IRAC Photometric Analysis and the Mid-IR Photometric Properties of Lyman Break Galaxies

TL;DR

This paper analyzes deep mid-infrared observations of Lyman Break Galaxies (LBGs) using Spitzer/IRAC, revealing their diverse colours, properties, and potential for distinguishing AGN from star-forming galaxies at z~3.

Contribution

It provides the first comprehensive mid-IR photometric analysis of a large LBG sample, expanding their spectral energy distribution and demonstrating IRAC 8microns as a diagnostic tool.

Findings

LBGs show a wide range of IRAC colours, indicating diverse properties.

IRAC 8microns band can distinguish AGN from star-forming galaxies at z~3.

LBGs detected at 8microns tend to have redder colours, suggesting different physical characteristics.

Abstract

We present photometric analysis of deep mid-infrared observations obtained by Spitzer/IRAC covering the fields Q1422+2309, Q2233+1341, DSF2237a,b, HDFN, SSA22a,b and B20902+34, giving the number counts and the depths for each field. In a sample of 751 LBGs lying in those fields, 443, 448, 137 and 152 are identified at 3.6microns, 4.5microns, 5.8microns, 8.0microns IRAC bands respectively, expanding their spectral energy distribution to rest-near-infrared and revealing that LBGs display a variety of colours. Their rest-near-infrared properties are rather inhomogeneous, ranging from those that are bright in IRAC bands and exhibit [R]-[3.6] > 1.5 colours to those that are faint or not detected at all in IRAC bands with [R]-[3.6] < 1.5 colours and these two groups of LBGs are investigated. We compare the mid-IR colours of the LBGs with the colours of star-forming galaxies and we find that LBGs have colours consistent with star-foming galaxies at z~3. The properties of the LBGs detected in the 8microns IRAC band (rest frame K-band) are examined separately, showing that they exhibit redder [R]-[3.6] colours than the rest of the population and that IRAC 8microns band can be used as a diagnostic tool, to separate AGN dominated objects from normal star-forming galaxies at z~3