- ID:
- ivo://CDS.VizieR/J/A+A/309/749
- Title:
- Fundamental plane of early type galaxies
- Short Name:
- J/A+A/309/749
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyse the residuals to the fundamental plane (FP) of elliptical galaxies as a function of stellar-population indicators; these are based on the line-strength parameter Mg2 and on UBVRI broad-band colors, and are partly derived from new observations. The effect of the stellar populations accounts for approximately half the observed variation of the mass-to-light ratio responsible for the FP tilt. The residual tilt can be explained by the contribution of two additional effects: the dependence of the rotational support, and possibly that of the spatial structure, on the luminosity. We conclude to a constancy of the dynamical-to-stellar mass ratio. This probably extends to globular clusters as well, but the dominant factor would be here the luminosity dependence of the structure rather than that of the stellar population. This result also implies a constancy of the fraction of dark matter over all the scalelength covered by stellar systems. Our compilation of internal stellar kinematics of galaxies is appended.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/176/59
- Title:
- FUSE survey of OVI in the disk of the Milky Way
- Short Name:
- J/ApJS/176/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To probe the distribution and physical characteristics of interstellar gas at temperatures T~3x10^5^K in the disk of the Milky Way, we have used the Far Ultraviolet Spectroscopic Explorer (FUSE) to observe absorption lines of OVI{lambda}1032 toward 148 early-type stars situated at distances >1kpc. After subtracting off a mild excess of OVI arising from the Local Bubble, combining our new results with earlier surveys of OVI, and eliminating stars that show conspicuous localized X-ray emission, we find an average OVI midplane density n_0_=1.3x10^-8^cm^-3^. The density decreases away from the plane of the Galaxy in a way that is consistent with an exponential scale height of 3.2kpc at negative latitudes or 4.6kpc at positive latitudes.
- ID:
- ivo://vopdc.obspm/gepi/gaia
- Title:
- Gaia catalog release 2
- Short Name:
- Gaia
- Date:
- 14 Nov 2018 00:30:00
- Publisher:
- Paris Astronomical Data Centre - GEPI
- Description:
- The second Gaia data release, Gaia DR2, encompasses astrometry, photometry, radial velocities, astrophysical parameters (stellar effective temperature, extinction, reddening, radius, and luminosity), and variability information for up to 1.6 billion stars. Gaia DR2 is based on the first 22 months of the nominal, five-year mission, processed by the Gaia Data Processing and Analysis Consortium (DPAC).
- ID:
- ivo://CDS.VizieR/J/A+A/638/A104
- Title:
- Gaia DR2 candidate RR Lyrae of Sgr stream & dwarf
- Short Name:
- J/A+A/638/A104
- Date:
- 14 Jan 2022 08:12:04
- Publisher:
- CDS
- Description:
- The Sagittarius (Sgr) stream is one of the best tools that we currently have to estimate the mass and shape of our Galaxy. However, assigning membership and obtaining the phase-space distribution of the stars that form the tails is quite challenging. Our goal is to produce a catalogue of RR Lyrae stars of Sgr and obtain an empiric measurement of the trends along the stream in sky position, distance and tangential velocities. We generate two initial samples from the Gaia DR2 RR Lyrae catalogue: one, selecting only the stars within +/-20{deg} of the orbital plane of Sagittarius (Strip) and the other, the result of applying the Pole Count Map (nGC3) algorithm. We then use the model-independent, deterministic method developed in this work to remove most of the contamination by detecting and isolating the stream in distance and proper motions. The output is two empiric catalogues: the Strip sample (higher-completeness, lower-purity) which contains 11677 stars, and the nGC3 sample (higher-purity, lower-completeness) with 6608 stars. We characterise the changes along the stream in all the available dimensions, the 5 astrometric ones plus the metallicity, covering more than 2{pi}rad in the sky and obtain new estimates for the apocentres and the mean [Fe/H] of the RR Lyrae population. Also, we show the first map of the two components of the tangential velocity, thanks to the combination of distances and proper motions. Finally, we detect the bifurcation in the leading arm and report no significant difference between the two branches, either in metallicity, kinematics or distance. We provide the largest sample of RR Lyrae candidates of Sgr, which can be used as an input for a spectroscopic follow-up or as a reference for the new generation of models of the stream through the interpolators in distance and velocity that we have constructed.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A59
- Title:
- Gaia DR2 confirmed new nearby open clusters
- Short Name:
- J/A+A/618/A59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The publication of the Gaia Data Release 2 (Gaia DR2) opens a new era in astronomy. It includes precise astrometric data (positions, proper motions, and parallaxes) for more than 1.3 billion sources, mostly stars. To analyse such a vast amount of new data, the use of data-mining techniques and machine-learning algorithms is mandatory. A great example of the application of such techniques and algorithms is the search for open clusters (OCs), groups of stars that were born and move together, located in the disc. Our aim is to develop a method to automatically explore the data space, requiring minimal manual intervention. We explore the performance of a density-based clustering algorithm, DBSCAN, to find clusters in the data together with a supervised learning method such as an artificial neural network (ANN) to automatically distinguish between real OCs and statistical clusters. The development and implementation of this method in a five-dimensional space (l, b, p, {mu}_{alpha}_^*^, {mu}_{delta}_) with the Tycho-Gaia Astrometric Solution (TGAS) data, and a posterior validation using Gaia DR2 data, lead to the proposal of a set of new nearby OCs. We have developed a method to find OCs in astrometric data, designed to be applied to the full Gaia DR2 archive.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A48
- Title:
- Gaia-DR2 extended kinematical maps. I.
- Short Name:
- J/A+A/621/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia Collaboration has used Gaia-DR2 sources with six-dimensional (6D) phase space information to derive kinematical maps within 5kpc of the Sun, which is a reachable range for stars with relative error in distance lower than 20%. Here we aim to extend the range of distances by a factor of two to three, thus adding the range of Galactocentric distances between 13kpc and 20kpc to the previous maps, with their corresponding error and root mean square values. We make use of the whole sample of stars of Gaia-DR2 including radial velocity measurements, which consists in more than seven million sources, and we apply a statistical deconvolution of the parallax errors based on the Lucy's inversion method of the Fredholm integral equations of the first kind, without assuming any prior. The new extended maps provide lots of new and corroborated information about the disk kinematics: significant departures of circularity in the mean orbits with radial Galactocentric velocities between -20 and +20km/s and vertical velocities between -10 and +10km/s; variations of the azimuthal velocity with position; asymmetries between the northern and the southern Galactic hemispheres, especially towards the anticenter that includes a larger azimuthal velocity in the south; and others. These extended kinematical maps can be used to investigate the different dynamical models of our Galaxy, and we will present our own analyses in the forthcoming second part of this paper. At present, it is evident that the Milky Way is far from a simple stationary configuration in rotational equilibrium, but is characterized by streaming motions in all velocity components with conspicuous velocity gradients.
- ID:
- ivo://CDS.VizieR/J/MNRAS/502/L90
- Title:
- Gaia DR2 Galactic bulge new star clusters
- Short Name:
- J/MNRAS/502/L90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of 34 new open clusters and candidates as a result of a systematic search carried out in 200 adjacent fields of 1x1 square degrees area projected towards the Galactic bulge, using Gaia DR2 data. The objects were identified and characterized by a joint analysis of their photometric, kinematic and spatial distribution, which has been consistently used and proved to be effective in our previous works. The discoveries were validated by cross-referencing the objects position and astrometric parameters with the available literature. Besides their coordinates and astrometric parameters, we also provide sizes, ages, distances and reddening for the discovered objects. In particular, 32 clusters are closer than 2kpc from the Sun, which represents an increment of nearly 39% of objects with astrophysical parameters determined in the nearby inner disk. Although these objects fill an important gap in the open clusters distribution along the Sagittarius arm, this arm, traced by known clusters, appears to be interrupted, which may be an artifact due to the incompleteness of the cluster census.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A99
- Title:
- Gaia DR2 Monoceros and ACS candidates
- Short Name:
- J/A+A/646/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia astrometric sample allows us to study the outermost Galactic disc, the halo, and their interface. It is precisely at the very edge of the disc where the effects of external perturbations are expected to be the most noticeable. Our goal is to detect the kinematic substructure present in the halo and at the edge of the Milky Way (MW) disc and provide observational constraints on their phase-space distribution. We download, one HP at a time, the proper motion histogram of distant stars, to which we apply a wavelet transformation to reveal the significant overdensities. We then analyse the large coherent structures that appear in the sky. We reveal a sharp yet complex anticentre dominated by Monoceros (MNC) and the Anticentre Stream (ACS) in the north - which we find have intensities comparable to the Magellanic Clouds and the Sagittarius stream - and by MNC South and TriAnd at negative latitudes. Our method allows us to perform a morpho-logical analysis of MNC and the ACS, both of which span more than 100{deg} in longitude, and to provide a high purity sample of giants with which we track MNC down to latitudes as low as ~5{deg}. Their colour-magnitude diagram is consistent with extended structures at a distance of ~10-11kpc that originated in the disc, with a very low ratio of RR-Lyrae over M giants, and with kinematics compatible with the rotation curve at those distances or slightly slower. We present a precise characterisation of MNC and the ACS, two previously known structures that our method reveals naturally, allowing us to detect them without limiting ourselves to a particular stellar type and, for the first time, using only kinematics. Our results will allow future studies to model their chemo-dynamics and evolution, thus constraining some of the most influential processes that shaped the MW.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A99
- Title:
- Gaia DR2 open clusters in the Milky Way. II
- Short Name:
- J/A+A/633/A99
- Date:
- 02 Mar 2022 11:45:02
- Publisher:
- CDS
- Description:
- Many of the open clusters listed in modern catalogues were first reported by visual astronomers as apparent over-densities of bright stars. As observational techniques and analysis methods improved, some of them have been shown to be chance alignments of stars and are not true clusters. Recent publications making use of Gaia DR2 data provided membership list for over a thousand clusters, but many nearby objects listed in the literature have so far evaded detection. We update the Gaia DR2 cluster census by performing membership determinations for known clusters that had been missed by previous studies, and for recently discovered clusters. We investigate a subset of non-detected clusters that according to their literature parameters should be easily visible in the Gaia . Confirming or disproving the existence of old, inner-disc, high-altitude clusters is especially important as their survival or disruption is linked to the dynamical processes that drive the evolution of the Milky Way. We employ the Gaia DR2 catalogue and a membership assignment procedure, as well as visual inspection of spatial, proper motion, and parallax distributions. We use membership lists provided by other authors when they are available. We derive membership lists for 150 objects, including 10 that were known prior to Gaia . We compile a final list of members for 1481 clusters. Among the objects that we are still unable to identify with Gaia data, we argue that many (mostly putative old, relatively nearby, high-altitude objects) are not true clusters. At present, the only confirmed cluster located further than 500pc away from the Galactic plane within the Solar circle is NGC 6791. It is likely that the objects discussed in this study only represent a fraction of the non-physical groupings erroneously listed in the catalogues as genuine open clusters, and that those lists need further cleaning.
- ID:
- ivo://CDS.VizieR/IV/35
- Title:
- Gaia DR2-WISE Galactic Plane Matches
- Short Name:
- IV/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Faint, hidden contaminants in the point-spread functions (PSFs) of stars cause shifts to their measured positions. Wilson & Naylor (2017MNRAS.468.2517W) showed failing to account for these shifts can lead to a drastic decrease in the number of returned catalogue matches in crowded fields. Here we highlight the effect these perturbations have on cross-matching, for matches between Gaia DR2 and WISE stars in a crowded Galactic plane region. Applying the uncertainties as quoted to Gaussian-based astrometric uncertainty functions (AUFs) can lead, in dense Galactic fields, to only matching 55% of the counterparts. We describe the construction of empirical descriptions for AUFs, building on the cross-matching method of Wilson & Naylor (2018MNRAS.473.5570W), utilising the magnitudes of both catalogues to discriminate between true and false counterparts. We apply the improved cross-matching method to the Galactic plane |b|<10. We provide the most likely counterpart matches and their respective probabilities. We also analyse several cases to verify the robustness of the results, highlighting some important caveats and considerations. Finally, we discuss the effect PSF resolution has by comparing the intra- catalogue nearest neighbour separation distributions of a sample of likely contaminated WISE objects and their corresponding Spitzer counterpart. We show that some WISE contaminants are resolved in Spitzer, with smaller intra-catalogue separations. We have highlighted the effect contaminant stars have on WISE, but it is important for all photometric catalogues, playing an important role in the next generation of surveys, such as LSST.
