Ministerio de Economía y Competitividad Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

Astrophysics Research Projects

The Local Universe

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Stellar Populations in Galaxies (P/309403)

S HIDALGO RODRÍGUEZ

Antonio Aparicio Juan, Edoardo Lagioia, Alfred Rosenberg González, Sara Murabito, Matteo Simioni, Margherita Bettinelli, Efsan Sökmen

 Colaboradores del IAC: Carme Gallart Gallart, Matteo Monelli, Ricardo Carrera Jiménez, Martín López Corredoira, Francisco Garzón López

Elena Valenti, Francisco Surot Madrid (ESO); J. Alonso, D. Minniti, M. Zoccali (PUC, Chile); N. Arimoto (NAOJ); S. Beaulieu (Univ. Waterloo); R. Buonanno, F. Fusco (Univ. Roma Tor Vergata); S. Cassisi, A. Pietrinferni (INAF-Téramo); L. Carigi (IA-UNAM); J.M. Carrasco, C. Jordi, F. Figueras (UB); K. Freeman (Research School of Astronomy & Astrophysics, Australia); E. Kirby (Univ. California at Irvine); E. Lokas (Centro Astronómico Nicolaus Copernicus); A. Milone (Australian National Univ.); T. Mineikis, D. Narbutis (Vilnius Astronomical Obs.); A. Monachesi (Univ. Michigan); S. Okamoto (KIAA-PKU); A. Piatti (Obs. Astronómico de Córdoba); V. Nascimbeni, G. Piotto (Univ. Padua); E. Skillman (Univ. Minnesotta):

Introduction

The general aim of the project is to research the structure, evolutionary history and formation of galaxies through the study of their resolved stellar populations, both from photometry and spectroscopy. The group research concentrates in the most nearby objects, namely the Local Group galaxies including the Milky Way and M33 under the hypothesis that they are a good representation of the general population of galaxies in the Universe.

The project can be divided in four research lines:

I. Star formation history in the Local Group.

The goal is to characterise the spatial and temporal structure of the galaxies of the Local Group through the observations of individual stars. The fundamental aim is to derive the detailed star formation history (SFH) of a given galaxy in all its evolutionary stages, in order to determine the impact of cosmological (e.g. reionization, self-shielding) and local processes (e.g. gas sweeping by supernovas, tidal forces, stellar migration).

II. Multiple stellar populations in globular clusters.

At odds of what it is classically predicted, there is evidence that globular clusters (GC) host more than one stellar population with different chemical composition. HST photometric observations of GC show strong evidence of multiple main sequences in the CMDs. The aim of this line is to characterise the aforementioned multiple populations in GC.

III. Structure and formation of the Milky Way.

The main purpose of this research line is to study the Milky Way via by using GAIA data (spacebased), and the ESO-VVV survey (Vista Telescope). These data are going to provide a perfect opportunity to study the star formation history of the Galactic disk and bulge. In order to use GAIA and VVV data we need to adapt the tools developed by our group to study stellar populations.

IV. Stellar evolution and synthetic color-magnitude diagram.

We have developed a new stellar evolutionary library. There is the need in the scientific community to increase the reliability and accuracy in the stellar models computation using the most updated results in Physics, such as the equation of state, new opacities, and nuclear sections.

Milestones

- It has been found that the youngest stellar populations in the GCs and with enhanced metallicity are more concentrated than the older ones. This is in agreement with the models of GCs formation that predict that the stars forms in the center and they migrate with time toward the external regions.

- A paper about the discovering of a new Einstein's ring has been published, the Canarias Einstein Ring. This is one of the most complete Einstein's ring known so far.

- A new method to obtain SFHs free as possible of observational effects has been developed. This method try to evaluate all the uncertainties affecting to the observed SFHs with the aim to be compared with models predictions, which are not taking into account these effects.

- By using the method described above, it has been found that a set of isolated dwarf galaxies of the LG (Cetus, Tucana, LGS-3 y Phoenix) show no effect of the reionization in their most inner part. However some of them could have been affected in their outermost regions.

- A dependency with time has been found in the mass-metallicity relation.  The result suggests that the dependency of the metallicity with the galaxy stellar mass increases with time, with a direct correlation. However the contribution of the SFR to the metallicity is constant with time but with an inverse correlation: for a fixed mass, those galaxies with larger SFRs shows lower metallicities.

- It has been found that the 75% of the second stellar population in the GCs are helium-enhanced compared to the first stellar population, with an average helium difference in mass of about 0.01

- It has been found no correlation between the RGB bump observed magnitude difference in F336W, F606W and F814W band and the cluster absolute magnitude and metallicity. The helium difference n F606W and F814W band is not correlated with the two previous cluster parameters.

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