The Cooling of Massive White Dwarfs from Gaia EDR3

We determine the distribution of cooling ages of massive Gaia EDR3 white dwarfs within 200 pc and with mass in the range $0.95 - 1.25 ~M_\odot$, identified with over 90% probability in the Gentile Fusillo et al. 2021 (arXiv:2106.07669) catalogue. Using three sets of publicly available models, we consider sub-samples of these white dwarfs sorted into three equally spaced mass bins. Under the assumption of a constant white dwarf formation rate, we find an excess of white dwarfs along the Q branch and below it, corresponding to stars that are in the process of freezing and those that are completely frozen. We compare the cooling age distributions for each of these bins to the recently determined time-varying star formation rate of Gaia DR2 main sequence stars (arXiv:1901.07564). For white dwarfs in the two lightest mass bins, spanning the mass range $0.95-1.15~M_\odot$, we find that the cumulative cooling age distribution is statistically consistent with the expectation from the star formation rate. For white dwarfs in the heaviest mass bin, $1.15-1.25~M_\odot$, we find that their cumulative distribution is inconsistent with the star formation rate for all of the models considered; instead, their cooling ages follow an approximately uniform distribution, as expected if mergers contribute a significant fraction of the most massive white dwarfs.