Extragalactic H<Subscript>2</Subscript>O maser sources and their properties

The properties of a sample of extragalactic H₂O maser sources over a wide spectral range are discussed. Based on a sample of 81 maser galaxies it is shown that mega- and kilomasers have completely different properties. In particular, for megamasers the strongest observed relationships are between the parameters of the H₂O line and the mass of the galactic nucleus, while the parameters of the line are uncorrelated with the x-ray, infrared, and radio emission. A weak correlation between megamaser emission and the surface (column) density of hydrogen is observed. As for kilomasers, their H₂O luminosity depends weakly on the x-ray emission, although in the case of soft x rays this dependence is significant. The H₂O luminosity of kilomasers is moderately correlated with the infrared and radio continuum luminosities, but the line parameters are independent of the mass of the nucleus and the surface density of hydrogen.     

The Eddington Ratio of H 2 O Maser Host AGN

The Eddington ratio λ was derived for the entire maser host AGN sample, based on the intrinsic X-ray luminosity, the X-ray bolometric correction C _X and the mass of central black hole. Further the [O III] bolometric correction C _{[O III]} was estimated for our sample. Possible relations were also investigated between the maser luminosity and the bolometric luminosity – the Eddington ratio.     

Molecular hydrogen in the central regions of southern infrared galaxies

An extensive set of molecular hydrogen observations of centers of southern infrared galaxies is presented. Our data are combined with published infrared and radio observations to investigate the relationship between nuclear and circumnuclear activity. We convert the observational data to absolute luminosities, by applying the known distances. The resulting dataset covers several decades in luminosity for the various parameters, which observe fairly tight correlations. The parameters of our (power law) fits are, at the level of accuracy achieved, not dependent on the type of nuclear activity: while the dataset comprises a mixture of alleged Seyfert, Liner & starburst galaxies, single fits match the complete sample well enough. In particular, non-thermal nuclei (AGN) present in some of the galaxies in the current sample, do not stand out in the parameters we investigated. The absence of a significant dependence on the nuclear type is consistent with the idea that the ever present starbursts energetically dominate a possible ‘AGN in a dusty environment’-component in most galaxy nuclei with infrared excesses.The size of the H₂ emitting region is found to be proportional to the square root of the 21 cm radio continuum luminosity. The excitation of the circumnuclear H₂ is dominated by shocks. If the H₂ extent marks the size of an inner cavity in the dense molecular material surrounding a galaxy nucleus and the radio luminosity is proportional to the mechanical luminosity of (circum)nuclear winds. This result then indicates that the cavity size occurs at constant pressure in the sample galaxies, in accordance with the superwind model by Heckman et al. (1990) [ApJS, 74, 833]. Our results, together with those obtained by others, thus suggest that luminosities and size scales of excited gas associated with active nuclei are dominated by the mechanical energy input. Given the difficulties of uniquely establishing the presence of an AGN, we cannot exclude that (a large fraction of the) infrared luminous galaxies procure part of their radiated energy through accretion onto a massive dark object.F. Duccio Macchetto     

Radio AGN in the local universe: unification,triggering and evolution

Associated with one of the most important forms of active galactic nucleus (AGN) feedback, and showing a strong preference for giant elliptical host galaxies, radio AGN (\(L_{1.4\,\mathrm{GHz}} > 10^{24}\) W \(\hbox {Hz}^{-1}\)) are a key sub-class of the overall AGN population. Recently their study has benefitted dramatically from the availability of high-quality data covering the X-ray to far-IR wavelength range obtained with the current generation of ground- and space-based telescope facilities. Reflecting this progress, here I review our current state of understanding of the population of radio AGN at low and intermediate redshifts (\(z < 0.7\)), concentrating on their nuclear AGN and host galaxy properties, and covering three interlocking themes: the classification of radio AGN and its interpretation; the triggering and fuelling of the jet and AGN activity; and the evolution of the host galaxies. I show that much of the observed diversity in the AGN properties of radio AGN can be explained in terms of a combination of orientation/anisotropy, mass accretion rate, and variability effects. The detailed morphologies of the host galaxies are consistent with the triggering of strong-line radio galaxies (SLRG) in galaxy mergers. However, the star formation properties and cool ISM contents suggest that the triggering mergers are relatively minor in terms of their gas masses in most cases, and would not lead to major growth of the supermassive black holes and stellar bulges; therefore, apart from a minority (<20 %) that show evidence for higher star formation rates and more massive cool ISM reservoirs, the SLRG represent late-time re-triggering of activity in mature giant elliptical galaxies. In contrast, the host and environmental properties of weak-line radio galaxies (WLRG) with Fanaroff–Riley class I radio morphologies are consistent with more gradual fuelling of the activity via gas accretion at low rates onto the supermassive black holes.     

Extragalactic H2O Megamaser Sources： Central Black Holes, Nuclear X-ray and Maser Emissions

Extragalactic H2O megamasers are typically found within the innermost few parsecs of active galaxy nuclei (AGN) and the maser emission is considered to be excited most likely by the X-ray irradiation of the AGN.We investigate a comprehensive sample of extragalactic H2O masers in a sample of 38 maser host AGN to check potential correlations of the megamaser emission with parameters of the AGN,such as X-ray luminosity and black hole (BH) masses.We find a relation between the maser luminosities and BH masses,LH2O∝ M3.64-0.4 BH,which supports basically the theoretical prediction.The relation between the maser emission and X-ray emission is also confirmed.     

Host galaxy morphologies of X-ray selected AGN: assessing the significance of different black hole fuelling mechanisms to the accretion density of the Universe at z∼ 1.

We use morphological information of X-ray selected active galactic nuclei (AGN) hosts to set limits on the fraction of the accretion density of the Universe at   z ≈ 1  that is not likely to be associated with major mergers. Deep X-ray observations are combined with high-resolution optical data from the Hubble Space Telescope in the All-wavelength Extended Groth strip International Survey, Great Observatories Origins Deep Survey (GOODS) North and GOODS South fields to explore the morphological breakdown of X-ray sources in the redshift interval  0.5 < z < 1.3  . The sample is split into discs, early-type bulge-dominated galaxies, peculiar systems and point sources in which the nuclear source outshines the host galaxy. The X-ray luminosity function and luminosity density of AGN at   z ≈ 1  are then calculated as a function of morphological type. We find that disc-dominated hosts contribute  30 ± 9  per cent to the total AGN space density and  23 ± 6  per cent to the luminosity density at   z ≈ 1  . We argue that AGN in disc galaxies are most likely fuelled not by major merger events but by minor interactions or internal instabilities. We find evidence that these mechanisms may be more efficient in producing luminous AGN     compared to predictions for the stochastic fuelling of massive black holes in disc galaxies.     

Host galaxies and the unification of radio-loud AGN

Our HST WFPC2 survey of 110 BL Lac objects, from six complete X-ray-, radio-, and optically-selected catalogs, probes the host galaxies of low-luminosity radio sources in the redshift range 0<z<1.35. The host galaxies are luminous ellipticals, well matched in radio power and galaxy magnitude to FR I radio galaxies. Similarly, the host galaxies of high luminosity quasars occupy the same region of this plane as FR II radio galaxies (matched in redshift). This strongly supports the unification of radio-loud AGN, and suggests that studying blazars at high redshift is a proxy for investigating less luminous (to us) but intrinsically identical radio galaxies, which are harder to find at high z. Accordingly, the difference between low-power jets in BL Lac objects and high-power jets in quasars can then be related to the FR I/FR II dichotomy; and the evolution of blazar host galaxies or their nuclei (jets) should correspond to the evolution of radio galaxies.     

A sample of radio-loud active galactic nuclei in the Sloan Digital Sky Survey

A sample of 2712 radio-luminous galaxies is defined from the second data release of the Sloan Digital Sky Survey (SDSS) by cross-comparing the main spectroscopic galaxy sample with two radio surveys: the National Radio Astronomy Observatories (NRAO) Very Large Array (VLA) Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty centimeters (FIRST) survey. The comparison is carried out in a multistage process and makes optimal use of both radio surveys by exploiting the sensitivity of the NVSS to extended and multicomponent radio sources in addition to the high angular resolution of the FIRST images. A radio source sample with 95 per cent completeness and 98.9 per cent reliability is achieved, far better than would be possible for this sample if only one of the surveys was used. The radio source sample is then divided into two classes: radio-loud active galactic nuclei (AGN) and galaxies in which the radio emission is dominated by star formation. The division is based on the location of a galaxy in the plane of 4000-Å break strength versus radio luminosity per unit stellar mass and provides a sample of 2215 radio-loud AGN and 497 star-forming galaxies brighter than 5 mJy at 1.4 GHz. A full catalogue of positions and radio properties is provided for these sources. The local radio luminosity function is then derived both for radio-loud AGN and for star-forming galaxies and is found to be in agreement with previous studies. By using the radio to far-infrared (FIR) correlation, the radio luminosity function of star-forming galaxies is also compared to the luminosity function derived in the FIR. It is found to agree well at high luminosities but less so at lower luminosities, confirming that the linearity of the radio to FIR correlation breaks down below about 10²² W Hz⁻¹ at 1.4 GHz.     

The fraction of galaxies that contain active nuclei and their accretion rates

We investigate the relationship between the present-day optical luminosity function of galaxies and the X-ray luminosity function of Seyfert 1s to determine the fraction of galaxies that host Seyfert 1 nuclei and their Eddington ratios. The local type 1 active galactic nuclei (AGN) X-ray luminosity function is well reproduced if ∼1 per cent of all galaxies are type 1 Seyferts which have Eddington ratios of ∼10⁻³. However, in such a model the X-ray luminosity function is completely dominated by AGN in E and S0 galaxies, contrary to the observed mix of Seyfert host galaxies. To obtain a plausible mix of AGN host galaxy morphologies requires that the most massive black holes in E and S0 galaxies accrete with lower Eddington ratios, or have a lower incidence of Seyfert activity, than the central black holes of later-type galaxies.     

The disc-dominated host galaxy of FR-I radio source B2 0722+30

We present new observational results that conclude that the nearby radio galaxy B2 0722+30 is one of the very few known disc galaxies in the low-redshift Universe that host a classical double-lobed radio source. In this paper, we use H  i observations, deep optical imaging, stellar population synthesis modelling and emission-line diagnostics to study the host galaxy, classify the active galactic nucleus (AGN) and investigate environmental properties under which a radio-loud AGN can occur in this system. Typical for spiral galaxies, B2 0722+30 has a regularly rotating gaseous disc throughout which star formation occurs. Dust heating by the ongoing star formation is likely responsible for the high infrared luminosity of the system. The optical emission-line properties of the central region identify a Low Ionization Nuclear Emission-line Region (LINER)-type nucleus with a relatively low [O  iii ] luminosity, in particular when compared with the total power of the Fanaroff & Riley type-I radio source that is present in this system. This classifies B2 0722+30 as a classical radio galaxy rather than a typical Seyfert galaxy. The environment of B2 0722+30 is extremely H  i -rich, with several nearby interacting galaxies. We argue that a gas-rich interaction involving B2 0722+30 is a likely cause for the triggering of the radio AGN and/or the fact that the radio source managed to escape the optical boundaries of the host galaxy.     

Broad-Band Radio to X-Ray Properties of Seyfert Galaxies

We report on the statistical analysis of a sample of AGNs (Seyferts and LINERs) selected from an RBSC-NVSS sample of the brightest X-ray sources. The sample is large enough and unbiased for a detailed study of multi-frequency (radio to X-ray) properties of AGN. There are no significant differences in X-ray, optical, far-infrared, and radio powers, core dominance, radio loudness, radio spectral index, and two-point radio-to-optical and optical-to-X-ray spectral indices of Seyfert types 1 and 2. These findings strongly support the unification model, and the observed differences between Sy1 and Sy2 are due to both the variable obscuration and different geometric orientation effects. The correlation between the X-ray and radio emission over many decades is primary and indicates the intrinsically similar origin of both radiations in Seyfert galaxies, powered mainly by AGN, rather than compact starbursts. For Seyfert galaxies we found that the slopes of the relations L _X - L _R and L _X - L _B are flat, which indicate the existence of components unrelated with X-ray. Perhaps only for LINERs is the observed L _X - L _R relation completely due to AGNs. The Sy1, Sy2, and LINER galaxies show different slopes in the relation L _X - L _1.4, and the relative contribution of extended radio components may be the cause of these differences. The possible effects of unresolved extended radio and X-ray components are quantitatively discussed.     

Long-term monitoring of the long-period variable Y Cassiopeiae in the 1.35-cm water-vapor line

Observations of the circumstellar maser emission from the long-period variable star Y Cas in the 1.35-cm water-vapor line are presented. The observations were performed with the RT-22 radio telescope at the Pushchino Radio Astronomy Observatory (Astrospace Center, Lebedev Physical Institute, Russian Academy of Sciences) in the period 1982–2005. The variations in the integrated flux F_int in the H₂O line correlate with the visual light curve of the star. The phase delay Δ? between the F_int variations and the light curve is 0.2–0.4P (P is the period of the star). The H₂O maser Y Cas belongs to transient sources: peaks of high maser activity alternate with intervals of a low emission level when the H₂O-line flux does not exceed (0.1–0.5) × 10^?20 W m^?2. A “superperiod” of ～5.7 yr was found in the occurrence of activity peaks. A particularly strong maximum of maser radio emission took place at the end of 1997, when the flux F_int reached 15.6 × 10^?20 W m^?2. A model for the H₂O maser variability in Y Cas is discussed. The variability is caused by a periodic action of shock waves driven by stellar pulsations. The H₂O maser flares may be associated with short-lived episodes of enhanced mass loss by the star or with the propagation of a particularly strong shock wave when a planet orbiting the star passes through its periastron.     

Halo masses for optically selected and for radio-loud AGN from clustering and galaxy–galaxy lensing

We compute two-point correlation functions and measure the shear signal due to galaxy–galaxy lensing for 80 000 optically identified and 5700 radio-loud active galactic nuclei (AGN) from Data Release 4 of the Sloan Digital Sky Survey. Halo occupation models are used to estimate halo masses and satellite fractions for these two types of AGN. The large sample size allows us to separate AGN according to the stellar mass of their host galaxies. We study how the halo masses of optical and radio AGN differ from those of the parent population at fixed   M _*  . Halo masses deduced from clustering and from lensing agree satisfactorily. Radio AGN are found in more massive haloes than optical AGN: in our samples, their mean halo masses are  1.6 × 10¹³  and  8 × 10¹¹  h ⁻¹ M_⊙  , respectively. Optical AGN follow the same relation between stellar mass and halo mass as galaxies selected without regard to nuclear properties, but radio-loud AGN deviate significantly from this relation. The dark matter haloes of radio-loud AGN are about twice as massive as those of control galaxies of the same stellar mass. This boost is independent of radio luminosity, and persists even when our analysis is restricted to field galaxies. The large-scale gaseous environment of the galaxy clearly plays a crucial role in producing observable radio emission. The dark matter halo masses that we derive for the AGN in our two samples are in good agreement with recent models in which feedback from radio AGN becomes dominant in haloes where gas cools quasi-statically.     

A flare of the H2O maser in the source Orion KL

In 1998, the intensity of the 1.35-cm H₂O maser radio line in the source Orion KL increased several hundreds of times. The observations of this flare and its behavior with time are presented.     

Searching for high-redshift centimeter-wave continuum, line and maser emission using the Square Kilometer Array

We discuss the detection of redshifted line and continuum emission at radio wavelengths using a Square Kilometer Array (SKA), specifically from low-excitation rotational molecular line transitions of CO and HCN (molecular lines), the recombination radiation from atomic transitions in almost-ionized hydrogen (radio recombination lines; RRLs), OH and H₂O maser lines, as well as from synchrotron and free–free continuum radiation and HI 21-cm line radiation. The detection of radio lines with the SKA offers the prospect to determine the redshifts and thus exact luminosities for some of the most distant and optically faint star-forming galaxies and active galactic nuclei, even those galaxies that are either deeply enshrouded in interstellar dust or shining prior to the end of reionization. Moreover, it provides an opportunity to study the astrophysical conditions and resolved morphologies of the most active regions in galaxies during the most active phase of star formation at redshift z 2. A sufficiently powerful and adaptable SKA correlator will enable wide-field three-dimensional redshift surveys at chosen specific high redshifts, and will allow new probes of the evolution of large-scale structure (LSS) in the distribution of galaxies. The detection of molecular line radiation favours pushing the operating frequencies of SKA up to at least 26 GHz, and ideally to 40 GHz, while very high redshift maser emissions requires access to about 100 MHz. To search for LSS the widest possible instantaneous field of view would be advantageous.     

Morphologies of AGN host galaxies using HST/ACS in the CDFS-GOODS field

Using HST/ACS images in four bands F435W, F606W, F775W and F850LP, we identify optical counterparts to the X-ray sources in the Chandra Deep Field South in the GOODS South field. A detailed study has been made of these sources to study their morphological types. We use methods like decomposition of galaxy luminosity profiles, color maps and visual inspection of 192 galaxies which are identified as possible optical counterparts of Chandra X-ray sources in the CDFS-GOODS field. We find that most moderate luminosity AGN hosts are bulge dominated in the redshift range (z≈0.4–1.3), but not merging/interacting galaxies. This implies probable fueling of the moderate luminosity AGN by mechanisms other than those merger driven.     

The host galaxies of active galactic nuclei

We examine the properties of the host galaxies of 22 623 narrow-line active galactic nuclei (AGN) with  0.02 < z < 0.3  selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O  iii ]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L [O  iii ]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early types. The hosts of high-luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high-luminosity AGN have strong Hδ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O  iii ] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O  iii ] luminosities.     

The Seyfert-Liner Galaxy NGC 7213: An XMM-Newton Observation

We examine the XMM X-ray spectrum of the low-ionisation nuclear emission-line region (LINER)-AGN NGC 7213, which is best fit with a power law, Kα emission lines from Fe i, Fe xxv and Fe xxvi and a soft X-ray collisionally ionised thermal plasma with kT = 0.18^+0.03_−0.01 keV. We find a luminosity of 7× 10⁻⁴ L_Edd, and a lack of soft X-ray excess emission, suggesting a truncated accretion disc. NGC 7213 has intermediate X-ray spectral properties, between those of the weak AGN found in the LINER M 81 and higher luminosity Seyfert galaxies. This supports the notion of a continuous sequence of X-ray properties from the Galactic Centre through LINER galaxies to Seyferts, likely determined by the amount of material available for accretion in the central regions. This work is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).     

A comparative HST imaging study of the host galaxies of radio-quiet quasars, radio-loud quasars and radio galaxies – I

We present the first results from a major HST WFPC2 imaging study aimed at providing the first statistically meaningful comparison of the morphologies, luminosities, scalelengths and colours of the host galaxies of radio-quiet quasars, radio-loud quasars and radio galaxies. We describe the design of this study and present the images that have been obtained for the first half of our 33-source sample. We find that the hosts of all three classes of luminous AGN are massive elliptical galaxies, with scalelengths ≃10 kpc, and R − K colours consistent with mature stellar populations. Most importantly, this is first unambiguous evidence that, just like radio-loud quasars, essentially all radio-quiet quasars brighter than M _R =−24 reside in massive ellipticals. This result removes the possibility that radio 'loudness' is directly linked to host galaxy morphology, but is however in excellent accord with the black hole/spheroid mass correlation recently highlighted by Magorrian et al. We apply the relations given by Magorrian et al. to infer the expected Eddington luminosity of the putative black hole at the centre of each of the spheroidal host galaxies we have uncovered. Comparison with the actual nuclear R -band luminosities suggests that the black holes in most of these galaxies are radiating at a few per cent of the Eddington luminosity; the brightest host galaxies in our low- z sample are capable of hosting quasars with M _R ≃− 28, comparable to the most luminous quasars at z ≃3. Finally, we discuss our host-derived black hole masses in the context of the radio luminosity:black hole mass correlation recently uncovered for nearby galaxies by Franceschini et al., and consider the resulting implications for the physical origin of radio loudness.