47 research outputs found
Extreme Tidal Stripping May Explain the Overmassive Black Hole in Leo I: a Proof of Concept
Leo I, at a distance of 255 kpc, is the most distant dwarf spheroidal galaxy
of the Milky Way. A recent study found dynamical evidence of a supermassive
black hole of at its center. This black
hole, comparable in mass to the Milky Way's Sgr A*, places the system >2 orders
of magnitude above the standard relation. We investigate
the possibility that Leo I's stellar system was originally much more massive,
thus closer to the relation. Extreme tidal disruption from one or two close
passages within the Milky Way's virial radius could have removed most of its
stellar mass. A simple analytical model suggests that the progenitor of Leo I
could have experienced a mass loss of from a single pericenter
passage. This mass loss percentage increases to if the pericenter
occurs at the lower limit current orbital reconstructions allow. Detailed
N-body simulations show that the mass loss could reach with up to
two pericenter passages. Despite very significant uncertainties in the
properties of Leo I, we reproduce its current position and velocity dispersion,
as well as the final stellar mass enclosed in 1 kpc () within a factor <2. The most recent tidal stream produced is directed
along our line of sight toward Leo I, making it challenging to detect. Evidence
from this extreme tidal disruption event could be present in current Gaia data
in the form of extended tidal streams.Comment: Submitted for publication in The Astrophysical Journal Letters. 8
pages, 4 figures. Includes comments from the first round of referee report
Detecting Wandering Intermediate-Mass Black Holes with AXIS in the Milky Way and Local Massive Galaxies
This white paper explores the detectability of intermediate-mass black holes
(IMBHs) wandering in the Milky Way (MW) and massive local galaxies, with a
particular emphasis on the role of AXIS. IMBHs, ranging within , are commonly found at the centers of dwarf galaxies and may exist,
yet undiscovered, in the MW. By using model spectra for advection-dominated
accretion flows (ADAFs), we calculated the expected fluxes emitted by a
population of wandering IMBHs with a mass of in various MW
environments and extrapolated our results to massive local galaxies. Around
of the potential population of wandering IMBHs in the MW can be detected
in an AXIS deep field. We proposed criteria to aid in selecting IMBH candidates
using already available optical surveys. We also showed that IMBHs wandering in
galaxies within Mpc can be easily detected with AXIS when passing
within dense galactic environments (e.g., molecular clouds and cold neutral
medium). In summary, we highlighted the potential X-ray detectability of
wandering IMBHs in local galaxies and provided insights for guiding future
surveys. Detecting wandering IMBHs is crucial for understanding their
demographics, evolution, and the merging history of galaxies.Comment: This White Paper is part of a series commissioned for the AXIS Probe
Concept Mission; additional AXIS White Papers can be found at the AXIS
website: http://axis.astro.umd.edu/ with a mission overview here:
arXiv:2311.00780. Review article, 7 pages, 3 figure
Super-resolution simulation of the Fuzzy Dark Matter cosmological model
AI super-resolution, combining deep learning and N-body simulations has been
shown to successfully reproduce the large scale structure and halo abundances
in the Lambda Cold Dark Matter cosmological model. Here, we extend its use to
models with a different dark matter content, in this case Fuzzy Dark Matter
(FDM), in the approximation that the difference is encoded in the initial power
spectrum. We focus on redshift z = 2, with simulations that model smaller
scales and lower masses, the latter by two orders of magnitude, than has been
done in previous AI super-resolution work. We find that the super-resolution
technique can reproduce the power spectrum and halo mass function to within a
few percent of full high resolution calculations. We also find that halo
artifacts, caused by spurious numerical fragmentation of filaments, are equally
present in the super-resolution outputs. Although we have not trained the
super-resolution algorithm using full quantum pressure FDM simulations, the
fact that it performs well at the relevant length and mass scales means that it
has promise as technique which could avoid the very high computational cost of
the latter, in some contexts. We conclude that AI super-resolution can become a
useful tool to extend the range of dark matter models covered in mock catalogs.Comment: 7 pages, 4 figure
Probabilistic reconstruction of Dark Matter fields from biased tracers using diffusion models
Galaxies are biased tracers of the underlying cosmic web, which is dominated
by dark matter components that cannot be directly observed. The relationship
between dark matter density fields and galaxy distributions can be sensitive to
assumptions in cosmology and astrophysical processes embedded in the galaxy
formation models, that remain uncertain in many aspects. Based on
state-of-the-art galaxy formation simulation suites with varied cosmological
parameters and sub-grid astrophysics, we develop a diffusion generative model
to predict the unbiased posterior distribution of the underlying dark matter
fields from the given stellar mass fields, while being able to marginalize over
the uncertainties in cosmology and galaxy formation
Fly-by galaxy encounters with multiple black holes produce star-forming linear wakes
We look for simulated star-forming linear wakes such as the one recently
discovered by van Dokkum et al. (2023) in the cosmological hydrodynamical
simulation ASTRID. Amongst the runaway black holes in ASTRID, none are able to
produce clear star-forming wakes. Meanwhile, fly-by encounters, typically
involving a compact galaxy (with a central black hole) and a star-forming
galaxy (with a duo of black holes) reproduce remarkably well many of the key
properties (its length and linearity; recent star formation, etc.) of the
observed star-forming linear feature. We predict the feature to persist for
approximately 100 Myr in such a system and hence constitute a rare event. The
feature contains a partly stripped galaxy (with ) and a dual BH system () in
its brightest knot. X-ray emission from AGN in the knot should be detectable in
such systems. After from the first fly-by, the
galaxies merge leaving behind a triple black hole system in a (still) actively
star-forming early-type remnant of mass .
Follow-up JWST observations may be key for revealing the nature of these linear
features by potentially detecting the older stellar populations constituting
the bright knot. Confirmation of such detections may therefore help
discriminate a fly-by encounter from a massive BH wake to reveal the origin of
such features.Comment: 8 pages, 5 figures, comments welcom