The origins of off-centre massive black holes in dwarf galaxies
ABSTRACT Massive black holes often exist within dwarf galaxies, and both simulations and observations have shown that a substantial fraction of these may be off-centre with respect to their hosts. We trace the evolution of off-centre massive black holes (MBHs) in dwarf galaxies using cosmological hydrodynamical simulations, and show that the reason for off-centre locations is mainly due to galaxy–galaxy mergers. We calculate dynamical time-scales and show that off-centre MBHs are unlikely to sink to their galaxys’ centres within a Hubble time, due to the shape of the hosts’ potential wells and low stellar densities. These wandering MBHs are unlikely to be detected electromagnetically, nor is there a measurable dynamical effect on the galaxy’s stellar population. We conclude that off-centre MBHs may be common in dwarfs, especially if the mass of the MBH is small or the stellar mass of the host galaxy is large. However, detecting them is extremely challenging, because their accretion luminosities are very low and they do not measurably alter the dynamics of their host galaxies.
Authors:
; ; ; ; ; ; ; ; ; ; ;
Award ID(s):
Publication Date:
NSF-PAR ID:
10283508
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
505
Issue:
4
Page Range or eLocation-ID:
5129 to 5141
ISSN:
0035-8711
National Science Foundation
##### More Like this
1. ABSTRACT Recent systematic searches for massive black holes (BHs) in local dwarf galaxies led to the discovery of a population of faint active galactic nuclei (AGNs). We investigate the agreement of the BH and AGN populations in the Illustris, TNG, Horizon-AGN, EAGLE, and SIMBA simulations with current observational constraints in low-mass galaxies. We find that some of these simulations produce BHs that are too massive, and that the BH occupation fraction (OF) at z = 0 is not inherited from the simulation seeding modelling. The ability of BHs and their host galaxies to power an AGN depends on BH and galaxy subgrid modelling. The fraction of AGN in low-mass galaxies is not used to calibrate the simulations, and thus can be used to differentiate galaxy formation models. AGN fractions at z = 0 span two orders of magnitude at fixed galaxy stellar mass in simulations, similarly to observational constraints, but uncertainties and degeneracies affect both observations and simulations. The agreement is difficult to interpret due to differences in the masses of simulated and observed BHs, BH OF affected by numerical choices, and an unknown fraction of obscured AGN. Our work advocates for more thorough comparisons with observations to improve the modelling ofmore »
2. ABSTRACT

We study a suite of extremely high-resolution cosmological Feedback in Realistic Environments simulations of dwarf galaxies ($M_{\rm halo} \lesssim 10^{10}\rm \, M_{\odot }$), run to z = 0 with $30\, \mathrm{M}_{\odot }$ resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with $M_{\rm halo} \gtrsim 10^{8.6}\, \mathrm{M}_{\odot }$ is populated by a resolved stellar galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field. Our ultra-faint dwarfs (UFDs; $M_{\ast }\lt 10^{5}\, \mathrm{M}_{\odot }$) have their star formation (SF) truncated early (z ≳ 2), likely by reionization, while classical dwarfs ($M_{\ast }\gt 10^{5}\, \mathrm{M}_{\odot }$) continue forming stars to z < 0.5. The systems have bursty star formation histories, forming most of their stars in periods of elevated SF strongly clustered in both space and time. This allows our dwarf with M*/Mhalo > 10−4 to form a dark matter core ${\gt}200\rm \, pc$, while lower mass UFDs exhibit cusps down to ${\lesssim}100\rm \, pc$, as expected from energetic arguments. Our dwarfs with $M_{\ast }\gt 10^{4}\, \mathrm{M}_{\odot }$ have half-mass radii (R1/2) in agreement with Local Group (LG) dwarfs (dynamical mass versus R1/2 and stellar rotation also resemble observations).more »

3. ABSTRACT

In this work, we establish and test methods for implementing dynamical friction (DF) for massive black hole pairs that form in large volume cosmological hydrodynamical simulations that include galaxy formation and black hole growth. We verify our models and parameters both for individual black hole dynamics and for the black hole population in cosmological volumes. Using our model of DF from collisionless particles, black holes can effectively sink close to the galaxy centre, provided that the black hole’s dynamical mass is at least twice that of the lowest mass resolution particles in the simulation. Gas drag also plays a role in assisting the black holes’ orbital decay, but it is typically less effective than that from collisionless particles, especially after the first billion years of the black hole’s evolution. DF from gas becomes less than $1{{\ \rm per\ cent}}$ of DF from collisionless particles for BH masses >107 M⊙. Using our best DF model, we calculate the merger rate down to z = 1.1 using an Lbox = 35 Mpc h−1 simulation box. We predict ∼2 mergers per year for z > 1.1 peaking at z ∼ 2. These merger rates are within the range obtained in previous work using similar resolution hydrodynamical simulations.more »

4. Abstract

Tidal disruption events (TDEs) provide a unique opportunity to probe the stellar populations around supermassive black holes (SMBHs). By combining light-curve modeling with spectral line information and knowledge about the stellar populations in the host galaxies, we are able to constrain the properties of the disrupted star for three TDEs. The TDEs in our sample have UV spectra, and measurements of the UV Niiito Ciiiline ratios enabled estimates of the nitrogen-to-carbon abundance ratios for these events. We show that the measured nitrogen line widths are consistent with originating from the disrupted stellar material dispersed by the central SMBH. We find that these nitrogen-to-carbon abundance ratios necessitate the disruption of moderately massive stars (≳1–2M). We determine that these moderately massive disruptions are overrepresented by a factor of ≳102when compared to the overall stellar population of the post-starburst galaxy hosts. This implies that SMBHs are preferentially disrupting higher mass stars, possibly due to ongoing top-heavy star formation in nuclear star clusters or to dynamical mechanisms that preferentially transport higher mass stars to their tidal radii.

5. Abstract

We present ALMA [C ii] line and far-infrared (FIR) continuum observations of three $z \gt 6$ low-luminosity quasars ($M_{\rm 1450} \gt -25$ mag) discovered by our Subaru Hyper Suprime-Cam (HSC) survey. The [C ii] line was detected in all three targets with luminosities of $(2.4\mbox{--}9.5) \times 10^8\, L_{\odot }$, about one order of magnitude smaller than optically luminous ($M_{\rm 1450} \lesssim -25$ mag) quasars. The FIR continuum luminosities range from $\lt 9 \times 10^{10}\, L_{\odot }$ (3 $\sigma$ limit) to ${\sim } 2 \times 10^{12}\, L_{\odot }$, indicating a wide range in star formation rates in these galaxies. Most of the HSC quasars studied thus far show [C ii]/ FIR luminosity ratios similar to local star-forming galaxies. Using the [C ii]-based dynamical mass ($M_{\rm dyn}$) as a surrogate for bulge stellar mass ($M_{\rm\, bulge}$), we find that a significant fraction of low-luminosity quasars are located on or even below the local $M_{\rm\, BH}$–$M_{\rm\, bulge}$ relation, particularly at the massive end of the galaxy mass distribution. In contrast, previous studies of optically luminous quasars have found that black holes are overmassive relative to the local relation. Given the low luminosities of our targets, we are exploring the nature of the early co-evolution of supermassive black holes andmore »