We analyse the kinematics and dynamics of a homogeneous sample of red clump stars selected from the second Gaia data release catalogue in the direction of the Galactic poles. The level of completeness of the sample at heights between 0.6 and 3.5 kpc is asserted by comparison with the 2 Micron All Sky Survey catalogue. We show that both the density distribution and velocity dispersion are significantly more perturbed in the North than in the South, in all analysed regions of our Galactic neighbourhoods. We provide a detailed assessment of these North-South asymmetries at large heights. We then proceed to evaluate how such asymmetries could affect determinations of the dynamical matter density under equilibrium assumptions. We find that a Jeans analysis delivers relatively similar vertical forces and integrated dynamical surface densities at large heights above the plane in both hemispheres. At these heights, the densities of stars and gas are very low and the surface density is largely dominated by dark matter, which allows to estimate, separately in the North and South, the local dark matter density derived under equilibrium assumptions. In the presence of vertical perturbations, such values should be considered as an upper limit. This Jeans analysis yields values of the local dark matter density above 2~kpc, $ρ_{\rm DM} \sim 0.013 \, {\rm M}_\odot/{\rm pc}^3$ ($ \sim 0.509 \, {\rm GeV/cm}^3$) in the perturbed Northern hemisphere, and $ρ_{\rm DM} \sim 0.010 \, {\rm M}_\odot/{\rm pc}^3$ ($ \sim 0.374 \, {\rm GeV/cm}^3$) in the much less perturbed South. As a comparison, we determine the local dark matter density by fitting a global phase-space distribution to the data. We end up with a value in the range of $ρ_{\rm DM} \sim 0.011 - 0.014 \, {\rm M}_\odot/{\rm pc}^3$ in global agreement with Jeans analysis.
In this first paper we simulate the population of disc Red Clump stars to be observed by Gaia. We generate a set of test particles and we evolve it in a 3D barred Milky Way like galactic potential. We assign physical properties of the Red Clump trace population and a realistic 3D interstellar extinction model. We add Gaia observational constraints and an error model according to the pre-commissioning scientific performance assessments. We present and analyse two mock catalogues, offered to the community, that are an excellent test bed for testing tools being developed for the future scientific…
We propose a new way to search for hypervelocity stars in the Galactic bulge, by using red clump (RC) giants, that are good distance indicators. The 2nd Gaia Data Release and the near-IR data from the VISTA Variables in the Via Lactea (VVV) Survey led to the selection of a volume limited sample of 34 bulge RC stars. A search in this combined data set leads to the discovery of seven candidate hypervelocity red clump stars in the Milky Way bulge. Based on this search we estimate the total production rate of hypervelocity RC stars from the central supermassive black hole (SMBH) to be $N_{HVRC} = …
Using a sample of nearly 140,000 red clump stars selected from the LAMOST and Gaia Galactic surveys, we have mapped mean vertical velocity $\overline{V_{z}}$ in the $X$-$Y$ plane for a large volume of the Galactic disk (6 $< R < 16$ kpc; $-20 <ϕ< 50^{\circ}$; $|Z| < 1$ kpc). A clear signature where $\overline{V_{z}}$ increases with $R$ is detected for the chemically thin disk. The signature for the thick disk is however not significant, in line with the hot nature of this disk component. For the thin disk, the warp signature shows significant variations in both radial and azimuthal directions,…
The systematic offset of Gaia parallaxes has been widely reported with Gaia's second data release, and it is expected to persist in future Gaia data. In order to use Gaia parallaxes to infer distances to high precision, we develop a hierarchical probabilistic model to determine the Gaia parallax zero point offset along with the calibration of an empirical model for luminosity of red clump stars by combining astrometric and photometric measurements. Using a cross-matched sample of red clump stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and Gaia Data Release 2 (D…
We have analyzed the space velocities of stars with the proper motions and trigonometric parallaxes from the Gaia TGAS catalogue in combination with the line-of-sight velocities from the RAVE5 catalogue. In the (V,\sqrt{U^2+2V^2}) velocity plane we have identified three clumps, BB17-1, BB17-2, and BB17-3, in the region of large velocities (V<-150 km/s). The stars of the BB17-1 and BB17-2 clumps are associated with the kinematic groups VelHel-6 and VelHel-7 detected previously by Helmi et al. We give the greatest attention to the BB17-3 clump. The latter is shown to be most closely linked with …
Gaia Data Release 1 allows to recalibrate standard candles such as the Red Clump stars. To use those, they first need to be accurately characterised. In particular, colours are needed to derive the interstellar extinction. As no filter is available for the first Gaia data release and to avoid the atmosphere model mismatch, an empirical calibration is unavoidable. The purpose of this work is to provide the first complete and robust photometric empirical calibration of the Gaia Red Clump stars of the solar neighbourhood, through colour-colour, effective temperature-colour and absolute magnitude-…
By combining LAMOST DR4 and Gaia DR2 common red clump stars with age and proper motion, we analyze the amplitude evolution of the stellar warp independently of any assumption with a simple model. The greatest height of the warp disk increases with Galactocentric distance in different populations and it is dependent on the age: the younger stellar populations exhibit stronger warp features than the old ones, accompanied with the warp amplitude $γ({\rm age})$ decreasing with age and its first derivative $\dotγ ({\rm age})$ is different from zero. The azimuth of line of nodes $ϕ_w$ is stable at $…
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 $\sim$ 12-15 \,kpc, Z $\sim$ 1.5 \,kpc] discovered in \citet{Wang2018b, Wang2018c}) in the radial and azimuthal velocity. For the vertical velocity, we detect …
Recent results have suggested that there is tension between the Gaia DR1 TGAS distances and the distances obtained using luminosities determined by eclipsing binaries or asteroseismology on red giant stars. We use the $K_s$-band luminosities of red clump stars, identified and characterized by asteroseismology, to make independent distance estimates. Our results suggest that Gaia TGAS distances contain a systematic error that decreases with increasing distance. We propose a correction to mitigate this offset as a function of parallax that is valid for the Kepler field and values of parallax tha…
We present an independent examination of the parallax zero-point of the Third Gaia Early Data Release (hereafter EDR3), using the LAMOST primary red clump (PRC) stellar sample. A median parallax offset of around $26 μ$as, slightly larger than that found by examination of distant quasars, is found for both the five- and six-parameter solutions in EDR3, based on samples of over 63,000 and 2000 PRC stars, respectively. Similar to the previous investigation of Lindegren et al., to which we compare our results, the parallax zero-point exhibits clear dependencies on the $G$ magnitudes, colors, and p…
We present a sample of $\sim$ 140,000 primary red clump (RC) stars of spectral signal-to-noise ratios higher than 20 from the LAMOST Galactic spectroscopic surveys, selected based on their positions in the metallicity-dependent effective temperature--surface gravity and color--metallicity diagrams, supervised by high-quality $Kepler$ asteroseismology data. The stellar masses and ages of those stars are further determined from the LAMOST spectra, using the Kernel Principal Component Analysis method, trained with thousands of RCs in the LAMOST-$Kepler$ fields with accurate asteroseismic mass mea…
Based on the Gaia DR1 TGAS parallaxes and photometry from the Tycho-2, Gaia, 2MASS, and WISE catalogues, we have produced a sample of about 100 000 clump red giants within about 800 pc of the Sun. The systematic variations of the mode of their absolute magnitude as a function of the distance, magnitude, and other parameters have been analyzed. We show that these variations reach 0.7 mag and cannot be explained by variations in the interstellar extinction or intrinsic properties of stars and by selection. The only explanation seems to be a systematic error of the Gaia DR1 TGAS parallax dependen…
Although core helium-burning red clump (RC) stars are faint at ultraviolet wavelengths, their ultraviolet-optical color is a unique and accessible probe of their physical properties. Using data from the GALEX All Sky Imaging Survey, Gaia Data Release 2 and the SDSS APOGEE DR14 survey, we find that spectroscopic metallicity is strongly correlated with the location of an RC star in the UV-optical color magnitude diagram. The RC has a wide spread in (NUV - G)$_0$ color, over 4 magnitudes, compared to a 0.7-magnitude range in (G$_{BP}$ - G$_{RP}$)$_0$. We propose a photometric, dust-corrected, ult…
Using a sample of 96,201 primary red clump (RC) stars selected from the LAMOST and Gaia surveys, we investigate the stellar structure of the Galactic disk. The sample stars show two separated sequences of high-[α/Fe] and low-[α/Fe] in the [α/Fe]-[Fe/H] plane. We divide the sample stars into five mono-abundance populations (MAPs) with different ranges of [α/Fe] and [Fe/H], named as the high-[α/Fe], high-[α/Fe] & high-[Fe/H], low-[Fe/H], solar, high-[Fe/H] MAPs respectively. We present the stellar number density distributions in the R R Z plane, and the scale heights and scale lengths of the ind…
We consider a complete sample of 101810 giants with Gaia DR2 parallaxes $\varpi$ within the red clump domain of the Hertzsprung-Russell diagram in the space cylinder with a radius of 700 pc around the Sun and a height of $|Z|=1800$ pc. We use the Gaia DR2 $G_\mathrm{BP}$, $G_\mathrm{RP}$ and WISE $W3$ photometry. We describe the spatial variations of the modes of the observables $G_\mathrm{BP}-G_\mathrm{RP}$, $G_\mathrm{RP}-W3$, $G_\mathrm{BP}+5+5\,\log_{10}\varpi$, $G_\mathrm{RP}+5+5\,\log_{10}\varpi$, and $W3+5+5\,\log_{10}\varpi$ by extinction and reddening in combination with linear vertic…
We perform analysis of the three-dimensional kinematics of Milky Way disk stars in mono-age populations. We focus on stars between Galactocentric distances of $R=6$ and 14 \,kpc, selected from the combined LAMOST 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 disk asymmetrical motions near the anticenter 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 no…
Mapping the Galactic disk with the LAMOST and Gaia Red clump sample: VIII: Mapping the kinematics of the Galactic disk using mono-age and mono-abundance stellar populations
This study presents the multi-wavelength investigation of the absolute magnitudes and colours of the red clump (RC) stars selected from APOGEE and GALAH DR2 combined catalogue which is complemented with {\it Gaia} DR2 astrometric data and multi-wavelength photometric data of {\it GALEX} GR6/7, SDSS DR7, {\it Gaia} DR2, 2MASS and {\it WISE} sky surveys. The analyses are centred on the different distance estimation methods using {\it Gaia} trigonometric parallaxes, (1/$\varpi$) and Bayes statistics, and chemically defined Galactic disc populations on [$α$/Fe]$\times$[Fe/H] plane. Such investigat…
Mapping the Milky Way with Gaia Bp/Rp spectra-IV: the broken and asymmetric density profile of the stellar disk traced by a large sample of red clumps
Institute of Astronomy and Physics, Inner Mongolia University（内蒙古大学天文与物理学院）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna（拉各纳大学）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Key Laboratory of Survey Science of Yunnan Province, Yunnan University（云南省测绘科学重点实验室）
Distances to individual stars in our own Galaxy are critical in order to piece together the nature of its velocity and spatial structure. Core helium burning red clump (RC) stars have similar luminosities, are abundant throughout the Galaxy, and thus constitute good standard candles. We build a hierarchical probabilistic model to quantify the quality of RC stars as standard candles using parallax measurements from the first Gaia data release. A unique aspect of our methodology is to fully account for (and marginalize over) parallax, photometry, and dust corrections uncertainties, which leads t…
Using a sample of nearly 140,000 primary red clump stars selected from the LAMOST and $Gaia$ surveys, we have identified a large sample of "young" [$α$/Fe]-enhanced stars with stellar ages younger than 6.0 Gyr and [$α$/Fe] ratios greater than 0.15 dex. The stellar ages and [$α$/Fe] ratios are measured from LAMOST spectra, using a machine learning method trained with common stars in the LAMOST-APOGEE fields (for [$α$/Fe]) and in the LAMOST-$Kepler$ fields (for stellar age). The existence of these "young" [$α$/Fe]-enhanced stars is not expected from the classical Galactic chemical evolution mode…
We explore the possibility of detecting and characterizing the warp of the stellar disc of our Galaxy using synthetic Gaia data. The availability of proper motions and, for the brightest stars radial velocities, adds a new dimension to this study. A family of Great Circle Cell Counts (GC3) methods is used. They are ideally suited to find the tilt and twist of a collection of rings, which allow us to detect and measure the warp parameters. To test them, we use random realizations of test particles which evolve in a realistic Galactic potential warped adiabatically to various final configuration…
We have demonstrated the advantage of combining multi-wavelength observations, from the ultraviolet (UV) to near-infrared, to study Kron 3, a massive star cluster in the Small Magellanic Cloud. We have estimated the radius of the cluster Kron 3 to be 2.'0 and for the first time, we report the identification of NUV-bright red clump (RC) stars and the extension of the RCin colour and magnitude in the NUV vs (NUV-optical) colour-magnitude diagram (CMD). We found that extension of the RC is an intrinsic property of the cluster and it is not due to contamination of field stars or differential redde…
We use the SDSS-Gaia Catalogue to identify six new pieces of halo substructure. SDSS-Gaia is an astrometric catalogue that exploits SDSS data release 9 to provide first epoch photometry for objects in the Gaia source catalogue. We use a version of the catalogue containing $245\,316$ stars with all phase space coordinates within a heliocentric distance of $\sim 10$ kpc. We devise a method to assess the significance of halo substructures based on their clustering in velocity space. The two most substantial structures are multiple wraps of a stream which has undergone considerable phase mixing (S…
The Blanco DECam Bulge Survey (BDBS) VIII: Chemo-kinematics in the southern Galactic bulge from 2.3 million red clump stars with Gaia DR3 proper motions
Testing the asteroseismic estimates of stellar radii with surface brightness-colour relations and {\it Gaia} DR3 parallaxes. II. Red giants and red clump stars from the {\it Kepler} catalogue
Unveiling the Sagittarius Dwarf Spheroidal Galaxy Core with Gaia DR3: A Red Clump Distance Precise to 2%
The University of Texas at Austin（德克萨斯大学奥斯汀分校）；Whitman College（惠特曼学院）；Institute for Astronomy, University of Hawai‘i（夏威夷大学天体物理研究所）；Texas Christian University（得克萨斯基督教大学）；Maunakea Spectroscopic Explorer, Canada-France-Hawaii-Telescope（莫纳克亚光谱巡天项目，加拿大法国夏威夷望远镜）
We search for metal-rich Sausage-kinematic (MRSK) stars with [Fe/H]> -0.8 and -100<Vphi<50 km/s in LAMOST DR5 in order to investigate the influence of the Gaia-Sausage-Enceladus (GSE) merger event on the Galactic disk. For the first time, we find a group of low-alpha MRSK stars, and classify it as a metal-rich tail of the GSE galaxy based on the chemical and kinematical properties. This group has slightly larger Rapo, Zmax and Etot distributions than a previously-reported high-alpha group. Its low-alpha ratio does not allow for an origin resulting from the splash process of the GSE merger even…
We derive the vertical velocities of disk stars in the range of Galactocentric radii of R=5-16 kpc within 2 kpc in height from the Galactic plane. This kinematic information is connected to dynamical aspects in the formation and evolution of the Milky Way, such as the passage of satellites and vertical resonance and determines whether the warp is a long-lived or a transient feature. We used the proper motions of the PPMXL survey, correcting of systematic errors with the reference of quasars. From the color-magnitude diagram K versus (J-K) we selected the standard candles corresponding to red c…
In the coming decade the Gaia satellite will precisely measure the positions and velocities of millions of stars in the Galactic halo, including stars in many tidal streams. These streams, the products of hierarchical accretion of satellite galaxies by the Milky Way (MW), can be used to infer the Galactic gravitational potential thanks to their initial compactness in phase space. Plans for observations to extend Gaia's radial velocity (RV) measurements to faint stars, and to determine precise distances to RR Lyrae (RRLe) in streams, would further extend the power of Gaia's kinematic catalog to…
Red clump stars (RCs) are useful tracers of distances, extinction, chemical abundances, and Galactic structures and kinematics. Accurate estimation of the RC parameters -- absolute magnitude and intrinsic color -- is the basis for obtaining high-precision RC distances. By combining astrometric data from Gaia, spectroscopic data from APOGEE and LAMOST, and multi-band photometric data from Gaia, APASS, Pan-STARRS1, 2MASS, and WISE surveys, we use the Gaussian process regression to train machine learners to derive the multi-band absolute magnitudes $M_λ$ and intrinsic colors $(λ_1-λ_2)_0$ for eac…
We explore the phase-space structure of nearby halo stars identified kinematically from Gaia DR2 data. We focus on their distribution in velocity and in "integrals of motion" space as well as on their photometric properties. Our sample of stars selected to be moving at a relative velocity of at least 210 km/s with respect to the Local Standard of Rest, contains an important contribution from the low rotational velocity tail of the disk(s). The $V_R$-distribution of these stars depicts a small asymmetry similar to that seen for the faster rotating thin disk stars near the Sun. We also identify …
Using the cross-matched data of Gaia EDR3 and the 2MASS Point Source Catalog, a sample of RC stars with parallax accuracies better than 20% is identified and used to reveal the nearby spiral pattern traced by old stars. As shown in the overdensity distribution of RC stars, there is an arc-like feature extended from $l~\sim$ 90$^\circ$ to $\sim$ 243$^\circ$, which passed close to the Sun. This feature is probably an arm segment traced by old stars, indicating the Galaxy potential in the vicinity of the Sun. By comparing to the spiral arms depicted by young objects, we found that there are consi…
It has recently been suggested that all giant stars with mass below 2 $M_{\odot}$ suffer an episode of surface lithium enrichment between the tip of the red giant branch (RGB) and the red clump (RC). We test if the above result can be confirmed in a sample of RC and RGB stars that are members of open clusters. We discuss Li abundances in six open clusters with ages between 1.5 and 4.9 Gyr (turn-off masses between 1.1 and 1.7 $M_{\odot}$). These observations are compared with the predictions of different models that include rotation-induced mixing, thermohaline instability, mixing induced by th…
The physical nature of a series of 20 new open clusters is confirmed employing existing data on putative star members, mainly from second Gaia Data Release (DR2). The clusters were discovered as overdensities of stars by visual inspection of either photographic DSS plates or proper motion plots of random source fields. The reported objects are not present in the most comprehensive or recent catalogs of stellar clusters and associations. For all of them, clumps of comoving stars are revealed in the proper motion space. The parallaxes of the clumped stars are compatible with the real existence o…
CONTEXT. Claims of an X-shaped Galactic bulge were based on the assumption of red clump stars as standard candles in some lines of sight crossing the off-plane bulge. However, some doubts have been cast on whether the two peaks in star counts along the line of sight really represent a double peak in the density distribution, or whether there is something wrong with the assumption of a unique constant absolute magnitude for all of these stars. AIMS. With the advent of Gaia-DR2 parallaxes in combination with near-infrared VISTA-VVV data, we are able to check which of the hypotheses is correct. M…
We present the discovery of stellar tidal tails around the Large and the Small Magellanic Clouds in the Gaia DR1 data. In between the Clouds, their tidal arms are stretched towards each other to form an almost continuous stellar bridge. Our analysis relies on the exquisite quality of the Gaia's photometric catalogue to build detailed star-count maps of the Clouds. We demonstrate that the Gaia DR1 data can be used to detect variable stars across the whole sky, and in particular, RR Lyrae stars in and around the LMC and the SMC. Additionally, we use a combination of Gaia and Gale to follow the d…
Context. The astrometric satellite Gaia is expected to significantly increase our knowledge as to the properties of the Milky Way. The Gaia Early Data Release 3 (Gaia EDR3) provides the most precise parallaxes for many OB stars, which can be used to delineate the Galactic spiral structure. Aims. We investigate the local spiral structure with the largest sample of spectroscopically confirmed young OB stars available to date, and we compare it with what was traced by the parallax measurements of masers. Methods. A sample consisting of three different groups of massive young stars, including O-B2…
We report the serendipitous discovery of three new open clusters, named UFMG 1, UFMG 2 and UFMG 3 in the field of the intermediate-age cluster NGC 5999, by using Gaia DR2 data. A colour-magnitude filter tailored for a proper selection of main-sequence stars and red clump giants turned evident the presence of NGC 5999 and these three new stellar groups in proper motion space. Their structural parameters were derived from King-profile fittings over their projected stellar distributions and isochrone fits were performed on the clusters cleaned colour-magnitude diagrams built with Gaia bands to de…
The presence of two red clumps (RCs) in high latitude fields of the Milky Way bulge is interpreted as evidence for an X-shaped structure originated from the bar instability. Here we show, however, that this double RC phenomenon is more likely to be another manifestation of multiple populations observed in globular clusters (GCs) in the metal-rich regime. As in the bulge GC Terzan 5, the helium enhanced second generation stars (G2) in the classical bulge component of the Milky Way are placed on the bright RC, which is about 0.5 mag brighter than the normal RC originated from the first generatio…
Light escaping from a gravitational potential suffers a redshift with magnitude proportional to the depth of the potential. This "gravitational redshift" is easily measurable in dense stars such as white dwarfs, but is much weaker and has evaded unambiguous detection in main-sequence stars. I show that the effect is directly measurable in the Gaia DR3 radial velocities (RVs) of the components of wide binary stars. In a sample of $\sim$500 wide binaries containing a solar-type main-sequence star and a red giant or red clump companion, the apparent RV of the giant is on average $0.49 \pm 0.02 \,…
Open Clusters have long been used to study the chemo-dynamical evolution of the Galactic disk. This requires an homogeneously analysed sample covering a wide range of ages and distances. In this aper we present the OCCASO second data release. This comprises a sample of high-resolution ($R>65,000$) and high signal-to-noise spectra of 115 Red Clump stars in 18 Open Clusters. We derive atmospheric parameters ($T_{\mathrm{eff}}$, $\log g$, $ξ$), and [Fe/H] abundances using two analysis techniques: equivalent widths and spectral synthesis. A detailed comparison and a critical review of the results …
Towards Galactic Archaeology with Inferred Ages of Giant Stars From Gaia Spectra
Mullard Space Science Laboratory, University College London（穆拉德空间科学实验室，伦敦大学学院）；National Astronomical Observatory of Japan（日本国立天文台）；Kavli Institute for Particle Astrophysics & Cosmology (KIPAC), Stanford University（卡弗里粒子天体物理与宇宙学研究所（KIPAC），斯坦福大学）；Research School of Astronomy and Astrophysics, Australian National University（天文与天体物理研究学院，澳大利亚国立大学）；School of Computing, Australian National University（计算机学院，澳大利亚国立大学）；Department of Physics and Astronomy, University College London（物理与天文学系，伦敦大学学院）；Dipartimento di Fisica e Astronomia, Universita´ degli Studi di Bologna（物理与天文学系，博洛尼亚大学）；INAF – Osservatorio di Astrofisica e Scienza dello Spazio（意大利国家天体物理研究所-空间天体物理与科学观测站）
We present molecular line and dust continuum observations of a Planck-detected cold cloud, G074.11+00.11. The cloud consists of a system of curved filaments and a central star-forming clump. The clump is associated with several infrared sources and H2O maser emission. We aim to determine the mass distribution and gas dynamics within the clump, to investigate if the filamentary structure seen around the clump repeats itself on a smaller scale, and to estimate the fractions of mass contained in dense cores and filaments. The velocity distribution of pristine dense gas can be used to investigate …
The quality and quantity of 6D stellar position-velocity measurements in the second Gaia data release (DR2) allows to study small-scale structure in the orbit distribution of the Galactic disc beyond the immediate Solar neighborhood. We investigate the distribution of orbital actions $(J_R,J_ϕ=L_z,J_z)$ of $\sim 3.5$ million stars within $1.5~\text{kpc}$ of the Sun, for which precise actions can be calculated from Gaia DR2 alone. This distribution $n(J_R,L_z)$ reveals a remarkable amount of sub-structure. The known moving groups in the $(U,V)$-plane of the Solar neighborhood correspond to over…
Many massive star forming disc galaxies in the redshift range 3 to 0.5 are observed to have a clumpy morphology showing giant clumps of size $\sim$1 kpc and masses of about $10^7M_{\odot}$ to $10^{10} M_{\odot}$. The nature and fate of these giant clumps is still under debate. In this work we use 19 high-resolution simulations of disc galaxies from the NIHAO sample to study the formation and the evolution of clumps in the discs of high redshift galaxies. We use mock HST - CANDELS observations created with the radiative transfer code GRASIL-3D to carry out, for the first time, a quantitative co…
The finding of a double red clump in the luminosity function of the Milky Way bulge has been interpreted as evidence for an X-shaped structure. Recently, an alternative explanation has been suggested, where the double red clump is an effect of multiple stellar populations in a classical spheroid. In this letter we provide an observational assessment of this scenario and show that it is not consistent with the behaviour of the red clump across different lines of sight, particularly at high distances from the Galactic plane. Instead, we confirm that the shape of the red clump magnitude distribut…
Star cluster complexes such as the Carina Nebula can have formed in turbulent giant molecular clouds. We perform a series of $N$-body simulations starting from subclustering initial conditions based on hydrodynamic simulations of turbulent molecular clouds. These simulations finally result in the formation of star cluster complexes consisting of several subclusters (clumps). We obtain the inter-clump velocity distribution, the size of the region, and the mass of the most massive cluster in our simulated complex and compare the results with observed ones (the Carina Nebula and NGC 2264). The on…
We present an updated version of the semi-analytic Just-Jahreiß (JJ) model of the Galactic disk and constrain its parameters in the Solar neighbourhood. The new features of the JJ model include a simple two-component gaseous disk, a star-formation rate (SFR) function of the thick disk that has been extended in time, and a correlation between the kinematics of molecular gas and thin-disk populations. Here, we study the vertical number density profiles and W-velocity distributions determined from ~2 million local stars of the Gaia DR2. We also investigate an apparent Hess diagram of the Gaia sta…
