R. Mauersberger

Bio: R. Mauersberger is an academic researcher from Max Planck Society. The author has contributed to research in topics: Galaxy & Galactic Center. The author has an hindex of 6, co-authored 16 publications receiving 182 citations. Previous affiliations of R. Mauersberger include University of Chile.

Dense molecular gas in galactic nuclei

Abstract: The nuclear regions of many galaxies are not accessible at optical wavelengths and are devoid of HI, but contain large quantities of molecular gas and dust. With recent advances in instrumentation it is now possible to probe the kinematics and physical state of the cool dense interstellar medium, thus providing a new and important tool to investigate the circumnuclear gas in galaxies that are more ‘active’ than our own. The scope of this review is to summarize results related to the subject with an emphasis on observational data. Sects. 1 and 2 present a general introduction, followed by a discussion of molecular mass estimates. In Sect. 3 correlations between nuclear and global galactic properties are discussed. Sects. 4 and 5 summarize observational results for nearby strongly interacting galaxies, properties of molecular bars and rings, and theoretical advances in modelling the data. The main part of the review (Sects. 6–8) describes the kinematics and the physical and chemical properties of the dense gas, including masers, and compares them with the nuclear region of the Galaxy. Molecular gas in distant galaxies and the evolution of active galaxies are discussed in Sect. 9. Some promising avenues for future research are outlined in Sect. 10.

A survey of the Galactic center region in HCO+, H13CO+, and SiO

Abstract: Aims. A large-scale survey of the Galactic center region in the 3 mm rotational transitions of SiO, HCO+ and H13 CO+ (beamsize ${\sim}3\farcm 6$~3′6) was conducted to provide an estimate of cloud conditions, heating mechanisms, chemistry, and other properties.Methods. Using the NANTEN 4 m telescope from Nagoya University, a region between $-5\fdg75 = 1 → 0 lines of HCO+ and H13 CO+ and in the J = 2 → 1 line of SiO with a spacing of $3\farcm 75$3′75 (HCO+ ) and $1\farcm 875$1′875 (SiO and H13 CO+ ).Results. Velocity channel maps, longitude-velocity maps, and latitude-velocity maps are presented. We identify 51 molecular clouds; 33 of them belong to the Galactic center and 18 to disk gas. We derive an average of the luminosity ratio of SiO(J = 2 → 1) / CO(J = 1 → 0) in clouds belonging to the Galactic center of 4.9 × 10-3 and for disk clouds of 3.4 × 10-3 . The luminosity ratio of HCO + (J = 1 → 0)/CO(J = 1 → 0) in the Galactic center is 3.5 × 10-2 , and for disk clouds it is 1.5 × 10-2 . We can distinguish clearly between regions where the SiO or HCO+ dominate.

Molecular line emission in NGC 4945, imaged with ALMA

Abstract: NGC 4945 is one of the nearest (D ≈ 3.8 Mpc; 1″ ≈ 19 pc) starburst galaxies. To investigate the structure, dynamics, and composition of the dense nuclear gas of this galaxy, ALMA band 3 (λ ≈ 3−4 mm) observations were carried out with ≈2″ resolution. Three HCN and two HCO+ isotopologues, CS, C3H2, SiO, HCO, and CH3C2H were measured. 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 deprojected velocity of ≈50 km s−1. All our molecular lines, with the notable exception of CH3 C2H, show significant absorption near the systemic velocity (≈571 km s−1), within the range ≈500–660 km s−1. Apparently, only molecular transitions with low critical H2 density (ncrit ≲ 104 cm−3) do not show absorption. The velocity field of the nuclear disk, derived from CH3 C2H, provides evidence for rigid rotation in the inner few arcseconds and a dynamical mass of Mtot = (2.1 ± 0.2) × 108 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 14N/15N ≈ 200–450 is estimated. This range of values is much higher then previously reported on a tentative basis. Therefore, because 15N is less abundant than expected, the question for strong 15N enrichment by massive star ejecta in starbursts still remains to be settled.

The diffuse molecular component in the nuclear bulge of the Milky Way

Abstract: Context. The bulk of the molecular gas in the central molecular zone (CMZ) of the Galactic center region shows warm kinetic temperatures, ranging from >20 K in the coldest and densest regions (n ~ 104-5 cm-3 ) up to more than 100 K for densities of about n ~ 103 cm-3 . Recently, a more diffuse, hotter (n ~ 100 cm-3 , T ~ 250 K) gas component was discovered through absorption observations of H3 + . This component may be widespread in the Galactic center, and low density gas detectable in absorption may be present even outside the CMZ along sightlines crossing the extended bulge of the Galaxy.Aim. We aim to observe and characterize diffuse and low density gas using observations of 3-mm molecular transitions seen in absorption.Methods. Using the Atacama Large (sub)Millimeter Array (ALMA) we observed the absorption against the quasar J1744-312, which is located toward the Galactic bulge region at (l , b ) = (−2°.13, −1°.0), but outside the main molecular complexes.Results. ALMA observations in absorption against the J1744-312 quasar reveal a rich and complex chemistry in low density molecular and presumably diffuse clouds. We detected three velocity components at ~0, −153, and −192 km s−1 . The component at ~0 km s−1 could represent gas in the Galactic disk while the velocity components at −153, and −192 km s−1 likely originate from the Galactic bulge. We detected 12 molecules in the survey, but only 7 in the Galactic bulge gas.

Interstellar CNO isotope Ratios

Abstract: In an interpretation of interstellar, circumstellar, and solar system CNO isotope ratios, we find two scenarios which are free of internal inconsistencies. The first requires that the early solar system was enriched by material from massive stars, leading to enhanced 12C/13C and 18O/17O ratios and to a reduced 14N/15N ratio. The second involves infall of gas onto the galactic disk after the formation of the solar system. Both scenarios require that the bulk of the interstellar 16O, 18O and 15N originates from massive stars (>8M⊙), with 18O and perhaps 15N being destroyed in lower mass stars. 17O is mainly synthesized in stars of intermediate mass while 12C, 13C, and 14N are produced in stars of high and intermediate masses.

The Orion molecular cloud and star forming region

Abstract: La structure du nuage moleculaire geant Orion, sa compostion stellaire, l'interaction entre les etoiles OB de Orion A et le nuage, et la region de formation stellaire BN-IRc 2 sont etudiees. De nombreuses references bibliographiques sont citees

Spatially resolved chemistry in nearby galaxies. I. The center of IC 342

Abstract: We have imaged emission from the millimeter lines of eight molecules—C2H, C 34 S, N2H + ,C H3OH, HNCO, HNC, HC3N, and SO—in the central half-kiloparsec of the nearby spiral galaxy IC 342. The 5 00 (� 50 pc) resolution images were made with the Owens Valley Millimeter Array. Using these and previously published CO and HCN images, we obtain a picture of the chemistry within the nuclear region on the size scales of individual giant molecular clouds. Bright emission is detected from all but SO. There are marked differences in morphology for the different molecules. A principal-component analysis is performed to quantify similarities and differences among the images. This analysis reveals that while all molecules are to zeroth order correlated, that is, that they are all found in dense molecular clouds, there are three distinct groups of molecules distinguished by the location of their emission within the nuclear region. N2H + ,C 18 O, HNC, and HCN are widespread and bright, good overall tracers of dense molecular gas. C2 Ha nd C 34 S, tracers of photodissociation region chemistry, originate exclusively from the central 50–100 pc region, where radiation fields are high. The third group of molecules, CH3OH and HNCO, correlates well with the expected locations of bar-induced orbital shocks. The good correlation of HNCO with the established shock tracer molecule CH3OH is evidence that this molecule, whose chemistry has been uncertain, is indeed produced by the processing of grain mantles. HC3N is observed to correlate tightly with 3 mm continuum emission, demonstrating that the young starbursts are the sites of the warmest and densest molecular gas. We compare our HNC images with the HCN images of Downes and coworkers to produce the first highresolution, extragalactic HCN/HNC map: the HNC/HCN ratio is near unity across the nucleus, and the correlation of both of these gas tracers with star formation is excellent. The ratio exhibits no obvious correlation with gas temperature or star formation strength. Subject headings: astrochemistry — galaxies: individual (IC 342) — galaxies: ISM — galaxies: starburst — radio lines: galaxies

Infall Regions of Galaxy Clusters

Abstract: In hierarchical clustering, galaxy clusters accrete mass through the aggregation of smaller systems. Thus, the velocity field of the infall regions of clusters contains significant random motion superimposed on radial infall. Because the purely spherical infall model does not predict the amplitude of the velocity field correctly, methods estimating the cosmological density parameter Omega_0 based on this model yield unreliable biased results. In fact, the amplitude of the velocity field depends on local dynamics and only very weakly on the global properties of the universe. We use N-body simulations of flat and open universes to show that the amplitude of the velocity field of the infall regions of dark matter halos is a direct measure of the escape velocity within these regions. We can use this amplitude to estimate the mass of dark matter halos within a few megaparsecs from the halo center. In this region dynamical equilibrium assumptions do not hold. The method yields a mass estimate with better than 30% accuracy. If galaxies trace the velocity field of the infall regions of clusters reliably, this method provides a straightforward way to estimate the amount of mass surrounding rich galaxy clusters from redshift data alone.

LOFAR Two-metre Sky Survey

Abstract: The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120–168 MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45°00′00″ to 57°00′00″) were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325 694 sources are detected with a signal of at least five times the noise, and the source density is a factor of ∼10 higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S144 MHz = 71 μJy beam−1 and the point-source completeness is 90% at an integrated flux density of 0.45 mJy. The resolution of the images is 6″ and the positional accuracy is within 0.2″. This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further ∼20 articles that highlight the scientific potential of LoTSS.

CO (J = 2-1) Line Observations of the Galactic Center Molecular Cloud Complex. II Dynamical Structure and Physical Conditions

Abstract: A large-scale 12C16O (J = 2-1) survey of the inner few hundred parsecs of the Galaxy has been conducted using the University of Tokyo-Nobeyama Radio Observatory 60 cm survey telescope We have taken about 70012C16O (J = 2-1) spectra in the region -25 ? l ? 25 and |b| ? 1? with 0125 grid spacing, covering the entire region of the huge molecular cloud complex in the Galactic center We refer to the CO (J = 1-0) data taken with the Columbia 12 m telescope and calculate the J = 2-1 to J = 1-0 intensity ratio Velocity channel maps and longitude-velocity maps of CO (J = 2-1) line are presented, with corresponding maps of J = 2-1/J = 1-0 intensity ratio Large-scale CO maps enable us to identify several giant molecular cloud complexes and many characteristic features of molecular gas We identify 15 molecular cloud complexes larger than ~30 pc in our CO (J = 2-1) data Their virial masses are at least 1 order of magnitude larger than the masses estimated from the CO luminosity This discrepancy can be removed if we notice that they may not be gravitationally bound but are in pressure equilibrium with the hot gas and/or magnetic field in this region Using the expressions of virial mass and CO mass for a cloud in the pressure equilibrium case, we get the X-factor for the Galactic center molecular clouds as X = 024 ? 1020 cm-2 (K km s-1)-1, which is 1 order of magnitude lower than that in the Galactic disk (X = 30 ? 1020 cm-2 [K km s-1]-1) We estimate the total molecular mass in the Galactic center as M(H2) 2 ? 107 M? as a lower limit; the actual total gas mass within the central 400 pc of the Galaxy must be M(H2) = (2-6) ? 107 M? We diagnose the physical conditions of the molecular gas in the Galactic center using the intensity ratio between the J = 2-1 and J = 1-0 lines Although the CO J = 2-1/J = 1-0 line intensity ratio is high (~074) in the midplane, molecular gas at |b| ? 025 exhibits low J = 2-1/J = 1-0 ratios (~06) The overall J = 2-1/J = 1-0 luminosity ratio is R(2-1)/(1-0) = 064 ? 001 if we include all the emission within |b| ? 1?, -25 ? l ? 25, and |VLSR| ? 150 km s-1 This indicates that low-density gas 50 pc away from the plane dominates the total CO luminosity of the central 400 pc of the Galaxy The fractional distribution of the molecular gas with R(2-1)/(1-0) for each cloud complex clearly demonstrates the close relationship between the gas with a very high ratio [R(2-1)/(1-0) ? 10] and associated UV sources