General
Galaxy formation and evolution is a fundamental Astrophysical problem. Its study requires “travelling back in time”, for which there are two complementary approaches. One is to analyse galaxy properties as a function of red-shift. Our team focuses on the other approach, called “Galactic Archaeology”. It is based on the determination of galaxy properties from the study of their resolved stars. Depending on their mass, stars can live as long as a Hubble time, thus allowing to study in exquisite detail how galaxies have evolved from the early Universe to the present time. This research is one of the main drivers of major international projects, both observational (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), and theoretical (such as Nihao, Magic and Auriga hydrodynamical cosmological simulations), in most of which members of our team are involved. This ensures that Galactic Archaelogy will be at the forefront of astronomical research for a long time.
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, and which, therefore can be studied in a detail impossible elsewhere. In particular, 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 aim to derive their evolutionary history using a set of complementary techniques: I) 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; ii) spectroscopic studies of individual stars add direct information on the kinematics and chemical abundances of the different stellar populations; iii) for the most nearby systems, the inclusion of accurate astrometric measurements yields information on the distance (and thus absolute brightness), the orbital motion of the system and can even deliver the full 6D phase-space information of sub-samples of stars; iv) 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, that can be interpreted using hydrodynamic cosmological simulations of galaxy formation that model a wide range of important physical processes.
Members
Results
Below a list of highlights from the group activities in 2020-2021. For a more general overview see publication list and this webpage.
1. Using HST data of the ultra-faint dwarf (UFD) Eridanus II, we determined (Gallart+2021) that its only star formatio event, occurred 13 Gyr ago, was very short (100-500Myr). The associated SNe energy could be enough to expel the remaining gas, casting doubts on the need to invoke cosmic reionization as the preferred explanation for the early quenching of UFD galaxies.
2. The various star formation episodes, extended to few hundred million years ago, which we have precisely dated in the dwarf spheroidal galaxies Fornax (Rusakov+2021) and Leo I (Ruiz-Lara+2021), have shed light on the effects of interactions and mergers in the star formation history of dwarf galaxies.
3. By performing for the first time a joint dynamical modeling of the internal stellar and HI gas kinematics of a Local Group dwarf galaxy, WLM, we were able to determine that its dark matter halo is likely both cored and has a prolate shape, where the co-existence of these features might pose a problem for self-interacting dark matter models (Leung+2021).
4. For the first time using cosmological simulations, we demonstrated that mergers are a viable explanation for the presence of prolate rotation in the stellar component of galaxies also on the scale of dwarf galaxies (Cardona-Barrero+2021)
5. Robert Grand ran the highest resolution MHD cosmological Milky Way simulation in the world (Grand+2021), run on MPCDF Raven large compute system for which the PI had rolling access as an MPA fellow.
Scientific activity
Related publications
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Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). I. The final word on the origin of NGC 6388 and NGC 6441We present CARMA, the Cluster Ages to Reconstruct the Milky Way Assembly project, the aim of which is to determine precise and accurate age measurements for the entire system of known Galactic globular clusters (GCs) and to use them to trace the most significant merger events experienced by the Milky Way. The strength of CARMA relies on the use ofMassari, Davide et al.
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122023 -
Oxygen, sulfur, and iron radial abundance gradients of classical Cepheids across the Galactic thin disk★★★Context. Classical Cepheids (CCs) are solid distance indicators and tracers of young stellar populations. Dating back to the beginning of the 20th century, they have been safely adopted to trace the rotation, kinematics, and chemical enrichment history of the Galactic thin disk. Aims: The main aim of this investigation is to provide iron, oxygenda Silva, R. et al.
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102023 -
Impact of the Galactic bar on tidal streams within the Galactic disc. The case of the tidal stream of the HyadesTidal streams of disrupted clusters are powerful probes of the gravitational potential of the Galaxy and they are routinely detected in the stellar halo of the Milky Way. It was recently shown that tidal streams of open clusters can now also be detected within the Milky Way disc. In this work, we highlight the fact that disc tidal streams alsoThomas, Guillaume F. et al.
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102023 -
Binary star population of the Sculptor dwarf galaxyAims: We aim to compute the binary fraction of "classical" dwarf spheroidal galaxies (dSphs) that are satellites of the Milky Way (MW). This value can offer insights into the binary fraction in environments that are less dense and more metal-poor than our own galaxy. Additionally, knowledge of the binary fraction in dwarf galaxies is important withArroyo-Polonio, José María et al.
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92023 -
The Pristine dwarf galaxy survey-V. The edges of the dwarf galaxy HerculesWe present a new spectroscopic study of 175 stars in the vicinity of the dwarf galaxy Hercules (d ~ 132 kpc) with data from the Anglo-Australian Telescope and its AAOmega spectrograph together with the Two Degree Field multi-object system to solve the conundrum that whether Hercules is tidally disrupting. We combine broad-band photometry, properLongeard, Nicolas et al.
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102023 -
The extended 'stellar halo' of the Ursa Minor dwarf galaxyStellar candidates in the Ursa Minor (UMi) dwarf galaxy have been found using a new Bayesian algorithm applied to Gaia EDR3 data. Five of these targets are located in the extreme outskirts of UMi, from ~5 to 12 elliptical half-light radii (r h), where r h(UMi) = 17.32 ± 0.11 arcmin, and have been observed with the high-resolution Gemini RemoteSestito, Federico et al.
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102023 -
A Bayesian estimation of the Milky Way's circular velocity curve using Gaia DR3Aims: Our goal is to calculate the circular velocity curve of the Milky Way, along with corresponding uncertainties that quantify various sources of systematic uncertainty in a self-consistent manner. Methods: The observed rotational velocities are described as circular velocities minus the asymmetric drift. The latter is described by the radialPõder, Sven et al.
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82023 -
Constraining gas metal mixing strength in simulations using observations of the Milky Way's discThis work explores the mixing rate of metals in the interstellar medium (ISM), comparing observational constraints from our solar neighbourhood to high resolution cosmological hydrodynamical simulations of Milky Way (MW)-like galaxies. The mixing rate, described by the coefficient C, is varied in simulations between 0 and 0.05, with resultantSarrato-Alós, J. et al.
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102023 -
The PAndAS View of the Andromeda Satellite System. IV. Global PropertiesWe build a statistical framework to infer the global properties of the satellite system of the Andromeda galaxy (M31) from the properties of individual dwarf galaxies located in the Pan-Andromeda Archaelogical Survey (PAndAS) and the previously determined completeness of the survey. Using forward modeling, we infer the slope of the luminosityDoliva-Dolinsky, Amandine et al.
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72023 -
A 3D view of dwarf galaxies with Gaia and VLT/FLAMES. I. The Sculptor dwarf spheroidalWe present a new homogeneous survey of VLT/FLAMES LR8 line-of-sight radial velocities (v los) for 1604 resolved red giant branch stars in the Sculptor dwarf spheroidal galaxy. In addition, we provide reliable Ca II triplet metallicities, [Fe/H], for 1339 of these stars. From this combination of new observations (2257 individual spectra) with ESOTolstoy, Eline et al.
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72023 -
StarHorse results for spectroscopic surveys and Gaia DR3: Chrono-chemical populations in the solar vicinity, the genuine thick disk, and young alpha-rich starsThe Gaia mission has provided an invaluable wealth of astrometric data for more than a billion stars in our Galaxy. The synergy between Gaia astrometry, photometry, and spectroscopic surveys gives us comprehensive information about the Milky Way. Using the Bayesian isochrone-fitting code StarHorse, we derive distances and extinctions for more thanQueiroz, A. B. A. et al.
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52023 -
On the anticorrelation between pericentric distance and inner dark matter density of Milky Way's dwarf spheroidal galaxiesAn anticorrelation between the central density of the dark matter (DM) halo (ρ 150, DM) and the pericentric distances (r p) of the Milky Way's (MW's) dwarf spheroidal galaxies (dSphs) has been reported in the literature. The existence and origin of such anticorrelation are, however, controversial, one possibility being that only the densest dSphsCardona-Barrero, Salvador et al.
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62023 -
The Undiscovered Ultradiffuse Galaxies of the Local GroupUltradiffuse galaxies (UDGs) are attractive candidates to probe cosmological models and test theories of galaxy formation at low masses; however, they are difficult to detect because of their low surface brightness. In the Local Group a handful of UDGs have been found to date, most of which are satellites of the Milky Way and M31, and only two areNewton, Oliver et al.
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42023 -
RR Lyrae Mid-infrared Period-Luminosity-Metallicity and Period-Wesenheit-Metallicity Relations Based on Gaia DR3 ParallaxesWe present new empirical infrared period-luminosity-metallicity (PLZ) and period-Wesenheit-metallicity (PWZ) relations for RR Lyae based on the latest Gaia Early Data Release 3 (EDR3) parallaxes. The relations are provided in the Wide-field Infrared Survey Explorer (WISE) W1 and W2 bands, as well as in the W(W1, V - W1) and W(W2, V - W2) WesenheitMullen, Joseph P. et al.
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32023 -
A probabilistic deep learning model to distinguish cusps and cores in dwarf galaxiesNumerical simulations within a cold dark matter (DM) cosmology form haloes whose density profiles have a steep inner slope ('cusp'), yet observations of galaxies often point towards a flat central 'core'. We develop a convolutional mixture density neural network model to derive a probability density function (PDF) of the inner density slopes of DMExpósito-Márquez, J. et al.
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32023 -
Metallicity profiles of ultradiffuse galaxies in NIHAO simulationsSupernovae feedback driven expansion has proven to be a viable mechanism to explain the average properties, such as size, colour, mass, and internal kinematics, of a large fraction of ultradiffuse galaxies (UDGs). Here, we explore the origin of stellar metallicity gradients in feedback driven simulated UDGs from the NIHAO project and compare themCardona-Barrero, S. et al.
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22023 -
The Pristine survey - XIX. Cu and Zn abundances in metal-poor giantsMetal-poor stars formed from a gas enriched by the ejecta of the explosion of one/few generations of first massive stars. With the Pristine photometry combined with the Gaia data, we selected a sample of bright giants metal-poor candidates to be observed at high resolution. Of the 43 stars observed, 36 were confirmed to be metal-poor, supportingCaffau, E. et al.
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12023 -
On the use of field RR Lyrae as galactic probes - VI. Mixed mode RR Lyrae variables in Fornax and in nearby dwarf galaxiesWe investigate the properties of the mixed-mode (RRd) RR Lyrae (RRL) variables in the Fornax dwarf spheroidal (dSph) galaxy by using B- and V-band time series collected over 24 yr. We compare the properties of the RRds in Fornax with those in the Magellanic Clouds and in nearby dSphs, with special focus on Sculptor. We found that the ratio of RRdsBraga, V. F. et al.
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122022 -
The impact of two massive early accretion events in a Milky Way-like galaxy: repercussions for the buildup of the stellar disc and haloWe identify and characterize a Milky Way-like realization from the Auriga simulations with two consecutive massive mergers $\sim 2$ Gyr apart at high redshift, comparable to the reported Kraken and Gaia-Sausage-Enceladus. The Kraken-like merger (z = 1.6, $M_{\rm Tot}=8\times 10^{10}\, \rm {M_{\odot }}$) is gas-rich, deposits most of its mass in theOrkney, Matthew D. A. et al.
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112022 -
Asymmetrical tidal tails of open star clusters: stars crossing their cluster's práh<SUP>†</SUP> challenge Newtonian gravitationAfter their birth a significant fraction of all stars pass through the tidal threshold (práh) of their cluster of origin into the classical tidal tails. The asymmetry between the number of stars in the leading and trailing tails tests gravitational theory. All five open clusters with tail data (Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, NGCKroupa, Pavel et al.
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122022
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