8 research outputs found
Evidence of Environmental Dependencies of Type Ia Supernovae from the Nearby Supernova Factory indicated by Local H{\alpha}
(Abridged) We study the host galaxy regions in close proximity to Type Ia
supernovae (SNe Ia) to analyze relations between the properties of SN Ia events
and environments most similar to where their progenitors formed. We focus on
local H\alpha\ emission as an indicator of young environments. The Nearby
Supernova Factory has obtained flux-calibrated spectral timeseries for SNe Ia
using integral field spectroscopy, allowing the simultaneous measurement of the
SN and its immediate vicinity. For 89 SNe Ia we measure H\alpha\ emission
tracing ongoing star formation within a 1 kpc radius around each SN. This
constitutes the first direct study of the local environment for a large sample
of SNe Ia also having accurate luminosity, color and stretch measurements. We
find that SNe Ia with local H\alpha\ emission are redder by 0.036+/-0.017 mag,
and that the previously-noted correlation between stretch and host mass is
entirely driven by the SNe Ia coming from passive regions. Most importantly,
the mean standardized brightness for SNe Ia with local H\alpha\ emission is
0.094+/-0.031 mag fainter than for those without. This offset arises from a
bimodal structure in the Hubble residuals, that also explains the
previously-known host-mass bias. We combine this bimodality with the cosmic
star-formation rate to predict changes with redshift in the mean SN Ia
brightness and the host-mass bias. This change is confirmed using high-redshift
SNe Ia from the literature. These environmental dependences point to remaining
systematic errors in SNe Ia standardization. The observed brightness offset is
predicted to cause a significant bias in measurements of the dark energy
equation of state. Recognition of these effects offers new opportunities to
improve SNe Ia as cosmological probes - e.g. SNe Ia having local H\alpha\
emission are more homogeneous, having a brightness dispersion of 0.105+/-0.012
mag.Comment: accepted for publication in Section 3. Cosmology of A&A (The official
date of acceptance is 30/08/2013
Type Ia Supernova Hubble Residuals and Host-Galaxy Properties
Kim et al. (2013) [K13] introduced a new methodology for determining
peak-brightness absolute magnitudes of type Ia supernovae from multi-band light
curves. We examine the relation between their parameterization of light curves
and Hubble residuals, based on photometry synthesized from the Nearby Supernova
Factory spectrophotometric time series, with global host-galaxy properties. The
K13 Hubble residual step with host mass is mag for a supernova
subsample with data coverage corresponding to the K13 training; at , the step is not significant and lower than previous measurements.
Relaxing the data coverage requirement the Hubble residual step with host mass
is mag for the larger sample; a calculation using the modes of
the distributions, less sensitive to outliers, yields a step of 0.019 mag. The
analysis of this article uses K13 inferred luminosities, as distinguished from
previous works that use magnitude corrections as a function of SALT2 color and
stretch parameters: Steps at significance are found in SALT2 Hubble
residuals in samples split by the values of their K13 and
light-curve parameters. affects the light-curve width and color around
peak (similar to the and stretch parameters), and
affects colors, the near-UV light-curve width, and the light-curve decline 20
to 30 days after peak brightness. The novel light-curve analysis, increased
parameter set, and magnitude corrections of K13 may be capturing features of
SN~Ia diversity arising from progenitor stellar evolution.Comment: 17 pages, 6 figures. Accepted by Astrophysical Journa