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Issue A&A
Volume 436, Number 1, June II 2005
Page(s) 75 - 90
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20042175



A&A 436, 75-90 (2005)
DOI: 10.1051/0004-6361:20042175

New H $_\mathsf{2}$O masers in Seyfert and FIR bright galaxies

C. Henkel1, A. B. Peck2, A. Tarchi3, 4, N. M. Nagar5, 6, 7, J. A. Braatz8, P. Castangia4, 9 and L. Moscadelli4

1  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    e-mail: chenkel@mpifr-bonn.mpg.de
2  Harvard-Smithsonian Center for Astrophysics, SAO/SMA Project, 654 N. A'ohoku Pl., Hilo, HI 96720, USA
3  Istituto di Radioastronomia, CNR, via Gobetti 101, 40129-Bologna, Italy
4  INAF - Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy
5  INAF, Arcetri Observatory, Largo E. Fermi 5, 50125 Florence, Italy
6  Kapteyn Instituut, Postbus 800, 9700 AV Groningen, The Netherlands
7  Astronomy Group, Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción, Chile
8  National Radio Astronomy Observatory, PO Box 2, Green Bank, WV 24944, USA
9  Universitá di Cagliari, Dipartimento di Fisica, Cittadella Universitaria, 09012 Capoterra (CA), Italy

(Received 14 October 2004 / Accepted 16 February 2005 )

Abstract
Using the Effelsberg 100-m telescope, detections of four extragalactic water vapor masers are reported. Isotropic luminosities are ~50, 1000, 1 and 230 $L_{\odot}$ for Mrk 1066 (UGC 2456), Mrk 34, NGC 3556 and Arp 299, respectively. Mrk 34 contains by far the most distant and one of the most luminous water vapor megamasers so far reported in a Seyfert galaxy. The interacting system Arp 299 appears to show two maser hotspots separated by approximately 20´´. With these new results and even more recent data from Braatz et al. (2004, ApJ, 617, L29), the detection rate in our sample of Seyferts with known jet-Narrow Line Region interactions becomes 50% (7/14), while in star forming galaxies with high ( $S_{\rm 100~\mu m}>50$ Jy) far infrared fluxes the detection rate is 22% (10/45). The jet-NLR interaction sample may not only contain "jet-masers" but also a significant number of accretion "disk-masers" like those seen in NGC 4258. A statistical analysis of 53 extragalactic H2O sources (excluding the Galaxy and the Magellanic Clouds) indicates (1) that the correlation between IRAS Point Source and H2O luminosities, established for individual star forming regions in the galactic disk, also holds for AGN-dominated megamaser galaxies; (2) that maser luminosities are not correlated with 60 $\mu$m/100 $\mu$m color temperatures; and (3) that only a small fraction of the luminous megamasers ( $L_{\rm H_2O} > 100$ $L_{\odot}$) detectable with 100-m sized telescopes have so far been identified. The H2O luminosity function (LF) suggests that the number of galaxies with 1 $L_{\odot} < L_{\rm H_2O} < 10$ $L_{\odot}$, the transition range between "kilomasers" (mostly star formation) and "megamasers" (active galactic nuclei), is small. The overall slope of the LF, ~-1.5, indicates that the number of detectable masers is almost independent of their luminosity. If the LF is not steepening at very high maser luminosities and if it is possible to find suitable candidate sources, H2O megamasers at significant redshifts should be detectable even with present day state-of-the-art facilities.


Key words: masers -- galaxies: active -- galaxies: jets -- galaxies: Seyfert -- galaxies: starburst -- radio lines: galaxies

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© ESO 2005


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