Tracing the co-evolution path of super massive black holes and spheroids with AKARI-selected ultra-luminous IR galaxies at intermediate redshifts

TL;DR

This study investigates the properties of ULIRGs at intermediate redshifts, revealing their stellar populations, outflows, and AGN activity, challenging traditional merger-driven galaxy evolution models.

Contribution

It provides a comprehensive analysis of ULIRGs using AKARI, SDSS, and Subaru data, highlighting the coexistence of starbursts and outflows, and questioning merger-based evolutionary scenarios.

Findings

Massive, star-forming ULIRGs with intense outflows.

Correlation between outflow velocity and AGN luminosity.

No clear difference in stellar properties between AGN- and starburst-dominated ULIRGs.

Abstract

We present the stellar population and ionized-gas outflow properties of ultra-luminous IR galaxies (ULIRGs) at $z=$ 0.1-1.0, which are selected from AKARI FIR all-sky survey. We construct a catalog of 1077 ULIRGs to examine feedback effect after major mergers. 202 out of the 1077 ULIRGs are spectroscopically identified by SDSS and Subaru/FOCAS observations. Thanks to deeper depth and higher resolution of AKARI compared to the previous IRAS survey, and reliable identification from WISE MIR pointing, the sample is unique in identifying optically-faint (i$\sim$20) IR-bright galaxies, which could be missed in previous surveys. A self-consistent spectrum-SED decomposition method, which constrains stellar population properties in SED modeling based on spectral fitting results, has been employed for 149 ULIRGs whose optical continua are dominated by host galaxies. They are massive galaxies ($M_{\rm star}\sim10^{11}$-$10^{12}$ M$_{\odot}$), associated with intense star formation activities (SFR $\sim$ 200-2000 M$_{\odot}$ yr$^{-1}$). The sample covers a range of AGN bolometric luminosity of $10^{10}$-$10^{13}$ L$_{\odot}$, and the outflow velocity measured from [OIII] 5007A line shows a correlation with AGN luminosity. Eight galaxies show extremely fast outflows with velocity up to 1500-2000 km s$^{-1}$. However, the co-existence of vigorous starbursts and strong outflows suggests the star formation has not been quenched during the ULIRG phase. By deriving stellar mass and mass fraction of young stellar population, we find no significant discrepancies between stellar properties of ULIRGs with weak and powerful AGNs. The results are not consistent with the merger-induced evolutionary scenario, which predicts that SF-dominated ULIRGs show smaller stellar mass and younger stellar populations compared to AGN-dominated ULIRGs.