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 $\Lambda$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 $6 \times 10^{-4}$ 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 $8 \times 10^{-3}$. 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 ($\delta$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 < $\nu$ < 35MHz corresponding to 40 < z < 46. However, a 10GeV mass WIMP may be detectable at the 1-3mK level in the frequency range 55MHz < $\nu$ < 119MHz corresponding to 11 < z < 25, and at the 1-10mK level in the frequency range 30MHz < $\nu$ < 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 $z=15$ 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 ($M^*$) 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. $M^*$ 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 $M^*$. We chained neural networks, improving the predictions on SFR to some extent. For SFR, we time-averaged this value between $z=0$ and $z=0.1$, which improved results for $z=0$. 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 Geofísica