arXiv subjects

David Burstein

Publications and source records attributed to David Burstein.

At least 37 records · Page 2Linked to original sources

arXiv2000

The Peculiar Motions of Early-Type Galaxies in Two Distant Regions VI: The Maximum Likelihood Gaussian Algorithm

The EFAR project is designed to measure the properties and peculiar motions of early-type galaxies in two distant regions. Here we describe the maximum likelihood algorithm we developed to investigate the correlations between the parameters of the EFAR database. One-, two-, and three-dimensional gaussian models are constructed to determine the mean value and intrinsic spread of the parameters, and the slopes and intrinsic parallel and orthogonal spread of the Mgb'-Mg2, Mg2-sigma, Mgb'-sigma relations, and the Fundamental Plane. In the latter case, the cluster peculiar velocities are also determined. We show that this method is superior to ``canonical'' approaches of least-squares type, which give biased slopes and biased peculiar velocities. We test the algorithm with Monte Carlo simulations of mock EFAR catalogues and derive the systematic and random errors on the estimated parameters. We find that random errors are always dominant. We estimate the influence of systematic errors due to the way clusters were selected and the hard limits and uncertainties in the selection function parameters for the galaxies. We explore the influence of uniform distributions in the Fundamental Plane parameters and the errors. We conclude that the mean peculiar motions of the EFAR clusters can be determined reliably. In particular, the placement of the two EFAR sample regions relative to the Lauer and Postman dipole allows us to strongly constrain the amplitude of the bulk motion in this direction.

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arXiv2000

The Cuspy LINER Nucleus of the S0/a Galaxy NGC 2681

The nucleus of the bulge-dominated, multiply-barred S0/a galaxy NGC 2681 is studied in detail, using high resolution Hubble Space Telescope FOC and NICMOS imaging and FOS spectroscopy. The ionised gas central velocity dispersion is found to increase by a factor ~2 when narrowing the aperture from R~1.5" (ground) to R~0.1" (FOS). Dynamical modeling of these velocity dispersions suggests that NGC 2681 does host a supermassive black hole (BH) for which one can estimate a firm mass upper limit M_BH < 6*10^7 Solar Masses. This upper limit is consistent with the relation between the central BH mass and velocity dispersion M_BH - sigma known for other galaxies. The emission line ratios place the nucleus of NGC 2681 among LINERs. It is likely that the emission line region comes from a rather mild, but steady, feeding of gas to the central BH in this galaxy. The inner stellar population lacks any measurable color gradient (to a radius of 0.6 kpc) from the infrared to the ultraviolet, consistently with FOC, FOS and IUE data, all indicating that this system underwent a starburst ~1 Gyr ago that encompassed its whole interior, down to its very center. The most likely source of such a widely-distributed starburst is the dumping of tidally-extruded gas from a galaxy neighbor. If so, then NGC 2681 can be considered as the older brother of M82, seen face-on as opposed to the edge-on view we have for M82.

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arXiv2000

The Quest for the Dominant Stellar Population in the Giant Elliptical NGC 5018

Newly obtained HST/WFPC2 images of the disturbed elliptical galaxy NGC 5018 show that the average amount of internal reddening due to the its complex ``dust web'' is as low as E(B-V)~0.02 within the IUE aperture, thus implying that its observed and intrinsic energy distributions do not differ significantly down to UV wavelengths. This, in turn, is quite relevant to the current debate on the age of its dominant stellar population.

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arXiv1999

EFAR peculiar velocities and bulk motions

The EFAR project has measured peculiar motions in two distant volumes of the universe using Fundamental Plane (FP) distances for 85 clusters with cz=6000-15000 km/s. The scatter in distance about the FP is observed to be 20% per galaxy for EFAR sample, resulting in peculiar velocities with a median precision of 1075 km/s for the 50 clusters with 3 or more galaxies. We find that there is no evidence for a large bulk flow within either of the two volumes sampled by the EFAR clusters. The measured bulk motion in both regions is small and consistent with zero. The Lauer and Postman (1994) bulk motion is ruled out at the 4-sigma level. There is no evidence supporting the SMAC (Hudson et al. 1999) or LP10K (Willick 1999) bulk motions, but the directionality of the EFAR sample would only allow a weak (2-sigma) detection at best.

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arXiv1999

Elliptical Galaxy Dynamics: The Issues Pertaining to Galaxy Formation

How elliptical galaxy dynamics relate to galaxy structure, stellar populations, spiral galaxies and environment are reviewed. The evidence assembled shows that most, if not all, galaxies originally classified as gE contain disks within them. Taken together, the existing evidence are most consistent with the gravitational, hierarchical, clustering, merging (HCM) concept that all galaxies, including gE, are formed from the combination of much smaller galaxies. Within the HCM picture, the evidence also strongly suggests that the subunits which go into forming galaxies must be related in specific ways both to the mass of the galaxy they will form, and to the environment in which the galaxy forms. Despite the extensive data that we now have on galaxies that can constrain their formation history, the lack of a physical understanding of the stellar initial mass function prevents us from developing realistic physical models for galaxy formation.

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arXiv1999

A Re-Examination of the Origins of the Peculiar Velocity Field Within the Local Supercluster

The recent re-evaulation of the peculiar velocity field outside the Local Supercluster (Dekel et al. 1999, ApJ 522) has permitted a re-examination of the origins of the peculiar velocity field within the Local Supercluster using the Mark III Catalog of Galaxy Peculiar Velocities for spiral galaxies. It is shown that the large-scale coherent pattern of peculiar velocities within the LSC are well-fit by a combination of the Outside-Region-(generated)-Motions (O-R-M) from the Potent model with a Virgocentric infall pattern that produces 220 km/s of Virgocentric infall at the Local Group (LG) towards the Virgo cluster moving at 88 km/s towards the LG. The part of the Cosmic Microwave Background motion of the LG this model cannot fit is that perpendicular to the Supergalactic plane (the SGZ direction). On what size scale the remaing 270 km/s CMB SGZ motion of the LG is shared by neighboring galaxies cannot be determined from the present data set, but may be found if we can accurately measure galaxy distances close to the Galactic plane.

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arXiv1999

The Mini AGN at the Center of the Elliptical Galaxy NGC 4552 with HST

The complex phenomenology shown by the UV-bright, variable spike first detected with the Hubble Space Telescope (HST) at the center of the otherwise normal galaxy NGC 4552 is further investigated with both HST imaging (FOC) and spectroscopy (FOS). HST/FOC images taken in 1991, 1993, and 1996 in the near UV have been analyzed in a homogeneous fashion, showing that the central spike has brightened by a factor ~4.5 between 1991 and 1993, and has decreased its luminosity by a factor ~2.0 between 1993 and 1996. FOS spectroscopy extending from the near UV to the red side of the optical spectrum reveals a strong UV continuum over the spectrum of the underlying galaxy, along with several emission lines in both the UV and the optical ranges. In spite of the low luminosity of the UV continuum of the spike (~3*10^5 Lsolar), the spike is definitely placed among AGNs by current diagnostics based on the emission line intensity ratios, being just on the borderline between Seyferts and LINERs. Line profiles are very broad, and both permitted and forbidden lines are best modelled with a combination of broad and narrow components, with FWHM of ~3000 km s^-1 and ~700 km s^-1, respectively. This evidence argues for the variable central spike being produced by a modest accretion event onto a central massive black hole (BH), with the accreted material having possibly being stripped from a a star in a close fly by with the BH. The 1996 broad Halpha luminosity of this mini-AGN is ~5.6*10^37 erg s^-1, about a factor of two less than that of the nucleus of NGC 4395, heretofore considered to be the faintest known AGN.

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arXiv1999

Central UV Spikes in two Galactic Spheroids

FOS spectra and FOC photometry of two centrally located, UV-bright spikes in the elliptical galaxy NGC 4552 and the bulge-dominated early spiral NGC 2681, are presented. These spectra reveal that such point-like UV sources detected by means of HST within a relatively large fraction ~15% of bulges can be related to radically different phenomena. While the UV unresolved emission in NGC 4552 represents a transient event likely induced by an accretion event onto a supermassive black hole, the spike seen at the center of NGC 2681 is not variable and it is stellar in nature.

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arXiv1999

Objects in NGC 205 Resolved into Stellar Associations by HST Ultraviolet Imaging

We have obtained high resolution UV images with the HST+WFPC2 of the central region of the dwarf elliptical galaxy NGC 205. Our images reveal that many of the hot UV stars previously detected and studied from the ground are actually multiple systems, open clusters and star associations. We have performed photometry of two such clusters and we find our data are consistent with stellar ages of 50 and 100 Myr, respectively. From the number of massive stars in NGC 205 we estimate that the star formation episode in this galaxy has turned ~1,000 Msolar of gas into stars over the last 100 Myr.

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arXiv1998

The peculiar motions of early-type galaxies in two distant regions - II. The spectroscopic data

We present the spectroscopic data for the galaxies studied in the EFAR project, which is designed to measure the properties and peculiar motions of early-type galaxies in two distant regions. We have obtained 1319 spectra of 714 early-type galaxies over 33 observing runs on 10 different telescopes. We describe the observations and data reductions used to measure redshifts, velocity dispersions and the Mgb and Mg2 Lick linestrength indices. Detailed simulations and intercomparison of the large number of repeat observations lead to reliable error estimates for all quantities. The measurements from different observing runs are calibrated to a common zeropoint or scale before being combined, yielding a total of 706 redshifts, 676 velocity dispersions, 676 Mgb linestrengths and 582 Mg2 linestrengths. The median estimated errors in the combined measurements are dcz=20 km/s, dsigma/sigma=9.1%, dMgb/Mgb=7.2% and dMg2=0.015 mag. Comparison of our measurements with published datasets shows no systematic errors in the redshifts or velocity dispersions and only small zeropoint corrections to bring our linestrengths onto the standard Lick system. We have assigned galaxies to physical clusters by examining the line-of-sight velocity distributions based on EFAR and ZCAT redshifts, together with the projected distributions on the sky. We derive mean redshifts and velocity dispersions for these clusters, which will be used in estimating distances and peculiar velocities and to test for trends in the galaxy population with cluster mass. The spectroscopic parameters presented here for 706 galaxies combine high quality data, uniform reduction and measurement procedures, and detailed error analysis. They form the largest single set of velocity dispersions and linestrengths for early-type galaxies published to date.

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arXiv1998

The peculiar motions of early-type galaxies in two distant regions - V. The Mg-sigma relation, age and metallicity

We examine the Mg-sigma relation for early-type galaxies in the EFAR sample and its dependence on cluster properties. A maximum likelihood fit gives global Mg-sigma relations of Mgb'=0.131log(sigma)-0.131 and Mg2=0.257log(sigma)-0.305, with intrinsic scatter of 0.016 mag in Mgb' and 0.023 mag in Mg2. The zeropoint for cD galaxies is higher than for E/S0 galaxies, implying cDs are older and/or more metal-rich than E/S0s with the same sigma. Mg-sigma zeropoint variations between clusters are consistent with the number of galaxies observed per cluster and the global intrinsic scatter in Mg-sigma. We find no significant correlation between the Mg-sigma zeropoint and the cluster velocity dispersion, X-ray luminosity or X-ray temperature over a wide range in cluster mass. We compare the intrinsic scatter in the Mg-sigma and Fundamental Plane (FP) relations with stellar population models to constrain the dispersion in ages, metallicities and M/L ratios for early-type galaxies at fixed sigma. Variations in age alone or metallicity alone cannot explain the measured intrinsic scatter in both Mg-sigma and the FP. We derive the joint constraints on the dispersion in age and metallicity implied by the scatter in the Mg-sigma and FP relations for a simple Gaussian model. We find upper limits on the dispersions at fixed sigma of 32% in dt/t and 38% in dZ/Z if variations in age and metallicity are uncorrelated; only strongly anti-correlated variations lead to significantly higher upper limits. The joint distribution of residuals from the Mg-sigma and FP relations is only marginally consistent with a model having no correlation between age and metallicity, and is better-matched by a model in which age and metallicity variations are moderately anti-correlated, with younger galaxies being more metal-rich. (Abridged)

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arXiv1998

Ring structure and warp of NGC5907 -- Interaction with dwarf galaxies

The edge-on, nearby spiral galaxy NGC5907 has long been used as the prototype of a ``non-interacting'' warped galaxy. We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture. First, a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy. The ring is elliptical in shape with the center of NGC5907 close to one of the ring's foci. This suggests the ring material is in orbit around NGC5907. No gaseous component to the ring has been detected either with deep H$α$ images or in Very Large Array (VLA) HI 21-cm line maps. The visible material in the ring has an integrated luminosity <= 10^8 L_sun and its brightest part has a color R-I ~ 0.9. All of these properties are consistent with the ring being a tidally-disrupted dwarf spheroidal galaxy. Second, we find that NGC5907 has a dwarf companion galaxy, PGC54419, projected to be only 36.9 kpc from the center of NGC5907, close in radial velocity (ΔV = 45 km s^{-1}) to the giant spiral galaxy. This dwarf is seen at the tip of the HI warp and in the direction of the warp. Hence, NGC5907 can no longer be considered ``non-interacting,'' but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies. These results, coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies, suggest that tidal interaction with companions, even if containing a mere 1% of the mass of the parent galaxy, might be sufficient to excite the warps found in the disks of many large spiral galaxies.

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arXiv1997

Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters

We present absorption-line strengths on the Lick/IDS line-strength system of 381 galaxies and 38 globular clusters in the 4000--6400 Åregion. All galaxies were observed at Lick Observatory between 1972 and 1984 with the Cassegrain Image Dissector Scanner spectrograph, making this study one of the largest homogeneous collections of galaxy spectral line data to date. We also present a catalogue of nuclear velocity dispersions used to correct the absorption-line strengths onto the stellar Lick/IDS system. Extensive discussion of both random and systematic errors of the Lick/IDS system is provided. Indices are seen to fall into three families: α-element-like indices (including CN, Mg, Na D, and TiO_2) that correlate positively with velocity dispersion; Fe-like indices (including Ca, the G band, TiO_1, and all Fe indices) that correlate only weakly with velocity dispersion and the αindices; and Hβwhich anti-correlates with both velocity dispersion and the αindices. C_2 4668 seems to be intermediate between the αand Fe groups. These groupings probably represent different element abundance families with different nucleosynthesis histories.

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arXiv1997

Global Relationships Among the Physical Properties of Stellar Systems

The kappa-space three-dimensional parameter system was originally defined for the physical properties of dynamically hot galaxies. Here we define self-consistent kappa-parameters for disk galaxies, galaxy groups and clusters, and globular clusters and project an integrated view of the major classes of self-gravitating, equilibrium stellar systems in the universe. Six different fundamental planes exist that are interrelated and interconnected - the ``cosmic metaplane.'' The kappa-3 vs. kappa-1 projection (M/L vs. Mass) views all planes edge-on, M/L increasing or constant with Mass. Within the cosmic metaplane (kappa-2 vs. kappa-1 projection), no stellar system violates the rule that kappa-1 + kappa-2 < 8, meaning the maximum volume luminosity density of stellar systems varies as a (K times M^{-4/3}; the ``zone of exclusion''). Galaxies march away from ZOE as a function of Hubble type: DHGs closest, Sm-Irr's furthest away. We test current ideas of galaxy formation via hierarchical clustering and merging and find them to be broadly consistent with the properties of the cosmic metaplane. Four key questions are raised by this study: Why do galaxy groups form a bridge between galaxy clusters and galaxies? Why do galaxies march away from the ZOE? Why are isotropic galaxies only found in a limited mass range? What causes M/L to vary so smoothly with M to produce the cosmic metaplane? This study is but the first step along a long road, limited by existing data to the B passband of major stellar systems, whose light is dominated by stars. K-band data would be high desirable, as well as data that can probe the gaseous content (cold and hot) of stellar systems, and data for other classes of stellar systems.

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arXiv1997

Spectrophotometry of 237 stars in 7 Open Clusters

Photoelectric spectrophotometry is presented for 237 stars in the Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC~4665, and M39 open clusters. 16 bandpasses were observed from 350 nm to 778 nm, with 3.2 to 6.4 nm bandwidth. Data are standardized to the Hayes-Latham system to mutual accuracy of 0.016 mag per passband. By comparison to SIMBAD-available BV and ubvy colors on the one hand, and to 1993 Kurucz synthetic spectra on the other, we show our data to be accurate to 0.01 mag for the 13 passbands at or above 400 nm, and 0.02 mag for the 3 passbands below 400 nm. We also show that the scatter in the fits of the spectrophotometric colors and the uvby filter colors is a reasonable way to identify the observations of which specific stars are accurate to 1-sigma, 2-sigma, ... The very good agreement between the models and these data verifies the accuracy of these data, and also verifies the usefulness of the Kurucz models to define spectrophotometry for stars in this temperature range (>5000 K). These data define accurate spectrophotometry of bright, open cluster stars that can be used as a secondary flux calibration for CCD-based spectrophotometric surveys.

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arXiv1996

An Einstein X-ray Survey of Optically-Selected Galaxies: I. Data

We present the results of a complete Einstein Imaging Proportional Counter (IPC) X-ray survey of optically-selected galaxies from Shapley-Ames Catalog, Uppsala General Catalog and the European Southern Observatory Catalog. X-ray fluxes for 1018 galaxies have been surveyed, 21% of which are detected. 827 galaxies have either independent distance estimates or radial velocities. Associated optical, redshift and distance data has been assembled. The five large data tables in the paper are in easily-accessible ascii formats with an ADC-style README file, for easy electronic data handling. The accuracy of the X-ray fluxes has been checked in three different ways; all are consistent with the derived X-ray fluxes being of $\le$0.1 dex accuracy. In particular, there is agreement with previous published X-ray fluxes for galaxies in common with Roberts et al. (1991) and Fabbiano et al. (1992). The data presented here will be used in further studies to characterize the X-ray output of galaxies of various morphological types and thus to enable the determination of the major sources contributing to the X-ray emission from galaxies.

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arXiv1996

Measuring Omega

We were asked to debate the value of the cosmological mass-density parameter Omega. Is Omega_m=1 in accordance with the simplest model? Is Omega_m much smaller as indicated by some observations? There is conflicting evidence. We lay out the various methods for measuring Omega_m, mention new developments and current estimates, and focus on prospects versus the associated difficulties. We try to shed light on the uncertainties that are responsible for the span of estimates for Omega_m. We divide the methods into the following four classes: a. Global measures of the properties of space-time that constrain combinations of Omega_m and the other cosmological parameters (Lambda, Ho, to). b. Virialized Systems. Nonlinear dynamics within galaxies and clusters on comoving scales 1-10 Mpc/h. c. Large-scale structure. Mildly-nonlinear gravitational dynamics of fluctuations on scales 10-100 Mpc/h, in particular cosmic flows. d. Growth rate of fluctuations from the last scattering of the CMB or from high redshift galaxies to the present. Methods (b) typically yield low values of Omega_m=0.2-0.3. Methods (a) and (c) typically indicate higher values of Omega_m=0.4-1.

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arXiv1996

Homogeneous Velocity-Distance Data for Peculiar Velocity Analysis. III. The Mark III Catalog of Galaxy Peculiar Velocities

This is the third in a series of papers in which we assemble and analyze a homogeneous catalog of peculiar velocity data. In Papers I and II, we described the Tully-Fisher (TF) redshift-distance samples that constitute the bulk of the catalog, and our methodology for obtaining mutually consistent TF calibrations for these samples. In this paper, we supply further technical details of the treatment of the data, and present a subset of the catalog in tabular form. The full catalog, known as the Mark III Catalog of Galaxy Peculiar Velocities, is available in accessible on-line databases, as described herein. The electronic catalog incorporates not only the TF samples discussed in Papers I and II, but also elliptical galaxy Dn-sigma samples originally presented elsewhere. The relative zeropointing of the elliptical and spiral data sets is discussed here. The basic elements of the Mark III Catalog are the observables for each object (redshift, magnitude, velocity width, etc.) and inferred distances derived from the TF or Dn-sigma relations. Malmquist bias-corrected distances are computed for each catalog object using density fields obtained from the IRAS 1.2 Jy redshift survey. Distances for both individual objects and groups are provided. A variety of auxiliary data, including distances and local densities predicted from the IRAS redshift survey reconstruction method, are tabulated as well. We study the distributions of TF residuals for three of our samples and conclude that they are well-approximated as Gaussian. For the Mathewson et al. sample we demonstrate a significant decrease in TF scatter with increasing velocity width. We test for, but find no evidence of, a correlation between TF residuals and galaxy morphology.

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