Accretion-Inhibited Star Formation in the Warm Molecular Disk of the Green-valley Elliptical Galaxy NGC 3226?
Abstract
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 Hi filaments. Imaging at 8 and 16 mu m 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 x 10(7) M-circle dot detected within the central kiloparsec. Sensitive upper limits to the detection of cold molecular gas may indicate that a large fraction of the H-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 similar to 0.04M(circle dot) yr(-1) averaged over the last 100 Myr. A mid-IR component to the spectral energy distribution (SED) contributes similar to 20% of the IR luminosity of the galaxy, and 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.
Additional Information
© 2014 American Astronomical Society. Received 2014 June 17; accepted 2014 October 26; published 2014 December 5. We thank an anonymous referee for very helpful suggestions on how to improve the paper. This work is based, in part, on observations (and archival observations) made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The work is also based, in part, on observations made with Herschel, a European Space Agency Cornerstone Mission with significant participation by NASA. Partial support for this work was provided by NASA through an award issued by JPL/Caltech. M.L. acknowledges support from the National Radio Astronomy Observatory (NRAO). NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. T.B. and V.C. acknowledge partial support from EU FP7 grant PIRSESGA-20120-316788. C.G.M. acknowledges support from the Wolfson Foundation, the Royal Society and the Science and Technology Facilities Council. U.L. acknowledges support by the research projects AYA2011-24728 from the Spanish Ministerio de Ciencia y Educaciόn and the Junta de Andalucía (Spain) grants FQM108. P.A. thanks Marc Sarzi and Tim de Zeeuw for information about the ionized gas in NGC3226 based on unpublished ATLAS3D data, and Sergio Fajado-Acosta for advice on the calibration of the IRS peak-up mode.Attached Files
Published - 0004-637X_797_2_117.pdf
Submitted - 1410.7347v2.pdf
Erratum - 0004-637X_802_1_70.pdf
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Additional details
- Eprint ID
- 53779
- Resolver ID
- CaltechAUTHORS:20150115-104813908
- NASA/JPL/Caltech
- National Radio Astronomy Observatory
- PIRSESGA-20120-316788
- Marie Curie Fellowship
- Royal Society
- Science and Technology Facilities Council (STFC)
- AYA2011-24728
- Ministerio de Ciencia y Educaciόn (MEC)
- FQM108
- Junta de Andalucía
- Created
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2015-01-15Created from EPrint's datestamp field
- Updated
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2023-06-01Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)