Infrared spectra and photometry of complete samples of PG and 2MASS quasars

TL;DR

This study provides comprehensive infrared spectra and photometry of PG and 2MASS quasars, analyzing their spectral features, dust emission, and star formation contributions to better understand quasar central engines and host galaxies.

Contribution

It offers the first complete infrared spectral and photometric dataset for low-redshift PG and 2MASS quasars, including analysis of spectral features and star formation indicators.

Findings

Mid-IR spectral shape is largely independent of IR luminosity.

No significant difference between PG and 2MASS quasars except for silicate features.

IR color correlates with aromatic feature strength, indicating star formation influence.

Abstract

As a step toward a comprehensive overview of the infrared diagnostics of the central engines and host galaxies of quasars at low redshift, we present Spitzer Space Telescope spectroscopic (5-40 {\mu}m) and photometric (24, 70 and 160 {\mu}m) measurements of all Palomar-Green (PG) quasars at z < 0.5 and 2MASS quasars at z < 0.3. We supplement these data with Herschel measurements at 160 {\mu}m. The sample is composed of 87 optically selected PG quasars and 52 near-IR selected 2MASS quasars. Here we present the data, measure the prominent spectral features, and separate emission due to star formation from that emitted by the dusty circumnuclear torus. We find that the mid-IR (5-30 {\mu}m) spectral shape for the torus is largely independent of quasar IR luminosity with scatter in the SED shape of ~ 0.2 dex. Except for the silicate features, no large difference is observed between PG (unobscured - silicate emission) and 2MASS (obscured - silicate absorption) quasars. Only mild silicate features are observed in both cases. When in emission, the peak wavelength of the silicate feature tends to be longer than 9.7 {\mu}m, possibly indicating effects on grain properties near the AGN. The IR color is shown to correlate with the equivalent width of the aromatic features, indicating that the slope of the quasar mid- to far-IR SED is to first order driven by the fraction of radiation from star formation in the IR bands.