Projected distances to host galaxy reduce SNIa dispersion

Ryley Hill,R Trotta,W Parker,D A Van Dyk,H Shariff,L B Lucy,M Paulus,S Ali-Khan,S-K Moon,Y Liu,X Jiao

doi:10.1093/mnras/sty2510

Abstract

We use multi-band imagery data from the Sloan Digital Sky Survey (SDSS) to measure projected distances of 302 supernova type Ia (SNIa) from the centre of their host galaxies, normalized to the galaxy's brightness scale length, with a Bayesian approach. We test the hypothesis that SNIas further away from the centre of their host galaxy are less subject to dust contamination (as the dust column density in their environment is smaller) and/or come from a more homogeneous environment. Using the Mann-Whitney U test, we find a statistically significant difference in the observed colour correction distribution between SNIas that are near and those that are far from the centre of their host. The local p-value is 3 x 10^{-3}, which is significant at the 5 per cent level after look-elsewhere effect correction. We estimate the residual scatter of the two subgroups to be 0.073 +/- 0.018 for the far SNIas, compared to 0.114 +/- 0.009 for the near SNIas -- an improvement of 30 per cent, albeit with a low statistical significance of 2sigma. This confirms the importance of host galaxy properties in correctly interpreting SNIa observations for cosmological inference.

Highlights

The Nobel Prize for Physics 2011 was awarded for the discovery that the universe is accelerating
We investigate the 368 SNIae from the Sloan Digital Sky Survey (SDSS) II Supernova Survey (Sako et al 2014) contained in the Joint Light-curve Analysis (JLA) supernova type Ia (SNIa) compilation (Betoule et al 2014), spanning the redshift range 0.04 ≤ z ≤ 0.4 and with median redshift zmed = 0.2
The significance of the difference is approximately 2.0σ. While this is not strongly significant, we emphasize the small sample size (NSNIa = 49 for the dr ≥ 3 sub-group), which results in a fairly wide posterior distribution for σres. This means that SNIae at large galactocentric distances show better standardization properties than the whole data set

Summary

Introduction

The Nobel Prize for Physics 2011 was awarded for the discovery that the universe is accelerating. The number of SNIa observations since that seminal discovery has grown rapidly: we have hundreds of spectroscopically confirmed SNIae (e.g., Astier et al 2006; WoodVasey et al 2007; Amanullah et al 2010; Kowalski et al 2008; Kessler et al 2009; Freedman et al 2009; Contreras et al 2010; Balland et al 2009; Bailey et al 2008; Hicken et al 2009; Suzuki et al 2012; Rest et al 2014; Betoule et al 2014), which have been used to measure the distance modulus to z ∼ 1.9 (Jones et al 2013) This low-redshift probe of the expansion history of the Universe, coupled with the high-redshift measurements of the Cosmic Microwave Background anisotropies, has been a vital tool for determining. The diversity of SNIae appears to suggest that SNIae are produced by more than one progenitor channel: no single channel (i.e, single degenerate scenario, where a CO white dwarf accretes mass from a non-degenerate companion start; or double degenerate scenario, the merging of two white dwarfes) can account for all of the available observations (see e.g. Maeda & Terada 2016 for a recent review)

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Conclusion