BR Photometry of the Globular Cluster System of NGC 3115
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BR Photometry of the Globular Cluster System of NGC 3115 by S.J. Bickerton A thesis submitted in the Department of Physics in conformit?; with the requirements for the degree of Master of Science Queen's Kingston. Ontario. Canada January. 2002 @ copyright S.J. Bickerton. 2002 National Library Bibliothèque nationale 1 of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 WeUulglon Street 395. rue Wellingtan Otiawa ON KiA ON4 OnawaON K1AûN4 canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence diowing the exclusive pemettant à la National Librq of Canada to Bibliothèque nationale du Canada de reproduce, loan, distriiute or sel reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la fonne de microfiche/film, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or othenwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. ii Abstract The lenticular galavy NGC 3113 sits in isolation in the constellation Sextans. Photometric observations of the gala~ymade with the CFHlZK detector at the Canada- France-Hawaii 3.6m telescope have provided the deepest wide field images of the galavy to date. revealing nearly its entire globular cluster system. The com- preiiensive data show an apparent multimodality in the colour distribution of NGC 31 15. This is suggestive of a complicated formation or evolutionary history and is more consistent with a hierarchical formation mode1 than with one of monolithic collapse. Globular cluster luniinosity functions (GCLFs) wre made using both B ancl R fil ters and yielded apparent turnover niagnit udes of ms =ZL-E1tO.O-I. and rnR=21.9-lf0.O-l. These yield a distance modulus of rn~- -\fB=30.0Tf 0.28 for XGC 3113 and an absolute GCLF turnover in R of .\IR=-7.99k0.10. Tests of the metal- licity/colour effects on the GCLF turnover magnitude (Ashman. Conti. and Zepf. 1995) werr perfornied iising separate GCLFs for three colour groups. Observations supported the proposed systernatic trend. The radial density distribution of globular cliisters was found to be somemhat niore distendeci than the intensity of halo light. So significant difference in object density aas found between 'blue' and 'red' cluster populations. The specific frequency ivas found to be SLv = 1.7 I:::a value typical for an SO galiuy not in a large cluster. Acknowledgement s 1 wish to thank a number of people who have tiad a very positive influence on rny aork here at Queen's. First and foremost. 1 thank rny supervisor Dave Hanes and the Department of Physics at Queen's University. Having arrived as a geophysicist. iinfamiliar with astronomy ou took a chance in providing me the opportunity to study a new discipline. I've enjoyed my work. and I've enjoyed rny time here at Queen's. 1 look fornard to continuing in astronomy. hlany thanks! Three friends aithin the department have on countless occassions willingly provided rnuch needed scientific and technical council. My most sincere thanks go to Kathy Perrett. Steve Biitterworth. and Doug IIcSeil: 1 sirnply can't espress how much I've appreciated your aclvicc and assistance. For assisting me tvith al1 the bureaucratie details inher- eiit in an acadeniic program. my thanks go to llargaret Ilorris. Terry Busse. and Janie Barr. Kithout your help L niight aell have forgotten to register. 1 also wish to thank rny parents and my sisters for their support. For every meal that nasn't eaten in front of a cornputer. I can't tliank ou enough. For yars of hockey. thank ou to virtually everyone in geologv and geophysics. The choice to pursue astronomy carne at the erpense of discontinuing my studies in geophysics. The many geolo- gists and geophysicists who invested so much of their time in my education have continued to be supportive and have provided encouragement through every step. To Colin Thomson. Gerhardt Pratt. John Hanes. Ron Peterson and everyone in the Department of Geology for the past seven years. thank ou! CONTENTS Table of Contents .............................. iv ListofTables ................................. vi ... List of Figures ................................ viii 1 . Introduction ................................. 1 2 . Background .................................. 5 2.1 Photometry. co!our . and the magnitude scale .............. 3 - 2.2 Galas? Formation ............................. i '2.3 GlobularClusters ............................. 8 2.3.1 The Globular Cluster Luminosity Function ........... 10 '2.3.2 The CoIour Distribution ..................... 11 2.3.3 The Colour Gradient ....................... 12 2.3.4 The Radial and Angular Profiles ................. 13 2.3. The Specific Frequency ...................... 13 3 . The Target: NGC 3115. the Spindle Galawy ............. 16 4 . Data Reduction ............................... 18 Contents v 1 Observations ................................ 18 4.2 Frame Preprocessing ........................... 20 4.3 Photometry ................................ 23 4.4 Estimation of recovery using artificial stars: the corripleteness func tion 25 4.5 Object Classification ........................... 30 4.6 Calibrations ................................ 32 4.6.1 The Aperture Correction ..................... 35 4-62 Transformation to thestandardphotornetricsystem ...... 36 4.6.3 Reddening Corrections ...................... 39 5 . AnalysisandResults ............................ 40 .3 .1 The Colour Distribution ......................... 41 5.1.1 Evaliilating the significance of the rnultimodality ........ 43 5.2 The Globular Cluster Luminosity Function ............... 53 5.2.1 The effects of rnetallicity on the GCLF peak .......... 39 5.3 Spatial distributions and relations hips .................. 63 5.3.1 The colour gradient ........................ 66 3 .2 The Radial profiles ........................ 67 5.3.3 The angular profiles ....................... -Pia -.- 5 .4 The Specific Frequency .......................... i i 6 . Discussion and Conclusions ........................ 81 6.1 llultirnodality in the colour distribution ................ 81 6.2 The GCLF and the distance to XGC 3115 ............... 82 Contents vi 6.3 The effects of rnetallicity on the GCLF turnover ............ 83 6.4 Spatial distributions and relationships .................. 84 6.4.1 The colour gradient ........................ 81 6.4.2 The radial distribution ...................... 85 6.4.3 The angular distribution ..................... 86 6.5 The specific frequency .......................... 87 6.6 Conclusions ................................ 88 References ................................... 91 A . The Use of sliding-keroel distributions ................. 9-4 A.1 Sornialization to a niiniber density ................... 9-1 A.? Cncertainty ................................ 96 B . Supplemeatary Figures .......................... 97 C. Coordinates. magnitudes and colours of the globular cluster can- didates .....................................120 LIST OF TABLES 3.1 Physical parameters for SCC 3113 . Al1 values were retrieved from the NASA Estragalactic Database (NED. 200 1) .............. 16 4 1 Perceritages of data culleci for both artificial and real objects ..... 34 4.2 Aperture correct ion factors ........................ 36 4 .3 Calibration coefficients .......................... 38 4.4 RMS resictuals for calibratioris ...................... 35 5 .1 Best-fit Gaiissian pararneters for the GCLFs .............. 56 .?.2 Peaks for the GCLFs with final uncertainties .............. 56 3.3 Estimates of the GCLF peak in B .................... j9 5.4 Best-fit Gaussian parameters for the GCLFs .............. 60 - - 3.3 Distance moduli computed using separate (B-R) subgroups ...... 63 5 6 Least-squares fit radial profile parameters ................ 72 - - 3 Least-squares fit a parameters for al1 data. and (B-R) subgroups ... 7-1 6.1 Typical SN values compiled by Harris ( 1991).............. 87 C.1 Coordiriates . magnitudes and colours of the globular cluster candi- dates (Detector 1)............................. 120 vii ... List of Tables VIU C. 2 Coordinat es. niagni t udes and colours of the globular cluster candi- dates (Detector 2). .........................123 C.3 Coordinates. magnitudes and colours of the globular cluster candi- dates (Detector 3). ............................ 126 C.4 Coordinates. magnitudes and colours of the globular cluster candi- dates (Detector 1). ........................128 LIST OF FIGURES Digitized sky suryey (DSS) image of SGC 3115 ............ 3 The CFH1X detector .......................... 19 The passbands for the filters at CFHT ................. 19 Tlie preprocessed niosaic image of SGC 3115 .................> 9 Schematic Aow of the photomet- algorithm .............. 24 Tlie niedian filtered niosaic image of SGC 3 113 ............ 26 Conipleteness fiinct ions for dctertor 1 .................. 29 Tlie pliotometric scatter of artificial stars iidded to detector .... 31 Th r-2 classification diagram for the itrtificinl stars for d~tector1 . 33 The r-2 classification diagrani for t lie real data ............ 33 The cluster candidate . and background object regions for