AMUSE-VIRGO. III: mid-infrared photometry of early-type galaxies and limits on obscured nuclear emission

Abstract

We complete our census of low-level nuclear activity in Virgo Cluster early-type galaxies by searching for obscured emission using Spitzer Space Telescope mid-infrared (MIR) imaging at 24mu. Of a total sample of 95 early-type galaxies, 53 objects are detected, including 16 showing kiloparsec-scale dust in optical images. One dimensional and two dimensional surface photometry of the 37 detections without extended dust features reveals that the MIR light is more centrally concentrated than the optical light as traced by Hubble Space Telescope F850LP-band images. No such modeling was performed for the sources with dust detected in the optical images. We explore several possible sources of the MIR excess emission, including obscured nuclear emission. We find that radial metallicity gradients in the stellar population appear to be a natural and most likely explanation for the observed behavior in a majority of the sources. Alternatively, if the concentrated MIR emission were due to nuclear activity, it would imply a MIR-to-X luminosity ratio ~5-10 for the low luminosity AGN detected in X-rays by our survey. This ratio is an order of magnitude larger than that of typical low-luminosity AGN and would imply an unusual spectral energy distribution. We conclude that the black holes found by our survey in quiescent early-type galaxies in Virgo have low bolometric Eddington ratios arising from low accretion rates and/or highly radiatively inefficient accretion.

17 pages, 8 figures; accepted for publication in ApJ

References in corpus (14)

• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era
• Multiwavelength study of massive galaxies at z~2. II. Widespread Compton thick AGN and the concurrent growth of black holes and bulges
• Spitzer's Contribution to the AGN Population
• Chandra and Spitzer unveil heavily obscured quasars in the SWIRE/Chandra Survey
• Spatially resolved spectroscopy of early-type galaxies over a range in mass
• Early-type galaxies at large galactocentric radii - II. Metallicity gradients, and the [Z/H]--mass, [alpha/Fe]--mass relations
• AMUSE-Virgo I. Super-massive black holes in low-mass spheroids
• SPITZER IRS spectra of Virgo early type galaxies: detection of stellar silicate emission
• The Mid-Infrared Emission of M87
• The mid-infrared colour-magnitude relation of early-type galaxies in the Coma cluster as measured by Spitzer-IRS
• The Spitzer view of FR-I radio galaxies: on the origin of the nuclear mid-infrared continuum
• The Ages of Elliptical Galaxies from Infrared Spectral Energy Distributions
• The Mid-Infrared Spectral Energy Distribution, Surface Brightness and Color Profiles in Elliptical Galaxies
• Mid-infrared colour gradients and the colour-magnitude relation in Virgo early-type galaxies

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• An Environmental Study of the Ultraluminous X-ray Source Population in Early-type Galaxies
• Sub-Eddington super-massive black hole activity in Fornax early type galaxies
• Mid-IR Enhanced Galaxies in the Coma & Virgo Cluster: lenticulars with a high star formation rate