ABSTRACT We have detected in ALMA observations CO emission from the nucleus of the Seyfert galaxy NGC 1068. The low-velocity (up to 70 km s−1 relative to systemic) CO emission resolves into a 12 × 7 ...pc structure, roughly aligned with the nuclear radio source. Higher-velocity emission (up to 400 km s−1) is consistent with a bipolar outflow in a direction nearly perpendicular ( 80°) to the nuclear disk. The position-velocity diagram shows that in addition to the outflow, the velocity field may also contain rotation about the disk axis. These observations provide compelling evidence in support of the disk-wind scenario for the active galactic nucleus obscuring torus.
In Papers I and II from the Megamaser Cosmology Project, we reported initial observations of H sub(2)O masers in an accretion disk of a supermassive black hole at the center of the galaxy UGC 3789, ...which gave an angular-diameter distance to the galaxy and an estimate of H sub(0) with 16% uncertainty. We have since conducted more very long baseline interferometric observations of the spatial-velocity structure of these H sub(2)O masers, as well as continued monitoring of its spectrum to better measure maser accelerations. These more extensive observations, combined with improved modeling of the masers in the accretion disk of the central supermassive black hole, confirm our previous results, but with significantly improved accuracy. We find H sub(0) = 68.9 + or - 7.1 km s super(-1) Mpc super(-1); this estimate of H sub(0) is independent of other methods and is accurate to + or -10%, including sources of systematic error. This places UGC 3789 at an angular-diameter distance of 49.6 + or -5.1 Mpc, with a central supermassive black hole of (1.16 + or - 0.12) x 10 super(7) M sub(middot in circle).
ABSTRACT As part of the Megamaser Cosmology Project, here we present a new geometric distance measurement to the megamaser galaxy NGC 5765b. Through a series of very long baseline interferometry ...observations, we have confirmed the water masers trace a thin, sub-parsec Keplerian disk around the nucleus, implying an enclosed mass of 4.55 0.40 × 107 M . Meanwhile, from single-dish monitoring of the maser spectra over two years, we measured the secular drifts of maser features near the systemic velocity of the galaxy with rates between 0.5 and 1.2 km s−1 yr−1. Fitting a warped, thin-disk model to these measurements, we determine a Hubble Constant H0 of 66.0 6.0 km s−1 Mpc−1 with an angular-diameter distance to NGC 5765b of 126.3 11.6 Mpc. Apart from the distance measurement, we also investigate some physical properties related to the maser disk in NGC 5765b. The high-velocity features are spatially distributed into several clumps, which may indicate the existence of a spiral density wave associated with the accretion disk. For the redshifted features, the envelope defined by the peak maser intensities increases with radius. The profile of the systemic masers in NGC 5765b is smooth and shows almost no structural changes over the two years of monitoring time, which differs from the more variable case of NGC 4258.
We present a detailed description of the special procedures for calibration and quality assurance of Atacama Large Millimeter/submillimeter Array (ALMA) observations in Very Long Baseline ...Interferometry (VLBI) mode. These procedures are required to turn the phased ALMA array into a fully calibrated VLBI station. As an illustration of these methodologies, we present full-polarization observations carried out with ALMA as a phased array at 3 mm (Band 3) and 1.3 mm (Band 6) as part of Cycle-4. These are the first VLBI science observations conducted with ALMA and were obtained during a 2017 VLBI campaign in concert with other telescopes worldwide as part of the Global mm-VLBI Array (GMVA, April 1-3) and the Event Horizon Telescope (EHT, April 5-11) in ALMA Bands 3 and 6, respectively.
We present the final data release of the APEX low-redshift legacy survey for molecular gas (ALLSMOG), comprising CO(2–1) emission line observations of 88 nearby, low-mass (108.5<M∗ M⊙ < 1010) ...star-forming galaxies carried out with the 230 GHz APEX-1 receiver on the APEX telescope. The main goal of ALLSMOG is to probe the molecular gas content of more typical and lower stellar mass galaxies than have been studied by previous CO surveys. We also present IRAM 30 m observations of the CO(1–0) and CO(2–1) emission lines in nine galaxies aimed at increasing the M∗< 109M⊙ sample size. In this paper we describe the observations, data reduction and analysis methods and we present the final CO spectra together with archival Hi 21 cm line observations for the entire sample of 97 galaxies. At the sensitivity limit of ALLSMOG, we register a total CO detection rate of 47%. Galaxies with higher M∗, SFR, nebular extinction (AV), gas-phase metallicity (O/H), and Hi gas mass have systematically higher CO detection rates. In particular, the parameter according to which CO detections and non-detections show the strongest statistical differences is the gas-phase metallicity, for any of the five metallicity calibrations examined in this work. We investigate scaling relations between the CO(1–0) line luminosity (L'CO(1-0)) and galaxy-averaged properties using ALLSMOG and a sub-sample of COLD GASS for a total of 185 sources that probe the local main sequence (MS) of star-forming galaxies and its ± 0.3 dex intrinsic scatter from M∗ = 108.5M⊙ to M∗ = 1011M⊙. L'CO(1-0) is most strongly correlated with the SFR, but the correlation with M∗ is closer to linear and almost comparably tight. The relation between L'CO(1-0) and metallicity is the steepest one, although deeper CO observations of galaxies with AV< 0.5 mag may reveal an as much steep correlation with AV. Our results suggest that star-forming galaxies across more than two orders of magnitude in M∗ obey similar scaling relations between CO luminosity and the galaxy properties examined in this work. Besides SFR, the CO luminosity is likely most fundamentally linked to M∗, although we note that stellar mass alone cannot explain all of the variation in CO emission observed as a function of O/H and MHI.
We present ALLSMOG, the APEX Low-redshift Legacy Survey for MOlecular Gas. ALLSMOG is a survey designed to observe the CO(2 − 1) emission line with the APEX telescope, in a sample of local galaxies ...(0.01 < z < 0.03), with stellar masses in the range 8.5 < log(M*/M⊙) < 10. This paper is a data release and initial analysis of the first two semesters of observations, consisting of 42 galaxies observed in CO(2 − 1). By combining these new CO(2 − 1) emission line data with archival H i data and SDSS optical spectroscopy, we compile a sample of low-mass galaxies with well-defined molecular gas masses, atomic gas masses, and gas-phase metallicities. We explore scaling relations of gas fraction and gas consumption time-scale, and test the extent to which our findings are dependent on a varying CO/H2 conversion factor. We find an increase in the H2/H i mass ratio with stellar mass which closely matches semi-analytic predictions. We find a mean molecular gas fraction for ALLSMOG galaxies of M
H2/M
* = (0.09–0.13), which decreases with stellar mass. This decrease in total gas fraction with stellar mass is in excess of some model predictions at low stellar masses. We measure a mean molecular gas consumption time-scale for ALLSMOG galaxies of 0.4–0.7 Gyr. We also confirm the non-universality of the molecular gas consumption time-scale, which varies (with stellar mass) from ∼100 Myr to ∼2 Gyr. Importantly, we find that the trends in the H2/H i mass ratio, gas fraction, and the non-universal molecular gas consumption time-scale are all robust to a range of recent metallicity-dependent CO/H2 conversion factors.
ABSTRACT As part of the Megamaser Cosmology Project, we present VLBI maps of nuclear water masers toward five galaxies. The masers originate in sub-parsec circumnuclear disks. For three of the ...galaxies, we fit Keplerian rotation curves to estimate their supermassive black hole (SMBH) masses, and determine (2.9 0.3) × 106 M for J0437+2456, (1.7 0.1) × 107 M for ESO 558-G009, and (1.1 0.2) × 107 M for NGC 5495. In the other two galaxies, Mrk 1029 and NGC 1320, the geometry and dynamics are more complicated and preclude robust black hole mass estimates. Including our new results, we compiled a list of 15 VLBI-confirmed disk maser galaxies with robust SMBH mass measurements. With this sample, we confirm the empirical relation of Rout ∝ 0.3MSMBH reported in Wardle & Yusef-Zadeh. We also find a tentative correlation between maser disk outer radii and Wide-Field Infrared Survey Explorer luminosity. We find no correlations of maser disk size with X-ray 2-10 keV luminosity or O iii luminosity.
We present the direct measurement of the Hubble constant, yielding the direct measurement of the angular-diameter distance to NGC 6264 using the H sub(2)O megamaser technique. Our measurement is ...based on sensitive observations of the circumnuclear megamaser disk from four observations with the Very Long Baseline Array, the Green Bank Telescope (GBT), and the Effelsberg telescope. We also monitored the maser spectral profile for 2.3 years using the GBT to measure accelerations of maser lines by tracking their line-of-sight velocities as they change with time. The measured accelerations suggest that the systemic maser spots have a significantly wider radial distribution than in the archetypal megamaser in NGC 4258. We model the maser emission as arising from a circumnuclear disk with orbits dominated by the central black hole. The best fit of the data gives a Hubble constant of H sub(0) = 68 + or - 9 km s super(-1) Mpc super(-1), which corresponds to an angular-diameter distance of 144 + or - 19 Mpc. In addition, the fit also gives a mass of the central black hole of (3.09 + or - 0.42) x 10 super(7) M sub(middot in circle). The result demonstrates the feasibility of measuring distances to galaxies located well into the Hubble flow by using circumnuclear megamaser disks.
We present a measurement of the Hubble constant made using geometric distance measurements to megamaser-hosting galaxies. We have applied an improved approach for fitting maser data and obtained ...better distance estimates for four galaxies previously published by the Megamaser Cosmology Project: UGC 3789, NGC 6264, NGC 6323, and NGC 5765b. Combining these updated distance measurements with those for the maser galaxies CGCG 074-064 and NGC 4258, and assuming a fixed velocity uncertainty of 250 km s−1 associated with peculiar motions, we constrain the Hubble constant to be H0 = 73.9 3.0 km s−1 Mpc−1 independent of distance ladders and the cosmic microwave background. This best value relies solely on maser-based distance and velocity measurements, and it does not use any peculiar velocity corrections. Different approaches for correcting peculiar velocities do not modify H0 by more than 1 , with the full range of best-fit Hubble constant values spanning 71.8-76.9 km s−1 Mpc−1. We corroborate prior indications that the local value of H0 exceeds the early-universe value, with a confidence level varying from 95% to 99% for different treatments of the peculiar velocities.
Water megamasers from circumnuclear disks in galaxy centers provide the most accurate measurements of supermassive black hole masses and uniquely probe the subparsec accretion processes. At the same ...time, these systems offer independent crucial constraints of the Hubble constant in the nearby universe, and thus, the arguably best single constraint on the nature of dark energy. The chances of finding these golden standards are, however, abysmally low, at 3% overall for any level of water maser emission detected at 22 GHz and 1% for those exhibiting disk-like configuration. We provide here a thorough summary of the current state of detection of water megamaser disks along with a novel investigation of the likelihood of increasing their detection rates based on a multivariate parameter analysis of the optical and mid-infrared (mid-IR) photometric properties of the largest database of galaxies surveyed for 22 GHz emission. We find that galaxies with water megamaser emission tend to be associated with strong emission in all Wide-field Infrared Survey Explorer mid-IR wavelengths, with the strongest enhancement in the W4 band, at 22 m, as well as with previously proposed and newly found indicators of active galactic nucleus strength in the mid-IR, such as red W1 − W2 and W1 − W4 colors, and the integrated mid-IR luminosity of the host galaxy. These trends offer a potential boost of the megamaser detection rates to 6%-15%, or a factor of 2-8 relative to the current rates, depending on the chosen sample selection criteria, while fostering real chances for discovering 20 new megamaser disks.
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