Mapping Quasar Light Echoes in 3D with Lyα Forest Tomography
Abstract
The intense radiation emitted by luminous quasars dramatically alters the ionization state of their surrounding IGM. This so-called proximity effect extends out to tens of Mpc, and manifests as large coherent regions of enhanced Lyα (Lyα) forest transmission in absorption spectra of background sightlines. Here, we present a novel method based on Lyα forest tomography, which is capable of mapping these quasar “light echoes” in three dimensions. Using a dense grid (10-100) of faint ({m}r≈ 24.7 {mag}) background galaxies as absorption probes, one can measure the ionization state of the IGM in the vicinity of a foreground quasar, yielding detailed information about the quasar’s radiative history and emission geometry. An end-to-end analysis—combining cosmological hydrodynamical simulations post-processed with a quasar emission model, realistic estimates of galaxy number densities, and instrument + telescope throughput—is conducted to explore the feasibility of detecting quasar light echoes. We present a new, fully Bayesian statistical method that allows one to reconstruct quasar light echoes from thousands of individual low-S/N transmission measurements. Armed with this tool, we undertake an exhaustive parameter study and show that light echoes can be convincingly detected for luminous (M 1450 < -27.5 mag, corresponding to m 1450 < 18.4 mag at z≃ 3.6) quasars at redshifts 3 < z QSO < 5, and that a relative precision better than 20% on the quasar age can be achieved for individual objects in the expected range of ages between 1 and 100 Myr. The observational requirements are relatively modest: moderate-resolution (R ≳ 750), multiobject spectroscopy at a low signal-to-noise ratio (S/N > 5) is sufficient, requiring three-hour integrations using existing instruments on 8 m class telescopes.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2019
- DOI:
- 10.3847/1538-4357/ab2fcb
- arXiv:
- arXiv:1810.05156
- Bibcode:
- 2019ApJ...882..165S
- Keywords:
-
- dark ages;
- reionization;
- first stars;
- intergalactic medium;
- quasars: general;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 22 pages, 21 figures