Cool Gas in Brightest Cluster Galaxies
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Cool Gas in Brightest Cluster Galaxies Cool Gas in Brightest Cluster Galaxies Proefschrift ter verkrijging van de graad van Doctor aan de Universiteit Leiden, op gezag van de Rector Magnificus prof. mr. P.F. van der Heijden, volgens besluit van het College voor Promoties te verdedigen op donderdag 6 oktober 2011 klokke 11.15 uur door Johannes Bernardus Raymond Oonk geboren te Hengelo in 1981 Promotiecommissie Promotor: Prof. dr. W. Jaffe Overige leden: Dr. J. Brinchmann Prof. dr. A. C. Fabian (University of Cambridge) Prof. dr. F. P. Israel Prof. dr. K. Kuijken ISBN: 978-94-6191-031-8 Contents vii Contents Page Chapter 1. Introduction 1 1.1 Galaxy Clusters ................................... 1 1.2 Cool-core Clusters ................................. 1 1.3 ThehotgasatT>107 K .............................. 2 1.4 ThecoolgasatT<104 K .............................. 2 1.5 This Thesis ..................................... 3 1.6 Outlook ....................................... 5 Chapter 2. Warm Molecular Gas in Abell 2597 and Sersic 159-03 7 2.1 Introduction .................................... 8 2.1.1 This project ................................. 10 2.2 Observations and reduction ............................ 10 2.2.1 Near Infrared Data ............................. 10 2.2.2 X-ray Data ................................. 13 2.2.3 Radio Data ................................. 14 2.3 Abell 2597 – Gas Distribution ........................... 14 2.3.1 Molecular gas ................................ 15 2.3.2 Ionised gas ................................. 16 2.4 Abell 2597 – Gas Kinematics ........................... 16 2.4.1 Molecular gas ................................ 17 2.4.2 Ionised gas ................................. 18 2.4.3 Filaments .................................. 18 2.5 Sersic 159-03 – Gas Distribution .......................... 19 2.5.1 Molecular gas ................................ 20 2.5.2 Ionised gas ................................. 20 2.6 Sersic 159-03 – Gas Kinematics .......................... 21 2.6.1 Molecular gas ................................ 21 2.6.2 Ionised gas ................................. 22 2.6.3 Filaments .................................. 22 2.7 Physical Conditions in the Warm Molecular Gas ................. 22 2.7.1 A2597: Selected regions .......................... 23 2.7.2 S159: Selected regions ........................... 24 2.7.3 Thermal excitation of the molecular gas .................. 24 2.7.4 Luminosity of the Warm Molecular Gas .................. 26 2.7.5 Mass of the Warm Molecular Gas ..................... 27 2.7.6 Mass of the Ionised Gas .......................... 27 2.7.7 Stability of the Filaments .......................... 28 2.8 X-ray and Radio Emission ............................. 29 viii Contents 2.8.1 X-ray emission ............................... 29 2.8.2 Radio emission ............................... 30 2.9 Summary ...................................... 32 2.10 Conclusions .................................... 35 A.1 ........................................... 58 A.2 ........................................... 58 A.3 ........................................... 58 Chapter 3. FUV emission in Abell 2597 and Abell 2204 67 3.1 Introduction .................................... 68 3.1.1 This project ................................. 69 3.2 ........................................... 70 3.2.1 HST ACS-SBC imaging .......................... 70 3.2.2 Optical data ................................. 71 3.2.3 Radio data .................................. 71 3.2.4 X-ray data .................................. 72 3.3 ........................................... 72 3.3.1 FUV: A2597 and A2204. .......................... 72 3.3.2 Optical: A2597 and A2204 ......................... 73 3.3.3 Radio and X-ray emission ......................... 73 3.3.4 Surface brightness profiles ......................... 75 3.4 Total FUV/U emission ............................... 76 3.4.1 Bruzual & Charlot 2003 SSP models .................... 76 3.5 Excess FUV/U: Stellar Origin ? .......................... 77 3.5.1 Contamination by line emission ...................... 77 3.5.2 Removing the old stellar population .................... 79 3.5.3 The FUVν,exc/Uν,exc excess ratio ...................... 80 3.5.4 Nebular continuum emission ........................ 81 3.5.5 Dust intrinsic to the BCG .......................... 82 3.6 Star formation ................................... 83 3.6.1 TheHα nebula ............................... 83 3.6.2 FUVandHα star formation rates ...................... 84 3.6.3 Dust and gas mass estimates from AV ................... 85 3.7 Excess FUV/U: Non-stellar Origin ? ........................ 86 3.7.1 Active Galactic Nuclei ........................... 86 3.7.2 Non-thermal processes ........................... 86 3.8 ........................................... 86 3.8.1 Crawford & Fabian 1993 .......................... 86 3.8.2 Hicks et al. 2010 .............................. 88 3.8.3 The extinction law in BCGs ........................ 88 3.8.4 A2597 versus A2204 ............................ 90 3.9 ........................................... 91 B.1 ........................................... 116 B.2 ........................................... 119 B.3 ........................................... 121 Contents ix Chapter 4. Herschel photometry of brightest cluster galaxies in cooling flow clusters 123 4.1 Introduction .................................... 124 4.2 Observations .................................... 124 4.2.1 PACS Data ................................. 125 4.2.2 SPIRE Data ................................. 125 4.3 Results ....................................... 126 4.4 Discussion and conclusions ............................ 128 4.5 Acknowledgements ................................. 129 Chapter 5. Herschel observations of FIR emission lines in brightest cluster galaxies 135 5.1 Introduction .................................... 136 5.2 Observations .................................... 137 5.3 Results ....................................... 138 5.4 Discussion ..................................... 140 5.5 Conclusions .................................... 141 5.6 Acknowledgements ................................. 141 Chapter 6. Optical Line Emission in BCGs 143 6.1 Introduction .................................... 144 6.1.1 This Project ................................. 144 6.1.2 Targets ................................... 145 6.2 ........................................... 145 6.3 ........................................... 146 6.3.1 Spatially integrated spectra ......................... 147 6.3.2 Variations along the Slit .......................... 148 6.4 Diagnostic diagrams ................................ 149 6.5 ........................................... 150 6.5.1 Dust ..................................... 150 6.5.2 Temperature ................................. 151 6.5.3 Density ................................... 151 6.5.4 Metallicity ................................. 152 6.5.5 Ionisation Parameter ............................ 152 6.6 MAPPINGS III line modelling ........................... 153 6.6.1 Stars ..................................... 154 6.6.2 AGN .................................... 155 6.6.3 Bremsstrahlung ............................... 156 6.7 Combining Stars and Bremsstrahlung ....................... 157 6.7.1 The combined model grid ......................... 157 6.7.2 Exploring the best-fit combined models .................. 158 6.7.3 Gas heating in A2597 ............................ 161 6.8 ........................................... 165 6.8.1 Warm, low-ionisation gas in BCGs ..................... 165 6.8.2 Comparison with previous studies ..................... 167 6.9 ........................................... 169 C.1 ........................................... 196 x Contents C.1.1 Photon spectra A2597 ........................... 196 C.1.2 Ionisation fractions A2597 ......................... 203 Nederlandse samenvatting 205 Curriculum Vitae 213 Nawoord 215 Chapter 1 Introduction 1.1 Galaxy Clusters Clusters of galaxies were originally discovered by Charles Messier and William Herschel. Their extragalactic nature was first established by Vesto Slipher and Edwin Hubble. They are the most 13 15 massive (M 10 − M ), gravitationally bound structures in the known universe and they are the objects∼ in which the⊙ need for dark matter was first pointed out by Fritz Zwicky in 1937. Recent investigations show that the baryonic matter represents about 16% of their total mass. Dark matter makes up the remaining 84% of the mass. About 80% of the baryons are situated in the intracluster medium (ICM). The rest is situated in the stars that make up the galaxies within the cluster (e.g. see Peterson & Fabian 2006, for a recent review). One of the major goals in modern astronomy is to understand the formation of large-scale structure and the evolution of galaxies. Galaxy clusters provide us with the means to do just this. Hierarchical structure formation dictates that the most massive objects, i.e. clusters, form last, which means now. Studying the clustering of galaxies allows us to constrain cosmological models. The dense and crowded environment strongly affects the evolution of galaxies living in clusters and allows us to study important physical processes such as gas stripping and kinemat- ical segregation. The lensing properties of galaxy clusters also make them great tools to study their mass, the properties of dark matter and the details of high-redshift galaxies. In recent years it has