Scale-free equilibria of self-gravitating gaseous disks with flat rotation curves

We introduce exact analytical solutions of the steady-state hydrodynamic equations of scale-free, self-gravitating gaseous disks with flat rotation curves. We express the velocity field in terms of a stream function and obtain a third-order ordinary differential equation (ODE) for the angular part of the stream function. We present the closed-form solutions of the obtained ODE and construct hydrodynamical counterparts of the power-law and elliptic disks, for which self-consistent stellar dynamical models are known. We show that the kinematics of the Large Magellanic Cloud can well be explained by our findings for scale-free elliptic disks.Comment: AAS preprint format, 21 pages, 8 figures, accepted for publication in The Astrophysical Journa

The Mass Inflow Rate in the Barred Galaxy NGC 1530

Mass inflow in barred galaxies has been invoked to account for a wide variety of phenomena, but until now direct evidence for inflow has been lacking. We present Fabry-Perot H-alpha observations of the barred spiral galaxy NGC 1530 from which we determine velocities of the ionized gas for the entire region swept by the bar. We compare the velocity field to models of gas flow in barred spirals and show that it is well reproduced by ideal gas hydrodynamic models. Inspection of the models and observations reveals that gas entering the bar dust lanes streams directly down the dust lanes toward the 2 kpc radius nuclear ring. The models predict that approximately 20% of the gas flowing down the dust lane enters the nuclear ring; the remaining gas sprays around the ring to the other bar dust lane. The fraction of the gas entering the ring is relatively insensitive to the shape or size of the bar. Our observations of the velocity field and dust optical depth yield a mass inflow rate into the nuclear ring of 1 solar mass per year.Comment: 13 pages, 3 figures, aastex 4.0, accepted for publication in Ap J Letter

Inner Molecular Rings in Barred Galaxies: BIMA SONG CO Observations

Although inner star-forming rings are common in optical images of barred spiral galaxies, observational evidence for the accompanying molecular gas has been scarce. In this paper we present images of molecular inner rings, traced using the CO (1-0) emission line, from the Berkeley-Illinois-Maryland-Association Survey of Nearby Galaxies (BIMA SONG). We detect inner ring CO emission from all five SONG barred galaxies classified as inner ring (type (r)). We also examine the seven SONG barred galaxies classified as inner spiral (type (s)); in one of these, NGC 3627, we find morphological and kinematic evidence for a molecular inner ring. Inner ring galaxies have been classified as such based on optical images, which emphasize recent star formation. We consider the possibility that there may exist inner rings in which star formation efficiency is not enhanced. However, we find that in NGC 3627 the inner ring star formation efficiency is enhanced relative to most other regions in that galaxy. We note that the SONG (r) galaxies have a paucity of CO and H alpha emission interior to the inner ring (except near the nucleus), while NGC 3627 has relatively bright bar CO and H alpha emission; we suggest that galaxies with inner rings such as NGC 3627 may be misclassified if there are significant amounts of gas and star formation in the bar.Comment: To be published in the Astrophysical Journal, July 2002 A version of the paper with full resolution figures is available at: http://www.astro.umd.edu/~mregan/ms.ps.g

The Galactic centre mini-spiral in the mm-regime

The mini-spiral is a feature of the interstellar medium in the central ~2 pc of the Galactic center. It is composed of several streamers of dust and ionised and atomic gas with temperatures between a few 100 K to 10^4 K. There is evidence that these streamers are related to the so-called circumnuclear disk of molecular gas and are ionized by photons from massive, hot stars in the central parsec. We attempt to constrain the emission mechanisms and physical properties of the ionized gas and dust of the mini-spiral region with the help of our multiwavelength data sets. Our observations were carried out at 1.3 mm and 3 mm with the mm interferometric array CARMA in California in March and April 2009, with the MIR instrument VISIR at ESO's VLT in June 2006, and the NIR Br-gamma with VLT NACO in August 2009. We present high resolution maps of the mini-spiral, and obtain a spectral index of 0.5 for Sgr A*, indicating an inverted synchrotron spectrum. We find electron densities within the range 0.8-1.5x10^4 cm-3 for the mini-spiral from the radio continuum maps, along with a dust mass contribution of ~0.25 solar masses from the MIR dust continuum, and extinctions ranging from 1.8-3 at 2.16 micron in the Br-gamma line. We observe a mixture of negative and positive spectral indices in our 1.3 mm and 3 mm observations of the extended emission of the mini-spiral, which we interpret as evidence that there are a range of contributions to the thermal free-free emission by the ionized gas emission and by dust at 1.3 mm.Comment: 9 pages, 11 figures, accepted to A&

Bar Diagnostics in Edge-On Spiral Galaxies. II. Hydrodynamical Simulations

We develop diagnostics based on gas kinematics to identify the presence of a bar in an edge-on spiral galaxy and determine its orientation. We use position-velocity diagrams (PVDs) obtained by projecting edge-on two-dimensional hydrodynamical simulations of the gas flow in a barred galaxy potential. We show that when a nuclear spiral is formed, the presence of a gap in the PVDs, between the signature of the nuclear spiral and that of the outer parts of the disk, reliably indicates the presence of a bar. This gap is due to the presence of shocks and inflows in the simulations, leading to a depletion of the gas in the outer bar region. If no nuclear spiral signature is present in a PVD, only indirect arguments can be used to argue for the presence of a bar. The shape of the signature of the nuclear spiral, and to a lesser extent that of the outer bar region, allows to determine the orientation of the bar with respect to the line-of-sight. The presence of dust can also help to discriminate between viewing angles on either side of the bar. Simulations covering a large fraction of parameter space constrain the bar properties and mass distribution of observed galaxies. The strongest constraint comes from the presence or absence of the signature of a nuclear spiral in the PVD.Comment: 25 pages (AASTeX, aaspp4.sty), 11 jpg figures. Accepted for publication in The Astrophysical Journal. Online manuscript with PostScript figures available at: http://www.strw.leidenuniv.nl/~bureau/pub_list.htm

Fabry Perot Halpha Observations of the Barred Spiral NGC 3367

We report the gross properties of the velocity field of the barred spiral galaxy NGC 3367. The following values were found: inclination with respect to the plane of the sky, i=30 deg; position angle (PA) of receding semi major axis PA=51 and systemic velocity V(sys)=3032 km/s. Large velocity dispersion are observed of upt o 120 km/s in the nuclear region, of up to 70 km/s near the eastern bright sources just beyond the edge of the stellar bar where three spiral arms seem to start and in the western bright sources at about 10 kpc. Deviations from normal circular velocities are observed from all the disk but mainly from the semi circle formed by the string of south western Halpha sources. An estimate of the dynamical mass is M(dyn)=2x10^11 Msolar.Comment: Accepted to be published in May 2001 issue in the A.J. 19 pages, 7 figure

CARMA Large Area Star Formation Survey: Observational Analysis of Filaments in the Serpens South Molecular Cloud

We present the N2H+(J=1-0) map of the Serpens South molecular cloud obtained as part of the CARMA Large Area Star Formation Survey (CLASSy). The observations cover 250 square arcminutes and fully sample structures from 3000 AU to 3 pc with a velocity resolution of 0.16 km/s, and they can be used to constrain the origin and evolution of molecular cloud filaments. The spatial distribution of the N2H+ emission is characterized by long filaments that resemble those observed in the dust continuum emission by Herschel. However, the gas filaments are typically narrower such that, in some cases, two or three quasi-parallel N2H+ filaments comprise a single observed dust continuum filament. The difference between the dust and gas filament widths casts doubt on Herschel ability to resolve the Serpens South filaments. Some molecular filaments show velocity gradients along their major axis, and two are characterized by a steep velocity gradient in the direction perpendicular to the filament axis. The observed velocity gradient along one of these filaments was previously postulated as evidence for mass infall toward the central cluster, but these kind of gradients can be interpreted as projection of large-scale turbulence.Comment: 12 pages, 4 figures, published in ApJL (July 2014