Showing papers in "The Astronomical Journal in 2003"

The usno-b catalog

Abstract: USNO-B is an all-sky catalog that presents positions, proper motions, magnitudes in various optical passbands, and star/galaxy estimators for 1,042,618,261 objects derived from 3,643,201,733 separate observations. The data were obtained from scans of 7435 Schmidt plates taken for the various sky surveys during the last 50 years. USNO-B1.0 is believed to provide all-sky coverage, completeness down to V = 21, 02 astrometric accuracy at J2000, 0.3 mag photometric accuracy in up to five colors, and 85% accuracy for distinguishing stars from nonstellar objects. A brief discussion of various issues is given here, but the actual data are available from the US Naval Observatory Web site and others.

The IRAS Revised Bright Galaxy Sample

Abstract: IRAS flux densities, redshifts, and infrared luminosities are reported for all sources identified in the IRAS Revised Bright Galaxy Sample (RBGS), a complete flux-limited survey of all extragalactic objects with total 60 μm flux density greater than 5.24 Jy, covering the entire sky surveyed by IRAS at Galactic latitudes |b| > 5°. The RBGS includes 629 objects, with median and mean sample redshifts of 0.0082 and 0.0126, respectively, and a maximum redshift of 0.0876. The RBGS supersedes the previous two-part IRAS Bright Galaxy Samples (BGS1+BGS2), which were compiled before the final (Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGS also makes use of more accurate and consistent automated methods to measure the flux of objects with extended emission. The RBGS contains 39 objects that were not present in the BGS1+BGS2, and 28 objects from the BGS1+BGS2 have been dropped from RBGS because their revised 60 μm flux densities are not greater than 5.24 Jy. Comparison of revised flux measurements for sources in both surveys shows that most flux differences are in the range ~5%–25%, although some faint sources at 12 and 25 μm differ by as much as a factor of 2. Basic properties of the RBGS sources are summarized, including estimated total infrared luminosities, as well as updates to cross identifications with sources from optical galaxy catalogs established using the NASA/IPAC Extragalactic Database. In addition, an atlas of images from the Digitized Sky Survey with overlays of the IRAS position uncertainty ellipse and annotated scale bars is provided for ease in visualizing the optical morphology in context with the angular and metric size of each object. The revised bolometric infrared luminosity function, (Lir), for infrared-bright galaxies in the local universe remains best fit by a double power law, (L) ∝ Lα, with α = -0.6(±0.1) and α = -2.2(±0.1) below and above the "characteristic" infrared luminosity L ~ 1010.5 L⊙, respectively. A companion paper provides IRAS High Resolution (HIRES) processing of over 100 RBGS sources where improved spatial resolution often provides better IRAS source positions or allows for deconvolution of close galaxy pairs.

The 2MASS Large Galaxy Atlas

Abstract: We present the largest galaxies as seen in the near-infrared (1–2 μm), imaged with the Two Micron All Sky Survey (2MASS), ranging in angular size from 1' to 15. We highlight the 100 largest in the sample. The galaxies span all Hubble morphological types, including elliptical galaxies, normal and barred spirals, and dwarf and peculiar classes. The 2MASS Large Galaxy Atlas provides the necessary sensitivity and angular resolution to examine in detail morphologies in the near-infrared, which may be radically different from those in the optical. Internal structures such as spirals, bulges, warps, rings, bars, and star formation regions are resolved by 2MASS. In addition to large mosaic images, the atlas includes astrometric, photometric, and shape global measurements for each galaxy. A comparison of fundamental measures (e.g., surface brightness, Hubble type) is carried out for the sample and compared with the Third Reference Catalogue. We further showcase NGC 253 and M51 (NGC 5194/5195) to demonstrate the quality and depth of the data. The atlas represents the first uniform, all-sky, dust-penetrated view of galaxies of every type, as seen in the near-infrared wavelength window that is most sensitive to the dominant mass component of galaxies. The images and catalogs are available through the NASA/IPAC Extragalactic Database and Infrared Science Archive and are part of the 2MASS Extended Source Catalog.

Astrometric Calibration of the Sloan Digital Sky Survey

Abstract: The astrometric calibration of the Sloan Digital Sky Survey is described. For point sources brighter than r ~ 20, the astrometric accuracy is 45 mas rms per coordinate when reduced against the USNO CCD Astrograph Catalog and 75 mas rms when reduced against Tycho-2, with an additional 20–30 mas systematic error in both cases. The rms errors are dominated by anomalous refraction and random errors in the primary reference catalogs. The relative astrometric accuracy between the r filter and each of the other filters (u, g, i, z) is 25–35 mas rms. At the survey limit (r ~ 22), the astrometric accuracy is limited by photon statistics to approximately 100 mas rms for typical seeing. Anomalous refraction is shown to contain components correlated over 2° or more on the sky.

The first data release of the sloan digital sky survey

Abstract: The Sloan Digital Sky Survey (SDSS) has validated and made publicly available its First Data Release. This consists of 2099 deg2 of five-band (u, g, r, i, z) imaging data, 186,240 spectra of galaxies, quasars, stars and calibrating blank sky patches selected over 1360 deg2 of this area, and tables of measured parameters from these data. The imaging data go to a depth of r ≈ 22.6 and are photometrically and astrometrically calibrated to 2% rms and 100 mas rms per coordinate, respectively. The spectra cover the range 3800–9200 A, with a resolution of 1800–2100. This paper describes the characteristics of the data with emphasis on improvements since the release of commissioning data (the SDSS Early Data Release) and serves as a pointer to extensive published and on-line documentation of the survey.

The Chandra Deep Field North Survey. XIII. 2 Ms Point-Source Catalogs

Abstract: We present point-source catalogs for the ?2 Ms exposure of the Chandra Deep Field North, currently the deepest X-ray observation of the universe in the 0.5?8.0 keV band. Five hundred and three (503) X-ray sources are detected over an ?448 arcmin2 area in up to seven X-ray bands. Twenty (20) of these X-ray sources lie in the central ?5.3 arcmin2 Hubble Deep Field North (13,600 sources deg-2). The on-axis sensitivity limits are ?2.5 ? 10-17 ergs cm-2 s-1 (0.5?2.0 keV) and ?1.4 ? 10-16 ergs cm-2 s-1 (2?8 keV). Source positions are determined using matched-filter and centroiding techniques; the median positional uncertainty is ?03. The X-ray colors of the detected sources indicate a broad variety of source types, although absorbed AGNs (including a small number of possible Compton-thick sources) are clearly the dominant type. We also match lower significance X-ray sources to optical counterparts and provide a list of 79 optically bright (R 23) lower significance Chandra sources. The majority of these sources appear to be starburst and normal galaxies. The average backgrounds in the 0.5?2.0 keV and 2?8 keV bands are 0.056 and 0.135 counts Ms-1 pixel-1, respectively. The background count distributions are very similar to Poisson distributions. We show that this ?2 Ms exposure is approximately photon limited in all seven X-ray bands for regions close to the aim point, and we predict that exposures up to ?25 Ms (0.5?2.0 keV) and ?4 Ms (2?8 keV) should remain nearly photon limited. We demonstrate that this observation does not suffer from source confusion within ?6' of the aim point, and future observations are unlikely to be source-confusion limited within ?3' of the aim point even for source densities exceeding 100,000 deg-2. These analyses directly show that Chandra can achieve significantly higher sensitivities in an efficient, nearly photon-limited manner and be largely free of source confusion. To allow consistent comparisons, we have also produced point-source catalogs for the ?1 Ms Chandra Deep Field South (CDF-S). Three hundred and twenty-six (326) X-ray sources are included in the main Chandra catalog, and an additional 42 optically bright X-ray sources are included in a lower significance Chandra catalog. We find good agreement with the photometry of the previously published CDF-S catalogs; however, we provide significantly improved positional accuracy.

A Survey of z > 5.7 Quasars in the Sloan Digital Sky Survey. II. Discovery of Three Additional Quasars at z > 6

Abstract: We present the discovery of three new quasars at z > 6 in ~ 1300 deg2 of Sloan Digital Sky Survey imaging data, J114816.64+525150.3 (z = 6.43), J104845.05+463718.3 (z = 6.23), and J163033.90+401209.6 (z = 6.05). The first two objects have weak Lyα emission lines; their redshifts are determined from the positions of the Lyman break. They are only accurate to ~0.05 and could be affected by the presence of broad absorption line systems. The last object has a Lyα strength more typical of lower redshift quasars. Based on a sample of six quasars at z > 5.7 that cover 2870 deg2 presented in this paper and in Paper I, we estimate the comoving density of luminous quasars at z ~ 6 and M1450 5.7 quasars and high-resolution, ground-based images (seeing ~04) of three additional z > 5.7 quasars show that none of them is gravitationally lensed. The luminosity distribution of the high-redshift quasar sample suggests the bright-end slope of the quasar luminosity function at z ~ 6 is shallower than Ψ ∝ L-3.5 (2 σ), consistent with the absence of strongly lensed objects.

Spectral Irradiance Calibration in the Infrared. XIV. The Absolute Calibration of 2MASS

Abstract: Element by element, we have combined the optical components in the three cameras of the Two Micron All Sky Survey (2MASS), and incorporated detector quantum efficiency curves and site-specific atmospheric transmissions, to create three relative spectral response curves (RSRs). We provide the absolute 2MASS attributes associated with "zero magnitude" in the JHKs bands so that these RSRs may be used for synthetic photometry. The RSRs tie 2MASS to the "Cohen-Walker-Witteborn" framework of absolute photometry and stellar spectra for the purpose of using 2MASS data to support the development of absolute calibrators for the Infrared Array Camera and pairwise cross-calibrators between all three SIRTF instruments. We examine the robustness of these RSRs to changes in water vapor within a night. We compare the observed 2MASS magnitudes of 33 stars (converted from the precision optical calibrators of Landolt and Carter-Meadows into absolute infrared calibrators from 1.2 to 35 μm) with our predictions, thereby deriving 2MASS "zero-point offsets" from the ensemble. These offsets are the final ingredients essential to merge 2MASS JHKs data with our other absolutely calibrated bands and stellar spectra, and to support the creation of faint calibration stars for SIRTF.

The Canadian Galactic Plane Survey

Abstract: The Canadian Galactic Plane Survey (CGPS) is a project to combine radio, millimeter, and infrared surveys of the Galactic plane to provide arcminute-scale images of all major components of the interstellar medium over a large portion of the Galactic disk. We describe in detail the observations for the low-frequency component of the CGPS, the radio surveys carried out at the Dominion Radio Astrophysical Observatory (DRAO), and summarize the properties of the merged database of surveys that comprises the CGPS. The DRAO Synthesis Telescope surveys have imaged a 73° section of the Galactic plane, using ~85% of the telescope time between 1995 April and 2000 June. The observations provide simultaneous radio continuum images at two frequencies, 408 and 1420 MHz, and spectral-line images of the λ = 21 cm transition of neutral atomic hydrogen. In the radio continuum at 1420 MHz, dual-polarization receivers provide images in all four Stokes parameters. The surveys cover the region 742 < l < 1473, with latitude extent -36 < b < +56 at 1420 MHz and -67 < b < +87 at 408 MHz. By integration of data from single-antenna observations, the survey images provide complete information on all scales of emission structures down to the resolution limit, which is just below 1' × 1' csc δ at 1420 MHz and 34 × 34 csc δ at 408 MHz. The continuum images have a dynamic range of several thousand, yielding essentially noise-limited images with an rms of ~0.3 mJy beam-1 at 1420 MHz and ~3 mJy beam-1 at 408 MHz. The spectral-line data are noise limited with rms brightness temperature ΔTB ~ 3 K in a 0.82 km s-1 channel. The complete CGPS data set, including the DRAO surveys and data at similar resolution in 12CO (1–0) and in infrared emission from dust, all imaged to an identical Galactic coordinate grid and map projection, are being made publicly available through the Canadian Astronomy Data Centre.

An efficient targeting strategy for multiobject spectrograph surveys: The Sloan digital sky survey "tiling" algorithm

Abstract: Large surveys using multiobject spectrographs require automated methods for deciding how to efficiently point observations and how to assign targets to each pointing. The Sloan Digital Sky Survey (SDSS) will observe around 10 6 spectra from targets distributed over an area of about 10,000 deg 2 , using a multiobject fiber spectrograph that can simultaneously observe 640 objects in a circular field of view (referred to as a ‘‘ tile ’’) 1=49 in radius. No two fibers can be placed closer than 55 00 during the same observation; multiple targets closer than this distance are said to ‘‘ collide.’’ We present here a method of allocating fibers to desired targets given a set of tile centers that includes the effects of collisions and that is nearly optimally efficient and uniform. Because of large-scale structure in the galaxy distribution (which form the bulk of the SDSS targets), a naive covering of the sky with equally spaced tiles does not yield uniform sampling. Thus, we present a heuristic for perturbing the centers of the tiles from the equally spaced distribution that provides more uniform completeness. For the SDSS sample, we can attain a sampling rate of greater than 92% for all targets, and greater than 99% for the set of targets that do not collide with each other, with an efficiency greater than 90% (defined as the fraction of available fibers assigned to targets). The methods used here may prove useful to those planning other large surveys.

Estimating Fixed-Frame Galaxy Magnitudes in the Sloan Digital Sky Survey

Abstract: Broadband measurements of flux for galaxies at different redshifts measure different regions of the rest-frame galaxy spectrum. Certain astronomical questions, such as the evolution of the luminosity function of galaxies, require transforming these inherently redshift-dependent magnitudes into redshift-independent quantities. To prepare to address these astronomical questions, investigated in detail in subsequent papers, we fit spectral energy distributions (SEDs) to broadband photometric observations in the context of the optical observations of the Sloan Digital Sky Survey (SDSS). Linear combinations of four spectral templates can reproduce the five SDSS magnitudes of all galaxies to the precision of the photometry. Expressed in the appropriate coordinate system, the locus of the coefficients multiplying the templates is planar and, in fact, nearly linear. The resulting reconstructed SEDs can be used to recover fixed-frame magnitudes over a range of redshifts. This process yields consistent results in the sense that, within each sample, the intrinsic colors of similar type galaxies are nearly constant with redshift. We compare our results with simpler interpolation methods and galaxy spectrophotometry from the SDSS. The software that generates these results is publicly available and easily adapted to handle a wide range of galaxy observations.

VLT/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies. I. Nucleosynthesis and Abundance Ratios*

Abstract: We have used the Ultraviolet Echelle Spectrograph (UVES) on Kueyen (UT2) of the Very Large Telescope to take spectra of 15 individual red giants in the Sculptor, Fornax, Carina, and Leo I dwarf spheroidal galaxies (dSph's). We measure the abundances of α-, iron peak, first s-process, second s-process, and r-process elements. No dSph giants in our sample show the deep mixing abundance pattern (O and sometimes Mg depleted, while Na and Al are enhanced) seen in nearly all globular clusters. At a given metallicity the dSph giants exhibit lower [el/Fe] abundance ratios for the α-elements than stars in the Galactic halo. The low α abundances at low metallicities can be caused by a slow star formation rate and contribution from Type Ia SNe, and/or a small star formation event (low total mass) and mass-dependent Type II SN yields. In addition, Leo I and Sculptor exhibit a declining even-Z [el/Fe] pattern with increasing metallicity, while Fornax exhibits no significant slope. In contrast, Carina shows a large spread in the even-Z abundance pattern, even over small metallicity ranges, as might be expected from a bursting star formation history. The metal-poor stars in these dSph galaxies ([Fe/H] < -1) have halo-like s- and r-process abundances, but not every dSph exhibits the same evolution in the s- and r-process abundance pattern. Carina, Sculptor, and Fornax show a rise in the s-/r-process ratio with increasing metallicity, evolving from a pure r-process ratio to a solar-like s- and r-process ratio. On the other hand, Leo I, appears to show an r-process–dominated ratio over the range in metallicities sampled. At present, we attribute these differences in the star formation histories of these galaxies. Comparison of the dSph abundances with those of the halo reveals some consistencies with the Galactic halo. In particular, Nissen & Shuster found that their metal-rich, high Rmax high zmax halo stars exhibited low [α/Fe], [Na/Fe] and [Ni/Fe] abundance ratios. In the same abundance range our dSph exhibit the same abundance pattern, supporting their suggestions that disrupted dSph's may explain up to 50% of the metal-rich halo. Unfortunately, similar comparisons with the metal-poor Galactic halo have not revealed similar consistencies, suggesting that the majority of the metal-poor Galactic halo could not have been formed from objects similar to the dSph studied here. We use the dSph abundances to place new constraints on the nucleosynthetic origins of several elements. We attribute differences in the evolution of [Y/Fe] in the dSph stars versus the halo stars to a very weak AGB or SN Ia yield of Y (especially compared with Ba). That a lower and flatter Ba/Y ratio is seen in the halo is most likely a result of the pattern being erased by the large metallicity dispersion in the halo. Also, we find [Cu/Fe] and [Mn/Fe] are flat and halo-like over the metallicity city range -2 < [Fe/H] < -1.2, and that the [Cu/α] ratios are flat. Combining these abundances with knowledge of the age spread in these galaxies suggests that SNe Ia are not the main site for the production of Cu (and Mn) in very metal-poor stars. We suggest that metallicity-dependent SN yields may be more promising.

A Direct Measurement of Major Galaxy Mergers at z 3

Abstract: This paper presents direct evidence for hierarchical galaxy assembly out to redshifts z ~ 3. We identify major mergers using the model-independent CAS (concentration, asymmetry, clumpiness) physical morphological system on galaxies detected, and photometrically selected, in the WFPC2 and NICMOS Hubble Deep Field North. We specifically use the asymmetric distributions of rest-frame optical light measured through the asymmetry parameter (A) to determine the fraction of galaxies undergoing major mergers as a function of redshift (z), stellar mass (M*), and absolute magnitude (MB). We find that the fraction of galaxies consistent with undergoing a major merger increases with redshift for all galaxies, but most significantly, at 5?10 ? confidence, for the most luminous and massive systems. The highest merger fractions we find are 40%?50% for galaxies with MB 1010 M? at z > 2.5, e.g., objects identified as Lyman-break galaxies. Using these results, we model the merger fraction evolution in the form fm(A, M*, MB, z) = f0 ? (1 + z). We find mA values ~4?6 for the most luminous and massive galaxies, while lower mass and less luminous galaxies have smaller mA values. We use these merger fractions, combined with merger timescales calculated from N-body simulations, to derive galaxy merger rates to z ~ 3. We also use stellar masses of HDF-N galaxies to determine the mass accretion rate of field galaxies involved in major mergers. We find an average stellar mass accretion rate of G ~ 4 ? 108 M? Gyr-1 per galaxy at z ~ 1 for galaxies with stellar masses M* > 109 M?. This accretion rate changes with redshift as G = 1.6 ? 108(1 + z)0.99?0.32 M? Gyr-1 per galaxy. We also find that the fraction of stellar mass density in galaxies involved in major mergers increases with redshift, with a peak mass fraction ~0.5 for the brightest, MB 1010 M?, systems near z ~ 2.5. By comparing merger fractions predicted in cold dark matter semianalytic models with our results we find a reasonably good agreement for the largest and brightest systems, although we find more low-mass galaxy mergers at lower redshifts than what these models predict.

The Progenitors of Dwarf Spheroidal Galaxies

Abstract: The gas-deficient dwarf spheroidal (dSph) galaxies present an evolutionary puzzle that we explore in 40 early-type and late-type dwarfs in the Local Group and nearby field. Although dSph’s experienced star formation over extended time spans in their youths, today all but one are completely free of detectable interstellar material, even in the Fornax dSph, where stars formed in the last 100 Myr. Combining photometric and spectroscopic stellar metallicity estimates for red giant branches with high-sensitivity H i 21 cm line data from the literature, we show that the well-established offset in luminosity-metallicity relationships for dSph’s and dwarf irregular (dIrr) galaxies exists also when confining the comparison to their old stellar populations: dSph’s have higher mean stellar metallicities for a fixed optical luminosity. Evidently star formation in younger dSph’s was more vigorous than in the youthful dIrr’s, leading to more efficient enrichment. Dwarf galaxies, whose locus in the luminosity-metallicity diagram is consistent with that of dSph’s, even when baryonic luminosities are considered, are the ‘‘ transition-type dwarfs ’’ Phoenix, DDO 210, LGS 3, Antlia, and KKR 25. These dwarfs have mixed dIrr/dSph morphologies, low stellar masses, low angular momentum, and H i contents of at most a few 10 6 M� . Unlike dIrr’s many transition-type dwarfs would closely resemble dSph’s if their gas were removed, as required to become a dSph; they are likely dSph progenitors. As gas removal is the key factor for such a transition, we consider the empirical evidence in favor and against various gas removal processes. We suggest that internal gas removal mechanisms are inadequate and favor ram-pressure stripping to clean the bulk of interstellar matter from galaxies to make dSph’s. A combination of initial conditions and environment seems to support the formation of dSph’s: nearby dSph’s appear to form from small galaxies with active early star formation, whose evolution halts due to externally induced gas loss. Transition-type dwarfs, then, are dSph’s that kept their interstellar medium and therefore should replace dSph’s in isolated locations where stripping is ineffective.

Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.

Abstract: We have embarked on a project, under the aegis of the Nearby Stars (NStars)/Space Interferometry Mission Preparatory Science Program, to obtain spectra, spectral types, and, where feasible, basic physical parameters for the 3600 dwarf and giant stars earlier than M0 within 40 pc of the Sun. In this paper, we report on the results of this project for the first 664 stars in the northern hemisphere. These results include precise, homogeneous spectral types, basic physical parameters (including the effective temperature, surface gravity, and overall metallicity [M/H]), and measures of the chromospheric activity of our program stars. Observed and derived data presented in this paper are also available on the project's Web site.

Meeting the Cool Neighbors. V. A 2MASS-Selected Sample of Ultracool Dwarfs

Abstract: We present the initial results of our effort to create a statistically robust, volume-limited sample of ultracool dwarfs from the Two Micron All Sky Survey Second Incremental Data Release. We are engaged in a multifaceted search for nearby late-type objects, and this is the first installment of our search using purely photometric selection. The goal of this work is a determination of the low-mass star and brown dwarf luminosity function in the infrared. Here we outline the construction of the sample, dubbed 2MU2, and present our first results, including the discovery of 186 M7–L6 dwarfs—47 of which are likely to be within 20 pc of the Sun. These results represent 66% of the ultracool candidates in our sample yet constitute a 127% increase in the number of ultracool dwarfs known within the volume searched (covering 40% of the sky out to 20 pc). In addition, we have identified 10 M4–M6.5 objects that are likely to be within 20 pc (or within 1 σ). Finally, based on these initial data, we present a preliminary luminosity function and discuss several interesting features of the partial sample presented here. Once our sample is complete, we will use our measured luminosity function to constrain the mass function of low-mass stars and brown dwarfs.

HST Photometry of Dwarf Elliptical Galaxies in Coma, and an Explanation for the Alleged Structural Dichotomy between Dwarf and Bright Elliptical Galaxies

Abstract: As part of a research program exploring how and why dwarf elliptical (dE) galaxies depart from the fundamental plane defined by luminous elliptical (E) galaxies, we have analyzed archival Hubble Space Telescope F606W images of a sample of 18 dE galaxy candidates in the Coma Cluster We model the full radial extent of their light profiles by simultaneously fitting a point-spread function (PSF) convolved Sersic R1/n model and, when necessary, either a central point source or a central PSF-convolved Gaussian Nucleation was detected in all but two of our final sample of 15 dE galaxies When detected, the luminosities of the central component, Lnuc, scale with the host galaxy luminosity Lgal such that Lnuc = 10476±010(Lgal/107)087±026 We confirm that the light profiles of the underlying host galaxies display systematic departures from an exponential model that are correlated with the model-independent host galaxy luminosity and are not due to biasing from the nuclear component The Pearson correlation coefficient between log n and central galaxy surface brightness μ0 (excluding the flux from extraneous central components) is -083 at a significance level of 9999% Excluding one outlier, the Pearson correlation coefficient between the logarithm of the Sersic index n and the host galaxy magnitude is -077 at a significance of 999% We explain the observed relationship between dE galaxy luminosity and the inner logarithmic profile slope γ' as a by-product of the correlation between luminosity and Sersic index n Including, from the literature, an additional 232 dE and E galaxies spanning 10 mag in absolute magnitude M, the dE galaxies are shown to display a continuous sequence with the brighter E galaxies, such that μ0 brightens linearly with M until core formation causes the most luminous (MB -205) E galaxies to deviate from this relation The different behavior of dE and E galaxies in the M-μe (and M-μe) diagram and the μe–log Re diagram has nothing to do with core formation and is in fact expected from the continuous and linear relation between M and μ0, and M and log n

Red and reddened quasars in the sloan digital sky survey

Abstract: We investigate the overall continuum and emission-line properties of quasars as a function of their optical/UV spectral energy distributions. Our sample consists of 4576 quasars from the Sloan Digital Sky Survey (SDSS) that were chosen using homogeneous selection criteria. Expanding on our previous work, which demonstrated that the optical/UV color distribution of quasars is roughly Gaussian but with a red tail, here we distinguish between (1) quasars that have intrinsically blue (optically flat) power-law continua, (2) quasars that have intrinsically red (optically steep) power-law continua, and (3) quasars whose colors are inconsistent with a single power-law continuum. We find that 273 (6.0%) of the quasars in our sample fall into the latter category and appear to be redder because of SMC-like dust extinction and reddening rather than because of synchrotron emission. Even though the SDSS quasar survey is optically selected and flux-limited, we demonstrate that it is sensitive to dust reddened quasars with E(B-V) 0.5, assuming a classical SMC extinction curve. The color distribution of our SDSS quasar sample suggests that the population of moderately dust reddened, but otherwise normal (i.e., type 1) quasars is smaller than the population of unobscured quasars: we estimate that a further 10% of the quasar population with Mi < -25.61 is missing from the SDSS sample because of extinction, bringing the total fraction of dust-reddened quasars to 15% of broad-line quasars. We also investigate the emission- and absorption-line properties of these quasars as a function of color and comment on how some of these results relate to Boroson-Green–type eigenvectors. Quasars with intrinsically red (optically steep) power-law continua tend to have narrower Balmer lines and weaker C IV, C III], He II, and 3000 A bump emission as compared with bluer (optically flatter) quasars. The change in strength of the 3000 A bump appears to be dominated by the Balmer continuum and not by Fe II emission. The dust-reddened quasars have even narrower Balmer lines and weaker 3000 A bumps, in addition to having considerably larger equivalent widths of [O II] and [O III] emission. The fraction of broad absorption line quasars (BALQSOs) increases from ~3.4% for the bluest quasars to perhaps as large as 20% for the dust-reddened quasars, but the intrinsic color distribution will be much bluer if all BALQSOs are affected by dust reddening.

Candidate type ii quasars from the sloan digital sky survey. i. selection and optical properties of a sample at 0.3 < z < 0.83

Abstract: Type II quasars are the long-sought luminous analogs of type 2 (narrow emission line) Seyfert galaxies, suggested by unification models of active galactic nuclei (AGNs) and postulated to account for an appreciable fraction of the cosmic hard X-ray background. We present a sample of 291 type II AGNs at redshifts 0.3 < Z < 0.83 from the spectroscopic data of the Sloan Digital Sky Survey. These objects have narrow (FWHM < 2000 km s-1), high equivalent width emission lines with high-ionization line ratios. We describe the selection procedure and discuss the optical properties of the sample. About 50% of the objects have [O III] λ5008 line luminosities in the range 3 × 108–1010 L⊙, comparable to those of luminous (-27 < MB < -23) quasars; this, along with other evidence, suggests that the objects in the luminous subsample are type II quasars.

Optical and Infrared Properties of the 2 Ms Chandra Deep Field North X-Ray Sources

Abstract: We present an optical and near-infrared catalog for the X-ray sources in the ?2 Ms Chandra observation of the Hubble Deep Field North region. We have high-quality multicolor imaging data for all 503 X-ray point sources in the X-ray?selected catalog and reliable spectroscopic redshifts for 284. We spectroscopically identify six high-redshift (z > 1) type II quasars (L2?8keV > 1044 ergs s-1) in our sample. Our spectroscopic completeness for the R ? 24 sources is 87%. The spectroscopic redshift distribution shows two broad redshift spikes that have clearly grown over those originally seen in the ?1 Ms exposure. The spectroscopically identified extragalactic sources already comprise 75% of the measured 2?8 keV light. Redshift slices versus 2?8 keV flux show that an impressive 54% of the measured 2?8 keV light arises from sources at z 5.7 that would classify them as extremely red objects (EROs). The photometric redshifts of these EROs are all between z ~ 1.5 and z ~ 2.5. We use our wide wavelength coverage to determine rest-frame colors for the X-ray sources with spectroscopic or photometric redshifts. We find that many of the X-ray sources have the rest-frame colors of evolved red galaxies and that there is very little evolution in these colors with redshift. We also determine absolute magnitudes and find that many of the non?broad-line sources are more luminous than M, even at high redshifts. We therefore infer that deep X-ray observations may provide an effective way of locating M* galaxies with colors similar to present-day early-type galaxies to high redshifts.

Early-Type Galaxies in the Sloan Digital Sky Survey. III. The Fundamental Plane

Abstract: A magnitude-limited sample of nearly 9000 early-type galaxies in the redshift range 0.01 ≤ z ≤ 0.3 was selected from the Sloan Digital Sky Survey (SDSS) using morphological and spectral criteria. The fundamental plane relation in this sample is Ro ∝ σ1.49±0.05I in the r* band. It is approximately the same in the g*, i*, and z* bands. Relative to the population at the median redshift in the sample, galaxies at lower and higher redshifts have evolved only a little. If the fundamental plane is used to quantify this evolution, then the apparent magnitude limit can masquerade as evolution; once this selection effect has been accounted for, the evolution is consistent with that of a passively evolving population that formed the bulk of its stars about 9 Gyr ago. One of the principal advantages of the SDSS sample over previous samples is that the galaxies in it lie in environments ranging from isolation in the field to the dense cores of clusters. The fundamental plane shows that galaxies in dense regions are slightly different from galaxies in less dense regions.

The iau 2000 resolutions for astrometry celestial mechanics and metrology in the relativistic framework: explanatory supplement

Abstract: We discuss the IAU resolutions B1.3, B1.4, B1.5, and B1.9 that were adopted during the 24th General Assembly in Manchester, 2000, and provides details on and explanations for these resolutions. It is explained why they present significant progress over the corresponding IAU 1991 resolutions and why they are necessary in the light of present accuracies in astrometry, celestial mechanics, and metrology. In fact, most of these resolutions are consistent with astronomical models and software already in use. The metric tensors and gravitational potentials of both the Barycentric Celestial Reference System and the Geocentric Celestial Reference System are defined and discussed. The necessity and relevance of the two celestial reference systems are explained. The transformations of coordinates and gravitational potentials are discussed. Potential coefficients parameterizing the post-Newtonian gravitational potentials are expounded. Simplified versions of the time transformations suitable for modern clock accuracies are elucidated. Various approximations used in the resolutions are explicated and justified. Some models (e.g., for higher spin moments) that serve the purpose of estimating orders of magnitude have actually never been published before.

Multiplicity of Nearby Free-floating Ultracool Dwarfs: A Hubble Space Telescope WFPC2 Search for Companions

Abstract: We present Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) observations of a sample of 134 ultracool objects (spectral types later than M7) coming from the Deep Near Infrared Survey (DENIS), Two Micron All Sky Survey (2MASS), and Sloan Digital Sky Survey (SDSS), with distances estimated to range from 7 to 105 pc. Fifteen new ultracool binary candidates are reported here. Eleven known binaries are confirmed, and orbital motion is detected in some of them. We estimate that the closest binary systems in this sample have periods between 5 and 20 yr, and thus dynamical masses will be derived in the near future. For the calculation of binary frequency, we restrict ourselves to systems with distances less than 20 pc. After correction of the binaries bias, we find a ratio of visual binaries (at the HST limit of detection) of around 10%, and that ~15% of the 26 objects within 20 pc are binary systems with separations between 1 and 8 AU. The observed frequency of ultracool binaries is similar to that of binaries with G-type primaries in the separation range from 2.1 to 140 AU. There is also a clear deficit of ultracool binaries with separations greater than 15 AU, and a possible tendency for the binaries to have mass ratios near unity. Most systems have indeed visual and near-infrared brightness ratios between 1 and 0.3. We discuss our results in the framework of current scenarios for the formation and evolution of free-floating brown dwarfs.

The Frequency and Radio Properties of Broad Absorption Line Quasars

Abstract: A sample of 67 broad absorption line quasars (BALQSOs) from the Large Bright Quasar Survey (LBQS) is used to estimate the observed and intrinsic fraction of BAL quasars in optically selected samples at intermediate (BJ 18.5) magnitudes. The observed BALQSO fraction in the redshift range 1.5 ≤ z ≤ 3.0 is 15% ± 3%. A well-determined empirical k-correction, to allow for the differences in the spectral energy distributions of non-BALQSOs and BALQSOs shortward of 2100 A in the rest frame, is applied to the sample. The result is an estimate of the intrinsic fraction of BALQSOs of 22% ± 4% for the redshift range 1.5 ≤ z ≤ 3.0. This value is twice that commonly cited for the occurrence of BALQSOs in optically selected samples, and the figure is in reasonable agreement with that from a preliminary analysis of the SDSS Early Data Release. The fraction of BALQSOs predicted to be present in an optical survey with flux limits equivalent to that of the FIRST Bright Quasar Survey (FBQS) is shown to be 20%. The BALQSO fractions derived from the FBQS and the LBQS suggest that optically bright BALQSOs are half as likely as non-BALQSOs to be detectable as S1.4 GHz 1 mJy radio sources.

Early-type Galaxies in the Sloan Digital Sky Survey. II. Correlations between Observables

Abstract: A magnitude-limited sample of nearly 9000 early-type galaxies, in the redshift range 0.01 ≤ z ≤ 0.3, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. The sample was used to study how early-type galaxy observables, including luminosity L, effective radius Ro, surface brightness Io, color, and velocity dispersion σ, are correlated with one another. Measurement biases are understood with mock catalogs that reproduce all of the observed scaling relations and their dependences on fitting technique. At any given redshift, the intrinsic distribution of luminosities, sizes, and velocity dispersions in our sample are all approximately Gaussian. A maximum likelihood analysis shows that σ ∝ L0.25±0.012, Ro ∝ L0.63±0.025, and Ro ∝ I-0.75±0.02 in the r* band. In addition, the mass-to-light ratio within the effective radius scales as Mo/L ∝ L0.14±0.02 or Mo/L ∝ M, and galaxies with larger effective masses have smaller effective densities: Δo ∝ M. These relations are approximately the same in the g*, i*, and z* bands. Relative to the population at the median redshift in the sample, galaxies at lower and higher redshifts have evolved only little, with more evolution in the bluer bands. The luminosity function is consistent with weak passive luminosity evolution and a formation time of about 9 Gyr ago.

Probing the Ionization State of the Universe at z > 6*

Abstract: We present high signal-to-noise ratio Keck ESI spectra of the two quasars known to have Gunn-Peterson absorption troughs, SDSS J1030+0524 (z = 6.28) and SDSS J1148+5251 (z = 6.37). The Lyα and Lyβ troughs for SDSS J1030+0524 are very black and show no evidence of any emission over a redshift interval of ~0.2, starting at z = 6. On the other hand, SDSS J1148+5251 shows a number of emission peaks in the Lyβ Gunn-Peterson trough along with a single weak peak in the Lyα trough. The Lyα emission has corresponding Lyβ emission, suggesting that it is indeed a region of lower optical depth in the intergalactic medium at z = 6.08. The stronger Lyβ peaks in the spectrum of SDSS J1148+5251 could also conceivably be the result of "leaks" in the intergalactic medium (IGM), but we suggest instead that they are Lyα emission from an intervening galaxy at z = 4.9. This hypothesis gains credence from a strong complex of C IV absorption at the same redshift and from the detection of continuum emission in the Lyα trough at the expected brightness. If this proposal is correct, the quasar light has probably been magnified through gravitational lensing by the intervening galaxy. The Stromgren sphere observed in the absorption spectrum of SDSS J1148+5251 is significantly smaller than expected on the basis of its brightness, which is consistent with the hypothesis that the quasar is lensed. If our argument for lensing is correct, the optical depths derived from the troughs of SDSS J1148+5251 are only lower limits [albeit still quite strong, with τ(Lyα) > 16 inferred from the Lyβ trough]. The Lyβ absorption trough of SDSS J1030+0524 gives the single best measurement of the IGM transmission at z > 6, with an inferred optical depth of τ(Lyα) > 22.

Continuum and Emission-Line Properties of Broad Absorption Line Quasars

Abstract: We investigate the continuum and emission-line properties of 224 broad absorption line quasars (BALQSOs) with 0.9 z 4.4 drawn from the Sloan Digital Sky Survey Early Data Release, which contains 3814 bona fide quasars. We find that low-ionization BALQSOs (LoBALs) are significantly reddened as compared with normal quasars, in agreement with previous work. High-ionization BALQSOs (HiBALs) are also more reddened than the average non-BALQSO. Assuming SMC-like dust reddening at the quasar redshift, the amount of reddening needed to explain HiBALs is E(B-V) ~ 0.023 and LoBALs is E(B-V) ~ 0.077 (compared with the ensemble average of the entire quasar sample). We find that there are differences in the emission-line properties between the average HiBAL, LoBAL, and non-BAL quasar. These differences, along with differences in the absorption-line troughs, may be related to intrinsic quasar properties such as the slope of the intrinsic (unreddened) continuum; more extreme absorption properties are correlated with bluer intrinsic continua. Despite the differences among BALQSO subtypes and non-BALQSOs, BALQSOs appear to be drawn from the same parent population as non-BALQSOs when both are selected by their UV/optical properties. We find that the overall fraction of traditionally defined BALQSOs, after correcting for color-dependent selection effects due to different SEDs of BALQSOs and non-BALQSOs, is 13.4% ± 1.2% and shows no significant redshift dependence for 1.7 ≤ z ≤ 3.45. After a rough completeness correction for the effects of dust extinction, we find that approximately one in every six quasars is a BALQSO.

Early-Type Galaxies in the Sloan Digital Sky Survey. I. The Sample

Abstract: A sample of nearly 9000 early-type galaxies, in the redshift range 0.01 ≤ z ≤ 0.3, was selected from the Sloan Digital Sky Survey (SDSS) using morphological and spectral criteria. This paper describes how the sample was selected, presents examples of images and seeing-corrected fits to the observed surface brightness profiles, describes our method for estimating K-corrections, and shows that the SDSS spectra are of sufficiently high quality to measure velocity dispersions accurately. It also provides catalogs of the measured photometric and spectroscopic parameters. In related papers, these data are used to study how early-type galaxy observables, including luminosity, effective radius, surface brightness, color, and velocity dispersion, are correlated with one another.

A New Empirical Model for the Structural Analysis of Early-Type Galaxies, and A Critical Review of the Nuker Model*

Abstract: The Nuker law was designed to match the inner few (~3–10) arcseconds of predominantly nearby (30 Mpc) early-type galaxy light profiles; it was never intended to describe an entire profile. The Sersic model, on the other hand, was developed to fit the entire profile; however, because of the presence of partially depleted galaxy cores, the Sersic model cannot always describe the very inner region. We have therefore developed a new empirical model consisting of an inner power law, a transition region, and an outer Sersic model to connect the inner and outer structure of elliptical galaxies. We have additionally explored the stability of the Nuker model parameters. Surprisingly, none are found to be stable quantities; all are shown to vary systematically with a profile's fitted radial extent, and often by more than 100%. Considering elliptical galaxies spanning a range of 7.5 mag, we reveal that the central stellar densities of the underlying host galaxies increase with galaxy luminosity until the onset of core formation, detected only in the brightest elliptical galaxies. We suggest that the so-called power-law galaxies may actually be described by the Sersic model over their entire radial range.

VLT/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies. II. Implications for Understanding Galaxy Evolution*

Abstract: We have used the Ultraviolet Visual-Echelle Spectrograph (UVES) on Kueyen (UT2) of the Very Large Telescope to take spectra of 15 individual red giant stars in the centers of four nearby dwarf spheroidal galaxies (dSph's): Sculptor, Fornax, Carina, and Leo I. We measure the abundance variations of numerous elements in these low-mass stars with a range of ages (1–15 Gyr old). This means that we can effectively measure the chemical evolution of these galaxies with time. Our results show a significant spread in metallicity with age, but an overall trend consistent with what might be expected from a closed- (or perhaps leaky-) box chemical evolution scenario over the last 10–15 Gyr. We make comparisons between the properties of stars observed in dSph's and in our Galaxy's disk and halo, as well as globular cluster populations in our Galaxy and in the Large Magellanic Cloud. We also look for the signature of the earliest star formation in the universe, which may have occurred in these small systems. We notice that each of these galaxies show broadly similar abundance patterns for all elements measured. This suggests a fairly uniform progression of chemical evolution with time, despite quite a large range of star formation histories. It seems likely that these galaxies had similar initial conditions, and that they evolve in a similar manner with star formation occurring at a uniformly low rate, even if at different times. With our accurate measurements we find evidence for small variations in abundances, which seem to be correlated to variations in star formation histories between different galaxies. The α-element abundances suggest that dSph chemical evolution has not been affected by very high mass stars (>15–20 M⊙). The abundance patterns we measure for stars in dSph's are significantly different from those typically observed in the disk, bulge, and inner halo of our Galaxy. This means that, as far as we can tell from the (limited) data available to date, it is impossible to construct a significant fraction of our disk, inner halo, or bulge from stars formed in dSph's such as we see today, which subsequently merged into our own. Any merger scenario involving dSph's has to occur in the very early universe while they are still gas-rich, so the majority of mass transfer is gas and few stars.