Environmental dependence of 8 µm luminosity functions of galaxies at z ~ 0.8. Comparison between RXJ1716.4+6708 and the AKARI NEP-deep field
Im, M.; Lee, H. M.; Inami, H.; Serjeant, S.; Ohyama, Y.; Pearson, C.; Takagi, T.; Goto, T.; Matsuhara, H.; Oyabu, S.; Wada, T.; Koyama, Y.; Shim, H.; Lee, M. G.; Malkan, M.; Okamura, S.; Takeuchi, T. T.; Kodama, T.; Nakagawa, T.; Hwang, N.; Hanami, H.; Imai, K.; Ishigaki, T.
United States, Japan, United Kingdom, Canada, South Korea, Italy, Taiwan
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 L^* 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.