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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The Galaxy "Missing Dark Matter" NGC 1052-DF4 is Undergoing Tidal DisruptionThe existence of long-lived galaxies lacking dark matter represents a challenge to our understanding of how galaxies form. Here, we present evidence that explains the lack of dark matter in one such galaxy: NGC 1052-DF4. Deep optical imaging of the system has detected tidal tails in this object caused by its interaction with its neighboring galaxyMontes, Mireia et al.
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122020 -
The recurrent impact of the Sagittarius dwarf on the star formation history of the Milky WaySatellites orbiting disk galaxies can induce phase space features such as spirality, vertical heating and phase-mixing in their disks. Such features have also been observed in our own Galaxy, but the complexity of the Milky Way disk has only recently been fully mapped by Gaia Data Release 2 (DR2) data. This complex behaviour is mainly ascribed toRuiz-Lara, Tomás et al.
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52020 -
The chemical evolution of the dwarf spheroidal galaxy SextansWe present our analysis of the FLAMES dataset targeting the central 25' region of the Sextans dwarf spheroidal galaxy (dSph). This dataset is the third major part of the high-resolution spectroscopic section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team. Our sample is composed of red giantTheler, R. et al.
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102020 -
"Observations" of simulated dwarf galaxies. Star-formation histories from color-magnitude diagramsContext. Apparent deviations between properties of dwarf galaxies from observations and simulations are known to exist, such as the "Missing Dwarfs" problem, the too-big-to-fail problem, and the cusp-core problem, to name a few. Recent studies have shown that these issues can at least be partially resolved by taking into account the systematicRathi, Shivangee et al.
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102020 -
SMASHing the low surface brightness SMCThe periphery of the Small Magellanic Cloud (SMC) can unlock important information regarding galaxy formation and evolution in interacting systems. Here, we present a detailed study of the extended stellar structure of the SMC using deep colour-magnitude diagrams, obtained as part of the Survey of the MAgellanic Stellar History (SMASH). SpecialMassana, Pol et al.
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82020 -
The Large Magellanic Cloud stellar content with SMASH. I. Assessing the stability of the Magellanic spiral armsThe Large Magellanic Cloud (LMC) is the closest and most studied example of an irregular galaxy. Among its principal defining morphological features, its off-centred bar and single spiral arm stand out, defining a whole family of galaxies known as the Magellanic spirals (Sm). These structures are thought to be triggered by tidal interactions andRuiz-Lara, T. et al.
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72020 -
On the Metamorphosis of the Bailey Diagram for RR Lyrae StarsWe collected over 6000 high-resolution spectra of four dozen field RR Lyrae (RRL) variables pulsating either in the fundamental (39 RRab) or in the first overtone (9 RRc) mode. We measured radial velocities (RVs) of four strong metallic and four Balmer lines along the entire pulsational cycle and derived RV amplitudes with accuracies better than 1Bono, G. et al.
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62020 -
Explaining the chemical trajectories of accreted and in-situ halo stars of the Milky WayThe Milky Way underwent its last significant merger ten billion years ago, when the Gaia-Enceladus-Sausage (GES) was accreted. Accreted GES stars and progenitor stars born prior to the merger make up the bulk of the inner halo. Even though these two main populations of halo stars have similar durations of star formation prior to their merger, theyBrook, Chris B. et al.
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42020 -
The Lazy Giants: APOGEE Abundances Reveal Low Star Formation Efficiencies in the Magellanic CloudsWe report the first APOGEE metallicities and α-element abundances measured for 3600 red giant stars spanning a large radial range of both the Large (LMC) and Small Magellanic Clouds, the largest Milky Way (MW) dwarf galaxies. Our sample is an order of magnitude larger than that of previous studies and extends to much larger radial distances. TheseNidever, David L. et al.
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62020 -
Revealing the tidal scars of the Small Magellanic CloudDue to their close proximity, the Large and Small Magellanic Clouds (LMC/SMC) provide natural laboratories for understanding how galaxies form and evolve. With the goal of determining the structure and dynamical state of the SMC, we present new spectroscopic data for ∼3000 SMC red giant branch stars observed using the AAOmega spectrograph at theDe Leo, Michele et al.
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42020 -
The mass of our Galaxy from satellite proper motions in the Gaia eraWe use Gaia DR2 systemic proper motions of 45 satellite galaxies to constrain the mass of the Milky Way using the scale-free mass estimator of Watkins et al. (2010). We first determine the anisotropy parameter β, and the tracer satellites' radial density index γ to be β = $-0.67^{+0.45}_{-0.62}$ and γ = 2.11 ± 0.23. When we exclude possible formerFritz, T. K. et al.
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42020 -
The Tucana dwarf spheroidal galaxy: not such a massive failure after allContext. Isolated local group (LG) dwarf galaxies have evolved most or all of their life unaffected by interactions with the large LG spirals and therefore offer the opportunity to learn about the intrinsic characteristics of this class of objects. Aims: Our aim is to explore the internal kinematic and metallicity properties of one of the threeTaibi, S. et al.
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32020 -
Two Ultra-faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration SurveyWe report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238─4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of ${\text{}}{D}_{\odot }={116.3}_{-0.6}^{+0.6}\,\mathrm{kpc}$ , aMau, S. et al.
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22020 -
A dwarf-dwarf merger and dark matter core as a solution to the globular cluster problems in the Fornax dSphThe five globular clusters (GCs) of the Fornax dwarf spheroidal galaxy are puzzling for two reasons; the mass in GCs is high with respect to the galaxy's old stellar mass and their survival and large distance (>1 kpc) is at odds with naive expectations of dynamical friction. We present here a semi-analytic model, simultaneously addressing bothLeung, Gigi Y. C. et al.
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32020 -
Kinematic and metallicity properties of the Aquarius dwarf galaxy from FORS2 MXU spectroscopy⋆Context. Dwarf galaxies found in isolation in the Local Group (LG) are unlikely to have interacted with the large LG spirals, and therefore environmental effects such as tidal and ram-pressure stripping should not be the main drivers of their evolution. Aims: We provide insight into the internal mechanisms shaping LG dwarf galaxies by increasingHermosa Muñoz, L. et al.
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22020 -
Metallicity and α-Element Abundance Gradients along the Sagittarius Stream as Seen by APOGEEUsing 3D positions and kinematics of stars relative to the Sagittarius (Sgr) orbital plane and angular momentum, we identify 166 Sgr stream members observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) that also have Gaia DR2 astrometry. This sample of 63/103 stars in the Sgr trailing/leading arm is combined with an APOGEEHayes, Christian R. et al.
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12020 -
The HST/ACS star formation history of the Tucana dwarf spheroidal galaxy: clues from the horizontal branchWe report a new star formation history for the Tucana dwarf spheroidal galaxy, obtained from a new look at a deep HST/ACS colour-magnitude diagram. We combined information from the main sequence turn-off and the horizontal branch to resolve the ancient star formation rates on a finer temporal scale than previously possible. We show that TucanaSavino, A. et al.
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102019 -
On the Use of Field RR Lyrae as Galactic Probes. I. The Oosterhoff Dichotomy Based on Fundamental VariablesWe collected a large data set of field RR Lyrae stars (RRLs) by using catalogs already available in the literature and Gaia DR2. We estimated the iron abundances for a subsample of 2382 fundamental RRLs (∆S method: Ca II K, Hβ, Hγ, and Hδ lines) for which there are publicly available medium-resolution SDSS-SEGUE spectra. We also included similarFabrizio, M. et al.
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92019 -
Nature of a shell of young stars in the outskirts of the Small Magellanic CloudContext. Understanding the evolutionary history of the Magellanic Clouds requires an in-depth exploration and characterization of the stellar content in their outer regions, which ultimately are key to tracing the epochs and nature of past interactions. Aims: We present new deep images of a shell-like overdensity of stars in the outskirts of theMartínez-Delgado, David et al.
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112019 -
A DECam view of the diffuse dwarf galaxy Crater II - Variable starsTime series observations of a single dithered field centred on the diffuse dwarf satellite galaxy Crater II were obtained with the Dark Energy Camera (DECam) at the 4m Blanco Telescope at Cerro Tololo Inter-American Observatory, Chile, uniformly covering up to two half-light radii. Analysis of the g and i time series results in the identificationVivas, A. Katherina et al.
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22020
