THE BLACK HOLE
IN DWARF GALAXIES
The scaling relations between central black hole mass and host galaxy properties, e.g., the bulge mass component and bulge velocity dispersion of stars, hint to a joint evolution of black holes and galaxies. Estimating the dynamical mass of black holes and their host galaxies at different redshifts is fundamental to establish their growth scenarios over the cosmic time.
Supermassive black hole seeds
The highest redshift quasar (z=7.085) known already had black hole mass is 2 billions solar masses only 770 million years after Big Bang (Mortlock 2011, Banados 2018).The mass is based on quasar's luminosity and on its Mg II line width. As we know, the black holes accreate surround materials at Eddington limit; and they clearly could not reach to their mass only in 770 million years with Eddington limit if the formed in death of normal massive stars. Consequently, they formed by intermediate-mass black holes.
ULAS J1120 +0641
(Mortlock 2011)
IMBH Formation paths
There are three primatry theoretical chanels for intermediate-mass black hole and supermassive black holes formations: The deaths of the first (or called pop-III) stars, direct collapse, gravitational runaway. By studying relation of central black hole mass and velocity dispersion, occupation fraction, ... we can know which path dominated the formations
Figure 3. The statistics of measured black holes.
While there are numerous galaxies that estimated black hole mass and velocity dispersion in the range 1e6 - 1e9 solar mass, there are only a few galaxies with (sub)million solar mass BHs that are estimated dynamically, including M32, NGC 4395, NGC 404, NGC 4414, NGC 205, NGC 5102 and NGC 5206. These results also have wide uncertainty
Observation problems
Massive black holes with masses between 1e6-1e9 are commonly found in the centers of massive galaxies. However, it is difficult to determine the demographics of black holes in low-mass galaxies due to the decreasing radius of influence with increasing distance and black hole mass. Current observations are limited to a resolution of approximately 100 milliarcseconds, which means that the farthest distance at which a black hole with a mass of 1e6 can be observed is around 3 Mpc.
In the near future, the James Webb Space Telescope may directly detect the formation of supermassive black hole seeds in the early universe at redshifts of around z~10-20 in the form of quasi-stars. Additionally, the Extremely Large Telescope, with its high angular resolution of four milliarcseconds (ELT/HARMONI), will be able to probe dwarf galaxies. These instruments will provide future mass measurements and enable statistical analysis of the astrophysical issues discussed above.
“With the ELT we’re going to see things that were impossible to see before. We’re going to see things and we’re going to be surprised!”