Polar Dust Emission in Quasar IR SEDs and Its Correlation with Narrow-line Regions

Abstract

Polar dust has been found to play an important role in the mid-infrared emission of nearby Seyfert nuclei. If and how often polar dust exists among the quasar population is unknown due to the lack of spatially resolved observations. In this Letter, we report correlations between the prominence of active galactic nucleus (AGN) forbidden line emission (commonly associated with the narrow-line region) and the dust mid-IR energy output among the archetypal Palomar-Green quasar sample and other bright type-1 AGNs drawn from the Sloan Digital Sky Survey, Spitzer, and Wide-field Infrared Survey Explorer (WISE) archives. The AGN mid-IR color differences traced by WISE W2 (∼4.6 μm)−W3 (∼12 μm) and W2 (∼4.6 μm)−W4 (∼22 μm), and near-IR to mid-IR spectral energy distributions (SEDs) constrained with the Two Micron All Sky Survey, WISE, and Spitzer data have clear trends with the relative strength of the forbidden line regions traced by the optical [O iii] and mid-IR [O iv] emission lines. These observations indicate that, where the lines are strong, a large fraction of the AGN emission at λ ≳ 5 μm comes from dust in the forbidden line regions. We find that the widely quoted universal AGN template is a result of averaging quasar SEDs with different levels of polar dust emission above the torus output and that the typical intrinsic IR SED of compact torus dust emission alone falls with increasing wavelength past 5 μm (in νF ν ). In addition, the association of polar dust with the forbidden lines suggests an alternative to the receding torus hypothesis for the decrease in infrared output with increasing AGN luminosity.

A Complex Dust Morphology in the High-luminosity AGN Mrk 876

“…High-angular resolution mid-IR imaging (Ramos Almeida et al 2011) and mid-IR interferometry (e.g., Tristram et al 2009;Burtscher et al 2013) of a dozen nearby and bright AGNs have delivered useful upper limits on the extent of the dusty torus (of up to a few parsecs). Such spatially resolved observations have also revealed a significant warm dust component perpendicular to the plane of the accretion disk, referred to as "polar dust" (Hönig et al 2013;Tristram et al 2014;Gámez Rosas et al 2022;Isbell et al 2022;Lyu & Rieke 2022b), which was also evident from SED studies (Landt et al 2010;Isbell et al 2021). GRAVITY, the near-IR interferometric instrument at the Very Large Telescope, has started to resolve the innermost and hottest part of the central dusty structure in some nearby luminous sources (Gravity Collaboration et al 2020), and further progress is expected from an upgrade in sensitivity to GRAVITY+.…”

What Is the Nature of Little Red Dots and what Is Not, MIRI SMILES Edition

“…In the ∼0.5-3 μm region where the MIRI measurements fall, there is general agreement on the shape of the intrinsic template, as determined by averaging the behavior of large samples (e.g., Elvis et al 1994;Glikman et al 2006;Richards et al 2006;. Lyu & Rieke (2022b) show that this is an appropriate average behavior including the variations such as warm dust deficient and hot-dust deficient (HDD) cases . It is therefore the appropriate foundation for fitting the LRD photometry, but with the large attenuations required to match the SED slope.…”

Active Galactic Nuclei Selection and Demographics: A New Age with JWST/MIRI

“…17 For a typical AGN with a BH mass ∼10 7 M e , the light-crossing time for the UV/optical disk is 0.06-6 days; the observed relative continuum time lags in the rest-frame UV/optical band are a few days (see review by, e.g., Cackett et al 2021). Meanwhile, the rest-frame near-IR emission of the AGN torus is typically time lagged to the optical emission by t ~100 ( )   L L 10 11 0.5 days with the variability signals quickly going away at longer wavelengths (see review by Lyu & Rieke 2022b). Given the fact that most AGNs are obscured and the time lag is further diluted by redshift with a factor of (1 + z), AGN variability should not impact the JADES+SMILES photometry for SED analysis in general.…”

“…We adopt a uniform prior for tau_opt = [0, 3.0] and tau_ir = [0, 20.0] as these ranges cover the majority of AGN obscuration without too much redundancy. For the purpose of AGN selections, we also adopt the normal AGN template followingLyu et al (2022),Lyu & Rieke (2022b). In total, there are three parameters for the AGN component: (1) AGN luminosity (L_AGN), (2) AGN SMC extinction level (tau_opt), and (3) AGN IR extinction level (tau_ir).During the SED fittings, we fix the redshift if the object has a spectroscopic or grism redshift (from FRESCO or 3D-HST).…”