SHARP – VI. Evidence for CO (1–0) molecular gas extended on kpc-scales in AGN star-forming galaxies at high redshift

Abstract

We present a study of the stellar host galaxy, CO (1–0) molecular gas distribution and AGN emission on 50–500 pc-scales of the gravitationally lensed dust-obscured AGN MG J0751+2716 and JVAS B1938+666 at redshifts 3.200 and 2.059, respectively. By correcting for the lensing distortion using a grid-based lens modelling technique, we spatially locate the different emitting regions in the source plane for the first time. Both AGN host galaxies have 300–500 pc-scale size and surface brightness consistent with a bulge/pseudo-bulge, and 2 kpc-scale AGN radio jets that are embedded in extended molecular gas reservoirs that are 5–20 kpc in size. The CO (1–0) velocity fields show structures possibly associated with discs (elongated velocity gradients) and interacting objects (off-axis velocity components). There is evidence for a decrement in the CO (1–0) surface brightness at the location of the host galaxy, which may indicate radiative feedback from the AGN, or offset star formation. We find CO–H2 conversion factors of around αCO = 1.5 ± 0.5 (K km s−1 pc2)−1, molecular gas masses of >3 × 1010 M⊙, dynamical masses of ∼1011 M⊙, and gas fractions of around 60 per cent. The intrinsic CO line luminosities are comparable to those of unobscured AGN and dusty star-forming galaxies at similar redshifts, but the infrared luminosities are lower, suggesting that the targets are less efficient at forming stars. Therefore, they may belong to the AGN feedback phase predicted by galaxy formation models, because they are not efficiently forming stars considering their large amount of molecular gas.

Super

“…Sharon et al (2016) looked for differences between AGN and SMGs and find the two samples to be consistent in their CO and FIR properties for both CO(3-2) and CO(1-0) transitions. Conversely, Spingola et al (2020) observed two lensed AGN at z ≈ 2−3 and find larger CO(1-0) luminosities with respect to their FIR emission when compared with star-forming galaxies, meaning that they may be less efficient at forming stars.…”

“…Some indications of this scenario at higher redshift are provided by lensed AGN. Spingola et al (2020) and Paraficz et al (2018) observed a decrease in the surface brightness of the CO(1-0) and (2-1) emission (at z ≈ 2 and 0.6), respectively, at the location of the AGN emission and the center of host galaxies. This is interpreted as a potential decrement in the molecular gas at low excitation close to the AGN possibly due to AGN radiative feedback.…”

“…Since the redshift 1 < z < 3, the so-called cosmic noon, corresponds to the peak of accretion activity of SMBHs (Madau & Dickinson 2014;Aird et al 2015), when the energy injected into the host galaxy may be maximized, this cosmic epoch is a crucial laboratory to look for AGN feedback effects. In particular, some studies find reduced molecular gas fractions (i.e., the molecular gas mass per unit stellar mass, f gas = M mol /M * ) and depletion timescales (i.e., the timescale needed to consume the available molecular gas content given the current SFR, t dep = M mol /SFR) of AGN compared with the parent population of inactive galaxies (Carilli & Walter 2013;Brusa et al 2015;Carniani et al 2017;Kakkad et al 2017;Fiore et al 2017;Perna et al 2018;Talia et al 2018;Loiacono et al 2019, but see also Kirkpatrick et al 2019;Herrera-Camus et al 2019;Spingola et al 2020). This has been interpreted as evidence for highly efficient gas consumption possibly related to AGN feedback affecting the gas reservoir of the host galaxies.…”

High-resolution imaging with the International LOFAR Telescope: Observations of the gravitational lenses MG 0751+2716 and CLASS B1600+434

“…The core-jet system is gravitationally lensed, resulting in a complex structure stretched out along an arc of emission (Lehar et al 1997). In addition to being a source of strong radio emission, the quasar was discovered to be a source of CO molecular line emission (Barvainis et al 2002;Alloin et al 2007;Riechers et al 2011;Spingola et al 2020) as well as sub-millimetre continuum (Wu et al 2009;Stacey et al 2018).…”

“…Many studies of radio lenses have attempted to do the same (e.g. Kochanek et al 1989;Lehar et al 1993;King et al 1997;Wucknitz 2004;Wucknitz et al 2004;Hartley et al 2019;Spingola et al 2020;Stacey et al 2020) and study the relation of the radio source components to other components of the source emitting at other wavebands. The relation of steep-spectrum, synchrotron radio components with other source components can also be investigated, given sufficient resolution at low frequency, which no instrument other than the Low-Frequency Array (LOFAR) operated by the International LOFAR Telescope (ILT) foundation is capable of providing.…”