Hot Gas, Cold Gas and Sub-Halos in a Lyman-alpha Blob at Redshift 2.38

TL;DR

This study uses high-resolution integral field spectroscopy to analyze a Lyman-alpha blob at redshift 2.38, revealing complex gas dynamics, hot and cold gas interactions, and sub-halo contributions to Lyman-alpha emission.

Contribution

It provides new insights into the multi-phase gas environment and sub-halo activity within a Lyman-alpha blob, with improved spectral resolution and combined observational data.

Findings

Detection of extremely narrow velocity components (<100 km/s) in the gas.

Identification of hot gas likely from merger-induced starbursts.

Lyman-alpha emission mainly from sub-halos and gas interactions.

Abstract

We present integral field spectroscopy of a Lyman-alpha blob at redshift 2.38, with a spectral resolution three times better than previous published work. As with previous observations, the blob has a chaotic velocity structure, much of which breaks up into multiple components. Our spectroscopy shows, however, that some of these multiple components are extremely narrow: they have velocity widths of less than 100 km/s. Combining these new data with previous observations, we argue that this Lyman-alpha blob resides in a dark-matter halo of around 10^13 solar masses. At the centre of this halo are two compact red massive galaxies. They are surrounded by hot gas, probably a super-wind from merger-induced nuclear starbursts. This hot gas has shut down star formation in the non-nuclear region of these galaxies, leading to their red-and-dead colours. A filament or lump of infalling cold gas is colliding with the hot gas phase and being shocked to high temperatures, while still around 30kpc from the red galaxies. The shock region is self-absorbed in Lyman-alpha but produces C IV emission. Further out still, the cold gas in a number of sub-halos is being lit up, most likely by a combination of tidally triggered star formation, bow-shocks as they plough through the hot halo medium, resonant scattering of Lyman-alpha from the filament collision, and tidal stripping of gas which enhances the Lyman-alpha escape fraction. The observed Lyman-alpha emission from the Blob is dominated by the sum of the emission from these sub-halos. On statistical grounds, we argue that Lyman-alpha blobs are not greatly elongated in shape, and that most are not powered by ionisation or scattering from a central active galactic nucleus or starburst.