140 likes | 195 Views
“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
E N D
“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 SNAP/SCP Journal Club
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 SNAP/SCP Journal Club
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 SNAP/SCP Journal Club
Typical Light Curves(Filippenko, AARA 1997) SNAP/SCP Journal Club
Si(6150) Purity of Ia sample identified with UV deficit signature is estimated at 90% for z > 1 SNAP/SCP Journal Club Fig. 1: blue = SNII, green = SNII, red = SNIa
includes R=100 grism SNAP/SCP Journal Club
f775w f850lp f660w lobs = lrest (1 + z) for z=1, Balmer lines have lobs < 8000 angstroms SNAP/SCP Journal Club
Fig. 3: SN Ia 2002fw (z=1.3) observed in ACS grism (red curve) and SNIa 1981B with hi-res spectroscopy SiII(4120) CaII SNAP/SCP Journal Club
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) SNAP/SCP Journal Club
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 spectroscopic conf UV deficit ID SNAP/SCP Journal Club
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 SNAP/SCP Journal Club
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 SNAP/SCP Journal Club
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 SNAP/SCP Journal Club
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. SNAP/SCP Journal Club