Sullivan, M. and Conley, A. and Howell, D. A. and Neill, J. D. and Astier, P. and Balland, C. and Basa, S. and Carlberg, R. G. and Fouchez, D. and Guy, J. and Hardin, D. and Hook, I. M. and Pain, R. and Palanque-Delabrouille, N. and Perrett, K. M. and Pritchet, C. J. and Regnault, N. and Rich, J. and Ruhlmann-Kleider, V. and Baumont, S. and Hsiao, E. and Kronborg, T. and Lidman, C. and Perlmutter, S. and Walker, E. S. (2010) The dependence of Type Ia Supernovae luminosities on their host galaxies. Monthly Notices of the Royal Astronomical Society, 406 (2). pp. 782-802. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20100831-152257012
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Precision cosmology with Type Ia supernovae (SNe Ia) makes use of the fact that SN Ia luminosities depend on their light-curve shapes and colours. Using Supernova Legacy Survey (SNLS) and other data, we show that there is an additional dependence on the global characteristics of their host galaxies: events of the same light-curve shape and colour are, on average, 0.08 mag (≃4.0σ) brighter in massive host galaxies (presumably metal-rich) and galaxies with low specific star formation rates (sSFR). These trends do not depend on any assumed cosmological model, and are independent of the SN light-curve width: both fast and slow-declining events show the same trends. SNe Ia in galaxies with a low sSFR also have a smaller slope (‘β’) between their luminosities and colours with ~2.7σ significance, and a smaller scatter on SN Ia Hubble diagrams (at 95 per cent confidence), though the significance of these effects is dependent on the reddest SNe. SN Ia colours are similar between low-mass and high-mass hosts, leading us to interpret their luminosity differences as an intrinsic property of the SNe and not of some external factor such as dust. If the host stellar mass is interpreted as a metallicity indicator using galaxy mass–metallicity relations, the luminosity trends are in qualitative agreement with theoretical predictions. We show that the average stellar mass, and therefore the average metallicity, of our SN Ia host galaxies decreases with redshift. The SN Ia luminosity differences consequently introduce a systematic error in cosmological analyses, comparable to the current statistical uncertainties on parameters such as w, the equation of state of dark energy. We show that the use of two SN Ia absolute magnitudes, one for events in high-mass (metal-rich) galaxies and the other for events in low-mass (metal-poor) galaxies, adequately corrects for the differences. Cosmological fits incorporating these terms give a significant reduction in χ^2 (3.8σ–4.5σ); linear corrections based on host parameters do not perform as well. We conclude that all future SN Ia cosmological analyses should use a correction of this (or similar) form to control demographic shifts in the underlying galaxy population.
|Additional Information:||© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 March 26. Received 2010 March 26; in original form 2010 February 26. Article first published online: 4 May 2010. MS acknowledges support from the Royal Society. This paper is based in part on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada–France– Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France and the University of Hawaii. This work is based in part on data products produced at the Canadian Astronomy Data Centre as part of the CFHT Legacy Survey, a collaborative project of NRC and CNRS. Based in part on observations obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX, the WIRDS (WIRcam Deep Survey) consortium, and the Canadian Astronomy Data Centre. This research was supported by a grant from the Agence Nationale de la Recherche ANR-07- BLAN-0228. Canadian collaboration members acknowledge support from NSERC and CIAR; French collaboration members from CNRS/IN2P3, CNRS/INSU and CEA. Based in part on observations made with ESO Telescopes at the Paranal Observatory under program IDs 171.A-0486 and 176.A-0589. Based in part on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministrio da Cincia e Tecnologia (Brazil) andMinisterio de Ciencia, Tecnologa e Innovacin Productiva (Argentina). The programmes under which data were obtained at the Gemini Observatory are: GS-2003BQ- 8, GN-2003B-Q-9, GS-2004A-Q-11, GN-2004A-Q-19, GS- 2004B-Q-31, GN-2004B-Q-16, GS-2005A-Q-11, GN-2005A-11, GS-2005B-Q-6, GN-2005B-Q-7, GN-2006A-Q-7 and GN-2006BQ- 10. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and theNational Aeronautics and SpaceAdministration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.|
|Subject Keywords:||supernovae: general; cosmology: observations; distance scale|
|Official Citation:||Sullivan, M., Conley, A., Howell, D. A., Neill, J. D., Astier, P., Balland, C., Basa, S., Carlberg, R. G., Fouchez, D., Guy, J., Hardin, D., Hook, I. M., Pain, R., Palanque-Delabrouille, N., Perrett, K. M., Pritchet, C. J., Regnault, N., Rich, J., Ruhlmann-Kleider, V., Baumont, S., Hsiao, E., Kronborg, T., Lidman, C., Perlmutter, S. and Walker, E. S. (2010), The dependence of Type Ia Supernovae luminosities on their host galaxies. Monthly Notices of the Royal Astronomical Society, 406: 782–802. doi: 10.1111/j.1365-2966.2010.16731.x|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||08 Sep 2010 15:52|
|Last Modified:||26 Dec 2012 12:23|
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