Environmental dependence of 8  μm luminosity functions of galaxies at z ~ 0.8^*,**

Comparison between RXJ1716.4+6708 and the AKARI NEP-deep field

¹ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA e-mail: tomo@ifa.hawaii.edu
² National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³ Department of Astronomy, School of Science, The University of Tokyo, Tokyo 113-0033, Japan
⁴ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 229-8510, Japan
⁵ Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
⁶ Department of Physics, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta T1J 1B1, Canada
⁷ Astrophysics Group, Department of Physics, The Open University, Milton Keynes, MK7 6AA, UK
⁸ Department of Physics & Astronomy, FPRD, Seoul National University, Shillim-Dong, Kwanak-Gu, Seoul 151-742, Korea
⁹ Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA
¹⁰ Department of Astronomical Science, The Graduate University for Advanced Studies
¹¹ Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547, USA
¹² Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
¹³ Academia Sinica, Institute of Astronomy and Astrophysics, Taiwan
¹⁴ Physics Section, Faculty of Humanities and Social Sciences, Iwate University, Morioka 020-8550, Japan
¹⁵ TOME R&D Inc. Kawasaki, Kanagawa 213 0012, Japan
¹⁶ Asahikawa National College of Technology, 2-1-6 2-jo Shunkohdai, Asahikawa-shi, Hokkaido 071-8142, Japan

Received: 14 October 2009
Accepted: 22 December 2009

Abstract

Aims. We aim to reveal environmental dependence of infrared luminosity functions (IR LFs) of galaxies at z ~ 0.8 using the AKARI satellite. AKARI's wide field of view and unique mid-IR filters help us to construct restframe 8 μm LFs directly without relying on SED models.

Methods. We construct restframe 8 μm IR LFs in the cluster region RXJ1716.4+6708 at z = 0.81, and compare them with a blank field using the AKARI north ecliptic pole deep field data at the same redshift. AKARI's wide field of view (10' × 10') is suitable to investigate wide range of galaxy environments. AKARI's 15 μm filter is advantageous here since it directly probes restframe 8 μm at z ~ 0.8, without relying on a large extrapolation based on a SED fit, which was the largest uncertainty in previous work.

Results. We have found that cluster IR LFs at restframe 8 μm have a factor of 2.4 smaller and a steeper faint-end slope than that of the field. Confirming this trend, we also found that faint-end slopes of the cluster LFs becomes flatter and flatter with decreasing local galaxy density. These changes in LFs cannot be explained by a simple infall of field galaxy population into a cluster. Physics that can preferentially suppress IR luminous galaxies in high density regions is required to explain the observed results.