The (black hole mass)-(color) relations for early- and late-type galaxies: red and blue sequences

Tight correlations between supermassive black hole (SMBH) mass (M_(BH)) and the properties of the host galaxy have useful implications for our understanding of the growth of SMBHs and evolution of galaxies. Here, we present newly observed correlations between M_(BH) and the host galaxy total UV− [3.6] color (C_(UV,tot), Pearson’s r = 0.6 − 0.7) for a sample of 67 galaxies (20 early-type galaxies and 47 late-type galaxies) with directly measured MBH in the GALEX /S^(4)G survey. The colors are carefully measured in a homogeneous manner using the galaxies’ FUV, NUV and 3.6 µm magnitudes and their multi-component structural decompositions in the literature. We find that more massive SMBHs are hosted by (early- and late-type) galaxies with redder colors, but the M_(BH)−C_(UV,tot) relations for the two morphological types have slopes that differ at ∼ 2σ level. Early-type galaxies define a red sequence in the M_(BH) – C_(UV,tot) diagrams, while late-type galaxies trace a blue sequence. Within the assumption that the specific star formation rate of a galaxy (sSFR) is well traced by L_(UV)/L_(3.6), it follows that the SMBH masses for late-type galaxies exhibit a steeper dependence on sSFR than those for early-type galaxies. The M_(BH) – C_(UV,tot) and M_(BH) – L_(3.6,tot) relations for the sample galaxies reveal a comparable level of vertical scatter in the log MBH direction, roughly 5% − 27% more than the vertical scatter of the M_(BH) −σ relation. Our M_(BH) – C_(UV,tot) relations suggest different channels of SMBH growth for early- and late-type galaxies, consistent with their distinct formation and evolution scenarios. These new relations offer the prospect of estimating SMBH masses reliably using only the galaxy color. Furthermore, we show that they are capable of estimating intermediate black hole masses in low-mass, early- and late-type galaxies.