An X-ray Significantly Variable, Luminous, Type 2 Quasar at z = 2.99 with a Massive Host Galaxy

TL;DR

This study analyzes a highly luminous, variable type 2 quasar at z=2.99, revealing significant changes in X-ray obscuration and flux over 2.5 years, and characterizes its host galaxy's extreme star formation and mass.

Contribution

It provides the first detailed multi-epoch X-ray analysis of a luminous, variable high-redshift type 2 quasar with comprehensive SED fitting of its host galaxy.

Findings

X-ray obscuration varied from Compton-thick to Compton-thin within 2.5 years.

The quasar's bolometric luminosity is approximately 2.5 x 10^47 erg/s.

Host galaxy exhibits a star formation rate of about 1280 solar masses per year.

Abstract

We present a comprehensive X-ray analysis and spectral energy distribution (SED) fitting of WISEA J171419.96+602724.6, an extremely luminous type 2 quasar at $z$ = 2.99. The source was suggested as a candidate Compton-thick (column density N$_{\rm H}>$1.5 $\times$ 10$^{24}$ cm$^{-2}$) quasar by a short XMM-Newton observation in 2011. We recently observed the source with deep NuSTAR and XMM-Newton exposures in 2021 and found that the source has a lower obscuration of N$_{\rm H}\sim$5 $\times$ 10$^{22}$ cm$^{-2}$ with an about four times lower flux. The two epochs of observations suggested that the source was significantly variable in X-ray obscuration, flux, and intrinsic luminosity at 2-3~$\sigma$ in less than 2.5 years (in the source rest frame). We performed SED fitting of this source using CIGALE thanks to its great availability of multiwavelength data (from hard X-rays to radio). The source is very luminous with a bolometric luminosity of $L_{\rm BOL}\sim$ 2.5 $\times$ 10$^{47}$ erg s$^{-1}$. Its host galaxy has a huge star formation rate (SFR) of $\sim$1280 Solar mass yr$^{-1}$ and a huge stellar mass of $\sim$1.1 $\times$ 10$^{12}$ Solar mass. The correlation between the SFR and stellar mass of this source is consistent with what was measured in the high-$z$ quasars. It is also consistent with what was measured in the main-sequence star-forming galaxies, suggesting that the presence of the active nucleus in our target does not enhance or suppress the SFR of its host galaxy. The source is an Infrared hyper-luminous, obscured galaxy with significant amount of hot dust in its torus and shares many similar properties with hot, dust obscured galaxies.