ABSTRACT
We present the results of the first dedicated survey for 22 GHz H2O maser emission in dwarf galaxies outside of the Local Group, with the aim of discovering disc masers. Studies of disc ...masers yield accurate and precise measurements of black hole (BH) mass, and such measurements in dwarf galaxies would be key to understanding the low-mass end of BH–galaxy coevolution. We used the Green Bank Telescope to survey 100 nearby (z ≲ 0.055) dwarf galaxies (M* ≲ 109.5 M⊙) with optical emission line ratios indicative of accretion on to a massive black hole. We detected no new masers down to a limit of ∼12 mJy (5σ). We compared the properties of our sample with those of ∼1850 known detections and non-detections in massive galaxies. We find, in agreement with previous studies, that masers are preferentially hosted by Seyferts and highly obscured, O iii-bright active galactic nuclei (AGNs). Our sample has fewer Seyferts, is less obscured, and is O iii-faint. Though the overall maser detection rate is ∼3 per cent in massive galaxies, the predicted rate for our sample, weighted by its optical properties, is ∼0.6–1.7 per cent, corresponding to a probability of making no detections of ∼20–50 per cent. We also found a slight increase in the detection rate with increased stellar mass in previously surveyed galaxies. However, further observations are required to discern whether there is an intrinsic difference between the maser fraction in active dwarf galaxies and in their massive counterparts for the same AGN properties.
Aims. We study the connection between the masing disk and obscuring torus in Seyfert 2 galaxies. Methods. We present a uniform X-ray spectral analysis of the high energy properties of 14 nearby ...megamaser active galactic nuclei observed by NuSTAR. We use a simple analytical model to localize the maser disk and understand its connection with the torus by combining NuSTAR spectral parameters with the available physical quantities from VLBI mapping. Results. Most of the sources that we analyzed are heavily obscured, showing a column density in excess of ~1023 cm-2; in particular, 79% are Compton-thick (NH > 1.5 × 1024 cm-2). When using column densities measured by NuSTAR with the assumption that the torus is the extension of the maser disk, and further assuming a reasonable density profile, we can predict the torus dimensions. They are found to be consistent with mid-IR interferometry parsec-scale observations of Circinus and NGC 1068. In this picture, the maser disk is intimately connected to the inner part of the torus. It is probably made of a large number of molecular clouds that connect the torus and the outer part of the accretion disk, giving rise to a thin disk rotating in most cases in Keplerian or sub-Keplerian motion. This toy model explains the established close connection between water megamaser emission and nuclear obscuration as a geometric effect.
Observations of H2O masers from circumnuclear disks in active galaxies for the Megamaser Cosmology Project (MCP) allow accurate measurement of the mass of supermassive black holes (BH) in these ...galaxies. We present the Very Long Baseline Interferometry images and kinematics of water maser emission in six active galaxies: NGC 1194, NGC 2273, NGC 2960 (Mrk 1419), NGC 4388, NGC 6264 and NGC 6323. We use the Keplerian rotation curves of these six megamaser galaxies, plus a seventh previously published, to determine accurate enclosed masses within the central ~0.3 pc of these galaxies, smaller than the radius of the sphere of influence of the central mass in all cases. We also set lower limits to the central mass densities of between 0.12 X 1010 and 61 X 1010 M pc--3. For six of the seven disks, the high central densities rule out clusters of stars or stellar remnants as the central objects, and this result further supports our assumption that the enclosed mass can be attributed predominantly to a supermassive BH. The seven BHs have masses ranging between 0.75 X 107 and 6.5 X 107 M , with the mass errors dominated by the uncertainty of the Hubble constant. We compare the megamaser BH mass determination with BH mass measured from the virial estimation method. The virial estimation BH mass in four galaxies is consistent with the megamaser BH mass, but the virial mass uncertainty is much greater. Circumnuclear megamaser disks allow the best mass determination of the central BH mass in external galaxies and significantly improve the observational basis at the low-mass end of the M- Delta *s relation. The M- Delta *s relation may not be a single, low-scatter power law as originally proposed. MCP observations continue and we expect to obtain more maser BH masses in the future.
We present the results of the first dedicated survey for 22 GHz H$_2$O maser
emission in dwarf galaxies outside of the local group, with the aim of
discovering disc masers. Studies of disc masers ...yield accurate and precise
measurements of black hole mass, and such measurements in dwarf galaxies would
be key to understanding the low-mass end of BH-galaxy co-evolution. We used the
Green Bank Telescope to survey 100 nearby ($z \lesssim 0.055$) dwarf galaxies
($M_* \lesssim 10^{9.5}~M_{\odot}$) with optical emission line ratios
indicative of accretion onto a massive black hole. We detected no new masers
down to a limit of $\sim$12 mJy (5$\sigma$). We compared the properties of our
sample with those of $\sim$1,850 known detections and non-detections in massive
galaxies. We find, in agreement with previous studies, that masers are
preferentially hosted by Seyferts and highly-obscured, O III-bright AGNs. Our
sample has fewer Seyferts, is less obscured, and is O III-faint. Though the
overall maser detection rate is $\sim$3% in massive galaxies, the predicted
rate for our sample, weighted by its optical properties, is $\sim$0.6-1.7%,
corresponding to a probability of making no detections of $\sim$20-50%. We also
found a slight increase in the detection rate with increased stellar mass in
previously surveyed galaxies. However, further observations are required to
discern whether there is an intrinsic difference between the maser fraction in
active dwarf galaxies and in their massive counterparts for the same AGN
properties.
Roughly 10% of quasars are "radio-loud", producing copious radio emission in large jets. The origin of the low-level radio emission seen from the remaining 90% of quasars is unclear. Observing a ...sample of eight radio-quiet quasars with the Very Long Baseline Array, we discovered that their radio properties depend strongly on their Eddington ratio (r_Edd=L_AGN/L_Edd). At lower Eddington ratios (r_Edd < 0.3), the total radio emission of the AGN predominately originates from an extremely compact region, possibly as small as the accretion disk. At higher Eddington ratios (r_Edd > 0.3), the relative contribution of this compact region decreases significantly, and though the total radio power remains about the same, the emission now originates from regions >100 pc large. The change in the physical origin of the radio-emitting plasma region with r_Edd is unexpected, as the properties of radio-loud quasars show no dependence with Eddington ratio. Our results suggest that at lower Eddington ratios the magnetised plasma is likely confined by the accretion disk corona, and only at higher Eddington ratios escapes to larger scales. Stellar-mass black holes show a similar dependence of their radio properties on the accretion rate, supporting the paradigm which unifies the accretion onto black holes across the mass range.
We present the results of the first dedicated survey for 22 GHz H\(_2\)O maser emission in dwarf galaxies outside of the local group, with the aim of discovering disc masers. Studies of disc masers ...yield accurate and precise measurements of black hole mass, and such measurements in dwarf galaxies would be key to understanding the low-mass end of BH-galaxy co-evolution. We used the Green Bank Telescope to survey 100 nearby (\(z \lesssim 0.055\)) dwarf galaxies (\(M_* \lesssim 10^{9.5}~M_{\odot}\)) with optical emission line ratios indicative of accretion onto a massive black hole. We detected no new masers down to a limit of \(\sim\)12 mJy (5\(\sigma\)). We compared the properties of our sample with those of \(\sim\)1,850 known detections and non-detections in massive galaxies. We find, in agreement with previous studies, that masers are preferentially hosted by Seyferts and highly-obscured, O III-bright AGNs. Our sample has fewer Seyferts, is less obscured, and is O III-faint. Though the overall maser detection rate is \(\sim\)3% in massive galaxies, the predicted rate for our sample, weighted by its optical properties, is \(\sim\)0.6-1.7%, corresponding to a probability of making no detections of \(\sim\)20-50%. We also found a slight increase in the detection rate with increased stellar mass in previously surveyed galaxies. However, further observations are required to discern whether there is an intrinsic difference between the maser fraction in active dwarf galaxies and in their massive counterparts for the same AGN properties.
Congenital supraglottic laryngeal obstruction still is being described as subglottic stenosis. There are three clearly defined types of congenital laryngeal atresia, which result from arrest at ...consecutive developmental stages. Type 1 consists of a supraglottic obstruction, absent vestibule, and stenotic infraglottis, and type 2 is a supraglottic obstruction that separates a shallow primitive vestibule above from a nonstenotic infraglottis. These two types usually are accompanied by other defects, many of them severe. In type 3, a perforated membrane partly obstructs the glottis. Arrest of the dorsal advance of the chondrifying cricoid before the ends meet to form the dorsal lamina results in a complete laryngeal cleft, and incomplete fusion of the ends may leave a notch and/or foramen within the lamina. Failure of the interarytenoid tissue to develop will produce a local cleft, and maldevelopment of the cricoid cartilage or infraglottic submucosa can result in true subglottic stenosis without supraglottic obstruction.
Water megamasers from circumnuclear disks in galaxy centers provide the most accurate measurements of supermassive black hole masses and uniquely probe the sub-parsec accretion processes. At the same ...time, these systems offer independent crucial constraints of the Hubble Constant in the nearby universe, and thus, the arguably best single constraint on the nature of dark energy. The chances of finding these golden standards are however abysmally low, at an overall =< 3% for any level of water maser emission detected at 22 GHz, and =< 1% for those exhibiting the disk-like configuration. We provide here a thorough summary of the current state of the detection of water megamaser disks, along with a novel investigation of the likelihood of increasing their detection rates based on a multivariate parameter analysis of optical and mid-infrared photometric properties of the largest database of galaxies surveyed for the 22 GHz emission. We find that galaxies with water megamaser emission tend to associate with strong emission in all WISE mid-infrared wavelengths, with the strongest enhancement in the W4 band, at 22 micron, as well as with previously proposed and newly found indicators of AGN strength in the mid-infrared, such as red W1-W2 and W1-W4 colors, and the integrated mid-infrared luminosity of the host galaxy. These trends offer a potential boost of the megamaser detection rates to 6 - 15%, or a factor of 2-8 relative to the current rates, depending on the chosen sample selection criteria, while fostering real chances for discovering >= 20 new megamaser disks.
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