Spectral Energy Distribution Modeling of Broad Emission Line Quasars: From X-ray to Radio Wavelengths


Wednesday, 25 September 2024 7 a.m. — 8 a.m. MST

AURA Lecture Hall

NOIRLab South Colloquia
Avinanda Chakraborty (Arcetri Astrophysical Observatory, Florence, Italy)
While it is known that, based on radio emission, quasars can be classified into two categories - radio-loud (RL) and radio-quiet (RQ), the underlying mechanism for this dichotomy has long been a matter of debate. In our previous work, using the quasar catalog from the Sloan Digital Sky Survey (SDSS), we showed that the radio-loud fraction (RLF) for high broad line (HBL) quasars, containing Hβ FWHM greater than 15,000 km/s, is ∼ 57% which we found possibly because of their accretion disk structure. In addition to their intrinsic differences, the presence of a strong radio jet in RL quasars may distinguish them from RQ quasars in how they affect the dynamics of their host galaxies. While previous studies involved modeling the spectral energy distributions (SED) of normal and active galaxies, the modeling of quasar-host galaxy SEDs, particularly classified by their radio emission, remains relatively unexplored. In my presentation, I will discuss our study on the differences in physical properties of quasar-host galaxies using an optically selected (SDSS; Shen et al. 2011) sample of RL and RQ quasars which we have further cross-matched with the VLA-FIRST survey catalog. The sources in our sample have broad Hβ and MgII emission lines and include broad emission line quasars (1000 km/s < FWHM < 15000 km/s) with a subsample of extremely high broad line quasars (FWHM > 15000 km/s). We constructed the broadband SED of our broad line quasars using multi-wavelength archival data and targeted observations with the AstroSat telescope to perform the SED analysis of our RL and RQ quasars. Using the state-of-the-art SED modeling code X-CIGALE (Yang et al. 2022) we modeled the SEDs and determined the best-fit physical parameters of the quasar host galaxies namely their star formation rate (SFR), main sequence stellar mass, luminosity absorbed by dust, e-folding time and stellar population age. Our study has found some differences between the host galaxy properties of RL and RQ quasars. In addition, we found the emission from the host galaxy for our sources is between 20%-35% as they are mostly dominated by the central quasars. Using our best-fit estimates for the SED modeling we reconstruct the optical spectra of our quasars which show remarkable agreement in reproducing multiple features in the observed SDSS spectra of the same sources. Our analysis, thus, provides a completely independent route in studying the host galaxy correlations of quasars and addressing the radio dichotomy problem from the host galaxy perspective.