MOIRCS Deep Survey. VII. NIR morphologies of star-forming galaxies at redshift z ∼ 1

Abstract

We investigated rest-frame near-infrared (NIR) morphologies of a sample of 139 galaxies with Ms ≥ 1 × 1010M⊙ at z = 0.8-1.2 in the GOODS-North field using our deep NIR imaging data (MOIRCS Deep Survey, MODS). We focused on Luminous Infrared Galaxies (LIRGs), which dominate a high star formation rate (SFR) density at z ∼ 1, in a sample identified by cross-correlating with the Spitzer/MIPS 24 μm source catalog. We performed twodimensional light profile fittings of z ∼ 1 galaxies in the Ks-band (rest-frame J -band) with a single-component Sérsic model. We found that at z ∼ 1, ∼ 90% of the LIRGs have low Sérsic indices (n < 2.5, similar to disk-like galaxies) in the Ks-band, and that those disk-like LIRGs consist of ∼ 60% of the whole disk-like sample above Ms ≥ 3 × 1010M⊙ The z ∼ 1 disk-like LIRGs are comparable to or ∼ 20% smaller at the maximum in size compared to local disk-like galaxies in the same stellar mass range. When we examined rest-frame UV-optical morphologies using the HST/ACS images, the rest-frame B-band sizes of the z ∼ 1 disk-like galaxies were found to be comparable to those of the local disk-like galaxies, as reported by previous studies on the size evolution of disklike galaxies in the rest-frame optical band. By measuring color gradients (galaxy sizes as a function of wavelength) of the z ∼ 1 and local disk-like galaxies, we found that the z ∼ 1 disk-like galaxies have a 3-5 times steeper color gradient than the local ones. Our results indicate that (i) more than a half of the relatively massive disk-like galaxies at z ∼ 1 are in violent star-formation epochs observed as LIRGs, and also (ii) that most of those LIRGs are constructing their fundamental disk structure vigorously. The high SFR density in the universe at z ∼ 1 may be dominated by such star formation in the disk region in massive galaxies. © 2011 Astronomical Society of Japan.