Spectroscopic Signatures of Multiple Populations in Globular Clusters By James T Banister A thesis submitted in partial fulfilment for the requirements for the degree of MSc (by Research) at the University of Central Lancashire & The Jeremiah Horrocks Institute September 2020 STUDENT DECLARATION FORM Type of Award MSc (By Research) School Natural Sciences Sections marked * delete as appropriate 1. Concurrent registration for two or more academic awards Either *I declare that while registered as a candidate for the research degree, I have not been a registered candidate or enrolled student for another award of the University or other academic or professional institution 2. Material submitted for another award Either *I declare that no material contained in the thesis has been used in any other submission for an academic award and is solely my own work 3. Collaboration Where a candidate’s research programme is part of a collaborative project, the thesis must indicate in addition clearly the candidate’s individual contribution and the extent of the collaboration. Please state below: _________________________________________________________________________ 4. Use of a Proof-reader or *No proof-reading service was used in the compilation of this thesis. Signature of Candidate Print name: James Thomas Banister i Spectroscopic Signatures of Multiple Populations in Globular Clusters James T Banister Abstract This thesis presents a study of the integrated light spectra of local globular clusters, looking for chemical enhancements which could be the signatures of multiple populations. Using data from the WiFeS Atlas of Galactic Globular cluster Spectra: the spectra are fit to SSP models via penalised pixel fitting techniques looking for poor fitting regions which could signify chemical enhancements. Line indices of key regions are measured, and nitrogen enhancements are found in the CN region ∼4100 Å for almost all globular clusters with evidence for elemental abundance variations in other regions. Also, nitrogen enhancement is found in other compact stellar systems (UCDs and some cEs) and the inner light of high mass galaxies, suggesting a possible relation between high stellar density and nitrogen enhancement. September, 2020 Supervisors: Mark Norris, Ph.D. and Joanne Pledger, Ph.D. University of Central Lancashire Jeremiah Horrocks Institute ii Contents Declaration i List of Figures vii List of Tables ix 1 Introduction 1 1.1 Globular Clusters . 1 1.2 Multiple Populations . 2 1.3 Integrated Light Observation . 3 1.4 A Brief Preamble to Available Globular Cluster Data . 4 2 Theory 5 2.1 Globular Clusters . 5 2.1.1 Milky Way Globular Clusters & Halo Enrichment Via Tidal Effects . 7 2.1.2 Magellanic Cloud and Fornax DSG Globular Clusters . 9 2.1.3 Extragalactic Globular Clusters . 12 2.2 Multiple Populations . 13 2.2.1 Chemical Abundance Variations & Correlations . 15 2.2.2 Single Population Globular Clusters . 19 2.3 Formation Theories of Multiple Populations . 20 2.3.1 AGB Stars . 21 2.3.2 Fast Rotating Massive Stars (FRMS) . 22 2.3.3 Binary Interactions . 23 2.3.4 Black Hole Accretion Disk Nucleosynthesis . 24 3 Data & Data Reduction 26 3.1 WAGGS . 26 3.1.1 Globular Cluster Selection . 27 iii 3.1.2 Observations . 28 3.1.3 Equipment & Data . 31 3.2 Reduction . 32 3.2.1 Redshift . 33 3.2.2 Combination . 36 3.2.3 Error Spectra . 38 3.2.4 Omitted Globular Clusters . 39 3.3 Additional Data . 39 3.3.1 Galaxies -Trager . 40 3.3.2 M31 GCs -Schiavon . 40 3.3.3 M87 GCs and UCDs . 40 3.3.4 MODS Objects . 41 3.3.5 SDSS Galaxy Bins . 41 4 Fitting to SSP Models 43 4.1 pPXF . 43 4.2 Single Stellar Population Models . 44 4.2.1 MILES SSPs . 44 4.2.2 Conroy . 46 4.3 Fitting Procedure . 46 4.3.1 Example Fitting Procedure . 48 4.3.2 Regions of interest . 48 4.3.3 Fit Comparison . 50 4.3.4 Error calculations . 50 5 Measuring Indices 52 5.1 Line Index Systems . 52 5.1.1 LICK/IDS & LIS . 52 5.2 Measurements . 54 5.3 Offsets from Literature . 54 5.3.1 Current Published Works . 54 5.3.2 Offset Calculation . 55 5.3.3 Thomas SSP Models . 57 6 Signatures of Multiple Populations 59 6.1 Single Stellar Population Fitting . 59 6.1.1 Other Poor Fitting Regions . 61 iv 6.2 Line Index systems . 64 6.2.1 Alpha Insensitive Metallicity Index . 64 6.2.2 Globular Clusters . 64 6.2.3 Extragalactic Stellar Systems . 67 6.2.4 Uncertainty Calculations . 70 7 Conclusions and Discussion of Future Work 73 7.1 Evidence of Multiple Populations . 73 7.1.1 N enhancement in Dense Stellar Systems . 75 7.2 Age Estimation Problem . 76 7.3 Conclusion . 78 7.4 Future Research . 79 Bibliography 81 8 APPENDIX 86 v Acknowledgements Firstly I would like to thank Dr Mark Norris for continued support and advice on the research, without which I would undoubtedly not be here, and thanks for providing additional stellar system data and for prompt replies to any question regardless of time or day. I would also like to thank Dr Chris Usher for providing extra information on the WAGGS survey and data set. Thanks to Thomas Davison and David Glass for advice on the proper use of pPXF and thanks again to Thomas Davison for providing binned SDSS galaxy spectra. For all of the support from the people who shared an office with me before Covid-19 forced us out, I would like to give my thanks. I would also like to thank Covid-19 for giving me no choice but to stay inside these last few months giving me more time to work on the thesis. vi List of Figures 2.1 The CMD of NGC 2808 . 7 2.2 Position of the Sagittarius Dwarf Galaxy relative to the Milky Way . 8 2.3 Age metallicity plot of globular clusters in the Magellanic Clouds . 10 2.4 The positions of globular clusters in the Fornax dwarf spheroidal galaxy . 11 2.5 The CMD of NGC 5139 showing multiple main sequence turn off points . 14 2.6 The first detection of multiple populations in globular clusters . 15 2.7 The elemental correlations present in globular clusters due to multiple popula- tions, here plotted over photometric data of NGC 6752 . 16 2.8 A plot of the split main sequence, multiple turn off points of NGC 5139 with isochrones plotted over the top . 18 2.9 A plot showing how the split main sequence of a globular cluster is detected . 20 3.1 [Fe/H] against Age for the globular clusters in the WAGGS sample. 26 3.2 Field-of-view of the WAGGS observations for 3 GCs . 30 3.3 The fraction of the V-band luminosity in the WiFeS field-of-view compared tothe full v-band luminosity of the GC . 31 3.4 The grating efficiencies of the WiFeS gratings at the most efficient angle of incidence 32 3.5 The redshift adjusted B7000 grating spectra for the majority of the globular clusters separated according to [Fe/H] into 8 bins. 33 3.6 A diagram of the spectra of NGC 2808 during the redshift adjusting and regrid- ding process . 35 3.7 A diagram of the grating combination process used for the WAGGS spectra . 37 3.8 A full WAGGS spectrum with associated 1σ errors for NGC 5694 . 38 3.9 The Voronoi diagram describing the bins of the SDSS galaxy spectra . 42 4.1 An example of the new linearly combined SSP models . 45 4.2 pPXF fit and mass fraction plot of NGC 104 with no regions omitted . 48 4.3 pPXF fit and mass fraction plot of NGC 104 with omitted regions . 49 vii 4.4 A comparison between the mass fraction plots in literature and those found in this project for NGC 6715 . 51 5.1 Example of Lick indices, CN1 and CN2 over the spectra of NGC 104 . 53 5.2 The Offsets between WAGGS line indices and those of literature . 56 6.1 pPXF fit of NGC 104 with omitted regions . 60 6.2 Conroy models showing where C and N effect a stellar spectrum between 3800 and 4600 Å ...................................... 60 6.3 pPXF fit and mass fraction plot of NGC 104 with omitted regions . 62 6.4 Spectral indices plot of CN1 against metallicity showing WAGGS GCs and SSP models with a colour bar of age for the WAGGS globular clusters . 65 6.5 Spectral indices plot of CN2 against metallicity showing WAGGS and M31 GCs and SSP models with a colour bar of age for the WAGGS globular clusters . 66 6.6 Spectral indices plot of CN1 against metallicity showing WAGGS and M31 GCs and enhanced SSP models with a colour bar of age for the WAGGS globular clusters 67 6.7 Spectral indices plot of CN1 against metallicity showing GCs, UCDs, cEs and enhanced SSP models with a colour bar of age for the globular clusters . 68 6.8 Spectral indices plot of CN1 against metallicity showing GCs, UCDs, enhanced SSP models, SDSS binned galaxies and galactic core spectral indices, with a colour bar of age for the globular clusters . 70 6.9 Spectral indices plot of CN1 against metallicity showing GCs, UCDs, cEs, en- hanced SSP models and SDSS binned galaxies with a colour bar of mass in the galaxies . 72 7.1 Spectral indices plot of CN1 against metallicity showing GCs, UCDs, enhanced SSP models and SDSS binned galaxies with a colour bar of stellar density in the galaxies . 76 viii List of Tables 3.1 Signal to noise ratios of the WAGGS data.