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Register a new userDiscovery of a relationship between spiral arm morphology and supermassive black hole mass in disk galaxies
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We present a relationship between spiral arm pitch angle (a measure of the tightness of spiral structure) and the mass of supermassive black holes (BHs) in the nuclei of disk galaxies. We argue that this relationship is expected through a combination of other relationships, whose existence has already been demonstrated. The recent discovery of AGN in bulgeless disk galaxies suggests that halo concentration or virial mass may be one of the determining factors in BH mass. Taken together with the result that mass concentration seems to determine spiral arm pitch angle, one would expect a relation to exist between spiral arm pitch angle and supermassive BH mass in disk galaxies, and we find that this is indeed the case. We conclude that this relationship may be important for estimating evolution in BH masses in disk galaxies out to intermediate redshifts, since regular spiral arm structure can be seen in galaxies out to z~1.
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In this paper, we investigate the dark matter halo density profile of M33. We find that the HI rotation curve of M33 is best described by a NFW dark matter halo density profile model, with a halo concentration of cvir = 4.0pm1.0 and a virial mass of Mvir = (2.2pm0.1)times10^11 Msun. We go on to use the NFW concentration (cvir)of M33, along with the values derived for other galaxies (as found in the literature), to show that cvir correlates with both spiral arm pitch angle and supermassive black hole mass.
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Observations suggest that a large fraction of black hole growth occurs in normal star-forming disk galaxies. Here we describe simulations of black hole accretion in isolated disk galaxies with sufficient resolution (~5 pc) to track the formation of giant molecular clouds that feed the black hole. Black holes in z=2 gas-rich disks (fgas=50%) occasionally undergo ~10 Myr episodes of Eddington-limited accretion driven by stochastic collisions with massive, dense clouds. We predict that these gas-rich disks host weak AGNs 1/4 of the time, and moderate/strong AGNs 10% of the time. Averaged over 100 Myr timescales and the full distribution of accretion rates, the black holes grow at a few per cent of the Eddington limit -- sufficient to match observations and keep the galaxies on the MBH-Mbulge relation. This suggests that dense cloud accretion in isolated z=2 disks could dominate cosmic black hole growth. In z=0 disks with fgas=10%, Eddington-limited growth is extremely rare because typical gas clouds are smaller and more susceptible to disruption by AGN feedback. This results in an average black hole growth rate in high-fgas galaxies that is up to 1000 times higher than that in low-fgas galaxies. In all our simulations, accretion shows variability by factors of 10^4 on a variety of time scales, with variability at 1 Myr scales driven by the structure of the interstellar medium.
We present estimates of black hole accretion rates and nuclear, extended, and total star-formation rates for a complete sample of Seyfert galaxies. Using data from the Spitzer Space Telescope, we measure the active galactic nucleus (AGN) luminosity using the [O IV] 25.89 micron emission line and the star-forming luminosity using the 11.3 micron aromatic feature and extended 24 micron continuum emission. We find that black hole growth is strongly correlated with nuclear (r<1 kpc) star formation, but only weakly correlated with extended (r>1 kpc) star formation in the host galaxy. In particular, the nuclear star-formation rate (SFR) traced by the 11.3 micron aromatic feature follows a relationship with the black hole accretion rate (BHAR) of the form SFRproptoBHAR^0.8, with an observed scatter of 0.5 dex. This SFR-BHAR relationship persists when additional star formation in physically matched r=1 kpc apertures is included, taking the form SFRproptoBHAR^0.6. However, the relationship becomes almost indiscernible when total SFRs are considered. This suggests a physical connection between the gas on sub-kpc and sub-pc scales in local Seyfert galaxies that is not related to external processes in the host galaxy. It also suggests that the observed scaling between star formation and black hole growth for samples of AGNs will depend on whether the star formation is dominated by a nuclear or extended component. We estimate the integrated black hole and bulge growth that occurs in these galaxies and find that an AGN duty cycle of 5-10% would maintain the ratio between black hole and bulge masses seen in the local universe.
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