Herschel Observed Stripe 82 Quasars and Their Host Galaxies: Connections Between Agn Activity and Host Galaxy Star Formation

Abstract

In this work, we present a study of 207 quasars selected from the Sloan Digital Sky Survey quasar catalogs and the Herschel Stripe 82 survey. Quasars within this sample are high-luminosity quasars with a mean bolometric luminosity of 10 46.4 erg s −1 . The redshift range of this sample is within z < 4, with a mean value of 1.5 ± 0.78. Because we only selected quasars that have been detected in all three Herschel-SPIRE bands, the quasar sample is complete yet highly biased. Based on the multi-wavelength photometric observation data, we conducted a spectral energy distribution (SED) fitting through UV to FIR. Parameters such as active galactic nucleus (AGN) luminosity, far-IR (FIR) luminosity, stellar mass, as well as many other AGN and galaxy properties are deduced from the SED fitting results. The mean star formation rate (SFR) of the sample is 419 M e yr −1 and the mean gas mass is ∼10 11.3 M e . All of these results point to an IR luminous quasar system. Compared with star formation main sequence (MS) galaxies, at least 80 out of 207 quasars are hosted by starburst galaxies. This supports the statement that luminous AGNs are more likely to be associated with major mergers. The SFR increases with the redshift up to z = 2. It is correlated with the AGN bolometric luminosity, where µ  L L FIR Bol 0.46 0.03 . The AGN bolometric luminosity is also correlated with the host galaxy mass and gas mass. Yet the correlation between L FIR and L Bol has higher significant level, implies that the link between AGN accretion and the SFR is more primal. The M BH /M * ratio of our sample is 0.02, higher than the value 0.005 in the local universe. It might indicate an evolutionary trend of the M BH -M * scaling relation.

Fundamental differences in the radio properties of red and blue quasars: enhanced compact AGN emission in red quasars

“…This suggests that SF only significantly contaminates the radio emission in QSOs at R −5. Since the C3GHz data only covers a small area, it will miss the most extreme star-forming QSOs: therefore to test whether this boundary in L 6µm -L 1.4GHz does indeed isolate the majority of the star-forming population, we take a sample of 148 Herschel-observed QSOs in Stripe 82 (sample from Dong & Wu 2016), requiring W1, W2, W3 SNR > 2 and 0.2 < z < 2.4. We calculated L 6µm for these QSOs following the same approach as Section 2.1.2.…”

“…We calculated L 6µm for these QSOs following the same approach as Section 2.1.2. After removing the AGN contribution to the FIR luminosity, Dong & Wu (2016) then convert this to a SFR using the Kennicutt (1998) equation. After converting the SFRs into radio emission using the Kennicutt & Evans (2012) relation, we find 94% (139/148) of the sample have R < −5 (full range: −6.6 < R < −4.8).…”

The Intrinsic Far-infrared Continua of Type-1 Quasars

“…To measure the IR star formation rates (SFRs) of quasar host galaxies, a proper handling of the AGN far-IR contribution is critical. A number of papers have analyzed the quasar IR SEDs with a combination of the SED library from some torus model and templates/models for the host galaxies, and derived the host SFRs from the IR luminosities of the latter component (e.g., Delvecchio et al 2014;Leipski et al 2014;Dong & Wu 2016;Netzer et al 2016). However, since none of the torus models have been observationally well constrained in the far-IR, the accuracy of the SFR measurements is not always guaranteed, even if the fitting residuals are tiny.…”

Hyperluminous starburst gives up its secrets

“…While only a very small fraction of these rest-frame far-IR-selected galaxies are associated with Type-1 AGN, Knudsen et al (2003) describe a submm-selected, intrinsically hyperluminous quasar, SMM J04135+10277, lensed by the galaxy cluster Abell 478, and Herschel led to the detection of many more (e.g. Ma & Yan 2015;Pitchford et al 2016;Dong & Wu 2016). Some others have Type-2 AGN, or objects believed to be transitioning from Type-2 to Type-1 in the evolutionary scheme proposed by Sanders et al (1988), e.g.…”