An HI selected sample of galaxies - The HI mass function and the surface brightness distribution

Results from the Arecibo HI Strip Survey, an unbiased extragalactic HI survey, combined with optical and 21cm follow-up observations, determine the HI Mass Function and the cosmological mass density of HI at the present epoch. Both are consistent with earlier estimates, computed for the population of optically selected galaxies. This consistency occurs because, although the distribution of optical central surface brightnesses among galaxies is flat, we fail to find a population of galaxies with central surface brightnesses fainter than 24 B-mag/arcsec^2, even though there is no observational selection against them.Comment: 5 pages, including 3 encapsulated postscript figures. Presented at the workshop `HI in the Local Universe', Sydney, May 13-15 1996. Accepted for publication by PASA. Also available from http://www.atnf.csiro.au/Publications/HI_workshop/proceedings.htm

The HI Mass Function of Galaxies from a Deep Survey in the 21cm Line

The HI mass function (HIMF) for galaxies in the local universe is constructed from the results of the Arecibo HI Strip Survey, a blind extragalactic survey in the 21cm line. The survey consists of two strips covering in total 65 square degrees of sky, with a depth of cz = 7400 km/s and was optimized to detect column densities of neutral gas N_HI > 10^18 cm^-2 (5 sigma). The survey yielded 66 significant extragalactic signals of which approximately 50% are cataloged galaxies. No free floating HI clouds without stars are found. VLA follow-up observations of all signals have been used to obtain better measurements of the positions and fluxes and allow an alternate determination of the achieved survey sensitivity. The resulting HIMF has a shallow faint end slope (alpha ~ 1.2), and is consistent with earlier estimates computed for the population of optically selected gas rich galaxies. This implies that there is not a large population of gas rich low luminosity or low surface brightness galaxies that has gone unnoticed by optical surveys. The cosmological mass density of HI at the present time determined from the survey, Omega_HI = (2.0 +/- 0.5) x 10^-4, is in good agreement with earlier estimates. We determine lower limits to the average column densities of the galaxies detected in the survey and find that none of the galaxies have below 10^19.7 cm^-2, although there are no observational selection criteria against finding lower density systems.Comment: 34 pages, including 8 figures. To appear in The Astrophysical Journa

Overview of the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We present an overview of the instrumentation, the main technical requirements and challenges, and the current status of the project.Comment: 11 pages, 4 figure

Overview of the instrumentation for the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) embarked on an ambitious 5 yr survey in 2021 May to explore the nature of dark energy with spectroscopic measurements of 40 million galaxies and quasars. DESI will determine precise redshifts and employ the baryon acoustic oscillation method to measure distances from the nearby universe to beyond redshift z > 3.5, and employ redshift space distortions to measure the growth of structure and probe potential modifications to general relativity. We describe the significant instrumentation we developed to conduct the DESI survey. This includes: a wide-field, 3.°2 diameter prime-focus corrector; a focal plane system with 5020 fiber positioners on the 0.812 m diameter, aspheric focal surface; 10 continuous, high-efficiency fiber cable bundles that connect the focal plane to the spectrographs; and 10 identical spectrographs. Each spectrograph employs a pair of dichroics to split the light into three channels that together record the light from 360–980 nm with a spectral resolution that ranges from 2000–5000. We describe the science requirements, their connection to the technical requirements, the management of the project, and interfaces between subsystems. DESI was installed at the 4 m Mayall Telescope at Kitt Peak National Observatory and has achieved all of its performance goals. Some performance highlights include an rms positioner accuracy of better than 0.″1 and a median signal-to-noise ratio of 7 of the [O ii] doublet at 8 × 10−17 erg s−1 cm−2 in 1000 s for galaxies at z = 1.4–1.6. We conclude with additional highlights from the on-sky validation and commissioning, key successes, and lessons learned

Cosmological implications of low surface brightness galaxies.

This dissertation briefly presents the results of a survey for galaxies that have been overlooked by previous surveys because their surface brightness, or brightness per unit area on the night sky, is too low. This dissertation then makes use of the survey results to estimate the density of these galaxies and to delineate some of their properties. Chapter 1 describes the selection bias against finding galaxies of low surface brightness and outlines the importance of these galaxies for a more complete knowledge of the true local galaxy population. Chapter 2 discusses the techniques employed for identifying low surface brightness (LSB) galaxies for the survey, calibrating the photometry, and estimating the survey incompleteness as a function of galaxy parameters. Chapter 3 presents luminosity functions for the low surface brightness galaxies identified in the present survey, and for a combined sample of low surface brightness and high surface brightness galaxies. The overall space density of low surface brightness galaxies is about one-fourth to one-third as great as the density determined from standard field galaxy luminosity functions, and that the total luminosity density due to these low surface brightness galaxies is about one-third to one-half the level derived from other surveys. Chapter 4 presents 21 cm profiles and CCD surface photometry for a subset of the low surface brightness spiral galaxies found by the survey. The general trend of the LSB galaxies in the Tully-Fisher relation, relative to the trend of higher surface brightness galaxies, forms the basis of the conclusion that LSB spiral generally have mass-to-light ratios comparable to that of higher surface brightness spirals but with a much larger scatter. Various possible reasons for the higher scatter are explored. Chapter 5 presents CCD surface photometry and optical spectroscopy for a sample of eight low surface brightness spiral galaxies that are extraordinary because of their large physical sizes and high total luminosities. The properties of these galaxies are analyzed and compared to those of more normal spirals. Chapter 6 summarizes the findings of the preceding chapters and presents some ideas for future investigations

The Academic Community and Foreign Policy Formation

(Statement of Responsibility) by David Sprayberry(Thesis) Thesis (B.A.) -- New College of Florida, 1975(Electronic Access) RESTRICTED TO NCF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE(Bibliography) Includes bibliographical references.(Source of Description) This bibliographic record is available under the Creative Commons CC0 public domain dedication. The New College of Florida, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.(Local) Faculty Sponsor: Benedetti, Rober