Local Group Analogues by Ryan Speller A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Master of Science in Physics Waterloo, Ontario, Canada, 2012 c Ryan Speller 2012 I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii Abstract The abundance of satellite galaxies is a critical small-scale test of the standard cosmo- logical model. From comparing the predictions of structure formation in simulations with observations of Local Group dwarf galaxies there is a clear mismatch in the abundance, leading to the so-called \missing satellites" problem. The comparison between simulation and observation have, however, suffered from a limited sample of satellite galaxies, with the only reasonably complete sample being from the most local galaxy groups. It is un- known whether the observed abundance of dwarf satellite galaxies of the nearest groups is statistically representative of the abundance of dwarf satellites in the greater universe. We construct a volume-limited sample of galaxies down to a well-defined stellar mass limit 9 (M? ≥ 6 × 10 M ) using the Atlas3D parent sample of spiral and ellipsoidal galaxies by Cappellari et al. 2011 [18]. In order to statistically identify bound satellites around galax- ies in our primary catalogue, we apply cuts on the background based on the properties of known dwarf satellites of the Local Group using both the Sloan Digital Sky Survey Data Release 8 (SDSS DR8) (http://www.sdss3.org/dr8/) spectroscopic and photomet- ric galaxy catalogues. We detect an over-density of faint objects at projected separations of < 500 kpc at S/N ∼ 8, corresponding to an average of 4:8 ± 0:65 satellite detections per primary after stacking these systems and subtracting the background. We further find that the over-density of faint objects strongly depends on primary morphology and magnitude. While the Milky Way seems to be unusual in its number of bright satellites, our faint end satellite abundances are in agreement from the ∆m luminosity function for primaries in our sample as bright as the Milky Way. Our work has extended the work of previous authors by several magnitudes further down the faint end of the luminosity function. iii Acknowledgements I owe a debt of gratitude to my supervisor, Dr. James Taylor, who took a risk in taking me on as a graduate student and whose valuable knowledge and advice have benefited me greatly in this endeavour and the experience with whom will surely leave a significant impact on me long after my graduate experience. I would like to thank the members of my committee for taking the time to read my thesis and also for the feedback from committee meetings. I am also most grateful to my fellow graduate student Jonathan Grossauer, for many illuminating discussions. Lastly, I would like to acknowledge the love and support of my parents, David and Cor- rine Speller, and my fianc´eKrista Burke, whose understanding and encouragement have made this work possible. iv Table of Contents List of Tables vii List of Figures viii 1 Introduction1 1.1 Background Theory...............................3 1.1.1 Cosmology................................3 1.1.2 Structure Formation..........................7 1.2 Galaxies.....................................8 1.2.1 Dwarf galaxies............................. 11 2 The Local Group and Neighbouring Galaxy Groups 12 2.1 The Local Group of Galaxies.......................... 13 2.1.1 Local Group Dwarf Satellites..................... 13 2.2 The Karachentsev Catalogue.......................... 21 2.2.1 The M81 Group............................. 21 2.2.2 The Centaurus A/M83 Group..................... 22 2.2.3 The IC342/Maffei Group........................ 23 2.2.4 Spatial Distribution of Satellite Galaxies............... 23 2.2.5 Velocity Offset............................. 24 2.2.6 The Curious Case of Centaurus A................... 28 2.2.7 Sample Completeness.......................... 30 v 3 Searching for Faint Satellites in SDSS 32 3.1 Foreground................................... 33 3.1.1 Atlas3D................................. 33 3.1.2 Isolation Criteria............................ 34 3.2 Background................................... 34 3.2.1 SDSS................................... 34 3.2.2 Masking................................. 37 3.2.3 Cuts................................... 41 3.3 Preliminary Estimate.............................. 43 3.4 Comparison With Other Groups........................ 43 3.4.1 Guo et al. 2011............................. 44 3.4.2 Lares et al. 2011............................ 45 3.4.3 Liu et al. 2011............................. 45 3.4.4 Strigari et al. 2012........................... 46 3.4.5 Nierenberg et al. 2011/2012...................... 47 4 Results 48 4.1 Density Profile................................. 49 4.2 Number Profile................................. 52 4.3 Number vs. ∆M................................ 59 4.4 Velocity Offset................................. 60 4.5 Comparison With Previous Results..................... 63 4.5.1 Guo et al. 2011............................. 66 4.5.2 Lares et al. 2011............................ 66 4.5.3 Liu et al. 2011............................. 67 4.5.4 Strigari et al. 2012........................... 67 4.5.5 Nierenberg et al. 2011/2012...................... 67 5 Discussion and Conclusion 68 References 72 vi List of Tables 1.1 Hubble T morphological scale......................... 10 2.1 Properties of the known dwarf spheroidal satellites and the Magellanic Clouds of the Milky Way................................ 18 2.2 Properties of the known dwarf spheroidal satellites of Andromeda..... 20 vii List of Figures 1.1 The Hubble Sequence morphological classification of galaxies........9 2.1 Cumulative Milky Way satellite count vs. galactic declination....... 14 2.2 Local Group luminosity function........................ 16 2.3 Absolute magnitude vs. half-light radius of the Local Group dwarf galaxies 17 2.4 Local Group dwarf colour vs. absolute (B-band) magnitude......... 19 2.5 Cumulative satellite number counts of the Local Group and neighbouring galaxy groups.................................. 25 2.6 Projected satellite positions of the Local Group and neighbouring galaxy groups...................................... 26 2.7 Projected positions of satellite galaxies of the Centaurus A subgroup... 27 2.8 Velocity offset vs. projected separation of the satellites of the Local Group and neighbouring galaxy groups........................ 28 2.9 Absolute magnitudes of known galaxies vs. distance............. 31 3.1 Selection Criteria Schematic Diagram..................... 36 3.2 Masking detection in simulated galaxy distributions............. 38 3.3 Masking correction model........................... 39 3.4 Total masked area vs projected separation.................. 40 3.5 Size-magnitude diagram of SDSS data with the Local Group dwarf galaxies seen from a distance of 25 Mpc........................ 42 4.1 Projected radial density profile........................ 50 viii 4.2 Logarithmic projected radial density profile.................. 51 4.3 Cumulative number over-density profile.................... 53 4.4 Cumulative number over-density profile by magnitude............ 55 4.5 Cumulative number over-density profile by morphology........... 56 4.6 Signal to noise on cumulative number over-density profile by magnitude.. 57 4.7 Signal to noise on cumulative number over-density profile by morphology. 58 4.8 Cumulative excess clustering signal binned by difference in apparent mag- nitude from central galaxy unweighted and weighted versions........ 61 4.9 Cumulative excess clustering signal binned by difference in apparent mag- nitude from central galaxy........................... 62 4.10 Binned and cumulative number over-density profile for the spectroscopic sample...................................... 64 4.11 Velocity offset from central host vs projected separation for spectroscopic detections.................................... 65 ix Chapter 1 Introduction In the early 20th century there was Great Debate regarding the scale of the universe. The \Great Debate" between astronomers Harlow Shapley and Heber Curtis began in 1920 and concerned observations of spiral nebulae. Curtis thought of the universe as composed of many galaxies like the Milky Way, as suggested by observations of the spiral nebulae. Shapley opposed this view, taking the stance that the observed spiral nebulae were gas clouds within the Milky Way and that the universe consisted solely of the Milky Way galaxy. The debate was settled when Edwin Hubble first identified Cepheid variable stars in the neighbouring Andromeda galaxy in the mid 1920s. Using the Cepheid variable stars, Hubble was able to calculate the distance to Andromeda, finding that it was large enough to be considered a distinct galaxy. Since this time, the number of known galaxies has increased to the hundreds of billions, populating an intricate web of structure that is presently the focus of much research in astrophysics and cosmology. The structure that we see in the universe today is the result of early fluctuations in the primordial plasma of baryons, photons, and dark matter that filled the early universe which have been amplified over time. Galaxy clusters are the largest virialized structures in the universe, and the satellite abundances of galaxy