Paola Castangia

A gravitationally lensed water maser in the early Universe

Water masers are found in dense molecular clouds closely associated with supermassive black holes at the centres of active galaxies. On the basis of the understanding of the local water-maser luminosity function, it was expected that masers at intermediate and high redshifts would be extremely rare. However, galaxies at redshifts z > 2 might be quite different from those found locally, not least because of more frequent mergers and interaction events. Here we use gravitational lensing to search for masers at higher redshifts than would otherwise be possible, and find a water maser at redshift 2.64 in the dust- and gas-rich, gravitationally lensed type-1 quasar MG J0414+0534 (refs 6–13). The isotropic luminosity is 10,000 (, solar luminosity), which is twice that of the most powerful local water maser and half that of the most distant maser previously known. Using the locally determined luminosity function, the probability of finding a maser this luminous associated with any single active galaxy is 10-6. The fact that we see such a maser in the first galaxy we observe must mean that the volume densities and luminosities of masers are higher at redshift 2.64.

Evidence of a pure starburst nature of the nuclear region of NGC 253

We present high-resolution spectral line and continuum VLBI and VLA observations of the nuclear region of NGC 253 at 22 GHz. While the water vapor masers in this region were detected on arcsecond and milliarcsecond scales, we could not detect any compact continuum emission with a 5σ upper limit of ∼1 mJy. The observations reveal that the water maser emission is not related to a possible low-luminosity active galactic nucleus but is almost certainly associated with star-formation activity. Not detecting any compact continuum source on milliarcsecond scales also questions the presence of a – previously assumed – active nucleus in NGC 253.

A search for gravitationally lensed water masers in dusty quasars and star-forming galaxies

Luminous extra-galactic water masers are known to be associated with active galactic nuclei and have provided accurate estimates for the mass of the central supermassive black hole and the size and structure of the circumnuclear accretion disk i n nearby galaxies. To find water maser systems at much higher redshifts, we have begun a survey of known gravitationally lensed quasars and star-forming galaxies. In this paper, we present a search for 22 GHz (rest frame) water masers toward five dusty, gravitationally lens ed quasars and star-forming galaxies at redshifts between 2.3 and 2.9 with the Effelsberg radio telescope and the Expanded Very Large Array. Our observations do not find any new definite exam ples of high redshift water maser galaxies, suggesting that large reservoirs of dust an d gas are not a sufficient condition for powerful water maser emission. However, we do find the ten tative detection of a water maser system in the active galaxy IRAS 10214+4724 at redshift 2.285. Our survey has now doubled the number of gravitationally lensed galaxies and quasars that have been searched for high redshift water maser emission. We also present an updated analysis of the high redshift water maser luminosity function that is based on the results presented here and from the only cosmologically distant (z > 1) water maser galaxy found thus far, MG J0414+0534 at redshift 2.64. By comparing with the water maser luminosity function locally and at moderate redshifts, we find that there must be some evolution in the luminosity function of water maser galaxies at high redshifts. By assuming a moderate evolution [(1 + z) 4 ] in the water maser luminosity function, we find that blind surveys for water maser galaxies are only worthwhile with extremely high sensitivity like that of the planned Square Kilometre Array (Phase 2), which is scheduled to be completed by 2020. However, instruments like the EVLA and MeerKAT will be capable of detecting water maser systems similar to the one found from MG J0414+0534 through dedicated pointed observations, providing suitable high-redshift targets can be selected.

Water vapour at high redshift: Arecibo monitoring of the megamaser in MG J0414+0534

Aims: The study of water masers at cosmological distances would allow us to investigate the parsec-scale environment around powerful radio sources, to probe the physical conditions of the molecular gas in the inner parsecs of quasars, and to estimate their nuclear engine masses in the early universe. To derive this information, the nature of the maser source needs to be assessed through a detailed investigation of the observational characteristics of the line emission. This will determine whether the emission is from a jet- or disk-maser source. Methods: We monitored the maser line in the lensed quasar MG J0414+0534 at z = 2.64 with the 300-m Arecibo telescope for ~15 months to detect possible additional maser components and to measure a potential velocity drift of the lines. In addition, we followed the maser and continuum emissions to reveal significant variations in their flux density and to determine whether correlation or time-lag exists between them. Results: 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-1. A new maser component was tentatively detected in October 2008, and is redshifted by 470 km s-1 compared to the systemic velocity of the quasar. The line width of the main maser feature increased by a factor of two between the discovery Effelsberg and EVLA observations and the first epoch of the Arecibo monitoring campaign. After correcting for the lens magnification, we find that the total H2O isotropic luminosity of the maser in MG J0414+0534 is now ~30 000 L⊙, 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. The integrated flux density instead shows significant variations on monthly time scales, possibly due to changes in the individual velocity components. We place an upper limit on the velocity drift of the peak of the line emission of 2 km s-1 yr-1. Conclusions: The large line width of the main maser line and the absence of a clear triple-peak pattern in the maser spectrum of MG J0414+0534 favours the jet-maser scenario. However, the stability of the line and continuum emission, and the presence of the tentative new maser component, which is potentially identified as a high-velocity feature of a rotating disk, seems to partly contradict this interpretation. Sensitive monitoring on a longer time scale and VLBI observations are mandatory for drawing a definite conclusion.

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.

X‐ray vs. H2Omaser emission in AGN

Correlations between X‐ray and water maser emission in AGN have been recently reported. However, the lack of systematic studies affects the confidence level of these results. In the following, we introduce a project aimed at studying all the water maser sources believed to be associated with AGN activity through X‐ray data obtained with the XRT and BAT instruments on‐board the Swift satellite. Preliminary results of this work indicate a promising rate of XRT detections allowing us to refine follow‐up observing strategies focused on investigating the nuclei of individual galaxies and deriving, on statistical basis, the main characteristics of water maser hosts. In addition, a cross‐correlation between our sample and the BAT 22‐months all‐sky survey provides an exceptionally high detection rate at hard X‐ray energies when compared to other AGN‐related catalogs.

X-ray vs. H[sub 2]O maser emission in AGN

Correlations between X‐ray and water maser emission in AGN have been recently reported. However, the lack of systematic studies affects the confidence level of these results. In the following, we introduce a project aimed at studying all the water maser sources believed to be associated with AGN activity through X‐ray data obtained with the XRT and BAT instruments on‐board the Swift satellite. Preliminary results of this work indicate a promising rate of XRT detections allowing us to refine follow‐up observing strategies focused on investigating the nuclei of individual galaxies and deriving, on statistical basis, the main characteristics of water maser hosts. In addition, a cross‐correlation between our sample and the BAT 22‐months all‐sky survey provides an exceptionally high detection rate at hard X‐ray energies when compared to other AGN‐related catalogs.

X‐ray vs. H2O maser emission in AGN

Correlations between X‐ray and water maser emission in AGN have been recently reported. However, the lack of systematic studies affects the confidence level of these results. In the following, we introduce a project aimed at studying all the water maser sources believed to be associated with AGN activity through X‐ray data obtained with the XRT and BAT instruments on‐board the Swift satellite. Preliminary results of this work indicate a promising rate of XRT detections allowing us to refine follow‐up observing strategies focused on investigating the nuclei of individual galaxies and deriving, on statistical basis, the main characteristics of water maser hosts. In addition, a cross‐correlation between our sample and the BAT 22‐months all‐sky survey provides an exceptionally high detection rate at hard X‐ray energies when compared to other AGN‐related catalogs.

X-ray vs. water maser emission in AGN

Correlations between X‐ray and water maser emission in AGN have been recently reported. However, the lack of systematic studies affects the confidence level of these results. In the following, we introduce a project aimed at studying all the water maser sources believed to be associated with AGN activity through X‐ray data obtained with the XRT and BAT instruments on‐board the Swift satellite. Preliminary results of this work indicate a promising rate of XRT detections allowing us to refine follow‐up observing strategies focused on investigating the nuclei of individual galaxies and deriving, on statistical basis, the main characteristics of water maser hosts. In addition, a cross‐correlation between our sample and the BAT 22‐months all‐sky survey provides an exceptionally high detection rate at hard X‐ray energies when compared to other AGN‐related catalogs.

Water masers in Southern FIR-bright galaxies: detection and interferometric follow-ups

G. Surcis∗,a,b,c†A. Tarchi,a,d C. Henkel,c J. Ott,e, f ‡J. Lovell,g and P. Castangia,a a INAF-Osservatorio astronomico di Cagliari Loc. Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy b Argelander-Institut für Astronomie (Universität Bonn) Auf dem Hügel 71, 53121 Bonn, Germany c Max-Planck Institut für Radioastronomie Auf dem Hügel 69, 53121 Bonn, Germany d INAF-Istituto di Radioastronomia Via Gobetti 101, 40129 Bologna, Italy e National Radio Astronomy Observatory 520 Edgemont Road, Charlottesville, VA 22903, USA f California Institute of Technology 1200 E California Blvd, Caltech Astronomy 105-24, Pasadena , CA 91125, USA g Department of Maths and Physics, Univerisity of Tasmania Private Bag 21, Hobart, Tasmania 7001, Australia E-mail: gsurcis@astro.uni-bonn.de,atarchi@ca.astro.it, p220hen@mpifr-bonn.mpg.de,jott@nrao.edu, Jim.Lovell@utas.edu.au, pcastang@ca.astro.it