# Presentation: 247785

## SNe Ia and host galaxies in the SNLS

***Mark Sullivan ***
*University of Toronto*
*http://legacy.astro.utoronto.ca/*
*http://cfht.hawaii.edu/SNLS/*

## Host galaxies impact SN properties

- Some evidence that SNe Ia in ellipticals show smaller scatter

- Sullivan et al. (2003)

- e.g. Hamuy et al. (2000)

- SN Ia Light-curve shape depends on morphology

- Low stretch

- High stretch

## Typing of SNLS SN Ia hosts

**Passive**

**Star-forming**

**Starbursting**

-  Little morphological information available
-  CFHT u*g’r’i’z’ imaging via the Legacy program.
-  PEGASE2 is used to fit SED templates to the optical data.
-  Recent star-formation rate, total stellar mass, mean age are estimated.
-  Hosts classified according to physical parameters instead of “what they look like”.

- Sullivan et al. (2006)

## Spec-z/Phot-z for host galaxies

- All SN hosts brighter than i’=25 (Vega)
- Δz/(1+z)≈0.042

## SNLS: SN rate as a function of sSFR

**SN Ia hosts classified by star-formation activity**
- Per unit stellar mass, SNe are at least an order of magnitude more common in more vigorously star-forming galaxies

**SNLS “passive” galaxies**

- Efficiencies from Neill et al. (2006)
- (see SDSS talk)

## SNLS selection of hosts

- D2 ACS imaging
- Plenty of irregular/late-type systems
- Few genuine ellipiticals

**Notes:**
Point is: look at diversity of host types!

## SN Ia Stretch dependencies

**170 SNe Ia**
- (Update from Sullivan et al. 2006; better zeropoints, host photometry, more SNe)

- Passive

- Star-forming

- Stretch versus mean age

- Stretch by galaxy star-formation activity

**The majority of SN Ia come from young stellar populations**

## Recent SNLS evidence for two components for SNe Ia

**Older progenitor SNe**
- Empirically, SN Rate is proportional to galaxy mass
- Preferentially found in old stellar environments
- Typically fainter with faster light-curves (low stretch)

**Younger progenitor SNe**
- Empirically, SN rate is proportional to galaxy star formation rate
- Exclusively found in later type star-forming galaxies
- Typically brighter with slower light-curves (high stretch)
- (Extreme example: SNLS-03D3bb?)

- Two component model discussed in: Mannucci et al. 2006, 2006; Scannapieco & Bildsten 2006; Sullivan et al. 2006 etc.

## SN population drift?

- Relative mix of evolves with redshift
- A+B predictions, but similar for any two component model

**Sullivan et al. 2006**

## Stretch versus redshift (3rd year)

- ?

## Effect of selection on stretch-redshift

- Simulations of SNLS completeness including detection and spectroscopic selection
- (Perrett et al. in prep)

- Redshift

- Mean Stretch

## Evolution in Stretch?

**Evolution in Stretch?**
- Gaussians – predicted evolution from A+B model
- Average stretch, and thus average *intrinsic* brightness of SNe Ia evolves with redshift
- but
**if stretch correction works perfectly, this should not affect cosmology**

- Howell et al. 2007

- Nearby

- z<0.75

- z>0.75

## Split by s (preliminary)

| S | ΩM | α | β |
| --- | --- | --- | --- |
| <0.95 |  |  |  |
| >0.95 |  |  |  |

## Stretch correction across environments

- Conley et al. 2006

**No evidence for gross differences between light-curves in passive and active galaxies**

- Rest-frame B composite light-curve

## Split by host galaxy

**Problems: Low-redshift sample very small, Malmquist correction likely to be different**

- Passive

- Star-forming

- σ~0.10 mag

- σ~0.14 mag

**Preliminary**

## Stretch residuals (preliminary)

## Colour residuals (preliminary)

## Summary

- SNe Ia have a range of progenitor ages
- Impacts on light-curve shape: faster/older & slower/younger
- SNe in passive galaxies are better standard candles?
- More homogeneous stellar population? Less dust?
- Can large samples of local SNe in elliptical galaxies break the colour degeneracy?