The Intracluster Light of the Coma Cluster as a Luminosity and Mass Budget

The Coma cluster holds the best-studied reservoir of intracluster light in the nearby universe, yet its diffuse component is usually quoted as a single percentage whose consequences are rarely worked through. Taking the galaxy luminosity within 1.5 Mpc of the centre as 8.60e+11 solar luminosities in the V band and the intracluster fraction of the total light as 0.35, the diffuse component carries 4.63e+11 solar luminosities, the combined stellar light reaches 1.32e+12 solar luminosities, and the intracluster stars weigh 1.48e+12 solar masses at a mass-to-light ratio of 3.2. Spread over the inner 600 kpc that light averages a surface brightness of 27.37 magnitudes per square arcsecond, rising to 26.62 inside 300 kpc. The intracluster mass is only 0.012 of the hot-gas mass and 1.14e-03 of the total cluster mass, which is why this component, dominant among the stars at large radius, remains a trace constituent of the cluster as a whole. The full literature range of the fraction, 0.25 to 0.45, moves the diffuse luminosity between 2.87e+11 and 7.04e+11 solar luminosities; every conclusion below is stated across that range rather than at the central value alone.