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Title:
Searching For Water Megamasers In Type-2 QSOs
Authors:
Bennert, Nicola; Barvainis, R.; Henkel, C.; Antonucci, R.
Affiliation:
AA(University of California Santa Barbara), AB(National Science Foundation), AC(Max-Planck-Institut fuer Radioastronomie, Germany), AD(University of California Santa Barbara)
Publication:
American Astronomical Society, AAS Meeting #213, #342.03; Bulletin of the American Astronomical Society, Vol. 41, p.476
Publication Date:
01/2009
Origin:
AAS
Bibliographic Code:
2009AAS...21334203B

Abstract

Using the Robert C. Byrd Green Bank Telescope and the Effelsberg 100-m radio telescope, we searched for water megamasers in 274 SDSS type-2 AGNs (0.3 < z < 0.83; Zakamska et al. 2003), half of which can be classified as type-2 QSOs on the basis of their [OIII] 5007 luminosity. While this survey lead to the discovery of the most luminous water vapor megamaser known so far, the gigamaser SDSS J080430.99+360718.1 (Barvainis & Antonucci 2005), no additional line emission is found. We discuss possible scenarios leading to this high rate of non-detections. From the extragalactic water masers known to date, a water maser luminosity function (LF) is created. The extrapolation to the higher luminosities of gigamasers that we would have been able to detect, given the sensitivity of our survey, suggests that gigamasers may simply be rare. We compile the properties of the known megamasers and discuss possible intrinsic differences between these low-luminous AGNs, mainly Seyfert-2 galaxies and LINERs in the local universe, and our sample consisting of high-luminous AGNs at higher redshift. It is notable that the known megamasers reside almost exclusively in spiral galaxies while our sample most likely consists of elliptical host galaxies. Also, the properties of the dust torus, in which the maser emission is thought to arise, might evolve with AGN luminosity. However, at this point, we cannot distinguish between the different possibilities discussed. Detecting megamasers at cosmological distances remains a challenging and yet, if successful, highly rewarding project not only for its potential to determine black hole masses but especially to constrain distances and thus probe the existence and properties of the elusive dark energy.
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