Author/Authors :
Tonry، John L. نويسنده , , Schmidt، Brian P. نويسنده , , Barris، Brian نويسنده , , Challis، Peter نويسنده , , Clocchiatti، Alejandro نويسنده , , Filippenko، Alexei V. نويسنده , , Jha، Saurabh نويسنده , , Kirshner، Robert P. نويسنده , , Li، Weidong نويسنده , , Chornock، Ryan نويسنده , , Matheson، Thomas نويسنده , , Hicken، Malcolm نويسنده , , RIESS، ADAM G. نويسنده , , KRISCIUNAS، KEVIN نويسنده , , PRIETO، JOSE LUIS نويسنده , , REST، ARMIN نويسنده , , BLONDIN، STEPHANE نويسنده , , DESSART، LUC نويسنده , , LEIBUNDGUT، BRUNO نويسنده , , BRANCH، DAVID نويسنده , , HOFLICH، PETER نويسنده , , FOLEY، RYAN J. نويسنده , , SOLLERMAN، JESPER نويسنده , , SPYROMILIO، JASON نويسنده , , WOOD-VASEY، W. MICHAEL نويسنده , , AGUILERA، CLAUDIO نويسنده , , BECKER، ANDREW C. نويسنده , , COVARRUBIAS، RICARDO نويسنده , , DAVIS، TAMARA M. نويسنده , , GARNAVICH، PETER نويسنده , , MICELI، ANTHONY نويسنده , , MIKNAITIS، GAJUS نويسنده , , PIGNATA، GIULIANO نويسنده , , SALVO، MARIA ELENA نويسنده , , SMITH، R. CHRIS نويسنده , , STUBBS، CHRISTOPHER W. نويسنده , , SUNTZEFF، NICHOLAS B. نويسنده ,
Abstract :
Using archival data of low-redshift (z < 0.01; Center for Astrophysics and SUSPECT databases) Type Ia supernovae (SNe Ia) and recent observations of highredshift (0.16 < z < 0.64) SNe Ia, we study the "uniformity" of the spectroscopic properties of nearby and distant SNe Ia. We find no difference in the measurements we describe here. In this paper we base our analysis solely on line-profile morphology, focusing on measurements of the velocity location of maximum absorption (vabs) and peak emission (vpeak). Our measurement technique makes it easier to compare low and high signal-to-noise ratio observations. We also quantify the associated sources of error, assessing the effect of line blending with assistance from the parameterized code SYNOW. We find that the evolution of vabs and vpeak for our sample lines (Ca II (lambda)3945, Si II (lambda)6355, and S II (lambda)(lambda)5454, 5640) is similar for both the low- and high-redshift samples. We find that vabs for the weak S II (lambda)(lambda)5454, 5640 lines and vpeak for S II (lambda)5454 can be used to identify fast-declining [(delta) m15(B) > 1.7] SNe Ia, which are also subluminous. In addition, we give the first direct evidence in two high-z SN Ia spectra of a double-absorption feature in Ca II (lambda) 3945, an event also observed, although infrequently, in low-redshift SN Ia spectra (6 out of 22 SNe Ia in our local sample). Moreover, echoing the recent studies of Dessart & Hillier in the context of Type II supernovae (SNe II), we see similar P Cygni line profiles in our large sample of SN Ia spectra. First, the magnitude of the velocity location at maximum profile absorption may underestimate that at the continuum photosphere, as observed, for example, in the optically thinner line S II (lambda)5640. Second, we report for the first time the unambiguous and systematic intrinsic blueshift of peak emission of optical P Cygni line profiles in SN Ia spectra, by as much as 8000 km s^-1. All the high-z SNe Ia analyzed in this paper were discovered and followed up by the ESSENCE collaboration and are now publicly available.
