Search

In this work a search was carried out for globular clusters belonging to the Sagittarius (Sgr) tidal stream using the analysis of spatial positions, radial velocities relative to the Galactic Standard of Rest (V_{GSR}),proper motions and ratio of "age -- metallicity" ([Fe/H]) for globular clusters and for stars in the tidal stream. As a result, three categories of globular clusters were obtained: A -- most certainly in the stream: Terzan 8, Whiting 1, Arp 2, NGC 6715, Terzan 7, Pal 12; B -- kinematic outliers: Pal 5, NGC 5904, NGC 5024, NGC 5053, NGC 5272, NGC 288; C -- lowest rank candidates: NGC 6864, NGC 5466, NGC 5897, NGC 7492, NGC 4147.

Dwarf galaxies are dark matter-dominated and therefore promising targets for the search for weakly interacting massive particles (WIMPs), which are well-known candidates for dark matter. Annihilation of WIMPs produce ultra-relativistic cosmic-ray electrons and positrons that emit synchrotron radiation in the presence of magnetic fields. For typical magnetic field strengths (few $\mu $G) and $\mathcal O$(GeV--TeV) WIMP masses, this emission peaks at hundreds of MHz. Here, we use the non-detection of 150-MHz radio continuum emission from the dwarf spheroidal galaxy Canes Venatici I with the LOw-Frequency ARray (LOFAR) to derive constraints on the annihilation cross section of WIMPs into primary electron-positron and other fundamental particle-antiparticle pairs. Our main underlying assumption is that the transport of the cosmic rays can be described by the diffusion approximation, thus requiring a non-zero magnetic field strength with small-scale structure. In particular, by adopting magnetic field strengths of $\mathcal O(1\,\mu$G) and diffusion coefficients $\sim 10^{27}~\rm cm^2\,s^{-1}$, we obtain limits that are comparable with those set by \emph{Fermi} Large Area Telescope using gamma-ray observations of this particular galaxy. Assuming s-wave annihilation and WIMPs making up 100 per cent of the DM density, our benchmark limits exclude several thermal WIMP realisations in the $[2,20]$-GeV mass range. We caution, however, that our limits for the cross section are subject to enormous uncertainties which we also quantitatively assess. In particular, variations on the propagation parameters or on the DM halo can shift our limits up by several orders of magnitude (in the pessimistic scenario)., Comment: 11 pages, 12 figures. Matches published version

We obtain distances to a sample of RR Lyrae in the central core of the Sagittarius dwarf spheroidal galaxy from OGLE data. We use these distances, along with RR Lyrae from Gaia DR2, to measure the shape of the stellar distribution within the central ∼2 kpc. The best-fitting stellar distribution is triaxial, with axis ratios 1 : 0.76 : 0.43. A prolate-spheroid model is ruled out at high statistical significance relative to the triaxial model. The major axis is aligned nearly parallel to the sky plane as seen by an Earth-based observer and is nearly perpendicular to the direction of the Galactic Centre. This result may be compared to cosmological simulations which generally predict that the major axis of the dark matter distribution of subhalos is aligned with the Galactic Centre. The triaxial structure that we obtain can provide important constraints on the Sagittarius progenitor, as well as the central dark matter distribution under the assumption of dynamical equilibrium.

We present an analysis of Murchison Widefield Array radio telescope data from $\omega$ Cen, possibly a stripped dwarf spheroidal galaxy core captured by our Galaxy. Recent interpretations of Fermi-LAT $\gamma$-ray data by Brown {\it et al.} (2019) and Reynoso-Cordova {\it et al.} (2019) suggest that $\omega$ Cen may contain significant Dark Matter. We utilise their best-fit Dark Matter annihilation models, and an estimate of the magnetic field strength in $\omega$ Cen, to calculate the expected radio synchrotron signal from annihilation, and show that one can usefully rule out significant parts of the magnetic field - diffusion coefficient plane using our current observational limits on the radio emission. Improvement by a factor of 10-100 on these limits could constrain the models even more tightly., Comment: Accepted in Physics of the Dark Universe, 7 pages, 4 figures, 1 table

The dark matter (DM) content of the Fornax dwarf spheroidal galaxy inferred from its kinematics is substantially lower than expected from LCDM cosmological simulations. We use N-body simulations to examine whether this may be the result of Galactic tides. We find that, despite improved proper motions from the Gaia mission, the pericentric distance of Fornax remains poorly constrained, mainly because its largest velocity component is roughly anti-parallel to the solar motion. Translating Fornax's proper motion into a Galactocentric velocity is thus sensitively dependent on Fornax's assumed distance: the observed distance uncertainty, $\pm 8\%$, implies pericentric distances that vary between $r_{\rm peri}\sim 50$ and $r_{\rm peri}\sim 150$ kpc. Our simulations show that for $r_{\rm peri}$ in the lower range of that estimate, a LCDM subhalo with maximum circular velocity $V_{\rm max}=40$ km s$^{-1}$ (or virial mass $M_{200}\approx 10^{10} M_\odot$, as expected from LCDM) would be tidally stripped to $V_{\rm max} \sim 23$ km s$^{-1}$ over $10$ Gyr. This would reduce the DM mass within the Fornax stellar half-mass radius to about half its initial value, bringing it into agreement with observations. Tidal stripping affects mainly Fornax's DM halo; its stellar component is affected little, losing less than $5\%$ of its initial mass in the process. We also explore the effect of Galactic tides on the dynamical friction decay times of Fornax's population of globular clusters (GC) and find little evidence for substantial changes, compared with models run in isolation. A population of GCs with initial orbital radii between $1$ and $2$ kpc is consistent with the present-day spatial distribution of Fornax GCs, despite assuming a cuspy halo. Neither the DM content nor the spatial distribution of GCs seem inconsistent with a simple model where Fornax inhabits a tidally-stripped cuspy cold DM halo., Comment: 10 pages, 8 figures, 4 tables. Accepted for publication in MNRAS

Full list of authors: Gilmore, G.; Randich, S.; Worley, C. C.; Hourihane, A.; Gonneau, A.; Sacco, G. G.; Lewis, J. R.; Magrini, L.; Francois, P.; Jeffries, R. D.; Koposov, S. E.; Bragaglia, A.; Alfaro, E. J.; Allende Prieto, C.; Blomme, R.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Recio-Blanco, A.; Smiljanic, R.; Van Eck, S.; Zwitter, T.; Bensby, T.; Flaccomio, E.; Irwin, M. J.; Franciosini, E.; Morbidelli, L.; Damiani, F.; Bonito, R.; Friel, E. D.; Vink, J. S.; Prisinzano, L.; Abbas, U.; Hatzidimitriou, D.; Held, E., V; Jordi, C.; Paunzen, E.; Spagna, A.; Jackson, R. J.; Maiz Apellaniz, J.; Asplund, M.; Bonifacio, P.; Feltzing, S.; Binney, J.; Drew, J.; Ferguson, A. M. N.; Micela, G.; Negueruela, I; Prusti, T.; Rix, H-W; Vallenari, A.; Bergemann, M.; Casey, A. R.; de Laverny, P.; Frasca, A.; Hill, V; Lind, K.; Sbordone, L.; Sousa, S. G.; Adibekyan, V; Caffau, E.; Daflon, S.; Feuillet, D. K.; Gebran, M.; Gonzalez Hernandez, J., I; Guiglion, G.; Herrero, A.; Lobel, A.; Montes, D.; Morel, T.; Ruchti, G.; Soubiran, C.; Tabernero, H. M.; Tautvaisiene, G.; Traven, G.; Valentini, M.; Van der Swaelmen, M.; Villanova, S.; Vazquez, C. Viscasillas; Bayo, A.; Biazzo, K.; Carraro, G.; Edvardsson, B.; Heiter, U.; Jofre, P.; Marconi, G.; Martayan, C.; Masseron, T.; Monaco, L.; Walton, N. A.; Zaggia, S.; Borsen-Koch, V. Aguirre; Alves, J.; Balaguer-Nunez, L.; Barklem, P. S.; Barrado, D.; Bellazzini, M.; Berlanas, S. R.; Binks, A. S.; Bressan, A.; Capuzzo-Dolcetta, R.; Casagrande, L.; Casamiquela, L.; Collins, R. S.; D'Orazi, V; Dantas, M. L. L.; Debattista, V. P.; Delgado-Mena, E.; Di Marcantonio, P.; Drazdauskas, A.; Evans, N. W.; Famaey, B.; Franchini, M.; Fremat, Y.; Fu, X.; Geisler, D.; Gerhard, O.; Solares, E. A. Gonzalez; Grebel, E. K.; Gutierrez Albarran, M. L.; Jimenez-Esteban, F.; Jonsson, H.; Khachaturyants, T.; Kordopatis, G.; Kos, J.; Lagarde, N.; Ludwig, H-G; Mahy, L.; Mapelli, M.; Marfil, E.; Martell, S. L.; Messina, S.; Miglio, A.; Minchev, I; Moitinho, A.; Montalban, J.; Monteiro, M. J. P. F. G.; Morossi, C.; Mowlavi, N.; Mucciarelli, A.; Murphy, D. N. A.; Nardetto, N.; Ortolani, S.; Paletou, F.; Palous, J.; Pickering, J. C.; Quirrenbach, A.; Fiorentin, P. Re; Read, J., I; Romano, D.; Ryde, N.; Sanna, N.; Santos, W.; Seabroke, G. M.; Spina, L.; Steinmetz, M.; Stonkute, E.; Sutorius, E.; Thevenin, F.; Tosi, M.; Tsantaki, M.; Wright, N.; Wyse, R. F. G.; Zoccali, M.; Zorec, J.; Zucker, D. B.-- This is an Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., Context. The Gaia-ESO Public Spectroscopic Survey is an ambitious project designed to obtain astrophysical parameters and elemental abundances for 100 000 stars, including large representative samples of the stellar populations in the Galaxy, and a well-defined sample of 60 (plus 20 archive) open clusters. We provide internally consistent results calibrated on benchmark stars and star clusters, extending across a very wide range of abundances and ages. This provides a legacy data set of intrinsic value, and equally a large wide-ranging dataset that is of value for the homogenisation of other and future stellar surveys and Gaia's astrophysical parameters. Aims. This article provides an overview of the survey methodology, the scientific aims, and the implementation, including a description of the data processing for the GIRAFFE spectra. A companion paper introduces the survey results. Methods. Gaia-ESO aspires to quantify both random and systematic contributions to measurement uncertainties. Thus, all available spectroscopic analysis techniques are utilised, each spectrum being analysed by up to several different analysis pipelines, with considerable effort being made to homogenise and calibrate the resulting parameters. We describe here the sequence of activities up to delivery of processed data products to the ESO Science Archive Facility for open use. Results. The Gaia-ESO Survey obtained 202 000 spectra of 115 000 stars using 340 allocated VLT nights between December 2011 and January 2018 from GIRAFFE and UVES. © G. Gilmore et al. 2022. Conclusions. The full consistently reduced final data set of spectra was released through the ESO Science Archive Facility in late 2020, with the full astrophysical parameters sets following in 2022. A companion article reviews the survey implementation, scientific highlights, the open cluster survey, and data products., Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. Public access to the data products is via the ESO SAF, and the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell’ Istruzione, dell’ Università’ e della Ricerca (MIUR) in the form of the grant “Premiale VLT 2012”. The project presented here benefited in development from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. R.S. acknowledges support from the National Science Centre, Poland (2014/15/B/ST9/03981). This work was partly supported by the INAF grant for mainstream projects: “Enhancing the legacy of the Gaia-ESO Survey for open cluster science”. F.J.E. acknowledges financial support from the Spanish MINECO/FEDER through the grant AYA2017-84089 and MDM-2017-0737 at Centro de Astrobiología (CSIC-INTA), Unidad de Excelencia María de Maeztu, and from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement no. 824064 through the ESCAPE – the European Science Cluster of Astronomy and Particle Physics ESFRI Research Infrastructures project. T.B. was funded by the “The New Milky Way” project grant from the Knut and Alice Wallenberg Foundation. S.R.B. acknowledges support by the Spanish Government under grants AYA2015-68012-C2-2-P and PGC2018-093741-B-C21/C22 (MICIU/AEI/FEDER, UE). W.J.S. acknowledges CAPES for a PhD studentship. J.M.A. acknowledges support from the Spanish Government Ministerio de Ciencia e Innovación through grants AYA2013-40611-P, AYA2016-75931-C2-2-P, and PGC2018-095049-B-C22. T.M. and others from STAR institute, Liege, Belgium are grateful to Belgian F.R.S.-FNRS for support, and are also indebted for an ESA/PRODEX Belspo contract related to the Gaia Data Processing and Analysis Consortium and for support through an ARC grant for Concerted Research Actions financed by the Federation Wallonie-Brussels.. This research has been partially supported by the following grants: MIUR Premiale “Gaia-ESO survey” (PI S. Randich), MIUR Premiale “MiTiC: Mining the Cosmos” (PI B. Garilli), the ASI-INAF contract 2014-049-R.O: “Realizzazione attività tecniche/scientifiche presso ASDC” (PI Angelo Antonelli), Fondazione Cassa di Risparmio di Firenze, progetto: “Know the star, know the planet” (PI E. Pancino), and Progetto Main Stream INAF: “Chemo-dynamics of globular clusters: the Gaia revolution” (PI E. Pancino). V.A. acknowledges the support from Fundação para a Ciência e Tecnologia (FCT) through Investigador FCT contract nr. IF/00650/2015/CP1273/CT0001. A.J.K. acknowledges support by the Swedish National Space Agency (SNSA). A.B. acknowledges support by ANID, – Millennium Science Initiative Program – NCN19_171, and FONDECYT regular 1190748. E.M. acknowledges financial support from the Spanish State Research Agency (AEI) through project MDM-2017-0737 Unidad de Excelencia “María de Maeztu” – Centro de Astrobiología (CSIC-INTA). T.Z. acknowledges financial support of the Slovenian Research Agency (research core funding no. P1-0188) and the European Space Agency (Prodex Experiment Arrangement No. C4000127986). P.J. acknowledges support FONDECYT Regular 1200703. The work of I.N. is partially supported by the Spanish Government Ministerio de Ciencia, Innovación y Universidades under grant PGC2018-093741-B-C21 (MICIU/AEI/FEDER, UE). Funding for this work has been provided by the ARC Future Fellowship FT160100402. C.A.P. acknowledges financial support from the Spanish Government through research grants MINECO AYA 2014-56359-P, MINECO AYA2017-86389-P, and MICINN PID2020-117493GB-I00. S.F. was supported by the grants 2011-5042 and 2016-03412 from the Swedish Research Council and the project grant “The New Milky Way” from the Knut and Alice Wallenberg Foundation. C.A.S.U. is supported through STFC grants: ST/H004157/1, ST/J00541X/1, ST/M007626/1, ST/N005805/1, ST/T003081/1. Work reported here benefited from support through the GREAT-ITN FP7 project Grant agreement ID: 264895. D.K.F. acknowledges funds from the Alexander von Humboldt Foundation in the framework of the Sofja Kovalevskaja Award endowed by the Federal Ministry of Education and Research and the grant 2016-03412 from the Swedish Research Council. A.H. acknowledges support from the Spanish Government Ministerio de Ciencia e Innovación and ERD Funds through grants PGC-2018-091 3741-B-C22 and CEX2019-000920-S. X.F. acknowledges the support of China Postdoctoral Science Foundation 2020M670023. M.L.L.D. acknowledges the Polish NCN grant number 2019/34/E/ST9/00133. Part of this work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 138713538 – SFB 881 (“The Milky Way System”, subproject A09). M.Z. acknowledges support from the National Agency for Research and Development (ANID) grants: FONDECYT Regular 1191505, Millennium Institute of Astrophysics ICN12-009, BASAL Center for Astrophysics and Associated Technologies AFB-170002. R.B. acknowledges support from the project PRIN-INAF 2019 “Spectroscopically Tracing the Disk Dispersal Evolution”. H.M.T. acknowledges financial support from the Agencia Estatal de Investigación of the Ministerio de Ciencia, Innovación y Universidades through projects PID2019-109522GB-C51,54/AEI/10.13039/501100011033, and the Centre of Excellence “María de Maeztu” award to Centro de Astrobiología (MDM-2017-0737). J.I.G.H. acknowledges financial support from the Spanish Ministry of Science and Innovation (MICINN) project AYA2017-86389-P, and also from the Spanish MICINN under 2013 Ramѳn y Cajal program RYC-2013-14875. V.P.D. is supported by STFC Consolidated grant ST/R000786/1. N.L. acknowledges financial support from “Programme National de Physique Stellaire” (PNPS) and the “Programme National Cosmology et Galaxies (PNCG)” of CNRS/INSU, France. A.R.C. is supported in part by the Australian Research Council through a Discovery Early Career Researcher Award (DE190100656). Parts of this research were supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. P.S.B. is supported by the Swedish Research Council through individual project grants with contract Nos. 2016-03765 and 2020-03404. A.M. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 772293 – project ASTEROCHRONOMETRY). J.P. was supported by the project RVO: 67985815. E.D.M. acknowledges the support from FCT through the research grants UIDB/04434/2020 & UIDP/04434/2020 and through Investigador FCT contract IF/00849/2015/CP1273/CT0003. This work was (partially) supported by the Spanish Ministry of Science, Innovation and University (MICIU/FEDER, UE) through grant RTI2018-095076-B-C21, and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia 'María de Maeztu’) through grant CEX2019-000918-M. S.L.M. acknowledges the support of the UNSW Scientia Fellowship program and the Australian Research Council through Discovery Project grant DP180101791. GT acknowledges financial support of the Slovenian Research Agency (research core funding No. P1-0188) and the European Space Agency (Prodex Experiment Arrangement No. C4000127986). S.G.S acknowledges the support from FCT through Investigador FCT contract nr. CEECIND/00826/2018 and POPH/FSE (EC). H.G.L. acknowledges financial support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 138713538 – SFB 881 (“The Milky Way System”, subproject A04). This work was (partially) supported by the Spanish Ministry of Science, Innovation and University (MICIU/FEDER, UE) through grant RTI2018-095076-B-C21, and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia ’María de Maeztu’) through grant CEX2019-000918-M. T.K. is supported by STFC Consolidated grant ST/R000786/1. M.V. acknowledges the support of the Deutsche Forschungsgemeinschaft (DFG, project number: 428473034). T.M. is supported by a grant from the Fondation ULB. We acknowledge financial support from the Universidad Complutense de Madrid (UCM) and by the Spanish Ministerio de Ciencia, Innovación y Universidades, Ministerio de Economía y Competitividad, from project AYA2016-79425-C3-1-P and PID2019-109522GB-C5[4]/AEI/10.13039/501100011033. U.H. acknowledges support from the Swedish National Space Agency (SNSA/Rymdstyrelsen). D.G. gratefully acknowledges support from the Chilean Centro de Excelencia en Astrofísica y Tecnologías Afines (CATA) BASAL grant AFB-170002. D.G. also acknowledges financial support from the Dirección de Investigación y Desarrollo de la Universidad de La Serena through the Programa de Incentivo a la Investigación de Académicos (PIA-DIDULS). A. Lobel acknowledges support in part by the Belgian Federal Science Policy Office under contract No. BR/143/A2/BRASS. We acknowledge financial support from the Universidad Complutense de Madrid (UCM) and by the Spanish Ministerio de Ciencia, Innovación y Universidades, Ministerio de Economía y Competitividad, from project AYA2016-79425-C3-1-P and PID2019-109522GB-C5[4]/AEI/10.13039/501100011033. A.M. acknowledges the support from the Portuguese Fundação para a Ciência e a Tecnologia (FCT) through the Portuguese Strategic Programme UID/FIS/00099/2019 for CENTRA. T.M. acknowledges financial support from the Spanish Ministry of Science and Innovation (MICINN) through the Spanish State Research Agency, under the Severo Ochoa Program 2020-2023 (CEX2019-000920-S). E.J.A. acknowledges funding from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de An- dalucía (SEV-2017-0709).

The Fermi Bubbles are giant, γ-ray emitting lobes emanating from the nucleus of the Milky Way [1, 2] discovered in ∼1-100 GeV data collected by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope [3]. Previous work [4] has revealed substructure within the Fermi Bubbles that has been interpreted as a signature of collimated outflows from the Galaxy’s super-massive black hole. Here we show that much of the γ-ray emission associated to the brightest region of substructure – the so-called cocoon – is actually due to the Sagittarius dwarf spheroidal (Sgr dSph) galaxy. This large Milky Way satellite is viewed through the Fermi Bubbles from the position of the Solar System. As a tidally and ram-pressure stripped remnant, the Sgr dSph has no on-going star formation, but we demonstrate that its γ-ray signal is naturally explained by inverse Compton scattering of cosmic microwave back-ground photons by high-energy electron-positron pairs injected by the dwarf’s millisecond pulsar (MSP) population, combined with these objects’ magnetospheric emission. This finding suggests that MSPs likely produce significant γ-ray emission amongst old stellar populations, potentially confounding indirect dark matter searches in regions such as the Galactic Centre, the Andromeda galaxy, and other massive Milky Way dwarf spheroidals.

Globular clusters (GCs) are important tools to rebuild the accretion history of a galaxy. There are newly discovered GCs in the Sagittarius (Sgr) dwarf galaxy, that can be used as probes of the accretion event onto the Milky Way (MW). Our main aim is to characterize the Sgr GC system by measuring its main physical parameters. We build the optical and near-IR color-magnitude diagrams (CMDs) for 21 new Sgr GCs using the VISTA Variables in the Via Lactea Extended Survey (VVVX) near-IR database combined with the Gaia EDR3 optical database. We derive metallicities and ages for all targets, using the isochrone-fitting method and the RGB-slope and metallicity relation. The total luminosities are calculated both in the near-IR and in the optical. We construct the metallicity distribution (MD), the globular cluster luminosity function (GCLF), and the age-metallicity relation for the Sgr GC system. We find 17 metal-rich GCs with -0.9, Comment: 18 pages, 9 figures, accepted for publication in Astronomy & Astrophysics

The gas evolution of a typical Dwarf Spheroidal Galaxy is investigated by means of 3D hydrodynamic simulations, taking into account the feedback of type II and Ia supernovae, the outflow of an Intermediate Massive Black Hole (IMBH) and a static cored dark matter potential. When the IMBH’s outflow is simulated in an homogeneous medium a jet structure is created and a small fraction of the gas is pushed away from the galaxy. No jet structure can be seen, however, when the medium is disturbed by supernovae, but gas is still pushed away. In this case, the main driver of the gas removal are the supernovae. The interplay between the stellar feedback and the IMBH’s outflow should be taken into account.

Moderate resolution spectra of four globular clusters in the dwarf spheroidal galaxy IKN obtained with the 6-m telescope of the Special Astrophysical Observatory have been used to determine the radial velocities, ages, and metallicities of the clusters, and also to derive the first approximate estimates of the abundances of Mg, Ca, and C. Cross-correlation with radial-velocity standards, fitting of the observed spectra with model spectra, diagnostic diagrams based on the Lick absorption indices, and comparison of the spectra and absorption indices with those of Galactic globular clusters are applied. The integrated spectrum of the two bright clusters IKN4 and IKN5, which are close to the center of the galaxy in projection on the celestial sphere, yields the heliocentric radial velocity Vh = 38 ± 30 km/s, age T =12.6 ± 2 Gyr, metallicity [Fe/H] = −2.1 ± 0.2 dex, and abundance of α-process elements [α/Fe] ∼ 0.5 dex. The integrated spectrum of the two weaker clusters IKN1 and IKN3, which are far from the center of the galaxy, yielded the radial velocity Vh = −39 ± 50 km/s. Despite the low signal-to-noise ratio in the integrated spectrum for IKN1 and IKN3, all the analysis methods applied indicate that these two objects have approximately the same age and metallicity as IKN4 and IKN5. According to the measured Lick indices $${{\rm{H}}_{\delta {\rm{F}}}}$$ and Hβ, the studied globular clusters in IKN have blue horizontal branches.

Dwarf spheroidal galaxies (dSphs) appear to be some of the most dark matter 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 tidal fields. We investigate the implication of the assumption of equilibrium focusing on the Sculptor dSph by means of ad-hoc $N$-body simulations tuned to reproduce the observed properties of Sculptor following the evolution along some observationally motivated orbits in the Milky Way gravitational field. For this purpose, we used state-of-the-art spectroscopic and photometric samples of Sculptor's stars. We found that the stellar component of the simulated object is not directly influenced by the tidal field, while $\approx 30\%-60\%$ the mass of the more diffuse DM halo is stripped. We conclude that, considering the most recent estimate of the Sculptor proper motion, the system is not affected by the tides and the stellar kinematics represents a robust tracer of the internal dynamics. In the simulations that match the observed properties of Sculptor, the present-day dark-to-luminous mass ratio is $\approx 6$ within the stellar half-light radius ($\approx0.3$ kpc) and $>50$ within the maximum radius of the analysed dataset ($\approx1.5^\circ\approx2$ kpc)., 19 pages, 10 figures, accepted for publication in MNRAS. V3: updated after editor comments See our playlist for simulation videos: https://av.tib.eu/series/633/supplemental+videos+of+the+paper+the+effect+of+tides+on+the+sculptor+dwarf+spheroidal+galaxy

Looking for variable stars in the M31 dwarf spheroidal satellite Andromeda XXV (And XXV), which we have observed with the LBC at the LBT, we serendipitously discovered a clustering of stars (Gep I) of 12 arcsec in diameter, near the center of And XXV. This is one of the very few clusters known to be associated with a dwarf spheroidal galaxy. The half light radius (rh) of Gep I at the distance of And XXV corresponds to 25 pc in linear extension. Radius and absolute V (MV∼ −4.9 mag) magnitude place Gep I in the region of the MV-rh plane that seems to be forbidden to ordinary globular clusters (GCs). The seeing-limited resolution of our photometry could resolve only a few bright stars in Gep I. The CMD of these sources is compatible with an old stellar population placed at a heliocentric distance of ∼750–800 kpc, thus confirming a real concentration of old stars. The ground-based CMD of Gep I is severely incomplete. Future high resolution imaging and spectroscopy of the brightest stars will permit to disentangle the puzzle on the real nature of Gep I.

Nuclear star clusters hosted by dwarf galaxies exhibit similar characteristics to high-mass, metal complex globular clusters. This type of globular clusters could, therefore, be former nuclei from accreted galaxies. M54 resides in the photometric center of the Sagittarius dwarf galaxy, at a distance where resolving stars is possible. M54 offers the opportunity to study a nucleus before the stripping of their host by the tidal field effects of the Milky Way. We use a MUSE data set to perform a detailed analysis of over 6600 stars. We characterize the stars by metallicity, age, and kinematics, identifying the presence of three stellar populations: a young metal-rich (YMR), an intermediate-age metal-rich (IMR), and an old metal-poor (OMP). The evidence suggests that the OMP population is the result of accretion of globular clusters in the center of the host, while the YMR population was born in-situ in the center of the OMP population.

In hidden sector models, dark matter does not directly couple to the particle content of the Standard Model, strongly suppressing rates at direct detection experiments, while still allowing for large signals from annihilation. In this paper, we conduct an extensive study of hidden sector dark matter, covering a wide range of dark matter spins, mediator spins, interaction diagrams, and annihilation final states, in each case determining whether the annihilations are s-wave (thus enabling efficient annihilation in the universe today). We then go on to consider a variety of portal interactions that allow the hidden sector annihilation products to decay into the Standard Model. We broadly classify constraints from relic density requirements and dwarf spheroidal galaxy observations. In the scenario that the hidden sector was in equilibrium with the Standard Model in the early universe, we place a lower bound on the portal coupling, as well as on the dark matter's elastic scattering cross section with nuclei. We apply our hidden sector results to the observed Galactic Center gamma-ray excess and the cosmic-ray antiproton excess. We find that both of these excesses can be simultaneously explained by a variety of hidden sector models, without any tension with constraints from observations of dwarf spheroidal galaxies., Comment: 40 pages, 11 figures, matches the JHEP version, references added

The aim of the present work is to better understand the gravitational drag forces, i.e. dynamical friction, acting on massive objects moving through a self-interacting Bose-Einstein condensate, also known as a superfluid, at finite temperatures. This is relevant for light scalar models of dark matter with weak self-interactions that require nonzero temperatures, or that have been heated inside galaxies. We derived expressions for dynamical friction using linear perturbation theory, and compared these to numerical simulations in which nonlinear effects are included. After testing the linear result, it was applied to the Fornax dwarf spheroidal galaxy, and two of its gravitationally bound globular clusters. Dwarf spheroidals are well-suited for indirectly probing properties of dark matter, and so by estimating the rate at which these globular clusters are expected to sink into their host halo due to dynamical friction, we inferred limits on the superfluid dark matter parameter space. The dynamical friction in a finite-temperature superfluid is found to behave very similarly to the zero-temperature limit, even when the thermal contributions are large. However, when a critical velocity for the superfluid flow is included, the friction force can transition from the zero-temperature value to the value in a conventional fluid. Increasing the mass of the perturbing object induces a similar transition to when lowering the critical velocity. When applied to two of Fornax's globular clusters, we find that the parameter space preferred in the literature for a zero-temperature superfluid yields decay times that are in agreement with observations. However, the present work suggests that increasing the temperature, which is expected to change the preferred parameter space, may lead to very small decay times, and therefore pose a problem for finite-temperature superfluid models of dark matter., Comment: 16 pages, 8 figures, 3 tables. Accepted for publication in A&A

We discuss a theoretical model for the early evolution of massive star clusters and confront it with the ALMA, radio and infrared observations of the young stellar cluster highly obscured by the molecular cloud D1 in the nearby dwarf spheroidal galaxy NGC 5253. We show that a large turbulent pressure in the central zones of D1 cluster may cause individual wind-blown bubbles to reach pressure confinement before encountering their neighbors. In this case stellar winds are added to the hot shocked wind pockets of gas around individual massive stars that leads them to meet and produce a cluster wind in time-scales less than $10^5$ yrs. In order to inhibit the possibility of cloud dispersal, or the early negative star formation feedback, one should account for mass loading that may come, for example, from pre-main sequence (PMS) low-mass stars through photo-evaporation of their proto-stellar disks. Mass loading at a rate in excess of 8$\times 10^{-9}$ M$_{\odot}$ yr$^{-1}$ per each PMS star is required to extend the hidden star cluster phase in this particular cluster. In this regime, the parental cloud remains relatively unperturbed, while pockets of molecular, photoionized and hot gas coexist within the star forming region. Nevertheless, the most likely scenario for cloud D1 and its embedded cluster is that the hot shocked winds around individual massive stars should merge at an age of a few millions of years when the PMS star proto-stellar disks vanish and mass loading ceases that allows a cluster to form a global wind., Comment: 12 pages, 10 figures, accepted for publication in MNRAS

We use MUSE spectroscopic observations of the dwarf spheroidal galaxy Leo T between 470 and 935 nm to search for radiative decays of axion like particles (ALPs). Under the assumption that ALPs constitute the dark matter component of the Leo T halo, we derive bounds on the effective ALP-two-photon coupling. We improve existing limits by more than one order of magnitude in the ALP mass range 2.7-5.3 eV., Comment: 11 pages, 5 figures. v2: minor revision, matching the version to appear in PLB

We present a catalogue of 285 RR Lyrae stars (RRLs) in the Draco dwarf spheroidal galaxy (dSph), obtained by combining data from a number of different surveys including the second data release (DR2) of the European Space Agency (ESA) cornerstone mission Gaia. We have determined individual distances to the RRLs in our sample using for the first time a Gaia G-band luminosity-metallicity relation (MG - [Fe/H]) and study the structure of the Draco dSph as traced by its RRL population. We find that the RRLs located in the western/south-western region of Draco appear to be closer to us, which may be a clue of interaction between Draco and the Milky Way (MW). The average distance modulus of Draco measured with the RRLs is 19.53 +/- 0.07 mag, corresponding to a distance of 80.5 +/- 2.6 kpc, in good agreement with previous determinations in the literature. Based on the pulsation properties of the RRLs we confirm the Oosterhoff-intermediate nature of Draco. We present an additional sample of 41 candidate RRLs in Draco, which we selected from the Gaia DR2 catalogue based on the uncertainty of their G-band magnitudes. Additional epoch data that will become available in the Gaia third data release (DR3) will help to confirm whether these candidates are bona-fide Draco RRLs., Comment: 15 pages, 14 figures, 5 tables. Accepted for publication in MNRAS

Fornax 4 is the most distinctive globular cluster in the Fornax dwarf spheroidal. Located close to the centre of the galaxy, more metal-rich and potentially younger than its four companions (namely, Fornax clusters number 1, 2, 3 and 5), it has been suggested to have experienced a different formation than the other clusters in the galaxy. Here we use HST/WFC3 photometry to characterize the stellar population content of this system and shed new light on its nature. By means of a detailed comparison of synthetic horizontal branch and red giant branch with the observed colour-magnitude diagrams, we find that this system likely hosts stellar sub-populations characterized by a significant iron spread up to $\Delta$[Fe/H]$\sim$0.4 dex and possibly by also some degree of He abundance variations $\Delta$Y$\sim0.03$. We argue that this purely observational evidence, combined with the other peculiarities characterizing this system, supports the possibility that Fornax 4 is the nuclear star cluster of the Fornax dwarf spheroidal galaxy. A spectroscopic follow-up for a large number of resolved member stars is needed to confirm this interesting result and to study in detail the formation and early evolution of this system and more in general the process of galaxy nucleation., Comment: Accepted for publication in MNRAS. 12 pages, 11 figures

The velocity distributions of stellar tracers in general exhibit weak non-Gaussianity encoding information on the orbital composition of a galaxy and the underlying potential. The standard solution for measuring non-Gaussianity involves constructing a series expansion (e.g. the Gauss-Hermite series) which can produce regions of negative probability density. This is a significant issue for the modelling of discrete data with heteroskedastic uncertainties. Here, we introduce a method to construct positive-definite probability distributions by the convolution of a given kernel with a Gaussian distribution. Further convolutions by observational uncertainties are trivial. The statistics (moments and cumulants) of the resulting distributions are governed by the kernel distribution. Two kernels (uniform and Laplace) offer simple drop-in replacements for a Gauss-Hermite series for negative and positive excess kurtosis distributions with the option of skewness. We demonstrate the power of our method by an application to real and mock line-of-sight velocity datasets on dwarf spheroidal galaxies, where kurtosis is indicative of orbital anisotropy and hence a route to breaking the mass-anisotropy degeneracy for the identification of cusped versus cored dark matter profiles. Data on the Fornax dwarf spheroidal galaxy indicate positive excess kurtosis and hence favour a cored dark matter profile. Although designed for discrete data, the analytic Fourier transforms of the new models also make them appropriate for spectral fitting, which could improve the fits of high quality data by avoiding unphysical negative wings in the line-of-sight velocity distribution., Comment: 21 pages, 12 figures, accepted for publication in MNRAS, slight adjustment of parameterization to match normalized definition of Gauss-Hermite coefficients (results unchanged)

A new family of self-consistent DF-based models of stellar systems is explored. The stellar component of the models is described by a distribution function (DF) depending on the action integrals, previously used to model the Fornax dwarf spheroidal galaxy (dSph). The stellar component may cohabit with either a dark halo, also described by a DF, or with a massive central black hole. In all cases we solve for the model's self-consistent potential. Focussing on spherically symmetric models, we show how the stellar observables vary with the anisotropy prescribed by the DF, with the dominance and nature of the dark halo, and with the mass of the black hole. We show that precise fits to the observed surface brightness profiles of four globular clusters can be obtained for a wide range of prescribed velocity anisotropies. We also obtain precise fits to the observed projected densities of four dSphs. Finally, we present a three-component model of the Scupltor dSph with distinct DFs for the red and blue horizontal branch stars and the dark matter halo., submitted to MNRAS

We use a new mass modelling method, GravSphere, to measure the central dark matter density profile of the Draco dwarf spheroidal galaxy. Draco's star formation shut down long ago, making it a prime candidate for hosting a 'pristine' dark matter cusp, unaffected by stellar feedback during galaxy formation. We first test GravSphere on a suite of tidally stripped mock 'Draco'-like dwarfs. We show that we are able to correctly infer the dark matter density profile of both cusped and cored mocks within our 95% confidence intervals. While we obtain only a weak inference on the logarithmic slope of these density profiles, we are able to obtain a robust inference of the amplitude of the inner dark matter density at 150pc, $\rho_{\rm DM}(150\,{\rm pc})$. We show that, combined with constraints on the density profile at larger radii, this is sufficient to distinguish a $\Lambda$ Cold Dark Matter ($\Lambda$CDM) cusp $-$ that has $\rho_{\rm DM}(150\,{\rm pc}) > 1.8 \times 10^8\,{\rm M}_\odot \,{\rm kpc}^{-3}$ $-$ from alternative dark matter models that have lower inner densities. We then apply GravSphere to the real Draco data. We find that Draco has an inner dark matter density of $\rho_{\rm DM}(150\,{\rm pc}) = 2.4_{-0.6}^{+0.5} \times 10^8\,{\rm M}_\odot \,{\rm kpc}^{-3}$, consistent with a $\Lambda$CDM cusp. Using a velocity independent SIDM model, calibrated on $\Lambda$SIDM cosmological simulations, we show that Draco's high central density gives an upper bound on the SIDM cross section of $\sigma/m < 0.57\,{\rm cm}^2\,{\rm g}^{-1}$ at 99% confidence. We conclude that the inner density of nearby dwarf galaxies like Draco provides a new and competitive probe of dark matter models., Comment: 19 pages, 11 Figures. Final version accepted for publication in MNRAS

We present results from a non-cosmological, three-dimensional hydrodynamic simulation of an outflow from an intermediate-mass black hole in Dwarf Spheroidal Galaxies. Assuming an initial baryonic-to-dark-matter ratio derived from the CMB radiation and a cored, static dark matter potential, we evolved the galactic gas distribution over 3 Gyr, taking into account the outflow of a black hole. Our results indicate that in a homogeneous medium the outflow propagates freely in both directions with the same velocity and its capable of removing a fraction of the gas from the galaxy (it depends on the initial conditions of the outflow). When the SNe are taken into account, the effect of the outflow is substantially reduced. It is necessary an initial velocity around 1000 km/s and a density larger than 0.003 particles.cm−3 for the outflow to propagate. In these conditions, the removal of gas from the galaxy is almost negligible at the end of the 3 Gyr of the simulation.

We have identified two channels for the formation of compact dwarf galaxies in the Illustris simulation by reconstructing mass and distance histories of candidates located in the vicinity of the simulation's most massive cluster galaxies. One channel is tidal stripping of Milky Way mass galaxies that form outside of clusters and eventually sink into them, spiraling in toward central massive objects. Second channel of formation is an in-situ formation (in reference to the parent cluster) of dwarf mass galaxies, with negligible evolution and limited change in stellar mass. We find 19 compact dwarf galaxies at the centers of 14 clusters, consistent with observations. 30% of them have external origin while 70% are formed in-situ., Comment: 11 pages, 8 figures. Accepted by MNRAS

The aim of this work is to examine the environmental dependence of K-band luminosity in the Main, Low Redshift (LOWZ), and Constant Mass (CMASS) galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10). Overall, the environmental dependence of K-band luminosity is very mild. In two volume-limited Main samples with the luminosity −20.5 ≤ Mr ≤ −18.5 and −22.5 ≤ Mr ≤ −20.5, respectively, we find that the environmental dependence of K-band luminosity in the luminous volume-limited Main galaxy sample still can be observed, but this dependence in the faint volume-limited Main galaxy sample is very weak. Considering the disadvantages of the use of volume-limited samples, we apply the apparent magnitude-limited Main galaxy sample, divide the Main galaxy sample of the SDSS DR10 into subsamples with a redshift binning size of Δz=0.01, and then analyze the environmental dependence of K-band luminosity of subsamples in each redshift bin. Such a method also is used in the LOWZ and CMASS galaxy samples. K-band luminosity of the Main galaxies shows substantial correlation with the local environment in many redshift bins. In the LOWZ galaxy sample, K-band luminosity of galaxies shows substantial correlation with the local environment only in the redshift region 0.16 ≤ z ≤ 0.21, while K-band luminosity of CMASS galaxy sample is only weakly correlated with the local environment. Statistical results also show that in the apparent magnitude-limited main galaxy sample and the LOWZ galaxy sample, environmental dependence of K-band luminosity becomes weak with increasing redshift.

We present the analysis of medium-resolution spectra obtained at the Southern African Large Telescope (SALT) for nuclear globular clusters (GCs) in two dwarf spheroidal galaxies (dSphs). The galaxies have similar star formation histories, but they are situated in completely different environments. ESO269-66 is a close neighbour of the giant S0 NGC5128. KKs3 is one of the few truly isolated dSphs within 10 Mpc. We estimate the helium abundance $Y=0.3$, $\rm age=12.6\pm1$ Gyr, $[Fe/H]=-1.5,-1.55\pm0.2$ dex, and abundances of C, N, Mg, Ca, Ti, and Cr for the nuclei of ESO269-66 and KKs3. Our surface photometry results using HST images yield the half-light radius of the cluster in KKs3, $\rm r_h=4.8\pm0.2$ pc. We demonstrate the similarities of medium-resolution spectra, ages, chemical compositions, and structure for GCs in ESO269-66 and KKs3 and for several massive Galactic GCs with $[Fe/H]\sim-1.6$ dex. All Galactic GCs posses Extended Blue Horizontal Branches and multiple stellar populations. Five of the selected Galactic objects are iron-complex GCs. Our results indicate that the sample GCs observed now in different environments had similar conditions of their formation $\sim$1 Gyr after the Big Bang., Comment: 14 pages, 8 figures, 10 tables. Table 1 and two references were corrected. Accepted for publication in MNRAS

We studied the nearby edge-on galaxy NGC4656 and its dwarf low surface brightness companion with the enhanced UV brightness, NGC4656UV, belonging to the interacting system NGC4631/56. Regular photometric structure and relatively big size of NGC4656UV allows to consider this dwarf galaxy as a separate group member rather than a tidal dwarf. Spectral long-slit observations were used to obtain the kinematical parameters and gas-phase metallicity of NGC4656UV and NGC4656. Our rough estimate of the total dynamical mass of NGC4656UV allowed us to conclude that this galaxy is the dark-matter dominated LSB dwarf or ultra diffuse galaxy. Young stellar population of NGC4656UV, as well as strong local non-circular gas motions in NGC4656 and the low oxygen gas abundance in the region of this galaxy adjacent to its dwarf companion, give evidence in favour of the accretion of metal-poor gas onto the discs of both galaxies., 8 pages, 2 tables, 9 figures, accepted for publication in MNRAS

We derive the specific baryonic angular momentum of five gas rich dwarf galaxies from HI kinematics complemented by stellar mass profiles. Since the gas mass of these galaxies is much larger than the stellar mass, the angular momentum can be determined with relatively little uncertainty arising from the uncertainties in the stellar mass to light ratio. We compare the relation between the specific baryonic angular momentum (j) and the total baryonic mass (M) for these galaxies with that found for spiral galaxies. Our combined sample explores the j-M plane over 3 orders of magnitude in baryon mass. We find that our sample dwarf have significantly higher specific angular momentum than expected from the relation found for spiral galaxies. The probability that these gas rich dwarf galaxies follow the same relation as spirals is found to be $, 10 Pages, 7 figures. Accepted for publication in MNRAS

Many dwarf galaxies have disproportionately rich globular cluster (GC) systems for their luminosities. Moreover, the GCs tend to be preferentially associated with the most metal-poor stellar populations in their parent galaxies, making them attractive tracers of the halos of dwarf (and larger) galaxies. In this contribution, I briefly discuss some constraints on cluster disruption obtained from studies of metal-poor GCs in dwarf galaxies. I then discuss our recent work on detailed abundance analysis from integrated-light spectroscopy of GCs in Local Group dwarf galaxies.

This work aims to explore the different processes of formation and evolution of dwarf spheroidal galaxies in the Local Group analyzing internal and external feedbacks, taking Leo II as a model of parametrization due to its adequate large distance to the Milky Way, in order to minimize potential external effects. We present a discussion of the first results regarding the processes of formation and galactic evolution from the gas hydrodynamics. Combined with previous studies for other similar systems, such results have the potential to establish strong links for the elaboration of a consistent and coherent scenario of formation and evolution of the dwarf spheroidal galaxies in the Local Group.

In this work, we performed two distinct non-cosmological, three-dimensional hydrodynamic simulations that evolved the gas component of a galaxy similar to the classical dwarf spheroidal galaxy Ursa Minor. Both simulations take into account types II and Ia supernovae feedback constrained by chemical evolution models, while ram-pressure stripping mechanism is added into one of them considering an intergalactic medium and a galactic velocity that resemble what is observed nowadays for the Ursa Minor galaxy. Our results show no difference in the amount of gas left inside the galaxy until 400 Myr of evolution. Moreover, the ram-pressure wind was stalled and inverted by thermal pressure of the interstellar medium and supernovae feedback during the same interval.

As part of a large Hubble Space Telescope investigation aiming at reaching the faintest stars in the Galactic globular cluster NGC 6752, an ACS/WFC field was the subject of deep optical observations reaching magnitudes as faint as V~30. In this field we report the discovery of Bedin I a dwarf spheroidal galaxy too faint and too close to the core of NGC 6752 for detection in earlier surveys. As it is of broad interest to complete the census of galaxies in the local Universe, in this Letter we provide the position of this new object along with preliminary assessments of its main param eters. Assuming the same reddening as for NGC 6752, we estimate a distance modulus of (m-M)_0 = 29.70+/-0.13 from the observed red giant branch, i.e., 8.7 (+0.5 -0.7) Mpc, and size of ~840x340pc, about 1/5 the size of the LMC. A comparison of the observed colour-magnitude diagram with synthetic counterparts that account for the galaxy distance modulus, reddening and photometric errors, suggests the presence of an old (~13Gyr) and metal poor ([Fe/H]~-1.3) population. This object is most likely a relatively isolated satellite dwarf spheroidal galaxy of the nearby great spiral NGC 6744, or potentially the most distant isolated dwarf spheroidal known with a secure distance., Comment: 5 pages, 1 table, 3 figures (2 in low resolution). Published on MNRAS Letters and freely available https://academic.oup.com/mnrasl/article/484/1/L54/5288002 Related press releases: https://media.stsci.edu/news_release/news/2019-09 and https://www.spacetelescope.org/news/heic1903/ , (and only in italian: https://www.youtube.com/watch?v=VZCop_j3KOo )

We present the analysis of the FLAMES dataset targeting the central 25 arcmin region of the Sextans 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 (DART). Our sample is composed of red giant branch stars down to the level of the horizontal branch in Sextans. It allows to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide [Fe/H]=$-$3.2 to $-$1.5 dex range. The abundances of 10 other elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu. Despite its small mass, Sextans is a chemically evolved system, with evidence for the contribution of core-collapse and Type Ia supernovae as well as low metallicity AGBs. This new FLAMES sample offers a sufficiently large number of stars with chemical abundances derived at high accuracy to firmly establish the existence of a plateau in [$\alpha$/Fe] at $\sim 0.4$ dex, followed by a decrease above [Fe/H]$\sim-2$ dex. This is in stark similarity with the Fornax and Sculptor dSphs despite their very different masses and star formation histories. This suggests that these three galaxies had very similar star formation efficiencies in their early formation phases, probably driven by the early accretion of smaller galactic fragments, until the UV-background heating impacted them in different ways. The parallel between the Sculptor and Sextans dSph is also striking when considering Ba and Eu. Finally, as to the iron-peak elements, the decline of [Co/Fe] and [Ni/Fe] above [Fe/H]$\sim -2$ implies that the production yields of Ni and Co in SNeIa is lower than that of Fe. The decrease in [Ni/Fe] favours models of SNeIa based on the explosion of double degenerate sub-Chandrasekhar mass white dwarfs., Comment: Accepted for publication in A&A. All tables included

Synergetic observations of multi-band coincidence signals from merging neutron stars have definitively marked the significance of multi-messenger astronomy. We present a new generic signature of neutron star mergers, positron emission and the associated 511 keV radiation, produced from ejected neutron-rich radioactive merger material. Accounting for historical neutron star mergers within the Milky Way allows to readily explain the origin of the long-observed 511 keV emission line from the Galactic Center. Further, we draw a direct link between heavy element production ($r$-process nucleosynthesis) and 511 keV emission, which signifies the surprising recent observations of Reticulum II ultra-faint dwarf spheroidal galaxy as a smoking gun of our proposal. This novel tracer of neutron star mergers provides a distinct handle for exploring binary merger history., Comment: 7 pages, 2 figures. Proceedings of the 36th International Cosmic Ray Conference (ICRC-2019), Madison, Wisconsin, USA

The cluster M54 lies at the centre of the Sagittarius dwarf spheroidal galaxy, and therefore may be the closest example of a nuclear star cluster. Either in-situ star formation, inspiralling globular clusters, or a combination have been invoked to explain the wide variety of stellar sub-populations in nuclear star clusters. Globular clusters are known to exhibit light element variations, which can be identified using the photometric construct called a chromosome map. In this letter, we create chromosome maps for three distinct age-metallicity sub-populations in the vicinity of M54. We find that the old, metal-poor population shows the signature of light element variations, while the young and intermediate-age metal rich populations do not. We conclude that the nucleus of Sagittarius formed through a combination of in-situ star formation and globular cluster accretion. This letter demonstrates that properly constructed chromosome maps of iron-complex globular clusters can provide insight into the formation locations of the different stellar populations., Comment: Accepted by MNRAS Letters

We present an unprecedented, deep study of the primordial low-mass X-ray binary population in an isolated, lower-metallicity environment. We perform followup observations of previously-identified X-ray binary candidates in the Sculptor Dwarf Galaxy by combining a second Chandra observation with Spitzer and Gemini photometry, as well as Gemini spectroscopy of selected targets. Of the original nine bright X-ray sources identified, we are able to classify all but one as quasars, active galactic nuclei, or background galaxies. We further discover four new X-ray sources in the second-epoch Chandra observation. Three of these new sources are background sources and one is a foreground flaring star. We have found that Sculptor is effectively devoid of X-ray sources above a few 1e34 erg/s. If Sculptor is able to retain primordial binaries at a similar rate to globular clusters, this implies that bright X-ray binaries observed in globular clusters in the present epoch are all formed dynamically., Comment: MNRAS in press; 19 pages, 12 figures

The aim of this work is to find a progenitor for Canes Venatici I (CVn I), under the assumption that it is a dark matter free object that is undergoing tidal disruption. With a simple point mass integrator, we searched for an orbit for this galaxy using its current position, position angle, and radial velocity in the sky as constraints. The orbit that gives the best results has the pair of proper motions $\mu_\alpha$ = -0.099 mas yr$^{-1}$ and $\mu_\delta$ = -0.147 mas yr$^{-1}$, that is an apogalactic distance of 242.79 kpc and a perigalactic distance of 20.01 kpc. Using a dark matter free progenitor that undergoes tidal disruption, the best-fitting model matches the final mass, surface brightness, effective radius, and velocity dispersion of CVn I simultaneously. This model has an initial Plummer mass of 2.47 x $10^7$ M$_\odot$ and a Plummer radius of 653 pc, producing a remnant after 10 Gyr with a final mass of 2.45 x 10$^5$ M$_\odot$, a central surface brightness of 26.9 mag arcsec$^{-2}$, an effective radius of 545.7 pc, and a velocity dispersion with the value 7.58 km s$^{-1}$. Furthermore, it is matching the position angle and ellipticity of the projected object in the sky., Comment: 11 pages, 14 figures, accepted by A&A

In this letter, we report the discovery of an intriguing HVS (J1443+1453) candidate that is probably from the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph). The star is an old and very metal-poor low-mass main-sequence turn-off star (age $\sim14.0$ Gyr and [Fe/H] $= -2.23$ dex) and has a total velocity of $559.01^{+135.07}_{-87.40}$ km s$^{-1}$ in the Galactic rest-frame and a heliocentric distance of $2.90^{+0.72}_{-0.48}$ kpc. The velocity of J1443+1453 is larger than the escape speed at its position, suggesting it a promising HVS candidate. By reconstructing its trajectory in the Galactic potential, we find that the orbit of J1443+1453 intersects closely with that of the Sgr dSph $37.8^{+4.6}_{-6.0}$ Myr ago, when the latter has its latest pericentric passage through the Milky Way. The encounter occurs at a distance $2.42^{+1.80}_{-0.77}$ kpc from the centre of Sgr dSph, smaller than the size of the Sgr dSph. Chemical properties of this star are also consistent with those of one Sgr dSph associated globular cluster or of the Sgr stream member stars. Our finding suggests that J1443+1453 is an HVS either tidally stripped from the Sgr dSph or ejected from the Sgr dSph by the gravitational slingshot effect, requiring a (central) massive/intermediate-mass black hole or a (central) massive primordial black hole in the Sgr dSph., Comment: 6 pages, 4 figures, 2 tables, accepted for publication in ApJL

We present a detailed study of the internal structure and kinematics of the core of the Sagittarius dwarf spheroidal galaxy (Sgr). Using machine-learning techniques, we have combined the information provided by 3300 RR Lyrae stars, more than 2000 spectroscopically observed stars, and the Gaia second data release to derive the full phase space, i.e. 3D positions and kinematics, of more than $1.2\times10^5$ member stars in the core of the galaxy. Our results show that Sgr has a bar structure $\sim 2.5$ kpc long, and that tidal tails emerge from its tips to form what it is known as the Sgr stream. The main body of the galaxy, strongly sheared by tidal forces, is a triaxial (almost prolate) ellipsoid with its longest principal axis of inertia inclined $43^\circ\pm6^\circ$ with respect to the plane of the sky and axis ratios of 1:0.67:0.60. Its external regions are expanding mainly along its longest principal axis, yet the galaxy conserves an inner core of about $500\times330\times300$ pc that shows no net expansion and is rotating at $v_{\rm rot} = 4.13 \pm 0.16$ ${\rm{ km \ s^{-1}}}$. The internal angular momentum of Sgr forms an angle $\theta = 18^\circ\pm6^\circ$ with respect to its orbital angular momentum, meaning that the galaxy is in an inclined prograde orbit around the Milky Way. We compared our results with predictions from $N$-body models with spherical, pressure-supported progenitors and a model whose progenitor is a flattened rotating disk. Only the rotating model, based on preexisting simulations aimed at reproducing the line-of-sight velocity gradients observed in Sgr, was able to reproduce the observed properties in the core of the galaxy., Comment: 37 pages, 26 figures, 2 tables. Accepted for publication in the Astrophysical Journal

We present a novel analysis of the internal kinematics of the Fornax dwarf spheroidal galaxy. Our results are based on the largest sample of spectroscopic data for Fornax stars presently available ($> 2500$ stars), for which we have chemical and kinematic information. We introduce new software, Beacon, designed to detect chemo-kinematic patterns among stars of different stellar populations using their metallicity and velocity along the line of sight. Applying Beacon to Fornax we have detected non-negligible rotation signals around main optical axes of the galaxy, characteristic for a triaxial system partially supported by rotation. The dominant rotation pattern is relatively strong ($\sim 12$ km s$^{-1}$), but the galaxy also shows additional weaker albeit complex rotation patterns. Using the information available from the star formation history of Fornax we have also derived the average age of the different chemo-kinematic components found by Beacon, which has allowed us to obtain its kinematic history. Our results point to a possible major merger suffered by Fornax at redshift $z\sim1$, in agreement with previous works., 17 pages, 16 figures. Accepted for publication in MNRAS

We have investigated the effect of group environment on residual star formation in galaxies, using Galaxy Evolution Explorer near-ultraviolet (NUV) galaxy photometry with the Sloan Digital Sky Survey group catalogue of Yang et al. We compared the (NUV - r) colours of grouped and non-grouped galaxies, and find a significant increase in the fraction of red sequence galaxies with blue (NUV - r) colours outside of groups. When comparing galaxies in mass-matched samples of satellite (non-central), and non-grouped galaxies, we found a >4 sigma difference in the distribution of (NUV - r) colours, and an (NUV - r) blue fraction >3 sigma higher outside groups. A comparison of satellite and non-grouped samples has found the NUV fraction is a factor of similar to 2 lower for satellite galaxies between 10(10.5) and 10(10.7)M(circle dot), showing that higher mass galaxies are more likely to have residual star formation when not influenced by a group potential. There was a higher (NUV - r) blue fraction of galaxies with lower Sersic indices (n

The dwarf satellite galaxies of the Milky Way are structures that are distributed around the galaxy in an anisotropic manner on a structure called VPOS or DoS. This structure does not match the predictions made by the cold dark matter cosmological model. This model predicts a fully isotropic distribution around the Milky Way. To explain the spatial distribution of the satellite several models have been raised. One of which raises the possibility that these galaxies and their spatial distribution were generated by the collision of two disk galaxies several billion years ago. This paper shows N-body performed with Gadget-2 to determine through their results if it is possible that this event occurred in this way. An analysis for different mass ratios between the incident galaxy, called ghost galaxy, and the host galaxy or target galaxy is performed. Finally a cluster analysis on the remaining collision is performed to determine the spatial distribution of the satellites.

We study integrated characteristics of ~14000 low-redshift (0, Comment: 8 pages, 10 figures, accepted for publication in MNRAS

The extent to which dwarf galaxies represent essentially scaled down versions of giant galaxies is an important question with regards the formation and evolution of the galaxy population as a whole. Here we address the specific question of whether dwarf galaxies behave like smaller versions of giants in terms of their X-ray properties. We discuss two samples of around 100 objects each, dwarfs in the Virgo Cluster and dwarfs in a large northern hemisphere area. We find nine dwarfs in each sample with Chanda detections. For the Virgo sample, these are in dwarf elliptical (or dwarf lenticular) galaxies and we assume that these are (mostly) low mass X-ray binaries (some may be nuclear sources). We find a detection rate entirely consistent with scaling down from massive ellipticals, viz. about 1 bright (i.e. $L_X > 10^{38}$ erg~s$^{-1}$) LMXB per $5 \times 10^9 M_{\odot}$ of stars. For the field sample, we find one (known) Seyfert nucleus, in a galaxy which appears to be the lowest mass dwarf with a confirmed X-ray emitting nucleus. The other detections are in star forming dwarf irregular or blue compact dwarf galaxies and are presumably high mass X-ray binaries. This time, we find a very similar detection rate to that in large late type galaxies if we scale down by star formation rate, roughly 1 HMXB for a rate of $0.3 M_{\odot}$ per year. Nevertheless, there does seem to be one clear difference, in that the dwarf late type galaxies with X-ray sources appear strongly biased to very low metallicity systems.

We study the characteristic length scale of galactic halos in the Bose-Einstein condensate (or scalar field) dark matter model. Considering the evolution of the density perturbation we show that the average background matter density determines the quantum Jeans mass and hence the spatial size of galaxies at a given epoch. In this model the minimum size of galaxies increases while the minimum mass of the galaxies decreases as the universe expands. The observed values of the mass and the size of the dwarf galaxies are successfully reproduced with the dark matter particle mass $m\simeq 5\times 10^{-22}eV$. The minimum size is about $6\times 10^{-3}\sqrt{m/H}\lambda_c$ and the typical rotation velocity of the dwarf galaxies is $O(\sqrt{H/m}$) c, where $H$ is the Hubble parameter and $\lambda_c$ is the Compton wave length of the particle. We also suggest that ultra compact dwarf galaxies are the remnants of the dwarf galaxies formed in the early universe., Comment: Accepted for publication in Physics letters B

We present wide-field $g$ and $i$ band stellar photometry of the Sextans dwarf spheroidal galaxy and its surrounding area out to four times its half-light radius ($r_h=695\,$pc), based on images obtained with the Dark Energy Camera at the 4-m Blanco telescope at CTIO. We find clear evidence of stellar substructure associated with the galaxy, extending to a distance of $82\arcmin$ (2\,kpc) from its centre. We perform a statistical analysis of the over-densities and find three distinct features, as well as an extended halo-like structure, to be significant at the $99.7\%$ confidence level or higher. Unlike the extremely elongated and extended substructures surrounding the Hercules dwarf spheroidal galaxy, the over-densities seen around Sextans are distributed evenly about its centre, and do not appear to form noticeable tidal tails. Fitting a King model to the radial distribution of Sextans stars yields a tidal radius $r_t =83.2\arcmin\pm7.1\arcmin$ (2.08$\pm$0.18\,kpc), which implies the majority of detected substructure is gravitationally bound to the galaxy. This finding suggests that Sextans is not undergoing significant tidal disruption from the Milky Way, supporting the scenario in which the orbit of Sextans has a low eccentricity., 16 pages, 15 figures, 3 tables. Accepted to MNRAS 2016 April 20

Recent observations have revealed the existence of an abundant population of faint, low surface brightness (SB) galaxies, which appear to be numerous and ubiquitous in nearby galaxy clusters, including the Virgo, Coma and Fornax clusters. With median stellar masses of dwarf galaxies, these ultra-diffuse galaxies (UDGs) have unexpectedly large sizes, corresponding to a mean SB of $24\lesssim\langle\mu_e\rangle_r\ {\rm mag}^{-1} {\rm arcsec}^2\lesssim27$ within the effective radius. We show that the UDG population represents the tail of galaxies formed in dwarf-sized haloes with higher-than-average angular momentum. By adopting the standard model of disk formation -- in which the size of galaxies is set by the spin of the halo -- we recover both the abundance of UDGs as a function of the host cluster mass and the distribution of sizes within the UDG population. According to this model, UDGs are not failed $L_*$ galaxies, but genuine dwarfs, and their low SB is not uniquely connected to the harsh cluster environment. We therefore expect a correspondingly abundant population of UDGs in the field, with likely different morphologies and colours., Comment: MNRAS Letters, accepted version