SpitzerQuasar and ULIRG Evolution Study (QUEST). II. The Spectral Energy Distributions of Palomar‐Green Quasars

Abstract

This is the second paper studying the QSOs in the Spitzer QUEST sample. Previously we presented new PAH measurements and argued that most of the observed far-infrared ( FIR) radiation is due to star-forming activity. Here we present spectral energy distributions (SEDs) by supplementing our data with optical, NIR, and FIR observations. We define two subgroups, of ''weak FIR'' and ''strong FIR'' QSOs, and a third group of FIR nondetections. Assuming a starburst origin for the FIR, we obtain ''intrinsic'' active galactic nucleus (AGN) SEDs by subtracting a starburst template from the mean SEDs. The resulting SEDs are remarkably similar for all groups. They show three distinct peaks corresponding to two silicate emission features and a 3 m bump, which we interpret as the signature of the hottest AGN dust. They also display drops beyond $20 m that we interpret as the signature of the minimum temperature ($200 K) dust. This component must be optically thin to explain the silicate emission and the slope of the long-wavelength continuum. We discuss the merits of an alternative model in which most of the FIR emission is due to AGN heating. Such models are unlikely to explain the properties of our QSOs, but they cannot be ruled out for more luminous objects. We also find correlations between the luminosity at 5100 8 and two infrared starburst indicators: L(60 m) and L(PAH 7:7 m). The correlation of L(5100 8) with L(60 m) can be used to measure the relative growth rates and lifetimes of the black hole and the new stars.

Observational evidence that positive and negative AGN feedback depends on galaxy mass and jet power

“…Netzer et al (2007) found for luminous PG QSOs that this relationship has a slope of α ≈ 0.8 (see black dotted line in Fig. 9).…”

“…Therefore, we interpret the FIR emission as being powered by star formation (e.g. Rowan-Robinson 1995; Schweitzer et al 2006;Netzer et al 2007), and we represent it with a black-body modified by frequencydependent emissivity component (Hildebrand 1983), given by…”

“…The correlation between the FIR and AGN luminosity based on the Netzer et al (2007) QSO sample is presented in Fig. 9.…”

The near-to-mid infrared spectrum of quasars

“…Lutz et al 2008;Hernán-Caballero et al 2009) as well as low redshift ones (e.g. Netzer et al 2007). However, at shorter wavelengths the continuum slope is increasingly steep and interrupted only by a prominent Paschen α line.…”

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

“…A popular method to distinguish star formation and AGN activity is to rely on Spectral Energy Distribution (SED) models. Some studies involving SED analysis are Elvis et al (1994), Richards et al (2006), Netzer et al (2007), Mor & Netzer (2012), Leipski et al (2013Leipski et al ( , 2014, and Xu et al (2015aXu et al ( , 2015b. In this work, we use a Python-based custom-written SED fitting routine (available upon inquiry).…”