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The Origin of [O II] Emission in Recently Quenched Active Galaxy Nucleus Hosts

Kocevski, Dale D. and Lemaux, Brian C. and Lubin, Lori M. and Shapley, Alice E. and Gal, Roy R. and Squires, Gordon K. (2011) The Origin of [O II] Emission in Recently Quenched Active Galaxy Nucleus Hosts. Astrophysical Journal Letters, 737 (2). Art. No. L38. ISSN 2041-8205.

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We have employed emission-line diagnostics derived from DEIMOS and NIRSPEC spectroscopy to determine the origin of the [O II] emission line observed in six active galactic nucleus (AGN) hosts at z ~ 0.9. These galaxies are a subsample of AGN hosts detected in the Cl1604 supercluster that exhibit strong Balmer absorption lines in their spectra and appear to be in a post-starburst or post-quenched phase, if not for their [O II] emission. Examining the flux ratio of the [N II] to Hα lines, we find that in five of the six hosts the dominant source of ionizing flux is AGN continuum emission. Furthermore, we find that four of the six galaxies have over twice the [O II] line luminosity that could be generated by star formation alone given their Hα line luminosities. This strongly suggests that AGN-excited narrow-line emission is contaminating the [O II] line flux. A comparison of star formation rates calculated from extinction-corrected [O II] and Hα line luminosities indicates that the former yields a five-fold overestimate of the current activity in these galaxies. Our findings reveal the [O II] line to be a poor indicator of star formation activity in a majority of these moderate-luminosity Seyferts. This result bolsters our previous findings that an increased fraction of AGN at high redshifts is hosted by galaxies in a post-starburst phase. The relatively high fraction of AGN hosts in the Cl1604 supercluster that show signs of recently truncated star formation activity may suggest that AGN feedback plays an increasingly important role in suppressing ongoing activity in large-scale structures at high redshift.

Item Type:Article
Related URLs:
URLURL TypeDescription
Lemaux, Brian C.0000-0002-1428-7036
Shapley, Alice E.0000-0003-3509-4855
Squires, Gordon K.0000-0002-1977-5717
Additional Information:© 2011 The American Astronomical Society. Received 2010 December 26; accepted 2011 June 13; published 2011 August 4.
Subject Keywords:galaxies: active; galaxies: clusters: general; galaxies: evolution; X-rays: galaxies
Issue or Number:2
Classification Code:PACS: 98.54.Cm; 98.54.Ep; 98.62.Bj; 98.54.Aj; 98.65.Cw; 98.62.Js; 98.62.Ai; 98.62.Py
Record Number:CaltechAUTHORS:20111003-085429423
Persistent URL:
Official Citation:The Origin of [O II] Emission in Recently Quenched Active Galactic Nucleus Hosts Dale D. Kocevski et al. 2011 ApJ 737 L38
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:25518
Deposited By: Ruth Sustaita
Deposited On:03 Oct 2011 16:25
Last Modified:09 Mar 2020 13:19

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