Decelerating and Dustfree: Dark Energy Studies of Supernovae with the Hubble Space Telescope

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Decelerating and Dustfree Dark Energy Studies
of Supernovae with the Hubble Space Telescope

• Kyle Dawson
• March 16, 2008
• For the SuperNova Cosmology Project

RDCS 1252.9 _at_ z1.23 (ISAAC and ACS)
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Supernovae and the Accelerating Universe

• Brief discussion of systematics probably heard
  it all before from J. Guy
• Our HST program to combat the dust systematic
• Some initial results

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The Problem with Dust

• Host galaxy dust extinction
• If host galaxy is similar to Milky Way then
• DMBRBE(B-V) with RB 4
• Color error 0.1 gt Magnitude error 0.4
• Extinction correction dominates
• measurement error!

Before extinction correction
After extinction correction
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What About Intrinsic Color of SNe?
Extinction DMBRBE(B-V) Conventional dust
extinction predicts RB 4. However, dispersion
in SNe color contributes to observed B-V as
well. Introduce color correction b to account
for intrinsic color host extinction mBmmaxB
M a(s-1) - bc Measure s, c, mmaxB, fit M, a,
and b SNe are better fit with b 2.5 (depending
on who you ask).
ß4.1
Residual without c-correction
Sullivan et al. 08
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The Problem with Dust

• Host galaxy dust extinction
• DMBRBE(B-V) with RB 4
• Degeneracy between intrinsic color of SNe and
  reddening from host lead to poorly constrained
  extinction correction

Or is it 2.5???
Before extinction correction
The error increases at higher redshift AND Correct
ions may be biased due to incomplete
understanding of dust properties at high z!
After extinction correction
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One Possible Solution Use SNe Hosted by
Dust-Free Elliptical Galaxies
M. Sullivan et al. (SCP) 2003, MNRAS, 340,
1057.

• Galaxy type Dispersion (no Ext Corr)
• Elliptical E/S0 s0.16 mag
• Spiral Sa/Sb/Sc s0.20 mag
• Irregular Scd/Irr s0.27 mag

Solution Use Ellipticals and dont apply the
extinction correction. But, at z0.5, only 1 in
5 SNe Ia is hosted by an elliptical galaxy.
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Minimizing host galaxy dust extinction

• SN color With few exceptions, SNe
• hosted by early type galaxies exhibit
• color consistent with no host extinction

B-V color of low-z SNe

• Elliptical Galaxies Clusters
• Elliptical galaxies (E/S0) have
• little star-formation dust.
• Clusters concentration of nearly
• dust free Elliptical galaxies.

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No dust in elliptical (cluster) galaxies?

• Ellipticals in massive clusters
• are among the earliest (oldest)
• objects in the Universe.

How do we know these galaxies are dust-free?
Small scatter in color for cluster galaxies
uniform population Uniform color within a
galaxy (dust is clumpy) No emission at 200
microns (dust emission)
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Coherent evolution of cluster environment

• Scatter of color of ellipticals
• galaxies in clusters is very small
• (consistent with current resolution).
• Evolution from date of formation
• (z3) appears consistent for clusters
• over wide range of redshifts.
• Strong constraints on host environment.

Blakeslee et al. ApJL (2003)
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Decelerating and
Dustfree Targeting SNe in Very High Redshift
Galaxy Clusters

• Major cycle 14 HST Program in collaboration with
  several galaxy cluster groups (219 orbits over 18
  months).
• searched 25 recently discovered massive galaxy
  clusters at z 1 with ACS.
• Why clusters?
• Dominated by nearly dust-free Elliptical (E/S0)
  galaxies.
• 5 times higher density of Elliptical galaxies at
  high redshift.
• Scientific goals
• Significantly improve SN constraints of dark
  energy - reduce the statistical and systematic
  uncertainties.
• Cluster studies weak lensing, galaxy morphology,
  and color-magnitude relationship.

Spitzer
XMMVLT
VLT
ACS
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What Sort of Improvement are we Looking For?
Left Panel Simulated 68 confidence region on w'
vs. w0 for the current literature SN sample but
with underlying cosmology(w0 -1 w 0). The
parameters are poorly constrained because color
errors are magnified by RB 4. Center Panel
Demonstration of bias introduced from assuming a
prior. Solid filled curve-RB4.1, dashed curve,
RB2.5. Right Panel The goal of this project is
shown as a confidence region for a simulated new
sample of 10 z gt 1 SNe Ia found in ellipticals,
together with 5 in ellipticals from the past and
ongoing GOODS searches, as well as 120 SNe Ia in
ellipticals at the lower redshifts now being
produced by the ground-based CFHT SN Legacy
Survey, the CTIO Essence survey, and (at z lt 0.1)
the Nearby SN Factory
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The Clusters

• Weak lensing mass estimates for 18 clusters
• Red-sequence modeled from extensive ground-based
  spectroscopy 2 band ACS imaging
• Richness estimates for all 25 clusters Ngal
  from red-seq
• Consistent with model from SDSS (dotted line)
• M proportional to Ngal1.2

• All SNe discovered in richest clusters ? unshaded
  region

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Observing Program 25 massive galaxy clusters at
z 1
HST Rolling Search 20-26 day cadence ACS z,
i bands.
Search and follow Continuous flow of ACS
data Followup NICMOS J-band scheduled 10 days
after discovery Spectroscopy At least one
night/month
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Intensive Ground-based Spectroscopy Follow-up

• Goal Establish redshift, host type, and often SN
  type
• Subaru 10 half-nights/semester
• Keck 2 nights/semester
• VLT 10 hours/semester (queue mode) Directors
  Discretionary time
• E Host ? SNIa with high confidence

Preliminary spectra from this program
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Results SNe Discoveries in HST Program
15 zgt1 SNe discovered, 9 hosted by E type
galaxies Full multi-color light curves for 8/9
hosted by E type galaxies Full light curves for
4/7 zgt0.95 SNe hosted by late-type
galaxies Twice the SN/orbit as previous SN
searches in random fields using HST Three times
the E hosted-SN/orbit!
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Factors to Consider for ACS Photometry

• Many issues contributing at the 5 level
  were solved in 2007
• Time variation of distortion corrections
• Time variation of bias levels
• Relative astrometry corrections
• PSF variation across FOV
• Variation/gradient in flat field
• Backscattering of NIR photons
• K-corrections of different templates
• Gravitational lensing of SNe behind clusters

K-corrections using various lightcurve templates

• Almost there! Still blinded but expect to put
  E-hosted SNe on Hubble diagram very soon

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The Elliptical host (E/S0) Hubble DiagramNo
extinction correction
Example of Eonly Hubble Diagram

• Seven SNe Ia in elliptical galaxies observed with
  complete lightcurves.
• No extinction correction applied

Sullivan et al. Knop et al.
This program

• other analyses
• SN Ia rate in cluster environment
• Host Properties
• Cluster studies (collaborators)
• Weak lensing
• Red Sequence Scatter
• Etc.

Preliminary
(David Rubin)
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Summary

• 219 orbits with HST to search for SNe in high z
  clusters
• Efficient observing strategy, finding 3x E hosted
  SNe/orbit over previous GOODS searches
• Each E-hosted SN worth 9 normal SNe
• Results soon, photometry complete, unblinding
• SNe results will include cosmology, properties of
  SNe by host type, rates
• Lots of parallel science weak lensing mass
  estimates, morphology, evolution, spectral
  properties