Infrared-red Cores in Nearby Elliptical Galaxies

TL;DR

This study uses Spitzer IRAC observations to identify infrared signatures of nuclear activity in nearby elliptical galaxies, revealing a strong link between infrared excess and AGN activity.

Contribution

First infrared survey of local elliptical galaxies linking infrared excess to nuclear activity and hot dust heated by AGN.

Findings

Infrared excess detected in 9 out of 36 galaxies.

Infrared excess correlates with radio and X-ray nuclear emissions.

Circumnuclear dust observed in optical images of active galaxies.

Abstract

We present the Spitzer Space Telescope Infrared Array Camera (IRAC) observations for a sample of local elliptical galaxies to study later stages of AGN activities. A sample of 36 elliptical galaxies is selected from the Palomar spectroscopic survey. We detect nuclear non-stellar infrared emission in 9 of them. There is unambiguous evidence of circumnuclear dust in these 9 galaxies in their optical images. We also find a remarkable correlation between the infrared excess emission and the nuclear radio/X-ray emission, suggesting that infrared excess emission is tightly related with nuclear activity. Possible origin of infrared excess emission from hot dust heated by the central AGN is supported by spectral indices of IR excess emission.