Abstract
We report a measurement of the Type Ia supernova (SN Ia) rate in galaxy clusters at 0.9 < z < 1.45 from the Hubble Space Telescope (HST) Cluster Supernova Survey. This is the first cluster SN Ia rate measurement with detected z > 0.9 SNe. Finding 8 +/- 1 cluster SNe Ia, we determine a SN Ia rate of 0.50 +0.23-0.19 (stat) +0.10-0.09 (sys) SNuB (SNuB = 10^-12 SNe L_{sun,B}^-1 yr^-1). In units of stellar mass, this translates to 0.36 +0.16-0.13 (stat) +0.07-0.06 (sys) SNuM (SNuM = 10^-12 SNe M_sun^-1 yr^-1). This represents a factor of approximately 5 +/- 2 increase over measurements of the cluster rate at z < 0.2. We parameterize the late-time SN Ia delay time distribution with a power law (proportional to t^s). Under the assumption of a cluster formation redshift of z_f = 3, our rate measurement in combination with lower-redshift cluster SN Ia rates constrains s = -1.41 +0.47/-0.40, consistent with measurements of the delay time distribution in the field. This measurement is generally consistent with expectations for the "double degenerate" scenario and inconsistent with some models for the "single degenerate" scenario predicting a steeper delay time distribution at large delay times. We check for environmental dependence and the influence of younger stellar populations by calculating the rate specifically in cluster red-sequence galaxies and in morphologically early-type galaxies, finding results similar to the full cluster rate. Finally, the upper limit of one host-less cluster SN Ia detected in the survey implies that the fraction of stars in the intra-cluster medium is less than 0.47 (95% confidence), consistent with measurements at lower redshifts.
Highlights
Type Ia supernovae (SNe Ia) are widely accepted to be the result of the thermonuclear explosion of a carbon-oxygen (CO) white dwarf (WD)
We derive a rate in the full cluster, in red-sequence galaxies only, and in redsequence early-type galaxies only
Each subset includes a different number of SNe: As discussed in §3.4, we have discovered 8 ± 1 cluster SNe, where the quoted uncertainty is due to classification uncertainty
Summary
Type Ia supernovae (SNe Ia) are widely accepted to be the result of the thermonuclear explosion of a carbon-oxygen (CO) white dwarf (WD). The explosion is believed to occur as the WD nears the Chandrasekhar mass by accreting mass from its companion star in a binary system. Despite the confidence in this basic model, many uncertainties remain about the process that leads to SNe Ia (see Livio 2001, for a review). Chief amongst them is the nature of the companion donor star. The leading models fall into two classes: the single degenerate scenario (SD; Whelan & Iben 1973), and the double degenerate scenario (DD; Iben & Tutukov 1984; Webbink 1984). In the SD scenario the companion is a red giant or main sequence star that overflows its Roche lobe. In the DD scenario, the companion is a second WD which merges with the primary after orbital decay due to the emission of gravitational radiation
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