On the Nature of the Strong Emission-Line Galaxies in Cluster Cl 0024+1654: Are Some the Progenitors of Low Mass Spheroidals?

Abstract

We present new size, line ratio, and velocity width measurements for six strong emission-line galaxies in the galaxy cluster, Cl 0024+1654, at redshift z~0.4. The velocity widths from Keck spectra are all narrow (30<sigma<120 km/s), with three profiles showing double peaks. Four galaxies have low masses (M<10^{10} Mo). Whereas three galaxies were previously reported to be possible AGNs, none exhibit AGN-like emission line ratios or velocity widths. Two or three appear as very blue spirals with the remainder more akin to luminous H-II galaxies undergoing a strong burst of star formation. We propose that after the burst subsides, these galaxies will transform into quiescent dwarfs, and are thus progenitors of some cluster spheroidals (We adopt the nomenclature suggested by Kormendy & Bender (1994), i.e., low-density, dwarf ellipsoidal galaxies like NGC 205 are called `spheroidals' instead of `dwarf ellipticals') seen today.