Keywords

A spectral analysis of the vertical positions and velocities of 374 open star clusters (OSCs) was carried out. We took these OSCs from the Hunt and Reffert catalog; they have an average age of about 10 million years, and are located on the galactic plane XY in a narrow zone inclined by 25° to the galactic axis Y. The following estimates of the parameters of the Radcliffe wave were obtained: (a) the maximum value in periodic perturbations of vertical coordinates ${Z}_{\max }=92\pm 10$ pc with the wavelength of these perturbations λ_z = 4.82 ± 0.09 kpc; (b) the maximum value of the velocity of vertical disturbances ${W}_{\max }=4.36\pm 0.12$ km s⁻¹ with disturbance wavelength λ_W = 1.78 ± 0.02 kpc. Note that the results of the vertical velocity analysis are first-class in accuracy and completely new.

The structural parameters of a galaxy can be used to gain insight into its formation and evolution history. In this paper, we strive to compare the Milky Way's structural parameters to other, primarily edge-on, spiral galaxies in order to determine how our Galaxy measures up to the Local Universe. For our comparison, we use the galaxy structural parameters gathered from a variety of literature sources in the optical and near-infrared wave bands. We compare the scale length, scale height, and disk flatness for both the thin and thick disks, the thick-to-thin disk mass ratio, the bulge-to-total luminosity ratio, and the mean pitch angle of the Milky Way's spiral arms to those in other galaxies. We conclude that many of the Milky Way's structural parameters are largely ordinary and typical of spiral galaxies in the Local Universe, though the Galaxy's thick disk appears to be appreciably thinner and less extended than expected from zoom-in cosmological simulations of Milky Way-mass galaxies with a significant contribution of galaxy mergers involving satellite galaxies.

The star-forming clumps in star-bursting dwarf galaxies provide valuable insights into understanding the evolution of dwarf galaxies. In this paper, we focus on five star-bursting dwarf galaxies featuring off-centered clumps in the Mapping Nearby Galaxies at Apache Point Observatory survey. Using the stellar population synthesis software Fitting Analysis using Differential evolution Optimization, we obtain the spatially resolved distribution of the star formation history, which allows us to construct the g-band images of the five galaxies at different ages. These images can help us to probe the evolution of the morphological structures of these galaxies. While images of a stellar population older than 1 Gyr are typically smooth, images of a stellar population younger than 1 Gyr reveal significant clumps, including multiple clumps which appear at different locations and even different ages. To study the evolutionary connections of these five galaxies to other dwarf galaxies before their star-forming clumps appear, we construct the images of the stellar populations older than three age nodes, and define them to be the images of the "host" galaxies. We find that the properties such as the central surface brightness and the effective radii of the hosts of the five galaxies are in between those of dwarf ellipticals (dEs) and dwarf irregulars (dIrrs), with two clearly more similar to dEs and one more similar to dIrrs. Among the five galaxies, 8257-3704 is particularly interesting, as it shows a previous starburst event that is not quite visible from its gri image, but only visible from images of the stellar population at a few hundred million years. The star-forming clump associated with this event may have appeared at around 600 Myr ago and disappeared at around 40 Myr ago.

This paper is an initial stage of consideration of the general problem of joint modeling of the vertical structure of a Galactic flat subsystem and the average surface of the disk of the Galaxy, taking into account the natural and measurement dispersions. We approximate the average surface of the Galactic disk in the region covered by the data with a general (polynomial) model and determine its parameters by minimizing the squared deviations of objects along the normal to the model surface. The smoothness of the model, i.e., its order n, is optimized. An outlier elimination algorithm is applied. The developed method allows us to simultaneously identify significant details of the Galactic warping and estimate the offset z_☉ of the Sun relative to the average (in general, non-flat) surface of the Galactic disk and the vertical scale of the object system under consideration for an arbitrary area of the disk covered by data. The method is applied to data on classical Cepheids. Significant local extremes of the average disk surface model were found based on Cepheid data: the minimum in the first Galactic quadrant and the maximum in the second. A well-known warp (lowering of the disk surface) in the third quadrant has been confirmed. The optimal order of the model describing all these warping details was found to be n_o = 4. The local (for a small neighborhood of the Sun, n_o = 0) estimate of ${z}_{\odot }=28.1\pm {\left.6.1\right|}_{{\rm{stat}}.}{\left.\pm 1.3\right|}_{{\rm{cal}}.}$ pc is close to the non-local (taking into account warping, n_o = 4) ${z}_{\odot }=27.1\pm {\left.8.8\right|}_{\mathrm{stat}.}{\left.{}_{-1.2}^{+1.3}\right|}_{\mathrm{cal}.}$ pc (statistical and calibration uncertainties are indicated), which suggests that the proposed modeling method eliminates the influence of warping on the z_☉ estimate. However, the non-local estimate of the vertical standard deviation of Cepheids ${\sigma }_{\rho }=132.0\pm {\left.3.7\right|}_{\mathrm{stat}.}{\left.{}_{-5.9}^{+6.3}\right|}_{\mathrm{cal}.}$ pc differs significantly from the local ${\sigma }_{\rho }={\left.76.5\pm 4.4\right|}_{\mathrm{stat}.}{\left.{}_{-3.4}^{+3.6}\right|}_{\mathrm{cal}.}$ pc, which implies the need to introduce more complex models for the vertical distribution outside the Sun's vicinity.

With a collecting area of 9400 m², the Xinjiang QiTai 110 m radio Telescope (QTT) will allow for a significant advance in the search and observation of pulsars. We have updated the galactic electron density model, scattering model, spectral distribution, and radial distribution of PsrPopPy to generate the population of isolate radio pulsars in the Galaxy. The spiral arm, including the local spiral arm, is considered when generating pulsar locations. By simulation, we estimate the number of previously undetected radio pulsars that QTT will discover with its possible receivers for different strategies. Using the PAF receiver, 2200 previously unknown pulsars could be discovered in 43 days. The 96-beam PAF receiver can produce ∼10.56 GB of data per second.

Based on the data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey (LAMOST DR5) and the Gaia Early Data Release 3 (Gaia EDR3), we construct a sample containing 46,109 giant (log g ≤ 3.5 dex) stars with heliocentric distance d ≤ 4 kpc, and the sample is further divided into two groups of the inner (R_GC < 8.34 kpc) and outer region (R_GC > 8.34 kpc). The L_Z distributions of our program stars in the panels with different [Fe/H] and [α/Fe] suggest that the thick-disk consists of two distinct components with different chemical compositions and kinematic properties. For the inner region, the metal-weak thick disk (MWTD) significantly contributes when [α/Fe] > +0.2 dex and [Fe/H] < −0.8 dex, while the canonical thick-disk (TD) dominates when [Fe/H] > −0.8 dex. However, MWTD clearly appears only when [α/Fe] > +0.2 dex and [Fe/H] < −1.2 dex for the outer region, and its proportion is lower than that of the inner region within the same metallicity. Similar results can be obtained from the V_ϕ distribution. The higher fraction of MWTD in the inner region than that in the outer region implies that MWTD may form in the inner disk, and is observational evidence about the inside-out disk formation scenario.

The Milky Way is a unique laboratory in which stellar properties can be measured and analyzed in detail. In particular, stars in the older populations encode information on the mechanisms that led to the formation of our Galaxy. In this article, we analyze the kinematics, spatial distribution, and chemistry of a large number of stars in the solar neighborhood, where all of the main Galactic components are well represented. We find that the thick disk comprises two distinct and overlapping stellar populations with different kinematic properties and chemical compositions. The metal-weak thick disk (MWTD) contains two-times less metal content than the canonical thick disk, and exhibits enrichment of light elements typical of the oldest stellar populations of the Galaxy. The rotational velocity of the MWTD around the Galactic center is ∼150 km s⁻¹, corresponding to a rotational lag of 30 km s⁻¹ relative to the canonical thick disk (∼180 km s⁻¹), with a velocity dispersion of 60 km s⁻¹. This stellar population likely originated from the merger of a dwarf galaxy during the early phases of our Galaxy's assembly, or it is a precursor disk, formed in the inner Galaxy and brought into the solar neighborhood by bar instability or spiral-arm formation mechanisms.

We investigate the three-dimensional asymmetrical kinematics and present time stamps of the Milky Way disk between Galactocentric distances of R = 12 and 15 kpc, using red clump stars selected from the LAMOST Galactic survey, also with proper motion measurements provided by the Gaia DR2. We discover velocity substructure above the Galactic plane corresponding to a density dip found recently ("South-middle opposite" density structure [R ∼ 12–15 kpc, Z ∼ 1.5 kpc] discovered in Wang et al.) in the radial and azimuthal velocity. For the vertical velocity, we detect clear vertical bulk motions or bending mode motions, which has no clear North–South asymmetry corresponding to the in-plane asymmetrical features. In the subsample of stars with different ages, we find that there is little temporal evolution of the in-plane asymmetry from 0 to 14 Gyr, which means the structure is possibly sensitive to the perturbations in almost cosmic time. We propose that the possible scenario of this asymmetric velocity structure is caused by the mechanisms generated in-plane, rather than vertical perturbations.

The number and properties of observed gravitational microlensing events depend on the distribution and kinematics of stars and other compact objects along the line of sight. In particular, precise measurements of the microlensing optical depth and event rate toward the Galactic bulge enable strict tests of competing models of the Milky Way. Previous estimates, based on samples of up to a few hundred events, gave larger values than expected from the Galactic models and were difficult to reconcile with other constraints on the Galactic structure. Here we used long-term photometric observations of the Galactic bulge by the Optical Gravitational Lensing Experiment (OGLE) to select a homogeneous sample of 8000 gravitational microlensing events. We created the largest and most accurate microlensing optical depth and event rate maps of the Galactic bulge. The new maps ease the tension between the previous measurements and Galactic models. They are consistent with some earlier calculations based on bright stars and are systematically ∼30% smaller than the other estimates based on "all-source" samples of microlensing events. The difference is caused by the careful estimation of the source star population. The new maps agree well with predictions based on the Besançon model of the Galaxy. Apart from testing the Milky Way models, our maps may have numerous other applications, such as the measurement of the initial mass function or constraining the dark matter content in the Milky Way center. The new maps will also inform the planning of future space-based microlensing experiments by revising the expected number of events.

The morphology of thin stellar streams can be used to test the nature of dark matter. It is therefore crucial to extend searches for globular cluster (GC) streams to other galaxies than the Milky Way. In this paper, we investigate the current and future prospects of detecting GC streams in external galaxies in resolved stars (e.g., with Wide Field InfraRed Survey Telescope (WFIRST)) and using integrated light (e.g., with Hyper Suprime-cam (HSC), the Large Synoptic Survey Telescope (LSST), and Euclid). In particular, we inject mock streams to data from the PAndAS M31 survey and produce simulated M31 backgrounds mimicking what WFIRST will observe in M31. Additionally, we estimate the distance limit to which GC streams will be observable. Our results demonstrate that for a 1 hr (1000 s) exposure, using conservative estimates, WFIRST should detect GC streams in resolved stars in galaxies out to distances of ∼3.5 Mpc (∼2 Mpc). This volume contains 199 (122) galaxies, of which >90% are dwarfs. With integrated light, thin streams can be resolved out to ∼100 Mpc with HSC and LSST and to ∼600 Mpc with WFIRST and Euclid. The low surface brightness of the streams (typically >30 mag arcsec⁻²), however, will make them difficult to detect, unless the streams originate from very young clusters. We emphasize that if the external galaxies do not host spiral arms or galactic bars, gaps in their stellar streams provide an ideal test case for evidence of interactions with dark matter subhalos. Furthermore, obtaining a large samples of thin stellar streams can help constrain the orbital structure and hence the potentials of external halos.