Polycyclic aromatic hydrocarbon (PAH) luminous galaxies at z ~ 1

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...

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Published in:Astronomy and astrophysics (Berlin) 2010-05, Vol.514, p.A5
Main Authors: Takagi, T., Ohyama, Y., Goto, T., Matsuhara, H., Oyabu, S., Wada, T., Pearson, C. P., Lee, H. M., Im, M., Lee, M. G., Shim, H., Hanami, H., Ishigaki, T., Imai, K., White, G. J., Serjeant, S., Malkan, M.
Format: Article
Language:English
Subjects:
galaxies : evolution
galaxies: active
galaxies: starburst
infrared: galaxies
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Summary: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 $M_\odot$ and therefore are moderately massive.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/200913466