A physical model for z∼ 2 dust-obscured galaxies★

Abstract

We present a physical model for the origin of z~2 Dust-Obscured Galaxies\n(DOGs), a class of high-redshift ULIRGs selected at 24 micron which are\nparticularly optically faint (24/R>1000). By combining N-body/SPH simulations\nof high redshift galaxy evolution with 3D polychromatic dust radiative transfer\nmodels, we find that luminous DOGs (with F24 > 0.3 mJy at z~2 are well-modeled\nas extreme gas-rich mergers in massive (~5x10^12-10^13 Msun) halos, with\nelevated star formation rates (~500-1000 Msun/yr) and/or significant AGN growth\n(Mdot > 0.5 Msun/yr), whereas less luminous DOGs are more diverse in nature. At\nfinal coalescence, merger-driven DOGs transition from being starburst dominated\nto AGN dominated, evolving from a "bump" to a power-law shaped mid-IR (IRAC)\nspectral energy distribution (SED). After the DOG phase, the galaxy settles\nback to exhibiting a "bump" SED with bluer colors and lower star formation\nrates. While canonically power-law galaxies are associated with being\nAGN-dominated, we find that the power-law mid-IR SED can owe both to direct AGN\ncontribution, as well as to a heavily dust obscured stellar bump at times that\nthe galaxy is starburst dominated. Thus power-law galaxies can be either\nstarburst or AGN dominated. Less luminous DOGs can be well-represented either\nby mergers, or by massive ($M_{\\rm baryon} ~5x10^11 Msun) secularly evolving\ngas-rich disc galaxies (with SFR > 50 Msun/yr). By utilising similar models as\nthose employed in the SMG formation study of Narayanan et al. (2010), we\ninvestigate the connection between DOGs and SMGs. We find that the most heavily\nstar-forming merger driven DOGs can be selected as Submillimetre Galaxies\n(SMGs), while both merger-driven and secularly evolving DOGs typically satisfy\nthe BzK selection criteria.\n