%0 Journal Article %J The Astrophysical Journal %D 2007 %T New Hubble Space Telescope Discoveries of Type Ia Supernovae at z >= 1: Narrowing Constraints on the Early Behavior of Dark Energy %A Riess, Adam G. %A Strolger, Louis-Gregory %A Casertano, Stefano %A Ferguson, Henry C. %A Mobasher, Bahram %A Gold, Ben %A Challis, Peter J. %A Filippenko, Alexei V. %A Jha, Saurabh %A Li, Weidong %A Tonry, John %A Foley, Ryan %A Kirshner, Robert P. %A Dickinson, Mark %A MacDonald, Emily %A Eisenstein, Daniel %A Livio, Mario %A Younger, Josh %A Xu, Chun %A Dahlén, Tomas %A Stern, Daniel %X

We have discovered 21 new Type Ia supernovae (SNe Ia) with the HubbleSpace Telescope (HST) and have used them to trace the history of cosmicexpansion over the last 10 billion yr. These objects, which include 13spectroscopically confirmed SNe Ia at z>=1, were discovered during 14epochs of reimaging of the GOODS fields North and South over 2 yr withthe Advanced Camera for Surveys on HST. Together with a recalibrationof our previous HST-discovered SNe Ia, the full sample of 23 SNe Ia atz>=1 provides the highest redshift sample known. Combining these datawith previous SN Ia data sets, we measured H(z) at discrete,

%B The Astrophysical Journal %V 659 %P 98-121 %8 April 1, 2007 %G eng %U http://adsabs.harvard.edu/abs/2007ApJ...659...98R %3 eprintid: arXiv:astro-ph/0611572