Peculiar Velocities from Type Ia Supernovae

Abstract

Type Ia supernovae have only recently been employed to measure the peculiar motions of galaxies. The great distances to which SNe Ia can be seen makes them particularly well-suited to constraining large-scale velocity flows. The high precision of SN Ia distance measurements limits the contamination of such measurements by Malmquist or sample selection biases. I review the recent use of SNe Ia to measure the motion of the Local Group (updated to include 44 SNe Ia). The direction of the best-fit motion remains consistent with that inferred from the CMB (though modest bulk flows cannot be ruled out) and inconsistent with the Lauer-Postman frame. Comparisons between SN Ia peculiar velocities and gravity maps from IRAS and ORS galaxies yields constraints on the mass density which gives rise to the gravitationally induced peculiar motions. Indications are for $β$=0.4 from IRAS, and 0.3 from the ORS, with $β>0.7$ and $β<0.15$ ruled out at 95% confidence levels from the IRAS comparison. The contributions of SNe Ia to peculiar velocity studies are limited by statistics, but the great increase in the recent discovery rate suggests SNe Ia may become increasingly important in constraining flows.