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A Survey of Dwarf Irregular Galaxies in the Local Sheet

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A Survey of Dwarf Irregular Galaxies in the Local Sheet A SURVEY OF DWARF IRREGULAR GALAXIES IN THE LOCAL SHEET ROBIN LEIGH FINGERHUT A DISSERTATION SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY GRADUATE PROGRAM IN PHYSICS AND ASTRONOMY YORK UNIVERSITY, TORONTO, ONTARIO DECEMBER 2011 Library and Archives Bibliotheque et Canada Archives Canada Published Heritage Direction du 1*1 Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A 0N4 Ottawa ON K1A 0N4 Canada Canada NOTICE: AVIS: The author has granted a non­ L'auteur a accorc exclusive license allowing Library and permettant a la E Archives Canada to reproduce, Canada de reprc publish, archive, preserve, conserve, sauvegarder, cor communicate to the public by par telecommuni telecommunication or on the Internet, distribuer et venc loan, distrbute and sell theses monde, a des fin worldwide, for commercial or non­ support microfori commercial purposes, in microform, autres formats. paper, electronic and/or any other formats. The author retains copyright L'auteur conserv ownership and moral rights in this et des droits mor thesis. Neither the thesis nor la these ni des e: substantial extracts from it may be ne doivent etre ir printed or otherwise reproduced reproduits sans s without the author's permission. Abstract This dissertation delineates and examines a sheet-like structure of galaxies embedded within the Local Supercluster. It is shown that this structure, coined "The Local Sheet", has a non-isotropic boundary at a mean distance of ~4 Mpc from the Milky Way, with the vast majority of its galaxies situated within 0.5 Mpc of the Supergalactic Plane. Its thickness is -10% of its length, which is over twice as thin as the Local Supercluster out to -10 Mpc. Upon establishing the definition of Local Sheet membership, a set of diagnostics of the luminous mass and dynamics of the Sheet's most plentiful constituents, its dwarf irregular galaxies (dls), is presented. Luminous masses were gauged from photometry in the near-infrared (Ks), where more than 95% of a dl's light can be attributed to the stars which make up the bulk of a dl's mass. To this end, an extensive Ks imaging survey of over 70 Sheet dls was conducted. The spatial distributions of the dwarf properties were then investigated for environmental influences and compared with predictions for a dynamically equilibrated sheet-like structure. To establish a framework for these observations, the same investigations were pursued using a sample of 8 theoretical sheets extracted from an N-body simulation of structure formation in the standard ACDM cosmology. Both the Local Sheet and the theoretical sheets are found to have vertical crossing times which exceed half the Universe's Age. This indicates that the Local Sheet's - iv - galaxies are making their first traversal of the Sheet's vertical extent. Nevertheless, the vertical dynamics of the dark matter halos in the theoretical sheets exhibit similarities with the predictions for an equilibrated sheet for which the density declines exponentially with altitude. Further evidence of dynamical equilibrium is found in the vertical density profiles of both the Local Sheet and the theoretical sheets, which closely match an exponential model. Tentative evidence is found for a correlation between a sheet's dynamical and structural parameters and its crossing time, in the sense that theoretical sheets with the shortest crossing times show the strongest agreement with the exponential density model for an equilibrated sheet. Based upon its comparatively long crossing time, the Local Sheet appears to be in the process of evolving into an equilibrated system. For a sheet to attain gravitational equilibrium, the exponential model requires that the sheet contains at least 1.5 times as much mass as is attached to its galaxies. The simulated sheets are estimated to possess at least this amount of mass in the form of dark matter below the approximate minimum mass of galaxy-sized halos. It is therefore concluded that the Local Sheet is pervaded by an intra-sheet population of dark matter which contains approximately as much mass as its galaxies. - v - Acknowledgements The completion of this dissertation was made possible by the unlimited patience and support of my supervisor, Dr. Marshall McCall. I have benefited immeasurably from his endless knowledge as well as from his demanding expectations. I am proud of all the work that we've done together. I would also like to thank my supervisory committee for their very helpful feedback. A special thank you goes to my entire examining committee for making the oral defense such a rewarding and memorable experience. Thank you to my mom, Beverley Fingerhut, an incredible person who makes anything possible. And finally, thank you to my husband, Dr. Robert Metcalfe, and my sons Jesse and Joey Metcalfe. Every day, at least one of you makes me laugh, and that makes life amazing. Thank you for being such super-awesome people. • VI - Table of Contents Abstract iv Acknowledgements vi Table of Contents vii L Introduction 1 1.1 Evidence for a Local Sheet of Galaxies 1 1.2 Scientific Justification for a Survey of dls in the Local Sheet 5 1.3 Features of this Study 8 1.4 Outline of this Dissertation 10 2. The Sample of Local Sheet dls 12 2.1 The Current Census of Nearby dls 12 2.1.1 Extinctions and cosmological corrections 15 2.1.2 Distances 16 2.2 The Local Sheet Reference Frame 22 2.3 Sample Definition 24 2.3.1 Extraction of the Local Sheet 24 2.3.2 Local Sheet candidates with uncertain distances 28 2.3.3 The Local Sheet survey region 29 2.4 The Local Sheet Sample 31 2.5 Sample Completeness 42 3. Theoretical Predictions of Sheets 48 3.1 The Current State of Cosmology 48 3.2 The ACDM Simulation and the Sheet Extraction Process 50 3.2.1 The overabundance of dwarf satellites predicted by the ACDM model 57 3.3 The Mass Functions of CDM Sheets 57 3.4 The Distribution of Mass in CDM Sheets 60 3.5 The Density Profiles of CDM Sheets 66 3.5.1 Construction of the vertical density profile 66 3.5.2 Vertical density models of equilibrated sheet-like systems 67 3.5.3 Fitting of the vertical density profile 70 - vii - 3.6 Peculiar Motions in CDM Sheets 81 3.6.1 The z-dependence of the vertical velocity dispersion 82 3.6.2 The relationship between the vertical and radial velocity dispersion 85 3.7 The Crossing Times of CDM Sheets 87 3.7.1 Are sheets evolving systems? 88 3.8 Surface Densities of CDM Sheets 95 4. The Near-Infrared Imaging Survey and Data Mining of Local Sheet dis 100 4.1 Ks Imaging Observations 100 4.1.1 CFHT observations 103 4.1.2 OAN-SPM observations 103 4.1.3 IRSF observations 104 4.1.4 CTIO observations 104 4.1.5 ESO observations 105 4.1.6 WIRCam observations 105 4.2 Ks Image Reduction 107 4.2.1 Image preprocessing 108 4.2.2 Sky subtraction 109 4.2.3 Photometric calibration 112 4.3 Ks Surface Photometry 113 4.4 Fitting of Surface Brightness Profiles in Ks 116 4.4.1 Radial range of the fits 117 4.4.2 Uncertainties in the fit parameters 118 4.4.3 Astrometry 119 4.5 Integrated Ks Magnitudes 132 4.5.1 Comparison with different facilities 133 4.5.2 Comparison with 2MASS photometric parameters 135 4.5.3 The dl Potential Plane 137 4.5.4 K, magnitudes for unobserved Sheet dis 138 4.6 Derived Masses of the Local Sheet dis 142 4.6.1 Stellar masses 142 4.6.2 Gas masses 143 5. Analysis of the Local Sheet 151 5.1 What We Can Learn From Our Own Backyard 151 5.2 The Distribution of Mass in the Local Sheet 154 5.2.1 Luminous mass 154 5.2.2 Gas fraction 160 5.2.3 (B-KJ o colour 164 5.3 The Density Profile of the Local Sheet 166 5.3.1 Effects of sample incompleteness 169 5.4 Peculiar Motions in the Local Sheet 171 5.4.1 The vertical velocity dispersion 176 - viii 5.5 The Crossing Time of the Local Sheet 177 5.6 The Surface Mass Density of the Local Sheet 179 6. Conclusions 185 6.1 Summary of Results 185 6.2 Future Work 191 7. References 193 - ix - 1. Introduction Kirk: "No, I'm from Iowa. I only work in outer space." 1.1 Evidence for a Local Sheet of Galaxies In the 1780s, the German-English musician William Herschel used a home-made 18.7-inch reflector to conduct the first systematic sweep of galaxies from his backyard in Bath, England. In his On the Construction of the Heavens (Herschel 1785), he made one of the first documented observations of large-scale structure in the Universe by describing a "collection of many hundreds of nebulae which are to be seen in what I have called the nebulous stratum of Coma Berenices." Edwin Hubble, shortly after his determination of the 1st definitive extragalactic distance using a Cepheid in M31, observed that the Milky Way is found within a much smaller-scale "stratum" composed of, at least, 7 members. In his Realm of the Nebulae, Hubble named this system "The Local Group" (Hubble 1936). The most recent census of the Local Group includes 35 galaxies spanning roughly 2 Mpc in extent (van den Bergh 2007). In 1958, George O. Abell published The Distribution of Rich Clusters of Galaxies containing over 2700 galaxy clusters (Abell 1958).
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