HOLYDWARFS

The star-formation histories and dark-matter content of faint dwarf elliptical galaxies

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 Obiettivo del progetto (Objective)

'In a cosmological context the dwarf galaxies (stellar masses M < 10^9 Msun) are crucially important because they hold keys to solve some of the most important questions in current extragalactic astronomy:

- What are the effects of the environment on the evolution of galaxies? Because of their low masses, dwarfs are ideal targets to study environmental processes such as ram-pressure stripping and galaxy harassment.

- What are the mechanisms controling star formation? Due to their shallow gravitational potential wells, dwarf galaxies are very sensitive to processes like supernova feedback. This feedback heats and disperses the gas, affecting the star-formation efficiency. In combination with environmental effects, it may even cause the gas to be lost from the host galaxy.

- What are the properties of the dark matter? Dwarf galaxies appear to be among the most dark matter dominated objects in the nearby universe, making them prime objects to study the properties and spatial distribution of this elusive ingredient of the universe.

While the dwarf galaxies below 10^7 Msun appear to be dark matter dominated, those more massive than 10^9 Msun are not. Our goal is to investigate the terra incognita between these two regimes, i.e. galaxies with stellar masses around 10^8 solar masses. Trough stellar population analysis, dynamical modeling and numerical simulations we will be able to shed light on the controlling mechanism of star formation and the role of the dark matter. We will study the dwarf dark-matter halo occupancy and investigate the physical processes that cause the photometric scaling relations to change slope around stellar mass M~10^8 solar masses.

This project calls for a multidisciplinary approach, combining the host institute's expertise in dynamical modeling and simulations with the applicant's expertise in stellar populations analysis.'

Introduzione (Teaser)

Galaxies come in many shapes and sizes. Among the smallest are dwarf galaxies, on which EU-funded astronomers focused to learn more about the evolution of the Universe and what the future has in store for our own Milky Way.

Descrizione progetto (Article)

In recent years, astronomers have discovered that dwarf galaxies are very different from their bigger relatives. While they spend billions of years in a dormant state, they occasionally experience spectacular periods of star formation. Bursts of star formation also occur in larger galaxies, but light from these bursts is obstructed by other emissions.

To get a clear look at this intriguing phenomenon, astronomers working on 'The star-formation histories and dark-matter content of faint dwarf elliptical galaxies' (HOLYDWARFS) project focused on the dwarf family of galaxies. In these smaller versions of 'normal' galaxies, some 30 times smaller than our own Galaxy, they searched for clues of the early history of the Universe.

The HOLYDWARFS scientists explored the evolution of galaxies, as star formation is triggered and quenched by environmental effects The main outcome was a unified picture of galaxies in a quiescent state, when all their stars are old, faint and red, with dwarfs that have new, hot and bright blue stars.

Thermonuclear reactions transform hydrogen and helium into heavier elements, so-called metals in the area of astronomy and this allows astronomers to follow galaxies' evolution. Project results have provided sufficiently detailed data of the abundance of metals to compare against high-resolution simulations. Comparing observations to simulations offered HOLYDWARFS scientists with a powerful approach to study the physical processed involved in star formation.

Hydrodynamical simulations used to form and evolve dwarf galaxies showed that metallicity gradually builds up. Once built up, the metal abundance is maintained in the absence of external disturbances. Besides agreeing with the observed metallicity profiles, the simulations' predictions are hoped to result in better models of dwarf galaxies.

According to the widely accepted models, dwarf galaxies that orbit our Milky Way form inside small clumps of dark matter and contain larger proportions of dark matter than their parent galaxy. But what is observed is very different. The HOLYDWARFS project embraced the challenge to uphold existing theories and models and filled some holes in our current understanding of galaxy formation.