Chris Pritchet

Toward a cosmological Hubble diagram for Type II-P supernovae

We present the first high-redshift Hubble diagram for Type II-P supernovae (SNe II-P) based on five events at redshift up to z ~ 0.3. This diagram was constructed using photometry from the Canada-France-Hawaii Telescope Supernova Legacy Survey and absorption-line spectroscopy from the Keck Observatory. The method used to measure distances to these supernovae is based on recent work by Hamuy & Pinto and exploits a correlation between the absolute brightness of SNe II-P and the expansion velocities derived from the minimum of the Fe II λ 5169 P Cygni feature observed during the plateau phases. We present three refinements to this method that significantly improve the practicality of measuring the distances of SNe II-P at cosmologically interesting redshifts. These are an extinction correction measurement based on the V-I colors at day 50, a cross-correlation measurement for the expansion velocity, and the ability to extrapolate such velocities accurately over almost the entire plateau phase. We apply this revised method to our data set of high-redshift SNe II-P and find that the resulting Hubble diagram has a scatter of only 0.26 mag, thus demonstrating the feasibility of measuring the expansion history, with present facilities, using a method independent of that based on supernovae of Type Ia.

Supernova Shock Breakout from a Red Supergiant

Massive stars undergo a violent death when the supply of nuclear fuel in their cores is exhausted, resulting in a catastrophic “core-collapse” supernova. Such events are usually only detected at least a few days after the star has exploded. Observations of the supernova SNLS-04D2dc with the Galaxy Evolution Explorer space telescope reveal a radiative precursor from the supernova shock before the shock reached the surface of the star and show the initial expansion of the star at the beginning of the explosion. Theoretical models of the ultraviolet light curve confirm that the progenitor was a red supergiant, as expected for this type of supernova. These observations provide a way to probe the physics of core-collapse supernovae and the internal structures of their progenitor stars.

INTRACLUSTER SUPERNOVAE IN THE MULTI-EPOCH NEARBY CLUSTER SURVEY

The Multi-Epoch Nearby Cluster Survey has discovered 23 cluster Type Ia supernovae (SNe Ia) in the 58 X-ray-selected galaxy clusters (0.05 z 0.15) surveyed. Four of our SN Ia events have no host galaxy on close inspection, and are likely intracluster SNe. Although one of the candidates, Abell399_3_14_0, appears to be associated in projection with the outskirts of a nearby red sequence galaxy, its velocity offset of ~1000 km s–1 indicates that it is unbound and therefore an intracluster SN. Another of our candidates, Abell85_6_08_0, has a spectrum consistent with an SN1991bg-like object, suggesting that at least some portion of intracluster stars belong to an old stellar population. Deep image stacks at the location of the candidate intracluster SNe put upper limits on the luminosities of faint hosts, with Mr –13.0 mag and Mg –12.5 mag in all cases. For such limits, the fraction of the cluster luminosity in faint dwarfs below our detection limit is 0.1%, assuming a standard cluster luminosity function. All four events occurred within ~600 kpc of the cluster center (projected), as defined by the position of the brightest cluster galaxy, and are more centrally concentrated than the cluster SN Ia population as a whole. After accounting for several observational biases that make intracluster SNe easier to discover and spectroscopically confirm, we calculate an intracluster stellar mass fraction of 0.16+0.13 –0.09 (68% confidence limit) for all objects within R 200. If we assume that the intracluster stellar population is exclusively old, and the cluster galaxies themselves have a mix of stellar ages, we derive an upper limit on the intracluster stellar mass fraction of <0.47 (84% one-sided confidence limit). When combined with the intragroup SNe results of McGee & Balogh, we confirm the declining intracluster stellar mass fraction as a function of halo mass reported by Gonzalez and collaborators.

The Multi-Epoch Nearby Cluster Survey: type Ia supernova rate measurement in z~0.1 clusters and the late-time delay time distribution

We describe the Multi-Epoch Nearby Cluster Survey, designed to measure the cluster Type Ia supernova (SN Ia) rate in a sample of 57 X-ray selected galaxy clusters, with redshifts of 0.05 2 Gyr) delay time distribution (DTD) of SN Ia assuming a cluster early-type galaxy star formation epoch of zf = 3. Assuming a power-law form for the DTD, Ψ(t)∝ts , we find s = –1.62 ± 0.54. This result is consistent with predictions for the double degenerate SN Ia progenitor scenario (s ~ –1) and is also in line with recent calculations for the double detonation explosion mechanism (s ~ –2). The most recent calculations of the single degenerate scenario DTD predicts an order-of-magnitude drop-off in SN Ia rate ~6-7 Gyr after stellar formation, and the observed cluster rates cannot rule this out.

The environmental dependence of the incidence of galactic tidal features

In a sample of 54 galaxy clusters (0.04 < z < 0.15) containing 3551 early-type galaxies suitable for study, we identify those with tidal features both interactively and automatically. We find that ~3% have tidal features that can be detected with data that reach a 3σ sensitivity limit of 26.5 mag arcsec–2. Regardless of the method used to classify tidal features, or the fidelity imposed on such classifications, we find a deficit of tidally disturbed galaxies with decreasing clustercentric radius that is most pronounced inside of ~0.5 R 200. We cannot distinguish whether the trend arises from an increasing likelihood of recent mergers with increasing clustercentric radius or a decrease in the lifetime of tidal features with decreasing clustercentric radius. We find no evidence for a relationship between local density and the incidence of tidal features, but our local density measure has large uncertainties. We find interesting behavior in the rate of tidal features among cluster early-types as a function of clustercentric radius and expect such results to provide constraints on the effect of the cluster environment on the structure of galaxy halos, the build-up of the red sequence of galaxies, and the origin of the intracluster stellar population.

CONFIRMATION OF HOSTLESS TYPE Ia SUPERNOVAE USING HUBBLE SPACE TELESCOPE IMAGING

We present deep Hubble Space Telescope imaging at the locations of four, potentially hostless, long-faded Type Ia supernovae (SNe Ia) in low-redshift, rich galaxy clusters that were identified in the Multi-Epoch Nearby Cluster Survey. Assuming a steep faint-end slope for the galaxy cluster luminosity function (

Research computing in a distributed cloud environment

\alpha_d=-1.5

Near-Infrared [Fe II] Emission in Starburst Galaxies. I. Measured Properties

), our data includes all but

Correlations between SDSS Type Ia Supernova Rates and Host Galaxy Properties

\lesssim0.2\%

CANFAR: the Canadian Advanced Network for Astronomical Research

percent of the stellar mass in cluster galaxies (