学术文献库

We present an analysis of the pitch angle distribution function (PADF) for nearby galaxies and its resulting black hole mass function (BHMF) via the well-known relationship between pitch angle and black hole mass. Our sample consists of a subset of 74 spiral galaxies from the Carnegie-Irvine Galaxy Survey with absolute $B$-band magnitude $\mathfrak{M}_{B}>-19.12$ mag and luminosity distance $D_{\mathrm{L}} \leq 25.4$ Mpc, which is an extension of a complementary set of 140 more luminous ($\mathfrak{M}_{B}\leq-19.12$ mag) late-type galaxies. We find the PADFs of the two samples are, somewhat surprisingly, not strongly dissimilar; a result that may hold important implications for spiral formation theories. Our data show a distinct bimodal population manifest in the pitch angles of the Sa-Sc types and separately the Scd-Sm types, with Sa-Sc types having tighter spiral arms on average. Importantly, we uncover a distinct bifurcation of the BHMF, such that the Sa-Sc galaxies typically host so-called "supermassive" black holes ($M_{\bullet}\gtrsim10^6\,\mathrm{M_{\odot}}$), whereas Scd-Sm galaxies accordingly harbor black holes that are "less-than-supermassive" ($M_{\bullet}\lesssim10^6\,\mathrm{M_{\odot}}$). It is amongst this latter population of galaxies where we expect fruitful bounties of elusive intermediate-mass black holes (IMBHs), through which a better understanding will help form more precise benchmarks for future generations of gravitational wave detectors.