P. Castangia

The Astronomical Observatory of Brera, Merate, Lombardy, Italy

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Publications (44)107.72 Total impact

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    ABSTRACT: A relationship between the water maser detection rate and large nuclear column densities in AGN has often been cited in the literature. Indeed, detailed studies of luminous water masers, typically associated with the nuclear activity, allow us to investigate the innermost regions of AGN, with an impact on the still debated Unified Model for this class of objects.We have recently entertained a search for maser emission in a well-defined sample of Compton-thick AGN aimed at investigating, on firm statistical bases, the aforementioned relationship. While the survey is still ongoing, and is matter of a forthcoming publication, a new luminous water maser has been detected in the lenticular (field) S0 galaxy IRAS15480-0344, whose origin, associated with an accretion disc or a nuclear outflow/jet, needs to be assessed. Multi-epoch single-dish observations and VLBI measurements were performed to investigate the distribution, spatial extension, and variability of the maser emission in order to infer the main characteristics of the water megamaser. The new detection in IRAS15480-0344 is reported: a megamaser with a total single-dish isotropic luminosity of ~200 Lsun and a profile composed of two main features, a broad line with a full width to half maximum (FWHM) linewidth of ~90 km/s and a narrow (FWHM<1 km/s) one. We performed a follow-up to the detection with the Very Long Baseline Array (VLBA) and confidently detected only the narrow component, which is coincident with the nuclear radio continuum emission detected with the Very Large Array at 8.4 GHz. A weak narrow feature has also been detected in the velocity range of the broad feature and is located 15 pc to the north-west with respect to the stronger component. Neither maser spot is associated with the compact radio continuum sources derived from the same VLBA dataset. [Abridged]
    No preview · Article · Jan 2016 · Astronomy and Astrophysics
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    ABSTRACT: 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, from 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).
    Preview · Article · Nov 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Very long baseline interferometry at millimetre/submillimetre wavelengths (mmVLBI) offers the highest achievable spatial resolution at any wavelength in astronomy. The anticipated inclusion of ALMA as a phased array into a global VLBI network will bring unprecedented sensitivity and a transformational leap in capabilities for mmVLBI. Building on years of pioneering efforts in the US and Europe the ongoing ALMA Phasing Project (APP), a US-led international collaboration with MPIfR-led European contributions, is expected to deliver a beamformer and VLBI capability to ALMA by the end of 2014 (APP: Fish et al. 2013, arXiv:1309.3519). This report focuses on the future use of mmVLBI by the international users community from a European viewpoint. Firstly, it highlights the intense science interest in Europe in future mmVLBI observations as compiled from the responses to a general call to the European community for future research projects. A wide range of research is presented that includes, amongst others: - Imaging the event horizon of the black hole at the centre of the Galaxy - Testing the theory of General Relativity an/or searching for alternative theories - Studying the origin of AGN jets and jet formation - Cosmological evolution of galaxies and BHs, AGN feedback - Masers in the Milky Way (in stars and star-forming regions) - Extragalactic emission lines and astro-chemistry - Redshifted absorption lines in distant galaxies and study of the ISM and circumnuclear gas - Pulsars, neutron stars, X-ray binaries - Testing cosmology - Testing fundamental physical constants
    Full-text · Article · Jun 2014
  • P. Castangia · F. Panessa · C. Henkel · M. Kadler · A. Tarchi
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    ABSTRACT: Large column densities, derived from X-ray studies, are typically measured towards active galactic nuclei (AGN) hosting water masers, especially when the H2O emission is associated with the nuclear accretion disc. 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, VII Zw 73 and IRAS 16288+3929, the amount of intrinsic absorption has been estimated, indicating column densities of 4–6 × 1023 cm−2. For UGC 3789 and NGC 6264 (the two confirmed disc-maser galaxies in our sample), column densities in excess of 1 × 1024 cm−2 are inferred from the large EW of the Fe Kα 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 > 1023 cm−2) and Compton-thick AGN is 96 (45/47) and 57 per cent (27/47), respectively. In addition, 86 per cent, 18/21 of disc-maser galaxies host Compton-thick AGN. The correlation between the galaxies’ bolometric luminosity and accretion disc radius, suggested in previous works, is also confirmed.
    No preview · Article · Dec 2013 · Monthly Notices of the Royal Astronomical Society
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    P. Castangia · F. Panessa · C. Henkel · M. Kadler · A. Tarchi
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    ABSTRACT: 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.
    Preview · Article · Sep 2013
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    ABSTRACT: 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.
    Preview · Article · Apr 2012 · Proceedings of the International Astronomical Union
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    ABSTRACT: The accretion-ejection mechanism acting in Active Galactic Nuclei (AGN) is one of the main astrophysical open issues, being connected to the role of AGN feedback in galaxy formation evolution studies. The X-ray emission in AGN, associated with the accretion flow, is strongly coupled with the radio emission, associated with a jet. Strong correlations between the X-ray and the radio luminosities are found both in radio-loud (RL) and in radio-quiet (RQ) AGN, despite the fact that in RQ AGN jets are often absent or very weak. For a well defined and complete INTEGRAL RQ AGN sample we have found a strong correlation between the 20-100 keV and the radio luminosity. Black hole mass estimates for half of the sample sources allow us to compute the "fundamental plane of black hole activity", sampling the high luminosity/high accretion rate parameter space. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
    No preview · Article · Jan 2012
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    A. Tarchi · P. Castangia · A. Columbano · F. Panessa · J. A. Braatz
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    ABSTRACT: [Abridged] 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. 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. 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 NGC5506 at subarcsec scales with the Very Large Array. We discovered maser emission in two NLS1 galaxies: IGRJ16385-2057, and IRAS03450+0055. In addition to the three previously known maser detections in the NLS1s Mrk766, NGC4051, and NGC5506, 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 10000 km/s. For NGC4051 and NGC5506, 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.
    Preview · Article · Jul 2011 · Astronomy and Astrophysics
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    ABSTRACT: 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]
    Full-text · Article · Mar 2011 · Astronomy and Astrophysics
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    ABSTRACT: The accretion-ejection mechanism acting in Active Galactic Nuclei (AGN) is one of the main astrophysical open questions. A strong correlation between the nuclear 2-10 keV X-ray versus core radio luminosities suggests that the accretion flow and the radio source are strongly coupled both in radio-quietAGN and in radio-loudAGN.We approach this topic fromthe hard X-ray point of view by discussing the radio versus X-ray correlation in a complete sample of INTEGRAL AGN, selected between 20-40 keV. A strong correlation between the 20-100 keV and NVSS radio luminosities is found, which is more significant than the correlation of the 2-10 keV and radio luminosities. When computed for an optically selected sample of local AGN, the correlation slope is steeper with respect to the one obtained for the INTEGRAL AGN sample. These results indicate that the X-ray versus radio correlations hold also for relatively high luminosity AGN, suggesting that in efficient accretion systems the two source of emission are in someway connected.
    Preview · Article · Jan 2011
  • A. Tarchi · P. Castangia · F. Panessa · J. A. Braatz
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    ABSTRACT: 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 in the optical (narrowest Balmer lines and strongest FeII emission) and in the X-rays. Recently, we have also discovered that the detection rate of water maser emission in NLS1 is surprisingly high, much higher than typically found in type 1 AGN and similar to that of Seyfert 2 galaxies. In this talk, we shed light on this unexpected result in the framework of the unified model for AGN. In particular, we introduce the case of the recently-discovered INTEGRAL source IGR J16385-2057, classified as a NLS1 galaxy and characterized by an unusual radio continuum and maser emission.
    No preview · Article · Jan 2011

  • No preview · Article · Jan 2011
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    ABSTRACT: Studies of water megamaser radio sources provide a unique way to map accretion disks and to estimate masses of the nuclear engines in Active Galactic Nuclei (AGN). Broadband X-ray spectroscopy (0.1-100 keV) of AGN allows us to estimate the amount of intrinsic absorption and to derive intrinsic AGN luminosities. Therefore, complementary radio and X-ray observations of AGN potentially constitute an essential tool to understand the physics of these objects. Here, we present preliminary results of a survey to search for water maser emission in a complete sample of AGN selected in the hard X-ray band, between 20 and 40 keV, from INTEGRAL/IBIS observations. To date, we have discovered a new water maser in the NLSy1 IGRJ16385-2057. With this new detection, the fraction of water maser hosts in our INTEGRAL AGN sample is of 17% (11/66), much higher than typical detection rates obtained in surveys of optically-selected samples of AGN.
    No preview · Article · Jan 2011
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    A. Tarchi · P. Castangia · C. Henkel · G. Surcis · K. M. Menten
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    ABSTRACT: 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 star-forming 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. Table 5 is only available in electronic form at http://www.aanda.org
    Full-text · Article · Jan 2011 · Astronomy and Astrophysics
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    A. Tarchi · P. Castangia · A. Columbano · F. Panessa · J. A. Braatz

    Preview · Article · Jan 2011
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    ABSTRACT: The gravitational lens system MG J0414+0534 is formed by an elliptical galaxy at redshift ~0.96 and a quasar at z~2.64. The system geometry is typical of lensing by an elliptical galaxy with the QSO close to and inside a fold caustic. It shows 4 images of the background source, and a partial Einstein ring is visible at optical wavelengths. It was observed with a global-VLBI array at 18 cm in June 2008. We present here the imaging results and a preliminary lens model constrained by these observations. Comment: submitted to the proceedings of 10th European-VLBI network Symposium. 6 pages, 1 figure
    Full-text · Article · Nov 2010
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    ABSTRACT: Providing bright, almost point like hotspots, water masers are a powerful tool to investigate the structure and dynamics of the emitting gas, because they can be mapped at submilliarcsecond resolution using VLBI. In particular, detailed studies of luminous water masers in AGN provide constraints on the accretion disk geometry, estimates of black-hole masses and of the distance to parent galaxies. Since, so far, detection rates of water maser searches have been disappointingly low, increasing the number of such sources is highly desirable. Here, we propose to observe with The 70-m Tidbinbilla a complete sample of southern AGN selected in the hard X-ray band between 20 and 40 keV from INTEGRAL/IBIS observations, in a search for water maser emission at 22 GHz. Our selection criterion is supported by recent observational evidences indicating the existence of a correlation between hard X-ray emission and the water maser phenomenon. Together with providing new maser sources, this study will also allow us to investigate, on a firm statistical basis, the interplay between hard X-ray and maser emission in AGN.
    No preview · Article · Oct 2010
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    ABSTRACT: Luminous extragalactic water masers are known to be associated with AGN and have provided accurate estimates for the mass of the central supermassive black hole and the size and structure of the accretion disk in nearby galaxies. To find water masers 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 lensed quasars and star-forming galaxies at redshifts 2.3--2.9 with the Effelsberg telescope and the EVLA. Our observations do not find any new definite examples of high redshift water maser galaxies, suggesting that large reservoirs of dust and gas are not a sufficient condition for powerful water maser emission. However, we do find the tentative 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 lensed galaxies and quasars that have been searched for high redshift water masers. We present an 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 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 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. 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 targeted observations. Comment: 10 pages, 4 figures, 4 tables, accepted for publication in MNRAS
    Full-text · Article · Sep 2010 · Monthly Notices of the Royal Astronomical Society
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    A. Tarchi · P. Castangia · C. Henkel · G. Surcis · K. M. Menten
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    ABSTRACT: 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 star 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 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 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. Comment: 19 pages, 11 figures, 5 tables. Accepted by Astronomy & Astrophysics
    Full-text · Article · Aug 2010
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    ABSTRACT: 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.
    No preview · Article · Jul 2010

Publication Stats

188 Citations
107.72 Total Impact Points

Institutions

  • 2014
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 2007-2009
    • Max Planck Institute for Radio Astronomy
      Bonn, North Rhine-Westphalia, Germany
  • 2004-2006
    • Università degli studi di Cagliari
      • Department of Physics
      Cagliari, Sardinia, Italy