Of 104 AGN known to exhibit H 2 O maser emission, X-ray data that enable estimation of column densities, or lower limits, are available for 42. Contributing to this, we report analysis of new and archival X-ray data for 8 galaxies and collation of values for three more. Maser emission is indicative of large columns of cold gas, and in five of the eight new cases, maser spectra point toward origins in accretion disks viewed close-to edge-on (a.k.a. "disk-maser" systems). In these, we detect hard continuum and Fe Kα emission with equivalent widths on the order of 1 keV, which is consistent with Compton reflection, fluorescence by cold material, and obscuring columns 10 24 cm −2 . Reviewing the full sample of 42, 95% exhibit N H > 10 23 cm −2 and 60% exhibit N H > 10 24 cm −2 . Half of these are now recognized to be disk masers (up from 13); in this sub-sample, which is likely to be more homogeneous vis-á-vis the origin of maser emission, 76% exhibit N H > 10 24 cm −2 . The probability of a common parent distribution of columns for disk-masers and other AGN masers is 3%. Because ground-based surveys of AGN to detect new disk masers are relatively unbiased with respect to Xray brightness and comparatively inexpensive, they may also be efficient guides for the sensitive pointed X-ray observations required to identify Compton-thick objects outside of shallow surveys.

-We present here the results from new Very Long Baseline Array observations at 1.6 and 5 GHz of 19 galaxies of a complete sample of 21 UGC FRI radio galaxies. New Chandra data of two sources, viz., UGC 00408 and UGC 08433, are combined with the Chandra archival data of 13 sources. The 5 GHz observations of ten "core-jet" sources are polarization-sensitive, while the 1.6 GHz observations constitute second epoch total intensity observations of nine "core-only" sources. Polarized emission is detected in the jets of seven sources at 5 GHz, but the cores are essentially unpolarized, except in M 87. Polarization is detected at the jet edges in several sources, and the inferred magnetic field is primarily aligned with the jet direction. This could be indicative of magnetic field "shearing" due to jet-medium interaction, or the presence of helical magnetic fields. The jet peak intensity I ν falls with distance d from the core, following the relation,where a is typically ∼ −1.5. Assuming that adiabatic expansion losses are primarily responsible for the jet intensity "dimming", two limiting cases are considered: [1] the jet has a constant speed on parsec-scales and is expanding gradually such that the jet radius r ∝ d 0.4 ; this expansion is however unobservable in the laterally unresolved jets at 5 GHz, and [2] the jet is cylindrical and is accelerating on parsec-scales. Accelerating parsec-scale jets are consistent with the phenomenon of "magnetic driving" in Poynting flux dominated jets. While slow jet expansion as predicted by case [2] is indeed observed in a few sources from the literature that are resolved laterally, on scales of tens or hundreds of parsec, case [2] cannot be ruled out in the present data, provided the jets become conical on scales larger than those probed by the VLBA. Chandra observations of 15 UGC FRIs detect X-ray jets in nine of them. The high frequency of occurance of X-ray jets in this complete sample suggests that they are a signature of a ubiquitous process in FRI jets. It appears that the FRI jets start out relativistically on parsec-scales but decelerate on kiloparsec scales, with the X-ray emission revealing the sites of bulk deceleration and particle reacceleration.

We present a new XMM-Newton spectrum of the Seyfert 2 nucleus of IC 2560, which hosts H 2 O maser emission from an inclined Keplerian accretion disk. The X-ray spectrum shows soft excess due to multitemperature ionized plasma, a hard continuum, and strong emission features, from Mg, Si, S, Ca, Fe, and Ni, mainly due to fluorescence. It is consistent with reflection of the continuum from a mostly neutral medium and obscuration due to a high column density, >10 24 cm À2 . The amplitude of the reflected component may exceed 10% of the central unobscured luminosity. This is higher than the reflected fraction of a few percent observed in other Seyfert 2 sources such as NGC 4945. We observe an emission line at 6.7 keV, possibly due to Fe xxv, undetected in previous Chandra observations. The absorption column density associated with this line is less than 10 23 cm À2 , which is lower than the obscuration of the central source. We hypothesize that this highly ionized Fe line emission originates in warm gas, which is also responsible for a scattered component of continuum emission that may dominate the spectrum between 1 and 3 keV. We compare X-ray and maser emission characteristics of IC 2560 and other AGNs that exhibit water maser emission originating in disk structures around central engines. The temperature for the region of the disk associated with maser action is consistent with the expected 400Y1000 K range. The clumpiness of disk structures (inferred from the maser distribution) may depend on the unobscured luminosities of the central engines.

Based on spectroscopic signatures, about one-third of known H 2 O maser sources in active galactic nuclei (AGN) are believed to arise in highly inclined accretion disks around central engines. These "disk maser candidates" are of interest primarily because angular structure and rotation curves can be resolved with interferometers, enabling dynamical study. We identify five new disk maser candidates in studies with the Green Bank Telescope, bringing the total number published to 30. We discovered two (NGC 1320, NGC 17) in a survey of 40 inclined active galaxies (v sys < 20000 km s −1 ). The remaining three disk maser candidates were identified in monitoring of known sources: NGC 449, NGC 2979, NGC 3735. We also confirm a previously marginal case in UGC 4203. For the disk maser candidates reported here, inferred rotation speeds are 130-500 km s −1 . Monitoring of three more rapidly rotating candidate disks (CG 211, NGC 6264, VV 340A) has enabled measurement of likely orbital centripetal acceleration, and estimation of central masses (2-7×10 7 M ⊙ ) and mean disk radii (0.2-0.4 pc). Accelerations may ultimately permit estimation of distances when combined with interferometer data. This is notable because the three AGN are relatively distant (10000 < v sys < 15000 km s −1 ), and fractional error in a derived Hubble constant, due to peculiar motion of the galaxies, would be small. As signposts of highly inclined geometries at galactocentric radii of ∼ 0.1-1 pc, disk masers also provide robust orientation references that allow analysis of (mis)alignment between AGN and surrounding galactic stellar disks, even without extensive interferometric mapping. We find no preference among published disk maser candidates to lie in high-inclination galaxies. This provides independent support for conclusions that in late-type galaxies, central engine accretion disks and galactic plane orientations are not correlated.

We present the results of Hubble Space Telescope (HST ) WFPC2 medium-band and narrowband imaging and Very Large Array and MERLIN2 radio imaging of three powerful radio galaxies: 3C 171, 3C 277.3, and PKS 2250À41. We obtained images of the rest frame [O iii] k5007 and [O ii] k3727 line emission using the linear ramp filters on WFPC2. The correlations of the emission-line morphology and the [O iii]/[O ii] line ratios with the radio emission seen in ground-based observations are clarified by the HST imaging. We confirm that the radio lobes and hot spots are preferentially associated with lower ionization gas. The galaxy 3C 171 exhibits high surface brightness emission-line gas mainly along the radio source axis. The lowest ionization gas is seen at the eastern hot spot. In 3C 277.3 there is bright high-ionization gas (and continuum) offset just to the east of the radio knot K1. Our observations are consistent with previous work suggesting that this emission is produced by precursor gas ionized by the shock being driven into the cloud by the deflected radio jet. In PKS 2250À41 we resolve the emission-line arc that wraps around the outer rim of the western lobe. The lower ionization [O ii] emission is nested just interior to the higher ionization [O iii] emission, suggesting that we have resolved the cooling region behind the bow shock. We also detect possible continuum emission from the secondary hot spot. Thus, our observations support the hypothesis that in these sources the interaction between the expanding radio source and the ambient gas strongly influences the morphology, kinematics, and ionization of the gas.