An infrared survey of brightest cluster galaxies: Paper I

TL;DR

This survey used the Spitzer Space Telescope to examine 62 brightest cluster galaxies, revealing that about half show signs of infrared excess likely due to star formation or dusty AGNs, with some classified as luminous infrared galaxies.

Contribution

First infrared survey of brightest cluster galaxies revealing infrared excess and potential dusty AGNs, providing insights into star formation and nuclear activity in cluster cores.

Findings

Approximately 50% of galaxies show infrared excess.

Four galaxies host dusty AGNs with hot dust signatures.

Nine galaxies are classified as luminous infrared galaxies (LIRGs).

Abstract

We report on an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission. These galaxies are located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky Survey. We find that about half of these sources have a sign of excess infrared emission; 22 objects out of 62 are detected at 70 microns, 18 have 8 to 5.8 micron flux ratios above 1.0 and 28 have 24 to 8 micron flux ratios above 1.0. Altogether 35 of 62 objects in our survey exhibit at least one of these signs of infrared excess. Four galaxies with infrared excesses have a 4.5/3.6 micron flux ratio indicating the presence of hot dust, and/or an unresolved nucleus at 8 microns. Three of these have high measured [OIII](5007A)/Hbeta flux ratios suggesting that these four, Abell 1068, Abell 2146, and Zwicky 2089, and R0821+07, host dusty active galactic nuclei (AGNs). 9 objects (including the four hosting dusty AGNs) have infrared luminosities greater than 10^11 L_sol and so can be classified as luminous infrared galaxies (LIRGs). Excluding the four systems hosting dusty AGNs, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation.