SDSS II Supernova Survey-

The Science

Wednesday 29th August 2007

DARK Summer Institute

Mathew Smith

In collaboration with B. Nichol (ICG) and the SDSS II SNe team

Outline

• Introduction to SDSS II

• Basic details

• The Survey to date

• Preliminary results

• Host galaxy properties

• Host galaxy systematics

• The data

The First Papers:• The SDSS II SNe Survey: Technical Summary

- J.Frieman & The SDSS II team - arXiv:0708.2749• The SDSS II SNe Survey: Search Algorithm and

Follow-up Observations

- M. Sako & The SDSS II team - arXiv:0708.2750

Coming Shortly:

The SDSS II Low-z Rate - B. Dilday

Spectroscopy in SDSS II - C. Zheng

+ Photometry (J.Holtzman), Galaxy Properties (M. Smith) and Cosmology (R.

Kessler)

The SDSS II Supernova Survey

• Aims: - bridge low-z (z<0.05; LOSS, SNF) and high-z (0.3<z<1.0; ESSENCE, SNLS) sources

- understand and minimize systematics of SN Ia as distance indicators (look at correlations with host galaxy properties)

9% measurement of w - comparable with SNLS6% measurement of w when combined with SNLS

Use the SDSS 2.5m telescope• September 1 - November 30 of 2005-2007• Scan 300 square degrees of the sky every 2 days• “Stripe82” (UKIDSS data)

Survey AreaSurvey Area

N S

Photometric Typing• Color-type SNe candidates using nightly g r i data

• fit light-curve for redshift, extinction, stretch for Ia

• Able to type with >90% efficiency after ~2 - 4 epochs

IaIa

IIII

SN2005hy

Team of 15 “hand-scanner” visually inspected 144,000 Team of 15 “hand-scanner” visually inspected 144,000 objects selecting nearly 10k SN targets!objects selecting nearly 10k SN targets!

The Data• Excellent photometry from 2.5m

SDSS telescope and others throughout the world

• Well sampled light-curves

•Excellent typing of objects•Multi-band (u,g,r,I,z) photometry•Very high efficiency (especially below z = 0.2

g

r

i

Search Template Diff

Follow-up Spectroscopy

International follow-up:

MDM 2.4m

NOT 2.6m

APO 3.5m

NTT 3.6m

KPNO 4m

WHT 4.2m

Subaru 8.2m

HET 9.2m

Keck 10m

SALT 10m

Numbers to Date From 2005 - 2006:• 327 spectroscopically confirmed Ia's

• 31 probable Ia’s• 44 confirmed other SN types

• Galaxy redshifts for 60 additional Ia candidates

• 1st year Analysis nearly complete (soon)

Highest number of any SN survey

~40% of all supernovae discovered in 2005 and 2006

spectroscopic SN Iaprobable SN Iacore-collapse SN

SDSS SN Ia Lightcurves @z = 0.09 z = 0.19 z = 0.36

data-- fit model

SDSS II - Hubble Diagram

• Accurate photometry

• Cosmology agrees with other measurements

Preliminary

2005 Data129 Ia Total74 after cuts

SDSS Hubble Diagram Residuals

‡ 0.08 mag added in quadrature to fitted as prescribed by MLCS2k2

preliminary

‡

dat

a –

fit

PRELIMINARY SDSS Rate: (2005 sample -- paper in preparation)

• Number of SN (z < 0.12) = 17

• Search eff ~ 100% from in-situ fake SN

• Analysis eff = 0.77 0.02 from detailed sim (loss mainly from temporal edge effects)

• SN Ia Rate (z < 0.12) = [2.9 0.7stat 0.3syst ] 10-5

(Mpc/h70)3 yr1

SN Ia Rate vs. Redshift

Prelim SDSS result previous results with spectroscopic confirmation

SNLS fit:

new fit in

progress

Now for a diversion-

My own work-

Host galaxy Properties

Two populations?• We need to confirm that SN Ia are

standardizable candles• Sullivan et al., using SNLS first year

data, showed the existence of 2 distinct populations.

•Possible existence of a relationship between Hubble diagram scatter and galaxy type•Similar results from Manucci et al.•Benetti et al. showed that there were possibly 3 SN Ia types from spectral evolution

The A + B model

• Mannucci et al. (and later Sullivan et al. (with SNLS data) proposed the “two component” model of type Ia supernovae.

• The supernova rate is affected by recent events of star-formation

• Those that occur in passive galaxies are “prompt supernovae”, in areas of recent SF they are “delayed supernovae”

B. Dilday, U.Chicago

SDSS Data• There are 129 spectroscopically confirmed Ia’s in the first year

SDSS dataset• 115 of them have clear and obvious hosts• After a redshift cut of z<0.25 70 remain - all with hosts• Photometry of hosts taken from SDSS coadd / DR5 (where

necessary)• All have Masses and SFR’s calculated from PEGASE code,

using redshift and magnitudes• A field sample of the coadd is used. Masses / SFR’s also

calculated with (and without) photo-z’s• It is incompleteness corrected for faint galaxies

• We are currently correcting for incompleteness!

The Samples• To investigate the properties of the host galaxies, they were

fitted to a PEGASE template. The redshift, was both fixed and left free, there was no significant change in the result.

• 23 galaxies were classified as passive galaxies, 26 as moderately starforming and 21 as star-burst.

• The SDSS coadd (10 epoch) has ~4.2 million galaxies• 1.1 million have been analysed with PEGASE• They were fit without a photo-z, but then compared to one• ~600,000 lie in the redshift range of interest• We are going to use the new 30 epoch coadd, to classify all

the hosts (~10 million objects!)

The PEGASE code

ug

r iz

•Contains 8/9 Galaxy tracks

•Each one is evaluated at 69 different time steps

•Making a total of 552 different SEDs

•Galaxies can be fit with / without redshifts

Incompleteness Corrections• There is a major bias in the spectroscopic sample - SNe in

spirals are more commonly targeted (as they are easier to distinguish)

• We have problems with getting final photometry for every object

• After correcting for incompleteness we have ~110 objects (of which 70 are spectroscopically confirmed)

• We want to get a spectroscopic redshift for every host (for host fitting)

• We have also corrected for efficiency of objects to pass through this extra stage

• We need to ensure that contamination is as small as possible

A Problematic Candidate- 7457

• This lightcurve passes at z=0.16 or z=0.36 (depending on cuts on photometry)

• The host is at z=0.255• Possible contamination

Star Formation Rate v Mass•Ellipticals show higher mass

•Large spread in mass values

•Population is split into 3 categories:

-Passive galaxies, moderately starforming and highly starforming

SN rate v Specific SFR

SN rate with Host Galaxy Mass

•Consistent with A+B model

•There is a trend in SN rate / galaxy with galaxy type

SN rate with Host SFR

•What is going on???

Unclear

result

-

Needs

Further

Analysis

Galaxy type with redshift

•There is an observed evolution of the redshift histograms with galaxy type

•Possible indication of Host galaxy v Stretch correlation

Galaxy - Supernova Properties

Hubble Residuals:Specific SFR - no correlation. So even in extreme SSFR hosts MLCS works.

No observed correlation with redshift (good)

~0.20 mag dispersion may be due to a “third” parameter (width and color are the first two)

SN Luminosity vs Specific SFR:

Bright AND faint SNIa happen in galaxies with SSFR u-z >2

But only bright SNIa occur in u-z <1

Those at low redshift seem to have higher SSFR

To date• The SDSS SN Survey has finished its first two years - one to

go!• 327 type Ia SNe discovered in the first 2 years• It provides an excellent data set, with small and well

understood systematic errors. • When combined with other measurements and surveys it can

constrain DE to ~10%.• Early Hubble diagram matches LCDM.• The SDSS dataset can be used to anchor future Hubble

diagrams.• There is an indication of the evolution of galaxy type with

redshift - possibly two populations of type Ia’s?• First papers are on astro-ph!

The dataset

• From the first two years there is a large amount of data available

• High quality photometry, with small systematic errors• Many scientifically useful spectra, with many objects

having multi-epochs (useful for tracking spectral evolution)

• Unique dataset in untapped redshift range• Well understood pipeline for tracking objects• Excellent template information for host information• Many confirmed Ia’s and other types• Lots of work to be done - lots of chances to do it!

SDSS-II SN Collaboration

Fermilab U.Chicago

APO SAAO

U.Washington Seoul Natl. U.

Wayne State U. Ohio State U.

U.Tokyo U.Notre Dame

NM State U. KIPAC/Stanford

STScI ICG Portsmouth

Rochester IT U.Pennsylvania

Penn State U. U.Texas

+

EUROPE

!!