Prospects for constraining quasar ages with fiber spectrographs: Quasar-induced Lyα emission from the intergalactic medium

• Published in: Monthly notices of the Royal Astronomical Society
• Main Authors: Hada, Ryuichiro, Takada, Masahiro, Inoue, Akio K
• Format: Journal Article
• Language: English
• Published: 04.06.2024
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stae1349

Abstract We present a theoretical framework for linking quasar properties, such as quasar age, to the surrounding Lyα emission intensity. In particular, we focus on a method for mapping the large-scale structure of Lyα emission intensity with galaxy spectra from wide-field spectroscopic surveys, e.g., the Subaru Prime Focus Spectrograph (PFS) or the Dark Energy Spectroscopic Instrument (DESI), and consider the quasar-induced Lyα emission from the intergalactic medium (IGM). To do this, we construct a theoretical model based on two physical processes: resonant scattering of quasar Lyα photons and fluorescence due to quasar ionizing photons, finding that the fluorescence contribution due to optically thick gas clouds is dominant. Taking into account the light cone effect and assuming a typical quasar spectrum, we calculate the fluorescence contribution to the spectrum stacked within each bin of the separation angle from the quasar as a function of quasar age. Furthermore, we compute the quasar-Lyα emission cross-correlation and its SNR for the planned PFS survey. The predicted signal can only account for $\sim 10~{{\%}}$ of the measurements indicated from the BOSS and eBOSS surveys in the outer region of $\gtrsim 10\ \rm {cMpc}\ \rm {h}^{-1}$, and the predicted SNR is not sufficient to detect the quasar-induced contribution. However, we found that our model, combined with the contribution of star-forming galaxies, is not in conflict with these measurements. We discuss other possible contributions to the Lyα emission excess around quasars, the efficiency of using spectroscopic fibers, and the redshift dependence of our model.