Stellar haloes in Milky-Way mass galaxies: From the inner to the outer haloes

We present a comprehensive study of the chemical properties of the stellar haloes of Milky-Way mass galaxies, analysing the transition between the inner to the outer haloes. We find the transition radius between the relative dominance of the inner-halo and outer-halo stellar populations to be ~15-20 kpc for most of our haloes, similar to that inferred for the Milky Way from recent observations. While the number density of stars in the simulated inner-halo populations decreases rapidly with distance, the outer-halo populations contribute about 20-40 per cent in the fiducial solar neighborhood, in particular at the lowest metallicities. We have determined [Fe/H] profiles for our simulated haloes; they exhibit flat or mild gradients, in the range [-0.002, -0.01 ] dex/kpc. The metallicity distribution functions exhibit different features, reflecting the different assembly history of the individual stellar haloes. We find that stellar haloes formed with larger contributions from massive subgalactic systems have steeper metallicity gradients. Very metal-poor stars are mainly contributed to the halo systems by lower-mass satellites. There is a clear trend among the predicted metallicity distribution functions that a higher fraction of low-metallicity stars are found with increasing radius. These properties are consistent with the range of behaviours observed for stellar haloes of nearby galaxies.Comment: 11 pages, 6 figures. Accepted MNRAS. Revised version after referee's comment

Analysis of Galaxy Formation with Hydrodynamics

We present a hydrodynamical code based on the Smooth Particle Hydrodynamics technique implemented in an AP3M code aimed at solving the hydrodynamical and gravitational equations in a cosmological frame. We analyze the ability of the code to reproduce standard tests and perform numerical simulations to study the formation of galaxies in a typical region of a CDM model. These numerical simulations include gas and dark matter particles and take into account physical processes such as shock waves, radiative cooling, and a simplified model of star formation. Several observed properties of normal galaxies such as $M_{gas}/M_{total}$ ratios, the luminosity function and the Tully-Fisher relation are analyzed within the limits imposed by numerical resolution.Comment: 21 pages, 2 postscript tables. Submitted MNRAS 04.03.9

The central spheroids of Milky Way mass-sized galaxies

Indexación: Scopus.PBT, DM and AM acknowledge partial support from the Nucleo UNAB 2015 DI-677-15/N of Universidad Andres Bello. PBT acknowledges partial support from Fondecyt Regular 1150334 and the Southern Astrophysics Network (SAN) collaboration funded by Conicyt, and PICT 2011-0959 and PIP 2012-0396 (Mincyt, Argentina). DM and MZ are supported by the BASAL Center for Astrophysics and Associated Technologies (CATA) through grant PFB-06, and the Ministry for the Economy, Development, and Tourism, Programa Iniciativa Cientifica Milenio through grant IC120009, awarded to the Millennium Institute of Astrophysics (MAS), and by FONDECYT Regular grant No. 1130196. DC and TCB acknowledge partial support for this work from grant PHY 14-30152; Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the US National Science Foundation. REGM acknowledges support from Ci?ncia sem Fronteiras (CNPq, Brazil).We study the properties of the central spheroids located within 10 kpc of the centre of mass of MilkyWay mass-sized galaxies simulated in a cosmological context. The simulated central regions are dominated by stars older than 10 Gyr, mostly formed in situ, with a contribution of ~30 per cent from accreted stars. These stars formed in well-defined starbursts, although accreted stars exhibit sharper and earlier ones. The fraction of accreted stars increases with galactocentric distance, so that at a radius of~8-10 kpc, a fraction of~40 per cent, on average, is detected. Accreted stars are slightly younger, lower metallicity, and more α-enhanced than in situ stars. A significant fraction of old stars in the central regions come from a few (2-3) massive satellites (~1010M⊙). The bulge components receive larger contributions of accreted stars formed in dwarfs smaller than ~109.5M⊙. The difference between the distributions of ages and metallicities of old stars is thus linked to the accretion histories - those central regions with a larger fraction of accreted stars are those with contributions from more massive satellites. The kinematical properties of in situ and accreted stars are consistent with the latter being supported by their velocity dispersions, while the former exhibit clear signatures of rotational support. Our simulations demonstrate a range of characteristics, with some systems exhibiting a co-existing bar and spheroid in their central regions, resembling in some respect the central region of the Milky Way. © 2016 The Authors.https://academic.oup.com/mnras/article/473/2/1656/422260

Building Blocks in Hierarchical Clustering Scenarios and their Connection with Damped Lyα\alpha Systems

We carried out a comprehensive analysis of the chemical properties of the interstellar medium (ISM) and the stellar population (SP) of current normal galaxies and their progenitors in a hierarchical clustering scenario. We compared the results with observations of Damped Lyman-$\alpha$ systems (DLAs) under the hypothesis that, at least, part of the observed DLAs could originate in the building blocks of today normal galaxies. We used a hydrodynamical cosmological code which includes star formation and chemical enrichment. Galaxy-like objects are identified at $z=0$ and then followed back in time. Random line-of-sights (LOS) are drawn through these structures in order to mimic Damped Lyman $\alpha$ systems. We then analysed the chemical properties of the ISM and SP along the LOS. We found that the progenitors of current galaxies in the field with mean $L <0.5 L^*$ and virial circular velocity of $100-250 {\rm km/sec}$ could be the associated DLA galaxies. For these systems we detected a trend for $$ to increase with redshift.(Abridged)Comment: 15 pages, 11 Postscript figures. Accepted to MNRA

Effects of Supernova Feedback on the Formation of Galaxies

We study the effects of Supernova (SN) feedback on the formation of galaxies using hydrodynamical simulations in a Lambda-CDM cosmology. We use an extended version of the code GADGET-2 which includes chemical enrichment and energy feedback by Type II and Type Ia SN, metal-dependent cooling and a multiphase model for the gas component. We focus on the effects of SN feedback on the star formation process, galaxy morphology, evolution of the specific angular momentum and chemical properties. We find that SN feedback plays a fundamental role in galaxy evolution, producing a self-regulated cycle for star formation, preventing the early consumption of gas and allowing disks to form at late times. The SN feedback model is able to reproduce the expected dependence on virial mass, with less massive systems being more strongly affected.Comment: To appear in "The Galaxy Disk in Cosmological Context"; Proceedings of IAU254; 9-13 June 2008; Copenhagen; v2: typo corrected; uses iaus.cl

Systematic uncertainties in the determination of the local dark matter density

A precise determination of the local dark matter density and an accurate control over the corresponding uncertainties are of paramount importance for Dark Matter (DM) searches. Using very recent high-resolution numerical simulations of a Milky Way like object, we study the systematic uncertainties that affect the determination of the local dark matter density based on dynamical measurements in the Galaxy. In particular, extracting from the simulation with baryons the orientation of the Galactic stellar disk with respect to the DM distribution, we study the DM density for an observer located at $\sim$8 kpc from the Galactic center {\it on the stellar disk}, $\rho_0$. This quantity is found to be always larger than the average density in a spherical shell of same radius $\bar{\rho}_0$, which is the quantity inferred from dynamical measurements in the Galaxy, and to vary in the range $\rho_0/\bar{\rho}_0=1.01-1.41$. This suggests that the actual dark matter density in the solar neighbourhood is on average 21\% larger than the value inferred from most dynamical measurements, and that the associated systematic errors are larger than the statistical errors recently discussed in the literature.Comment: 6 pages, 3 figures, matches published versio