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.
We present a spectroscopic study of metal-deficient dwarf galaxy candidates, selected from the SDSS DR12. The oxygen abundances were derived using the direct method in galaxies with the electron ...temperature-sensitive emission line O iiiλ4363 Å measured with an accuracy better than 30%. The oxygen abundances for the remaining galaxies with larger uncertainties of the O iiiλ4363 Å line fluxes were calculated using a strong-line semi-empirical method by Izotov and Thuan. The resulting sample consists of 287 low-metallicity candidates with oxygen abundances below 12 + log O/H = 7.65 including 23 extremely metal-deficient (XMD) candidates with 12 + log O/H ≤ 7.35. Ten out of sixteen XMDs known so far (or ~60%) have been discovered by our team using the direct method. Three XMDs were found in the present study. We study relations between global parameters of low-metallicity galaxies, including absolute optical magnitudes, Hβ luminosities (or equivalently star formation rates), stellar masses, mid-infrared colours, and oxygen abundances. Low-metallicity and XMD galaxies strongly deviate to lower metallicities in L–Z, L(Hβ)–Z and M∗–Z diagrams than in relations obtained for large samples of low-redshift, star-forming galaxies with non-restricted metallicities. These less chemically evolved galaxies with stellar masses ≈106–108M⊙, Hβ luminosities ≈1038–1041 erg s-1, SFR ≈ 0.01–1.0 M⊙ yr-1, and sSFR ~ 50 Gyr-1 have physical conditions which may be characteristic of high-redshift low-mass star-forming galaxies which are still awaiting discovery.
Aims. We investigate the fueling and the feedback of nuclear activity in the nearby (D = 14 Mpc) Seyfert 2 barred galaxy NGC 1068 by studying the distribution and kinematics of molecular gas in the ...torus and its connections to the host galaxy disk. Methods. We used the Atacama Large Millimeter Array (ALMA ) to image the emission of a set of molecular gas tracers in the circumnuclear disk (CND) and the torus of the galaxy using the CO(2–1), CO(3–2), and HCO+(4–3) lines and their underlying continuum emission with high spatial resolutions (0.03″ − 0.09″ ≃ 2 − 6 pc). These transitions, which span a wide range of physical conditions of molecular gas (n(H2)⊂103 − 107 cm−3), are instrumental in revealing the density radial stratification and the complex kinematics of the gas in the torus and its surroundings. Results. The ALMA images resolve the CND as an asymmetric ringed disk of D ≃ 400 pc in size and ≃1.4 × 108 M⊙ in mass. The CND shows a marked deficit of molecular gas in its central ≃130 pc region. The inner edge of the ring is associated with the presence of edge-brightened arcs of NIR polarized emission, which are identified with the current working surface of the ionized wind of the active galactic nucleus (AGN). ALMA proves the existence of an elongated molecular disk/torus in NGC 1068 of Mtorusgas ≃ 3 × 105 M⊙ M torus gas ≃ 3 × 10 5 M ⊙ $ M_{\mathrm{torus}}^{\mathrm{gas}}\simeq3\times10^{5}\,M_{{\odot}} $ , which extends over a large range of spatial scales D ≃ 10 − 30 pc around the central engine. The new observations evidence the density radial stratification of the torus: the HCO+(4–3) torus, with a full size DHCO+(4 − 3) = 11 ± 0.6 pc, is a factor of between two and three smaller than its CO(2–1) and CO(3–2) counterparts, which have full sizes of DCO(3 − 2) = 26 ± 0.6 pc and DCO(2 − 1) = 28 ± 0.6 pc, respectively. This result brings into light the many faces of the molecular torus. The torus is connected to the CND through a network of molecular gas streamers detected inside the CND ring. The kinematics of molecular gas show strong departures from circular motions in the torus, the gas streamers, and the CND ring. These velocity field distortions are interconnected and are part of a 3D outflow that reflects the effects of AGN feedback on the kinematics of molecular gas across a wide range of spatial scales around the central engine. In particular, we estimate through modeling that a significant fraction of the gas inside the torus ( ≃ 0.4 − 0.6 × Mtorusgas ≃ 0.4 − 0.6 × M torus gas $ {\simeq}0.4{-}0.6 \times M_{\mathrm{torus}}^{\mathrm{gas}} $ ) and a comparable amount of mass along the gas streamers are outflowing. However, the bulk of the mass, momentum, and energy of the molecular outflow of NGC 1068 is contained at larger radii in the CND region, where the AGN wind and the radio jet are currently pushing the gas assembled at the Inner Lindblad Resonance (ILR) ring of the nuclear stellar bar. Conclusions. In our favored scenario a wide-angle AGN wind launched from the accretion disk of NGC1068 is currently impacting a sizable fraction of the gas inside the torus. However, a large gas reservoir (≃1.2 − 1.8 × 105 M⊙), which lies close to the equatorial plane of the torus, remains unaffected by the feedback of the AGN wind and can therefore continue fueling the AGN for at least ≃1 − 4 Myr. Nevertheless, AGN fueling currently seems thwarted on intermediate scales (15 pc ≤r ≤ 50 pc).
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.
ABSTRACT We use new precision measurements of black hole (BH) masses from water megamaser disks to investigate scaling relations between macroscopic galaxy properties and supermassive BH mass. The ...megamaser-derived BH masses span 106-108 M , while all the galaxy properties that we examine (including total stellar mass, central mass density, and central velocity dispersion) lie within a narrower range. Thus, no galaxy property correlates tightly with M BH in ∼L* spiral galaxies as traced by megamaser disks. Of them all, stellar velocity dispersion provides the tightest relation, but at fixed * the mean megamaser M BH are offset by −0.6 0.1 dex relative to early-type galaxies. Spiral galaxies with non-maser dynamical BH masses do not appear to show this offset. At low mass, we do not yet know the full distribution of BH mass at fixed galaxy property; the non-maser dynamical measurements may miss the low-mass end of the BH distribution due to an inability to resolve their spheres of influence and/or megamasers may preferentially occur in lower-mass BHs.
We present new CO(2–1) observations of three low-z (d ~350 Mpc) ultra-luminous infrared galaxy (ULIRG) systems (six nuclei) observed with the Atacama large millimeter/submillimeter array (ALMA) at ...high spatial resolution (~500 pc). We detect massive cold molecular gas outflows in five out of six nuclei (Mout ~ (0.3−5) × 108 M⊙). These outflows are spatially resolved with deprojected effective radii between 250 pc and 1 kpc although high-velocity molecular gas is detected up to Rmax ~ 0.5−1.8 kpc (1–6 kpc deprojected). The mass outflow rates are 12–400 M⊙ yr−1 and the inclination corrected average velocity of the outflowing gas is 350–550 km s−1 (vmax = 500−900 km s−1). The origin of these outflows can be explained by the strong nuclear starbursts although the contribution of an obscured active galactic nucleus cannot be completely ruled out. The position angle (PA) of the outflowing gas along the kinematic minor axis of the nuclear molecular disk suggests that the outflow axis is perpendicular to the disk for three of these outflows. Only in one case is the outflow PA clearly not along the kinematic minor axis, which might indicate a different outflow geometry. The outflow depletion times are 15–80 Myr. These are comparable to, although slightly shorter than, the star-formation (SF) depletion times (30–80 Myr). However, we estimate that only 15–30% of the outflowing molecular gas will escape the gravitational potential of the nucleus. The majority of the outflowing gas will return to the disk after 5–10 Myr and become available to form new stars. Therefore, these outflows will not likely completely quench the nuclear starbursts. These star-forming powered molecular outflows would be consistent with being driven by radiation pressure from young stars (i.e., momentum-driven) only if the coupling between radiation and dust increases with increasing SF rates. This can be achieved if the dust optical depth is higher in objects with higher SF. This is the case in at least one of the studied objects. Alternatively, if the outflows are mainly driven by supernovae (SNe), the coupling efficiency between the interstellar medium and SNe must increase with increasing SF levels. The relatively small sizes (<1 kpc) and dynamical times (<3 Myr) of the cold molecular outflows suggests that molecular gas cannot survive longer in the outflow environment or that it cannot form efficiently beyond these distances or times. In addition, the ionized and hot molecular phases have been detected for several of these outflows, so this suggests that outflowing gas can experience phase changes and indicates that the outflowing gas is intrinsically multiphase, likely sharing similar kinematics, but different mass and, therefore, different energy and momentum contributions.
Recent progress in manipulating atomic and condensed matter systems has instigated a surge of interest in nonequilibrium physics, including many-body dynamics of trapped ultracold atoms and ions, ...near-field radiative heat transfer, and quantum friction. Under most circumstances the complexity of such nonequilibrium systems requires a number of approximations to make theoretical descriptions tractable. In particular, it is often assumed that spatially separated components of a system thermalize with their immediate surroundings, although the global state of the system is out of equilibrium. This powerful assumption reduces the complexity of nonequilibrium systems to the local application of well-founded equilibrium concepts. While this technique appears to be consistent for the description of some phenomena, we show that it fails for quantum friction by underestimating by approximately 80% the magnitude of the drag force. Our results show that the correlations among the components of driven, but steady-state, quantum systems invalidate the assumption of local thermal equilibrium, calling for a critical reexamination of this approach for describing the physics of nonequilibrium systems.
Context.
The Serpens filament, a prominent elongated structure in a relatively nearby molecular cloud, is believed to be at an early evolutionary stage, so studying its physical and chemical ...properties can shed light on filament formation and early evolution.
Aims.
The main goal is to address the physical and chemical properties as well as the dynamical state of the Serpens filament at a spatial resolution of ~0.07 pc and a spectral resolution of ≲0.1 km s
−1
.
Methods.
We performed
13
CO (1–0), C
18
O (1–0), C
17
O (1–0),
13
CO (2–1), C
18
O (2–1), and C
17
O (2–1) imaging observations toward the Serpens filament with the Institut de Radioastronomie Millimétrique 30-m and Atacama Pathfinder EXperiment telescopes.
Results.
Widespread narrow
13
CO (2–1) self-absorption is observed in this filament, causing the
13
CO morphology to be different from the filamentary structure traced by C
18
O and C
17
O. Our excitation analysis suggests that the opacities of C
18
O transitions become higher than unity in most regions, and this analysis confirms the presence of widespread CO depletion. Further we show that the local velocity gradients have a tendency to be perpendicular to the filament’s long axis in the outskirts and parallel to the large-scale magnetic field direction. The magnitudes of the local velocity gradients decrease toward the filament’s crest. The observed velocity structure can be a result of gravity-driven accretion flows. The isochronic evolutionary track of the C
18
O freeze-out process indicates the filament is young with an age of ≲2 Myr.
Conclusions.
We propose that the Serpens filament is a newly-formed slightly-supercritical structure which appears to be actively accreting material from its ambient gas.
We present a sample of low-redshift (z < 0.133) candidates for extremely low-metallicity star-forming galaxies with oxygen abundances 12 + log O/H < 7.4 selected from the Data Release 14 (DR14) of ...the Sloan Digital Sky Survey (SDSS). Three methods are used to derive their oxygen abundances. Among these methods two are based on strong O IIλ3727 Å, O IIIλ4959 Å, and O IIIλ5007 Å emission lines, which we call strong-line and semi-empirical methods. These were applied for all galaxies. We have developed one of these methods, the strong-line method, in this paper. This method is specifically focused on the accurate determination of metallicity in extremely low-metallicity galaxies and may not be used at higher metallicities with 12 + log O/H ≳ 7.5. The third, the direct Te method, was applied for galaxies with detected O IIIλ4363 emission lines. All three methods give consistent abundances and can be used in combination or separately for selection of lowest-metallicity candidates. However, the strong-line method is preferable for spectra with a poorly detected or undetected O IIIλ4363 emission line. In total, our list of selected candidates for extremely low-metallicity galaxies includes 66 objects.
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