SIMBAD references

Simple theoretical arguments indicate that cooled interstellar gas in bright elliptical galaxies forms into a young stellar population having a bottom-heavy but optically luminous initial mass function extending to ∼2 M_☉. When the colors and spectral features of this young population are combined with those of the underlying old stellar population, the apparent ages are significantly reduced, similar to the relatively young apparent ages observed in many elliptical galaxies. Galactic mergers are not required to resupply young stars. The sensitivity of continuous star formation to L_B and L_X/L_B is likely to account for the observed spread in apparent ages among elliptical galaxies. Local star formation is accompanied by enhanced stellar Hβ equivalent widths, stronger optical emission lines, more thermal X-ray emission, and lower apparent temperatures in the hot gas. The young stars should cause M/L to vary with galactic radius, perturbing the fundamental plane of the old stars alone.