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 <~ σ <~ 120 km s^-1), with three profiles showing double peaks. Four galaxies have low masses (M <~ 10¹⁰ M_solar). Whereas three galaxies were previously reported to be possible active galactic nuclei (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 that they are thus progenitors of some cluster spheroidals3 seen today.

Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology, and with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by AURA under NASA contract NAS 5-2655.