- ID:
- ivo://CDS.VizieR/J/ApJ/863/89
- Title:
- Gaia DR2 PMs of stars in ultra-faint MW satellites
- Short Name:
- J/ApJ/863/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The second data release from the Gaia mission (DR2) provides a comprehensive and unprecedented picture of the motions of astronomical sources in the plane of the sky, extending from the solar neighborhood to the outer reaches of the Milky Way. I present proper-motion measurements based on Gaia DR2 for 17 ultra-faint dwarf galaxies within 100kpc of the Milky Way. I compile the spectroscopically confirmed member stars in each dwarf bright enough for Gaia astrometry from the literature, producing member samples ranging from two stars in Triangulum II to 68 stars in Bootes I. From the spectroscopic member catalogs, I estimate the proper motion of each system. I find good agreement with the proper motions derived by the Gaia collaboration for Bootes I and Leo I. The tangential velocities for 14 of the 17 dwarfs are determined to better than 50km/s, more than doubling the sample of such measurements for Milky Way satellite galaxies. The orbital pericenters are well constrained, with a mean value of 38kpc. Only one satellite, Tucana III, is on an orbit passing within 15kpc of the Galactic center, suggesting that the remaining ultra-faint dwarfs are unlikely to have experienced severe tidal stripping. As a group, the ultra-faint dwarfs are on high-velocity, eccentric, retrograde trajectories, with nearly all of them having space motions exceeding 370km/s. A large majority of the objects are currently close to the pericenters of their orbits. In a low-mass (M_vir_=0.9x10^12^M_{sun}_) Milky Way potential, eight out of the 17 galaxies lack well-defined apocenters and appear likely to be on their first infall, indicating that the Milky Way mass may be larger than previously estimated or that many of the ultra-faint dwarfs are associated with the Magellanic Clouds. The median eccentricity of the ultra-faint dwarf orbits is 0.79, similar to the values seen in numerical simulations but distinct from the rounder orbits of the more luminous dwarf spheroidals.
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- ID:
- ivo://CDS.VizieR/VII/285
- Title:
- Gaia DR2 quasar and galaxy classification
- Short Name:
- VII/285
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide probabilistic quasar and galaxy classifications for 2.7 million sources in Gaia Data Release 2. This has been achieved using a supervised classification method (Gaussian Mixture Models) based only on photometric and astrometric data (8 features) in Gaia-DR2. The model is trained empirically to classify objects into three classes - star, quasar, galaxy - for all objects with G>=14.5mag down to the Gaia magnitude limit of G=21.0mag. We provide the probabilities for being a quasar (pqso) and a galaxy (pgal); the probability of being a star is pstar = 1-(pqso+pgal), and all other Gaia data can be obtained by cross-matching Gaia-DR2 using the source identifier. As our main goal is to identify extragalactic objects, we only report objects with pqso+pgal>0.5. These probabilities incorporate a sensible class prior, namely that quasars are 500 times rarer than stars, and that galaxies 7500 times rarer than stars. See the paper for details of the purity and completeness of samples drawn from this catalogue, and for more details of its construction, contents, and validation.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A12
- Title:
- Gaia DR2 sources in GC and dSph
- Short Name:
- J/A+A/616/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (iv) derive a lower limit for the mass of the Milky Way of 9.8^+6.7^_-2.7_x10^11^M_{sun}_ based on the assumption that the Leo~I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (vi) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A2
- Title:
- Gaia-ESO Survey abundances radial distribution
- Short Name:
- J/A+A/603/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spatial distribution of elemental abundances in the disc of our Galaxy gives insights both on its assembly process and subsequent evolution, and on the stellar nucleogenesis of the different elements. Gradients can be traced using several types of objects as, for instance, (young and old) stars, open clusters, HII regions, planetary nebulae. We aim to trace the radial distributions of abundances of elements produced through different nucleosynthetic channels - the {alpha}-elements O, Mg, Si, Ca and Ti, and the iron-peak elements Fe, Cr, Ni and Sc - by use of the Gaia-ESO IDR4 results for open clusters and young-field stars. From the UVES spectra of member stars, we have determined the average composition of clusters with ages >0.1Gyr. We derived statistical ages and distances of field stars. We traced the abundance gradients using the cluster and field populations and compared them with a chemo-dynamical Galactic evolutionary model. The adopted chemo-dynamical model, with the new generation of metallicity-dependent stellar yields for massive stars, is able to reproduce the observed spatial distributions of abundance ratios, in particular the abundance ratios of [O/Fe] and [Mg/Fe] in the inner disc (5kpc<R_GC_<7kpc), with their differences, that were usually poorly explained by chemical evolution models. Oxygen and magnesium are often considered to be equivalent in tracing {alpha}-element abundances and in deducing, for example, the formation timescales of different Galactic stellar populations. In addition, often [{alpha}/Fe] is computed combining several {alpha}-elements. Our results indicate, as expected, a complex and diverse nucleosynthesis of the various {alpha}-elements, in particular in the high metallicity regimes, pointing towards a different origin of these elements and highlighting the risk of considering them as a single class with common features.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A155
- Title:
- Gaia proper motions of 7 UFD galaxies
- Short Name:
- J/A+A/620/A155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present mean absolute proper motion measurements for seven ultra- faint dwarf galaxies orbiting the Milky Way, namely Bootes III, Carina II, Grus II, Reticulum II, Sagittarius II, Segue 2 and Tucana IV. For four of these dwarfs our proper motion estimate is the first ever provided. The adopted astrometric data come from the second data release of the Gaia mission. We determine the mean proper motion for each galaxy starting from an initial guess of likely members, based either on radial velocity measurements or using stars on the Horizontal Branch identified in the Gaia (G_BP_-G_RP_, G) colour-magnitude diagram in the field of view towards the UFD. We then refine their membership iteratively using both astrometry and photometry. We take into account the full covariance matrix among the astrometric parameters when deriving the mean proper motions for these systems. Our procedure provides mean proper motions with typical uncertainties of ~0.1mas/yr, even for galaxies without prior spectroscopic information. In the case of Segue 2 we find that using radial velocity members only leads to biased results, presumably because of the small number of stars with measured radial velocities. Conclusions: our procedure allows to maximize the number of member stars per galaxy regardless of the existence of prior spectroscopic information, and can therefore be applied on any faint or distant stellar system within reach of Gaia.
- ID:
- ivo://CDS.VizieR/VI/137
- Title:
- GaiaSimu Universe Model Snapshot
- Short Name:
- VI/137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Context: This study has been developed in the framework of the computational simulations that are executed for the preparation of the ESA Gaia astrometric mission. Aims: We focus on describing the objects and characteristics that Gaia will potentially observe without taking into consideration instrumental effects (detection efficiency, observing errors). Methods: The theoretical Universe Model prepared for the Gaia simulation has been statistically analysed at a given time. Ingredients of the model are described, with the greatest emphasis on the stellar content, the double and multiple stars, and variability. Results: In this simulation the errors have not yet been included. Hence we estimated the number of objects and their theoretical photometric, astrometric and spectroscopic characteristics if they are perfectly detected.We show that Gaia will be able to potentially observe 1.1 billion of stars (single or part of multiple star systems) of which about 2% are variable stars and 3% have one or two exoplanets. At the extragalactic level, observations will be potentially composed of several millions of galaxies, half a million to 1 million quasars and about 50,000 supernovae that will occur during the five years of the mission.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/140
- Title:
- 632 Gaia Ultracompact Dwarf galaxy candidates
- Short Name:
- J/ApJ/899/140
- Date:
- 14 Mar 2022 00:54:57
- Publisher:
- CDS
- Description:
- Tidally stripped galaxy nuclei and luminous globular clusters (GCs) are important tracers of the halos and assembly histories of nearby galaxies, but are difficult to reliably identify with typical ground-based imaging data. In this paper we present a new method to find these massive star clusters using Gaia DR2, focusing on the massive elliptical galaxy Centaurus A (Cen A). We show that stripped nuclei and GCs are partially resolved by Gaia at the distance of Cen A, showing characteristic astrometric and photometric signatures. We use this selection method to produce a list of 632 new candidate luminous clusters in the halo of Cen A out to a projected radius of 150kpc. Adding in broadband photometry and visual examination improves the accuracy of our classification. In a spectroscopic pilot program we have confirmed five new luminous clusters, which includes the 7th and 10th most luminous GC in Cen A. Three of the newly discovered GCs are further away from Cen A than all previously known GCs. Several of these are compelling candidates for stripped nuclei. We show that our novel Gaia selection method retains at least partial utility out to distances of ~25Mpc and hence is a powerful tool for finding and studying star clusters in the sparse outskirts of galaxies in the local universe.
- ID:
- ivo://CDS.VizieR/VIII/100
- Title:
- GaLactic and Extragalactic All-sky MWA survey
- Short Name:
- VIII/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Murchison Widefield Array (MWA), the low-frequency Square Kilometre Array (SKA1 LOW) precursor located in Western Australia, we have completed the GaLactic and Extragalactic All-sky MWA (GLEAM) survey, and present the resulting extragalactic catalogue, utilising the first year of observations. The catalogue covers 24,402 square degrees, over declinations south of +30{deg} and Galactic latitudes outside 10{deg} of the Galactic plane, excluding some areas such as the Magellanic Clouds. It contains 307,456 radio sources with 20 separate flux density measurements across 72-231MHz, selected from a time- and frequency- integrated image centred at 200MHz, with a resolution of ~=2'. Over the catalogued region, we estimate that the catalogue is 90% complete at 170mJy, and 50% complete at 55mJy, and large areas are complete at even lower flux density levels. Its reliability is 99.97% above the detection threshold of 5{sigma}, which itself is typically 50mJy. These observations constitute the widest fractional bandwidth and largest sky area survey at radio frequencies to date, and calibrate the low frequency flux density scale of the southern sky to better than 10%. This paper presents details of the flagging, imaging, mosaicking, and source extraction/characterisation, as well as estimates of the completeness and reliability. All source measurements and images are available online. This is the first in a series of publications describing the GLEAM survey results.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A117
- Title:
- Galactic Cepheids and RR Lyrae multiplicity. II
- Short Name:
- J/A+A/623/A117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The multiplicity of Classical Cepheids (CCs) and RR Lyrae stars (RRLs) is still imperfectly known, particularly for RRLs. In order to complement the close-in short orbital period systems presented in Paper I (Kervella et al., 2019, Cat. J/A+A/623/A16), we aim at detecting the wide, spatially resolved companions of the targets of our reference samples of Galactic CCs and RRLs. Angularly resolved common proper motion pairs are detected using a simple progressive selection algorithm to separate the most probable candidate companions from the unrelated field stars. We detect 27 resolved, high probability gravitationally bound systems with CCs out of 456 examined stars, and one unbound star embedded in the circumstellar dusty nebula of the long-period Cepheid RS Pup. We find 7 spatially resolved, probable bound systems with RRL primaries out of 789 investigated stars, and 22 additional candidate pairs. We report in particular new companions of three bright RRLs: OV And (companion of F4V spectral type), RR Leo (M0V) and SS Oct (K2V). In addition, we discovered resolved companions of 14 stars of various variability classes that were misclassified as RRLs. The detection of resolved common proper motion companions around CCs and RRLs facilitates the validation of their GDR2 parallaxes. The possibility to conduct a detailed analysis of the resolved coeval companions of CCs and old population RRLs will also be valuable to progress on our understanding of their evolutionary path.
- ID:
- ivo://CDS.VizieR/J/MNRAS/503/5351
- Title:
- Galactic extinction at low Galactic latitudes
- Short Name:
- J/MNRAS/503/5351
- Date:
- 19 Jan 2022 00:31:53
- Publisher:
- CDS
- Description:
- We use near-infrared (J-K) colours of bright 2MASS galaxies, measured within a 7-arcsec-radius aperture, to calibrate the Schlegel, Finkbeiner & Davis DIRBE/IRAS Galactic extinction map at low Galactic latitudes (|b|<10{deg}). Using 3460 galaxies covering a large range in extinction (up to A_K_=1.15mag or E(B-V)~=3.19mag), we derive a correction factor f=0.83+/-0.01 by fitting a linear regression to the colour-extinction relation, confirming that the Schlegel et al. maps overestimate the extinction. We argue that the use of only a small range in extinction (e.g., A_K_<0.4mag) increases the uncertainty in the correction factor and may overestimate it. Our data confirm the Fitzpatrick extinction law for the J- and K-band. We also tested four all-sky extinction maps based on Planck satellite data. All maps require a correction factor as well. In three cases, the application of the respective extinction correction to the galaxy colours results in a reduced scatter in the colour-extinction relation, indicating a more reliable extinction correction. Finally, the large galaxy sample allows an analysis of the calibration of the extinction maps as a function of Galactic longitude and latitude. For all but one extinction map, we find a marked offset between the Galactic Centre and Anticentre region, but not with the dipole of the cosmic microwave background. Based on our analysis, we recommend the use of the GNILC extinction map by Planck Collaboration XLVIII with a correction factor f=0.86+/-0.01.
