Research Highligths

2016

Measurements of [C/Fe] and [N/Fe] for about 95 individual Red Giant Branch stars in the Sculptor dwarf spheroidal galaxy (Lardo, Battaglia et al. 2016); this is the first time that [N/Fe] was measured for such a large number of stars in a dSph. Our measurements of both [C/Fe] and [N/Fe] are in good agreement with theoretical expectations for stars of similar luminosity and metallicity. We detect a spread in [C/Fe] The dispersion detected in the carbon abundance at a given [Fe/H], exceeding the measurement uncertainties, can be interpreted as the result of the contribution of different nucleosynthesis sources over time to a not well-mixed interstellar medium. We report the discovery of two new carbon-enhanced, metal-poor stars, which are likely the result of pollution from material enriched by asymptotic giant branch stars, as indicated by our estimates of [Ba/Fe] >+1.

Evidence for time evolution in the disc of M33 based on its star cluster system. We find that both the radial metallicity gradient of the disc and also the age-velocity dispersion of the disc evolves strongly with time (Beasley et al. 2015)

A new Local Group dwarf galaxy, Hydra II, found in the SMASH footprint (Martin et al., incl. Gallart, Monelli, Monteagudo-Narvíon, 2015)

At the edges of galaxy formation: the search for almost-dark dwarf galaxies. The SECCO survey is an LBT/LBC photometric campaign aimed at searching for the stellar counterpart of HI ultra-compact-high-velocity-clouds (UCHVCs), which were proposed by Adams et al. (2013) as candidate dark-matter mini-halos lying in the Local Group or its immediate surroundings. The first results and survey overview are presented in Bellazzini et al. incl. Battaglia (2015a). Via spectroscopic follow-up of a candidate stellar counterpart, we have discovered SECCO1, a nearly star-less star-forming dwarf galaxy displaying a ratio of HI versus luminosy M_HI/L_V >~ 20, the largest known so far for star-forming dwarf galaxies (Bellazzini et al. incl. Battaglia 2015b)

New evidence on the nature of the Milky Way Halo building blocks: The comparison of the pulsational properties of old RR Lyrae variable stars in the Milky Way dSph satellites and those in the Milky Way Halo has shown that the former lack High Amplitude Short Period (HASP) variables, which are present in the latter. This indicates that dwarf satellites similar to the surviving ones do not appear to be the major building-blocks of the Milky Way Halo, and points to larger, more metal-rich objects as building blocks. (Fiorentino et al. incl. Monelli, Gallart, Martínez-Vázquez 2015).

The peculiar SFH of the dSph galaxy And XVI: a detailed analysis of the stellar populations of this M31 satellites reveals that it esperienced extended star formation history, which quenched ~6 Gyr ago, and that the age of the youngest population is the samo across the main body of the galaxy (Monelli et al. incl. Martínez-Vázquez, Gallart, 2015 submitted)

The metallicity gradient in the old population of the Sculptor dSph galaxy: The study of the pulsational properties of ~550 RR Lyrae variable stars (318 of which are new discoveries) allowed to estimate that a metallicity spread of the order of 0.5 dex is present in the oldest stellar component of this galaxy, suggesting a fast chemical enrichment at very early epochs (Martínez-Vázquez et al. incl. Monelli, Gallart, in prep.)

Recovering star formation histories: Integrated-light analyses vs. stellar colour-magnitude diagrams: In the realm of external galaxies (beyond our Local Group), our understanding of their stellar content relies on the analysis of integrated spectra. In this study we test (and demonstrate) the good performance of state of the art inversion techniques that allow us to obtain complex SFH from integrated data. The recovered SFH in the bar region of the LMC (as a pilot example) using such techniques is in agreement to that found using more reliable CMD analysis (Ruiz-Lara et al. incl. Gallart, Monelli, Beasley, 2015).

Extended star formation histories found in the M31 dSph satellites And XVI and And II: These are first results from an ACS/HST Large program to derive star formation histories of a representative sample of M31 dSph satellites (Weisz et al. incl. Monelli, Gallart, 2014)

Constraning dwarf galaxy formation and evolution with the SFH of the Local Group dwarf galaxy IC1613: The star formation history of IC1613, obtained from a very deep color-magnitude diagram (14 ACS@HST orbits, the first precise SFH for a galaxy of this morphological type and stellar mass, ~10⁸ M_sun), is consistent with being constant. This is in contrast with predictions from cosmological models of galaxy evolution in which star formation follows mass accretion. In them, since most of the mass is in place at early times, most star formation should take place early. Models in which star formation follows mass accretion result in too many stars formed early and gas mass fractions that are too low today (the "over-cooling problem"). (Skillman et al., incl. Monelli, Gallart 2014)

Discovery of outside-in evolution in the outer LMC disk: in a study of the star formation history of three LMC outer fields, two main periods of star formation were identified: one at old ages (> 10 Gyr), and the second at intermediate and young ages (< 5 Gyr). The age of the youngest population significantly changes as a function of radius, getting younger when moving to the center of the LMC. Moreover, the relative important of the two main episodes of star formation changes with radius: the fraction of old population increases for increasing distance from the LMC center (Meschin, Gallart et al. incl Monelli, 2014). Preliminary results on this subject were first presented in Gallart et al. 2008.

The peculiar Carina dwarf spheroidal galaxy: star formation history from deep and wide-area data for the only Local Group dwarf spheroidal with a clearly bursty star formation (de Boer et al. incl. Battaglia 2014) and study of its extended structure with detection of likely signs of tidal disturbance (McMonigal et al. incl. Battaglia 2014; Battaglia et al. 2012)

Invited review article on the internal kinematics of Milky Way dwarf spheroidal galaxies and their dynamical modeling (Battaglia, Helmi, Breddels 2013).

Obtained a new calibration of the IR CaII triplet as metallicity indicator, (Carrera et al. incl. Gallart, 2013) extending previous relations (Carrera, Gallart et al. 2007) to the range -4 < [Fe/H] < +0.5.

The youth of the Local Group dIrr galaxy Leo A reflected in its population of variable stars: In a study of the population of variable stars in the irregular galaxy Leo A, based on HST/ACS data, a small number of RR Lyrae stars (10) were found.This supports independent findings (Cole et al., incl. Gallart, 2007) that the amount of old population in this galaxy is very small. This is unlike any other Local Group galaxy, making Leo A an unique object to-date. Moreover, we studied and classified 156 Cepheid stars (Bernard, Monelli, Gallart et al. 2013)
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