arXiv subjects

Victor H. Robles

Publications and source records attributed to Victor H. Robles.

23 records · Page 2Linked to original sources

arXiv2016

Scalar Field (Wave) Dark Matter

Recent high-quality observations of dwarf and low surface brightness (LSB) galaxies have shown that their dark matter (DM) halos prefer flat central density profiles. On the other hand the standard cold dark matter model simulations predict a more cuspy behavior. Feedback from star formation has been widely used to reconcile simulations with observations, this might be successful in field dwarf galaxies but its success in low mass galaxies remains uncertain. One model that have received much attention is the scalar field dark matter model. Here the dark matter is a self-interacting ultra light scalar field that forms a cosmological Bose-Einstein condensate, a mass of $10^{-22}$eV/c$^2$ is consistent with flat density profiles in the centers of dwarf spheroidal galaxies, reduces the abundance of small halos, might account for the rotation curves even to large radii in spiral galaxies and has an early galaxy formation. The next generation of telescopes will provide better constraints to the model that will help to distinguish this particular alternative to the standard model of cosmology shedding light into the nature of the mysterious dark matter.

astro-ph.GA↗

arXiv2015

Evolution of a dwarf satellite galaxy embedded in a scalar field dark matter halo

The cold dark matter (CDM) model has two unsolved issues: simulations overpredict the satellite abundance around the Milky Way (MW) and it disagrees with observations of the central densities of dwarf galaxies which prefer constant density (core) profiles.One alternative explanation known as the scalar field dark matter (SFDM) model, assumes that the dark matter is a scalar field of mass($\sim 10^{-22}$ eV/$c^2$); this model can reduce the overabundance issue due to the lack of halo formation below a mass scale of $\sim 10^8$M$_{\odot}$ and successfully fits the density distribution in dwarfs. One of the attractive features of the model is predicting core profiles in halos, although the determination of the core sizes is set by fitting the observational data. We perform \textit{N}-body simulations to explore the influence of tidal forces over a stellar distribution embedded in a SFDM halo orbiting a MW-like SFDM host halo with a disk. Our simulations intend to test the viability of SFDM as an alternative model by comparing the tidal effects that result in this paradigm with those obtained in CDM for similar mass halos. We found that galaxies in subhalos with core profiles and high central densities survive for 10 Gyr. The same occurs for galaxies in low density subhalos located far from the host disk influence, whereas satellites in low density DM halos and in tight orbits can eventually be stripped of stars. We conclude that SFDM shows consistency with results from CDM for dwarf galaxies, but naturally offer a possibility to solve the missing satellite problem.

astro-ph.GA↗

arXiv2015

SFDM: A new formation mechanism of tidal debris

Recent observations of tidal debris around galaxies have revealed that the structural properties of the spheroidal components of tidally disturbed galaxies are similar to those found in non-interacting early-type galaxies(ETGs), likely due to minor merging events that do not strongly affect the bulge region or to major mergers that happened a long time ago. We show that independently of merger events, tidal features like shells or rings can also arise if the the dark matter is an ultra light scalar field of mass ~10$^{-22}$eV/c$^2$. In the scalar field dark matter (SFDM) model the small mass precludes halo formation below ~10$^8$ M$_{\odot}$ reducing the number of small galaxies today, it produces shallow density profiles due to the uncertainty principle in contrast to the steep profiles found in the standard cold dark matter (CDM) paradigm, in addition to the usual soliton solution there exists dark matter haloes in multistates, characterized by ripples in their density profiles, which are stable provided that most of the halo mass resides in the ground state. We use the hydrodynamics code ZEUS to track the gas evolution in a background potential given by a superposition of the ground and first excited state of the scalar field, we study this configuration when it is initially unstable (excited state more massive than ground state) but by a population inversion in the states it eventually becomes stable, this could happen when haloes decoupled from the expansion of the universe and collapse to reach a state of equilibrium. We found that tidal structures like rings are formed at a particular radii as a direct consequence of the wavelike structure of the dark matter halo(abridged)

astro-ph.GA↗

arXiv2012

Exact Solution to Finite Temperature SFDM: Natural Cores without Feedback

Recent high-quality observations of low surface brightness (LSB) galaxies have shown that their dark matter (DM) halos prefer flat central density profiles. On the other hand, the standard cold dark matter model simulations predict a more cuspy behavior. One mechanism to reconcile the simulations with the observed data is the feedback from star formation, this might be successful in isolated dwarf galaxies but its success in LSB galaxies remains unclear. Additionally, including too much feedback in the simulations is a double-edged sword, in order to obtain a cored DM distribution from an initially cuspy one, the feedback recipes usually require to remove a large quantity of baryons from the center of galaxies, however, some feedback recipes produce twice more satellite galaxies of a given luminosity and with much smaller mass to light ratios from those that are observed. Therefore, one DM profile that produces cores naturally and that does not require large amounts of feedback would be preferable. We find both requirements to be satisfied in the scalar field dark matter model. Here, we consider that the dark matter is an auto-interacting real scalar field in a thermal bath at temperature T with an initial $Z_2$ symmetric potential, as the universe expands, the temperature drops so that the $Z_2$ symmetry is spontaneously broken and the field rolls down to a new minimum. We give an exact analytic solution to the Newtonian limit of this system and show that it can satisfy the two desired requirements and that the rotation curve profile is not longer universal.

astro-ph.CO↗

arXiv2012

Flat Central Density Profile and Constant DM Surface Density in Galaxies from Scalar Field Dark Matter

The scalar field dark matter (SFDM) model proposes that galaxies form by condensation of a scalar field (SF) very early in the universe forming Bose-Einstein Condensates (BEC) drops, i.e., in this model haloes of galaxies are gigantic drops of SF. Here big structures form like in the LCDM model, by hierarchy, thus all the predictions of the LCDM model at big scales are reproduced by SFDM. This model predicts that all galaxies must be very similar and exist for bigger redshifts than in the LCDM model. In this work we show that BEC dark matter haloes fit high-resolution rotation curves of a sample of thirteen low surface brightness galaxies. We compare our fits to those obtained using a Navarro-Frenk-White and Pseudo-Isothermal (PI) profiles and found a better agreement with the SFDM and PI profiles. The mean value of the logarithmic inner density slopes is -0.27 +/- 0.18. As a second result we find a natural way to define the core radius with the advantage of being model-independent. Using this new definition in the BEC density profile we find that the recent observation of the constant dark matter central surface density can be reproduced. We conclude that in light of the difficulties that the standard model is currently facing the SFDM model can be a worthy alternative to keep exploring further.

astro-ph.CO↗