Viewing the 21 cm sky : a slice of the neutral hydrogen universe.

Among the most fundamental problems in extragalactic astronomy are understanding the processes which led to galaxy formation and establishing the existence and nature of dark matter in the Universe. Before any attempt can be made to solve either of these problems, an accurate and thorough knowledge of the true population of galaxies is required. Unfortunately, there is mounting evidence that our knowledge of extragalactic space may be critically incomplete. This deficiency is due primarily to our dependence on galaxy statistics that are largely derived from observations at optical wavelengths. These statistics may include only a sub-population of extragalactic objects which have properties easily detected in that narrow wavelength range, rather than the true population which may have a more diverse range of properties. To steer ourselves away from this possible optical bias, and thus to obtain a more well-rounded census of galaxy sizes, types, and locations, we have conducted a large-scale, unbiased survey for atomic hydrogen (HI) at 21cm. Because the strength of 21cm emission does not depend on the same forces which drive optical emission, this survey allows us to not only augment the compiled database of galaxies by describing the properties of previously cataloged objects we detect, but more importantly search for new types of objects which have historically remained undetected due to optical biases. Using the NAIC Arecibo Telescope, we have systematically searched a slice of extragalactic space known to contain 48 cataloged galaxies. Our survey has re-detected 38 by their 21cm emission, and has failed to detect 10. We have also detected an additional 41 previously unknown objects. We present atomic hydrogen and optical data for all objects and demonstrate that the newly discovered galaxies represent a population which differs distinctly from the cataloged galaxies in having lower overall luminosities and masses, larger relative HI gas contents, and bluer colors. In addition we show that several extremely low-mass, low luminosity galaxies discovered within 5 Mpc of the Milky Way imply the presence of thousands of similar objects throughout the slice search region. These low-mass objects could, in their great numbers, represent a significant fraction of the total integrated mass of all galaxies in the region. As such, they could have a profound influence on the distribution and evolution processes of all extragalactic objects

A Deep Survey of HI-Selected Galaxies: The Sample and the Data

In a 21 cm neutral hydrogen survey of approximately 55 sq deg out to a redshift of cz=8340 km/s, we have identified 75 extragalactic HI sources. These objects comprise a well-defined sample of extragalactic sources chosen by means that are independent of optical surface brightness selection effects. In this paper we describe the Arecibo survey procedures and HI data, follow-up VLA HI observations made of several unusual sources, and Kitt Peak B-, R-, and I-band photometry for nearly all of the galaxies. We have also gathered information for some of the optically detected galaxies within the same search volume. We examine how samples generated by different types of search techniques overlap with selection by HI flux. Only the least massive HI object, which is among the lowest mass HI sources previously found, does not have a clear optical counterpart, but a nearby bright star may hide low surface brightness emission. However the newly-detected systems do have unusual optical properties. Most of the 40 galaxies that were not previously identified in magnitude-limited catalogs appear to be gas-dominated systems, and several of these systems have HI mass-to-light ratios among the largest values ever previously found. These gas-dominated objects also tend to have very blue colors, low surface brightnesses, and no central bulges, which correlate strongly with their relative star-to-gas content.Comment: 48 pages, 10 figures, Figure 3 included as 3 separate JPG images. To appear in Ap J Supplement

The 2MASS Redshift Survey - Description and Data Release

We present the results of the 2MASS Redshift Survey (2MRS), a ten-year project to map the full three-dimensional distribution of galaxies in the nearby Universe. The 2 Micron All-Sky Survey (2MASS) was completed in 2003 and its final data products, including an extended source catalog (XSC), are available on-line. The 2MASS XSC contains nearly a million galaxies with Ks <= 13.5 mag and is essentially complete and mostly unaffected by interstellar extinction and stellar confusion down to a galactic latitude of |b|=5 deg for bright galaxies. Near-infrared wavelengths are sensitive to the old stellar populations that dominate galaxy masses, making 2MASS an excellent starting point to study the distribution of matter in the nearby Universe. We selected a sample of 44,599 2MASS galaxies with Ks =5 deg (>= 8 deg towards the Galactic bulge) as the input catalog for our survey. We obtained spectroscopic observations for 11,000 galaxies and used previously-obtained velocities for the remainder of the sample to generate a redshift catalog that is 97.6% complete to well-defined limits and covers 91% of the sky. This provides an unprecedented census of galaxy (baryonic mass) concentrations within 300 Mpc. Earlier versions of our survey have been used in a number of publications that have studied the bulk motion of the Local Group, mapped the density and peculiar velocity fields out to 50 Mpc, detected galaxy groups, and estimated the values of several cosmological parameters. Additionally, we present morphological types for a nearly-complete sub-sample of 20,860 galaxies with Ks = 10 deg.Comment: Accepted for publication in The Astrophysical Journal Supplement Series. The 2MRS catalogs and a version of the paper with higher-resolution figures can be found at http://tdc-www.harvard.edu/2mrs

The IVS data input to ITRF2014

2015ivs..data....1N - GFZ Data Services, Helmoltz Centre, Potsdam, GermanyVery Long Baseline Interferometry (VLBI) is a primary space-geodetic technique for determining precise coordinates on the Earth, for monitoring the variable Earth rotation and orientation with highest precision, and for deriving many other parameters of the Earth system. The International VLBI Service for Geodesy and Astrometry (IVS, http://ivscc.gsfc.nasa.gov/) is a service of the International Association of Geodesy (IAG) and the International Astronomical Union (IAU). The datasets published here are the results of individual Very Long Baseline Interferometry (VLBI) sessions in the form of normal equations in SINEX 2.0 format (http://www.iers.org/IERS/EN/Organization/AnalysisCoordinator/SinexFormat/sinex.html, the SINEX 2.0 description is attached as pdf) provided by IVS as the input for the next release of the International Terrestrial Reference System (ITRF): ITRF2014. This is a new version of the ITRF2008 release (Bockmann et al., 2009). For each session/ file, the normal equation systems contain elements for the coordinate components of all stations having participated in the respective session as well as for the Earth orientation parameters (x-pole, y-pole, UT1 and its time derivatives plus offset to the IAU2006 precession-nutation components dX, dY (https://www.iau.org/static/resolutions/IAU2006_Resol1.pdf). The terrestrial part is free of datum. The data sets are the result of a weighted combination of the input of several IVS Analysis Centers. The IVS contribution for ITRF2014 is described in Bachmann et al (2015), Schuh and Behrend (2012) provide a general overview on the VLBI method, details on the internal data handling can be found at Behrend (2013)