Constraints on intragroup stellar mass from hostless Type Ia supernovae

We probe the diffuse stellar mass in a sample of 1401 low-redshift galaxy groups (1013-1014 h-1 M(circle dot)) by examining the rate of hostless Type Ia supernovae (SNe Ia) within the groups. We correlate the sample of confirmed SNe Ia from the Sloan Digital Sky Survey SN survey with the positions of our galaxy groups, as well as with the resolved galaxies within them. We find that 19 of the 59 SNe Ia within the group sample have no detectable host galaxy, with another three ambiguous instances. This gives a robust upper limit that a maximum of 2.69+1.58(-1.34) per cent of the group's total mass arises from diffuse stars in the intragroup medium. After correcting for a contribution from 'prompt' SNe occurring within galaxies, and including a contribution from those which arise in dwarf galaxies below our photometric limit, we find that only 1.32+0.78(-0.70) per cent of the group's total mass is likely in the form of diffuse stellar mass. Combining this result with the galaxy stellar mass functions of Yang, Mo and van den Bosch, we find that 47+16(-15) per cent of the stellar mass in our groups is in the form of diffuse light, so that stars make up a fraction 0.028+0.011(-0.010) of the total group mass. Galaxy groups appear to be very efficient in disrupting stellar mass into a diffuse component; however, stars still make up a small fraction of the group mass, comparable to that seen in rich clusters. This remains a challenge to galaxy formation models.