Contribution to Unresolved Infrared Fluctuations from Dwarf Galaxies at Redshifts of 2-3

TL;DR

This study uses stacking of deep infrared images to analyze faint, high-redshift dwarf galaxies, revealing their contribution to IR background fluctuations and their properties around redshift 2-3.

Contribution

It provides new constraints on the properties and contribution of faint dwarf galaxies to the infrared background at redshifts 2-3 using stacking analysis.

Findings

Faint sources have median flux of 130 nJy at 3.6 microns.

These sources account for 30-50% of IR background fluctuation power.

They contain 5-20% of stellar mass density at z~2.5.

Abstract

In order to understand the origin of clustered anisotropies detected in Spitzer images between 3.6 and 8 microns, we stack the Spitzer IRAC/Great Observatories Origins Deep Survey (GOODS) images at pixel locations corresponding to faint, z_{AB}~27 mag, optical sources with no obvious IR counterparts. We obtain a strong detection of the sources with a stacked median flux at 3.6 microns of 130+/-5 nJy above the background. The wealth of multi-wavelength imaging data in GOODS enables a similar stacking analysis to be undertaken at various wavelengths between the ultraviolet and near-infrared bands. We obtain strong stacked detections of these optically faint sources over the entire wavelength range which places constraints on the average properties of these sources. We find that the flux spectrum of the median, stacked source is consistent with a L<0.03 L_{*,UV} galaxy with a 90% confidence interval for the redshift of 1.9-2.7. These sources produce a 3.6 micron absolute background intensity between 0.1 and 0.35 nW/m^2/sr and the clustered IR light could account for ~30-50% of fluctuation power in the IR background at 4 arcminute angular scales. Although the exact redshift distribution of these sources is unknown, these galaxies appear to contain 5-20% of the co-moving stellar mass density at z~2.5.