Variation of Mid and Far-IR Luminosities among Early-Type Galaxies: Relation to Stellar Metallicity and Cold Dust

Abstract

The Hubble morphological sequence from early to late galaxies corresponds to an increasing rate of specific star formation. The Hubble sequence also follows a banana-shaped correlation between 24 and 70 micron luminosities, both normalized with the K-band luminosity. We show that this correlation is significantly tightened if galaxies with central AGN emission are removed, but the cosmic scatter of elliptical galaxies in both 24 and 70 micron luminosities remains significant along the correlation. We find that the 24 micron variation among ellipticals correlates with stellar metallicity, reflecting emission from hot dust in winds from asymptotic giant branch stars of varying metallicity. Infrared surface brightness variations in elliptical galaxies indicate that the K - 24 color profile is U-shaped for reasons that are unclear. In some elliptical galaxies cold interstellar dust emitting at 70 and 160 microns may arise from recent gas-rich mergers. However, we argue that most of the large range of 70 micron luminosity in elliptical galaxies is due to dust transported from galactic cores by feedback events in (currently IR-quiet) active galactic nuclei. Cooler dusty gas naturally accumulates in the cores of elliptical galaxies due to dust-cooled local stellar mass loss and may accrete onto the central black hole, releasing energy. AGN-heated gas can transport dust in cores 5-10 kpc out into the hot gas atmospheres where it radiates extended 70 micron emission but is eventually destroyed by sputtering. This, and some modest star formation, defines a cycle of dust creation and destruction. Elliptical galaxies evidently undergo large transient excursions in the banana plot in times comparable to the sputtering time or AGN duty cycle, 10 Myrs. Normally regarded as passive, elliptical galaxies are the most active galaxies in the IR color-color correlation.

17 pages, 8 figures, 2 tables, accepted for publication in ApJ

References in corpus (6)

• Age and metallicity gradients in early-type galaxies: A dwarf to giant sequence
• The Central Engines of 19 LINERs as Viewed by Chandra
• Mid- to Far-IR Emission and Star Formation in Early-Type Galaxies
• Spitzer Observations of Transient, Extended Dust in Two Elliptical Galaxies: New Evidence of Recent Feedback Energy Release in Galactic Cores
• Anatomy of a post-starburst minor merger: a multi-wavelength WFC3 study of NGC 4150
• The Mid-Infrared Spectral Energy Distribution, Surface Brightness and Color Profiles in Elliptical Galaxies

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• Hot gaseous atmospheres in galaxy groups and clusters are both heated and cooled by X-ray cavities
• Dust processing in elliptical galaxies
• VLA Radio Study of a Sample of Nearby X-ray and Optically Bright Early-Type Galaxies
• Dust evolution with active galactic nucleus feedback in elliptical galaxies
• The bivariate K-band-submillimetre luminosity functions of the local HRS galaxy sample
• Spectral Energy Distribution Mapping of Two Elliptical Galaxies on sub-kpc scales