Broadband Spectral Energy Distributions of SDSS-selected Quasars and of Their Host Galaxies: Intense Activity at the Onset of AGN Feedback

Abstract

We present the mean spectral energy distribution (SED) of a sample of optically selected quasars (QSOs) at redshifts of 1 ≤ z ≤ 5. To derive it, we exploit photometric information from SDSS, UKIDSS, and WISE surveys in combination with a stacking analysis of Herschel, AKARI, and Planck maps at the location of the QSOs. The near-UV and optical parts of the reconstructed mean rest-frame SED are similar to those found in other studies. However, the SED shows an excess at 1-2 µm (when compared to the aforementioned SEDs normalized in the near-UV) and a prominent bump around 4-6 µm, followed by a decrease out to ∼ 20 µm and a subsequent far-IR bump. From the fitted SEDs we estimate the average active galactic nuclei (AGN) luminosity L AGN and star formation rate (SFR) as function of cosmic time, finding typical L AGN ∼ 10 46 − 10 47 erg/s and SFR ∼ 50 − 1000 M /yr. We develop mid-IR based criteria to split the QSO sample, finding that these allow us to move along the average relationship in the SFR vs. L AGN diagram toward increasing AGN luminosities. When interpreted in the context of the in-situ coevolution scenario presented by Lapi et al. (2014), our results suggest that the detection in the far-IR band is an effective criterion to select objects where the star formation is on the verge of being affected by energy/momentum feedback from the central AGN.

Quantifying the thermal Sunyaev–Zel’dovich effect and excess millimetre emission in quasar environments

“…An optically thick synchrotron component ( Özel et al 2000;Inoue & Doi 2014;Behar et al 2015) with or without CO emission is the most viable alternative to explain the excess. The derived infrared emission is consistent with previous quasar studies with L IR,tot ∼ 10 12 L and effective dust temperatures in excess of that expected for non-active, star forming galaxies (Bianchini et al 2019;Hall et al 2018;Kirkpatrick et al 2012). However, more work is needed to disentangle the quasar host emission from dusty star forming galaxies in the same halo.…”

“…As pointed out by Soergel et al (2017), their dust properties are characteristic of the dusty star forming galaxies clustered around the more massive quasar hosts. While the ACT and Herschel data of C16 and this study do have contributions to the dust spectrum from clustered sources on scales of the one halo term, these datasets also have a higher contribution from the quasar host itself, where higher temperatures and different dust properties are expected (Bianchini et al 2019;Hall et al 2018;Kirkpatrick et al 2012).…”

“…Our base model uses two modified blackbodies to describe the thermal dust emission with one colder component and one warmer component. A two temperature modified blackbody dust emission model is supported by SED fitting of quasars (Bianchini et al 2019;Kirkpatrick et al 2012Kirkpatrick et al , 2015 and Herschel starburst galaxies (Pearson et al 2013). To explore variations on the base model, firstly we implement a version of the model in which β is a free parameter.…”

QSO photometric redshifts from SDSS, WISE, and GALEX colours

“…The excess at λ > ∼ 1 µm from the warm dust is also apparent (e.g. Bianchini et al 2019), although only the shape of the JHK profile shows any redshift dependence. An increase in the peak frequency, which would counter the redshift of the profile, would be expected as the luminosity (redshift) increases due to the higher peak temperature of a modified blackbody (Curran & Duchesne 2019 and references therein).…”

Cosmological and astrophysical results exploiting magnification bias with high-z sub-millimetre galaxies

“…14) Bonavera et al adopt the same sample of quasi-stellar object (QSOs) with 0.2 < z < 1.0 as in Ref. 15. They are selected from the publicly available Sloan Digital Sky Survey (SDSS-II and SDSS-III) Baryon Oscillation Spectroscopic Survey (BOSS) catalogues.…”