Selection of AGN candidates in the GOODS-South Field through SPITZER/MIPS 24 microns variability

TL;DR

This study introduces a new method for identifying AGN candidates using mid-infrared variability in the GOODS-South field, revealing a subset of potentially obscured or low-luminosity AGN missed by other techniques.

Contribution

The paper demonstrates that MIPS 24 micron variability can effectively identify AGN candidates, including dust-obscured and low-luminosity ones, complementing existing detection methods.

Findings

39 sources show long-term variability

55 sources show short-term variability

Approximately 50% of variable sources overlap with other AGN detection methods

Abstract

We present a study of galaxies showing mid-infrared variability in the deepest Spitzer/MIPS 24 $\mu$m surveys in the GOODS-South field. We divide the dataset in epochs and subepochs to study the long-term (months-years) and the short-term (days) variability. We use a $\chi^2$-statistics method to select AGN candidates with a probability $\leq$ 1% that the observed variability is due to statistical errors alone. We find 39 (1.7% of the parent sample) sources that show long-term variability and 55 (2.2% of the parent sample) showing short-term variability. We compare our candidates with AGN selected in the X-ray and radio bands, and AGN candidates selected by their IR emission. Approximately, 50% of the MIPS 24 $\mu$m variable sources would be identified as AGN with these other methods. Therefore, MIPS 24 $\mu$m variability is a new method to identify AGN candidates, possibly dust obscured and low luminosity AGN that might be missed by other methods. However, the contribution of the MIPS 24 $\mu$m variable identified AGN to the general AGN population is small ($\leq$ 13%) in GOODS-South.