Sebastian Trujillo-Gomez

Dark Matter Halos in the Standard Cosmological Model: Results from the Bolshoi Simulation

Lambda Cold Dark Matter (?CDM) is now the standard theory of structure formation in the universe. We present the first results from the new Bolshoi dissipationless cosmological ?CDM simulation that uses cosmological parameters favored by current observations. The Bolshoi simulation was run in a volume 250 h ?1?Mpc on a side using ~8 billion particles with mass and force resolution adequate to follow subhalos down to the completeness limit of V circ = 50?km?s?1 maximum circular velocity. Using merger trees derived from analysis of 180 stored time steps we find the circular velocities of satellites before they fall into their host halos. Using excellent statistics of halos and subhalos (~10 million at every moment and ~50 million over the whole history) we present accurate approximations for statistics such as the halo mass function, the concentrations for distinct halos and subhalos, the abundance of halos as a function of their circular velocity, and the abundance and the spatial distribution of subhalos. We find that at high redshifts the concentration falls to a minimum value of about 4.0 and then rises for higher values of halo mass?a new result. We present approximations for the velocity and mass functions of distinct halos as a function of redshift. We find that while the Sheth-Tormen (ST) approximation for the mass function of halos found by spherical overdensity is quite accurate at low redshifts, the ST formula overpredicts the abundance of halos by nearly an order of magnitude by z = 10. We find that the number of subhalos scales with the circular velocity of the host halo as V 1/2 host, and that subhalos have nearly the same radial distribution as dark matter particles at radii 0.3-2 times the host halo virial radius. The subhalo velocity function N(> V sub) scales as V ?3 circ. Combining the results of Bolshoi and Via Lactea-II simulations, we find that inside the virial radius of halos with the number of satellites is N(> V sub) = (V sub/58 km s?1)?3 for satellite circular velocities in the range 4 km s?1 < V sub < 150 km s?1.

GALAXIES IN ΛCDM WITH HALO ABUNDANCE MATCHING: LUMINOSITY-VELOCITY RELATION, BARYONIC MASS-VELOCITY RELATION, VELOCITY FUNCTION, AND CLUSTERING

It has long been regarded as difficult if not impossible 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 (DM). We find that the standard cosmological model, used in conjunction with halo abundance matching (HAM) and simple dynamical corrections, 1 fits—at least on average—all basic statistics of galaxies with circular velocities Vcirc > 80 km s − calculated at a radius of ∼10 kpc. Our primary observational constraint is the luminosity–velocity (LV) relation—which generalizes the Tully–Fisher and Faber–Jackson relations in allowing all types of galaxies to be included, and provides a fundamental benchmark to be reproduced by any theory of galaxy formation. We have compiled data for a variety of galaxies ranging from dwarf irregulars to giant ellipticals. The data present a clear monotonic LV relation from ∼50 km s −1 to ∼500 km s −1 , with a bend below ∼80 km s −1 and a systematic offset between lateand early-type galaxies. For comparison to theory, we employ our new ΛCDM “Bolshoi” simulation of DM, which has unprecedented mass and force resolution over a large cosmological volume, while using an up-to-date set of cosmological parameters. We use HAM to assign rank-ordered galaxy luminosities to the DM halos, a procedure that automatically fits the empirical luminosity function and provides a predicted LV relation that can be checked against observations. The adiabatic contraction of DM halos in response to the infall of the baryons is included as an optional model ingredient. The resulting predictions for the LV relation are in excellent agreement with the available data on both early-type and late-type galaxies for the luminosity range from Mr =− 14 to Mr =− 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 (VF) is also in agreement with the galaxy VF from 80 to 400 km s −1 ,u sing the HIPASS survey for late-type galaxies and Sloan Digital Sky Survey (SDSS) for early-type galaxies. However, in accord with other recent results, we find that the DM halos with Vcirc < 80 km s −1 are much more abundant than observed galaxies with the same Vcirc. Finally, we find that the two-point correlation function of bright galaxies in our model matches very well the results from the final data release of the SDSS, especially when a small amount of scatter is included in the HAM prescription.

Radiative feedback and the low efficiency of galaxy formation in low-mass haloes at high redshift

Any successful model of galaxy formation needs to explain the low rate of star formation in the small progenitors of todays galaxies. This inefficiency is necessary for reproducing the low stellar-to-virial mass fractions, suggested by current abundance matching models. A possible driver of this low efficiency is the radiation pressure exerted by ionizing photons from massive stars. The effect of radiation pressure in cosmological, zoom-in galaxy formation simulations is modeled as a non-thermal pressure that acts only in dense and optically thick star-forming regions. We also include photoionization and photoheating by massive stars. The full photoionization of hydrogen reduces the radiative cooling in the

Effects of baryon removal on the structure of dwarf spheroidal galaxies

10^{4-4.5}

Low-mass galaxy assembly in simulations: regulation of early star formation by radiation from massive stars

K regime. The main effect of radiation pressure is to regulate and limit the high values of gas density and the amount of gas available for star formation. This maintains a low star formation rate of

Hints against the cold and collisionless nature of dark matter from the galaxy velocity function

\sim 1 \ {\rm M_\odot} \ {\rm yr}^{-1}

Quenched Cold Accretion of a Large-scale Metal-poor Filament due to Virial Shocking in the Halo of a Massive z = 0.7 Galaxy

in halos with masses about

Constraining cosmology with the velocity function of low-mass galaxies

10^{11} \ {M_\odot}

AN EXTREME METALLICITY, LARGE-SCALE OUTFLOW FROM A STAR-FORMING GALAXY AT z ∼ 0.4

at

MAGIICAT III. Interpreting Self-similarity of the Circumgalactic Medium with Virial Mass Using Mg II Absorption

z\simeq3