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تسجيل مستخدم جديدWater masers in Compton-thick AGN II. The high detection rate and EVN observations of IRAS 15480-0344
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تأليف
P. Castangia
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Investigations of H$_2$O maser galaxies at X-ray energies reveal that most AGN associated with water masers are characterized by high levels of absorption. With the aim of finding new maser sources for possible interferometric follow-ups, we have searched for water maser emission in a well-defined sample of heavily absorbed AGN ($N_{rm H} > 10^{23}$ cm$^{-2}$), including Compton-thick (CT) sources. All the galaxies in the sample were already searched for 22 GHz water maser emission in previous surveys. With the goal of providing a detection or a stringent upper limit on the H$_2$O luminosity, we re-observed some of the non-detected sources with the Green Bank Telescope. A new luminous H$_2$O maser ($L_{rm H2O} sim 200,$L$_odot$) was detected in the mid-IR-bright Seyfert 2 galaxy IRAS 15480-0344 and then followed-up with the Very Long Baseline Array. In order to shed light on the origin of the maser (jet/outflow vs. disc), we recently observed the radio continuum emission in IRAS 15480-0344 with the European VLBI network (EVN) at 1.7 and 5.0 GHz. With the newly discovered megamaser in IRAS 15480-0344 revealing a narrow ($sim$0.6 km s$^{-1}$) and a broad ($sim$90 km s$^{-1}$) component, the maser detection rate of the CT AGN sample is 50% (18/36), which is one of the highest ever found in maser surveys. The EVN maps show two bright sources (labeled SW and NE) in the nuclear region of IRAS 15480-0344, which we interpret as jet knots tracing regions where the radio plasma impacts dense molecular clouds. [abridged]
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A relationship between the water maser detection rate and large nuclear column densities in AGN has often been cited in the literature. Indeed, detailed studies of luminous water masers, typically associated with the nuclear activity, allow us to inv
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