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Title: ACCRETION-INHIBITED STAR FORMATION IN THE WARM MOLECULAR DISK OF THE GREEN-VALLEY ELLIPTICAL GALAXY NGC 3226?

We present archival Spitzer photometry and spectroscopy and Herschel photometry of the peculiar ''Green Valley'' elliptical galaxy NGC 3226. The galaxy, which contains a low-luminosity active galactic nucleus (AGN), forms a pair with NGC 3227 and is shown to lie in a complex web of stellar and H I filaments. Imaging at 8 and 16 μm reveals a curved plume structure 3 kpc in extent, embedded within the core of the galaxy and coincident with the termination of a 30 kpc long H I tail. In situ star formation associated with the infrared (IR) plume is identified from narrowband Hubble Space Telescope (HST) imaging. The end of the IR plume coincides with a warm molecular hydrogen disk and dusty ring containing 0.7-1.1 × 10{sup 7} M {sub ☉} detected within the central kiloparsec. Sensitive upper limits to the detection of cold molecular gas may indicate that a large fraction of the H{sub 2} is in a warm state. Photometry derived from the ultraviolet (UV) to the far-IR shows evidence for a low star-formation rate of ∼0.04 M {sub ☉} yr{sup –1} averaged over the last 100 Myr. A mid-IR component to the spectral energy distribution (SED) contributes ∼20% of the IR luminosity of the galaxy, andmore » is consistent with emission associated with the AGN. The current measured star formation rate is insufficient to explain NGC 3226's global UV-optical ''green'' colors via the resurgence of star formation in a ''red and dead'' galaxy. This form of ''cold accretion'' from a tidal stream would appear to be an inefficient way to rejuvenate early-type galaxies and may actually inhibit star formation.« less
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8]
  1. NASAHerschel Science Center, Infrared Processing and Analysis Center, Caltech, 770S Wilson Avenue, Pasadena, CA 91125 (United States)
  2. Astrophysics Research Institute, John Moores University, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom)
  3. NRAO, Charlottesville, VA (United States)
  4. Spitzer NASAHerschel Science Center, 1200 East California Boulevard, Caltech, Pasadena, CA 91125 (United States)
  5. Department of Physics, University of Crete, GR-71003 Heraklion (Greece)
  6. Service d'Astrophysique, Laboratoire AIM, CEA-Saclay, Orme des Merisiers, Bat 709, F-91191 Gif sur Yvette (France)
  7. Dept. Fisica Teorica y del Cosmos, University of Granada, Edifica Mecenas, Granada (Spain)
  8. NASA Extragalactic Database, IPAC, Caltech, 1200 East California Boulevard, Caltech, Pasadena, CA 91125 (United States)
Publication Date:
OSTI Identifier:
22364835
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 797; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COLOR; DETECTION; ENERGY SPECTRA; FAR INFRARED RADIATION; GALAXIES; HYDROGEN; LUMINOSITY; PHOTOMETRY; SPACE; STAR CLUSTERS; STAR EVOLUTION; STARS; TELESCOPES; ULTRAVIOLET RADIATION