2,924 research outputs found
Dark Matter annihilation energy output and its effects on the high-z IGM
We study the case of DM self annihilation, in order to assess its importance
as an energy injection mechanism, to the IGM in general, and to the medium
within particular DM haloes. We consider thermal relic WIMP particles with
masses of 10GeV and 1TeV and we analyse in detail the clustering properties of
DM in a CDM cosmology, on all hierarchy levels, from haloes and their
mass function, to subhaloes and the DM density profiles within them,
considering adiabatic contraction by the presence of a SMBH. We then compute
the corresponding energy output, concluding that DM annihilation does not
constitute an important feedback mechanism. We also calculate the effects that
DM annihilation has on the IGM temperature and ionization fraction, and we find
that assuming maximal energy absorption, at z ~ 10, for the case of a 1TeV
WIMP, the ionization fraction could be raised to and the
temperature to 10K, and in the case of a 10GeV WIMP, the IGM temperature could
be raised to 200K and the ionization fraction to . We
conclude that DM annihilations cannot be regarded as an alternative
reionization scenario. Regarding the detectability of the WIMP through the
modifications to the 21 cm differential brightness temperature signal
(Tb), we conclude that a thermal relic WIMP with mass of 1TeV is not
likely to be detected from the global signal alone, except perhaps at the 1-3mK
level in the frequency range 30MHz < < 35MHz corresponding to 40 < z <
46. However, a 10GeV mass WIMP may be detectable at the 1-3mK level in the
frequency range 55MHz < < 119MHz corresponding to 11 < z < 25, and at the
1-10mK level in the frequency range 30MHz < < 40MHz corresponding to 35 <
z < 46.Comment: 23 pages, 12 figures, accepted for publication in MNRA
Black hole charges in dark matter haloes and the seeds of cosmic magnetic fields
We present improved estimates of the electric charge that black holes could
hold when these are embedded in the ionised plasma within dark matter haloes
(or galaxies) in the Universe. We have implemented the spontaneous emission of
charges of opposite sign to that of the black hole via athermal Hawking
evaporation, including its dependence on black hole spin, and we have estimated
the equilibrium charge that arises as this charge loss is balanced by the
continuous accretion of charges from the surrounding plasma. The resulting
charge can be several orders of magnitude lower than previously estimated upper
limits, but it can surpass the pair production limit noted by Gibbons (1974) by
a margin that increases with the amplitude of the black hole spin and the
density of the plasma. We also implement a calculation for the net charge and
magnetic moment of dark matter haloes when the dark matter is made of
primordial black holes and also for astrophysical black holes that form part of
the stellar halo of galaxies. We calculate the resulting magnetic fields of
haloes for these different cases, and show that both primordial black
holes and stellar ones could provide the magnetic field that can seed the
observed ones in present-day galaxies.Comment: prepared for submission to JCAP, comments welcom
Not Hydro: Using Neural Networks to estimate galaxy properties on a Dark-Matter-Only simulation
Using data from TNG300-2, we train a neural network (NN) to recreate the
stellar mass () and star formation rate (SFR) of central galaxies in a
dark-matter-only simulation. We consider 12 input properties from the halo and
sub-halo hosting the galaxy and the near environment. predictions are
robust, but the machine does not fully reproduce its scatter. The same happens
for SFR, but the predictions are not as good as for . We chained neural
networks, improving the predictions on SFR to some extent. For SFR, we
time-averaged this value between and , which improved results for
. Predictions of both variables have trouble reproducing values at lower
and higher ends. We also study the impact of each input variable in the
performance of the predictions using a leave-one-covariate-out approach, which
led to insights about the physical and statistical relation between input
variables. In terms of metrics, our machine outperforms similar studies, but
the main discoveries in this work are not linked with the quality of the
predictions themselves, but to how the predictions relate to the input
variables. We find that previously studied relations between physical variables
are meaningful to the machine. We also find that some merger tree properties
strongly impact the performance of the machine. %We highlight the value of
machine learning (ML) methods in helping understand the information contained
in different variables, since with its help we were able to obtain useful
insights resulting from studying the impact of input variables on the resulting
behaviour of galaxy properties. We conclude that ML models are useful tools to
understand the significance of physical different properties and their impact
on target characteristics, as well as strong candidates for potential
simulation methods.Comment: 17 pages, 16 figures, to be published in MNRA
Cosmic queuing: Galaxy satellites, building blocks and the hierarchical clustering paradigm
We study the properties of building blocks (BBs; i.e. accreted satellites) and surviving satellites of present-day galaxies using the semi-analytic model of galaxy formation SAG ('semi-analytic galaxies') in the context of a concordance Λ cold dark matter (ΛCDM) cosmology. We consider large number of dark matter (DM) halo merger trees spanning a wide range of masses (~1 × 1010-2.14 × 1015 M⊙). We find higher metallicities for BBs with respect to surviving satellites, an effect produced by the same processes behind the build up of the mass-metallicity relation. We prove that these metallicity differences arise from the higher peak height in the density fluctuation field occupied by BBs and central galaxies which have collapsed into a single object earlier than surviving satellites. BBs start to form stars earlier, during the peak 3/13/2011 ΛCDM, and build up half of their final stellar mass (measured at the moment of disruption) up to four times faster than surviving satellites. Surviving satellites keep increasing their stellar masses rather quiescently down to z ≃ 1. The difference between the metallicities of satellites, BBs and central galaxies depends on the host DM halo mass, in a way that can be used as a further test for the concordance cosmology.Facultad de Ciencias Astronómicas y GeofÃsica
- …