We present the Potsdam photographic plate library at the Leibniz Institute for Astrophysics Potsdam. It includes plate archives, data from plate index catalogues and extracts from astronomical logbooks, as well as digitized plate images... more
We present the Potsdam photographic plate library at the Leibniz Institute for Astrophysics Potsdam. It includes plate archives, data from plate index catalogues and extracts from astronomical logbooks, as well as digitized plate images and interfaces for accessing all the available information. The plate index catalogues and the digitized images of the Potsdam astronomical photographic plates are prepared according to the standards of the Wide-Field Plate Database and German Astrophysical Virtual Observatory. The high-resolution digitization of the plates (in standardized FITS file format), the low-resolution plate previews (in TIFF and JPEG file format), as well as suitable digitization of the catalogues, logbooks, and relevant scientific research papers (in JPEG and TIFF) are made using commercial flatbed scanners.
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s *********************************************************************************** THE WIDE-FIELD PLATE DATABASE: DEVELOPMENT AND ACCESS VIA INTERNET ∗ Milcho Tsvetkov e-mail: mtsvetkov@astro.bas.bg ACM Computing Classification System... more
s *********************************************************************************** THE WIDE-FIELD PLATE DATABASE: DEVELOPMENT AND ACCESS VIA INTERNET ∗ Milcho Tsvetkov e-mail: mtsvetkov@astro.bas.bg ACM Computing Classification System (1998): J.2.
We present the Potsdam photographic plate library at the Leibniz Institute for Astrophysics Potsdam. It includes plate archives, data from plate index catalogues and extracts from astronomical logbooks, as well as digitized plate images... more
We present the Potsdam photographic plate library at the Leibniz Institute for Astrophysics Potsdam. It includes plate archives, data from plate index catalogues and extracts from astronomical logbooks, as well as digitized plate images and interfaces for accessing all the available information. The plate index catalogues and the digitized images of the Potsdam astronomical photographic plates are prepared according to the standards of the Wide-Field Plate Database and German Astrophysical Virtual Observatory. The high-resolution digitization of the plates (in standardized FITS file format), the low-resolution plate previews (in TIFF and JPEG file format), as well as suitable digitization of the catalogues, logbooks, and relevant scientific research papers (in JPEG and TIFF) are made using commercial flatbed scanners. ACM Computing Classification System (1998): J.2.
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The 5th RAVE data release is based on 520,781 spectra (R ≈ 7500 in the CaT region at 8410 - 8795Å) of 457,588 unique stars. RAVE DR5 provides radial velocities, stellar parameters and individual abundances for up to seven elements and... more
The 5th RAVE data release is based on 520,781 spectra (R ≈ 7500 in the CaT region at 8410 - 8795Å) of 457,588 unique stars. RAVE DR5 provides radial velocities, stellar parameters and individual abundances for up to seven elements and distances found using isochrones for a considerable subset of these objects. In particular, RAVE DR5 has 255,922 stellar observations that also have parallaxes and proper motions from the Tycho-Gaia astrometric solution (TGAS) in Gaia DR1. The combination of RAVE and TGAS thus provides the currently largest overlap of spectroscopic and space-based astrometric data and thus can serve as a formidable preview of what Gaia is going to deliver in coming data releases. Basic properties of the RAVE+TGAS survey and its derived data products are presented as well as first applications w.r.t wave-like patterns in the disk structure. An outlook to the 6th RAVE data release is given.
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Throughout the past decade, significant advances have been made in the size and scope of large-scale spectroscopic surveys, allowing for the opportunity to study in-depth the formation history of the Milky Way. Using the fourth data... more
Throughout the past decade, significant advances have been made in the size and scope of large-scale spectroscopic surveys, allowing for the opportunity to study in-depth the formation history of the Milky Way. Using the fourth data release of the RAdial Velocity Experiment (RAVE), we study the age-metallicity-velocity space of ~ 100,000 FGK stars in the extended solar neighborhood in order to explore evolutionary processes. Combining these three parameters, we better constrain our understanding of these interconnected, fundamental processes.
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Research Interests: Physics, Organic Chemistry, Astrophysical Plasma, Astrophysics, Galaxy, and 3 moreMilky Way, Stars, and Disc
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The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems in astronomical spectroscopy, as DIBs... more
The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems in astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar spectra obtained by the massive spectroscopic survey RAVE (Radial Velocity Experiment) to produce the first pseudo-three-dimensional map of the strength of the DIB at 8620 angstroms covering the nearest 3 kiloparsecs from the Sun, and show that it follows our independently constructed spatial distribution of extinction by interstellar dust along the Galactic plane. Despite having a similar distribution in the Galactic plane, the DIB 8620 carrier has a significantly larger vertical scale height than the dust. Even if one DIB may not represent the general DIB population, our observations outline the future direction of DIB ...
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Research Interests: Physics, Astrophysics, Astrometry, Astronomy, Galaxy, and 4 moreMilky Way, Stars, Sky, and Astronomical
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The Radial Velocity Experiment (RAVE) is a large wide-field spectroscopic stellar survey of the Milky Way. Over the period 2003-2013, 574,630 spectra for 483,330 stars have been amassed at a resolution of R=7500 in the Ca-triplet region... more
The Radial Velocity Experiment (RAVE) is a large wide-field spectroscopic stellar survey of the Milky Way. Over the period 2003-2013, 574,630 spectra for 483,330 stars have been amassed at a resolution of R=7500 in the Ca-triplet region of 8410-8795\AA. Wavelength coverage and resolution are thus comparable to that anticipated from the Gaia RVS. Derived data products of RAVE include radial velocities, stellar parameters, chemicals abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni, and absorption measures based on the diffuse interstellar bands (DIB) at 8620\AA. Since more than 290000 RAVE targets are drawn from the Tycho-2 catalogue, RAVE will be an interesting prototype for the anticipated full Gaia data releases, in particular when combined with the early Gaia data releases, which contain astrometry but not yet stellar parameters and abundances.
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We have performed high resolution cosmological N-body simulations in which halos of 1011 M&sun; are resolved with over 700 particles. We report on the internal structure of group-sized halos (masses between 1011 M&sun; and 1014... more
We have performed high resolution cosmological N-body simulations in which halos of 1011 M&sun; are resolved with over 700 particles. We report on the internal structure of group-sized halos (masses between 1011 M&sun; and 1014 M&sun;), particularly on how the angular momentum within the halo correlates with the shape of the halo and with the angular momentum at other radii. We find that many halos have an inner region whose angular momentum is disconnected with that of the outer halo.
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We examine the orbits of satellite galaxies identified in a suite of N-body/gasdynamical simulations of the formation of $L_*$ galaxies in a LCDM universe. Most satellites follow conventional orbits; after turning around, they accrete... more
We examine the orbits of satellite galaxies identified in a suite of N-body/gasdynamical simulations of the formation of $L_*$ galaxies in a LCDM universe. Most satellites follow conventional orbits; after turning around, they accrete into their host halo and settle on orbits whose apocentric radii are steadily eroded by dynamical friction. However, a number of outliers are also present, we find that ~1/3 of satellites identified at $z=0$ are on unorthodox orbits, with apocenters that exceed their turnaround radii. This population of satellites on extreme orbits consists typically of the faint member of a satellite pair that has been ejected onto a highly-energetic orbit during its first approach to the primary. Since the concurrent accretion of multiple satellite systems is a defining feature of hierarchical models of galaxy formation, we speculate that this three-body ejection mechanism may be the origin of (i) some of the newly discovered high-speed satellites around M31 (such as Andromeda XIV); (ii) some of the distant fast-receding Local Group members, such as Leo I; and (iii) the oddly isolated dwarf spheroidals Cetus and Tucana in the outskirts of the Local Group. Our results suggest that care must be exercised when using the orbits of the most weakly bound satellites to place constraints on the total mass of the Local Group.
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We report results of a series of nonradiative N-body/SPH simulations in a ΛCDM cosmology, designed to study the growth of angular momentum in galaxy systems. A sample of 41 halos of differing mass and environment were selected from a... more
We report results of a series of nonradiative N-body/SPH simulations in a ΛCDM cosmology, designed to study the growth of angular momentum in galaxy systems. A sample of 41 halos of differing mass and environment were selected from a cosmological N-body simulation of size 32.5 h-1 Mpc and resimulated at higher resolution with the tree-SPH code GADGET. We find that the spin of the baryonic component correlates well with the spin of the dark matter, but there is a misalignment of typically 20° between these two components. The spin of the baryonic component is also on average larger than that of the dark matter component, and we find this effect to be more pronounced at lower redshifts. A significant fraction f of gas has negative angular momentum, and this fraction is found to increase with redshift. This trend can be explained as a result of increasing thermalization of the virializing gas with decreasing redshift. We describe a toy model in which the tangential velocities of particles are smeared by Gaussian random motions. This model is successful in explaining some of the global angular momentum properties, in particular the anticorrelation of f with the spin parameter λ and the shape of the angular momentum distributions (AMDs). We investigate in detail the AMDs of the gas and the dark matter components of the halo. We compare and contrast various techniques to determine the AMDs. We show that the technique of adding thermal velocities to streaming motions (broadening) is unsuitable for making comparisons between gas and dark matter AMDs because the shape of the broadened AMDs is predominantly determined by the dispersion and is insensitive to the underlying nonbroadened AMD. In order to bring both gas and dark matter to the same footing, we smooth the angular momentum of the particles over a fixed number of neighbors. The AMDs obtained by this method have a smooth and extended truncation as compared to earlier methods. We find that an analytical function in which the differential distribution of specific angular momentum j is given by P(j)=[1/jαdΓ(α)](j)α-1e-j/jd, where jd=jtot/α, can be used to describe a wide variety of profiles, with just one parameter α. The distribution of the shape parameter α for both gas and dark matter follows roughly a lognormal distribution. The mean and standard deviation of logα for gas are -0.04 and 0.11, respectively. About 90%-95% of halos have α<1.3, while exponential disks in Navarro-Frenk-White (NFW) halos would require 1.3<α<1.6. This implies that a typical halo in simulations has an excess of low angular momentum material as compared to that of observed exponential disks, a result that is consistent with the findings of earlier works. Parameter α for gas is correlated with that for dark matter (DM), but they have a significant scatter <αgas/αDM>=1.09+/-0.2. Parameter αgas is also biased toward slightly higher values compared to αDM. The angular momentum in halos is also found to have a significant spatial asymmetry with the asymmetry being more pronounced for dark matter.
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We combine predictions for several hierarchical cosmogonies with observational evidence on damped Lyman alpha systems to establish a correspondence between the high redshift galaxy population and the properties of damped Lyman alpha... more
We combine predictions for several hierarchical cosmogonies with observational evidence on damped Lyman alpha systems to establish a correspondence between the high redshift galaxy population and the properties of damped Lyman alpha systems. We assume that high redshift galaxies and damped Lyman alpha systems are hosted by the same dark matter halos and require consistency between the predicted halo space density, the rate of incidence and the velocity width distribution of damped Lyman alpha systems, and the observed galaxy luminosity function at the bright end. We arrive at the following results: (1) predicted impact parameters between the damped absorption system and the luminous part of the absorbing galaxy are expected to be very small (0.3 - 1arcsec) for most galaxies; (2) luminosities of galaxies causing damped absorption are generally fainter than m_R = 25 and damped Lyman alpha systems are predicted to sample preferentially the outer regions of galaxies at the faint end of the galaxy luminosity function at high redshift. Therefore, DLAS should currently provide the best probe of the progenitors of normal present-day galaxies.
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In this work we investigate the gravitationally lensed system B1422+231. High-quality VLBI image positions, fluxes and shapes as well as an optical HST lens galaxy position are used. First, two simple and smooth models for the lens galaxy... more
In this work we investigate the gravitationally lensed system B1422+231. High-quality VLBI image positions, fluxes and shapes as well as an optical HST lens galaxy position are used. First, two simple and smooth models for the lens galaxy are applied to fit observed image positions and fluxes; no even remotely acceptable model was found. Such models also do not accurately reproduce the image shapes. In order to fit the data successfully, mass substructure has to be added to the lens, and its level is estimated. To explore expectations about the level of substructure in galaxies and its influence on strong lensing, N-body simulation results of a model galaxy are employed. By using the mass distribution of this model galaxy as a lens, synthetic data sets of different four image system configurations are generated and simple lens models are again applied to fit them. The difficulties in fitting these lens systems turn out to be similar to the case of some real gravitationally lensed systems, thus possibly providing evidence for the presence and strong influence of substructure in the primary lens galaxy.
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An overview over the current status of modeling galaxies by means of numerical simulations is given. After a short description of how galaxies form in hierarchically clustering scenarios, success and failures of current simulations are... more
An overview over the current status of modeling galaxies by means of numerical simulations is given. After a short description of how galaxies form in hierarchically clustering scenarios, success and failures of current simulations are demonstrated using three different applications: the morphology of present day galaxies; the appearance of high redshift galaxies; and the nature of the Ly-alpha forest and metal absorption lines. It is shown that current simulations can qualitatively account for many observed features of galaxies. However, the objects which form in these simulations suffer from a strong overcooling problem. Star formation and feedback processes are likely to be indispensable ingredients for a realistic description even of the most basic parameters of a galaxy. The progenitors of todays galaxies are expected to be highly irregular and concentrated, as supported by recent observations. Though they exhibit a velocity dispersion similar to present day L > L^* galaxies, they may be much less massive. The filamentary distribution of the gas provides a natural explanation for Ly-alpha and metal absorption systems. Furthermore, numerical simulations can be used to avoid misinterpretations of observed data and are able to alleviate some apparent contradictions in the size estimates of Ly-alpha absorption systems.
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... Matthias; Bennett, Charles L.; Bucher, Martin; Burigana, Carlo; Capaccioli, Massimo; D&amp;#x27;Onofrio,Mauro; Durrer, Ruth; Gioia, Isabella; Hasinger, Günther; Lawrence, Charles; Longo, Giuseppe; Macias-Perez, Juan Francisco;... more
... Matthias; Bennett, Charles L.; Bucher, Martin; Burigana, Carlo; Capaccioli, Massimo; D&amp;#x27;Onofrio,Mauro; Durrer, Ruth; Gioia, Isabella; Hasinger, Günther; Lawrence, Charles; Longo, Giuseppe; Macias-Perez, Juan Francisco; Madau, Piero; Mather, John; Peacock, John; Popa ...
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(Abridged) We investigate how the shapes and angular momenta of galaxy and group mass dark matter halos in a LCDM N-body simulation are correlated internally, and how they are aligned with respect to the location and properties of... more
(Abridged) We investigate how the shapes and angular momenta of galaxy and group mass dark matter halos in a LCDM N-body simulation are correlated internally, and how they are aligned with respect to the location and properties of surrounding halos. We explore these relationships down to halos of much lower mass (10^11/h Msun) than previous studies. The halos are triaxial, with c/a ratios of 0.6+-0.1. More massive halos are more flattened. The principal axes are very well aligned within 0.6 r_vir. The angular momentum vectors are also reasonably well aligned except between the very outermost and very innermost regions of the halo. The angular momentum vectors tend to align with the minor axes, with a mean misalignment of ~25 degrees, and lie perpendicular to the major and intermediate axes. The properties of a halo at 0.4 r_vir are quite characteristic of the properties at most other radii within the halo. There is a very strong tendency for the minor axes of halos to lie perpendicular to large scale filaments. This alignment extends to much larger separations for group and cluster mass halos than for galaxy mass halos. As a consequence, the intrinsic alignments of galaxies are likely weaker than previous predictions, which were based on the shapes of cluster mass halos. The angular momenta of the highest concentration halos tend to point toward other halos. The angular momenta of galaxy mass halos point parallel to filaments, while those of group and cluster mass halos show a very strong tendency to point perpendicular to the filaments. This suggests that group and cluster mass halos acquire most of their angular momentum from major mergers along filaments, while the accretion history of mass and angular momentum onto galaxy mass halos has been smoother.
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We combine predictions for several hierarchical cosmogonies with observational evidence on damped Lyalpha systems (DLASs) to establish a correspondence between the high-redshift galaxy population and the properties of DLASs. We assume... more
We combine predictions for several hierarchical cosmogonies with observational evidence on damped Lyalpha systems (DLASs) to establish a correspondence between the high-redshift galaxy population and the properties of DLASs. We assume that high-redshift galaxies and damped Lyalpha systems are hosted by the same dark matter halos and require consistency between the predicted halo space density, the rate of incidence and the velocity width distribution of damped Lyalpha systems, and the observed galaxy luminosity function at the bright end. We arrive at the following results: (1) predicted impact parameters between the damped absorption system and the luminous parts of the absorbing galaxy are expected to be very small (0.3"-1") for most galaxies; (2) luminosities of galaxies causing damped absorption are generally fainter than mR=25, and damped Lyalpha systems are predicted to sample preferentially the outer regions of galaxies at the faint end of the galaxy luminosity function at high redshift. Therefore, DLASs should currently provide the best probe of the progenitors of normal present-day galaxies.
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We present a detailed analysis of the disk component of a simulated galaxy formed in the ΛCDM cosmogony. At redshift z=0, two distinct dynamical components are easily identified solely on the basis of the orbital parameters of stars in... more
We present a detailed analysis of the disk component of a simulated galaxy formed in the ΛCDM cosmogony. At redshift z=0, two distinct dynamical components are easily identified solely on the basis of the orbital parameters of stars in the galaxy: a slowly rotating, centrally concentrated spheroid and a disklike component largely supported by rotation. The disk may be further decomposed into a thin, dynamically cold component with stars on nearly circular orbits and a hotter, thicker component with orbital parameters transitional between the thin disk and the spheroid. Supporting evidence for the presence of distinct thick- and thin-disk components is provided, as in the Milky Way, by the double-exponential vertical structure of the disk and in abrupt changes in the vertical velocity distribution as a function of stellar age. The dynamical origin of these components offers intriguing clues to the assembly of spheroids and disks in the Milky Way and other spiral galaxies. The spheroid is old and has essentially no stars younger than the time elapsed since the last major accretion event, ~8 Gyr ago for the system we consider here. The majority of thin-disk stars, on the other hand, form after the merging activity is over, although a significant fraction (~15%) of thin-disk stars are old enough to predate the last major merger event. This unexpected population of old-disk stars consists mainly of the tidal debris of satellites whose orbital plane was coincident with the disk and whose orbits were circularized by dynamical friction prior to full disruption. More than half of the stars in the thick disk share this origin, part of a trend that becomes more pronounced with age: 9 out of 10 stars presently in the old (age of >~10 Gyr) disk component were actually brought into the disk by satellites. By contrast, only one in two stars belonging to the old spheroid are tidal debris; the rest may be traced to a major merger event that dispersed the luminous progenitor at z~1.5 and seeded the formation of the spheroid. Our results highlight the role of satellite accretion events in shaping the disk, as well as the spheroidal, component and reveal some of the clues to the assembly process of a galaxy preserved in the detailed dynamics of old stellar populations.
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We investigate the heavy element QSO absorption systems caused by gas condensations at high redshift that evolve into galaxies at the present epoch. Artificial QSO spectra were generated for a variety of lines of sight through regions of... more
We investigate the heavy element QSO absorption systems caused by gas condensations at high redshift that evolve into galaxies at the present epoch. Artificial QSO spectra were generated for a variety of lines of sight through regions of the universe simulated with a hydrodynamics code. The C IV and H I absorption features in these spectra closely resemble observed C IV and H I absorption systems if [C/H] ~ -3 to -2 is assumed. C IV absorption complexes with multiple-component structure and velocity spreads up to ~600 km s-1 are found. The broadest systems are caused by lines of sight passing through groups of protogalactic clumps aligned along filamentary structures expanding with the Hubble flow. Typical clumps have a radius of about 5--10 kpc, a baryonic mass of ~109 Msolar, and are surrounded by hot gas atmospheres with a radius of about 30 kpc. The temperature of a considerable fraction of the gas does not take the photoionization equilibrium value. This invalidates density and size estimates derived from thermal equilibrium models. Our model may be able to explain both high-ionization multicomponent heavy-element absorbers and damped Ly alpha systems as groups of small protogalactic clumps.
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Abstract Dispersion in the interstellar medium is a well known phenomenon that follows a simple relationship, which has been used to predict the time delay of dispersed radio pulses since the late 1960s. We performed wide-band... more
Abstract Dispersion in the interstellar medium is a well known phenomenon that follows a simple relationship, which has been used to predict the time delay of dispersed radio pulses since the late 1960s. We performed wide-band simultaneous observations of four pulsars ...
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(Abridged) We use numerical simulations to investigate the origin and structure of the luminous halos that surround isolated galaxies. These stellar structures extend out to several hundred kpc away from a galaxy, and consist of stars... more
(Abridged) We use numerical simulations to investigate the origin and structure of the luminous halos that surround isolated galaxies. These stellar structures extend out to several hundred kpc away from a galaxy, and consist of stars shed by merging subunits during the many accretion events that characterize the hierarchical assembly of galaxies. Such origin suggests that outer luminous halos are ubiquitous and that they should appear as an excess of light over extrapolations of the galaxy's inner profile beyond its traditional luminous radius. The mass profile of the accreted stellar component is well approximated by a model where the logarithmic slope steepens monotonically with radius; from -3 at the luminous edge of the galaxy to -4 or steeper near the virial radius of the system. Such spatial distribution is consistent with that of Galactic and M31 globular clusters, suggesting that many of the globulars were brought in by accretion events, in a manner akin to the classic Searle-Zinn scenario. The outer stellar spheroid is supported by a velocity dispersion tensor with a substantial and radially increasing radial anisotropy. These properties distinguish the stellar halo from the dark matter component, which is more isotropic in velocity space, as well as from some tracers of the outer spheroid such as satellite galaxies. Most stars in the outer halo formed in progenitors that have since merged with the central galaxy; very few stars in the halo are contributed by satellites that survive as self-bound entities at the present. These features are in reasonable agreement with recent observations of the outer halo of the MW, of M31, and of other isolated spirals, and suggest that all of these systems underwent an early period of active merging, as envisioned in hierarchical models of galaxy formation.
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We investigate the nature of the physical structures giving rise to damped Lyman alpha absorption systems (DLAS) at high redshift. In particular, we examine the suggestion that rapidly rotating large disks are the only viable explanation... more
We investigate the nature of the physical structures giving rise to damped Lyman alpha absorption systems (DLAS) at high redshift. In particular, we examine the suggestion that rapidly rotating large disks are the only viable explanation for the characteristic observed asymmetric profiles of low ionization absorption lines. We demonstrate using hydrodynamic simulations of galaxy formation in a cosmological context that irregular protogalactic clumps can reproduce the observed velocity width distribution and asymmetries of the absorption profiles equally well. The velocity broadening in the simulated clumps is due to a mixture of rotation, random motions, infall and merging. The observed velocity width correlates with the virial velocity of the dark matter halo of the forming protogalactic clump (v_{wid} ~ 0.6 times v_{vir} for the median values with a large scatter of order a factor two between different lines-of-sight). The typical virial velocity of the halos required to give rise to the DLAS population is about 100 km/s and most standard hierarchical structure formation scenarios can easily account even for the largest observed velocity widths. We conclude that the evidence that DLAS at high redshift are related to large rapidly rotating disks with v_circ >= 200 km/s is not compelling.
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The APL space for the Nordstrom catalogue exhibits a wealth of substructure, much of which can be linked to dynamical perturbations induced by spiral arms and the Galactic bar. However, our analysis also reveals a statistically... more
The APL space for the Nordstrom catalogue exhibits a wealth of substructure, much of which can be linked to dynamical perturbations induced by spiral arms and the Galactic bar. However, our analysis also reveals a statistically significant excess of stars on orbits of common (moderate) eccentricity, analogous to the pattern expected for merger debris. Besides being dynamically peculiar, the 274 stars in these substructures have very distinct metallicity and age distributions, providing further evidence of their extra-Galactic provenance. It is possible to identify among these stars, three coherent Groups with characteristic ages and metallicities, that, in all likelihood, correspond to the remains of disrupted satellites. [abridged]