Oral Abstract

Oral Contribution (O0.2) Fangyou Gao (Kapteyn Astronomical Institute)

The Nature of Hyperluminous Infrared Galaxies

Hyperluminous Infrared Galaxies (HLIRGs) were more abundant in early epochs. They are essential in understanding the relationship between black hole accretion activity and star-formation activity. Previous studies containing small samples are insufficient for drawing robust statistical conclusions regarding the physical properties and the power sources of these extreme infrared (IR) bright galaxies. We make use of multi-wavelength data of a large HLIRG sample to derive their main physical properties, e.g., their stellar mass and star-formation rate (SFR), volume density, contribution to the cosmic stellar mass density and to the cosmic SFR density. We also study the black hole (BH) growth rate and its relationship with the SFR of the host galaxy. We select 542 HLIRGs in three deep fields (Bo$\rm \ddot{o}$tes, Lockman-Hole, ELAIS-N1) and adopt two spectral energy distribution (SED) fitting codes, CIGALE, that is based on energy balance, and CYGNUS, that is based on radiative transfer models. We use two different active galactic nucleus (AGN) models in CIGALE and three AGN models in CYGNUS to compare the obtained results estimated using different SED fitting codes and different AGN models. The stellar mass, total IR luminosity and AGN luminosity agree well between different models with a typical median offset of 0.1 dex. The SFR estimates show the largest dispersions (up to $0.5$ dex). This dispersion has an impact on the subsequent analysis, which may suggest that previous contradictory results could partly be due to the different choice of methods. HLIRGs are ultra-massive galaxies with $99\%$ of them having stellar masses larger than $10^{11} M_{\odot}$. Our results reveal a higher space density of ultra-massive galaxies than found in previous surveys or predicted by simulations. We find that HLIRGs contribute more to cosmic SFR density as redshift increases. In terms of BH growth, the two SED fitting methods predict different results. We can see a clear trend in which SFR decreases as AGN luminosity increases when using CYGNUS estimates, possibly implying quenching by AGN, while this trend is much weaker when using CIGALE estimates. This inconsistency is also influenced by the dispersion between SFR estimates obtained by two codes.