Constraints on the Abundance of Highly Ionized Proto-Cluster Regions from the Absence of Large Voids in the Lyman Alpha Forest

TL;DR

This study searches for large voids in the Lyman alpha forest to constrain the presence of highly ionized proto-cluster regions, finding no evidence for such bubbles and limiting their volume filling factor at redshift 3.

Contribution

It provides the first observational constraints on the abundance of hot super-bubbles in proto-cluster regions at z=3 using quasar spectra.

Findings

No large voids detected in the SDSS quasar spectra.

Models with hot bubble volume filling factor exceeding 20% are ruled out.

Pre-heating mechanisms must avoid heating low-density gas in proto-clusters.

Abstract

Energetic feedback processes during the formation of galaxy clusters may have heated and ionized a large fraction of the intergalactic gas in proto-cluster regions. When such a highly ionized hot ``super-bubble'' falls along the sightline to a background quasar, it would be seen as a large void, with little or no absorption, in the Lyman alpha forest. We examine the spectra of 137 quasars in the Sloan Digital Sky Survey, to search for such voids, and find no clear evidence of their existence. The size distribution of voids in the range 5-70 Angstrom (corresponding to physical sizes of approximately 3-35 comoving Mpc/h) is consistent with the standard model for the Lyman alpha forest without additional hot bubbles. We adapt a physical model for HII bubble growth during cosmological reionization (Furlanetto, Zaldarriaga and Hernquist 2004), to describe the expected size-distribution of hot super-bubbles at redshift around z = 3. This model incorporates the conjoining of bubbles around individual neighboring galaxies. Using the non-detection of voids, we find that models in which the volume filling factor of hot bubbles exceeds approximately 20 percent at z=3 can be ruled out, primarily because they overproduce the number of large (40-50 Angstrom) voids. We conclude that any pre-heating mechanism that explains galaxy cluster observations must avoid heating the low-density gas in the proto-cluster regions, either by operating relatively recently (z<3) or by depositing entropy in the high-density regions.