Circumnuclear Molecular Gas in Low-redshift Quasars and Matched Star-forming Galaxies

Abstract

A series of gravitational instabilities in a circumnuclear gas disk (CND) are required to trigger gas transport to a central supermassive black hole (SMBH) and ignite Active Galactic Nuclei (AGNs). A test of this scenario is to investigate whether an enhanced molecular gas mass surface density (${\Sigma }_{\mathrm{mol}}$) is found in the CND-scale of quasars relative to a comparison sample of inactive galaxies. Here we performed sub-kpc resolution CO(2-1) observations with ALMA of four low-redshift ($z\sim 0.06$), luminous ($\sim 10^{45}$ erg s${}^{-1}$) quasars with each matched to a different star-forming galaxy, having similar redshift, stellar mass, and star-formation rate. We detected CO(2-1) emission from all quasars, which show diverse morphologies. Contrary to expectations, ${\Sigma }_{\mathrm{mol}}$ of the quasar sample, computed from the CO(2-1) luminosity, tends to be smaller than the comparison sample at $r<500$ pc; there is no systematic enhancement of ${\Sigma }_{\mathrm{mol}}$ in our quasars. We discuss four possible scenarios that would explain the lower molecular gas content (or CO(2-1) luminosity as an actual observable) at the CND-scale of quasars, i.e., AGN-driven outflows, gas-rich minor mergers, time-delay between the onsets of a starburst-phase and a quasar-phase, and X-ray-dominated region (XDR) effects on the gas chemical abundance and excitation. While not extensively discussed in the literature, XDR effects can have an impact on molecular mass measurements particularly in the vicinity of luminous quasar nuclei; therefore higher resolution molecular gas observations, which are now viable using ALMA, need to be considered.

17 pages, 8 figures, 4 tables (including 1 table and 1 figure in the appendix). Accepted for publication in ApJ; Minor updates after the acceptance

References in corpus (25)

• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: I. Galaxy Mergers & Quasar Activity
• xCOLD GASS: the complete IRAM-30m legacy survey of molecular gas for galaxy evolution studies
• Molecular line emission in NGC1068 imaged with ALMA. I An AGN-driven outflow in the dense molecular gas
• A Close Look at Star Formation around Active Galactic Nuclei
• The bulk of the black hole growth since z~1 occurs in a secular universe: No major merger-AGN connection
• Evidence for powerful AGN winds at high redshift: Dynamics of galactic outflows in radio galaxies during the "Quasar Era"
• Spitzer Quasar and ULIRG Evolution Study (QUEST): II. The Spectral Energy Distributions of Palomar-Green Quasars
• Fueling Low-Level AGN Activity Through the Stochastic Accretion of Cold Gas
• Evidence for Quasar Activity Triggered by Galaxy Mergers in HST Observations of Dust-reddened Quasars
• Black Holes on FIRE: Stellar Feedback Limits Early Feeding of Galactic Nuclei
• Galaxy Interactions Trigger Rapid Black Hole Growth: an unprecedented view from the Hyper Suprime-Cam Survey
• A Spitzer IRS Low-Resolution Spectroscopic Search for Buried AGNs in Nearby Ultraluminous Infrared Galaxies - A Constraint on Geometry between Energy Sources and Dust -
• Molecular line emission in NGC1068 imaged with ALMA: II. The chemistry of the dense molecular gas
• Dense Molecular Gas and the Role of Star Formation in the Host Galaxies of Quasi-Stellar Objects
• A compendium of AGN inclinations with corresponding UV/optical continuum polarization measurements
• Molecular gas in nearby low-luminosity QSO host galaxies
• High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel-PACS
• ALMA observations of cold molecular gas in AGN hosts at z~1.5 - Evidence of AGN feedback?
• An ALMA CO(2-1) Survey of Nearby Palomar-Green Quasars
• Integral field spectroscopy of nearby QSOs II. The molecular gas content and condition for star formation
• Circumnuclear Multi-phase Gas in Circinus Galaxy I: Non-LTE calculations of CO lines
• Spatially resolved CO SLED of the Luminous Merger Remnant NGC 1614 with ALMA
• Kinetic energy transfer from X-ray ultrafast outflows to mm/sub-mm cold molecular outflows in Seyfert galaxies
• Coevolution Between Supermassive Black Holes and Bulges Is Not Via Internal Feedback Regulation But By Rationed Gas Supply Due To Angular Momentum Distribution
• Morphological evidence for a past minor merger in the Seyfert galaxy NGC 1068

Cited by in corpus (4)

• The diverse cold molecular gas contents, morphologies, and kinematics of type-2 quasars as seen by ALMA
• Galaxy mergers can rapidly shut down star formation
• Interacting galaxies in the IllustrisTNG simulations -- IV: Enhanced Supermassive Black Hole Accretion Rates in Post-Merger Galaxies
• AllBRICQS: the All-sky BRIght, Complete Quasar Survey