MOIRCS Deep Survey. VII. NIR Morphologies of Star-Forming Galaxies at Redshift z 1

Abstract

Abstract We investigated rest-frame near-infrared (NIR) morphologies of a sample of 139 galaxies with $M_{\mathrm{s}}$$\geq$ 1 $\times$ 10$^{10}\ M_{\odot}$ at z$=$ 0.8–1.2 in the GOODS-North field using our deep NIR imaging data (MOIRCS Deep Survey, MODS). We focused on Luminous Infrared Galaxies (LIRGs), which dominate a high star formation rate (SFR) density at z$\sim $ 1, in a sample identified by cross-correlating with the Spitzer/MIPS 24 $\mu $m source catalog. We performed two-dimensional light profile fimonospaceings of z$\sim $ 1 galaxies in the $K_{\mathrm{s}}$-band (rest-frame $J$-band) with a single-component Sérsic model. We found that at z$\sim $ 1, $\sim $ 90% of the LIRGs have low Sérsic indices ($n$$\lt$ 2.5, similar to disk-like galaxies) in the $K_{\mathrm{s}}$-band, and that those disk-like LIRGs consist of $\sim $ 60% of the whole disk-like sample above $M_{\mathrm{s}}$$\geq$ 3 $\times$ 10$^{10}\ M_{\odot}$. The z$\sim $ 1 disk-like LIRGs are comparable to or $\sim $ 20% scer 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$\sim $ 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 disk-like galaxies in the rest-frame optical band. By measuring color gradients (galaxy sizes as a function of wavelength) of the z$\sim $ 1 and local disk-like galaxies, we found that the z$\sim $ 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$\sim $ 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$\sim $ 1 may be dominated by such star formation in the disk region in massive galaxies.