332 research outputs found

    The I-Band Tully-Fisher Relation and the Hubble Constant

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    The application of the I band Tully--Fisher relation towards determining the Hubble constant is reviewed, with particular attention to the impact of scatter and bias corrections in the relation. A template relation is derived from galaxies in 24 clusters. A subset of 14 clusters with cz ~ 4000 to 9000 km/s is used as an inertial frame to define the velocity zero point of the relation. Twelve galaxies with Cepheid distances are used to establish the absolute magnitude scale of the Tully--Fisher relation, and thus to determine a value of H_not = 70\pm5 km/s/Mpc. Estimates of the peculiar velocities of the Virgo and Fornax clusters are also given. Assuming that the distance to Fornax is 18.2 Mpc (N1365), H_not = 76\pm8 km/s/Mpc. Assuming that Virgo lies at 17.4 Mpc (M100, N4496, N4639), H_not = 67\pm8 km/s/Mpc.Comment: 18 pages, 5 tables, 5 figures embedded by psfig; uses AAS LaTex; to appear in proceedings of "The Extragalactic Distance Scale", a meeting held at STScI in May 1996; ed. by M. Livio, M. Donahue and N. Panagia, CU

    On the Scaling Relations of Disk Galaxies

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    The physical background of scaling laws of disk galaxies is reviewed. The match between analytically derived and observed scaling laws is briefly discussed. Accurate modeling of the fraction of baryons that end populating a disk, and the conversion efficiency of those into stars, remains a challenging task for numerical simulations. The measurement of rotational velocity tends to be made with criteria of convenience rather than through rigorous definition. And yet, the Tully-Fisher and the disk size vs. rotational velocity relations exhibit surprisingly low scatter. Practical recipes (and costs) to optimize the quality of template relations are considered.Comment: 8 pages with 4 figure

    ALFALFA: HI Cosmology in the Local Universe

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    For the last 25 years, the 21 cm line has been used productively to investigate the large-scale structure of the Universe, its peculiar velocity field and the measurement of cosmic parameters. In February 2005 a blind HI survey that will cover 7074 square degrees of the high latitude sky was started at Arecibo, using the 7-beam feed L-band feed array (ALFA). Known as the Arecibo Legacy Fast ALFA (ALFALFA) Survey, the program is producing a census of HI-bearing objects over a cosmologically significant volume of the local Universe. With respect to previous blind HI surveys, ALFALFA offers an improvement of about one order of magnitude in sensitivity, 4 times the angular resolution, 3 times the spectral resolution, and 1.6 times the total bandwidth of HIPASS. ALFALFA can detect 7 X 10**4 D**2 solar masses of HI, where D is the source distance in Mpc. As of mid 2007, 44% of the survey observations and 15% of the source extraction are completed. We discuss the status of the survey and present a few preliminary results, in particular with reference to the proposed "dark galaxy" VirgoHI21.Comment: To appear in Proceedings of IAU Symp #244, "Dark Galaxies and Lost Baryons", June 2007, 10 pages including 5 figure

    Optical Seeing and Infrared Atmospheric Transparency in the Upper Atacama Desert

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    With plans to build a large IR/optical telescope in the Atacama Desert, a site survey campaign has been underway since 1998 to characterize the optical seeing and the IR transparency in the Chajnantor Plateau region. Preliminary results indicate that the Chajnantor region offers excellent astronomical observing conditions in the optical and IR. The region is isolated yet easy to reach, and high quality services are available nearby. We can expect to find: median optical FWHM seeing approaching values of 0.5"--0.6", a percentage of photometric nights of 65% or better, of astronomically useful nights in excess of 80% and median PWV well below 1 mm (with best quartile below 0.5 mm).Comment: 8 pages, 4 figures, LaTex, to appear in Procs. of IAU Workshop "Astronomical Site Evaluation in the Optical and Radio Range" held at Marrakech, Nov. 200

    The Arecibo OH Megamaser Survey and the Galaxy Merger Rate

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    We present the current results of a survey for OH megamasers (OHMs) underway at the Arecibo Observatory. The survey is 2/3 complete and has produced a high OHM detection rate (1 in 6) from a redshift-selected sample of IRAS galaxies. The survey will relate the OHM luminosity function to the galaxy merger rate, allowing subsequent blind OHM surveys to measure the galaxy merger rate as a function of cosmic time. The survey has also made the first detection of strong variability in OHMs. Variability will provide a powerful tool for understanding the small-scale physical settings and mechanisms of OHMs.Comment: 2 pages, 1 figure; requires newpasp.sty. To appear in the proceedings of the conference "Gas and Galaxy Evolution" (ASP Conference Series), eds. J. Hibbard, M. Rupen, and J. van Gorko

    The Convergence Depth of the Local Peculiar Velocity Field

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    We have obtained Tully-Fisher (TF) measurements for some 3000 late-type galaxies in the field and in 76 clusters distributed throughout the sky between 10 and 200\h Mpc. The cluster data are applied to the construction of an I band TF template, resulting in a relation with a scatter of 0.35 magnitudes and a zero-point accurate to 0.02 magnitudes. Peculiar motions are computed by referral to the template relation, and the distribution of line-of-sight cluster peculiar motions is presented. The dipole of the reflex motion of the Local Group of galaxies with respect to galaxies with measured peculiar velocity converges to the CMB dipole within less than 6000 km/s. The progression of this convergence is well illustrated when the reflex motion is referred to a well-distributed sample of field galaxies, and it is maintained when the reflex motion is referred to the reference frame constituted by the distant clusters in our sample. The field and cluster samples exhibit bulk motion amplitudes of order 200 km/s or smaller. Finally, we apply our sample of cluster peculiar velocities to a test of the putative Hubble bubble recently claimed by Zehavi and coworkers. In contrast to their findings, our data support a relatively quiescent Hubble flow beyond 35\h Mpc.Comment: 14 pages LaTeX, with 8 embedded figures. Uses paspconf.sty. To appear in the proceedings of the Cosmic Flows Workshop, Victoria, Canada, July 1999, ed. S. Courteau, M. Strauss & J. Willick, ASP serie

    Extragalactic HI Surveys

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    We review the results of HI line surveys of extragalactic sources in the local Universe. In the last two decades major efforts have been made in establishing on firm statistical grounds the properties of the HI source population, the two most prominent being the HI Parkes All Sky Survey (HIPASS) and the Arecibo Legacy Fast ALFA survey (ALFALFA). We review the choices of technical parameters in the design and optimization of spectro-photometric "blind" HI surveys, which for the first time produced extensive HI-selected data sets. Particular attention is given to the relationship between optical and HI populations, the differences in their clustering properties and the importance of HI-selected samples in contributing to the understanding of apparent conflicts between observation and theory on the abundance of low mass halos. The last section of this paper provides an overview of currently ongoing and planned surveys which will explore the cosmic evolution of properties of the HI population.Comment: 40 pages, 22 figures Invited Review of Astronomy and Astrophysics Reviews, in pres

    Spectroscopy of Edge-on Spirals

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    We present HI line observations of 744 edge-on spiral galaxies, extracted from the Flat Galaxy Catalog of Karachentsev et al. (1993). Fluxes, systemic velocities and line widths are given for 587 detected galaxies, as well as search parameters for 157 undetected systems. Widths are corrected for instrumental broadening, smoothing, signal-to--noise and profile shape, and an estimate of the error on the width is given. When corrected for turbulent broadening and inclination angle of the disks, the velocity widths presented here can provide the appropriate line width parameter needed to derive distances via the Tully-Fisher relation.Comment: 9 pages (uses AAS LaTex), including 1 figure (.ps) and 2 tables (1 in LaTex, other in .ps format. To appear in A

    Las nubes de alta velocidad de la galaxia y la estructura del gas interestelar

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    Este trabajo presenta resultados que se proponen aclarar ulteriormente,los aspectos morfológicos y termodinámicos del medio interestelar en las regiones periféricas de la galaxia.Se divide en una parte de análisis eminentemente teórico,en el cual se postura una estructura jerárquica del gas, en tres fases de temperatura y densidades distintas. Y en una parte de carácter observacional,en el cual se presentan los resultados de observaciones radioastronómicas que tienden a corroborar los resultados teóricos.El cuadro resultante propuesto por este estudio es el de un gas galáctico periférico conformado en estructuras nebulares, que participan en la rotación galáctica y que estando presumiblemente a grandes distancias,presentan altos valores de la velocidad radial; pueden ser interpretadas como representativa de dos fases en equilibrio de presión, térmico y de ionización entre ellas y con una tercera fase, “internebular”,a temperatura mayor que 20000º K

    The Void Phenomenon Revisited

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    The Void Phenomenon consists in the apparent discrepancy between the number of observed dwarf halos in cosmic voids and that expected from CDM simulations. We approach the problem considering the challenging prospects of detecting field dwarf systems with halo masses < 10^9 solar, via their possible HI emission. A brief review of recent work is followed by preliminary results from the ALFALFA survey, which suggest the possibility, but not yet the proof, that such objects may have been already detected towards the outskirts of the Local Group.Comment: 6 pages, 2 postscript figure
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