Context. The assembly history experienced by the Milky Way is currently being unveiled thanks to the data provided by the Gaia mission. It is likely that the globular cluster system of our Galaxy has ...followed a similarly intricate formation path. Aims. To constrain this formation path, we explore the link between the globular clusters and the known merging events that the Milky Way has experienced. Methods. To this end, we combined the kinematic information provided by Gaia for almost all Galactic clusters, with the largest sample of cluster ages available after carefully correcting for systematic errors. To identify clusters with a common origin we analysed their dynamical properties, particularly in the space of integrals of motion. Results. We find that about 40% of the clusters likely formed in situ. A similarly large fraction, 35%, appear to be possibly associated to known merger events, in particular to Gaia-Enceladus (19%), the Sagittarius dwarf galaxy (5%), the progenitor of the Helmi streams (6%), and to the Sequoia galaxy (5%), although some uncertainty remains due to the degree of overlap in their dynamical characteristics. Of the remaining clusters, 16% are tentatively associated to a group with high binding energy, while the rest are all on loosely bound orbits and likely have a more heterogeneous origin. The resulting age–metallicity relations are remarkably tight and differ in their detailed properties depending on the progenitor, providing further confidence on the associations made. Conclusions. We provide a table listing the likely associations. Improved kinematic data by future Gaia data releases and especially a larger, systematic error-free sample of cluster ages would help to further solidify our conclusions.
Aims. We present mean absolute proper motion measurements for seven ultra-faint dwarf galaxies orbiting the Milky Way, namely Boötes 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. Methods. 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 (GBP – GRP, 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. Results. Our procedure provides mean proper motions with typical uncertainties of ∼0.1 mas yr−1, 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 the number of member stars per galaxy to be maximized regardless of the existence of prior spectroscopic information, and can therefore be applied to any faint or distant stellar system within reach of Gaia.
Purpose
This paper aims to examine firm characteristics and ownership structure determinants of corporate social and environmental voluntary disclosure (CSEVD) practices in Saudi Arabia to address ...the paucity of research in this field for Saudi listed firms.
Design/methodology/approach
The paper uses manual content and regression analyses for online annual report data for Saudi non-financial listed firms over the period 2016–2018 using CSEVD items drawing on global reporting initiative-G4 guidelines.
Findings
Models show that Saudi firm CSEVD has increased over time compared to previous studies to an average of 68% disclosure due to new corporate governance regulations and IFRS implementation. The models show that firm size, leverage, manufacturing industry type and government ownership are positive determinants of CSEVD, while family ownership is the negative driver of CSEVD. However, firm profitability, audit firm size, firm age and institutional ownership have no impact on the level of CSEVD.
Originality/value
Using legitimacy and stakeholder theories, the paper determines the influence of firm characteristics and ownership structure on CSEVD, identifying implications for firm stakeholders and providing some evidence on the impact of corporate governance regulation and IFRS implementation on such disclosure. The paper provides additional evidence on progress towards Saudi’s Vision 2030.
Context.
It has recently been shown that the halo near the Sun contains several kinematic substructures associated with past accretion events. For the more distant halo, there is evidence of ...large-scale density variations – in the form of stellar clouds or overdensities.
Aims.
We study the link between the local halo kinematic groups and three of these stellar clouds: the Hercules-Aquila cloud, the Virgo Overdensity, and the Eridanus-Phoenix overdensity.
Methods.
We perform orbital integrations in a standard Milky Way potential of a local halo sample extracted from
Gaia
EDR3 with the goal of predicting the location of the merger debris elsewhere in the Galaxy. We specifically focus on the regions occupied by the three stellar clouds and compare their kinematic and distance distributions with those predicted from the orbits of the nearby debris.
Results.
We find that the local halo substructures have families of orbits that tend to pile up in the regions where the stellar clouds have been found. The distances and velocities of the cloud’s member stars are in good agreement with those predicted from the orbit integrations, particularly for Gaia-Enceladus stars. This is the dominant contributor of all three overdensities, with a minor part stemming from the Helmi streams and to an even smaller extent from Sequoia. The orbital integrations predict no asymmetries in the sky distribution of halo stars, and they pinpoint where additional debris associated with the local halo substructures may be located.
PurposeThis study examines the impact of board composition and ownership structure variables on dividend payout policy in Saudi Arabian firms. In particular, it aims to determine the effect of board ...size, independence and meeting frequency, in addition to chief executive officer (CEO) duality, and state, institutional, managerial, family, and foreign ownership on both the propensity to pay dividends and dividend per share for Saudi-listed firms over the period 2016–2019.Design/methodology/approachThe paper captures dividend policy with two measures, propensity to pay dividends and dividend per share, and employs a range of regression methods (logistic, probit, ordinary least squares (OLS) and random effects regressions) along with a two-stage least squares (2SLS) model for robustness to account for heteroscedasticity, serial correlation and endogeneity issues. The data set is a large panel of 280 Saudi-listed firms over the period 2016 to 2019.FindingsThe results underline the importance of board composition and the ownership structure in explaining variations in dividend policy across Saudi firms. More specifically, there is a positive relationship between the propensity to pay dividends and board-meeting frequency, institutional ownership, firm profitability and firm age, while the degree of board independence, firm size and leverage exhibit a negative relation. Further, dividend per share is positively related to board meeting frequency, institutional ownership, foreign ownership, firm profitability and age, while it is negatively related to CEO duality, managerial ownership, and firm leverage. There is no evidence that family ownership exerts an impact on dividend payout policy in Saudi firms. The findings of this study support agency, signalling, substitute and outcome theories of dividend policy.Research limitations/implicationsThis study offers an important insight into the board characteristic and ownership structure drivers of dividend policy in the context of an emerging market. Moreover, the study has important implications for firms, managers, investors, policymakers, and regulators in Saudi Arabia.Originality/valueThis paper contributes to the existing literature by providing evidence on four board and five ownership characteristic drivers of dividend policy in Saudi Arabia as an emerging stock market, thereby improving on less comprehensive previous studies. The study recommends that investors consider board composition and ownership structure characteristics of firms as key drivers of dividend policy when making stock investment decisions to inform them about the propensity of investee firms to pay dividends and maintain a given dividend policy.
Aims.
We present the first three-dimensional internal motions for individual stars in the Draco dwarf spheroidal galaxy.
Methods.
By combining first-epoch
Hubble
Space Telescope observations and ...second-epoch
Gaia
Data Release 2 positions, we measured the proper motions of 149 sources in the direction of Draco. We determined the line-of-sight velocities for a sub-sample of 81 red giant branch stars using medium resolution spectra acquired with the DEIMOS spectrograph at the Keck II telescope. Altogether, this resulted in a final sample of 45 Draco members with high-precision and accurate 3D motions, which we present as a table in this paper.
Results.
Based on this high-quality dataset, we determined the velocity dispersions at a projected distance of ∼120 pc from the centre of Draco to be
σ
R
= 11.0
−1.5
+2.1
km s
−1
,
σ
T
= 9.9
−3.1
+2.3
km s
−1
and
σ
LOS
= 9.0
−1.1
+1.1
km s
−1
in the projected radial, tangential, and line-of-sight directions. This results in a velocity anisotropy
β
= 0.25
−1.38
+0.47
at
r
≳ 120 pc. Tighter constraints may be obtained using the spherical Jeans equations and assuming constant anisotropy and Navarro-Frenk-White (NFW) mass profiles, also based on the assumption that the 3D velocity dispersion should be lower than ≈1/3 of the escape velocity of the system. In this case, we constrain the maximum circular velocity
V
max
of Draco to be in the range of 10.2−17.0 km s
−1
. The corresponding mass range is in good agreement with previous estimates based on line-of-sight velocities only.
Conclusions.
Our Jeans modelling supports the case for a cuspy dark matter profile in this galaxy. Firmer conclusions may be drawn by applying more sophisticated models to this dataset and with new datasets from upcoming
Gaia
releases.
The evolution of the Milky Way disk, which contains most of the stars in the Galaxy, is affected by several phenomena. For example, the bar and the spiral arms of the Milky Way induce radial ...migration of stars
and can trap or scatter stars close to orbital resonances
. External perturbations from satellite galaxies can also have a role, causing dynamical heating of the Galaxy
, ring-like structures in the disk
and correlations between different components of the stellar velocity
. These perturbations can also cause 'phase wrapping' signatures in the disk
, such as arched velocity structures in the motions of stars in the Galactic plane. Some manifestations of these dynamical processes have already been detected, including kinematic substructure in samples of nearby stars
, density asymmetries and velocities across the Galactic disk that differ from the axisymmetric and equilibrium expectations
, especially in the vertical direction
, and signatures of incomplete phase mixing in the disk
. Here we report an analysis of the motions of six million stars in the Milky Way disk. We show that the phase-space distribution contains different substructures with various morphologies, such as snail shells and ridges, when spatial and velocity coordinates are combined. We infer that the disk must have been perturbed between 300 million and 900 million years ago, consistent with estimates of the previous pericentric passage of the Sagittarius dwarf galaxy. Our findings show that the Galactic disk is dynamically young and that modelling it as time-independent and axisymmetric is incorrect.
This study examines the impact of corporate governance mechanisms on the performance of listed firms in Saudi Arabia before and during the coronavirus disease (COVID-19) pandemic. The study applied ...univariate, bivariate, and multivariate analyses to data collected from 258 annual reports from 2019 to 2020. The results show that during the COVID-19 pandemic, firm market performance (Tobin's Q ratio) has decreased with larger board size, more board meetings, while it has increased with board experience, board education, and board gender (number of women on the board). Moreover, during the COVID-19 pandemic, board gender was found to have a significant positive impact on the firm's operational performance (return on assets), implying that gender diversity on boards plays a crucial role in times of crisis. The findings have significant implications for Saudi Arabian firms, managers, investors, and policymakers. Furthermore, the latest corporate governance regulations in Saudi Arabia are almost certain to have a significant impact on firm performance, particularly during times of crisis. In addition, corporate governance regulations should consider the importance of small board size, lower board independence, board member experience and education, and board gender diversity to improve corporate performance, especially in times of crisis. Governments and regulators should collaborate to reduce the financial and economic impact of the COVID-19 pandemic. Comprehensive policies are needed to address the negative consequences of current and future crises.
We present VLT FLAMES spectroscopic observations (R similar to 6500 ) in the Ca II triplet region for 470 probable kinematic members of the Sculptor (Scl) dwarf spheroidal galaxy. The accurate ...velocities ( plus or minus 2 km/s) and large area coverage of Scl allow us to measure a velocity gradient of 7.6 super(+3.0) km s-1 deg-1 along the projected major axis of Scl, likely a signature of intrinsic rotation. We also use our kinematic data to measure the mass distribution within this system. By considering independently the kinematics of the two distinct stellar components known to be present in Scl, we are able to relieve known degeneracies and find that the observed velocity dispersion profiles are best fitted by a cored dark matter halo with core radius rc = 0.5 kpc and mass enclosed within the last measured point M(<1.8 kpc) = (3.4 plus or minus 0.7) x 10 super(8) M <1.8, assuming an increasingly radially anisotropic velocity ellipsoid. This results in a mass-to-light ratio of 158 plus or minus 33 (M/L)solar inside 1.8 kpc. An NFW profile with concentration C = 20 and mass M(<1.8 kpc) = 2.2 super(+2) x 10 super(8) M sub(solar) statistically consistent with the observations, but it tends to yield poorer fits for the metal-rich stars.
Aims.
We aim to measure the proper motion along the Sagittarius stream, which is the missing piece in determining its full 6D phase space coordinates.
Methods.
We conduct a blind search of ...over-densities in proper motion from the
Gaia
second data release in a broad region around the Sagittarius stream by applying wavelet transform techniques.
Results.
We find that for most of the sky patches, the highest intensity peaks delineate the path of the Sagittarius stream. The 1500 peaks identified depict a continuous sequence spanning almost 2
π
in the sky, only obscured when the stream crosses the Galactic disk. Altogether, around 100 000 stars potentially belong to the stream as indicated by a coarse inspection of the color-magnitude diagrams. From these stars, we determine the proper motion along the Sagittarius stream, making it the proper-motion sequence with the largest span and continuity ever measured for a stream. A first comparison with existing
N
-body models of the stream reveals some discrepancies, especially near the pericenter of the trailing arm and an underestimation of the total proper motion for the leading arm.
Conclusions.
Our study provides a starting point for determining the variation of the population of stars along the stream, the distance to the stream from the red clump stars, and the solar motion. It also permits much more accurate measurement of the Milky Way potential.
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