# Presentation: 584316

## “Identification of Type Ia Supernovae at Redshift 1.3 and Beyond with the Advanced Camera for Surveys on HST”

- Riess, Strolger, Tonry et al
- astro-ph/0308185

## SN GO Piggyback Program

- subtraction within 6-18 hrs of GOODS repeat visit to identify candidates
- Keck and Magellan spectroscopy for most candidates with f850lp < 24 mag
- ACS (grism), NICMOS ToO follow-up if:
- host galaxy photometric redshift > 1.2
- UV deficit at host redshift
- 43 total Sne candidates reported in IAU Circulars
- 15 Sne Ia identified via UV deficit

## SNe Types

- Type I have no H2 Balmer lines near maximum
- Ia show silicon line at 6150; white dwarf progenitor
- scattering of UV off iron group metals => “UV deficit”
- Ib: no Si, but He 5876 (CC stripped of H)
- Ic: no Si or He  (CC stripped of H and He)
- Type II show emission and/or absorption at Balmer hydrogen energies near max
- IIP plateau in intensity, magnitude varies widely
- IIL decline in linear fashion, ~2.5 mag fainter than Ia
- II-n have narrow features in spectrum
- All but Ia are core collapse of massive stars

- also have weak UV,
-  but less common
- than II, and fainter

## Typical Light Curves(Filippenko, AARA 1997)

## Fig. 1:  blue = SNII, green = SNII, red = SNIa

- Si(6150)

- Purity of Ia sample
- identified with UV
- deficit signature
- is estimated at 90%
- for z > 1

## includes R=100

- grism

## obs = rest (1 + z)

- obs = rest (1 + z)
- for z=1, Balmer lines
- have obs  < 8000 angstroms

## Fig. 3:  SN Ia 2002fw (z=1.3) observed in ACS grism (red curve) and SNIa 1981B with hi-res spectroscopy

- CaII

- SiII(4120)

## ACS Filters

- f850lp
- used for image reference and discovery exposures
- survey limit ~25.8 mag
- 8000 - 10000 A covers B band for z ~ 1
- f775w
- used for follow-up of lower redshift objects
- 7000 -8500 covers B band for z ~ 0.7
- f606w
- narrow band at 6000 A
- Colors are used to identify SN Ia for z > 1
- f775w-f850lp ( i - z)
- f606w - f850lp  (v - z)

## Fig. 2:   Colors of Ia and II vs redshift ( from SEDs of Fig 1) and

- observed colors of 15 confirmed Ia’s

- f775w - f850lp

- f660w - f850lp

- UV deficit ID

- spectroscopic conf

## 0.2 < z< 1

- 4 SNe spectroscopically confirmed on ground
- 3 SNe confirmed with ACS grism
- but f606w bandpass is redward of 330 nm at z<1, so do not sample UV region and cannot use colors for Ia type identification

## 1 < z < 1.5

- 5 candidates had colors and host photo-z’s consistent with Ia and inconsistent with II
- ACS bandpasses sample UV region
- 4 of 5 were spectroscopically confirmed

## z > 1.5

- 2 candidates with colors and photo-z’s consistent with Ia
- f775w-f850lp between 2 and 2.5 mag
- absent in f606w to detection limit; f606w-f850lp > 3.2 mag

## Conclusions of Paper

- UV deficit is a useful tool to discriminate SNeI from Sne II at z > 1.
- MC simulations indicate < 10% false ID; no details shown in this paper
- Can also calculate likelihood of mis-ID for each candidate; not included in this paper
- No colors shown for non-Ia SNe
- To obtain light curves (needed to constrain epoch of observations, determine extinction via color excess, and to calibrate peak magnitude) requires near-IR observations with NICMOS.