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Hα Imaging of Nearby Seyfert Host Galaxies

Theios, Rachel L. and Malkan, Matthew A. and Ross, Nathaniel R. (2016) Hα Imaging of Nearby Seyfert Host Galaxies. Astrophysical Journal, 822 (1). Art. No. 45. ISSN 0004-637X.

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We used narrowband (Δλ = 70 Å) interference filters with the CCD imaging camera on the Nickel 1.0 m telescope at Lick Observatory to observe 31 nearby (z < 0.03) Seyfert galaxies in the 12 μm active galaxy sample. We obtained pure emission-line images of each galaxy, which reach down to a flux limit of 7.3 × 10^(−15) erg cm^(−2) s^(−1) arcsec^(−2), and corrected these images for [N ii] emission and extinction. We separated the Hα emission line of the "nucleus" (central 100–1000 pc) from that of the host galaxy. The extended Hα emission is expected to be powered by newly formed hot stars, and indeed correlates well with other indicators of current star formation rates (SFRs) in these galaxies: extended 7.7 μm polycyclic aromatic hydrocarbon, total far-infrared, and radio luminosity. Relative to what would be expected from recent star formation, there is a 0.8 dex excess of radio emission in our Seyfert galaxies. The Hα luminosity we measured in the centers of our galaxies is dominated by the active galactic nucleus (AGN), and is linearly correlated with the hard X-ray luminosity. There is, however, an upward offset of 1 dex in this correlation for the Seyfert 1s, because their nuclear Hα emission includes a strong additional contribution from the broad-line region. We found a correlation between SFR and AGN luminosity. In spite of selection effects, we concluded that the absence of bright Seyfert nuclei in galaxies with low SFRs is real, albeit only weakly significant. Finally, we used our measured spatial distributions of Hα emission to determine what these Seyfert galaxies would look like when observed through fixed apertures (e.g., a spectroscopic fiber) at high redshifts. We found that although all of these Seyfert galaxies would be detectable emission-line galaxies at any redshift, most of them would appear to be dominated by (>67%) their H ii region emission. Only the most luminous AGNs (log(L_(Hα) /erg s^(−1)) > 41.5) would still be identified as such at z ~ 0.3.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Theios, Rachel L.0000-0002-4236-1037
Malkan, Matthew A.0000-0001-6919-1237
Additional Information:© 2016 The American Astronomical Society. Received 2014 June 1; accepted 2016 March 9; published 2016 May 3. We gratefully acknowledge the expert assistance we have received from the members of the staff at Lick Observatory, including Elinor Gates and Paul Lyman. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III web site is SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University. Research at Lick Observatory is partially supported by a generous gift from Google.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Alfred P. Sloan FoundationUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Subject Keywords:galaxies: active; galaxies: Seyfert; galaxies: star formation
Issue or Number:1
Record Number:CaltechAUTHORS:20160623-142056691
Persistent URL:
Official Citation:Rachel L. Theios et al 2016 ApJ 822 45
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:68643
Deposited By: Ruth Sustaita
Deposited On:23 Jun 2016 21:56
Last Modified:09 Mar 2020 13:19

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