The IRAM M 33 CO(2–1) survey Druard, C; Braine, J; Schuster, K F ...
Astronomy and astrophysics (Berlin),
07/2014, Letnik:
567
Journal Article
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Odprti dostop
To study the interstellar medium and the interplay between the atomic and molecular components in a low-metallicity environment, we present a complete high angular and spectral resolution map and ...position-position-velocity data cube of the sup 12 CO(J = 2-1) emission from the Local Group galaxy Messier 33. Its metallicity is roughly half-solar, such that we can compare its interstellar medium with that of the Milky Way with the main changes being the metallicity and the gas mass fraction. Using the CO(2-1) emission to trace the molecular gas, the probability distribution function of the Hsub 2 column density shows an excess at high column density above a log-normal distribution.
Aims. We aim to better understand the imprints that the nuclear activity in galaxies leaves in the molecular gas. Methods. We used the IRAM 30 m telescope to observe the frequency range ~86−116 GHz ...towards the central regions of the starburst galaxies M 83, M 82, and NGC 253, the galaxies hosting an active galactic nucleus (AGN) M 51, NGC 1068, and NGC 7469, and the ultra-luminous infrared galaxies (ULIRGs) Arp 220 and Mrk 231. Assuming local thermodynamic equilibrium (LTE), we calculated the column densities of 27 molecules and 10 isotopologues (or their upper limits in case of non-detections). Results. Among others, we report the first tentative detections of CH3CHO, HNCO, and NS in M 82 and, for the first time in the extragalactic medium, HC5N in NGC 253. Hα recombination lines were only found in M 82 and NGC 253. Vibrationally excited lines of HC3N were only detected in Arp 220. CH3CCH emission is only seen in the starburst-dominated galaxies. By comparison of the fractional abundances among the galaxies, we looked for the molecules that are best suited to characterise the chemistry of each group of galaxies (starbursts, AGNs and ULIRGs), as well as the differences among galaxies within the same group. Conclusions. Suitable species for characterising and comparing starburst galaxies are CH3OH and HNCO as tracers of large-scale shocks, which dominate early to intermediate starburst stages, and CH3CCH, c-C3H2, and HCO as tracers of UV fields, which control the intermediate-to-old or post starburst phases. M 83 shows signs of a shock-dominated environment. NGC 253 is characterised by both strong shocks and some UV fields. M 82 stands out for its bright photo-dissociated region tracers, which indicate an UV field-dominated environment. Regarding AGNs, the abundances of HCN and CN (previously claimed as enhanced in AGNs) in M 51 are similar to those in starburst galaxies, while the HCN/HCO+ ratio is high in M 51 and NGC 1068, but not in NGC 7469. We did not find a correlation between the HCN/CS ratio (recently claimed as a possible starburst/AGN discriminator) and the AGN activity. However, a high enough spatial resolution to separate their circumnuclear disks from the surrounding star-forming regions is needed to find molecular abundance trends in AGNs. High abundances of H13CN and HC3N, as well as a similarity between the column densities of 13CO and C18O, are representative of the molecular interstellar medium in the ULIRGs. Furthermore, the chemistry of Arp 220 points towards a more starburst-dominated environment, while that of Mrk 231 more resembles the AGNs of our sample.
We present high-resolution (submas) Very Long Baseline Interferometry maps of nuclear H2O megamasers for seven galaxies. In UGC 6093, the well-aligned systemic masers and high-velocity masers ...originate in an edge-on, flat disk and we determine the mass of the central supermassive black holes (SMBH) to be MSMBH = 2.58 × 107 M ( 7%). For J1346+5228, the distribution of masers is consistent with a disk, but the faint high-velocity masers are only marginally detected, and we constrain the mass of the SMBH to be in the range (1.5-2.0) × 107 M . The origin of the masers in Mrk 1210 is less clear, as the systemic and high-velocity masers are misaligned and show a disorganized velocity structure. We present one possible model in which the masers originate in a tilted, warped disk, but we do not rule out the possibility of other explanations including outflow masers. In NGC 6926, we detect a set of redshifted masers, clustered within a parsec of each other, and a single blueshifted maser about 4.4 pc away, an offset that would be unusually large for a maser disk system. Nevertheless, if it is a disk system, we estimate the enclosed mass to be MSMBH < 4.8 × 107 M . For NGC 5793, we detect redshifted masers spaced about 1.4 pc from a clustered set of blueshifted features. The orientation of the structure supports a disk scenario as suggested by Hagiwara et al. We estimate the enclosed mass to be MSMBH < 1.3 × 107 M . For NGC 2824 and J0350−0127, the masers may be associated with parsec- or subparsec-scale jets or outflows.
ABSTRACT
We present the observations of ammonia emission lines toward the interstellar filament WB 673 hosting the dense clumps WB 673, WB 668, S233-IR, and G173.57+2.43. LTE analysis of the lines ...allows us to estimate gas kinetic temperature (≲30K in all the clumps), number density (7–17 × 103 cm−3), and ammonia column density (≈1–1.5 × 1015 cm−2) in the dense clumps. We find signatures of collapse in WB 673 and presence of compact spatially unresolved dense clumps in S233-IR. We reconstruct 1D density and temperature distributions in the clumps and estimate their ages using astrochemical modelling. Considering CO, CS, NH3, and N2H+ molecules (plus HCN and HNC for WB 673), we find a chemical age of tchem = 1–3 × 105 yrs, providing the best agreement between the simulated and observed column densities in all the clumps. Therefore, we consider tchem as the chemical age of the entire filament. A long preceding low-density stage of gas accumulation in the astrochemical model would break the agreement between the simulated and observed column densities. We suggest that rapid star formation over a ∼105 yrs time-scale take place in the filament.
Large column densities, derived from X-ray studies, are typically measured towards active galactic nuclei (AGN) hosting water masers, especially when the ... emission is associated with the nuclear ...accretion disc. In addition, possible correlations between the intrinsic X-ray luminosity and the characteristics of the ... maser emission have been put forward that, however, require confirmation. We have performed high-sensitivity XMM-Newton observations of a sample of five ... maser sources confidently detected in our ongoing survey with the Swift satellite of all known water masers in AGN, in order to obtain detailed X-ray information of these promising targets and to set up a systematic detailed study of the X-ray/... maser relation in AGN. For three galaxies, NGC 613, VII Zw 73 and IRAS 16288+3929, the amount of intrinsic absorption has been estimated, indicating column densities of 4-6 x ... cm... For UGC 3789 and NGC 6264 (the two confirmed disc-maser galaxies in our sample), column densities in excess of 1 x ... cm... are inferred from the large EW of the Fe Ka line. By adding our results to those obtained in past similar studies, we find that the percentage of water masers sources that host highly obscured (NH > ... cm...) and Compton-thick AGN is 96 (45/47) and 57 per cent (27/47), respectively. In addition, 86 per cent, 18/21 of disc-maser galaxies host Compton-thick AGN. The correlation between the galaxies' bolometric luminosity and accretion disc radius, suggested in previous works, is also confirmed. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT We used the Atacama Large Millimeter Array (ALMA) to map the emission of the CO(6-5) molecular line and the 432 m continuum emission from the 300 pc sized circumnuclear disk (CND) of the ...nearby Seyfert 2 galaxy NGC 1068 with a spatial resolution of ∼4 pc. These observations spatially resolve the CND and, for the first time, image the dust emission, the molecular gas distribution, and the kinematics from a 7-10 pc diameter disk that represents the submillimeter counterpart of the putative torus of NGC 1068. We fitted the nuclear spectral energy distribution of the torus using ALMA and near- and mid-infrared (NIR/MIR) data with CLUMPY torus models. The mass and radius of the best-fit solution for the torus are both consistent with the values derived from the ALMA data alone: M gas torus = ( 1 0.3 ) × 10 5 M ☉ and Rtorus = 3.5 0.5 pc. The dynamics of the molecular gas in the torus show strong non-circular motions and enhanced turbulence superposed on a surprisingly slow rotation pattern of the disk. By contrast with the nearly edge-on orientation of the H2O megamaser disk, we found evidence suggesting that the molecular torus is less inclined (i = 34°-66°) at larger radii. The lopsided morphology and complex kinematics of the torus could be the signature of the Papaloizou-Pringle instability, long predicted to likely drive the dynamical evolution of active galactic nuclei tori.
We present ALMA CO (1−0) observations toward the dust lane of the nearest elliptical and radio galaxy, NGC 5128 (Centaurus A), with high angular resolution (∼1″, or 18 pc), including information from ...large to small spatial scales and total flux. We find a total molecular gas mass of 1.6 × 109 M and reveal the presence of filamentary components more extended than previously seen, up to a radius of 4 kpc. We find that the global star formation rate is ∼1 M yr−1, which yields a star formation efficiency (SFE) of 0.6 Gyr−1 (depletion time τ = 1.5 Gyr), similar to those in disk galaxies. We show the most detailed view to date (40 pc resolution) of the relation between molecular gas and star formation within the stellar component of an elliptical galaxy, from a scale of several kiloparsecs to the circumnuclear region close to the powerful radio jet. Although on average the SFEs are similar to those of spiral galaxies, the circumnuclear disk (CND) presents SFEs of 0.3 Gyr−1, lower by a factor of 4 than the outer disk. The low SFE in the CND is in contrast to the high SFEs found in the literature for the circumnuclear regions of some nearby disk galaxies with nuclear activity, probably as a result of larger shear motions and longer active galactic nucleus feedback. The higher SFEs in the outer disk suggest that only central molecular gas or filaments with sufficient density and strong shear motions will remain in ∼1 Gyr, which will later result in the compact molecular distributions and low SFEs usually seen in other giant ellipticals with cold gas.
We studied a large sample of ~14 000 dwarf star-forming galaxies with strong emission lines. These low-metallicity galaxies with oxygen abundances of 12 +log O/H ~7.4−8.5 are selected from the Sloan ...Digital Sky Survey (SDSS) and distributed in the redshift range of z ~0−0.6. We modelled spectral energy distributions (SED) of all galaxies, which were based on the SDSS spectra in the visible range of 0.38 μm−0.92 μm and included both the stellar and ionised gas emission. These SEDs were extrapolated to the UV and mid-infrared ranges to cover the wavelength range of 0.1 μm−22 μm. The SDSS spectroscopic data were supplemented by photometric data from the GALEX, SDSS, 2MASS, WISE, IRAS, and NVSS all-sky surveys. Using these data, we derived global characteristics of the galaxies, such as their element abundances, luminosities, and stellar masses. The luminosities and stellar masses range within the sample over ~5 orders of magnitude, thereby linking low-mass and low-luminosity blue compact dwarf galaxies to luminous galaxies, which are similar to high-redshift Lyman-break galaxies. It was found that the luminosity L(Hβ) of the Hβ emission line, a characteristic of the youngest stellar population with an age of a few Myr, is correlated with luminosities in other wavelength ranges. This implies that the most recent burst of star formation makes a significant contribution to the emission in the visible range and dominates in other wavelength ranges. It was also found that the contribution of the young population to the galaxy luminosity is higher for galaxies with higher L(Hβ) and higher equivalent widths EW(Hβ). We found 20 galaxies with very red WISE mid-infrared m(3.4 μm)− m(4.6 μm) colour (≥2 mag), which suggests the important contribution of the hot (with a temperature of several hundred degree) dust emission in these galaxies. Our analysis of the balance between the luminosity in the WISE bands that covered a wavelength range of 3.4 μm−22 μm and the luminosity of the emission absorbed at shorter wavelengths showed that the luminosity of the hot dust emission is increased with increasing L(Hβ) and EW(Hβ). We demonstrated that the emission emerging from young star-forming regions is the dominant dust-heating source for temperatures to several hundred degrees in the sample star-forming galaxies.
The Megamaser Cosmology Project (MCP) seeks to measure the Hubble Constant (H 0) in order to improve the extragalactic distance scale and constrain the nature of dark energy. We are searching for ...sources of H2O maser emission from active galactic nuclei with sub-pc accretion disks, as in NGC 4258, and following up these discoveries with very long baseline interferometric (VLBI) imaging and spectral monitoring. Here we present a VLBI map of the H2O masers toward UGC 3789, a galaxy well into the Hubble Flow. We have observed masers moving at rotational speeds up to 800 km s-1 at radii as small as 0.08 pc. Our map reveals masers in a nearly edge-on disk in Keplerian rotation about a 107 M supermassive black hole. When combined with centripetal accelerations, obtained by observing spectral drifts of maser features (to be presented in Paper II), the UGC 3789 masers may provide an accurate determination of H 0, independent of luminosities and metallicity and extinction corrections.
We present observations of the 85.69 GHz continuum emission and H42α line emission from the central 30 arcsec within NGC 4945. Both sources of emission originate from nearly identical structures that ...can be modelled as exponential discs with scalelengths of ∼2.1 arcsec (or ∼40 pc). An analysis of the spectral energy distribution based on combining these data with archival data imply that 84 ± 10 per cent of the 85.69 GHz continuum emission originates from free–free emission. The electron temperature is 5400 ± 600 K, which is comparable to what has been measured near the centre of the Milky Way Galaxy. The star formation rate (SFR) based on the H42α and 85.69 GHz free–free emission (and using a distance of 3.8 Mpc) is 4.35 ± 0.25 M⊙ yr−1. This is consistent with the SFR from the total infrared flux and with previous measurements based on recombination line emission, and it is within a factor of ∼2 of SFRs derived from radio data. The Spitzer Space Telescope 24 μm data and Wide-field Infrared Survey Explorer 22 μm data yield SFRs ∼10× lower than the Atacama Large Millimeter/submillimeter Array measurements, most likely because the mid-infrared data are strongly affected by dust attenuation equivalent to AV
= 150. These results indicate that SFRs based on mid-infrared emission may be highly inaccurate for dusty, compact circumnuclear starbursts.
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