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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On a New Method to Estimate the Distance, Reddening, and Metallicity of RR Lyrae Stars Using Optical/Near-infrared (B, V, I, J, H, K) Mean Magnitudes: ω Centauri as a First Test CaseWe developed a new approach to provide accurate estimates of the metal content, reddening, and true distance modulus of RR Lyrae stars (RRLs). The method is based on homogeneous optical (BVI) and near-infrared (JHK) mean magnitudes and on predicted period–luminosity–metallicity relations (IJHK) and absolute mean magnitude–metallicity relations (BV)Bono, G. et al.
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12019 -
SMASHing the LMC: Mapping a Ring-like Stellar Overdensity in the LMC DiskWe explore the stellar structure of the Large Magellanic Cloud (LMC) disk using data from the Survey of the MAgellanic Stellar History and the Dark Energy Survey. We detect a ring-like stellar overdensity in the red clump star count map at a radius of ∼6° (∼5.2 kpc at the LMC distance) that is continuous over ∼270° in position angle and is onlyChoi, Y. et al.
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122018 -
Gaia DR2 proper motions of dwarf galaxies within 420 kpc. Orbits, Milky Way mass, tidal influences, planar alignments, and group infallA proper understanding of the Milky Way (MW) dwarf galaxies in a cosmological context requires knowledge of their 3D velocities and orbits. However, proper motion (PM) measurements have generally been of limited accuracy and are available only for more massive dwarfs. We therefore present a new study of the kinematics of the MW dwarf galaxies. WeFritz, T. K. et al.
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Stellar chemo-kinematics of the Cetus dwarf spheroidal galaxyContext. The great majority of early-type dwarf galaxies, in the Local Group as well as in other galaxy groups, are found in the vicinity of much larger galaxies, making it hard to disentangle the role of internal versus external effects in driving their evolution. Aims: In order to minimize environmental effects and gain an insight into theTaibi, S. et al.
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102018 -
SMASHing the LMC: A Tidally Induced Warp in the Outer LMC and a Large-scale Reddening MapWe present a study of the three-dimensional (3D) structure of the Large Magellanic Cloud (LMC) using ∼2.2 million red clump (RC) stars selected from the Survey of the MAgellanic Stellar History. To correct for line-of-sight dust extinction, the intrinsic RC color and magnitude and their radial dependence are carefully measured by using internalChoi, Yumi et al.
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102018 -
The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-faint GalaxiesAccording to LCDM theory, hierarchical evolution occurs on all mass scales, implying that satellites of the Milky Way should also have companions. The recent discovery of ultra-faint dwarf galaxy candidates in close proximity to the Magellanic Clouds provides an opportunity to test this theory. We present proper motion (PM) measurements for 13 ofKallivayalil, Nitya et al.
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Old-Aged Primary Distance IndicatorsOld-aged stellar distance indicators are present in all Galactic structures (halo, bulge, disk) and in galaxies of all Hubble types and, thus, are immensely powerful tools for understanding our Universe. Here we present a comprehensive review for three primary standard candles from Population II: (i) RR Lyrae type variables (RRL), (ii) type IIBeaton, Rachael L. et al.
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122018 -
Impact of Distance Determinations on Galactic Structure. II. Old TracersHere we review the efforts of a number of recent results that use old tracers to understand the build up of the Galaxy. Details that lead directly to using these old tracers to measure distances are discussed. We concentrate on the following: (1) the structure and evolution of the Galactic bulge and inner Galaxy constrained from the dynamics ofKunder, A. et al.
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82018 -
Integrated-light analyses vs. colour-magnitude diagrams. II. Leo A: an extremely young dwarf in the Local GroupContext. Most of our knowledge of the stellar component of galaxies is based on the analysis of distant systems and comes from integrated light data. It is important to test whether the results of the star formation histories (SFH) obtained with standard full-spectrum fitting methods are in agreement with those obtained through colour-magnitudeRuiz-Lara, T. et al.
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92018 -
The Proper Motion Field of the Small Magellanic Cloud: Kinematic Evidence for Its Tidal DisruptionWe present a new measurement of the systemic proper motion of the Small Magellanic Cloud (SMC), based on an expanded set of 30 fields containing background quasars and spanning a ∼3 year baseline, using the Hubble Space Telescope (HST) Wide Field Camera 3. Combining this data with our previous five HST fields, and an additional eight measurementsZivick, P. et al.
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92018 -
Chemical Compositions of Field and Globular Cluster RR Lyrae Stars. I. NGC 3201We present a detailed spectroscopic analysis of horizontal branch stars in the globular cluster NGC 3201. We collected optical (4580–5330 Å), high-resolution (∼34,000), high signal-to-noise ratio (∼200) spectra for 11 RR Lyrae stars and one red horizontal branch star with the multifiber spectrograph M2FS with the 6.5 m Magellan telescope at the LasMagurno, D. et al.
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92018 -
Appearances can be deceiving: clear signs of accretion in the seemingly ordinary Sextans dSphWe report the discovery of clear observational signs of past accretion/merger events in one of the Milky Way satellite galaxies, the Sextans dwarf spheroidal (dSph). These were uncovered in the spatial distribution, internal kinematics, and metallicity properties of Sextans stars using literature CTIO/DECam photometric and Magellan/MMFSCicuéndez, L. et al.
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102018 -
Dark halo structure in the Carina dwarf spheroidal galaxy: joint analysis of multiple stellar componentsPhotometric and spectroscopic observations of the Carina dSph revealed that this galaxy contains two dominant stellar populations of different age and kinematics. The coexistence of multiple populations provides new constraints on the dark halo structure of the galaxy, because different populations should be in equilibrium in the same dark matterHayashi, K. et al.
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Variable stars in local group galaxies - IV. RR Lyrae stars in the central regions of the low-density galaxy Crater IIWe present a search and analysis of variable stars in the recently discovered Crater II dwarf galaxy. Based on B, V, I data collected with the Isaac Newton Telescope (FoV˜0.44 deg2), we detected 37 variable stars, of which 34 are bone-fide RR Lyrae stars of Crater II (28 RRab, 4 RRc, 2 RRd). We applied the metal-independent (V, B - V) PeriodMonelli, M. et al.
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102018 -
On the early evolution of Local Group dwarf galaxy types: star formation and supernova feedbackAccording to star formation histories (SFHs), Local Group dwarf galaxies can be broadly classified in two types: those forming most of their stars before z = 2 (fast) and those with more extended SFHs (slow). The most precise SFHs are usually derived from deep but not very spatially extended photometric data; this might alter the ratio of old toBermejo-Climent, J. R. et al.
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92018 -
The Orbit and Origin of the Ultra-faint Dwarf Galaxy Segue 1We present the first proper motion measurement for an ultra-faint dwarf spheroidal galaxy, Segue 1, using data from the Sloan Digital Sky Survey (SDSS) and the Large Binocular Camera (LBC) as the first and second epochs separated by a baseline of ∼10 years. We obtain a motion of μ α cos(δ) = ‑0.37 ± 0.57 mas yr‑1 and μ δ = ‑3.39 ± 0.58 mas yr‑1Fritz, T. K. et al.
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62018 -
Spectroscopic characterization of the stellar content of ultra-diffuse galaxiesUnderstanding the peculiar properties of ultra-diffuse galaxies (UDGs) via spectroscopic analysis is a challenging task requiring very deep observations and exquisite data reduction. In this work, we perform one of the most complete characterizations of the stellar component of UDGs to date using deep optical spectroscopic data from OSIRIS at GranRuiz-Lara, T. et al.
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82018 -
Alone on a wide wide sea. The origin of SECCO 1, an isolated star-forming gas cloud in the Virgo cluster*†‡SECCO 1 is an extremely dark, low-mass (M⋆ ≃ 105 M⊙), star-forming stellar system lying in the low-velocity cloud (LVC) substructure of the Virgo cluster of galaxies, and hosting several H II regions. Here, we review our knowledge of this remarkable system, and present the results of (a) additional analysis of our panoramic spectroscopicCorrenti, M. et al.
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62018 -
NGC 6705 a young α-enhanced open cluster from OCCASO dataContext. The stellar [α/Fe] abundance is sometimes used as a proxy for stellar age, following standard chemical evolution models for the Galaxy, as seen by different observational results. Aim. In this work, we aim to show that the open cluster NGC 6705/M 11 has a significant α-enhancement [α/Fe] > 0.1 dex, despite its young age ( 300 Myr)Casamiquela, L. et al.
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On the RR Lyrae Stars in Globulars. V. The Complete Near-infrared (JHK s ) Census of ω Centauri RR Lyrae VariablesWe present a new complete near-infrared (NIR, JHK s ) census of RR Lyrae stars (RRLs) in the globular ω Cen (NGC 5139). We collected 15,472 JHK s images with 4–8 m class telescopes over 15 years (2000–2015) covering a sky area around the cluster center of 60 × 34 arcmin2. These images provided calibrated photometry for 182 out of the 198 clusterBraga, V. F. et al.
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