====================================================================== Apologies for not being online at the time of this meeting! SCP Collaboration Meeting November 2001 ======================================= "Verifying the Use of Type Ia Supernovae as Probes of the Cosmic Expansion" R. Ellis, M. Sullivan et al. Preliminary results can be found in: Ellis R., & Sullivan M., 2000, "Verifying the use of supernovae as probes of the cosmic expansion", IAU Symposium 201, eds A. Lasenby and A. Wilkinson, astro-ph/0011369 Submitted abstract of talk: =========================== "We review the results of an extensive survey which aims to characterise those galaxies which hosted Type Ia supernovae found by the Supernova Cosmology Project (SCP). Using Hubble Space Telescope images and intermediate dispersion Keck spectroscopy, we have classified each host galaxy into three morphological/spectral types in order to investigate the dependence of distant supernova properties with respect to the host galaxy class. Of particular interest is the subset of Type Ia supernovae hosted by spheroidal galaxies, which are expected to be dust-free and more tightly scattered about the Hubble diagram. The best-fit cosmology for this 'clean' subset agrees well with that previously measured by the SCP. The SN Ia subset in late-type irregulars also yields consistent results, with the expected larger scatter. Further spectroscopic programs at the Keck observatory will characterise the progenitor metallicity of selected high redshift supernovae for comparison with local data. This work was supported in part by the NASA Space Telescope Science Institute." Project Aims and Goals: ======================= The project is naturally split into two phases: * Properties of SN host galaxies: The objective of this project is to obtain STIS images, high resolution spectroscopy and multicolour photometry of distant galaxies known to have hosted Ia SN discovered by the SCP. The goal is to extend the SNe Ia Hubble diagram classed by galaxy type, enabling SNe to be considered as a function of their local environment. Data analysed so far (IAU article) suggests possible systematic effects arising from varying dust contents and perhaps star formation histories. * Progenitor evolution: We aim to constrain the progenitor metallicity via a concerted ESI spectroscopic campaign for 3-4 z=0.4-0.7 SNe newly discovered SNe. Using ESI we followed (very recently completed) the temporal spectral evolution of selected SNe Ia with at 2 epochs, alongside photometric monitoring. Progenitor metallicity may evolve with redshift and affect the relationship between peak luminosity and light curve shape; this project aims to test this via comparisons with local samples. Brief Summary of results to date: ================================= Our STIS images allow us to pinpoint the location of the SN explosion, as well as to assign a visual classification to the galaxy type. To further exploit the HST galaxies, we are undertaking a program of optical spectroscopy using the Echellette Spectrograph Imager (ESI) on the Keck-II telescope. The high spatial resolution of the STIS images and the astrometric location of the SN position enables us to accurately align the 20 arcsec ESI slit through the appropriate projected region of the galaxy. To date, 13 host galaxies have been studied in this way. The spectra allow an accurate spectral type (and confirmatory redshift) to be assigned to each galaxy, and estimates of the spatial variation in the star-formation characteristics and dust reddening (via the Halpha/Hbeta ratio) at different locations in the vicinity of the SN. We assign a host galaxy type in 3 broad categories: spheroidal (E/S0), spiral (Sa through Sc) and late (Scd/Irr), based on the synergy between three diagnostics available to us: i) The STIS imaging, ii) The Keck-II spectra, and iii) the R-I colour from ESI imaging or original detection images. Of particular interest is the SN Hubble diagram characterised by this host galaxy class. The preliminary results of our investigation continue to support the conclusions of Perlmutter et al. (1999): a Lambda-dominated cosmology is strongly preferred. However, the Hubble diagram categorised by galaxy class offers new insight into the origin of the scatter in the diagram. We find the scatter about the best-fit cosmology is greater when determined from SNe which occurred in late-type/irregular galaxies. Minimal scatter is found for SNe drawn from E/S0 galaxies as expected if dust is largely absent in these systems. A non-zero Lambda is supported by SNe arising from each galaxy type individually, with late-type galaxies implying a larger Lambda than E/S0 galaxies as might be expected when simple dust models are considered. Finally, little difference is found when the Hubble diagram is categorised according to SNe located at large and small projected distances from their host galaxy. While these initial results are promising, the current sample size is only around half that used in the full Hubble diagram in P99. Further HST imaging and spectroscopic studies of the host galaxy population are underway to confirm the initial findings presented here. In particular, the extended wavelength coverage of ESI ensures sensitivity to both Halpha and Hbeta to z~0.5. Rather than determine the absolute line of sight reddening, we aim to categorise each host galaxy in terms of uncertainties introduced by spatial variations in reddening. A key question is whether SNe occurring in those galaxies with spatial variations in reddening are systematically different from those in dust-free examples. Further details can be found in the IAU article; an updated web page for the project is in preparation. Observational/Data reduction Status: ==================================== Phase 1: [ This will form the basis of the AAS talk ] * The original (cycle 8) snapshot proposal has completed, obtaining STIS clear CCD imaging of 31/54 of the host galaxies of the SCP high-redshift supernovae, 20 of which are used in the current diagram of 42 type Ia SNe. The IAU conference article summarises our initial findings. * The second (cycle 10) STIS snapshot proposal is now underway; however the completion rate is low. * The comprehensive KECK-II ESI spectroscopic programme is nearly complete; high resolution spectra of most of the host galaxies (with a STIS image) have been secured. * Preliminary analysis in IAU article; ApJ article in preparation for submission early 2002. Phase 2: * The second phase of the project (testing progenitor metallicity) has recently started. 2 nights of Keck ESI time in October/November were used for this purpose; the data is currently being analysed in conjunction with the Paris team led by Reynald Pain. Initial results from this project may be presented at the AAS, time permitting! Please feel free to direct questions or comments to: mark.sullivan@durham.ac.uk Mark -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Dr. Mark Sullivan, Tel (Work) : +44 (0)191 374 4617 Room 312, Physics Department, (University of Durham), Science Labs, South Road, Fax : +44 (0)191 374 3749 Durham DH1 3LE, UK E-mail : Mark.Sullivan@durham.ac.uk -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-