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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Stellar dynamics and dark matter in Local Group dwarf galaxiesWhen interpreted within the standard framework of Newtonian gravity and dynamics, the kinematics of stars and gas in dwarf galaxies reveals that most of these systems are completely dominated by their dark matter halos. These dwarf galaxies are thus among the best astrophysical laboratories to study the structure of dark halos and the nature ofBattaglia, Giuseppina et al.
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52022 -
The Pristine survey - XVIII. C-19: tidal debris of a dark matter-dominated globular cluster?The recently discovered C-19 stellar stream is a collection of kinematically associated metal-poor stars in the halo of the Milky Way lacking an obvious progenitor. The stream spans across an arc of ~15° in the sky, and orbit-fitting suggests an apocentric distance of ${\sim} 20\, \mathrm{kpc}$ and a pericentre of ${\sim} 10\, \mathrm{kpc}$. TheErrani, Raphaël et al.
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82022 -
The Pristine survey - XVII. The C-19 stream is dynamically hot and more extended than previously thoughtThe C-19 stream is the most metal-poor stellar system ever discovered, with a mean metallicity [Fe/H] = -3.38 ± 0.06. Its low metallicity dispersion (σ [Fe/H] < 0.18 at the 95 per cent confidence level) and variations in sodium abundances strongly suggest a globular cluster origin. In this work, we use Very Large Telescope (VLT)/UV-Visual EchelleYuan, Zhen et al.
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82022 -
Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves. II. Period-Fourier-Metallicity Relations for First Overtone RR LyraeWe present new period-ϕ 31-[Fe/H] relations for first-overtone RRL stars (RRc), calibrated over a broad range of metallicities (-2.5 ≲ [Fe/H] ≲ 0.0) using the largest currently available set of Galactic halo field RRL with homogeneous spectroscopic metallicities. Our relations are defined in the optical (ASAS-SN V band) and, inaugurally, in theMullen, Joseph P. et al.
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62022 -
A new and Homogeneous metallicity scale for Galactic classical Cepheids. II. Abundance of iron and α elementsContext. Classical Cepheids are the most popular distance indicators and tracers of young stellar populations. The key advantage is that they are bright and they can be easily identified in Local Group and Local Volume galaxies. Their evolutionary and pulsation properties depend on their chemical abundances. Aims: The main aim of this investigationda Silva, R. et al.
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52022 -
The chemo-dynamical groups of Galactic globular clustersWe introduce a multicomponent chemo-dynamical method for splitting the Galactic population of globular clusters (GCs) into three distinct constituents: bulge, disc, and stellar halo. The latter is further decomposed into the individual large accretion events that built up the Galactic stellar halo: the Gaia-Enceladus-Sausage, Kraken and SequoiaCallingham, Thomas M. et al.
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72022 -
Local variations of the stellar velocity ellipsoid - II. The effect of the bar in the inner regions of Auriga galaxiesTheoretical works have shown that off-plane motions of bars can heat stars in the vertical direction during buckling but is not clear how do they affect the rest of components of the stellar velocity ellipsoid (SVE). We study the 2D spatial distribution of the vertical, σ z, azimuthal, σ ϕ, and radial, σ r velocity dispersions in the inner regionsWalo-Martín, Daniel et al.
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72022 -
The Cetus-Palca stream: A disrupted small dwarf galaxy. A prequel to the science possible with WEAVE with precise spectro-photometric distancesWe present a new fully data-driven approach to derive spectro-photometric distances based on artificial neural networks. The method was developed and tested on Sloan Extension for Galactic Understanding and Exploration survey (SEGUE) data and will serve as a reference for the Contributed Data Product SPDIST of the William Hershel Telescope EnhancedThomas, Guillaume F. et al.
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42022 -
The synchronized dance of the magellanic clouds' star formation historyWe use the SMASH survey to obtain unprecedented deep photometry reaching down to the oldest main-sequence turn-offs in the colour-magnitude diagrams (CMDs) of the Small Magellanic Cloud (SMC) and quantitatively derive its star formation history (SFH) using CMD fitting techniques. We identify five distinctive peaks of star formation in the last 3.5Massana, P. et al.
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62022 -
Survey of Surveys. I. The largest compilation of radial velocities for the GalaxyContext. In the present-day panorama of large spectroscopic surveys, the amount, diversity, and complexity of the available data continuously increase. The overarching goal of studying the formation and evolution of our Galaxy is hampered by the heterogeneity of instruments, selection functions, analysis methods, and measured quantities. Aims: WeTsantaki, M. et al.
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32022 -
AGC 226178 and NGVS 3543: Two Deceptive Dwarfs toward VirgoThe two sources AGC 226178 and NGVS 3543, an extremely faint, clumpy, blue stellar system and a low surface brightness dwarf spheroidal, are adjacent systems in the direction of the Virgo cluster. Both have been studied in detail previously, with it being suggested that they are unrelated normal dwarf galaxies or that NGVS 3543 recently lost itsJones, Michael G. et al.
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22022 -
The photo-astrometric vertical tracer density of the Milky Way - II. Results from GaiaWe use Gaia photometry and astrometry to estimate the vertical spatial structure of the Milky Way at the Solar radius, formally accounting for sample incompleteness (the selection function) and parallax measurement uncertainty. Our results show impressive precision demonstrating the power of the Gaia data. However, systematic errors dominate theEverall, Andrew et al.
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42022 -
The Photo-Astrometric vertical tracer density of the Milky Way - I. The methodWe introduce a method to infer the vertical distribution of stars in the Milky Way using a Poisson likelihood function, with a view to applying our method to the Gaia catalogue. We show how to account for the sample selection function and for parallax measurement uncertainties. Our method is validated against a simulated sample drawn from a modelEverall, Andrew et al.
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42022 -
Dark matter annihilation and the Galactic Centre ExcessWe compare the surface brightness profile and morphology of the Galactic Centre Excess (GCE) identified in wide-angle γ-ray maps from the Fermi-Large Area Telescope (LAT) to dark matter annihilation predictions derived from high-resolution Λ cold dark matter magnetohydrodynamic simulations of galaxy formation. These simulations produce isolatedGrand, Robert J. J. et al.
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32022 -
A stellar stream remnant of a globular cluster below the metallicity floorStellar ejecta gradually enrich the gas out of which subsequent stars form, making the least chemically enriched stellar systems direct fossils of structures formed in the early Universe 1. Although a few hundred stars with metal content below 1,000th of the solar iron content are known in the Galaxy 2-4, none of them inhabit globular clustersMartin, Nicolas F. et al.
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12022 -
Gaia early DR3 systemic motions of Local Group dwarf galaxies and orbital properties with a massive Large Magellanic CloudAims: We perform a comprehensive determination of the systemic proper motions of 74 dwarf galaxies and dwarf galaxy candidates in the Local Group based on Gaia early data release 3. The outputs of the analysis for each galaxy, including probabilities of membership, will be made publicly available. The analysis is augmented by a determination of theBattaglia, G. et al.
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12022 -
The Phantom Dark Matter Halos of the Local Volume in the Context of Modified Newtonian DynamicsWe explore the predictions of Milgromian gravity (MOND) in the local universe by considering the distribution of the "phantom" dark matter (PDM) that would source the MOND gravitational field in Newtonian gravity, allowing an easy comparison with the dark matter framework. For this, we specifically deal with the quasi-linear version of MOND (QUMONDOria, P. -A. et al.
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122021 -
APOGEE Chemical Abundance Patterns of the Massive Milky Way SatellitesThe SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey has obtained high-resolution spectra for thousands of red giant stars distributed among the massive satellite galaxies of the Milky Way (MW): the Large and Small Magellanic Clouds (LMC/SMC), the Sagittarius Dwarf Galaxy (Sgr), Fornax (Fnx), and the now fullyHasselquist, Sten et al.
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122021 -
Pisces VII: discovery of a possible satellite of Messier 33 in the DESI legacy imaging surveysWe report deep imaging observations with DOLoRes@TNG of an ultra-faint dwarf satellite candidate of the Triangulum galaxy (M33) found by visual inspection of the public imaging data release of the DESI Legacy Imaging Surveys. Pisces VII/Triangulum (Tri) III is found at a projected distance of $72\, {\rm kpc}$ from M33, and using the tip of the redMartínez-Delgado, David et al.
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12022 -
Variable Stars in Local Group Galaxies. VI. The Isolated Dwarfs VV 124 and KKr 25We present the discovery of variable stars in two isolated dwarf galaxies in the outskirts of the Local Group, VV 124 and KKr 25, using observations with the Hubble Space Telescope. VV 124 hosts stellar populations with a wide range of ages (>10 Gyr until the present) and therefore we find all types of classical pulsators. In VV 124, we detect aNeeley, Jillian R. et al.
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102021
