P. Castangia

New H2O masers in Seyfert and FIR bright galaxies II. The intermediate luminosity range

Context. 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 µm flux density >50 Jy and a declination >−30 ◦ . Aims. 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. Methods. A sample of 41 galaxies with 30 Jy −30 ◦ was observed with the 100-m telescope at Effelsberg in a search for the 22 GHz water vapor line. The average 3σ noise level of the survey is 40 mJy for a 1 km s −1 channel, corresponding to

New Compton-thick AGN in the circumnuclear H2O maser hosts UGC 3789 and NGC 6264

Large column densities, derived from X-ray studies, are typically measured towards AGN hosting water masers, especially when the H2O emission is associated with the nuclear accretion disk. In addition, possible correlations between the intrinsic X-ray luminosity and the characteristics of the H2O maser emission have been put forward that, however, require confirmation. We have performed high-sensitivity XMM-Newton observations of a sample of five H2O maser sources confidently detected in our ongoing survey with the Swift satellite of all known water masers in AGN, in order to obtain detailed X-ray information of these promising targets and to set up a systematic detailed study of the X-ray/H2O-maser relation in AGN. For three galaxies, NGC 613, VIIZw73, and IRAS 16288+3929, the amount of intrinsic absorption has been estimated, indicating column densities of 4-6x10^23 cm^-2. For UGC 3789 and NGC 6264 (the two confirmed disk-maser galaxies in our sample), column densities in excess of 1x10^24 cm^-2 are inferred from the large EW of the Fe Kalpha line. By adding our results to those obtained in past similar studies, we find that the percentage of water masers sources that host highly-obscured (NH>10^23 cm^-2) and Compton-thick AGN is 96% (45/47) and 57% (27/47), respectively. In addition, 86%, 18/21, of disk maser galaxies host Compton-thick AGN. The correlation between the galaxies bolometric luminosity and accretion disk radius, suggested in previous works, is also confirmed.

New H2O masers in Seyfert and FIR bright galaxies - IV. Interferometric follow-ups

Context. 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 related mostly to star formation activity, although the possibility exists that some of these sources may belong to the weak tail of the AGN maser distribution. Aims. It is particularly important to accurately locate the water maser emission to reveal its origin and shed light on extragalactic starforming activity or to elucidate the highly obscured central regions of galaxies. Methods. We performed interferometric observations of three galaxies, NGC 3556, Arp 299, and NGC 4151, where water emission was found. Statistical tools were used to study the relation between OH and H2O maser emission in galaxies. Results. The maser in NGC 3556 is associated with a compact radio continuum source that is most likely a supernova remnant or radio supernova. In Arp 299, 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, NGC 3690 and IC 694, and the region of overlap. In NGC 4151, only one of the two previously observed maser components has been tentatively detected. This feature, if real, is associated with the galaxy’s central region. The only galaxy, so far, where luminous maser emission from two maser species, OH and H2O, has been confidently detected is Arp 299. Weaker masers from these two species instead coexist in a number of objects. A search for emission from both maser species in a larger number of galaxies is, however, needed to assess these last two results better.

The 1.4-GHz radio properties of hard X-ray-selected AGN

We thank the anonymous referee for the valuable comments that improved this work. FP thanks Davide Burlon and Piergiorgio Casella for the fruitful scientific discussions. AT and PC would like to thank Matteo Murgia for useful suggestions on the analysis of radio data. EM acknowledges Paola Parma for the technical support during part of the radio data analysis. FP acknowledges support by INTEGRAL ASI/INAF no. 2013-025.R.O.

Narrow-line Seyfert 1 galaxies: an amasing class of AGN

Context. Narrow-line Seyfert 1 (NLS1) galaxies are a class of active galactic nuclei (AGN) that have all the properties of type 1 Seyfert galaxies but show peculiar characteristics, including the narrowest Balmer lines, strongest Fe II emission, and extreme properties in the X-rays. Line and continuum radio observations provide an optimal tool to access the (often) optically obscured innermost regions of AGN and reveal the kinematics of the gas around their central engines. Aims. We investigate the interplay between the peculiar NLS1 class of AGN and the maser phenomenon, to help us understand the nature of the maser emission in some NLS1s where water maser emission has been detected. Methods. We observed a sample of NLS1 galaxies with the Green Bank Telescope in a search for water maser emission at 22 GHz. We also reduced and analysed archival Green Bank Telescope and Very Large Array data and produced 22-GHz spectra for the five NLS1 galaxies with detected maser emission. In particular, we imaged the maser and nuclear radio continuum of NGC 5506 at subarcsec scales with the Very Large Array. Results. We discovered maser emission in two NLS1 galaxies: IGR J16385-2057, and IRAS 03450+0055. In addition to the three previously known maser detections in the NLS1s Mrk 766, NGC 4051, and NGC 5506, this yields a water maser detection rate in NLS1 galaxies of ∼7% (5/71). This value rises significantly to ∼21% (5/24) when considering only NLS1 galaxies at recessional velocities less than 10 000 km s −1 . For NGC 4051 and NGC 5506, we find that the water maser emission is located within 5 and 12 pc, respectively, of nuclear radio continuum knots, which are interpreted as core-jet structures. Conclusions. The water maser detection rate in NLS1s is surprisingly high, much higher than the detection rate obtained for type 1 AGN and similar to those in Seyfert 2 and low-ionization nuclear emission-line region galaxies. The masers in NGC 4051 and NGC 5506 are nuclear and associated with the AGN, either with an accretion disk, a radio jet, or a nuclear outflow. The apparent lack of high-velocity maser features and evidence, recently reported, of radiative outflows and radio jets in the host galaxies seems to favour interpretation as a jet or an outflow. A similar association is also seemingly true for the maser in Mrk 766, IGR J16385-2057, and IRAS 03450+0055, although, in these cases, without radio interferometric measurements we cannot rule out an off-nuclear origin of the emission.

The water megamaser in the merger system Arp 299

Abstract We present preliminary results of an interferometric study of the water megamaser in the merger system Arp 299. This system is composed of two main sources: IC 694 and NGC 3690. There is clear evidence that most of the water maser emission is associated with the nucleus of the latter, confirming the presence of an optically obscured AGN as previously suggested by X-ray observations. Furthermore, emission arises from the inner regions of IC 694, where an OH megamaser is also present. The velocity of the water maser line is blueshifted w.r.t. the optically determined systemic velocity and is consistent with that of the OH megamaser line. This finding might then indicate that both masers are associated with the same (expanding) structure and that, for the first time, strong 22xa0GHz H 2 O and 1.67xa0GHz OH maser emission has been found to coexist.

Sardinia Radio Telescope wide-band spectral-polarimetric observations of the galaxy cluster 3C 129

We present new observations of the galaxy cluster 3C 129 obtained with the Sardinia Radio Telescope in the frequency range 6000-7200 MHz, with the aim to image the large-angular-scale emission at high-frequency of the radio sources located in this cluster of galaxies. The data were acquired using the recently-commissioned ROACH2-based backend to produce full-Stokes image cubes of an area of 1 deg x 1 deg centered on the radio source 3C 129. We modeled and deconvolved the telescope beam pattern from the data. We also measured the instrumental polarization beam patterns to correct the polarization images for off-axis instrumental polarization. Total intensity images at an angular resolution of 2.9 arcmin were obtained for the tailed radio galaxy 3C 129 and for 13 more sources in the field, including 3C 129.1 at the galaxy cluster center. These data were used, in combination with literature data at lower frequencies, to derive the variation of the synchrotron spectrum of 3C 129 along the tail of the radio source. If the magnetic field is at the equipartition value, we showed that the lifetimes of radiating electrons result in a radiative age for 3C 129 of t_syn = 267 +/- 26 Myrs. Assuming a linear projected length of 488 kpc for the tail, we deduced that 3C 129 is moving supersonically with a Mach number of M=v_gal/c_s=1.47. Linearly polarized emission was clearly detected for both 3C 129 and 3C 129.1. The linear polarization measured for 3C 129 reaches levels as high as 70% in the faintest region of the source where the magnetic field is aligned with the direction of the tail.

New H2O 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. n nAims. 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. n nMethods. 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. n nResults. 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)Ou2000and OH masers in the FIR sample is also discussed.

The Sardinia Radio Telescope: From a Technological Project to a Radio Observatory

[Abridged] The Sardinia Radio Telescope (SRT) is the new 64-m dish operated by INAF (Italy). Its active surface will allow us to observe at frequencies of up to 116 GHz. At the moment, three receivers, one per focal position, have been installed and tested. The SRT was officially opened in October 2013, upon completion of its technical commissioning phase. In this paper, we provide an overview of the main science drivers for the SRT, describe the main outcomes from the scientific commissioning of the telescope, and discuss a set of observations demonstrating the SRTs scientific capabilities. One of the main objectives of scientific commissioning was the identification of deficiencies in the instrumentation and/or in the telescope sub-systems for further optimization. As a result, the overall telescope performance has been significantly improved. As part of the scientific commissioning activities, different observing modes were tested and validated, and first astronomical observations were carried out to demonstrate the science capabilities of the SRT. In addition, we developed astronomer-oriented software tools, to support future observers on-site. The astronomical validation activities were prioritized based on technical readiness and scientific impact. The highest priority was to make the SRT available for joint observations as part of European networks. As a result, the SRT started to participate (in shared-risk mode) in EVN (European VLBI Network) and LEAP (Large European Array for Pulsars) observing sessions in early 2014. The validation of single-dish operations for the suite of SRT first light receivers and backends continued in the following years, and was concluded with the first call for shared-risk/early-science observations issued at the end of 2015.

Dissecting the star formation history of starburst galaxies: the case of NGC 7673

We have collected archival data on NGC 7673 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 Hubble Space Telescope/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 and 2 Myr ago, with somewhat minor events between 3 and 6 Myr ago. The star clusters are characterized by an intrinsic reddening E(B-V) < 0.4 mag and a mass lower than 2 x 10 6 M ⊙ . 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 NGC 7673 between 1150 and 3350 A. 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 NGC 7673. The spectra have then been added together in a final, clusters integrated spectrum. This and the IUE, FUSE spectra of NGC 7673 have allowed us to describe the star formation history of the unresolved stars in the field as either exponentially decaying or multiburst. In the first case, we have derived an e-folding time of 700 (900) Myr and an initial star formation rate of 16 (13) M ⊙ yr -1 when the Fitzpatricks (Calzettis) extinction law is used. In the case of a multiburst star formation history, we have assumed that the same bursts which produced the star clusters built up also the field population. In this way, the field population turns out to be composed by a young (<40 Myr) component three (two) 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. These star formation histories fit equally well the observed UV spectrum of NGC 7673.