Polycyclic aromatic hydrocarbon (PAH) luminous galaxies at z ~ 1
T. Takagi1, Y. Ohyama2, T. Goto3,4, H. Matsuhara1, S. Oyabu1, T. Wada1, C. P. Pearson5, H. M. Lee6, M. Im6, M. G. Lee6, H. Shim6, H. Hanami7, T. Ishigaki8, K. Imai9, G. J. White5,10, S. Serjeant10 and M. Malkan11
Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency,
Sagamihara, Kanagawa 229-8510, Japan e-mail: email@example.com
2 Academia Sinica, Institute of Astronomy and Astrophysics, Taiwan
3 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI, 96822, USA
4 National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan
5 Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK
6 Department of Physics and Astronomy, FPRD, Seoul National University, Shilim-Dong, Kwanak-Gu, Seoul 151-742, Korea
7 Physics Section, Faculty of Humanities and Social Sciences, Iwate University, Morioka 020-8550, Japan
8 Asahikawa National College of Technology, Asahikawa, Hokkaido 071-8124, Japan
9 TOME R&D Inc. Kawasaki, Kanagawa 213-0012, Japan
10 Astrophysics Group, Department of Physics, The Open University, Milton Keynes, MK7 6AA, UK
11 Department of Physics and Astronomy, UCLA, Los Angeles, CA, USA
Accepted: 17 February 2010
Aims. The NEP-deep survey, an extragalactic AKARI survey towards the north ecliptic pole (NEP), provides a comprehensive wavelength coverage from 2 to 24 μm using all 9 photometric bands of the infrared camera (IRC). It allows us to photometrically identify galaxies whose mid-IR emission is clearly dominated by PAHs.
Methods. We propose a single-colour selection method to identify such galaxies, using two mid-IR flux ratios at 11-to-7 μm and 15-to-9 μm (PAH-to-continuum flux ratio in the rest frame), which are useful for identifying starburst galaxies at z ~ 0.5 and 1, respectively. We perform a fitting of the spectral energy distributions (SEDs) from optical to mid-IR wavelengths, using an evolutionary starburst model with a proper treatment of radiative transfer (SBURT), in order to investigate their nature.
Results. The SBURT model reproduces observed optical-to-mid-IR SEDs of more than a half of the PAH-selected galaxies. Based on the 8 μm luminosity, we find ultra luminous infrared galaxies (ULIRGs) among PAH-selected galaxies. Their PAH luminosity is higher than local ULIRGs with a similar luminosity, and the PAH-to-total IR luminosity ratio is consistent with that of less luminous starburst galaxies. They are a unique galaxy population at high redshifts, and we call these PAH-selected ULIRGs “PAH-luminous” galaxies. Although they are not as massive as submillimetre galaxies at z ~ 2, they have the stellar mass of > 3 × 1010 and therefore are moderately massive.
Key words: galaxies: starburst / infrared: galaxies / galaxies: active / galaxies : evolution
© ESO, 2010