Are There Blue, Massive E/S0 Galaxies at z<1? Kinematics of Blue Spheroidal Galaxy Candidates

Abstract

Several recent studies find that 10%-50% of morphologically selected field early-type galaxies at redshifts z<~1 have blue colors indicative of recent star formation. Such ``blue spheroids'' might be massive early-type galaxies with active star formation, perhaps induced by recent merger events. Alternatively, they could be starbursting, low-mass spheroids. To distinguish between these two choices, we have selected 10 ``Blue Spheroid Candidates'' (BSCs) from a quantitatively selected E/S0 sample to study their properties, including kinematics from Keck spectra obtained as part of the DEEP Groth Strip Survey (GSS). Most BSCs (70%) turn out to belong to two broad categories, while the remaining objects are likely to be misclassified objects. Type 1 BSCs have underlying red stellar components with bluer inner components. Type 2 BSCs do not show an obvious sign of the underlying red stellar component, and their overall colors are quite blue [(U-B)_rest<0]. Both type 1 and type 2 BSCs have internal velocity dispersions measured from emission lines σ<~80 km s^-1 and estimated dynamical masses of only a few ×10¹⁰ M_solar or less. For type 1 BSCs, we estimate σ of the red component using the fundamental plane relation of distant field absorption-line galaxies and find that these σ estimates are similar to the σ measured from emission lines. Overall, we conclude that our type 1 and type 2 BSCs are more likely to be star-forming low-mass spheroids than star-forming, massive, early-type galaxies.