# Presentation: 313815

## SDSS Measurement ofthe SN Ia Ratefor z < 0.12

- R. Kessler (U.Chicago)
- for the SDSS-II SN-Survey and
- Spectroscopic Follow-up Teams
- Jan 7, 2007

- The 209th Meeting of the American Astronomical Society, January 2007

## Motivation

- Repeat imaging of 300 sq deg, combined with an efficient SN-search pipeline, provides an ideal data set for SN rate measurement.
- SN Ia Rate vs. redshift probes delay times of explosion relative to star formation, which  can be related to the nature of SN progenitors.
- Nearby (z ~ .1) rate is limited by  small samples and biases from targeting known galaxies.

## Fall-2005 Data Sample (confirmed, z < 0.12)

- Begin analysis with 26 spectroscopically confirmed SN Ia (z < 0.12)
- To have well-understood efficiency, we require
-     * pre-max epoch
-     * epoch past 10 days in rest frame
-     * at least 5 epochs
-     * max SNR > 5 in  g,r,i
-     * MLCS2k2 lightcurve fit-prob > 0.01
-                           
-    15  SN Ia  in final sample for rate.

## Fall-2005 Data Sample (unconfirmed, z < 0.12)

- Post-survey analysis of ~1000 candidates lightcurves  with improved photometry and improved (MLCS2k2) lightcurve model:
-                                       

## Fall-2005 Data Sample (unconfirmed, z < 0.12)

- Post-survey analysis of ~1000 candidates lightcurves  with improved photometry and improved (MLCS2k2) lightcurve model:
-                                       
- recovered one highly extincted SN 1a  at z=0.036,  AV ~ 4 !

- Still have ~1000 more candidate lightcurves to process.
- Systematic error for unconfirmed SN Ia sample: 2.

## Fall-2005 Data Sample (excluded, z < 0.12)

- Note that two peculiar SN were rejected because MLCS fit-prob << 0.01
-    (and therefore the selection efficiency has large uncertainty):
-     * 2005gj (Ia/II hybrid)
-     * 2005hk (underluminous 2002cx-like)
- [See talk by J.Prieto for more details]

## Slide 7

## Slide 8

## Slide 9

## Gallery of SN Ia Spectra

- 2005ff
- (WHT)

- 2005fv
- (WHT)

- 2005hn
- (MDM)

- 2005gb
- (MDM)

- 2005ho
- (MDM)

- 2005hr
- (MDM)

- 2005hx
- (MDM)

- 2005hc
- (MDM)

- 2005if
- (MDM)

- 2005js
- (HET)

- 2005hj
- (HET:
- external
- confirmation)

- 2005jh
- (MDM)

- 2005ir
- (APO)

- 2005fh
- (APO)

- 2005kp
- (APO)

## Efficiency Determination

- Fake SN lightcurves inserted into images DURING SURVEY to monitor search efficiency.
- Lightcurve simulation to determine selection efficiency after cuts
-    (also used for cosmology systematics)

## Search Efficiency During Fall-2005 Survey(from fake SN inserted into images)

- Search Efficiency During Fall-2005 Survey(from fake SN inserted into images)

- SN search is
- 100% efficient
- for peakmag < 21

- Fake SN

- 16       17       18        19       20       21       22       23
-                   Peak g-band magnitude

## Search Efficiency During Fall-2005 Survey(from fake SN inserted into images)

- Search Efficiency During Fall-2005 Survey(from fake SN inserted into images)

- SN search is
- 100% efficient
- for peakmag < 21

- no cuts

- }

- Fake SN

- (z < 0.12)

- Confirmed SN Ia
- Simulation
-   (see next slide)

## Selection efficiency from lightcurve simulation 

- based on observed epochs: for each epoch use
-  measured PSF
-  measured sky noise
-  host-galaxy noise from
-     random galaxy
-  host extinction from
-     exp(-AV/0.4)
-  SN flux from
-    MLCS2k2 model
-    with random color
-    variations based on
-    model errors.

## Simulation Check on SN fluxes and errors

- for all 260 epochs with z<0.12

- Simulation has x10
- data statistics, and
- sim distributions are
- re-scaled to have
- same stats as data.
- Data and simulation
- have consistent
- distributions;
- adds confidence in
- using simulation to
- predict efficiency

## Selection Efficiencyfrom Simulation

- Efficiency(z<0.12)
-       = 0.83 ± 0.02stat ± 0.01syst
-       = 0.88  0.95

- MJD edge effects
- from pre-max
- and  +10 day
- requirements

- telescope
- efficiency
- (includes
- weather)

- vary host extinction
- distribution between
- exp(–AV/0.2) and
- exp(–AV/0.6)

##      Preliminary SDSS Result

- Acceptance  =  0.83 ± 0.03
- Comoving   Volume x Time :                              7.36 x105  (Mpc/h70)3  years
- No. of observed SN Ia  (Fall-2005) :  16
- Systematic error: 2/16 = 13%
- Mean redshift: 0.09
- SN Ia rate  (z < 0.12) =                                                    (2.7 ± 0.7stat  ± 0.3syst )  105  (Mpc/h70)3 yr1

- !!! most precise low-redshift rate measurement !!!

##         SN Ia Rate Comparisons

- Figure from SNLS: astro-ph/0605148
- (see Fig 1 caption for list of measurements

- SFH from Hopkins
- and Beacom (2006)

- Prelim
- SDSS
- result

##         SN Ia Rate Comparisons

- Figure from SNLS: astro-ph/0605148
- (see Fig 1 caption for list of measurements

- SFH from Hopkins
- and Beacom (2006)

- Prelim
- SDSS
- result

- similar method
- and systematics;
- x few better stats
- could show rate
- evolution

- Recent
- SNLS
- result

## SDSS Prospects for Increased Statistics

- x 2  volume if  zmax    0.15
- x 3  using all 3 seasons (2005,6,7)
- x 1.? relax selection requirements
- Potential 6-fold increase in statistics would give ~100 SN Ia for low-z rate.

## Preliminary SDSS Redshift Distribution

- Photometric
- Selection of
- SN Ia:
-  pre-max epoch
-  rest-frame epoch
-     past 18 days
-  5 or more epochs
-  max SNR > 5 (g,r,i)
-  MLCS fit-prob > 0.01
-  sane luminosity
-   parameter ( > -0.6)
-           
- Rejects all 13 confirmed
- non1a-type SN
- (2006 sample has 30
- more non1a to test cuts)

- sample for
- prelim rate

## Preliminary SDSS Redshift Distribution

- Simulation looks
- promising:
- photometric SN Ia
- might be useful
- for rates and for
- cosmology
- systematics.
- More host redshifts
- available soon.