Long term Arecibo monitoring of the water megamaser in MG J0414+0534

We monitored the 22 GHz maser line in the lensed quasar MG J0414+0534 at z=2.64 with the 300-m Arecibo telescope for almost two years to detect possible additional maser components and to measure a potential velocity drift of the lines. The main maser line profile is complex and can be resolved into a number of broad features with line widths of 30-160 km/s. A new maser component was tentatively detected in October 2008 at a velocity of +470 km/s. After correcting for the estimated lens magnification, we find that the H2O isotropic luminosity of the maser in MG J0414+0534 is about 26,000 solar luminosities, making this source the most luminous ever discovered. Both the main line peak and continuum flux densities are surprisingly stable throughout the period of the observations. An upper limit on the velocity drift of the main peak of the line has been estimated from our observations and is of the order of 2 km/s per year. We discuss the results of the monitoring in terms of the possible nature of the maser emission, associated with an accretion disk or a radio jet. This is the first time that such a study is performed in a water maser source at high redshift, potentially allowing us to study the parsec-scale environment around a powerful radio source at cosmological distances.Comment: 5 pages, 2 figures, to appear in the Proceedings of the IAU Symposium 287, 2012, "Cosmic masers: from OH to H0

New H_(2)O masers in Seyfert and FIR bright galaxies: III. The southern sample

Context. A relationship between the water maser detection rate and far infrared (FIR) flux densities was established as a result of two 22 GHz maser surveys in a complete sample of galaxies (Dec > −30°) with flux densities of >50 Jy and >30 Jy. Aims. We attempted to discover new maser sources and investigate the galaxies hosting the maser spots by extending previous surveys to southern galaxies with particular emphasis on the study of their nuclear regions. Methods. A sample of 12 galaxies with Dec 50 Jy was observed with the 70-m telescope of the Canberra deep space communication complex (CDSCC) at Tidbinbilla (Australia) in a search for water maser emission. The average 3σ noise level of the survey was 15 mJy for a 0.42 km s^(−1) channel, corresponding to a detection threshold of ∼0.1 L_☉ for the isotropic maser luminosity at a distance of 25 Mpc. Results. Two new detections are reported: a kilomaser with an isotropic luminosity L_(H_(2)O) ~ 5 L_☉ in NGC 3620 and a maser with about twice this luminosity in the merger system NGC 3256. The detections have been followed-up by continuum and spectral line interferometric observations with the Australia Telescope Compact Array (ATCA). In NGC 3256, a fraction (about a third) of the maser emission originates in two hot spots associated with star formation activity, which are offset from the galactic nuclei of the system. The remaining emission may originate in weaker centres of maser activity distributed over the central 50". For NGC 3620, the water maser is coincident with the nuclear region of the galaxy. Our continuum observations indicate that the nature of the nuclear emission is probably linked to particularly intense star formation. Including the historical detection in NGC 4945, the water maser detection rate in the southern sample is 15% (3/20), consistent with the northern sample. The high rate of maser detections in the complete all-sky FIR sample (23%, 15/65) confirms the existence of a link between overall FIR flux density and maser phenomena. A relation between H_(2)O and OH masers in the FIR sample is also discussed

VLBI observations of the H2O gigamaser in TXS2226-184

Outside the Milky Way, the most luminous H2O masers at 22 GHz, called 'megamasers' because of their extreme luminosity with respect to the Galactic and extragalactic H2O masers associated with star formation, are mainly detected in active galactic nuclei. In the case of the H2O maser detected in the nuclear region of the galaxy TXS2226-184 for the first time the term 'gigamaser' was used. However, the origin of this very luminous H2O maser emission has never been investigated into details. We study the nature of the H2O gigamaser in TXS2226-184 by measuring for the first time its absolute position at mas resolution, by comparing the morphology and characteristics of the maser emission at the VLBI scales after about 20 years, and by trying to detect its polarized emission. We observed the maser emission towards TXS2226-184 three times: the very first one with the VLBA (epoch 2017.45) and the next two times with the EVN (epochs 2017.83 and 2018.44). The first two epochs were observed in phase-reference mode, while the last epoch was observed in full-polarization mode but not in phase-reference mode to increase the on-source integration time. We also retrieved and analyzed the VLBA archival data at 22 GHz of TXS2226-184 observed in 1998.40. We detected 6 H2O maser features in epoch 2017.45 (VLBA), one in epoch 2017.83 (EVN), and two in epoch 2018.44 (EVN). All of them but one are red-shifted with respect to the systemic velocity of TXS2226-184, we detected only one blue-shifted maser feature and it is the weakest one. For the first time, we were able to measure the absolute position of the H2O maser features with errors below 1 mas. No linear and circular polarization was detected. We were able to associate the H2O maser features in TXS2226-184 with the most luminous radio continuum clump reported in the literature.Comment: 13 pages, 10 figures, 3 tables, accepted for publication by Astronomy & Astrophysic

IC 485:a new candidate disk-maser galaxy at ∼\sim100 Mpc distance. Milliarcsecond resolution study of the galaxy nucleus and of the H2OH_{2}O megamaser

Masers are a unique tool to investigate the emitting gas in the innermost regions of AGNs and to map accretion disks and tori orbiting around supermassive black holes. IC485, which is classified as a LINER or Seyfert galaxy, hosts a bright water maser whose nature is still under debate. Indeed, this might be either a nuclear disk maser, a jet/outflow maser, or even the very first `inclined water maser disk'. We aim to investigate the nature of the maser by determining the location and the distribution of the maser emission at mas resolution and by associating it with the main nuclear components of IC485. In a broader context, this work might also provide further information for better understanding the physics and the disk/jet geometry in LINER or Seyfert galaxies. We observed in 2018 the nuclear region of IC485 in continuum and spectral-line mode with the VLBA and the EVN at L, C, and K bands (linear scales from ~3 to 0.2 pc). We detected 2 water maser components separated in velocity by 472 km/s, with one centred at the systemic velocity of the nuclear region and the other at a red-shifted velocity. We measured for the first time the absolute positions of these components with an accuracy of ~0.1 mas. Assuming a maser associated with an edge-on disk in Keplerian rotation, the estimated enclosed mass is M_BH = 1.2 x 10^7 M_sun, consistent with the expected mass for a SMBH in a LINER or Seyfert galaxy. The linear distribution of the maser components and a comparison with the high sensitivity GBT spectrum strongly suggest that the bulk of the maser emission is associated with an edge-on accretion disk. This makes IC485 a new candidate for a disk-maser galaxy at the distance of 122 Mpc. In particular, thanks to the upcoming radio facilities (e.g., the SKA and the ngVLA) IC485 will play an important role in our understanding of AGNs in an unexplored volume of Universe.Comment: 13 pages, 10 figures, 6 tables, accepted by Astronomy & Astrophysic