We present a technique to extract ultra-deep diffuse-light spectra from the standard multi-object spectroscopic observations used to investigate extragalactic globular cluster ( GC ) systems .
This technique allows a clean extraction of the spectrum of the host galaxy diffuse light from the same slitlets as the GC targets .
We show the utility of the method for investigating the kinematics and stellar populations of galaxies at radii much greater than usually probed in longslit studies , at no additional expense in terms of telescope time .
To demonstrate this technique we present Gemini/GMOS spectroscopy of 29 GCs associated with the elliptical galaxy NGC 3923 .
We compare the measured stellar population parameters of the GC system with those of the spheroid of NGC 3923 at the same projected radii , and find the GCs to have old ages > 10 Gyr , [ \alpha /Fe ] \sim 0.3 and a range of metallicities running from [ Z/H ] = -1.8 to +0.35 .
The diffuse light of the galaxy is found to have ages , metallicities and [ \alpha /Fe ] abundance ratios indistinguishable from those of the red GCs .