High redshift galaxies already old?

Abstract

We have found 3 Lyman alpha emission line galaxies at redshift 2.38, near the QSO absorption line complex at that redshift in the spectrum of Q2139-4434. All 3 galaxies are strong Lyman alpha emitters, and have much redder continuum colors (I-K~5) than other optically-selected high redshift galaxies. We hypothesize that these 3 galaxies are QSO IIs; radio-quiet counterparts of high redshift radio galaxies, containing concealed QSO nuclei. The red colors are most easily modeled by an old (>0.5 Gyr), massive (>1011 solar masses) stellar population. If true, this implies that at least one galaxy cluster of mass >>3×10¹¹ solar masses had collapsed before redshift 5. A more detailed description may be found in Francis, Woodgate and Danks (1997). Show more