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

TelescopeTelescope

Kyle Dawson

March 16, 2008

For the SuperNova Cosmology Project

RDCS 1252.9 @ z=1.23 (ISAAC and ACS)

Supernovae and the Accelerating UniverseSupernovae 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

The Problem with DustThe Problem with Dust

Host galaxy dust extinction If host galaxy is similar to Milky Way then:

MB=RBE(B-V) with RB~ 4

Color error ~ 0.1 => Magnitude error ~0.4

Extinction correction dominates measurement error!

Before extinction correction

After extinction correction

What About Intrinsic Color of SNe?What About Intrinsic Color of SNe?

Extinction: MB=RBE(B-V)

Conventional dust extinction predicts RB~ 4. However, dispersion in SNe color contributes to observed B-V as well.

Introduce color correction to account for intrinsic color + host extinction

B=mmaxB – M + (s-1) - c

Measure s, c, mmaxB, fit M, , and

SNe are better fit with ~ 2.5 (depending on who you ask).

Sullivan et al. 08

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The Problem with DustThe Problem with DustHost galaxy dust extinction MB=RBE(B-V) with RB~ 4

Degeneracy between intrinsic color of SNe and reddening from host lead to poorly constrained extinction correction

Before extinction correction

After extinction correction

The error increases at higher redshiftANDCorrections may be biased due to incomplete understanding of dust properties at high z!

Or is it 2.5???

One Possible Solution: Use SNe Hosted by Dust-Free One Possible Solution: Use SNe Hosted by Dust-Free Elliptical GalaxiesElliptical Galaxies

Galaxy type Dispersion (no Ext Corr)

•Elliptical: E/S0 mag

•Spiral: Sa/Sb/Sc mag

•Irregular Scd/Irr mag

Solution: Use Ellipticals and don’t apply the extinction correction.

But, at z~0.5, only ~1 in 5 SNe Ia is hosted by an elliptical galaxy.

M. Sullivan et al. (SCP) 2003, MNRAS, 340, 1057.

Minimizing host galaxy dust extinction Minimizing host galaxy dust extinction

Elliptical Galaxies & Clusters

Elliptical galaxies (E/S0) have

little star-formation & dust.

Clusters: concentration of nearly

dust free Elliptical galaxies.

B-V colorof low-z SNe

SN color: With few exceptions, SNehosted by early type galaxies exhibitcolor consistent with no host extinction

No dust in elliptical (cluster) galaxies?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)

Coherent evolution of Coherent evolution of cluster environmentcluster environment

Scatter of color of ellipticals galaxies in clusters is very small (consistent with current resolution).

Evolution from date of formation(z~3) appears consistent for clustersover wide range of redshifts.

Strong constraints on host environment.

25 clusters with HST resolutionwill be added

Blakeslee et al. ApJL (2003)

Decelerating and Dustfree: Decelerating and Dustfree: Targeting SNe in Very High Redshift Galaxy ClustersTargeting 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 XMM+VLT

VLT ACS

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-RB=4.1, dashed curve, RB=2.5.

Right Panel: The goal of this project is shown as a confidence region for a simulated new sample of 10 z > 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 < 0.1) the Nearby SN Factory

What Sort of Improvement are we Looking For?

The ClustersThe 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

HST Rolling Search

20-26 day cadence

ACS z’, i’ bands.

Observing Program: Observing Program: 25 massive galaxy 25 massive galaxy clusters at z ≥ 1clusters at z ≥ 1

Search and follow: Continuous flow of ACS data

Followup: NICMOS J-band scheduled ~10 days after discovery

Spectroscopy: At least one night/month

Intensive Ground-based Spectroscopy Follow-upIntensive 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) + Director’s Discretionary time

E Host SNIa with high confidence

Preliminary spectra from this program

Results: SNe Discoveries in HST ProgramResults: SNe Discoveries in HST Program

15 z>1 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 z>0.95 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!

Factors to Consider for ACS PhotometryFactors 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

The Elliptical host (E/S0) Hubble DiagramThe Elliptical host (E/S0) Hubble DiagramNo extinction correctionNo extinction correction

Preliminary

Sullivan et al. & Knop et al.

This program

Seven SNe Ia in elliptical galaxies observed with complete lightcurves.

No extinction correction applied

(David Rubin)

Example of E–only Hubble Diagram

other analyses

• SN Ia rate in cluster environment

•Host Properties

• Cluster studies (collaborators)

•Weak lensing

•Red Sequence Scatter

•Etc.

SummarySummary

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