The Extragalactic Distance Scale The Cepheid Distance Scale and its Application to the Absolute Calibration of the Luminosity { Linewidth Relation A thesis presented by Lucas Mat´ıasMacri to The Department of Astronomy in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Astronomy Harvard University Cambridge, Massachusetts September 2001 c 2001, by Lucas Mat´ıasMacri All Rights Reserved ii The Extragalactic Distance Scale The Cepheid Distance Scale and its Application to the Absolute Calibration of the Luminosity { Linewidth Relation Advisor: John P. Huchra Lucas Mat´ıasMacri Abstract This Thesis presents research into several topics related to the Extragalactic Distance Scale; in particular, the Cepheid Period { Luminosity Relation and the Luminosity { Linewidth relation for spiral galaxies. The primary distance indicator of choice in the Local Supercluster is the Cepheid Period { Luminosity Relation. While its absolute calibration is still uncertain at the 10% level, it can yield precise relative distances. I present the discovery of Cepheids in, and the determination of distances to, two galaxies in the Local Supercluster: M33 and NGC 2841. I also present a test of the standard extinction law in other galaxies using near-infrared observations of Cepheids. One of the most-widely used secondary distance indicators for extragalactic work is the luminosity { linewidth relation of spiral galaxies, commonly referred to as the Tully { Fisher relation. I present a complete and consistent database of optical and infrared magnitudes of spiral galaxies that are suitable for the absolute calibration of that relation, and I perform that calibration in the RIHK bands. iii iv Contents Abstract . iii Table of Contents . v List of Figures . ix List of Tables . xiii Acknowledgments . xv Citations to Previously Published Work . xvii 1 Introduction and Summary 1 1.1 Structure of this thesis . 1 1.2 The Cepheid Distance Scale . 2 1.2.1 A historical introduction to Cepheid variables . 2 1.2.2 A modern introduction to Cepheid variables . 8 1.3 The Tully-Fisher relation . 15 2 A Cepheid distance to M33 21 2.1 Introduction . 22 2.2 Observations and data reduction . 23 2.3 Photometry . 26 2.3.1 Initial Processing . 26 2.3.2 Photometry of template images . 27 2.3.3 Photometry of individual frames . 28 2.3.4 Determination of aperture correction coefficients . 28 v 2.3.5 Standard star observations and photometric solutions . 30 2.3.6 Photometric comparisons . 32 2.3.7 Artificial star tests . 35 2.4 The star catalog . 39 2.5 Variable search and classification . 42 2.5.1 Previously-known variables in M33 . 74 2.6 A Cepheid Distance to M33 . 75 2.6.1 The P-L relation of LMC Cepheids . 79 2.6.2 Extinction corrections . 81 2.6.3 Blending bias . 86 2.6.4 The metallicity dependence of the P-L relation . 94 2.6.5 The distance to the LMC . 97 2.6.6 An absolute distance to M33 . 99 3 A Cepheid distance to NGC 2841 101 3.1 Introduction . 102 3.2 Observations and Data Reduction . 102 3.3 Photometry and Calibration . 103 3.4 The Cepheids found in NGC 2841 . 111 3.5 Period-Luminosity Relations and Distance Moduli . 113 3.5.1 Methodology . 113 3.5.2 Distance moduli . 133 3.5.3 Metallicity correction . 136 3.5.4 Error Budget . 136 3.6 Discussion . 138 3.7 Conclusions . 140 4 Infrared observations of extragalactic Cepheids 143 4.1 Introduction . 144 vi 4.2 Observations and Data Reduction . 145 4.2.1 Observations . 145 4.2.2 Data reduction . 146 4.3 Photometry . 148 4.3.1 Technique . 148 4.3.2 Absolute photometric calibrations . 149 4.3.3 Photometric recovery tests . 152 4.3.4 Photometry checks . 153 4.4 The Cepheid sample . 157 4.4.1 Sample selection and identification . 157 4.4.2 Period-Luminosity relations . 174 4.4.3 Observed distance moduli . 174 4.5 Blending effects in M101 Inner . 175 4.6 Consistency of reddening determinations . 191 4.6.1 Predicted relation between E(V{I) and E(V{H) . 191 4.6.2 Observed relation . 192 4.7 Summary . 196 5 Optical and infrared observations of Tully-Fisher calibrators 197 5.1 Introduction . 198 5.2 Optical observations and data reduction . 199 5.3 Infrared observations and data reduction . 201 5.4 Galaxy photometry . 204 5.4.1 Surface photometry measurements . 204 5.4.2 Photometry results and external comparisons . 212 5.5 21-cm linewidths . 215 5.6 Conclusions . 216 6 The absolute calibration of the luminosity{linewidth relation 219 vii 6.1 Introduction . 220 6.2 The calibrator sample . 221 6.3 Analysis . 222 6.4 An application to 2MASS data . 227 6.5 Conclusion . 230 viii List of Figures 1.1 Light and radial velocity curves of δ Cephei . 4 1.2 P-L relation of SMC Cepheids . 6 1.3 Evolutionary track of a 7M star . 9 1.4 P-L tracks for Cepheids of different masses . 14 1.5 The original B- and H-band line width-luminosity relations . 16 2.1 Location of DIRECT M33 fields . 24 2.2 Mosaic of DIRECT M33 fields . 25 2.3 Histogram of seeing values in our frames . 29 2.4 Growth curve corrections . 31 2.5 Test of the internal consistency of our photometry . 34 2.6 Test of the external consistency of our photometry . 36 2.7 Artificial star tests . 37 2.8 Cumulative luminosity functions . 40 2.9 Color-magnitude diagram of 56950 stars in M33 . 41 2.10 Phase coverage as a function of period . 43 2.11 Representative Cepheid light curves . 46 2.12 Representative eclipsing binary light curves . 47 2.13 Representative miscellaneous variable light curves . 48 2.14 Color-magnitude diagram of 682 variables in M33 . 72 2.15 Observed I-band P-L relation for all Cepheids . 73 2.16 LMC Cepheid P-L relations . 80 ix 2.17 Interstellar extinction curves . 83 2.18 Determination of the extinction towards a Cepheid . 83 2.19 Effect of blends on Cepheid colors . 84 2.20 Blending data for 91 Cepheids in our sample . 87 2.21 V and I P-L relations of 61 Cepheids in M33 . 90 2.22 Distribution of ∆µ0 vs. P for 61 Cepheids with V & I data . 91 2.23 Distribution of ∆µ0 vs. P for 20 Cepheids with B, V & I data . 93 2.24 Distribution of ∆µ0 vs. r for 20 Cepheids with B, V & I data. 96 3.1 Ground-based image of NGC 2841 . 105 3.2 Mosaic of the WFPC2 field of view of NGC 2841 . 106 3.3 Medianed images of the four WFPC2 chips . 114-117 3.4 Individual finding charts for the variables . 118 3.5 V and I light curves for the variables . 119-123 3.6 Color-magnitude diagram for the stars detected in our images . 124 3.7 Observed differential luminosity functions . 125 3.8 V-band P-L relation for the selected Cepheids in our sample . 134 3.9 I-band P-L relation for the selected Cepheids in our sample . 135 3.10 Distribution of Leo Cloud & Spur galaxies . 141 4.1 Growth curves for the NICMOS bandpasses . 150 4.2 Photometric recovery tests . 154-155 4.3 External photometry comparison . 159 4.4 Astrometric selection of candidates . 161 4.5 Color-color selection of candidates . 162-163 4.6 Images of the fields . 164-169 4.7 Individual finding charts . 170-171 4.8 Near-IR P-L relations . 176-181 4.9 Optical P-L relations . 182-186 x 4.10 Simulated M101 Inner fields . 188 4.11 P-L relations from simulated M101 Inner fields . ..