Strong dependence of Type Ia supernova standardization on the local specific star formation rate^⋆

¹ Université de Lyon, Université de Lyon 1, CNRS/IN2P3, Institut de Physique des Deux Infinis, Lyon, France
² Université Clermont Auvergne, CNRS/IN2P3, Laboratoire de Physique de Clermont, 63000 Clermont-Ferrand, France
e-mail: m.rigault@ipnl.in2p3.fr
³ Institut fur Physik, Humboldt-Universitat zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
⁴ Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
⁵ Laboratoire de Physique Nucléaire et des Hautes Énergies, Université Pierre et Marie Curie Paris 6, Université Paris Diderot Paris 7, CNRS-IN2P3, 4 place Jussieu, 75252 Paris Cedex 05, France
⁶ Department of Physics, Yale University, New Haven, CT 06250-8121, USA
⁷ Department of Physics, University of California Berkeley, 366 LeConte Hall MC 7300, Berkeley, CA 94720-7300, USA
⁸ Department of Physics and Astronomy, University of Southampton, Southampton, Hampshire SO17 1BJ, UK
⁹ The Oskar Klein Centre, Department of Physics, AlbaNova, Stockholm University, 106 91 Stockholm, Sweden
¹⁰ Aix Marseille Université, CNRS/IN2P3, CPPM UMR 7346, 13288 Marseille, France
¹¹ Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
¹² Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102, Goleta, CA 93117, USA
¹³ Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
¹⁴ Deutsches Elektronen-Synchrotron, 15735 Zeuthen, Germany
¹⁵ Tsinghua Center for Astrophysics, Tsinghua University, Beijing 100084, PR China
¹⁶ Centre de Recherche Astronomique de Lyon, Université Lyon 1, 9 Avenue Charles André, 69561 Saint Genis Laval Cedex, France
¹⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁸ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
¹⁹ Computational Cosmology Center, Computational Research Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road MS 50B-4206, Berkeley, CA 94720, USA
²⁰ Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan

Received: 6 January 2017
Accepted: 28 May 2020

Abstract

As part of an on-going effort to identify, understand and correct for astrophysics biases in the standardization of Type Ia supernovae (SN Ia) for cosmology, we have statistically classified a large sample of nearby SNe Ia into those that are located in predominantly younger or older environments. This classification is based on the specific star formation rate measured within a projected distance of 1 kpc from each SN location (LsSFR). This is an important refinement compared to using the local star formation rate directly, as it provides a normalization for relative numbers of available SN progenitors and is more robust against extinction by dust. We find that the SNe Ia in predominantly younger environments are Δ_Y = 0.163 ± 0.029 mag (5.7σ) fainter than those in predominantly older environments after conventional light-curve standardization. This is the strongest standardized SN Ia brightness systematic connected to the host-galaxy environment measured to date. The well-established step in standardized brightnesses between SNe Ia in hosts with lower or higher total stellar masses is smaller, at Δ_M = 0.119 ± 0.032 mag (4.5σ), for the same set of SNe Ia. When fit simultaneously, the environment-age offset remains very significant, with Δ_Y = 0.129 ± 0.032 mag (4.0σ), while the global stellar mass step is reduced to Δ_M = 0.064  ±  0.029 mag (2.2σ). Thus, approximately 70% of the variance from the stellar mass step is due to an underlying dependence on environment-based progenitor age. Also, we verify that using the local star formation rate alone is not as powerful as LsSFR at sorting SNe Ia into brighter and fainter subsets. Standardization that only uses the SNe Ia in younger environments reduces the total dispersion from 0.142  ±  0.008 mag to 0.120  ±  0.010 mag. We show that as environment-ages evolve with redshift, a strong bias, especially on the measurement of the derivative of the dark energy equation of state, can develop. Fortunately, data that measure and correct for this effect using our local specific star formation rate indicator, are likely to be available for many next-generation SN Ia cosmology experiments.