Search

We present a large catalogue of molecular clouds with accurate distance estimates in the Southern sky. Based on the three-dimensional dust extinction map and the best-fitting extinction and distance information of over 17 million stars presented in Guo et al. (2021, ApJ, 906, 47), we have identified 250 dust/molecular clouds in the Southern sky using a hierarchical structure identification algorithm. Amongst these are 71 clouds located at high Galactic latitudes (b < −10°). We have estimated the distances to the clouds by fitting the extinction versus distance profiles of the lines of sight overlapping with the clouds, using a simple Gaussian dust distribution model. The typical uncertainties of the distances are less than 7 per cent. We also provide the physical properties of the individual clouds, including the linear radius, mass and surface mass density. [ABSTRACT FROM AUTHOR]

We present a large, homogeneous catalogue of molecular clouds within 4 kpc from the Sun at low Galactic latitudes (| b | < 10°) with unprecedented accurate distance determinations. Based on the 3D dust reddening map and estimates of colour excesses and distances of over 32 million stars presented in Chen et al., we have identified 567 dust/molecular clouds with a hierarchical structure identification method and obtained their distance estimates by a dust model fitting algorithm. The typical distance uncertainty is less than 5 per cent. As far as we know, this is the first large catalogue of molecular clouds in the Galactic plane with distances derived in a direct manner. The clouds are seen to lie along the Sagittarius, Local and Perseus Arms. In addition to the known structures, we propose the existence of a possible spur , with a pitch angle of about 34°, connecting the Local and the Sagittarius Arms in the fourth quadrant. We have also derived the physical properties of those molecular clouds. The distribution of cloud properties in different parameter spaces agrees grossly with the previous results. Our cloud sample is an ideal starting point to study the concentration of dust and gas in the solar vicinity and their star formation activities. [ABSTRACT FROM AUTHOR]

We perform analysis of the 3D kinematics of Milky Way disc stars in mono-age populations. We focus on stars between Galactocentric distances of R  = 6 and 14  kpc, selected from the combined LAMOST Data Release 4 (DR4) red clump giant stars and Gaia DR2 proper motion catalogue. We confirm the 3D asymmetrical motions of recent works and provide time tagging of the Galactic outer disc asymmetrical motions near the anticentre direction out to Galactocentric distances of 14 kpc. Radial Galactocentric motions reach values up to 10 km s−1, depending on the age of the population, and present a north–south asymmetry in the region corresponding to density and velocity substructures that were sensitive to the perturbations in the early 6  Gyr. After that time, the disc stars in this asymmetrical structure have become kinematically hotter, and are thus not sensitive to perturbations, and we find the structure is a relatively younger population. With quantitative analysis, we find stars both above and below the plane at R ≳ 9 kpc that exhibit bending mode motions of which the sensitive duration is around 8  Gyr. We speculate that the in-plane asymmetries might not be mainly caused by a fast rotating bar, intrinsically elliptical outer disc, secular expansion of the disc, or streams. Spiral arm dynamics, out-of-equilibrium models, minor mergers or others are important contributors. Vertical motions might be dominated by bending and breathing modes induced by complicated inner or external perturbers. It is likely that many of these mechanisms are coupled together. [ABSTRACT FROM AUTHOR]

We present new three-dimensional (3D) interstellar dust reddening maps of the Galactic plane in three colours, E (G − K S), E (G BP − G RP), and E (H − K S). The maps have a spatial angular resolution of 6 arcmin and covers over 7000 deg2 of the Galactic plane for Galactic longitude 0° < l < 360° and latitude | b | < 10°. The maps are constructed from robust parallax estimates from the Gaia Data Release 2 (Gaia DR2) combined with the high-quality optical photometry from the Gaia DR2 and the infrared photometry from the Two Micron All Sky Survey and Wide-Field Infrared Survey Explorer survey. We estimate the colour excesses, E (G − K S), E (G BP − G RP), and E (H − K S), of over 56 million stars with the machine-learning algorithm Random Forest regression, using a training data set constructed from the large-scale spectroscopic surveys, Large Sky Area Multi-Object Fibre Spectroscopic Telescope, Sloan Extension for Galactic Understanding and Exploration, and Apache Point Observatory Galactic Evolution Experiment. The results reveal the large-scale dust distribution in the Galactic disc, showing a number of features consistent with the earlier studies. The Galactic dust disc is clearly warped and show complex structures possibly spatially associated with the Sagittarius, Local, and Perseus arms. We also provide the empirical extinction coefficients for the Gaia photometry that can be used to convert the colour excesses presented here to the line-of-sight extinction values in the Gaia photometric bands. [ABSTRACT FROM AUTHOR]

The rotation curve (RC) of the Milky Way out to ~100 kpc has been constructed using ~16 000 primary red clump giants (PRCGs) in the outer disc selected from the LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC) and the Sloan Digital Sky Survey (SDSS)-III/APOGEE survey, combined with ~5700 halo K giants (HKGs) selected from the SDSS/SEGUE survey. To derive the RC, the PRCG sample of the warm disc population and the HKG sample of halo stellar population are, respectively, analysed using a kinematical model allowing for the asymmetric drift corrections and re-analysed using the spherical Jeans equation along with measurements of the anisotropic parameter β currently available. The typical uncertainties of RC derived from the PRCG and HKG samples are, respectively, 5- 7 km s-1 and several tens km s-1.We determine a circular velocity at the solar position, Vc(R0) = 240 ± 6 km s-1 and an azimuthal peculiar speed of the Sun, V☉ = 12.1 ± 7.6 km s-1, both in good agreement with the previous determinations. The newly constructed RC has a generally flat value of 240 km s-1 within a Galactocentric distance r of 25 kpc and then decreases steadily to 150 km s-1 at r ~ 100 kpc. On top of this overall trend, the RC exhibits two prominent localized dips, one at r ~11 kpc and another at r ~ 19 kpc. From the newly constructed RC, combined with other constraints, we have built a parametrized mass model for the Galaxy, yielding a virial mass of the MilkyWay's dark matter halo of 0.90+0.07 -0.08 × 1012 M☉ and a local dark matter density, ρ☉,dm = 0.32+0.02 -0.02 GeV cm-3. [ABSTRACT FROM AUTHOR]

As a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anticentre (LSS-GAC) aims to survey a significant volume of the Galactic thin/thick discs and halo for a contiguous sky area of over 3400 deg2 centred on the Galactic anticentre (|b| ≤ 30°, 150 ≤ l ≤ 210°), and obtain λλ3700–9000 low-resolution (R ∼ 1800) spectra for a statistically complete sample of ∼3 M stars of all colours down to a limiting magnitude of r ∼ 17.8 mag (to 18.5 mag for limited fields). Together with Gaia, the LSS-GAC will yield a unique data set to advance our understanding of the structure and assemblage history of the Galaxy, in particular its disc(s). In addition to the main survey, the LSS-GAC will also target hundreds of thousands objects in the vicinity fields of M 31 and M 33 and survey a significant fraction (over a million) of randomly selected very bright stars (r ≤ 14 mag) in the Northern hemisphere. During the Pilot and the first year Regular Surveys of LAMOST, a total of 1042 586 [750 867] spectra of a signal-to-noise ratio S/N(7450 Å) ≥ 10 [S/N(4650 Å) ≥ 10] have been collected. In this paper, we present a detailed description of the target selection algorithm, survey design, observations and the first data release of value-added catalogues (including radial velocities, effective temperatures, surface gravities, metallicities, values of interstellar extinction, distances, proper motions and orbital parameters) of the LSS-GAC. [ABSTRACT FROM PUBLISHER]

We present a three-dimensional extinction map in the r band. The map has a spatial angular resolution, depending on latitude, between 3 and 9 arcmin and covers the entire Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC) survey area of over 6000 deg2 for Galactic longitude 140 < l < 240 deg and latitude −60 < b < 40 deg. By cross-matching the photometric catalogue of the XSTPS-GAC with those of 2MASS and WISE, we have built a multiband photometric stellar sample of about 30 million stars and applied spectral energy distribution (SED) fitting to the sample. By combining photometric data from the optical to the near-infrared, we are able to break the degeneracy between the intrinsic stellar colours and the amounts of extinction by dust grains for stars with high photometric accuracy, and trace the extinction as a function of distance for low Galactic latitude and thus highly extincted regions. This has allowed us to derive the best-fitting extinction and distance information of more than 13 million stars, which are used to construct the three-dimensional extinction map. We have also applied a Rayleigh–Jeans colour excess (RJCE) method to the data using the 2MASS and WISE colour (H − W2). The resulting RJCE extinction map is consistent with the integrated two-dimensional map deduced using the best-fitting SED algorithm. However for individual stars, the amounts of extinction yielded by the RJCE method suffer from larger errors than those given by the best-fitting SED algorithm. [ABSTRACT FROM PUBLISHER]