2004ApJ...600L.163R

We present discoveries of Type Ia supernovae (SNe Ia) at z>1 and the photometric diagnostic used to discriminate them from other types of SNe detected during the Great Observatories Origins Deep Survey (GOODS) Hubble Space Telescope Treasury Program with the Advanced Camera for Surveys (ACS). Photometric redshift measurements of the hosts combined with deep F606W, F775W, and F850LP imaging discriminates hydrogen-rich SNe II from SNe I at z>1 by exploiting the UV deficit in the energy distributions of SNe Ia. This sorting allows rapid follow-up of space-based discoveries. Subsequent spectroscopy of 11 GOODS SNe Ia obtained from the ground and with the grism on ACS confirmed the reliability of our photometric screening. We present the highest redshift spectrum of any SN published to date, SN Ia 2002fw at z=1.3 observed near maximum brightness with the ACS grism. The lack of UV flux for true SNe Ia provides an effective tool for our ongoing efforts to build a sample of SNe Ia at 1.2<z<1.8, which will extend the useful range of the magnitude-redshift relation of SNe Ia.