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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Uncovering fossils of the distant Milky Way with UNIONS: NGC 5466 and its stellar streamWe examine the spatial clustering of blue horizontal branch (BHB) stars from the u-band of the Canada-France Imaging Survey (CFIS, a component of the Ultraviolet Near-Infrared Optical Northern Survey, or UNIONS). All major groupings of stars are associated with previously known satellites, and among these is NGC 5466, a distant (16 kpc) globularJensen, Jaclyn et al.
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102021 -
Zero-metallicity Hypernova Uncovered by an Ultra-metal-poor Star in the Sculptor Dwarf Spheroidal GalaxyAlthough true metal-free "Population III" stars have so far escaped discovery, their nature, and that of their supernovae, is revealed in the chemical products left behind in the next generations of stars. Here we report the detection of an ultra-metal-poor star in the Sculptor dwarf spheroidal galaxy AS0039. With [Fe/H] LTE = -4.11, it is the mostSkúladóttir, Ása et al.
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72021 -
Origin of stellar prolate rotation in a cosmologically simulated faint dwarf galaxyStellar prolate rotation in dwarf galaxies is rather uncommon, with only two known galaxies in the Local Group showing such feature (Phoenix and And II). Cosmological simulations show that in massive early-type galaxies prolate rotation likely arises from major mergers. However, the origin of such kinematics in the dwarf galaxies regime has onlyCardona-Barrero, Salvador et al.
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72021 -
Charting the Galactic Acceleration Field. I. A Search for Stellar Streams with Gaia DR2 and EDR3 with Follow-up from ESPaDOnS and UVESWe present maps of the stellar streams detected in the Gaia Data Release 2 (DR2) and Early Data Release 3 (EDR3) catalogs using the STREAMFINDER algorithm. We also report the spectroscopic follow-up of the brighter DR2 stream members obtained with the high-resolution CFHT/ESPaDOnS and VLT/UVES spectrographs as well as with the medium-resolution NTTIbata, Rodrigo et al.
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62021 -
On the Use of Field RR Lyrae as Galactic Probes. III. The α-element AbundancesWe provide the largest and most homogeneous sample of α-element (Mg, Ca, Ti) and iron abundances for field RR Lyrae (RRLs; 162 variables) by using high-resolution spectra. The current measurements were complemented with similar abundances available in the literature for 46 field RRLs brought to our metallicity scale. We ended up with a sample ofCrestani, J. et al.
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62021 -
Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves. I. Period-Fourier-Metallicity Relations for Fundamental-mode RR LyraeWe present newly calibrated period-φ 31-[Fe/H] relations for fundamental-mode RR Lyrae stars in the optical and, for the first time, mid-infrared. This work's calibration data set provides the largest and most comprehensive span of parameter space to date, with homogeneous metallicities from -3 ≲ [Fe/H] ≲ 0.4 and accurate Fourier parameters derivedMullen, Joseph P. et al.
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52021 -
Metallicities from high-resolution spectra of 49 RR Lyrae variablesAccurate metallicities of RR Lyrae are extremely important in constraining period-luminosity-metallicity (PLZ) relationships, particularly in the near-infrared. We analyse 69 high-resolution spectra of Galactic RR Lyrae stars from the Southern African Large Telescope. We measure metallicities of 58 of these RR Lyrae stars with typical uncertaintiesGilligan, Christina K. et al.
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62021 -
Observing the Stellar Halo of Andromeda in Cosmological Simulations: The AURIGA2PANDAS PipelineWe present a direct comparison of the Pan-Andromeda Archaeological Survey (PAndAS) observations of the stellar halo of M31 with the stellar halos of six galaxies from the Auriga simulations. We process the simulated halos through the AURIGA2PANDAS pipeline and create PAndAS-like mocks that fold in all observational limitations of the survey dataThomas, Guillaume F. et al.
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42021 -
Solo dwarfs II: the stellar structure of isolated Local Group dwarf galaxiesThe Solo (Solitary Local) Dwarf Galaxy survey is a volume-limited, wide-field g- and i-band survey of all known nearby (<3 Mpc) and isolated (>300 kpc from the Milky Way or M31) dwarf galaxies. This set of 44 dwarfs is homogeneously analysed for quantitative comparisons to the satellite dwarf populations of the Milky Way and M31. In this paper, anHiggs, C. R. et al.
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52021 -
The Star Formation History of Eridanus II: On the Role of Supernova Feedback in the Quenching of Ultrafaint Dwarf GalaxiesEridanus II (Eri II) is an ultrafaint dwarf (UFD) galaxy (M V = -7.1) located at a distance close to the Milky Way virial radius. Early shallow color-magnitude diagrams (CMDs) indicated that it possibly hosted an intermediate-age or even young stellar population, which is unusual for a galaxy of this mass. In this paper, we present new Hubble SpaceGallart, C. et al.
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32021 -
On the Use of Field RR Lyrae as Galactic Probes. II. A New ΔS Calibration to Estimate Their MetallicityWe performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured ≍6300 high-resolution (HR, R ∼ 35,000) spectra for 143 RRLs (111 fundamental, RRab; 32 first-overtone, RRc). The atmospheric parameters were estimated by using the traditional approach and the iron abundances were measured by using an LTE lineCrestani, J. et al.
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22021 -
The bursty star formation history of the Fornax dwarf spheroidal galaxy revealed with the HSTWe present a new derivation of the star formation history (SFH) of the dSph galaxy Fornax in two central regions, characterized by unprecedented precision and age resolution. It reveals that star formation has proceeded in sharp bursts separated by periods of low level or quiescent activity. The SFH was derived through colour-magnitude diagram (CMDRusakov, V. et al.
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32021 -
The Second Data Release of the Survey of the MAgellanic Stellar History (SMASH)The Large and Small Magellanic Clouds (LMC and SMC) are the largest satellite galaxies of the Milky Way and close enough to allow for a detailed exploration of their structure and formation history. The Survey of the MAgellanic Stellar History (SMASH) is a community Dark Energy Camera (DECam) survey of the Magellanic Clouds using ∼50 nights toNidever, David L. et al.
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22021 -
Solo dwarfs - III. Exploring the orbital origins of isolated Local Group galaxies with Gaia Data Release 2We measure systemic proper motions for distant dwarf galaxies in the Local Group and investigate if these isolated galaxies have ever had an interaction with the Milky Way or M31. We cross-match photometry of isolated, star-forming, dwarf galaxies in the Local Group, taken as part of the Solo survey, with astrometric measurements from Gaia DataMcConnachie, Alan W. et al.
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22021 -
Dissecting the stellar content of Leo I: a dwarf irregular caught in transitionLeo I is considered one of the youngest dwarf spheroidals (dSph) in the Local Group. Its isolation, extended star formation history (SFH), and recent perigalacticon passage (∼1 Gyr ago) make Leo I one of the most interesting nearby stellar systems. Here, we analyse deep photometric Hubble Space Telescope data via colour-magnitude diagram fittingRuiz-Lara, T. et al.
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32021 -
Joint gas and stellar dynamical models of WLM: an isolated dwarf galaxy within a cored, prolate DM haloWe present multitracer dynamical models of the low-mass (M * ∼ 10 7), isolated dwarf irregular galaxy WLM in order to simultaneously constrain the inner slope of the dark matter (DM) halo density profile (γ) and flattening (q DM), and the stellar orbital anisotropy (β z, β r). For the first time, we show how jointly constraining the massLeung, Gigi Y. C. et al.
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12021 -
TOI-519 b: A short-period substellar object around an M dwarf validated using multicolour photometry and phase curve analysisContext. We report the discovery of TOI-519 b (TIC 218795833), a transiting substellar object (R = 1.07 R Jup) orbiting a faint M dwarf (V = 17.35) on a 1.26 d orbit. Brown dwarfs and massive planets orbiting M dwarfs on short-period orbits are rare, but more have already been discovered than expected from planet formation models. TOI-519 is aParviainen, H. et al.
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12021 -
Separation between RR Lyrae and type II Cepheids and their importance for a distance determination: the case of omega CenThe separation between RR Lyrae (RRLs) and type II Cepheid (T2Cs) variables based on their period is debated. Both types of variable stars are distance indicators, and we aim to promote the use of T2Cs as distance indicators in synergy with RRLs. We adopted new and existing optical and near-infrared (NIR) photometry of ω Cen to investigate severalBraga, V. F. et al.
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122020 -
Evolutionary and pulsation properties of Type II CepheidsWe discuss the observed pulsation properties of Type II Cepheids (TIICs) in the Galaxy and in the Magellanic Clouds. We found that period (P) distributions, luminosity amplitudes, and population ratios of the three different sub-groups (BL Herculis [BLH, P < 5 days], W Virginis [WV, 5 ≤ P < 20 days], RV Tauri [RVT, P > 20 days]) are quite similarBono, G. et al.
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122020 -
Homogeneity in the early chemical evolution of the Sextans dwarf spheroidal galaxyWe present the high-resolution spectroscopic analysis of two new extremely metal-poor star (EMPS) candidates in the dwarf spheroidal galaxy Sextans. These targets were preselected from medium-resolution spectra centered around the Ca II triplet in the near-infrared and were followed-up at higher resolution with VLT/UVES. We confirm their lowLucchesi, R. et al.
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122020
