arXiv subjects

Stefania Salvadori

Publications and source records attributed to Stefania Salvadori.

60 records · Page 4Linked to original sources

arXiv2012

Stellar archeology: a cosmological view of dwarf galaxies

The origin of dwarf spheroidal galaxies (dSphs) is investigated in a global cosmological context by simultaneously following the evolution of the Milky Way Galaxy and its dwarf satellites. This approach enable to study the formation of dSphs in their proper birth environment and to reconstruct their own merging histories. The proposed picture simultaneously accounts for several dSph and Milky Way properties, including the Metallicity Distribution Functions of metal-poor stars. The observed features are interpreted in terms of physical processes acting at high redshifts.

astro-ph.CO↗

arXiv2011

First stars in Damped Lyman Alpha systems

In order to characterize Damped Lyman Alpha systems (DLAs) potentially hosting first stars, we present a novel approach to investigate DLAs in the context of Milky Way (MW) formation, along with their connection with the most metal-poor stars and local dwarf spheroidal (dSph) galaxies. The merger tree method previously developed is extended to include inhomogeneous reionization and metal mixing, and it is validated by matching both the Metallicity Distribution Function of Galactic halo stars and the Fe-Luminosity relation of dSph galaxies. The model explains the observed NHI-Fe relation of DLAs along with the chemical abundances of [Fe/H] < -2 systems. In this picture, the recently discovered z_abs ~ 2.34 C-enhanced DLA (Cooke et al. 2011a), pertains to a new class of absorbers hosting first stars along with second-generation long-living low-mass stars. These "PopIII DLAs" are the descendants of H2-cooling minihalos with Mh ~ 10^7 Msun, that virialize at z > 8 in neutral, primordial regions of the MW environment and passively evolve after a short initial period of star formation. The gas in these systems is warm Tg \sim (40-1000) K, and strongly C-enriched by long-living, extremely metal-poor stars of total mass M* \sim 10^{2-4} Msun.

astro-ph.CO↗

arXiv2011

The origin of dust in high redshift QSOs: the case of SDSS J1148+5251

We present a semi-analytical model for the formation and evolution of a high redshift quasar (QSO). We reconstruct a set of hierarchical merger histories of a 10^13 Msun dark matter halo and model the evolution of the corresponding galaxy and of its central super massive black hole. The code GAMETE/QSODUST consistently follows: the black hole assembly via both coalescence with other black holes and gas accretion; the build up and star formation history of the quasar host galaxy, driven by binary mergers and mass accretion; the evolution of gas, stars, metals in the interstellar medium (ISM), accounting for mass exchanges with the external medium (infall and outflow processes); dust formation in Supernova (SN) ejecta and in the stellar atmosphere of Asymptotic Giant Branch (AGB) stars, dust destruction by interstellar shocks and grain growth in molecular clouds; the AGN feedback which powers a galactic-scale wind, self-regulating the black hole growth and eventually halting star formation.We use this model to study the case of SDSS J1148+5251 observed at redshift 6.4, exploring different star formation histories for the QSO host galaxy.

astro-ph.CO↗

arXiv2010

The faintest galaxies

We investigate the nature of Ultra Faint dwarf spheroidal galaxies (UF dSphs) in a general cosmological context, simultaneously accounting for various "classical" dSphs and Milky Way (MW) properties, including their Metallicity Distribution Function (MDF). The model successfully reproduces both the observed [Fe/H]-Luminosity relation and the mean MDF of UFs. According to our results UFs are the living fossils of H2-cooling minihaloes formed at z>8.5, i.e. before the end of reionization. They are the oldest and the most dark matter-dominated (M/L > 100) dSphs in the MW system, with a total mass of M = 10^(7-8) Msun. The model allows to interpret the different shape of UFs and classical dSphs MDF, along with the frequency of extremely metal-poor stars in these objects. We discuss the "missing satellites problem" by comparing the UF star formation efficiencies with those derived for minihaloes in the Via Lactea simulation.

astro-ph.CO↗

arXiv2009

Ultra faint dwarfs: probing early cosmic star formation

We investigate the nature of the newly discovered Ultra Faint dwarf spheroidal galaxies (UF dSphs) in a general cosmological context simultaneously accounting for various ``classical`` dSphs and Milky Way properties including their Metallicity Distribution Function (MDF). To this aim we extend the merger tree approach previously developed to include the presence of star-forming minihaloes, and an heuristic prescription for radiative feedback. The model successfully reproduces both the observed [Fe/H]-Luminosity relation and the mean MDF of UFs. In this picture UFs are the oldest, most dark matter-dominated (M/L > 100) dSphs with a total mass M= 10^{7-8}Msun; they are leftovers of H_2-cooling minihaloes formed at z > 8.5, i.e. before reionization. Their MDF is broader (because of a more prolonged SF) and shifted towards lower [Fe/H] (as a result of a lower gas metallicity at the time of formation) than that of classical dSphs. These systems are very ineffectively star-forming, turning into stars by z=0 only <3% of the potentially available baryons. We provide a useful fit for the star formation efficiency of dSphs.

astro-ph↗

arXiv2008

The puzzling origin of the 6Li plateau

We discuss the 6Li abundance evolution within a hierarchical model of Galaxy formation which correctly reproduces the [Fe/H] distribution of metal-poor halo stars. Contrary to previous findings, we find that neither the level (6Li/H=6x10^-12) nor the flatness of the 6Li distribution with [Fe/H] can be reproduced under the most favourable conditions by any model in which 6Li production is tied to a (data-constrained) Galactic star formation rate via cosmic ray spallation. Thus, the origin of the plateau might be due to some other early mechanism unrelated to star formation.

astro-ph↗