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Identification of Type Ia Supernovae Beyond Redshift 1.3 with ACS on HST

Learn about identifying Type Ia supernovae at higher redshifts using the Advanced Camera for Surveys on the Hubble Space Telescope. This includes techniques like spectroscopy, UV deficit analysis, and typical light curves for different supernova types.

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Identification of Type Ia Supernovae Beyond Redshift 1.3 with ACS on HST

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  1. “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

  2. 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

  3. 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

  4. Typical Light Curves(Filippenko, AARA 1997) SNAP/SCP Journal Club

  5. 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

  6. includes R=100 grism SNAP/SCP Journal Club

  7. f775w f850lp f660w lobs = lrest (1 + z) for z=1, Balmer lines have lobs < 8000 angstroms SNAP/SCP Journal Club

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

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