Searcharxiv⌕ Search

arXiv subjects

V. Avila-Reese

Publications and source records attributed to V. Avila-Reese.

At least 73 records · Page 4Linked to original sources
arXiv2003

The structure of halos in Self-Interacting Cold Dark Matter models

High-resolution numerical simulations were performed to study the structure and substructure of Milky Way- and cluster-sized halos in a LCDM cosmology with self-interacting (SI) dark particles, where the particle cross section, +AFw-sig, is assumed constant or inversely proportional to the relative velocity. We conclude that the cuspy halo problem at galaxy scales of the LCDM cosmogony can be solved in the latter case. In this case, the inner density of galaxy-cluster halos is only slightly affected by the SI, resulting in agreement with observational constraints. At the same time, the subhalo population in galaxy and cluster SI-CDM halos remains roughly similar to that seen on collisionless CDM halos.

astro-ph↗
arXiv2003

Physical processes behind the morphological Hubble sequence

The study of formation and evolution of galaxies is reviewed, making emphasis on the physical factors which are important to understand the origin of the galaxy Hubble sequence. We concentrate on predictions of the hierarchical Cold Dark Matter (CDM) scenario and the confrontation with observations. The mass assembling of the CDM halos, the baryonic processes within them, and the evolution of disks and spheroids are described. The successes and shortcomings are discussed. Disk evolution seems to be a quiescent and extended process driven by the cosmological initial conditions, while spheroids are formed probably in violent events, where several astrophysical processes are competing.

astro-ph↗
arXiv2003

The luminous and dark matter content of disk galaxies

For a compiled sample of disk galaxies with available photometry (B and K bands), velocity line-widths and HI integral fluxes, several parameters which trace the luminous, baryonic and dark matter contents were inferred. We investigated how these parameters do vary with different galaxy properties, and confronted the results with predictions of galaxy evolutionary models in the context of the LCDM cosmogony. The ratio of disk-to-total maximum circular velocity, vd/vt, depends mainly on the central disk surface density Sig_d (or surface brightness, SB), increasing roughly as Sig_d^0.15. While a fraction of high SB galaxies have a vd/vt ratio corresponding to the maximum disk solution, the low SB are completely dark matter dominated. The trend is similar for the models, although they have slightly smaller vd/vt ratios than observations. An analysis of residuals of the vd/vt-Sig_d relation shows that vd/vt tends to decrease as the galaxy is redder, more luminous (massive), and of earlier type. The models allow us to explain the physics of these results, which imply a connexion between halo structure and luminous properties. The estimated dynamical-to-baryon mass and dynamical mass-to-light ratios at a given radius, for observations and models, decrease with the SB and do not correlate with the galaxy scale, contrary to what has been reported in previous works, based on the analysis of rotation curve shapes. We discuss this difference and state the importance to solve the controversy on whether the dark and luminous contents in disk galaxies depend on SB or luminosity. The broad agreement between models and observations favors the LCDM scenario. However, the excess of dark matter inside the optical region of disk galaxies remains as the main difficulty. (abridged)

astro-ph↗
arXiv2003

Star formation and turbulent dissipation in models of disk galaxy evolution

The kinetic energy dissipation rate in the turbulent ISM of disk galaxies is a key ingredient in galaxy evolution models since it determines the effectiveness of large-scale star formation (SF) feedback. Using magneto-hydro-dynamic simulations, we find that the ISM dissipates efficiently the turbulent kinetic energy injected by sources of stellar nature. Thus, the SF process may be self-regulated by an energy balance only at the level of the disk ISM. The use of the self-regulation SF mechanism in galaxy evolutionary models, where disks form inside growing Cold Dark Matter halos, allows to predict the SF history of disk galaxies, including the Milky Way and the solar neighborhood, as well as the contribution of the whole population of disk galaxies to the cosmic SF history. The results are encouraging.

astro-ph↗
arXiv2002

Structure and Subhalo Population of Halos in a Self-Interacting Dark Matter Cosmology

We study the structure of Milky Way (MW)- and cluster-sized halos in a Lambda Cold Dark Matter (CDM) cosmology with self-interacting (SI) dark particles. The cross section per unit of particle mass has the form sigma = sig_0(1/v_100)^alpha, where sig_0 is a constant in units of cm^2/gr and v_100 is the relative velocity in units of 100 km/s. Different values for sigma with alpha= 0 or 1 were used. For small values of sigma = const. (sig_0<0.5), the core density of the halos at z=0 is typically higher at a given mass for lower values of sig_0 or, at a given sig_0, for lower masses. For values of sig_0 as high as 3.0, the halos may undergo the gravothermal catastrophe before z=0. When alpha = 1, the core density of cluster- and MW-sized halos is similar. Using sigma = 0.5-1.0x(1/v_100), our predictions agree with the central densities and the core scaling laws of halos both inferred from the observations of dwarf and LSB galaxies and clusters of galaxies. The cumulative Vmax-functions of subhalos in MW-sized halos with (sig_0,alpha) = (0.1,0.0), (0.5,0.0) and (0.5,1.0) agree roughly with observations (luminous satellites) for Vmax > 30 km/s, while at Vmax = 20 km/s the functions are a factor 5-8 higher, similar to the CDM predictions. The halos with SI have slightly more specific angular momentum at a given mass shell and are rounder than their CDM counterparts. We conclude that the introduction of SI particles with sigma \propto 1/v_100 may remedy the cuspy core problem of the CDM cosmogony, while the subhalo population number remains similar to that of the CDM halos.

astro-ph↗
arXiv2002

The shape of rotation curves: models vs. observations

We discuss the shape and decomposition of rotation curves (RCs) of galaxies formed within growing cold dark matter halos. The outer RC shape correlates mainly with the surface brightness (SB), the luminous mass fraction, fd, and the bulge fraction. In order the shapes of RC depend significantly on luminosity, fd should be a strong function of mass (feedback). For the preferred values of fd (\lesssim 0.03), the high SB models can be maximum disks only when the halos have a shallow core. The low SB models are sub-maximum disks. The residuals of the baryonic Tully-Fisher (TF) and disk mass-radius relations show a clear anti-correlation among them, but when one passes to the TF and luminosity-radius relations, the anti-correlation almost disappears. Therefore, the observed lack of correlation among the residuals of the last two relations should not be interpreted as an evidence of sub-maximal disks.

astro-ph↗
arXiv2002

Formation and evolution of galaxy disks: what is wrong with CDM?

We find that the density distribution of high and low surface brightness (SB) galaxy disks formed within LCDM halos under the assumption of detailed angular momentum conservation is in rough agreement with observations. The luminous-to-dark matter ratio of the model galaxies increases with SB. The lowest SB models tend to be minimum disks, but the high SB models hardly attain the maximum disk solution. With the introduction of shallow cores in the halos, high SB models become maximum disks. The shallow cores also help to improve the inner SB profiles of bulge-less low SB models and the zero-point of the Tully-Fisher relation. The models predict well this relation and its scatter, as well as the small correlation among the residuals of this and the luminosity-radius relation, in spite of the dependence of the rotation curve shapes on SB.

astro-ph↗
arXiv2001

A cosmological study of the star formation history in the solar neighbourhood

We use a cosmological galactic evolutionary approach to model the Milky Way. A detailed treatment of the mass aggregation and dynamical history of the growing dark halo is included, together with a self consistent physical treatment for the star formation processes within the growing galactic disc. This allows us to calculate the temporal evolution of star and gas surface densities at all galactic radii, in particular, the star formation history (SFH) at the solar radius. A large range of cosmological mass aggregation histories (MAHs) is capable of producing a galaxy with the present day properties of the Milky Way. The resulting SFHs for the solar neighbourhood bracket the available observational data for this feature, the most probable MAH yielding the optimal comparison with these observations. We also find that the rotation curve for our Galaxy implies the presence of a constant density core in its dark matter halo.

astro-ph↗
arXiv2001

Formation and structure of halos in a warm dark matter cosmology

(Abridged) Using high-resolution cosmological N-body simulations, we study how the density profiles of dark matter halos are affected by the filtering of the density power spectrum below a given scale length and by the introduction of a thermal velocity dispersion. In the warm dark matter (WDM) scenario, both the free-streaming scale, R_f, and the velocity dispersion, v_w, are determined by the mass m_w of the WDM particle. We find that v_w is too small to affect the density profiles of WDM halos. Down to the resolution attained in our simulations, there is not any significant difference in the density profiles and concentrations of halos obtained in simulations with and without the inclusion of v_w. The density profiles of halos with masses down to ~0.01 the filtering mass M_f can be described by the NFW shape; significant soft cores are not formed. Nevertheless, the concentrations of these halos are lower than those of the CDM counterparts and are approximately independent of mass. The lower concentrations of WDM halos with respect to their CDM counterparts can be accounted for their late formation epoch. Overall, our results point to a series of advantages of a WDM model over the CDM one. In addition to solving the substructure problem, a WDM model with R_f~0.16 Mpc (m_w~0.75 kev; flat cosmology with Omega_L=h=0.7) also predicts concentrations, a Tully-Fisher relation, and formation epochs for small halos which seems to be in better agreement with observations, relative to CDM predictions.

astro-ph↗
arXiv2001

Star formation history in the solar neighborhood: the link between stars and cosmology

Using a cosmological galactic evolutionary approach to model the Milky Way, we calculate the star formation history (SFH) of the solar neighborhood. The good agreement we obtain with the observational inferences suggests that our physical model describes accurately the long term/large spatial trends of the local and global Milky Way SFH. In this model, star formation is triggered by disk gravitational instabilities and self-regulated by an energy balance in the ISM. The drivers of the SFH are the cosmological gas infall rate and the gas surface density determined by the primordial spin parameter. A LambdaCDM cosmology was used throughout.

astro-ph↗
arXiv2001

Turbulent dissipation in the ISM: the coexistence of forced and decaying regimes and implications for galaxy formation and evolution

We discuss the dissipation of turbulent kinetic energy Ek in the global ISM by means of 2-D, MHD, non-isothermal simulations in the presence of model radiative heating and cooling. We argue that dissipation in 2D is representative of that in three dimensions as long as it is dominated by shocks rather than by a turbulent cascade. Energy is injected at a few isolated sites in space, over relatively small scales, and over short time periods. This leads to the coexistence of forced and decaying regimes in the same flow. We find that the ISM-like flow dissipates its turbulent energy rapidly. In simulations with forcing, the input parameters are the radius l_f of the forcing region, the total kinetic energy e_k each source deposits into the flow, and the rate of formation of those regions, sfr_OB. The global dissipation time t_d depends mainly on l_f. In terms of measurable properties of the ISM, t_d >= Sigma_g u_rms^2/(e_k sfr_OB), where Sigma_g is the average gas surface density and u_rms is the rms velocity dispersion. For the solar neighborhood, t_d >= 1.5x10^7 yr. The global dissipation time is consistently smaller than the crossing time of the largest energy-containing scales. In decaying simulations, Ek decreases with time as t^-n, where n~0.8-0.9. This suggests a decay with distance d as Ek\propto d^{-2n/(2-n)} in the mixed forced+decaying case. If applicable to the vertical direction, our results support models of galaxy evolution in which stellar energy injection provides significant support for the gas disk thickness, but not models of galaxy formation in which this energy injection is supposed to reheat an intra-halo medium at distances of up to 10-20 times the optical galaxy size, as the dissipation occurs on distances comparable to the disk height.

astro-ph↗
arXiv2000

Properties and evolution of disk galaxies in a hierarchical formation scenario

We highlight some results from disk galaxy evolution models conceived within a cosmological context. When disk mergers and strong disk-halo feedback are omitted, several properties and correlations of disk galaxies seem to be related to initial conditions given by the CDM model, for example, the intensive galaxy properties, the disk Hubble sequence, and the Tully-Fisher relation in the infrared bands.

astro-ph↗
arXiv2000

Constraints on dark matter physics from dwarf galaxies through galaxy cluster haloes

One of the predictions of the standard CDM is that dark haloes have centrally divergent density profiles. An extensive body of rotation curve observations of dwarf and low surface brightness galaxies shows the dark haloes of those systems to be characterized by soft constant density central cores. Several physical processes have been proposed to produce soft cores in dark haloes, each one with different scaling properties. With the aim of discriminating among them we have examined the rotation curves of dark matter dominated dwarf and low surface brightness galaxies and the inner mass profiles of two clusters of galaxies lacking a central cD galaxy and with evidence of soft cores in the centre. The core radii and central densities of these haloes scale in a well defined manner with the depth of their potential wells, as measured through the maximum circular velocity. As a result of our analysis we identify self-interacting CDM as a viable solution to the core problem, where a non-singular isothermal core is formed in the halo center surrounded by a Navarro, Frenk, & White profile in the outer parts. We show that this particular physical situation predicts core radii in agreement with observations. Furthermore, using the observed scalings, we derive an expression for the minimum cross section (σ) which has an explicit dependence with the halo dispersion velocity (v). If m_x is the mass of the dark matter particle: σ/m_x ~4 10^-25 (v/100 km s^-1)^-1 cm^2/Gev.

astro-ph↗
arXiv2000

Shallow cores in the dark matter halos: self-interaction in action?

Using observational data for a sample of dark matter dominated galaxies and two cluster of galaxies, we have found that the central halo density does not depend on its mass, and the core radius is roughly proportional to the maximum rotation velocity. A good agreement with these scaling laws is obtained for CDM halos whose dense inner parts were expanded by gravothermal instabilities if the particles efficiently self-interact only in these parts. We find that the particle cross-section is inversely proportional to the velocity dispersion.

astro-ph↗
arXiv2000

The evolution of disk galaxies

We study the evolution of disk galaxies using galaxy evolutionary models with initial and boundary conditions linked to the hierarchical formation scenario. Disks galaxies are modeled locally within growing cold dark matter halos and including a physical model for star formation. We focus our attention on predictions of the star formation history, size and surface brightness evolution and the evolution of the H- and B-band Tully-Fisher relations. Comparisons with available observational data are presented.

astro-ph↗
arXiv2000

Substructure and halo density profiles in a Warm Dark Matter Cosmology

We performed a series of high-resolution simulations designed to study the substructure of Milky Way-size galactic halos (host halos) and the density profiles of halos in a warm dark matter (WDM) scenario with a non-vanishing cosmological constant. The virial masses of the host halos range from 3.5 x 10^12 to 1.7 x 10^12 solar masses and they have more than 10^5 particles each. A key feature of the WDM power spectrum is the free-streaming length R_f which fixes an additional parameter for the model of structure formation. We analyze the substructure of host halos using three R_f values: 0.2, 0.1, and 0.05 Mpc and compare results to the predictions of the cold dark matter (CDM) model. We find that guest halos (satellites) do form in the WDM scenario but are more easily destroyed by dynamical friction and tidal disruption than their counterparts in a CDM model. The small number of guest halos that we find within the virial radii of host halos at z = 0 in the WDM models is the result of a less efficient halo accretion and a higher satellite destruction rate. Under the assumption that each guest halo hosts a luminous galaxy, we find that the observed circular velocity function of satellites around the Milky Way and Andromeda is well described by the R_f = 0.1 Mpc WDM model. In the R_f = 0.1-0.2 Mpc models, the surviving subhalos at z=0 have an average concentration parameter c_1/5 which is approximately twice smaller than that of the corresponding CDM subhalos. This difference, very likely, produces the higher satellite destruction rate found in the WDM models. The density profile of host halos is well described by the NFW fit whereas guest halos show a wide variety of density profiles (abridged).

astro-ph↗
arXiv2000

Turbulent dissipation in the interstellar medium: implications for galaxy formation and evolution

We study turbulent dissipation in the ISM and explore some implications for galaxy formation and evolution using 2D MHD numerical simulations of compressible fluids. The turbulent kinetic energy E_k is injected by stellar sources formed self-consistently in the simulation. In the ISM-like fluid, regimes of both forced and decaying turbulence coexist. In the active turbulent regions (forced regime), E_k is dissipated locally and efficiently. In the decaying regime (far from input sources), E_k(t) decays ~(1+t)^-0.8. The residual turbulent motions may propagate distances of the order of the observed disk height, suggesting that turbulence may be the responsible of vertical support and star formation self-regulation at the disk level, but not at the level of the whole cosmological halo, as would be required in some models of galaxy formation.

astro-ph↗