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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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 -
MuSCAT2 multicolour validation of TESS candidates: an ultra-short-period substellar object around an M dwarfContext. We report the discovery of TOI 263.01 (TIC 120916706), a transiting substellar object (R = 0.87 R Jup) orbiting a faint M3.5 V dwarf (V = 18.97) on a 0.56 d orbit. Aims: We setout to determine the nature of the Transiting Exoplanet Survey Satellite (TESS) planet candidate TOI 263.01 using ground-based multicolour transit photometry. TheParviainen, H. et al.
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12020 -
A DECam view of the diffuse dwarf galaxy Crater II: the colour-magnitude diagramWe present a deep Blanco/DECam colour-magnitude diagram (CMD) for the large but very diffuse Milky Way satellite dwarf galaxy Crater II. The CMD shows only old stars with a clearly bifurcated subgiant branch (SGB) that feeds a narrow red giant branch. The horizontal branch (HB) shows many RR Lyrae and red HB stars. Comparing the CMD with [Fe/H] =Walker, A. R. et al.
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122019 -
Uncovering the birth of the Milky Way through accurate stellar ages with GaiaKnowledge of the ages of the stars formed over a galaxy's lifetime is fundamental to an understanding of its formation and evolution. However, stellar ages are difficult to obtain since they cannot be measured from observations, but require comparison with stellar models 1. Alternatively, age distributions can be derived by applying the robustGallart, Carme et al.
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72019 -
OCCASO - III. Iron peak and α elements of 18 open clusters. Comparison with chemical evolution models and field starsThe study of open-cluster chemical abundances provides insights on stellar nucleosynthesis processes and on Galactic chemo-dynamical evolution. In this paper we present an extended abundance analysis of 10 species (Fe, Ni, Cr, V, Sc, Si, Ca, Ti, Mg, O) for red giant stars in 18 OCCASO clusters. This represents a homogeneous sample regarding theCasamiquela, L. et al.
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122019 -
SIGNALS: I. Survey descriptionSIGNALS, the Star formation, Ionized Gas, and Nebular Abundances Legacy Survey, is a large observing programme designed to investigate massive star formation and H II regions in a sample of local extended galaxies. The programme will use the imaging Fourier transform spectrograph SITELLE at the Canada-France-Hawaii Telescope. Over 355 h (54.7Rousseau-Nepton, L. et al.
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112019 -
Horizontal branch morphology: A new photometric parametrizationContext. Theory and observations indicate that the distribution of stars along the horizontal branch of Galactic globular clusters mainly depends on the metal content. However, the existence of globular clusters with similar metal content and absolute age but different horizontal branch morphologies, suggests the presence of another parameterTorelli, M. et al.
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92019 -
The TRGB Distance to the Second Galaxy “Missing Dark Matter”: Evidence for Two Groups of Galaxies at 13.5 and 19 Mpc in the Line of Sight of NGC 1052A second galaxy “missing dark matter” (NGC 1052-DF4) has been reported recently. Here we show, using the location of the tip of the red giant branch (TRGB), that the distance to this galaxy is 14.2 ± 0.7 Mpc. This locates the galaxy 6 Mpc closer than previously determined. We also analyze the distances to the brightest galaxies in the field of viewMonelli, Matteo et al.
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72019 -
Chemical Compositions of Field and Globular Cluster RR Lyrae Stars. II. ω CentauriWe present a detailed spectroscopic analysis of RR Lyrae (RRL) variables in the globular cluster NGC 5139 (ω Cen). We collected optical (4580–5330 Å), high-resolution (R ∼ 34,000), high signal-to-noise ratio (∼200) spectra for 113 RRLs with the multifiber spectrograph M2FS at the Magellan/Clay Telescope at Las Campanas Observatory. We also analyzedMagurno, D. et al.
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82019 -
The effect of tides on the Sculptor dwarf spheroidal galaxyDwarf spheroidal galaxies (dSphs) appear to be some of the most dark matter (DM)-dominated objects in the Universe. Their dynamical masses are commonly derived using the kinematics of stars under the assumption of equilibrium. However, these objects are satellites of massive galaxies (e.g. the Milky Way) and thus can be influenced by their tidalIorio, G. et al.
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82019 -
The Magellanic System: the puzzle of the leading gas streamThe Magellanic Clouds (MCs) are the most massive gas-bearing systems falling into the Galaxy at the present epoch. They show clear signs of interaction, manifested in particular by the Magellanic Stream, a spectacular gaseous wake that trails from the MCs extending more than 150° across the sky. Ahead of the MCs is the `Leading Arm' usuallyTepper-García, Thor et al.
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92019 -
An old, metal-poor globular cluster in Sextans A and the metallicity floor of globular cluster systemsWe report the confirmation of an old, metal-poor globular cluster (GC) in the nearby dwarf irregular galaxy Sextans A, the first GC known in this galaxy. The cluster, which we designate as Sextans A-GC1, lies some 4.4 arcmin (˜1.8 kpc) to the SW of the galaxy centre and clearly resolves into stars in sub-arcsecond seeing ground-based imaging. WeBeasley, Michael A. et al.
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82019 -
VLT/FLAMES high-resolution chemical abundances in Sculptor: a textbook dwarf spheroidal galaxyWe present detailed chemical abundances for 99 red-giant branch stars in the centre of the Sculptor dwarf spheroidal galaxy, which have been obtained from high-resolution VLT/FLAMES spectroscopy. The abundances of Li, Na, α-elements (O, Mg, Si, Ca Ti), iron-peak elements (Sc, Cr, Fe, Co, Ni, Zn), and r- and s-process elements (Ba, La, Nd, Eu) wereHill, V. et al.
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62019 -
Stellar content, planetary nebulae, and globular clusters of [KKS2000]04 (NGC 1052-DF2)[KKS2000]04 (NGC 1052-DF2) has become a controversial and well-studied galaxy after the claims suggesting a lack of dark matter and the presence of an anomalously bright globular cluster (GC) system around it. A precise determination of its overall star formation history (SFH) and a better characterization of its GC or planetary nebulae (PNe)Ruiz-Lara, T. et al.
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72019 -
A distance of 13 Mpc resolves the claimed anomalies of the galaxy lacking dark matterThe claimed detection of a diffuse galaxy lacking dark matter represents a possible challenge to our understanding of the properties of these galaxies and galaxy formation in general. The galaxy, already identified in photographic plates taken in the summer of 1976 at the UK 48-in Schmidt telescope, presents normal distance-independent propertiesTrujillo, I. et al.
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62019
