STELLAR POPULATIONS IN NEARBY GALAXIES

The deep expertise in the theory of stellar evolution at the Observatory of Padova offers a solid background for studies of the populations of resolved stars in external galaxies. Several projects conducted at OAPd aim at understanding the star formation process per se, and at measuring the star formation history in systems for which the Colour-Magnitude Diagram can be derived. These studies include both theoretical and observational efforts, with extensive use of the current most powerful facilities (HST, VLT).

The modes and triggers of the star formation process are investigated by deriving the age distributions of stars in the field and in clusters in the Magellanic Clouds, and comparing the spatially resolved SFH to the structures detected in atomic and molecular gas. Some researchers at OaPD are studying the Magellanic System with the aim of constraining the history of interactions between the Milky Way and the MCs, particularly focusing on the ages and kinematics of stars in the Magellanic Bridge. Some others are preparing the large VMC survey, which will image most of the Magellanic System with unprecedented depth and resolution in the near-infrared using VISTA.

The stellar populations in the halo of the Andromeda Galaxy are also studied, both in imaging and spectroscopic modes. The main goal of this research is to derive the star formation and mass assembly history of M31, especially to compare its evolutionary path to the one of the Milky Way.

A group of researchers at OAPd carry on a systematic study of the stellar populations in nearby dwarf galaxies, with the ultimate aim of testing the predictions of the hierarchical structure formation models, and the proposed mechanism for delaying star formation in shallow potential wells. The Local Group offers an ideal laboratory for this, since it includes dwarf irregulars, dwarf spheroidals and transition objects. Each type of dwarf galaxy is studied photometrically and spectroscopically, to address also the relation between the different types. Variable stars (RR-Lyrae and other types), carbon stars and blue-plume stars are used as tracers of star formation at old, intermediate, and young ages. The production of carbon stars in stellar populations with different ages and metallicities is probed with specific observational programs; another study is aimed at assessing the nature of blue plume stars in dwarf spheroidals, i.e. whether intermediate age objects or the result of the evolution of low mass stars in close binary systems. Studies of the stars formation history of galaxies beyond the Local Group have been conducted with the Advanced Camera for Surveys on the HST. Intensely star-forming dwarf galaxies, with their low metallicity and high gas content, are ideal benchmarks to understand how galaxies evolved in the early Universe. Deriving the SFH of a complete volume-limited sample of galaxies is the main target of the ANGST survey using the ACS.

Some researchers at OAPd are also investigating on the possible applications of future instrumentation (ESO-ELT, JWST) to the study of stellar populations in resolved galaxies. We are actively participating to the definition and refinement of detailed science cases.

 

Stellar Populations in Nearby Galaxies: Past Studies

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