arXiv subjects

M. J. Kurtz

Publications and source records attributed to M. J. Kurtz.

16 recordsLinked to original sources

arXiv2006

myADS-arXiv - a Tailor-Made, Open Access, Virtual Journal

The myADS-arXiv service provides the scientific community with a one stop shop for staying up-to-date with a researcher's field of interest. The service provides a powerful and unique filter on the enormous amount of bibliographic information added to the ADS on a daily basis. It also provides a complete view with the most relevant papers available in the subscriber's field of interest. With this service, the subscriber will get to know the lastest developments, popular trends and the most important papers. This makes the service not only unique from a technical point of view, but also from a content point of view. On this poster we will argue why myADS-arXiv is a tailor-made, open access, virtual journal and we will illustrate its unique character.

cs.DL↗

arXiv2004

CAIRNS: The Cluster And Infall Region Nearby Survey II. Environmental Dependence of Infrared Mass-to-Light Ratios

CAIRNS (Cluster And Infall Region Nearby Survey) is a spectroscopic survey of the infall regions surrounding nine nearby rich clusters of galaxies. In Paper I, we used redshifts within $\sim 10\Mpc$ of the centers of the clusters to determine the mass profiles of the clusters based on the phase space distribution of the galaxies. Here, we use 2MASS photometry and an additional \ncziinew redshifts to investigate the environmental dependence of near-infrared mass-to-light ratios. In the virial regions, the halo occupation function is non-linear; the number of bright galaxies per halo increases more slowly than the mass of the halo. On larger scales, the light contained in galaxies is less clustered than the mass in rich clusters. Specifically, the mass-to-light ratio inside the virial radius is a factor of $1.8\pm0.3$ larger than that outside the virial radius. This difference could result from changing fractions of baryonic to total matter or from variations in the efficiency of galaxy formation or disruption with environment. The average mass-to-light ratio $M/L_K = 53\pm 5 h$ implies $Ω_m = 0.18\pm 0.03$ (statistical) using the luminosity density based on 2dFGRS data. These results are difficult to reconcile with independent methods which suggest higher $Ω_m$. Reconciling these values by invoking bias requires that the typical value of $M/L_K$ changes significantly at densities of $\lesssim3ρ_c$.

astro-ph↗

arXiv2003

Surveying the Inner Halo of the Galaxy with 2MASS-Selected Horizontal Branch Candidates

We use 2MASS photometry to select blue horizontal branch (BHB) candidates covering the sky |b|>15 deg. A 12.5 50 deg. We insert simulated star streams into the data and conclude that the high Galactic latitude BHB candidates are consistent with having no ~5 deg wide star stream with density greater than 0.33 objects deg^-2 at the 95% confidence level. The absence of structure suggests there have been no major accretion events in the inner halo in the last few Gyr. However, at low Galactic latitudes a two-point angular correlation analysis reveals structure on angular scales <1 deg. This structure is apparently associated with stars in the thick disk, and has a physical scale of 10-100 pc. Interestingly, such structures are expected by cosmological simulations that predict the majority of the thick disk may arise from accretion and disruption of satellite mergers.

astro-ph↗

arXiv2003

CAIRNS: The Cluster And Infall Region Nearby Survey I. Redshifts and Mass Profiles

The CAIRNS (Cluster And Infall Region Nearby Survey) project is a spectroscopic survey of the infall regions surrounding eight nearby, rich, X-ray luminous clusters of galaxies. We collect 15665 redshifts (3471 new or remeasured) within \sim 5-10 Mpc of the centers of the clusters, making it the largest study of the infall regions of clusters. We determine cluster membership and the mass profiles of the clusters based on the phase space distribution of the galaxies. All of the clusters display decreasing velocity dispersion profiles. The mass profiles are fit well by functional forms based on numerical simulations but exclude an isothermal sphere. Specifically, NFW and Hernquist models provide good descriptions of cluster mass profiles to their turnaround radii. Our sample shows that the predicted infall pattern is ubiquitous in rich, X-ray luminous clusters over a large mass range. The caustic mass estimates are in excellent agreement with independent X-ray estimates at small radii and with virial estimates at intermediate radii. The mean ratio of the caustic mass to the X-ray mass is 1.03\pm0.11 and the mean ratio of the caustic mass to the virial mass (when corrected for the surface pressure term) is 0.93\pm0.07. We further demonstrate that the caustic technique provides reasonable mass estimates even in merging clusters.

astro-ph↗

arXiv2003

The Century Survey Galactic Halo Project I: Stellar Spectral Analysis

The Century Survey Galactic Halo Project is a photometric and spectroscopic survey from which we select relatively blue stars (V-R<0.30 mag) as probes of the Milky Way halo. The Survey strip spans the range of Galactic latitude 35<b<88 deg, allowing us to study the nature of populations of stars and their systematic motions as a function of Galactic latitude. One of our primary goals is to use blue horizontal-branch stars to trace potential star streams in the halo, and to test the hierarchical model for the formation of the Galaxy. In this paper we discuss spectroscopy and multi-passband photometry for a sample of 764 blue stars in the Century Survey region. Our sample consists predominantly of A- and F-type stars. We describe our techniques for determination of radial velocities, effective temperatures, metallicities, and surface gravities. Based on these measurements, we derive distance estimates by comparison with a set of calibrated isochrones. We devote special attention to the classification of blue horizontal-branch stars, and compare the results obtained from the application of the techniques of Kinman et al., Wilhelm et al., and Clewley et al. We identify 55 blue horizontal-branch stars. Our large sample of stars also uncovers a number of unusual objects, including three carbon-enhanced stars, a late B-type star located 0.8 kpc above the Galactic plane, and a DZ white dwarf.

astro-ph↗

arXiv2001

Infrared Mass-to-Light Profile Throughout the Infall Region of the Coma Cluster

Using a redshift survey of 1779 galaxies and photometry from the 2-Micron All-Sky Survey (2MASS) covering 200 square degrees, we calculate independent mass and light profiles for the infall region of the Coma cluster of galaxies. The redshift survey is complete to $K_s=12.2$ (622 galaxies), 1.2 magnitudes fainter than $M^*_{K_s}$ at the distance of Coma. We confirm the mass profile obtained by Geller, Diaferio, & Kurtz. The enclosed mass-to-light ratio measured in the $K_s$ band is approximately constant to a radius of $10 \Mpc$, where $M/L_{K_s}= 75\pm 23\mlsun$, in agreement with weak lensing results on similar scales. Within $2.5\Mpc$, X-ray estimates yield similar mass-to-light ratios (67$\pm32h$). The constant enclosed mass-to-light ratio with radius suggests that K-band light from bright galaxies in clusters traces the total mass on scales $\lesssim10 \Mpc$. Uncertainties in the mass profile imply that the mass-to-light ratio inside $r_{200}$ may be as much as a factor of 2.5 larger than that outside $r_{200}$. These data demonstrate that K-band light is not positively biased with respect to the mass; we cannot rule out antibias. These results imply $Ω_m = 0.17 \pm 0.05$. Estimates of possible variations in $M/L_{K_s}$ with radius suggest that the density parameter is no smaller than $Ω_m \approx 0.08$.

astro-ph↗

arXiv2001

Redshifts for 2410 Galaxies in the Century Survey Region

The `Century Survey' strip covers 102 square degrees within the limits 8.5h \leq α_{1950} \leq 16.5h, 29.0 degrees \leq δ_{1950} \leq 30.0 degrees. The strip passes through the Corona Borealis supercluster and the outer region of the Coma cluster. Within the Century Survey region, we have measured 2410 redshifts which constitute four overlapping complete redshift surveys: (1) 1728 galaxies with Kron-Cousins R_{phot} \leq 16.13 covering the entire strip, (2) 507 galaxies with R_{phot} \leq 16.4 in the right ascension range 8h 32m \leq α_{1950} \leq 10h 45m, (3) 1251 galaxies with absorption- and K-corrected R_{CCD, corr} \leq 16.2 covering the right ascension range 8.5h \leq α_{1950} \leq 13.5h and (4) 1255 galaxies with absorption- and K-corrected V_{CCD, corr} \leq 16.7 also covering the right ascension range 8.5h \leq α_{1950} \leq 13.5h. All of these redshift samples are more than 98 % complete to the specified magnitude limit.

astro-ph↗

arXiv2001

Star Formation in a Complete Spectroscopic Survey of Galaxies

The 15R-North galaxy redshift survey is a uniform spectroscopic survey (S/N $\sim $10) covering the range 3650---7400Åfor 3149 galaxies with median redshift 0.05. The sample is 90% complete to $R=15.4$. The median slit covering fraction is 24% of the galaxy, apparently sufficient to minimize the effects of aperture bias on the EW(H$α$). Forty-nine percent of the galaxes in the survey have one or more emission lines detected at $\geq 2 σ$. In agreement with previous surveys, the fraction of absorption-line galaxies increases steeply with galaxy luminosity. We use H$β$, O[III], H$α$, and [N\II] to discriminate between star-forming galaxies and AGNs. We use the EW(H$α$ + [N\II]) to estimate the Scalo birthrate parameter, $b$, the ratio of the current star formation rate to the time averaged star formation rate. Finally, we examine the way galaxies of different spectroscopic type trace the large-scale galaxy distribution.

astro-ph↗

arXiv2000

The NASA Astrophysics Data System: Overview

The NASA Astrophysics Data System Abstract Service has become a key component of astronomical research. It provides bibliographic information daily, or near daily, to a majority of astronomical researchers worldwide. We describe the history of the development of the system and its current status. We show several examples of how to use the ADS, and we show how ADS use has increased as a function of time. Currently it is still increasing exponentially, with a doubling time for number of queries of 17 months. Using the ADS logs we make the first detailed model of how scientific journals are read as a function of time since publication. The impact of the ADS on astronomy can be calculated after making some simple assumptions. We find that the ADS increases the efficiency of astronomical research by 333 Full Time Equivalent (2000 hour) research years per year, and that the value of the early development of the ADS for astronomy, compared with waiting for mature technologies to be adopted, is 2332 FTE research years. The ADS is available at http://adswww.harvard.edu/.

astro-ph↗

arXiv2000

The NASA Astrophysics Data System: The Search Engine and its User Interface

The ADS Abstract and Article Services provide access to the astronomical literature through the World Wide Web (WWW). The forms based user interface provides access to sophisticated searching capabilities that allow our users to find references in the fields of Astronomy, Physics/Geophysics, and astronomical Instrumentation and Engineering. The returned information includes links to other on-line information sources, creating an extensive astronomical digital library. Other interfaces to the ADS databases provide direct access to the ADS data to allow developers of other data systems to integrate our data into their system. The search engine is a custom-built software system that is specifically tailored to search astronomical references. It includes an extensive synonym list that contains discipline specific knowledge about search term equivalences. Search request logs show the usage pattern of the various search system capabilities. Access logs show the world-wide distribution of ADS users. The ADS can be accessed at http://adswww.harvard.edu

astro-ph↗

arXiv2000

The NASA Astrophysics Data System: Architecture

The powerful discovery capabilities available in the ADS bibliographic services are possible thanks to the design of a flexible search and retrieval system based on a relational database model. Bibliographic records are stored as a corpus of structured documents containing fielded data and metadata, while discipline-specific knowledge is segregated in a set of files independent of the bibliographic data itself. The creation and management of links to both internal and external resources associated with each bibliography in the database is made possible by representing them as a set of document properties and their attributes. To improve global access to the ADS data holdings, a number of mirror sites have been created by cloning the database contents and software on a variety of hardware and software platforms. The procedures used to create and manage the database and its mirrors have been written as a set of scripts that can be run in either an interactive or unsupervised fashion. The ADS can be accessed at http://adswww.harvard.edu

astro-ph↗

arXiv2000

The NASA Astrophysics Data System: Data Holdings

Since its inception in 1993, the ADS Abstract Service has become an indispensable research tool for astronomers and astrophysicists worldwide. In those seven years, much effort has been directed toward improving both the quantity and the quality of references in the database. From the original database of approximately 160,000 astronomy abstracts, our dataset has grown almost tenfold to approximately 1.5 million references covering astronomy, astrophysics, planetary sciences, physics, optics, and engineering. We collect and standardize data from approximately 200 journals and present the resulting information in a uniform, coherent manner. With the cooperation of journal publishers worldwide, we have been able to place scans of full journal articles on-line back to the first volumes of many astronomical journals, and we are able to link to current version of articles, abstracts, and datasets for essentially all of the current astronomy literature. The trend toward electronic publishing in the field, the use of electronic submission of abstracts for journal articles and conference proceedings, and the increasingly prominent use of the World Wide Web to disseminate information have enabled the ADS to build a database unparalleled in other disciplines. The ADS can be accessed at http://adswww.harvard.edu

astro-ph↗

arXiv1999

The Mass Profile of the Coma Galaxy Cluster

We use a new redshift survey complete to m_R=15.4 within 4.25 deg from the center of the Coma cluster to measure the mass profile of the cluster to r=5.5 Mpc/h. We extend the profile to r=10 Mpc/h with a further sample complete to m_R=15.4 in 42% of the area within a 10 deg radius and to m_{Zw}=15.5 in the remaining area. Galaxies within this region are falling onto the cluster on moderately radial orbits and thus do not satisfy virial equilibrium. Nonetheless, identification of the caustics in redshift space provides an estimate of the gravitational potential at radius r and hence of the system mass, M(<10 Mpc/h)=(1.65+-0.41)10^{15} M_\odot/h (1-sigma error). Previous mass estimates derived from optical and X-ray observations are limited to r<2.5 Mpc/h. Our mass profile is consistent with these estimates but extends to distances four times as large. Over the entire range, the mass increases with r at the rate expected for a Navarro, Frenk & White (1997) density profile.

astro-ph↗

arXiv1999

The Dynamics of Poor Systems of Galaxies

We assemble and observe a sample of poor galaxy systems that is suitable for testing N-body simulations of hierarchical clustering (Navarro, Frenk, & White 1997; NFW) and other dynamical halo models (e.g., Hernquist 1990). We (1) determine the parameters of the density profile rho(r) and the velocity dispersion profile sigma(R), (2) separate emission-line galaxies from absorption-line galaxies, examining the model parameters and as a function of spectroscopic type, and (3) for the best-behaved subsample, constrain the velocity anisotropy parameter, beta, which determines the shapes of the galaxy orbits. The NFW universal profile and the Hernquist (1990) model both provide good descriptions of the spatial data. In most cases an isothermal sphere is ruled out. Systems with declining sigma(R) are well-matched by theoretical profiles in which the star-forming galaxies have predominantly radial orbits (beta > 0); many of these galaxies are probably falling in for the first time. There is significant evidence for spatial segregation of the spectroscopic classes regardless of sigma(R).

astro-ph↗

arXiv1998

The Southern Sky Redshift Survey

We report redshifts, magnitudes and morphological classifications for 5369 galaxies with $m_B \leq 15.5$ and 57 galaxies fainter than this limit, in two regions covering a total of 1.70 steradians in the southern celestial hemisphere. The galaxy catalog is drawn primarily from the list of non-stellar objects identified in the Guide Star Catalog (Lasker et al. 1990, AJ 99, 2019; hereafter GSC). The galaxies have positions accurate to about 1 arc sec and magnitudes with an rms scatter of about 0.3 mag. We compute magnitudes ($m_{SSRS2}$) from the relation between instrumental GSC magnitudes and the photometry by Lauberts & Valentijn (1989). From a comparison with CCD photometry, we find that our system is homogeneous across the sky and corresponds to magnitudes measured at the isophotal level $\sim$ 26 mag arcsec$^{-2}$. The precision of the radial velocities is of \sim 40 km/s and the redshift survey is more than 99% complete to the $m_{SSRS2}$ = 15.5 magnitude limit. This sample is in the direction opposite to the CfA2; in combination the two surveys provide an important database for studies of the properties of galaxies and their large-scale distribution in the nearby Universe.

astro-ph↗

arXiv1996

A Medium-Deep Survey of a Mini-Slice at the North Galactic Pole. II. The Data

We report 328 redshifts, b$_J$ magnitudes and b$_J$--r$_F$ colors of galaxies measured in a redshift survey of a 4$^\circ$ $\times$ 0.67$^\circ$ slice close to the north Galactic pole. The faintest galaxies in this survey have a magnitude of b$_J$ $\sim$ 20.5. The redshifts present external errors of the order of 70 \kms, and we estimate that the mean photometry errors are $\sim$ 0.2 for magnitudes and $\sim$ 0.3 for colors. The redshift completeness level of the sample is of the order of $\sim$ 35\% at b$_J$=20, and part of this rather low completeness is the result of the combination of limitations imposed by the multifiber system with the clustering of galaxies, and an insufficient number of configurations. At the nominal magnitude limit of the survey, we were able to measure redshifts for $\sim$ 70 \% of the galaxies we observed. From the correlation between observed properties of the galaxies in this sample, we demonstrate that the mean surface brightness is a major limiting factor in our ability to measure redshifts of faint objects.

astro-ph↗