Spectroscopic observations of three lenticular (S0) galaxies (NGC 1167, NGC 4150, and NGC 6340) and one SBa galaxy (NGC 2273) have been taken with the 6-m telescope of the Special AstrophysicalObservatory of the Russian Academy of Sciences aimed to study the structure and kinematic properties of early-type disk galaxies. The radial profiles of the stellar radial velocities and the velocity dispersion are measured. N-body simulations are used to construct dynamical models of galaxies containing a stellar disk, bulge, and halo. The masses of individual components are estimated formaximum-mass disk models. A comparison of models with estimated rotational velocities and the stellar velocity dispersion suggests that the stellar disks in lenticular galaxies are "overheated"; i.e., there is a significant excess velocity dispersion over the minimum level required to maintain the stability of the disk. This supports the hypothesis that the stellar disks of S0 galaxies were subject to strong gravitational perturbations. The relative thickness of the stellar disks in the S0 galaxies considered substantially exceed the typical disk thickness of spiral galaxies.
We present kinematic measurements of thin and thick disk components in a sample of nine edge-on galaxies. We extract stellar and ionized gas rotation curves at and above the galaxies' midplanes using the Ca II triplet absorption features and H-alpha emission lines measured with the GMOS spectrographs on Gemini North and South. For the higher mass galaxies in the sample, we fail to detect differences between the thin and thick disk kinematics. In the lower mass galaxies, there is a wide range of thick disk behavior including thick disks with substantial lag and one counter-rotating thick disk. …
GAIA data will create a precise 3-dimensional map of the Galaxy, providing positional information, radial velocities, luminosity, temperature and chemical composition of a representative sample of stars. Here we present a new implementation of the Padova Galaxy Model, where kinematics simulations are included. A few examples of application to GAIA science are discussed, in particular concerning radial velocities determinations of the thin and thick disk.
We present kinematic measurements of the thick and thin disks in two edge-on galaxies. We have derived stellar rotation curves at and above the galaxies' midplanes using Ca II triplet features measured with the GMOS spectrograph on Gemini North. In one galaxy, FGC 1415, the kinematics above the plane show clear rotation that lags that of the midplane by ~20-50%, similar to the behavior seen in the Milky Way. However, the kinematics of the second galaxy, FGC 227, are quite different. The rotation above the plane is extremely slow, showing <25% of the rotation speed of the stars at the midplane.…
Different ways of the determination of masses of galactic disks, based on the kinematic data, are briefly discussed. The analysis of the rotation curves which reach maximum inside of a disk, and N-body modeling, reproducing the rotation curves and stellar velocity dispersion of real galaxies, enable to conclude that the mass of a disk is usually significantly less than the total mass of spherical components (bulge + dark halo) inside of optical borders of a galaxy, although the exceptions also exist.
We present high angular resolution millimeter wavelength continuum and 13CO(2-1) observations of the circumstellar disk surrounding the TTauri star DG Tauri. We show that the velocity pattern in the inner regions of the disk is consistent with Keplerian rotation about a central 0.67 Msun star. The disk rotation is also consistent with the toroidal velocity pattern in the initial channel of the optical jet, as inferred from HST spectra of the first de-projected 100 AU from the source. Our observations support the tight relationship between disk and jet kinematics postulated by the popular magne…
We have obtained integral field spectroscopy of a small sample of early-type galaxies to study the kinematical coupling between the stellar and gaseous components in their central regions.
I discuss how the chemical abundance distributions, kinematics and age distributions of stars in the thin and thick disks of the Galaxy can be used to decipher the merger history of the Milky Way, a typical large galaxy. The observational evidence points to a rather quiescent past merging history, unusual in the context of the `consensus' cold-dark-matter cosmology favoured from observations of structure on scales larger than individual galaxies.
We analyze the distribution of G and K type stars towards the Galactic poles using RAVE and ELODIE radial velocities, 2MASS photometric star counts, and UCAC2 proper motions. The combination of photometric and 3D kinematic data allows us to disentangle and describe the vertical distribution of dwarfs, sub-giants and giants and their kinematics. We identify discontinuities within the kinematics and magnitude counts that separate the thin disk, thick disk and a hotter component. The respective scale heights of the thin disk and thick disk are 225$\pm$10 pc and 1048$\pm$36 pc. We also constrain t…
To better understand our Galaxy, we investigate the pertinency of describing the sys tem of nearby disk stars in terms of a two-components Schwarzschild velocity distributio n.Using the proper motion and parallax information of Hipparcos database, we determine t he parameters characterizing the local stellar velocity field of a sample of 22000 disk stars. The sample we use is essentially the same as the one described by the criteria ad opted to study the LSR and the stream motion of the nearby stellar population
We present first results of new ATCA HI emission and absorption observations of Centaurus A. The large-scale disk is described via a tilted-ring model. A broader redshifted absorption than previously known as well as a blueshifted absorption component against the nucleus is found.
The disks of galaxies are primarily stellar systems, and fundamentally dynamical entities. Thus, to fully understand galactic disks, we must study their stellar kinematics as well as their morphologies. Observational techniques have now advanced to a point where quite detailed stellar-kinematic information can be extracted from spectral observations. This review presents three illustrative examples of analyses that make use of such information to study the formation and evolution of these systems: the derivation of the pattern speed of the bar in NGC 936; the calculation of the complete veloci…
We study, using direct orbit integrations, the kinematic response of the outer stellar disk to the presence of a central bar, as in the Milky-Way. We find that the bar's outer Lindblad resonance (OLR) causes significant perturbations of the velocity moments. With increasing velocity dispersion, the radius of these perturbations is shifted outwards, beyond the nominal position of the OLR, but also the disk becomes less responsive. If we follow Dehnen (2000) in assuming that the OLR occurs just inside the Solar circle and that the Sun lags the bar major axis by ~20 degrees, we find (1) no signif…
We report a kinematic signature associated with the observed asymmetry in the distribution of thick disk/inner halo stars interior to the Solar circle described in Paper I. In that paper we found a statistically significant excess (20% to 25 %) of stars in quadrant I (l ~ 20 deg to 55 deg) both above and below the plane (b ~ +/- 25 deg to +/- 45 deg) compared to the complementary region in quadrant IV. We have measured Doppler velocities for 741 stars, selected according to the same magnitude and color criteria, in the direction of the asymmetry and in the corresponding fields in quadrant IV. …
We present interferometric observations resolving the CO emission in the four gas-rich lenticular galaxies NGC 3032, NGC 4150, NGC 4459, and NGC 4526, and we compare the CO distribution and kinematics to those of the stars and ionized gas. Counterrotation documents an external origin for the gas in at least one case (NGC 3032), and the comparisons to stellar and ionized gas substructures in all four galaxies offer insights into their formation histories. The molecular gas is found in kpc-scale disks with mostly regular kinematics and average surface densities of 100 to 200 \msunsqpc. The disks…
Integral field spectroscopy of galaxies at redshift z~2 has revealed a population of early-forming, rotationally-supported disks. These high-redshift systems provide a potentially important clue to the formation processes that build disk galaxies in the universe. A particularly well-studied example is the z=2.38 galaxy BzK-15504, which was shown by Genzel et al. (2006) to be a rotationally supported disk despite the fact that its high star formation rate and short gas consumption timescale require a very rapid acquisition of mass. Previous kinematical analyses have suggested that z~2 disk gala…
We present the results of our investigation of three samples kinematically representative of the thin and thick disks and the Hercules stream using the catalogue of Soubiran & Girard (2005). We have observed abundance trends and age distribution of each component. Our results show that the two disks are chemically well separated, they overlap greatly in metallicity and both show parallel decreasing trends of alpha elements with increasing metallicity, in the interval -0.80 < [Fe/H] < -0.30. The thick disk is clearly older than the thin disk with a tentative evidence of an Age-Metallicity Relat…
We present the kinematics of a sample of 398 DA white dwarfs from the SPY project (ESO SN Ia Progenitor surveY) and discuss kinematic criteria for distinguishing thin-disk, thick-disk, and halo populations. This is the largest homogeneous sample of white dwarfs for which 3D space motions have been determined. Since the percentage of old stars among white dwarfs is higher than among main-sequence stars, they are presumably valuable tools in studies of old populations, such as the halo and the thick disk. Radial velocities and spectroscopic distances were combined with our measurements of proper…
We present a method for recovering the distribution functions of edge-on thin axisymmetric disks directly from their observable kinematic properties. The most generally observable properties of such a stellar system are the line-of-sight velocity distributions of the stars at different projected radii along the galaxy. If the gravitational potential is known, then the general two-integral distribution function can be reconstructed using the shapes of the high-velocity tails of these line-of-sight distributions. If the wrong gravitational potential is adopted, then a distribution function can s…
We present kinematics of a sample of 398 DA white dwarfs from the SPY project (ESO SN Ia Progenitor surveY) and discuss kinematic criteria for a distinction of thin disk, thick disk, and halo populations. This is the largest homogeneous sample of white dwarfs for which 3D space motions have been determined. Radial velocities and spectroscopic distances obtained by the SPY project are combined with our measurements of proper motions to derive 3D space motions. Galactic orbits and further kinematic parameters are computed. Our kinematic criteria for assigning population membership are deduced fr…
We analyse SAURON kinematic maps of the inner kpc of the early-type (Sa) barred spiral galaxy NGC 5448. The observed morphology and kinematics of the emission-line gas is patchy and perturbed, indicating clear departures from circular motion. The kinematics of the stars is more regular, and displays a small inner disk-like system embedded in a large-scale rotating structure. We focus on the [OIII] gas, and use a harmonic decomposition formalism to analyse the gas velocity field. The higher-order harmonic terms and the main kinematic features of the observed data are consistent with an analytic…
We present kinematics of a sample of 107 DA white dwarfs from the SPY project and discuss kinematic criteria for a distinction of thin disk, thick disk, and halo populations. This is the first homogeneous sample of white dwarfs for which 3D space motions have been determined. Studies of white dwarf kinematics can help determine the fraction of the total mass of our Galaxy contained in the form of thick disk and halo white dwarfs. Radial velocities and spectroscopic distances obtained by the SPY project are combined with our measurements of proper motions to derive 3D space motions. Galactic or…
We present a study of the internal kinematics and stellar populations of early-type galaxies in the Fornax cluster based on integral-field spectroscopic observations with Gemini South GMOS and VLT-VIMOS. Seven galaxies in a luminosity range of -21.3 < M_B < -17.7 have been observed with these integral field units (IFU). As first results, velocity and line strength maps are presented for NGC 1427 and NGC 1419.
We present new observational results on the kinematics of the damped lya systems. Our full sample is now comprised of 31 low-ion profiles and exhibits similar characteristics to the sample from Paper I. The primary exception is that the new distribution of velocity widths includes values out to a maximum of nearly 300 km/s, approx 100 km/s greater than the previous maximum. These high velocity width systems will significantly leverage models introduced to explain the damped lya systems. Comparing the characteristics from low-redshift and high-redshift sub-samples, we find no evidence for signi…
We consider the relationship between the total HI mass in late-type galaxies and the kinematic properties of their disks. The mass $M_HI$ for galaxies with a wide variety of properties, from dwarf dIrr galaxies with active star formation to giant low-brightness galaxies, is shown to correlate with the product $V_c R_0$ ($V_c$ is the rotational velocity, and $R_0$ is the radial photometric disks scale length), which characterizes the specific angular momentum of the disk. This relationship, along with the anticorrelation between the relative mass of HI in a galaxy and $V_c$, can be explained in…
We present a progress report on the kinematical analysis of the entire SPY (ESO SN Ia Progenitor surveY) sample of about one thousand white dwarfs and hot subdwarfs. In a previous study (Pauli et al. 2003, 2006) 398 DA white dwarfs have been analysed already. Here we extend the study to 634 DA white dwarfs. We discuss kinematic criteria for a distinction of thin disk, thick disk and halo populations. This is the largest homogeneous sample of white dwarfs for which accurate 3D space motions have been determined. They have been derived from radial velocities, spectroscopic distances and proper m…
We have analysed the kinematics of a sample of 114 hot subdwarf stars, for 2/3 of which we present new proper motions, spectroscopic and photometric data. The vast majority of the stars show a kinematic behaviour that is similar to that of Thick Disk stars. Some stars have velocities rather fitting to solar, i.e. Thin Disk, kinematics. 16 objects have orbital velocities which differ considerably from those of Disk stars. These are members of the Galactic Halo. We analysed the velocity dispersions and calculated orbits. Most stars feature orbits with disk character (eccentricity <= 0.5), a few …
We have obtained high angular resolution, high signal-to-noise spectra of the Calcium triplet absorption lines on the photometric axes of the stellar spheroid in the polar disk galaxy NGC4650A. Along the major axis, the observed rotation and velocity dispersion measurements show the presence of a kinematically decoupled nucleus, and a flat velocity dispersion profile. The minor axis kinematics is determined for the first time: along this direction some rotation is measured, and the velocity dispersion is nearly constant and slightly increases at larger distances from the center. The new high r…
I briefly review the growing evidence that thick stellar disks surround most edge-on disk galaxies. Recent studies show that these extragalactic thick disks have old ages, low metallicities, long scale lengths, and moderately flattened axial ratios, much like the thick disk of the Milky Way. However, the properties of thick disks change systematically with the mass of the galaxy. The thick disks of low mass galaxies are more prominent and somewhat more metal-poor than those surrounding massive disk galaxies. Given the strong evidence that thick disks are fossils from an early epoch of merging,…
We present a kinematic study of the outer regions (R_25<R<2 R_25) of 17 edge-on disk galaxies. Using deep long-slit spectroscopy (flux sensitivity a few 10^-19 erg s^-1 cm^-2 arcsec^-2), we search for H-alpha emission, which must be emitted at these flux levels by any accumulation of hydrogen due to the presence of the extragalactic UV background and any other, local source of UV flux. We present results from the individual galaxy spectra and a stacked composite. We detect H-alpha in many cases well beyond R_25 and sometimes as far as 2 R_25. The combination of sensitivity, spatial resolution,…
Full space velocities are computed for a sample of 130 nearby RR Lyrae variables using both ground-based and Hipparcos proper motions. In many cases proper motions from multiple sources have been averaged to produce a significant improvement in the transverse space velocity errors. In most cases, this exceeds the accuracy of Hipparcos proper motions alone. The velocity ellipsoids computed for halo and thick disk samples are in agreement with previous studies. No distinct sample of thin disk RR Lyraes has been isolated but there is kinematic evidence for some thin disk stars in our thick disk s…
We have completed a new fiber array, SparsePak, optimized for low-surface-brightness studies of extended sources on the WIYN telescope. We are now using this array as a measuring engine of velocity and velocity-dispersion fields of stars and ionized gas in disk galaxies from high to low surface-brightness. Here we present commissioning data on the velocity ellipsoids, surface densities and mass-to-light ratios in two blue, high surface-brightness, yet small disks. If our preliminary results survive further observation and more sophisticated analysis, then NGC 3949 has sigma_z/sigma_R >> 1, imp…
Characterizing rotation, infall and accretion disks around high-mass protostars is an important topic in massive star formation research. With the Australia Telescope Compact Array and the Very Large Array we studied a massive disk candidate at high angular resolution in ammonia (NH3(4,4) & (5,5)) tracing the warm disk but not the envelope. The observations resolved at ~0.4'' resolution (corresponding to ~1400AU) a velocity gradient indicative of rotation perpendicular to the molecular outflow. Assuming a Keplerian accretion disk, the estimated protostar-disk mass would be high, similar to the…
Close examination of so-called "pseudobulges" in several early-type disk galaxies indicates that they are actually composite structures consisting of both a flattened, kinematically cool disklike structure ("disky pseudobulge") and a rounder, kinematically hot spheroidal structure ("classical bulge"). This indicates that pseudobulges, thought to form from internal secular evolution, and classical bulges, thought to form from rapid mergers, are not exclusive phenomena: some galaxies can have both.
This is the third of a series of papers in which the structure and kinematics of disk galaxies is studied. Employing direct tilted-ring fits to the data cube as introduced in Paper I, we perform an analysis of the "Spindle" galaxy NGC 2685, previously regarded as two-ringed polar ring galaxy. Deep HI and optical (i'-band) observations are presented. The HI observations strongly suggest that the gaseous structure of NGC 2685 does not consist of two separate mutually inclined regions, but forms a coherent, extremely warped disk, the appearance of two rings being due to projection effects. By com…
We report high spectral resolution observations of the CO vibrational overtone emission from the young stellar object 1548C27; our observations include both the CO(2-0) and CO(5-3) bandhead regions. These data and similar observations of the young stellar object WL16, reported in a previous contribution to this journal, provide some of the most compelling evidence to date for the existence of inner disks around young stars. We describe the simple procedure that we use to synthesize bandhead emission from disks including the effect of thermal dissociation of CO and non-LTE excitation of the vib…
We have explored the galaxy disk/extended halo gas kinematic relationship using rotation curves (Keck/ESI) of ten intermediate redshift galaxies which were selected by MgII halo gas absorption observed in quasar spectra. Previous results of six edge-on galaxies, probed along their major axis, suggest that observed halo gas velocities are consistent with extended disk-like halo rotation at galactocentric distances of 25-72 kpc. Using our new sample, we demonstrate that the gas velocities are by and large not consistent with being directly coupled to the galaxy kinematics. Thus, mechanisms other…
In several nearby intermediate luminosity early-type galaxies, recent observations at large radii have shown a indications of a lack of dark matter, substantially at odds with the prediction from the CDM hierarchical merger models. Here we discuss a pilot observational project for the study of the internal kinematical and dynamical properties of this remarkable sample of galaxies. Using the VIMOS-IFU in its high spectral resolution mode, it would be possible to investigate the regions up to about 1.2 effective radii, taking advantage of the much larger field of view and telescope diameter. Thi…
The morphology and kinematics of the luminous blue starburst galaxy NGC 7673 are explored using the WIYN 3.5m telescope. Signs of a past kinematic disturbance are detected in the outer galaxy; the most notable feature is a luminous ripple located 1.55 arc minutes from the center of NGC 7673. Sub-arc second imaging in B and R filters also reveals red dust lanes and blue star clusters that delineate spiral arms in the bright inner disk and narrow band Halpha imaging shows that the luminous star clusters are associated with giant H II regions. The Halpha kinematics measured with echelle imaging s…
We use integral-field observation of the stellar kinematics obtained with SAURON in combination with Schwarzschild dynamical models to revisit our understanding of the classic (V/sigma)-epsilon anisotropy diagram of early-type galaxies.
Based upon QSO absorption line studies, galaxies at 0.3 < z < 1.0 are seen to have extended gaseous "halos". When the absorption lines are observed at high resolution, the velocity distribution of the absorbing gas gives clues as to where this gas actually arises in and around the galaxies. Cloud to cloud abundance ratios provide further clues, given that the ionization conditions and chemical evolution histories of outer halos clouds, spiral disk clouds, and clouds in elliptical galaxies are different. The key to interpreting the high redshift data is the Milky Way galaxy, the absorption line…
The panoramic integral-field spectrograph SAURON is currently being used to map the stellar kinematics, gaseous kinematics, and stellar populations of a large number of early-type galaxies and bulges. Here, we describe SAURON observations of cold stellar disks embedded in spheroids (NGC3384, NGC4459, NGC4526), we illustrate the kinematics and ionization state of large-scale gaseous disks (NGC4278, NGC7742), and we show preliminary comparisons of SAURON data with barred galaxy N-body simulations (NGC3623).
Gravity is scale free. Thus gravity may form similar structures in self-gravitating systems on different scales. Indeed, observations of the interstellar medium, spiral disks and cosmic structures, reveal similar characteristics. The structures in these systems are very lumpy and inhomogeneous. Moreover some of these structures do not seem to be of random nature, but obey certain power laws. Models of slightly dissipative self-gravitating disks show how such inhomogeneous structures can be maintained on the kpc-scale. The basic physical processes in these models are self-gravity, dissipation a…
We studied the bulge and the disk kinematic of the giant Low Surface Brightness (LSB) galaxy ESO 323-G064 in order to investigate its dynamics and its Dark Matter (DM) content. We observed the galaxy with the integral field spectroscopy (VLT/VIMOS, in IFU configuration). Results for the gaseous kinematics (bulge and disk) and stellar kinematics (bulge) are presented, together with a Jeans model for the stellar bulge kinematics.
We describe observations and abundance analysis of a high-resolution, high-S/N survey of 168 stars, most of which are metal-poor dwarfs. We follow a self-consistent LTE analysis technique to determine the stellar parameters and abundances, and estimate the effects of random and systematic uncertainties on the resulting abundances. Element-to-iron ratios are derived for key alpha, odd, Fe-peak, r- and s-process elements. Effects of Non-LTE on the analysis of Fe I lines are shown to be very small on the average. Spectroscopically determined surface gravities are derived that are generally close …
We have used the velocity dispersion as an age indicator to constrain the ages of a large sample of main sequence Vega-like stars in order to study the lifetimes and temporal evolution of the dust disks around them. We use HIPPARCOS measurements to compute stellar velocities in the sky plane. The velocity dispersion of Vega-like stars is found to be systematically smaller than that of the normal main sequence field stars for all spectral types, suggesting that the main sequence dusty systems, on average, are younger than normal field stars. The debris disks seem to survive longer around late t…
We present first results of a study of the halo kinematics for a sample of early type galaxies using planetary nebulae (PNe) as kinematical tracers. PNe allow to extend up to several effective radii (Re) the information from absorption line kinematics (confined to within 1 or 2 Re), providing valuable information and constraints for merger simulations and galaxy formation models. We find that the specific angular momentum per unit mass has a more complex radial dependence when the halo region is taken into account and that the halo velocity dispersion is related to the total galaxy luminosity,…
We have carried out a sample survey in UBVR photometry and proper motions in different directions in the Galaxy, as part of an investigation of galactic structure and evolution. Three fields in the direction of galactic anticentre, centre and antirotation have been surveyed. Using our new data together with wide-area surveys in other fields available to date, we discuss the radial and vertical structure of the Galaxy. The density laws for stars with M$_{V}\ge$3.5 follow a sum of two exponentials with scale heights of 260$\pm$50 pc (thin disk) and 760$\pm$50 pc, respectively. This second expone…
We present a comparison between ionized gas and stellar kinematics for a sample of 5 early-to-intermediate disk galaxies. We measured the major axis V and velocity dispersion radial profiles for both gas and stars, and the h_3 and h_4 radial profiles of the stars. We also derived from the R-band surface photometry of each galaxy the light contribution of their bulges and disks. In order to investigate the differences in the velocity fields of our sample galaxies we adopted the self-consistent dynamical model by Pignatelli & Galletta (1998), which takes into account the asymmetric drift effects…
The presence of non-circular and off-plane gas motions is frequently observed in the inner regions of disk galaxies. We have measured with integral-field spectroscopy the surface-brightness distribution and kinematics of the ionized gas in NGC 2855 and NGC 7049. These two early-type spiral galaxies were selected to possibly host a kinematically-decoupled gaseous component in orthogonal rotation with respect to the galaxy disk. We have modeled the ionized-gas kinematics and distribution of both galaxies assuming that the gaseous component is distributed either on two orthogonally-rotating disks…
We examine whether early-type galaxies in clusters may have evolved from later types by the fading of their disks (e.g., as a result of ram-pressure stripping or strangulation) or by enhancement of the bulge luminosity (e.g., due to tidal interactions and mergers). For this purpose, we compare the bulge and disk luminosities of early- and late-type galaxies and of galaxies at different radial distances from the cluster center. We find that, in order for early-type galaxies, including S0s, to have evolved from late-type galaxies, their bulge luminosities must have been physically enhanced. Disk…
Recent studies of elemental abundances in the Galactic halo and in the Galactic disk have underscored the possibility to kinematically separate different Galactic subcomponents. Correlations between the galactocentric rotation velocity and various element ratios were found, providing an important means to link different tracers of star formation and metal enrichment to the Galactic components of different origin (collapse vs. accretion). In the present work we determine stellar kinematics for a sample of 124 disk stars, which we derive from their orbits based on radial velocities and proper mo…
We present observations of the distribution and kinematics of neutral and ionized gas in NGC 1144, a galaxy that forms part of the Arp 118 system. Ionized gas is present over a huge spread in velocity (1100 km/s) in the disk of NGC 1144, but HI emission is detected over only 1/3 of this velocity range, in an area that corresponds to the NW half of the disk. In the nuclear region of NGC 1144, a jump in velocity in the ionized gas component of 600 km/s is observed. Faint, narrow HI absorption lines are also detected against radio sources in the SE part of the disk of NGC 1144, which includes reg…
(Abridged) The building blocks of galaxies are star clusters. These form with low-star formation efficiencies and, consequently, loose a large part of their stars that expand outwards once the residual gas is expelled by the action of the massive stars. Massive star clusters may thus add kinematically hot components to galactic field populations. This kinematical imprint on the stellar distribution function is estimated here by calculating the velocity distribution function for ensembles of star-clusters distributed as power-law or log-normal initial cluster mass functions (ICMFs). The resulti…
We quantify the mean asymmetry of 54 face-on, early type disk galaxies (S0 to Sab) using the amplitude of the m=1 azimuthal Fourier component of the R-band surface brightness. We find that the median lopsidedness, (A_1/A_0)_{mean}, of our sample is 0.11 and that the most lopsided 20% of our galaxies have (A_1/A_0)_{mean} >= 0.19. Asymmetries in early type disks appear to be of similar frequency and strength as in late type disk galaxies (Zaritsky and Rix 1997.) We have observed our early type disks in a bandpass (R-Band) in which the light is dominated by stars with ages greater than 10^9 yrs,…
We demonstrate in this paper that the velocity widths of the neutral gas in Damped Ly Alpha (DLA) systems are inconsistent with these systems originating in gas disks of galaxies similar to those seen in the local Universe. We examine the gas kinematics of local galaxies using the high quality HI 21-cm data from the HI Nearby Galaxies Survey (THINGS) and make a comparison with the velocity profiles measured in the low-ionization metal lines observed in DLAs at high redshifts. The median velocity width of z=0 HI gas above the DLA column density limit of N=2x10^20 cm-2 is approximately 30 km/s, …
A variety of processes play a role in the evolution of protostellar disks. Here I focus on the uncertain issue of magnetic field-disk coupling and its implications for magnetically-driven turbulence and disk-driven winds. At present it is clear that the magnetic field plays a crucial role in disk evolution, but detailed conclusions cannot be drawn because the complicated interplay between dynamics and the evolution of the grain population remains to be explored.
We present spectroscopic observations of the stellar motions in the disk of the superthin edge-on spiral galaxy IC 5249 and re-analyse synthesis observations of the HI. We find that the HI rotation curve rises initially to about 90-100 km/s, but contrary to the conclusion of Abe et al. (1999) flattens well before the edge of the optical disk. Over most part of the optical disk we have been able to establish that the (tangential) stellar velocity dispersion is 25-30 km/s. From earlier surface photometry we adopt a value for the radial scalelength of the disk of 7 +/- 1 kpc, a vertical scaleheig…
We have performed Smoothed Particle Hydrodynamic (SPH) simulations to study the response of molecular clouds in the Galactic disk to a rotating bar and their subsequent evolution in the Galactic Center (GC) region. The Galactic potential in our models is contributed by three axisymmetric components (massive halo, exponential disk, compact bulge) and a non-axisymmetric bar. These components are assumed to be invariant in time in the frame corotating with the bar. Some noticeable features such as an elliptical outer ring, spiral arms, a gas-depletion region, and a central concentration have been…
We present an alternative method for the kinematic analysis of high proper motion surveys and discuss its application to the survey of Oppenheimer et al. (2001) for the selection of reliable halo white dwarfs (WDs). The local WD space density we estimate is (1-2) 10^{-5}MSun/pc^{3}, which is about an order of magnitude smaller than the value derived in Oppenheimer et al. (2001), and is consistent with the values obtained from recent reanalyses of the same data (e.g. Reid et al. 2001, Reyle et al. 2001, Torres et al. 2002, Salim et al. 2004). Our result, which corresponds to a fraction of 0.1%-…
This is the first of a series of papers in which the kinematics of disk galaxies over a range of scales is scrutinised employing spectroscopy. A fundamental aspect of these studies is presented here: the new publicly available software tool TiRiFiC (http://www.astro.uni-bonn.de/~gjozsa/tirific.html) enables a direct fit of a ``tilted-ring model'' to spectroscopic data cubes. The algorithm generates model data cubes from the tilted-ring parametrisation of a rotating disk, which are automatically adjusted to reach an optimum fit via a chi-squared minimisation method to an observed data cube. The…
