The Infrared Emission and Vigorous Star Formation of Low-redshift Quasars
Yanxia Xie, Luis C. Ho, Ming-Yang Zhuang, J. Shangguan
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 μ m spectral energy distributions and high-resolution mid-infrared spectra of low-redshift ( z < 0.5) Palomar–Green quasars with bolometric luminosity of ∼10 44.5 –10 47.5 erg s −1 , we find, from comparison with an independent SFR indicator based on [Ne II ] 12.81 μ m and [Ne III ] 15.56 μ m, that the torus-subtracted, total infrared (8–1000 μ m) 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.