Galaxy Evolution in the Local Group

Description

The objective of this project is to understand the formation and evolution of galaxies of different morphological types, using the many local examples that can be resolved into individual stars, hence performing the so-called "galactic archaelogy". This branch of research is one of the main drivers of major international projects/facilities, such as the on-going Gaia mission and SDSS surveys, and the planned WHT/WEAVE, LSST, VISTA/4MOST, DESI, E-ELT/HARMONI, to name a few. This ensures that Galactic Archaelogy will be at the forefront of astronomical research for a long time.

Because of their relative proximity, Local Group galaxies can be resolved into stars. Therefore we can study them with a detail impossible elsewhere with present-day facilities and derive their evolutionary history using a set of complementary techniques. On the one hand, using deep photometry reaching the old main sequence turn-offs, it is possible to derive the full star formation history over the entire galaxy's life. Spectroscopic studies of individual stars add direct information on the kinematics and chemical abundances of the different stellar populations; for the most nearby systems, the inclusion of accurate astrometric measurements yields information on the orbital motion of the system and can even deliver the full 6D phase-space information of sub-samples of stars. Third, the study of variable stars such as Cepheids and RR Lyrae provide independent constraints on metallicities and ages of the populations they belong to. These observations offer invaluable, rich information to models of the formation and evolution of galactic structures in a cosmological context.

The Local Group and its immediate surroundings contain about 80 galaxies of different morphological types. Among these, the largest are spiral galaxies (the Milky Way, M31 and M33), a dozen of them are (dwarf) irregulars and the rest are early-type systems. Thus, we can study galaxies of different morphological types, from the Milky Way down to the smallest galactic scales, which are those challenging our understanding of what a "galaxy" is. We also aim at exploiting the detailed information from resolved stellar population studies to test the performance and applicability of integrated light techniques, which are applied to distant stellar systems.

Principal investigator
Project staff
Dr.
Robert Grand

Below a list of highlights from the group activities in 2019-2020. For a more general overview see publication list and this webpage

 

We have put a sequence to the events which gave rise to our Galaxy via the massive characterisation of ages of stars in the halo and thick disc of our Galaxy using Gaia data (Gallart et al. 2019).

2. We have analysed  (Fritz et al. 2019) a combination of VLT/FLAMES and Gaia data on four ultra-faint satellites of the Milky Way of unknown nature; we established that one of them is a galaxy and that it is a highly likely former satellite of the LMC. With this, the number of known likely former satellites of the LMC points to a large LMC dark matter halo mass.

3. With a combination of our own data and a re-analysis of literature data, we have determined that the Tucana dwarf spheroidal is no exception to the too-big-to-fail LambdaCMD problem, unlike what claimed in the literature (Taibi et al. 2019).

4. It has been shown that the star formation history of the Milky Way disk is characterized by three conspicuous star formation burst, occurred 5.7, 1.9 and 1.0 Gyr ago, coinciding with pericentric passages of the Sagittarius dwarf galaxy. This suggests that this relatively recent merger has had an important influence in the evolution of the Milky Way (Ruiz-Lara et al. 2020a)

2. The star formation history of the central region of the Large Magellanic Cloud, including its bar and spiral arm, has provided compelling evidence that this structure, characteristic of the galaxies of this morphological type, originated more than 2 Gyr ago, thus supporting the long term stability of these spiral arms (Ruiz-Lara et al. 2020b)

3. We present a semi-analytic model, addressing the puzzling population of globular clusters in the Fornax dwarf galaxy. We find that in order for four of the globular clusters to survive at their observed projected location, a dark matter core of size > 1.5 kpc and a dwarf merger with dynamical mass ratio of 1:5 -1:2 with Fornax is required (Leung et al. 2020).

 

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Related installation
WEAVE
WEAVE
WEAVE
Instrument
Spectrograph
HARMONI
HARMONI
HARMONI
Instrument
Spectrograph