585 research outputs found
Galaxies in LCDM with Halo Abundance Matching: luminosity-velocity relation, baryonic mass-velocity relation, velocity function and clustering
It has long been regarded as difficult for a cosmological model to account
simultaneously for the galaxy luminosity, mass, and velocity distributions. We
revisit this issue using a modern compilation of observational data along with
the best available large-scale cosmological simulation of dark matter. We find
that the standard cosmological model, used in conjunction with halo abundance
matching (HAM) and simple dynamical corrections, fits all basic statistics of
galaxies with circular velocities Vcirc > 80 km/s. Our observational constraint
is the luminosity-velocity relation which allows all types of galaxies to be
included. We have compiled data for a variety of galaxies ranging from dwarf
irregulars to giant ellipticals. The data present a clear monotonic
luminosity-velocity relation from 50 km/s to 500 km/s, with a bend below 80
km/s and a systematic offset between late- and early-type galaxies. For
comparison to theory, we employ our LCDM "Bolshoi" simulation of dark matter,
which has unprecedented mass and force resolution. We use halo abundance
matching to assign rank-ordered galaxy luminosities to the dark matter halos.
The resulting predictions for the luminosity-velocity relation are in excellent
agreement with the available data on both early-type and late-type galaxies for
the luminosity range from Mr = -14-22. We also compare our predictions for the
"cold" baryon mass (i.e., stars and cold gas) of galaxies as a function of
circular velocity with the available observations, again finding a very good
agreement. The predicted circular velocity function is in agreement with the
galaxy velocity function for 80-400 km/s. However, we find that the dark matter
halos with Vcirc < 80 km/s are much more abundant than observed galaxies with
the same Vcirc . We find that the two-point correlation function of galaxies in
our model matches very well the results from the SDSS.Comment: 40 pages, 18 figures, published in Ap
Hints against the cold and collisionless nature of dark matter from the galaxy velocity function
The observed number of dwarf galaxies as a function of rotation velocity is
significantly smaller than predicted by the standard model of cosmology. This
discrepancy cannot be simply solved by assuming strong baryonic feedback
processes, since they would violate the observed relation between maximum
circular velocity () and baryon mass of galaxies. A speculative
but tantalising possibility is that the mismatch between observation and theory
points towards the existence of non-cold or non-collisionless dark matter (DM).
In this paper, we investigate the effects of warm, mixed (i.e warm plus cold),
and self-interacting DM scenarios on the abundance of dwarf galaxies and the
relation between observed HI line-width and maximum circular velocity. Both
effects have the potential to alleviate the apparent mismatch between the
observed and theoretical abundance of galaxies as a function of .
For the case of warm and mixed DM, we show that the discrepancy disappears,
even for luke-warm models that evade stringent bounds from the Lyman-
forest. Self-interacting DM scenarios can also provide a solution as long as
they lead to extended ( kpc) dark matter cores in the density
profiles of dwarf galaxies. Only models with velocity-dependent cross sections
can yield such cores without violating other observational constraints at
larger scales.Comment: Matches published versio
Low-mass galaxy assembly in simulations: regulation of early star formation by radiation from massive stars
Despite recent success in forming realistic present-day galaxies, simulations
still form the bulk of their stars earlier than observations indicate. We
investigate the process of stellar mass assembly in low-mass field galaxies, a
dwarf and a typical spiral, focusing on the effects of radiation from young
stellar clusters on the star formation (SF) histories. We implement a novel
model of SF with a deterministic low efficiency per free-fall time, as observed
in molecular clouds. Stellar feedback is based on observations of star-forming
regions, and includes radiation pressure from massive stars, photoheating in H
II regions, supernovae and stellar winds. We find that stellar radiation has a
strong effect on the formation of low-mass galaxies, especially at z > 1, where
it efficiently suppresses SF by dispersing cold and dense gas, preventing
runaway growth of the stellar component. This behaviour is evident in a variety
of observations but had so far eluded analytical and numerical models without
radiation feedback. Compared to supernovae alone, radiation feedback reduces
the SF rate by a factor of ~100 at z < 2, yielding rising SF histories which
reproduce recent observations of Local Group dwarfs. Stellar radiation also
produces bulgeless spiral galaxies and may be responsible for excess thickening
of the stellar disc. The galaxies also feature rotation curves and baryon
fractions in excellent agreement with current data. Lastly, the dwarf galaxy
shows a very slow reduction of the central dark matter density caused by
radiation feedback over the last ~7 Gyr of cosmic evolution
Another baryon miracle? Testing solutions to the 'missing dwarfs' problem
The dearth of dwarf galaxies in the local universe is hard to reconcile with
the large number of low mass haloes expected within the concordance
CDM paradigm. In this paper we perform a systematic evaluation of the
uncertainties affecting the measurement of DM halo abundance using galaxy
kinematics. Using a large sample of dwarf galaxies with spatially resolved
kinematic data we derive a correction to obtain the observed abundance of
galaxies as a function of their halo maximum circular velocity from the
line-of-sight velocity function in the Local Volume. This estimate provides a
direct means of comparing the predictions of theoretical models and simulations
(including nonstandard cosmologies and novel galaxy formation physics) to the
observational constraints. The new "galactic " function is steeper
than the line-of-sight velocity function but still shallower than the
theoretical CDM expectation, showing that some unaccounted physical process is
necessary to reduce the abundance of galaxies and/or drastically modify their
density profiles compared to CDM haloes. Using this new galactic
function, we investigate the viability of baryonic solutions such as
feedback-powered outflows and photoevaporation of gas from an ionising
radiation background. At the 3- confidence level neither energetic
feedback nor photoevaporation are effective enough to reconcile the
disagreement. In the case of maximum baryonic effects, the theoretical estimate
still deviates significantly from the observations for km/s. CDM
predicts at least 1.8 times more galaxies with km/s and 2.5
times more than observed at km/s. Recent hydrodynamic simulations seem to
resolve the discrepancy but disagree with the properties of observed galaxies
with resolved kinematics. (abridged)Comment: 17 pages, 22 figures; major revisions include clarification of the
method, expanded comparison with simulations with a new figure, analysis of
uncertainties in model as well as pressure support corrections, and a new
table with nomenclatur
Globular cluster metallicity distributions in the E-MOSAICS simulations
The metallicity distributions of globular cluster (GC) systems in galaxies
are a critical test of any GC formation scenario. In this work, we investigate
the predicted GC metallicity distributions of galaxies in the MOdelling Star
cluster population Assembly In Cosmological Simulations within EAGLE
(E-MOSAICS) simulation of a representative cosmological volume (
comoving Mpc). We find that the predicted GC metallicity distributions and
median metallicities from the fiducial E-MOSAICS GC formation model agree well
the observed distributions, except for galaxies with masses M, which contain an overabundance of metal-rich GCs.
The predicted fraction of galaxies with bimodal GC metallicity distributions
( per cent in total; per cent for
M) is in good agreement with observed fractions ( per
cent), as are the mean metallicities of the metal-poor and metal-rich peaks. We
show that, for massive galaxies ( M), bimodal GC
distributions primarily occur as a result of cluster disruption from
initially-unimodal distributions, rather than as a result of cluster formation
processes. Based on the distribution of field stars with GC-like abundances in
the Milky Way, we suggest that the bimodal GC metallicity distribution of Milky
Way GCs also occurred as a result of cluster disruption, rather than formation
processes. We conclude that separate formation processes are not required to
explain metal-poor and metal-rich GCs, and that GCs can be considered as the
surviving analogues of young massive star clusters that are readily observed to
form in the local Universe today.Comment: 19 pages, 16 figures. Published in MNRA
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