The Dependence of Type Ia Supernova Luminosities on their Host Galaxies

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 05/2010; DOI: 10.1111/j.1365-2966.2010.16731.x
Source: OAI


(Abridged) 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,
0.08mag (~4.0sigma) brighter in massive host galaxies (presumably metal-rich)
and galaxies with low specific star-formation rates (sSFR). SNe Ia in galaxies
with a low sSFR also have a smaller slope ("beta") between their luminosities
and colours with ~2.7sigma significance, and a smaller scatter on SN Ia Hubble
diagrams (at 95% 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, 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. We show that
the use of two SN Ia absolute magnitudes, one for events in high-mass
(metal-rich) galaxies, and one for events in low-mass (metal-poor) galaxies,
adequately corrects for the differences. Cosmological fits incorporating these
terms give a significant reduction in chi^2 (3.8-4.5sigma). We conclude that
future SN Ia cosmological analyses should use a correction of this (or similar)
form to control demographic shifts in the galaxy population.

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Available from: Vanina Ruhlmann-Kleider, May 05, 2014
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    • "If so, the timing of the transition could determine how far the white dwarf expanded and thus how much 56 Ni was produced. Even with this assumption, however, it remains unclear why the outcome would depend on the population which the progenitor is in, i.e., why, as is observed, more luminous SN Ia preferentially occur in younger populations (Hamuy et al., 1995; Sullivan et al., 2010). "
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    ABSTRACT: Thermonuclear supernovae result when interaction with a companion reignites nuclear fusion in a carbon-oxygen white dwarf, causing a thermonuclear runaway, a catastrophic gain in pressure, and the disintegration of the whole white dwarf. It is usually thought that fusion is reignited in near-pycnonuclear conditions when the white dwarf approaches the Chandrasekhar mass. I briefly describe two long-standing problems faced by this scenario, and our suggestion that these supernovae instead result from mergers of carbon-oxygen white dwarfs, including those that produce sub-Chandrasekhar mass remnants. I then turn to possible observational tests, in particular those that test the absence or presence of electron captures during the burning.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 06/2013; 371(1992):20120236. DOI:10.1098/rsta.2012.0236 · 2.15 Impact Factor
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    • "At that time, however, there was only a small number (the order of tens) of observed SNe Ia in any of the available samples, so the uncertainties were statistically limited; the main task was gathering new, larger, uniform datasets. For the recent compilations and surveys [13] [14] [15] [16] [17] [18], and the more so for the future ones [19] [20] [21], we are no longer sample-limited; the urgency is again on the physics of the SN Ia phenomenon and all the aspects which – 1 – impact it: nature of progenitor binary system (single-degenerate versus double degenerate, tardy versus prompt events) [22] [23] [24], properties of host galaxy [25] [26], mechanisms of explosion [27], extinction/intrinsic color variations [28] [29], K-correction and template calibration [30] [31], flux calibration [32], inhomogeneities (peculiar velocities [33] [34], gravitational lensing [35] [36], etc). We would also like to call attention to the particularly clear, informative and up-to-date generic review articles on SNe Ia by Howell [37], Kirshner [38], and Goobar & Leibundgut [39]. "
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    ABSTRACT: By using the Sloan Digital Sky Survey (SDSS) first year type Ia supernova (SN Ia) compilation, we compare two different approaches (traditional \chi^2 and complete likelihood) to determine parameter constraints when the magnitude dispersion is to be estimated as well. We consider cosmological constant + Cold Dark Matter (\Lambda CDM) and spatially flat, constant w Dark Energy + Cold Dark Matter (FwCDM) cosmological models and show that, for current data, there is a small difference in the best fit values and $\sim$ 30% difference in confidence contour areas in case the MLCS2k2 light-curve fitter is adopted. For the SALT2 light-curve fitter the differences are less significant ($\lesssim$ 13% difference in areas). In both cases the likelihood approach gives more restrictive constraints. We argue for the importance of using the complete likelihood instead of the \chi^2 approach when dealing with parameters in the expression for the variance.
    Astronomy and Astrophysics 04/2011; 541. DOI:10.1051/0004-6361/201118599 · 4.38 Impact Factor
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    ABSTRACT: We present Keck high-quality rest-frame ultraviolet (UV) through optical spectra of 21 Type Ia supernovae (SNe Ia) in the redshift range 0.11 < z < 0.37 and a mean redshift of 0.22 that were discovered during the Sloan Digital Sky Survey-II (SDSS-II) SN Survey. Using the broad-band photometry of the SDSS survey, we are able to reconstruct the SN host-galaxy spectral energy distributions (SEDs), allowing for a correction for the host-galaxy contamination in the SN Ia spectra. Comparison of composite spectra constructed from a subsample of 17 high-quality spectra to those created from a low-redshift sample with otherwise similar properties shows that the Keck/SDSS objects have, on average, extremely similar rest-frame optical spectra but show a UV flux excess. This observation is confirmed by comparing synthesized broad-band colors of the individual spectra, showing a difference in mean colors at the 2.4-4.4 sigma level for various UV colors. We further see a slight difference in the UV spectral shape between objects with low-mass and high-mass host galaxies. Additionally, we detect a relationship between UV slope and peak luminosity that differs from that observed at low redshift. We find that objects with this UV excess will have their distances underestimated by ~0.1 mag if the incorrect SED is used for calibration. This effect only occurs when the data probe the rest-frame UV. The recently discovered "U-band anomaly," which is currently the largest systematic uncertainty in SN Ia cosmology and results in a large systematic shift in the dark energy equation-of-state parameter, has the same observational qualities as this effect. We suggest that this discrepancy could be the result of differences in the host-galaxy population of the two SN samples.
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