Re: Cluster science status

From: Kyle S Dawson (KDawson@lbl.gov)
Date: Wed Jun 28 2006 - 17:53:20 PDT

  • Next message: Saul Perlmutter: "Re: Cluster science status"

    Hi All,

    I also feel that I have not done a good job updating everyone with the
    status of the SN search, so let me take this oppurtunity to do so. I'll
    start with a simple laundry list of what we've found, and then summarize
    our initial interpretations and some issues yet unresolved.

    There are now 25 clusters in the program. Three of these were added in
    Dec-Apr using free orbits from supernova-less clusters. All three of
    these new clusters come from archival XMM data. Observations are
    complete for 19 clusters. If I remember correctly, the search for SNe
    in 5 of the remaining 6 clusters will end in late July, and the last
    cluster search will end in late Aug. Those dates need to be double checked.

    The full cluster list, images of SNe, etc can be found on the TWiki:
    http://hstclustersn.lbl.gov:8081/twiki/bin/view/Supernovae/WebHome
    usrname: TWikiGuest
    passwd: hstclustersn

    Current status:

    Orbits used: 158 ACS, 21 NICMOS
    Remaining UNscheduled orbits: 7 ACS, 9 NICMOS

    ***BEGIN LAUNDRY LIST*******

    SNe discovered:

    Active:
    A-004: Awaiting spectroscopy using Subaru and VLT this week. Host is
    red, possible early type, but SN is too bright to be associated with
    z=1.4 cluster. SN color/mag, consistent with z~1.0-1.2.

    Cluster E hosts:
    O-000: z=1.01
    K-000: z=1.41???Waiting better spectroscopy, hopefully tonight
    H-005: z=1.23

    Other cluster SNe
    C-001: z=0.98, spectroscopically confirmed Ia, host faint and uncertain

    SNe hosted by E type galaxies with no emission lines in background of
    clusters:
    O-006: z=1.31
    C-000: z=1.09
    G-004: z=1.35

    low z field SNe (probably not useful for cosmology, maybe for rates)
    N-010: z=0.203, type unknown
    P-001: z=0.92, type unknown
    P-009: z=0.821, Ia
    X-027: z=0.4, type unknown (probably core collapse)
    C-007: host uncertain, type unknown
    G-003: z=0.963, type unknown
    F-008: host uncertain, type unknown
    H-003: z=0.851, Ia
    Z-005: z=0.624, Ia

    possible z>1.5 SNe (based on SNe color/mag, host color/mag):
    X-018: one epoch, faint red host
    X-026: two epochs, faint red host
    T-001: one epoch, faint red host

    undetermined redshift, discovered this week in reverse subtractions
    (last epoch as ref, first epoch as search). Three have faint hosts that
    appear spiral or irregular, with SNe and host consistent with z>1. We
    hope to find emission lines in spectroscopic observations next spring.
    E-012: faint host
    F-012: faint host, SNe color, lightcurve consistent with z>1 Ia
    K-018: possible cluster E, z=1.41, SN probably not useful for cosmology
    due to poorly sampled lightcurve, very good for rates, spectroscopy of
    host tonight, weather permitting
    L-021: faint host

    And finally, one mystery object:
    F-006: galactic, extragalactic, z=0.54, quasar, SNIc, hypernova, pop
    III SN, star??????? Nothing in the lightcurve or spectrum resembles
    anything this group has seen before. The transient is hostless to a
    limiting mag z'>26.5, i'>26.5. At max, the transient has z'=21.2 and
    i'=21.1.
    The lightcurve has a risetime of 100 days with no evolution in color.
    The spectrum has features semi-consistent with a SNIc at z=0.54, but
    lacks key Fe features. We posted an IAUC, or CBET as they are now
    called, and have an article written about it here:
    http://www.newscientistspace.com/article/dn9360-enigmatic-object-baffles-supernova-team.html
    We got more data on this in poor conditions Sunday night at Keck and
    last night at Subaru, there is clear continuum but the spectra are still
    waiting to be reduced.

    Unresolved issues: several SNe hosts have not been observed. We got
    murdered with Mauna Kea weather this spring and lost almost all of our
    time. We will try to pick up these redshifts in spring 2007.

    *******END LAUNDRY LIST************

    Now, as it stands we do have unscheduled orbits. If these orbits are
    still free in Aug, we plan to return to the 5 RCS clusters in the 02-04
    hr range for a second round of searching. We will have deep references
    from the 2005 data for the search, and have Keck DEIMOS time scheduled
    to coincide with these HST visits. We will use 5-10 orbits, depending
    on how many are free. If a SN is found, we will follow the lightcurve
    using the remaining unscheduled orbits. If no SN is found, we will
    preserve those last orbits to use as ToO for a SN search using time
    awarded to PRME et al in cycle 15 for observations of a new set of IRAC
    clusters.

    One thing that is very interesting to note is that we have a fairly high
    rate of SNe with z>1 E hosts, but a low rate of late type hosts at this
    redshift. This is very surprising and we do not have an answer for the
    low rate of late type hosts. In terms of cosmology, the z>1 E hosts
    should be extremely useful. The SN are often un-typed, but we plan to
    obtain deep spectroscopy of the hosts in order to place constraints on
    star forming and argue for Ia SNe. We believe these SNe should be
    dust-free as well, but this clearly needs to be explored. These SNe are
    also in the background of massive clusters, and are therefore subject to
    magnification via lensing. In order to use these for cosmology, we will
    need to remove this bias using estimates of cluster masses. We have two
    students working on this, and I'd like them to explore different
    techniques of measuring cluster mass. We may be asking for some help
    with that. For the purposes of cosmology, a 2\sigma measurement of mass
    through weak lensing is probably fine, but it will be very good for the
    two students to learn the other methods as well.

    And finally, we plan to perform a rates analysis. This is the best data
    set of high z cluster SNe, and the measurement of rates in the cluster
    environment should be a very good result. To do so, we will need to
    come to some consensus on how to define the cluster environment. The
    cluster sample is clearly inhomogeneous so this may require a bit of
    work. Something to think about for this telecon Marc Postman suggests.

    -Kyle

    ----- Original Message -----
    From: Marc Postman <postman@stsci.edu>
    Date: Wednesday, June 28, 2006 9:13 am
    Subject: Cluster science status

    > Saul, Mike, et al.,
    >
    > I am wondering if others feel as out of the loop as I on what's
    > happening with the cluster science part of the program and who is
    > doing what now. If I am not alone in this, it might be time for a
    > telecon to at least get an update on progress and discussion of
    > possible new ideas to pursue with the data.
    >
    > -Marc
    >
    > -----------------------------------------------------------------
    > Marc Postman Email: postman@stsci.edu
    > STScI - CMO Phone: +1-410-338-4340
    > 3700 San Martin Drive Fax: +1-410-338-4796
    > Baltimore, MD 21218 U.S.A. http://www.stsci.edu/~postman
    >
    >
    >



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