University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations 1896 - February 2014 1-1-1996 Viewing the 21 cm sky : a slice of the neutral hydrogen universe. John G. Spitzak University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_1 Recommended Citation Spitzak, John G., "Viewing the 21 cm sky : a slice of the neutral hydrogen universe." (1996). Doctoral Dissertations 1896 - February 2014. 1961. https://scholarworks.umass.edu/dissertations_1/1961 This Open Access Dissertation is brought to you for free and open access by ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations 1896 - February 2014 by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. VIEWING THE 21 CM SKY: A SLICE OF THE NEUTRAL HYDROGEN UNIVERSE A Dissertation Presented by John G. Spitzak Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of Doctor of Philosophy May 1996 Department of Physics and Astronomy © Copyright John G. Spitzak 1996 All Rights Reserved VIEWING THE 21 CM SKY: A SLICE OF THE NEUTRALin rL< 1 KAL HYDROGEN UNIVERSE U A Dissertation Presented by John G. Spitzak Approved as to style and content by: Ronald L. Snell, Member Vg^^ a" , Vt^r ^ Jejinie H. Traschen, Outside Member Jcmn F. Dubach, Department Head Department of Physics and Astronomy ABSTRACT VIEWING THE 21 CM SKY: A SLICE OF THE NEUTRAL HYDROGEN UNIVERSE MAY 1996 JOHN G. SPITZAK, B.S., UNIVERSITY OF MASSACHUSETTS AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Stephen E. Schneider 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 be critically may 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 iii 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. iv TABLE OF CONTENTS Page ABSTRACT iii LIST OF TABLES vii LIST OF FIGURES viii Chapter 1. INTRODUCTION Big Questions, Big Problems 2 Dark Matter Galaxy Formation Why Do We Believe the Current Census May Not Be Complete? 6 Optical Selection Effects 6 Quasar Absorption Lines How Do We Fix the Surface Brightness Selection Problem? 15 Outline 2Q 2. HOW BEST TO CONDUCT AN HI SEARCH 25 Strategies for the Slice Search: How to Find What We Cannot See 26 Choosing a Telescope 29 Choosing a Search Region 39 Observing Method 43 Previous HI Searches 44 Deliberate 21 cm Searches 48 Non-Deliberate 21 cm Searches 53 An Ideal Search? 54 3. OBSERVATIONS 63 Original HI Slice Observations 63 Observation Strategy 63 The Observations 68 Low Velocity Test 69 v o Slice Position Naming Scheme 69 Detection Methods. 71 Visual Search Software Search ^ 76 Searches 1 and 2: Generate an Interference Table 78 Searches 3 and 4: Using the Interference Table as a Mask 9 Searches 5, 6, 7, 8 and 9: Eliminate Long-Term Interference ZIZZZ'ZZ 83 Final Tally of Detections Was the Software Search Worthwhile? It o5 Follow-up HI Observations: The Hex Procedure Optical Observations of the Slice Objects 91 Reduction 94 4. THE DATA ffl Data 10g Optical Data "° Derived Quantities Notes on Individual Objects Scaled Images 1 20 5. RESULTS AND ANALYSIS 146 Positions of the Slice Detections 1 48 The Shapes of the HI-Mass and Dynamic Mass Functions 151 Detection Rates for Optical and HI Surveys 155 Computing an HI Sensitivity Function 1 5g Adjusting the HI and Dynamic Mass Functions 160 Complications in the Interpretation of the HI Mass Function 163 Counting More Massive Galaxies 165 Another Look at - Dynamic Mass Where are the Biggest Galaxies? 166 HI Mass vs Dynamic Mass 168 Where are the Brightest Galaxies? 171 Mass-to-Light Ratios of the Slice Galaxies 172 The Slice Galaxy Colors 173 6. CONCLUSIONS 199 Implications of the Slice Search Results 199 Follow-up Work: The Next Slices 202 REFERENCES 204 vi . LIST OF TABLES Table Page 2. 1 Deliberate HI Searches. 58 2.2 Non-Deliberate HI Searches 59 3. 1 Software Search Performance.... 107 4. 1 HI Data for the Slice ObjectsJ 123 4.2 Optical Data for the Slice Objects j ^ 4.3 Derived Quantities for the Slice Objects , 3Q 4.4 Cataloged Object Names Cross-Reference , 33 vii LIST OF FIGURES Figure Page 1 . Spatial distribution 1 of the galaxies in the RC3 22 1.2 The relationship between absolute diameter and absolute magnitude for 1 1838 Bgalaxies from the RC3 (de Vaucouleurs, 1991) 23 1 .3 Absolute diameters and absolute magnitudes for 11838 galaxies from the RC3 in gray with additional objects in black 24 2. The survey time 1 required for Arecibo, GreenBank, and the VLA to detect model galaxies at distances from 0 to 1000 Mpc 6Q 2.2 RC3 galaxies in the declination range + 1 8 to +28 6 ! 2.3 HI mass sensitivity vs volume searched (at each sensitivity) for all HI searches 62 3. Schematic representation 1 of the slice search strategy 96 3.2 HI fluxes and velocity widths of slice objects detected by all software searches 97 3.3 HI fluxes and velocity widths of slice objects not detected by the software searches 98 3.4 HI fluxes and velocity widths of slice objects detected by software Search 1 99 3.5 HI fluxes and velocity widths of slice objects detected by software Search 2 100 3.6 HI fluxes velocity and widths of slice objects detected by software Search 4 101 3.7 HI fluxes and velocity widths of slice objects detected by software Search 5 102 3.8 HI fluxes and velocity widths of slice objects detected by software Search 6 103 3.9 HI fluxes and velocity widths of slice objects detected by software Search 7 104 3.10 HI fluxes and velocity widths of slice objects detected by software Search 8 105 3.11 HI fluxes and velocity widths of slice objects detected by software Search 9 106 4. 1 R-band images of the uncataloged objects detected in the HI slice search 135 4.2 R-band images of the cataloged objects detected in the HI slice search 139 4.3 R-band images of the slice objects not detected in the HI search 144 5. 1 Positions of the objects detected in the slice search 175 viii Slice 5.2 object positions vs RC3 objects in the declination range +18 to +28 , 76 5.3 Hydrogen masses of the slice objects J 177 5.4 Dynamical masses of the slice objects 178 5.5 Hydrogen masses of the slice galaxies plotted against their distances 179 5.6 Dynamical masses of the slice galaxies plotted against their distances , 80 5.7 HI fluxes of the slice galaxies plotted against their velocity widths 181 5.8 Ratios of the measured fluxes of the slice objects to the 5a flux level j 82 5.9 Hydrogen masses of all slice objects on a log scale 10 { 83 5.10 Dynamical masses of all slice objects on a log scale 10 184 5. 1 Observed and "corrected" 1 hydrogen masses of all slice objects on a log, scale 0 185 5. 12 Observed and "corrected" dynamical masses of all slice objects on a log scale 10 186 5.13 Observed and "corrected" integrated atomic hydrogen mass per decade of all slice objects lg7 5.14 Observed and "corrected" integrated dynamical mass per decade of all slice objects 188 5.15 The dynamical masses of slice galaxies plotted against their distances 1 89 5.16 Dynamical masses of the slice objects plotted against their HI masses 190 5.