Gravitational lensing reveals extreme dust-obscured star formation in quasar host galaxies

Abstract

We have observed 104 gravitationally-lensed quasars at z ∼ 1-4 with Herschel/SPIRE, the largest such sample ever studied. By targeting gravitational lenses, we probe intrinsic farinfrared (FIR) luminosities and star formation rates (SFRs) more typical of the population than the extremely luminous sources that are otherwise accessible. We detect 72 objects with Herschel/SPIRE and find 66 percent (69 sources) of the sample have spectral energy distributions (SEDs) characteristic of dust emission. For 53 objects with sufficiently constrained SEDs, we find a median effective dust temperature of 38 +12 −5 K. By applying the radio-infrared correlation, we find no evidence for an FIR excess which is consistent with star-formationheated dust. We derive a median magnification-corrected FIR luminosity of 3.6 +4.8 −2.4 × 10 11 L and median SFR of 120 +160 −80 M yr −1 for 94 quasars with redshifts. We find ∼ 10 percent of our sample have FIR properties similar to typical dusty star-forming galaxies at z ∼ 2-3 and a range of SFRs <20-10000 M yr −1 for our sample as a whole. These results are in line with current models of quasar evolution and suggests a coexistence of dust-obscured star formation and AGN activity is typical of most quasars. We do not find a statistically-significant difference in the FIR luminosities of quasars in our sample with a radio excess relative to the radio-infrared correlation. Synchrotron emission is found to dominate at FIR wavelengths for < 15 percent of those sources classified as powerful radio galaxies.

A flux-ratio anomaly in the CO spectral line emission from gravitationally lensed quasar MG J0414+0534

“…1). This combination is consistent with the overall FIR-radio spectral energy distribution of MG J0414+0534 (Stacey et al 2018). The total flux-density is S 340 GHz = 24.3 ± 1.2 mJy, of which about 50 percent is contained in the compact images.…”

“…Second, interferometric arrays such as ALMA can provide sufficiently high angular resolution (> 10 mas) such that any degeneracies between the inferred level of substructure and the source model (often assumed to be point-like) can be minimised. Finally, 70 percent of known gravitationally lensed quasars are FIR-bright (Stacey et al 2018), and so are expected to have detectable high excitation gas associated with the quasar. This, coupled with the large-scale lens surveys being carried out with DES, for example, will provide a large population of potential targets for this work in the near-term.…”

Strong lensing reveals jets in a sub-microJy radio-quiet quasar

“…RQQ PG 1115+080 has also been observed by Stacey et al (2018). Again, a relatively high dust temperature has been measured, suggesting that the object lies, with HS 0810+2554, on the radio-FIR correlation of Ivison et al (2010), yet X-ray observations by Chartas et al (2003) have again found evidence for a relativistic gas outflow.…”

“…Of further significance is that the FIR luminosity measurements made by Stacey et al (2018) found that HS 0810+2554 does not display the expected radio excess from the radio-FIR correlation typically associated with AGN activity. While we have found clear evidence for jetdominated radio emission, observations of X-ray absorbing gas by Chartas et al (2014Chartas et al ( , 2016 within HS 0810+2554 found evidence for a relativistic gas outflow.…”

A novel search for gravitationally lensed radio sources in wide-field VLBI imaging from the mJIVE-20 survey

“…Finally, gravitational lenses magnify the high redshift Universe, allowing detailed studies of galaxies that otherwise would not be detectable with current instruments (e.g. Barvainis & Ivison 2 C. Spingola et al 2002;Impellizzeri et al 2008;Riechers et al 2011;Sharon et al 2016;Stacey et al 2018).…”