Supermassive black holes and their host spheroids II. The red and blue sequence in the $M_{\rm BH} - M_{\rm *,sph}$ diagram

Giulia A. D. Savorgnan; Alister W. Graham; Alessandro Marconi; Eleonora Sani

doi:10.3847/0004-637X/817/1/21

paper

Supermassive black holes and their host spheroids II. The red and blue sequence in the $M_{BH} - M_{*, sph}$ diagram

arXiv:1511.07437 · doi:10.3847/0004-637X/817/1/21

Abstract

In our first paper, we performed a detailed (i.e. bulge, disks, bars, spiral arms, rings, halo, nucleus, etc.) decomposition of 66 galaxies, with directly measured black hole masses, $M_{B H}$ , that had been imaged at $3.6 μ m$ with Spitzer. Our sample is the largest to date and, for the first time, the decompositions were checked for consistency with the galaxy kinematics. We present correlations between $M_{B H}$ and the host spheroid (and galaxy) luminosity, $L_{s p h}$ (and $L_{g a l}$ ), and also stellar mass, $M_{*, s p h}$ . While most previous studies have used galaxy samples that were overwhelmingly dominated by high-mass, early-type galaxies, our sample includes 17 spiral galaxies, half of which have $M_{B H} < 1 0^{7} M_{⊙}$ , and allows us to better investigate the poorly studied low-mass end of the $M_{B H} - M_{*, s p h}$ correlation. The bulges of early-type galaxies follow $M_{B H} \propto M_{*, s p h}^{1.04 \pm 0.10}$ and define a tight red sequence with intrinsic scatter $ε = 0.43 \pm 0.06 d e x$ and a median $M_{B H} / M_{*, s p h}$ ratio of $0.68 \pm 0.04%$ , i.e.~a $\pm 2 σ$ range of 0.1-5%. At the low-mass end, the bulges of late-type galaxies define a much steeper blue sequence, with $M_{B H} \propto M_{*, s p h}^{2 - 3}$ , indicating that gas-rich processes feed the black hole more efficiently than the host bulge as they coevolve. We additionally report that: i) our Sersic galaxy sample follows a less steep sequence than previously reported; ii) bulges with Sersic index $n < 2$ , argued by some to be pseudo-bulges, are not offset to lower $M_{B H}$ from the correlation defined by the current bulge sample with $n > 2$ ; and iii) $L_{s p h}$ and $L_{g a l}$ correlate equally well with $M_{B H}$ , in terms of intrinsic scatter, only for early-type galaxies - once reasonable numbers of spiral galaxies are included, the correlation with $L_{s p h}$ is better than that with $L_{g a l}$ .

To appear in ApJ

Supermassive black holes and their host spheroids II. The red and blue sequence in the $M_{BH} - M_{*, sph}$ diagram

Abstract

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Supermassive black holes and their host spheroids II. The red and blue sequence in the $M_{BH} - M_{*, sph}$ diagram