Is the evidence for Dark Energy secure from supernova cosmology? Evidence for luminosity evolution of SN Ia from early-type host galaxies Young-Wook Lee Yonsei University, Seoul, Korea Yijung Kang (Yonsei), Young-Lo Kim (Lyon), Chul Chung (Yonsei) & Chang H. Ree (KASI)
Dark Energy: The most serious problem in astrophysics • Most direct evidence for Dark Energy is from Type Ia supernovae…
Discovery of Dark Energy from Type Ia SN Distances … fainter Hubble Residual (HR ≡ μSN – μz) HR Riess+98, Perlmutter+99 brighter Redshift
Type Ia SNe “Standardizable” Candle: Peak luminosity = f(light-curve shape, color) Light-curve shape & color parameters: Dm15(B), D , s, c Assume no evolution with z Luminosity Time
“Tinsley Effect”: Luminosity evolution of standard candle in observational cosmology Allan Sandage Luminosity (stellar population) evolution or Distance difference? Beatrice Tinsley 1968
Hicken et al. 2009: SALT2 Childress et al. 2014 fainter brighter Mean age difference of SNIa progenitor between z = 0.0 & 0.7 ~ 4 Gyr
What is the evidence that there is no evolution in SN Ia luminosity? • No correlation between SN luminosity (after standardization) and host galaxy properties (age related) at local universe (Riess+98; Schmidt+98; Perlmutter+99) N = 8 DHR = 0.006 +/- 0.07 mag. Between Early (old) & Late (young) Hosts • No Evolution But, this was based on small sample! N = 19 Schmidt et al. 1998
But, more recent data from CfA show different result (Hicken+09) DHR = 0.14 +/- 0.07 mag between E/SO & Scd/Sd/Irr ! After LC & extinction corrections Currently, there is no evidence that there is no evolution!
Other well-established correlations from host galaxy studies 1. SNe Ia in less massive host galaxies are fainter by ~0.1 mag (e.g., Sullivan+2010) 2. SNe Ia in locally star-forming environments are ~0.16 magfainter than those in passive environments (Rigault+2013, 18; Kim, Lee+2018) Most likely due to population age or metallicity..
Project YONSEI: YonseiNearbySupernovaeEvolutionInvestigation (Since 2011) High S/N spectra for ~70 nearby early-type host galaxies • 34 nights with LCO 2.5m & MMT 6.5m long-slit spec. • For the first time, directly obtain population age & metallicity from absorption lines (Hb, Fe, Mgb) & population synthesis models • ETGs preferred because of age dating & low extinction • SNANA(Kessler+09) is used for the SNe LC analysis
young old Kang, Kim, Lee+2016
Host Galaxy Data on Metallicity vs. H-beta Grid Yonsei Model Chung, Yoon, Lee 2013 Thomas+2011
Correlation between Host Mass (sv ) and Population Age: “Downsizing” (Kang, Lee+2016, 2019) Markov Chain Monte Carlo analysis Correlation is significant at ~ 4.2 sigma level! No apparent correlation with metallicity • Host mass – SN luminosity correlation is due to population age difference Open circles: Recent star-forming (“rejuvenated”) galaxies excluded as ages are seriously underestimated
Correlation between SN Luminosity & Population Age fainter brighter Correlation is significant at ~2.1 sigma level • SNe in younger hosts are fainter (after standardization) • Evidence for luminosity evolution! • ~0.15 mag fainter for dt = 4 Gyr (YEPS) Kang, Lee+2019, in prep.
Conclusion Our result (based on age) and other correlations (based on age related parameters) all indicate that SNe Ia in younger population environments are fainter! Evidence for luminosity evolution appears to be significant! Taken at face value, this effect can mimic a large fraction (~0.15 mag, ~63%) of the Hubble Residual used in the discovery of the dark energy! Is the evidence for Dark Energy secure from supernova cosmology?