Abstract
Abstract The star formation activity of the host galaxies of active galactic nuclei provides valuable insights into the complex interconnections between black hole growth and galaxy evolution. A major obstacle arises from the difficulty of estimating accurate star formation rates (SFRs) in the presence of a strong active galactic nucleus. Analyzing the 1–500 μm spectral energy distributions and high-resolution mid-infrared spectra of low-redshift (z < 0.5) Palomar–Green quasars with bolometric luminosity of ∼1044.5–1047.5 erg s−1, we find, from comparison with an independent SFR indicator based on [Ne II] 12.81 μm and [Ne III] 15.56 μm, that the torus-subtracted, total infrared (8–1000 μm) emission yields robust SFRs in the range of ∼1–250 M ⊙ yr−1. Combined with available stellar mass estimates, the vast majority (∼75%–90%) of the quasars lie on or above the main sequence of local star-forming galaxies, including a significant fraction (∼50%–70%) that would qualify as starburst systems. This is further supported by the high star formation efficiencies derived from the gas content inferred from the dust masses. Inspection of high-resolution Hubble Space Telescope images reveals a wide diversity of morphological types, including a number of starbursting hosts that have not experienced significant recent dynamical perturbations. The origin of the high star formation efficiency is unknown.
Highlights
Supermassive black holes (BHs) are widely regarded as being closely connected with the evolution of galaxies (Richstone et al 1998; Kormendy & Ho 2013; Heckman & Best 2014), but the exact manner in which active galactic nuclei (AGNs) truly impact their host galaxies remains a topic of lively debate
Does the BH grow in concert with the stars of the host, or does one component lag behind the other? Much attention has been devoted to the subject of AGN feedback (Fabian 2012), but does AGN feedback inhibit or stimulate star formation? These issues can be clarified if we have access to the ongoing star formation rate (SFR) and stellar mass (M∗) of the host galaxies of AGNs of different types and in different stages of their evolution
Using the Weibull distribution as implemented in the Python package lifelines3 (Davidson-Pilon et al 2020) to account for the interval of SFRNe allowed by the upper limits in the neon lines, we find that the median (16%, 84%) of the difference between the two SFRs is 0.02+−00..3444 dex
Summary
Supermassive black holes (BHs) are widely regarded as being closely connected with the evolution of galaxies (Richstone et al 1998; Kormendy & Ho 2013; Heckman & Best 2014), but the exact manner in which active galactic nuclei (AGNs) truly impact their host galaxies remains a topic of lively debate. In the context of the general galaxy population, star-forming galaxies occupy a well-defined main sequence, a relation between SFR and M∗ that encodes vital information on the manner and timescale in which galaxies acquire their stellar mass (e.g., Brinchmann et al 2004; Elbaz et al 2007; Noeske et al 2007; Peng et al 2010; Speagle et al 2014; Barro et al 2017) This same framework serves as a useful guide for probing AGN host galaxies and their relation to the overall galaxy population. At least in low-redshift quasars, far-IR emission, after properly accounting for contamination from the torus, yields robust SFRs. In concert with estimates of stellar masses and gas masses, we study the star formation properties of the host galaxies and discuss implications for AGN feedback. The SFRs and stellar masses in this paper are all scaled to the stellar initial mass function of Salpeter (1955)
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