Molecular Gas in Lensed z>2 Quasar Host Galaxies and the Star Formation Law for Galaxies with Luminous Active Galactic Nuclei

TL;DR

This study detects molecular gas in strongly lensed high-redshift quasars, demonstrating the feasibility of using millimeter interferometry to probe faint galaxies and examining the relationship between CO luminosity and far-infrared emission in quasars.

Contribution

It presents the first detection of CO emission in several lensed high-z quasars and analyzes the impact of AGN on the far-infrared luminosity in galaxies with luminous active nuclei.

Findings

Lensed quasars allow probing of molecular gas in intrinsically faint galaxies.

No significant difference in CO-FIR relation between quasars and non-AGN galaxies at high redshift.

Possible AGN contribution to FIR in low-L_FIR systems, but minor in luminous star-forming galaxies.

Abstract

We report the detection of luminous CO(2-1), CO(3-2), and CO(4-3) emission in the strongly lensed high-redshift quasars B1938+666 (z=2.059), HE0230-2130 (z=2.166), HE1104-1805 (z=2.322), and B1359+154 (z=3.240), using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). B1938+666 was identified in a `blind' CO redshift search, demonstrating the feasibility of such investigations with millimeter interferometers. These galaxies are lensing-amplified by factors of mu_L~11-170, and thus allow us to probe molecular gas in intrinsically fainter galaxies than currently possible without the aid of gravitational lensing. We report lensing-corrected intrinsic CO line luminosities of L'(CO) = 0.65-21 x 10^9 K km/s pc^2, translating to H2 masses of M(H2) = 0.52-17 x 10^9 (alpha_CO/0.8) M_sun. To investigate whether or not the AGN in luminous quasars substantially contribute to L_FIR, we study the L'(CO)-L_FIR relation for quasars relative to galaxies without a luminous AGN as a function of redshift. We find no substantial differences between submillimeter galaxies and high-z quasars, but marginal evidence for an excess in L_FIR in nearby low-L_FIR AGN galaxies. This may suggest that an AGN contribution to L_FIR is significant in systems with relatively low gas and dust content, but only minor in the most far-infrared-luminous galaxies (in which L_FIR is dominated by star formation).