results are placed on a firm statistical ground by ATLAS3D , a multi-wavelength study of a volume-limited sample of 260 morphologically selected ETGs (Cappellari et al. 2011a, hereafter Paper I). We find that as many as 80 per cent of all ETGs in the nearby Universe consist of nearly axisymmetric, fast rotating stellar systems (Krajnović et al. 2011, hereafter Paper II; Emsellem et al. 2011, hereafter Paper III), most of which resemble spiral galaxies with the arms removed (Cappellari et al. 2011b, hereafter Paper VII). The presence of a substantial disc and the occurrence of star formation in ETGs imply that cold gas has played an important role in their evolution. Indeed, Khochfar et al. (2011) suggest that most ETGs grow a stellar disc following gas cooling. In this respect, two fundamental lines of research are the direct observation of neutral hydrogen gas (H I) and molecular gas (H2 , observed through the radiation emitted by CO molecules). In spirals, H I is an essential constituent of the disc, and is the material from which H2 and subsequently new stars form. Understanding the H I and H2 properties of ETGs is therefore crucial to investigate the origin of their structure and star formation history; how they continue to evolve at z = 0; and why they a (...truncated)