Spitzer observations of extended Lyman-alpha Clouds in the SSA22 field

TL;DR

This study uses Spitzer infrared observations to analyze the properties of extended Lyman-alpha clouds in the SSA22 field, revealing a diverse population with signs of both star formation and active galactic nuclei, suggesting multiple ionization mechanisms.

Contribution

First infrared study of SSA22 LABs showing diverse galaxy populations and potential ionization mechanisms, bridging star-forming galaxies and AGNs.

Findings

Six LABs detected in IRAC and 24 micron, indicating nuclear activity or extreme star formation.

Detected LABs exhibit properties bridging star-forming galaxies and AGNs.

Non-detected LABs are consistent with pure star-forming systems.

Abstract

We present the results of a Spitzer IRAC and MIPS 24 micron study of extended Lyman-alpha clouds (or Lyman-alpha Blobs, LABs) within the SSA22 filamentary structure at z = 3.09. We detect 6/26 LABs in all IRAC filters, four of which are also detected at 24 micron, and find good correspondence with the 850 micron measurements of Geach et al. 2005. An analysis of the rest-frame ultraviolet, optical, near- and mid-infrared colors reveals that these six systems exhibit signs of nuclear activity (AGN)and/or extreme star formation. Notably, they have properties that bridge galaxies dominated by star formation (Lyman-break galaxies; LBGs) and those with AGNs (LBGs classified as QSOs). The LAB systems not detected in all four IRAC bands, on the other hand, are, as a group, consistent with pure star forming systems, similar to the majority of the LBGs within the filament. These results indicate that the galaxies within LABs do not comprise a homogeneous population, though they are also consistent with scenarios in which the gas halos are ionized through a common mechanism such as galaxy-scale winds driven by the galaxies within them, or gravitational heating of the collapsing cloud itself.