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Dive into the research topics where G. Battaglia is active.

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Featured researches published by G. Battaglia.


Astronomy and Astrophysics | 2010

The NIR Ca ii triplet at low metallicity - Searching for extremely low-metallicity stars in classical dwarf galaxies

Else Starkenburg; V. Hill; Eline Tolstoy; J. I. González Hernández; M. J. Irwin; Amina Helmi; G. Battaglia; Pascale Jablonka; M. Tafelmeyer; Matthew Shetrone; Kim A. Venn; T. J. L. de Boer

The NIR Ca II triplet absorption lines have proven to be an important tool for quantitative spectroscopy of individual red giant branch stars in the Local Group, providing a better understanding of metallicities of stars in the Milky Way and dwarf galaxies and thereby an opportunity to constrain their chemical evolution processes. An interesting puzzle in this field is the significant lack of extremely metal-poor stars, below [Fe/H] = -3, found in classical dwarf galaxies around the Milky Way using this technique. The question arises whether these stars are really absent, or if the empirical Ca II triplet method used to study these systems is biased in the low-metallicity regime. Here we present results of synthetic spectral analysis of the Ca II triplet, that is focused on a better understanding of spectroscopic measurements of low-metallicity giant stars. Our results start to deviate strongly from the widely-used and linear empirical calibrations at [Fe/H] = [Fe/H] >= -4. We subsequently apply this new calibration to current data sets and suggest that the classical dwarf galaxies are not so devoid of extremely low-metallicity stars as was previously thought.


Monthly Notices of the Royal Astronomical Society | 2011

Study of the Sextans dwarf spheroidal galaxy from the DART Ca ii triplet survey

G. Battaglia; Eline Tolstoy; Amina Helmi; M. J. Irwin; P. Parisi; V. Hill; Pascale Jablonka

We use Very Large Telescope (VLT)/Fibre Large Array Multi Element Spectrograph (FLAMES) intermediate-resolution (R˜ 6500) spectra of individual red giant branch stars in the near-infrared Ca II triplet (CaT) region to investigate the wide-area metallicity properties and internal kinematics of the Sextans dwarf spheroidal galaxy (dSph). Our final sample consists of 174 probable members of Sextans with accurate line-of-sight velocities (±2 km s-1) and CaT [Fe/H] measurements (±0.2 dex). We use the Mg I line at 8806.8 A as an empirical discriminator for distinguishing between probable members of the dSph (giant stars) and probable Galactic contaminants (dwarf stars). Sextans shows a similar chemodynamical behaviour to other Milky Way dSphs, with its central regions being more metal rich than the outer parts and with the more metal-rich stars displaying colder kinematics than the more metal-poor stars. Hints of a velocity gradient are found along the projected major axis and along an axis at position angle (PA) = 191°, however, a larger and more spatially extended sample may be necessary to pin down the amplitude and direction of this gradient. We detect a cold kinematic substructure at the centre of Sextans, consistent with being the remnant of a disrupted very metal poor stellar cluster. We derive the most extended line-of-sight velocity dispersion profile for Sextans, out to a projected radius of 1?6. From Jeans modelling of the observed line-of-sight velocity dispersion profile we find that this is consistent with both a cored dark matter halo with large core radius and cuspy halo with low concentration. The mass within the last measured point is in the range 2-4 × 108 M⊙, giving very large mass-to-light ratios, from 460 to 920 (M/L)V, ⊙. Based on FLAMES observations collected at the ESO, proposal 171.B-0588.


Monthly Notices of the Royal Astronomical Society | 2009

Blue straggler stars in dwarf spheroidal galaxies – II. Sculptor and Fornax

Michela Mapelli; E. Ripamonti; G. Battaglia; Eline Tolstoy; M. J. Irwin; Ben Moore; Steinn Sigurdsson

The existence of blue straggler stars (BSSs) in dwarf spheroidal galaxies (dSphs) is still an open question. In fact, many BSS candidates have been observed in the Local Group dSphs, but it is unclear whether they are real BSSs or young stars. Shedding light on the nature of these BSS candidates is crucial in order to understand the star formation history of dSphs. In this paper, we consider BSS candidates in Sculptor and Fornax. In Fornax, there are strong hints that the BSS population is contaminated by young stars, whereas in Sculptor there is no clear evidence of recent star formation. We derive the radial and luminosity distribution of BSS candidates from wide field imaging data extending beyond the nominal tidal radius of these galaxies. The observations are compared with the radial distribution of BSSs expected from dynamical simulations. In Sculptor, the radial distribution of BSS candidates is consistent with that of red horizontal branch (RHB) stars and is in agreement with theoretical expectations for BSSs generated via mass transfer in binaries. On the contrary, in Fornax, the radial distribution of BSS candidates is more concentrated than that of all the considered stellar populations. This result supports the hypothesis that most of BSS candidates in Fornax are young stars, and this is consistent with previous studies.


Conferences of the Assembling the Puzzle of the Milky Way | 2012

Schwarzschild models of the Sculptor dSph galaxy

Maarten A. Breddels; Amina Helmi; R. C. E. van den Bosch; G. van de Ven; G. Battaglia

We have developed a spherically symmetric dynamical model of a dwarf spheroidal galaxy using the Schwarzschild method. This type of modelling yields constraints both on the total mass distribution (e.g. enclosed mass and scale radius) as well as on the orbital structure of the system modelled (e.g. velocity anisotropy). Therefore not only can we derive the dark matter content of these systems, but also explore possible formation scenarios. Here we present preliminary results for the Sculptor dSph. We find that the mass of Sculptor within 1 kpc is 8.5 × 107±0.05 M๏, its anisotropy profile is tangentially biased and slightly more isotropic near the center. For an NFW profile, the preferred concentration (~15) is compatible with cosmological models. Very cuspy density profiles (steeper than NFW) are strongly disfavoured for Sculptor.


ESO-Arcetri Workshop on Chemical Abundances and Mixing in Stars in the Milky Way and its Satellites | 2006

Metallicities and kinematics for dwarf spheroidals in the local group

G. Battaglia; Eline Tolstoy; Amina Helmi; M. J. Irwin

We present the first results of Call triplet observations from VLT/FLAMES for Sculptor, Fornax and Sextans dSphs. For each galaxy, we obtained accurate velocity and metallicity measurements for hundreds of stars out to and beyond the tidal radius. In each case, we find clear evidence for the presence of two distinct stellar components with different spatial distribution and kinematics: the metal rich component is more centrally concentrated and kinematically colder than the metal poor one.


The Astrophysical Journal | 2004

Two Distinct Ancient Components in the Sculptor Dwarf Spheroidal Galaxy: First Results from the Dwarf Abundances and Radial Velocities Team

Eline Tolstoy; M. J. Irwin; Amina Helmi; G. Battaglia; Pascale Jablonka; V. Hill; Kim A. Venn; Matthew Shetrone; B. Letarte; Andrew A. Cole; F. Primas; P. Francois; Nobuo Arimoto; Kozo Sadakane; Andreas Kaufer; T. Szeifert; Tom Abel


Astronomy and Astrophysics | 2014

The episodic star formation history of the Carina dwarf spheroidal galaxy

T. J. L. de Boer; Eline Tolstoy; B. Lemasle; A. Saha; Edward W. Olszewski; Mario Mateo; M. J. Irwin; G. Battaglia


Eas Publications Series | 2007

Numerical simulations of the metallicity distribution in dwarf spheroidal galaxies

E. Ripamonti; Eline Tolstoy; Amina Helmi; G. Battaglia; Tom Abel


Astronomy and Astrophysics | 2011

Extremely metal-poor stars in classical dwarf spheroidal galaxies

M. Tafelmeyer; P. Jablonka; V. Hill; Matthew Shetrone; Eline Tolstoy; M. J. Irwin; G. Battaglia; Amina Helmi; Else Starkenburg; Kim A. Venn; Tom Abel; P. Francois; A. Kaufer; P. North; Francesca Primas; T. Szeifert


Astronomical Society of the Pacific Conference Series | 2008

The Star Formation History and Stellar Population Structures in the Sextans Dwarf Spheroidal Galaxy

Sakurako Okamoto; Nobuo Arimoto; Yoshihiko Yamada; M. Onodera; Eline Tolstoy; M. J. Irwin; Amina Helmi; G. Battaglia; P. Jablonka; V. Hill; K. Venn; Matthew Shetrone; B. Letarte; Francesca Primas; P. Francois; Kozo Sadakane; A. Kaufer; T. Szeifert; Tom Abel; Tadayuki Kodama; Toru Yamada; Kentaro Aoki

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M. J. Irwin

University of Cambridge

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Amina Helmi

Kapteyn Astronomical Institute

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Eline Tolstoy

Kapteyn Astronomical Institute

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V. Hill

University of Nice Sophia Antipolis

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Matthew Shetrone

University of Texas at Austin

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B. Letarte

Kapteyn Astronomical Institute

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T. Szeifert

European Southern Observatory

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