Coma Cluster Treasury SurveyAlister W. Graham (Swinburne), Helmut Jerjen (ANU), Terry J. Bridges (AAO & Aust. Gemini Office)

andDavid Carter (P.I.), Habib Khosroshahi, Mustapha Mouhcine, Susan Percival (Liverpool John Moores University, UK); Harry Ferguson, Paul Goudfrooij (Space Telescope Science Institute, USA); Thomas Puzia (Dominion Astrophysical Observatory, Canada); Carlos del Burgo (Dublin Institute For Advanced Studies, Ireland); Bryan Miller (Gemini Observatory, Southern Operations, Chile); Bianca Poggianti (INAF - Osservatorio Astronomico di Padova, Italy); Alfonso Aguerri, Marc Balcells (Instituto de Astrofisica de Canarias, Spain); Derek Hammer (Johns Hopkins University, USA); Reynier Peletier, Edwin Valentijn, Gijs Verdoes Kleijn (Kapteyn Astronomical Institute, Netherlands); Peter Erwin (Max-Planck-Insitute for Extraterrestrial Physics, Germany); Ann Hornschemeier (NASA Goddard Space Flight Center, USA); Yutaka Komiyama, Masafumi Yagi (National Astronomical Observatory of Japan, Japan); Jennifer Lotz (National Optical Astronomy Observatories, AURA, USA); Neal Miller (National Radio Astronomy Observatory & Johns Hopkins University, USA); Eric Peng (Peking University, China); Dan Batcheldor, David Merritt (Rochester Institute of Technology, USA); Ronald Marzke (San Francisco State University, USA); Avon Huxor, Steve Phillipps, James Price (University of Bristol, UK); Bahram Mobasher (University of California - Riverside, USA); Neil Trentham (University of Cambridge, UK); John Lucey, Ray Sharples, Russell Smith (University of Durham, UK); Rafael Guzman, Carlos Hoyos (University of Florida, USA); Kristin Chiboucas, R. Brent Tully (University of Hawaii, USA); Shardha Jogee (University of Texas at Austin, USA); Sadanori Okamura (University of Tokyo, Japan); Jonathan Davies (University of Wales, College of Cardiff, UK); Michael Hudson (University of Waterloo, Canada).

Project website: http://astronomy.swin.edu.au/coma

The United Kingdom Infra-Red Telescope (UKIRT) is providing wide field-of-view near-IR images. Galaxies in dense cluster environments are subject to various physical processes, yet detailed studies of galaxy evolution to date have tended to focus on large massive galaxies - those least sensitive to environmental influence. We are undertaking a near-IR imaging survey with the Wide Field Camera (WFCAM) to cover 4x4 square degrees around the centre of the Coma cluster, probing down to the dwarf galaxy regime. Stellar masses will also be obtained and compared with dynamical masses. (P.I.: Mustapha Mouchine)

The Subaru Telescope is providing deep, wide field-of-view B, R, i and H images. Ionised hydrogen gas traces current star formation in galaxies, and our survey has probed 100 times fainter than previous work, enabling us to see which galaxies are still under construction. Deep broadband exposures will provide colours for thousands of faint dwarf galaxies, allowing us to probe their past star formation history. (P.I.: Yutaka Komiyama)

The 6.5 m Multi Mirror Telescope (MMT) is providing, via Hectospec, galaxy redshifts along with ages and chemical compositions. Some 7000 objects have been observed to date. (P.I.: Ron Marzke, Ann Hornschemeier &Russell Smith)

The Canada-France-Hawaii Telescope (CFHT) will provide deep near-infrared imaging to complement the UKIRT data. (P.I.: Mike Hudson)

Galaxy Evolution Explorer (GALEX) has delivered near- and far-UV images of the Coma cluster. The UV emission from galaxies can originate from either young stellar populations or old post main-sequence stars in evolved galaxies. We are using this data to estimate the stellar ages of galaxies at various stages of their evolution. (P.I. : Derek Hammer & Ann Hornschemeier)

The Spitzer Space Telescope’s Infrared Array Camera (IRAC) has performed a wide-field survey of the Coma Cluster. The resulting 3.6 m galaxy luminosity function (LF) has revealed an intriguingly large population of faint red dwarf galaxies, giving a faint-end LF slope of -2.18 in the cluster core region. (P.I.: Leigh Jenkins)

The X-ray Multi-Mirror Newton telescope is providing X-ray images. It has a larger field-of-view and aperture than Chandra, and is therefore more sensitive; although the image resolution is 5” compared to 0”.5.(P.I.: Ann Hornschemeier)

The Chandra X-ray Observatory is providing data that will, among other things, determine if the X-ray to optical flux ratio is suppressed in cluster galaxies, and allow one to construct an X-ray luminosity function for such objects. (P.I.: Ann Hornschemeier)

The Very Large Array (VLA) in the USA has obtained the deepest ever 20 cm map of the Coma cluster. Radio emission from galaxies is a signature of either accretion of material onto a massive black hole or the formation of young stars. In conjunction with the optical redshift data, we will be able to construct the deepest radio luminosity function ever derived for a galaxy cluster. (P.I.: Neal Miller)

The twin Keck telescopes are pursuing, via DEIMOS on Keck II and LRIS on Keck I, redshifts (for cluster membership) and line strength indices (for ages and metallicities) for the faint galaxies. Ultra Compact Dwarf galaxies are also being hunted. (P.I.: R. Brent Tully)

The world’s largest optical/near-IR telescope, the Gran Telescopio Canarias (GTC) in the Spanish Canary Islands, is now online. The instrument EMIR will be used to obtain near-IR spectra. (P.I. Marc Balcells)

Overview: The heart of the Coma Cluster Treasury Survey is a Cycle 15 Hubble Space Telescope (HST) / Advanced Camera for Surveys (ACS) Treasury Program (Carter et al. 2008, ApJS, v.176, p.424-437) that was designed to survey both the core and an infall region of the richest local cluster of galaxies: the Coma cluster. The observations contain thousands of galaxies down to apparent magnitudes g=27.5 and I=26.6 mag. In addition, numerous supporting ground-based and space-based observing campaigns are being undertaken at other wavelengths. This shall result in a large, multi-wavelength, public database of calibrated images and derived catalogs.

Scientific objectives of the HST/ACS Treasury Program include the following.

To measure the relative abundances of bright and faint galaxies, down to MV = -9 mag.

To study globular star clusters associated with bright and faint galaxies, and learn what they can tell us about galaxy evolution.

To study the structure and morphology of galaxies, and to compare the various galaxy “scaling laws” with hierarchical and evolutionary models of galaxy formation.

To quantify the physical properties of the nuclear star clusters which are prevalent in dwarf galaxies; and explore the connection with, and possibly transition to, supermassive black holes.

To provide accurate measurements of the sizes of the depleted stellar regions around supermassive black holes at the centres of giant galaxies, enabling one to constrain their dry merger history.

To study the stellar populations from both global colours and radial colour gradients (F814W - F475W), and how the internal chemical evolution of galaxies is affected by interactions with the cluster environment.

To establish an accurate 3D picture of the Coma cluster, via SBF measurements, and additionally examine the effect of the cluster environment upon the morphological features of galaxies (such as disks, bulges, bars and spiral arms) and compare these structures with those in field galaxy samples.

To Identify dwarf galaxy samples, including ultra compact dwarfs, for further study with the new generation of multi-object spectrographs on 8-10 metre class telescopes such as Keck, Subaru, Gemini and the GTC.

Two colour (F814W, F465W) image from a single ACS pointing. The bright galaxy is NGC 4874. Many dwarf galaxies and numerous globular clusters are also clearly visible.

The Hubble Space Telescope in orbit, with mirror cover open.

The Coma Cluster Treasury Survey shall provide a key local, high-density benchmark for comparison to surveys of less dense galaxy environments (e.g., the Virgo, Fornax and Perseus galaxy clusters), high-redshift HST cluster surveys, and field surveys such as HUDF, GOODS and GEMS.

Annual Astronomical Society of Australia Meeting, Perth, July 2008