Deep optical spectroscopy of extended Lyman alpha emission around three radio-quiet z=4.5 quasars

TL;DR

This study uses deep optical spectroscopy with VLT to detect and analyze extended Lyman alpha emission around three high-redshift, radio-quiet quasars, revealing larger and fainter envelopes than previously modeled.

Contribution

First spectroscopic detection of extended Lyman alpha envelopes around z=4.5 quasars, providing new insights into their size, brightness, and structure compared to earlier models.

Findings

Detected Lyman alpha envelopes around two quasars, measuring 67 and 87 kpc.

Envelopes are 5-10 times larger and up to 100 times fainter than model predictions.

Envelope brightness correlates with quasar brightness, but size does not depend on quasar luminosity.

Abstract

We report the first results of a spectroscopic search for Lyman alpha, envelopes around three z=4.5 radio-quiet quasars. Our observational strategy uses the FORS2 spectrograph attached to the UT1 of the Very Large Telescope (VLT) in the multi-slit mode. This allows us to observe simultaneously the quasars and several PSF stars. The spectra of the latter are used to remove the point-like quasar from the data, and to unveil the faint underlying Lyman alpha, envelopes associated with the quasars with unprecedented depth. We clearly detect an envelope around two of the three quasars. These envelopes measure respectively 10" and 13" in extent (i.e. 67 kpc and 87 kpc). This is 5 to 10 times larger than predicted by the models of Haiman & Rees (2001) and up to 100 times fainter. Our observations better agree with models involing a clumpy envelope as in Alam & Miralda-Escude (2002) or Chelouche et al. (2008). We find that the brighter quasars also have the brighter envelopes but that the extend of the envelopes does not depend on the quasar luminosity. Although our results are based on only two objects with a detected Lyman alpha, envelope, the quality of the spatial deblending of the spectra lends considerable hope to estimate the luminosity function and surface brightness profiles of high redshift Lyman alpha, envelopes down to F= 2-3 10^{-21} erg/s/cm^2/A. We find that the best strategy to carry out such a project is to obtain both narrow-band images and deep slit-spectra.