NGC 4945 is one of the nearest (D≈3.8 Mpc; 1 ′′ ≈ 19 pc) starburst galaxies. To investigate structure, dynamics, and composition of its dense nuclear gas, ALMA band 3 (λ≈3-4 mm) observations were carried out with ≈2 ′′ resolution. Measured were three HCN and two HCO + isotopologues, CS, C3H2, SiO, HCO, and CH3C2H. Spectral line imaging demonstrates the presence of a rotating nuclear disk of projected size 10 ′′ ×2 ′′ reaching out to a galactocentric radius of r≈100 pc with position angle PA = 45 • ±2 • , inclination i = 75 • ±2 • and an unresolved bright central core of size < ∼ 2 ′′ . The continuum source, representing mostly free-free radiation from star forming regions, is more compact than the nuclear disk by a linear factor of two but shows the same position angle and is centered 0 . ′′ 39 ± 0 . ′′ 14 northeast of the nuclear accretion disk defined by H2O maser emission. Near the systemic velocity but outside the nuclear disk, both HCN J=1→0 and CS J=2→1 delineate molecular arms of length > ∼ 15 ′′ ( > ∼ 285 pc) on opposite sides of the dynamical center. These are connected by a (deprojected) ≈0.6 kpc sized molecular bridge, likely a dense gaseous bar seen almost ends-on, shifting gas from the front and back side into the nuclear disk. Modeling this nuclear disk located farther inside (r < ∼ 100 pc) with tilted rings provides a good fit by inferring a coplanar outflow reaching a characteristic deprojectd velocity of ≈50 km s −1 . All our molecular lines, with the notable exception of CH3C2H, show significant absorption near the systemic velocity (≈571 km s −1 ), within a range of ≈500 -660 km s −1 . Apparently, only molecular transitions with low critical H2-density (ncrit < ∼ 10 4 cm −3 ) do not show absorption. The velocity field of the nuclear disk, derived from CH3C2H, provides evidence for rigid rotation in the inner few arcseconds and a dynamical mass of Mtot = (2.1±0.2) × 10 8 M⊙ inside a galactocentric radius of 2 .′′ 45 (≈45 pc), with a significantly flattened rotation curve farther out. Velocity integrated line intensity maps with most pronounced absorption show molecular peak positions up to ≈1 .′′ 5 (≈30 pc) southwest of the continuum peak, presumably due to absorption, which appears to be most severe slightly northeast of the nuclear maser disk. A nitrogen isotope ratio of 14 N/ 15 N ≈ 200-450 is estimated. This range of values is much higher then previously reported on a tentative basis. Therefore, with 15 N being less abundant than expected, the question for strong 15 N enrichment by massive star ejecta in starbursts still remains to be settled.
We present VLBI images and kinematics of water maser emission in three active galaxies: NGC 5728, Mrk 1, and IRAS 08452−0011. IRAS 08452−0011, at a distance of ∼200 Mpc, is a triple-peaked H2O megamaser, consistent with a Keplerian rotating disk, indicating a black hole mass of (3.3±0.2) × 107M⊙. NGC 5728 and Mrk 1 display double-peaked spectra and VLBI imaging reveal complicated gas kinematics that do not allow for a robust determination of black hole mass. We show evidence that the masers in NGC 5728 are in a wind while the Mrk 1 maser system has both disk and outflow components. We also find that disturbed morphology and kinematics are a ubiquitous feature of all double-peaked maser systems, implying that these maser sources may reside in environments where AGN winds are prominent at ∼1 pc scale and have significant impact on the masing gas. Such AGN tend to have black hole masses MBH < 8× 106M⊙ and Eddington ratios λEdd ≳ 0.1, while the triple-peaked megamasers show an opposite trend.
Context. An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc sized accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of Low Luminosity Active Galactic Nuclei (LLAGNs). Aims. The project intends to examine the validity of this paradigm by measuring the radio continuum on the same physical scale as the accretion disks, to investigate any possible connection between these disks and the radio continuum. Methods. We observed a sample of 18 LLAGNs in the 4.8 GHz (6 cm) radio continuum using the Very Long Baseline Array (VLBA) with 3.3 to 6.5 milliarcseconds resolution. The sources were selected to show both an edge-on accretion disk revealed by 22 GHz H 2 O megamaser emission and signatures of a radio jet. Furthermore, the sources were previously detected in 33 GHz radio continuum observations made with the Very Large Array. Results. Five out of 18 galaxies observed were detected at 8 σ or higher levels (Mrk 0001, Mrk 1210, Mrk 1419, NGC 2273. While all these sources are known to have maser disks, four of these five sources exhibit a maser disk with known orientation. For all four sources, the radio continuum is misaligned relative to the rotation axis of the maser disk, but with a 99.1% confidence level, the orientations are not random and are confined to a cone within 32 • of the maser disk's normal. Among the four sources the misalignment of the radio continuum with respect to the normal vector to the maser disk is smaller when the inner radius of the maser disk is larger. Furthermore, a correlation is observed between the 5 GHz VLBA radio continuum and the [OIII] luminosity and also with the H 2 O maser disk's inner radius.
Context. Galaxies with H 2 O megamaser disks are active galaxies in whose edge-on accretion disks 22 GHz H 2 O maser emission has been detected. Because their geometry is known, they provide a unique view into the properties of active galactic nuclei. Aims. The goal of this work is to investigate the nuclear environment of galaxies with H 2 O maser disks and to relate the maser and host galaxy properties to those of the radio continuum emission of the galaxy. Methods. The 33 GHz (9 mm) radio continuum properties of 24 galaxies with reported 22 GHz H 2 O maser emission from their disks are studied in the context of the multiwavelength view of these sources. The 29-37 GHz Ka-band observations are made with the Jansky Very Large Array in B, CnB, or BnA configurations, achieving a resolution of ∼ 0.2 -0.5 arcseconds. Hard X-ray data from the Swift/BAT survey and 22 µm infrared data from WISE, 22 GHz H 2 O maser data and 1.4 GHz data from NVSS and FIRST surveys are also included in the analysis. Results. Eighty-seven percent (21 out of 24) galaxies in our sample show 33 GHz radio continuum emission at levels of 4.5 -240 σ. Five sources show extended emission (deconvolved source size larger than 2.5 times the major axis of the beam), including one source with two main components and one with three main components. The remaining detected 16 sources (and also some of the above-mentioned targets) exhibit compact cores within the sensitivity limits. Little evidence is found for extended jets (>300 pc) in most sources. Either they do not exist, or our chosen frequency of 33 GHz is too high for a detection of these supposedly steep spectrum features. In only one source among those with known maser disk orientation, NGC 4388, did we find an extended jet-like feature that appears to be oriented perpendicular to the H 2 O megamaser disk. NGC 2273 is another candidate whose radio continuum source might be elongated perpendicular to the maser disk. Smaller 100-300 pc sized jets might also be present, as is suggested by the beam-deconvolved morphology of our sources. Whenever possible, central positions with accuracies of 20-280 mas are provided. A correlation analysis shows that the 33 GHz luminosity weakly correlates with the infrared luminosity. The 33 GHz luminosity is anticorrelated with the circular velocity of the galaxy. The black hole masses show stronger correlations with H 2 O maser luminosity than with 1.4 GHz, 33 GHz, or hard X-ray luminosities. Furthermore, the inner radii of the disks show stronger correlations with 1.4 GHz, 33 GHz, and hard X-ray luminosities than their outer radii, suggesting that the outer radii may be affected by disk warping, star formation, or peculiar density distributions.
The Galactic Center is the closest galactic nucleus that allows us to determine the multi-frequency behavior of the supermassive black hole counterpart Sagittarius A* in great detail. We put SgrA*, as a nucleus with weak activity, into the context of nearby low luminosity nuclei. Possible hints for galaxy evolution of these sources across the [NII]-based diagnostic diagram can be inferred from dependencies on the masses, excitation ratios, and radio luminosities within this diagram. For SgrA* we also discuss responsible radiation mechanisms covering results from the radio, infrared, and X-ray regime. We also address the question of justifying the hot-spot model for describing flare profiles in light curves. Since the brightness of LLAGN is also linked to star formation we briefly discuss the possibility of having stars formed in the immediate vicinity of supermassive black holes and possibly even in a mildly relativistic environment. Multifrequency Behavior ofHigh Energy Cosmic Sources -XII
Since the IAU (maser-)Symposium 287 in Stellenbosch/South Africa (Jan. 2012), great progress has been achieved in studying extragalactic maser sources. Sensitivity has reached a level allowing for dedicated maser surveys of extragalactic objects. These included, during the last years, water vapor (H2O), methanol (CH3OH), and formaldehyde (H2CO), while surveys related to hydroxyl (OH), cyanoacetylene (HC3N) and ammonia (NH3) may soon become (again) relevant. Overall, with the upgraded Very Large Array (VLA), the Atacama Large Millimeter/submillimeter Array (ALMA), FAST (Five hundred meter Aperture Synthesis Telescope) and the low frequency arrays APERTIF (APERture Tile in Focus), ASKAP (Australian Square Kilometer Array Pathfinder) and MeerKAT (Meer Karoo Array Telescope), extragalactic maser studies are expected to flourish during the upcoming years. The following article provides a brief sketch of past achievements, ongoing projects and future perspectives.
We present VLBI images and kinematics of water maser emission in three active galaxies: NGC 5728, Mrk 1, and IRAS 08452−0011. IRAS 08452−0011 is a triple-peaked H 2 O megamaser, consistent with a Keplerian rotating disk, indicating a black hole mass of (3.2±0.2)×10 7 M ⊙ . NGC 5728 and Mrk 1 display double-peaked spectra and VLBI imaging reveal complicated gas kinematics, which do not allow for a robust determination of black hole mass. The two systems are either gas disks perturbed by AGN winds or part of outflows. We find that disturbed morphology and kinematics are a ubiquitous feature of all double-peaked maser systems, implying that these maser sources may reside in environments where AGN winds are prominent at ∼1 pc scale and have significant impact on the masing gas. Such AGN tend to have black hole mass M BH < 8×10 6 M ⊙ and Eddington ratios λ Edd 0.1, while the triple-peaked megamasers show an opposite trend.
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