We have analyzed the NVSS and SUMSS data at 1.4 GHz and 843 MHz for a well defined complete sample of hard X-ray AGN observed by INTEGRAL. A large number (70/79) of sources are detected in the radio band, showing a wide range of radio morphologies, f
rom unresolved or slightly resolved cores to extended emission over several hundreds of kpc scales. The radio fluxes have been correlated with the 2-10 keV and 20-100 keV emission, revealing significant correlations with slopes consistent with those expected for radiatively efficient accreting systems. The high energy emission coming from the inner accretion regions correlates with the radio emission averaged over hundreds of kpc scales (i.e., thousands of years).
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 mase
r 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.
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, jet or disk-maser, needs to be assessed through a detailed investigation of the observational characteristics of the line emission. We monitored the maser line in the lensed quasar MGJ0414+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 follow the maser and continuum emissions to reveal significant variations in their flux density and to determine correlation or time-lag, if any, between them. 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 that is redshifted by 470 km/s w.r.t the systemic velocity of the quasar. The line width of the main maser feature increased by a factor of two between the Effelsberg and EVLA observations reported by Impellizzeri et al. (2008) 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 MGJ0414+0534 is now ~30,000 Lsun, making this source the most luminous ever discovered.[Abridged]
Very luminous extragalactic water masers, the megamasers, are associated with active galactic nuclei (AGN) in galaxies characterized by accretion disks, radio jets, and nuclear outflows. Weaker masers, the kilomasers, seem to be mostly related to sta
r formation activity, although the possibility exists that some of these sources may belong to the weak tail of the AGN maser distribution. It is of particular importance to accurately locate the water maser emission to reveal its origin and shed light onto extragalactic star forming activity or to elucidate the highly obscured central regions of galaxies. We performed interferometric observations of three galaxies, NGC3556, Arp299, and NGC4151, where water emission was found. Statistical tools have been used to study the relation between OH and water maser emission in galaxies. The maser in NGC3556 is associated with a compact radio continuum source that is most likely a supernova remnant or radio supernova. In Arp299, the luminous water maser has been decomposed in three main emitting regions associated with the nuclear regions of the two main galaxies of the system, NGC3690 and IC694, and the region of overlap. In NGC4151, only one of the two previously observed maser components has been tentatively detected. This feature, if real, is associated with the galaxys central region. The only galaxy, so far, where luminous maser emission from two maser species, OH and H2O has been confidently detected is Arp299. Weaker masers from these two species do instead coexist in a number of objects. A larger number of objects searched for both maser species are, however, necessary to better assess these last two results.
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 com
pact continuum emission with a 5 sigma 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.
Water masers are found in dense molecular clouds closely associated with supermassive black holes in the centres of active galaxies. Based upon the understanding of the local water maser luminosity function, it was expected that masers at intermediat
e and high redshifts would be extremely rare, but galaxies at redshifts z > 2 might be quite different from those found locally, not least because of more frequent mergers and interaction events. Using gravitational lensing as a tool to enable us to search higher redshifts than would otherwise be possible, we have embarked on a survey of lensed galaxies, looking for masers. Here we report the discovery of a water maser at redshift 2.64 in the dust- and gas-rich gravitationally lensed type 1 quasar MG J0414+0534, which, with an isotropic luminosity of 10,000 L_solar, is twice as luminous as 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 saw such a maser in the first galaxy we observed must mean that the volume densities and luminosities of masers are higher at redshift 2.64.
We have collected archival data on NGC7673 to constrain the star-formation history that produced the young star clusters and the field stellar population in this galaxy during the last 2 Gyr. We have considered the sample of 50 star clusters detected
by HST/WFPC2 in the UV, V and I bands and estimated their age, intrinsic reddening, and mass via comparison of their colours with STARBURST99 models. We have found two prominent epochs of cluster formation occurred about 20 Myr and 2 Myr ago, with somewhat minor events between 3 Myr and 6 Myr ago. The star clusters are characterised by an intrinsic reddening E(B-V) < 0.4 mag and a mass lower than 2e+06 solar masses. Out of the 50 star clusters, we have selected 31 located within the boundaries of the IUE large slit that was employed to obtain the spectrum of NGC7673 between 1150 Ang. and 3350 Ang. For each cluster, we have built a synthetic spectrum corresponding to the age, mass and intrinsic reddening derived from the cluster colours, properly redshifted to NGC7673. The spectra have then been added together in a final, clusters integrated spectrum. This and the IUE and FUSE spectra of NGC7673 have allowed us to describe the star-formation history of the unresolved stars in the field as either exponentially decaying or multi-burst. In the first case, we have derived an e-folding time of 700 (900) Myr and an initial star-formation rate of 16 (13) solar masses per year when the Fitzpatricks (Calzettis) extinction law is used. In the case of a multi-burst star-formation history, the field population turns out to be composed by a young (< 40 Myr) component 3 (2) times brighter than the star clusters, and a component as old as 850 (450) Myr, about 200 (100) times more massive than the star clusters together.
Recently, a relationship between the water maser detection rate and far infrared (FIR) flux density has been found as a result of a 22 GHz maser survey in a sample comprised of northern galaxies with 100 micron flux density > 50 Jy and a declination
>-30 degrees. The survey has been extended toward galaxies with lower FIR flux densities in order to confirm this correlation and to discover additional maser sources for relevant follow-up interferometric studies. A sample of 41 galaxies with 30 Jy < S(100 micron) < 50 Jy and Dec. > -30 degrees was observed with the 100-m telescope at Effelsberg in a search for the 22 GHz water vapor line. The average 3-sigma noise level of the survey is 40 mJy for a 1 km/s channel, corresponding to a detection threshold for the isotropic maser luminosity of about 0.5 solar luminosities at a distance of 25 Mpc. Two detections are reported: a megamaser with an isotropic luminosity of approximately 35 solar luminosities in the Seyfert/HII galaxy NGC613 and a kilomaser of approximately 1 solar luminosity in the merger system NGC520.[abridged]
