Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAnalysis of galaxy kinematics based on Cepheids from the Gaia DR2 Catalogue
68
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
To construct the rotation curve of the Galaxy, classical Cepheids with proper motions, parallaxes and line-of-sight velocities from the Gaia DR2 Catalog are used in large part. The working sample formed from literature data contains about 800 Cepheids with estimates of their age. We determined that the linear rotation velocity of the Galaxy at a solar distance is $V_0=240pm3$~km s$^{-1}$. In this case, the distance from the Sun to the axis of rotation of the Galaxy is found to be $R_0=8.27pm0.10$~kpc. A spectral analysis of radial and residual tangential velocities of Cepheids younger than 120 Myr showed close estimates of the parameters of the spiral density wave obtained from data both at present time and in the past. So, the value of the wavelength $lambda_{R,theta}$ is in the range of [2.4--3.0] kpc, the pitch angle $i_{R,theta}$ is in the range of [$-13^circ$,$-10^circ$] for a four-arm pattern model, the amplitudes of the radial and tangential perturbations are $f_Rsim12$~km s$^{-1}$ and $f_thetasim9$~km s$^{-1}$, respectively. Velocities of Cepheids older than 120 Myr are currently giving a wavelength $lambda_{R,theta}sim5$~kpc. This value differs significantly from one that we obtained from the samples of young Cepheids. An analysis of positions and velocities of old Cepheids, calculated by integrating their orbits backward in time, made it possible to determine significantly more reliable values of the parameters of the spiral density wave: wavelength $lambda_{R,theta}=2.7$~kpc, amplitudes of radial and tangential perturbations are $f_R=7.9$~km s$^{-1}$ and $f_theta=5$~km s$^{-1}$, respectively.
rate research
Read More
We have studied a sample of more than 25 000 young stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The relative errors of their parallaxes do not exceed 10%. The selection of stars belonging to active star-forming regions was made by Marton et al. based on data from the Gaia DR2 catalogue by invoking infrared measurements from the WISE and Planck catalogues. Low-mass T Tauri stars constitute the majority of sample stars. The following parameters of the angular velocity of Galactic rotation have been found from them: $Omega_0 =28.40pm0.11$ km s$^{-1}$ kpc$^{-1}$, $Omega^{}_0=-3.933pm0.033$ km s$^{-1}$ kpc$^{-2}$ and $Omega^{}_0=0.804pm0.040$ km s$^{-1}$ kpc$^{-3}$. The Oort constants are $A=15.73pm0.32$ km s$^{-1}$ kpc$^{-1}$ and $B=-12.67pm0.34$ km s$^{-1}$ kpc$^{-1}$, while the circular rotation velocity of the solar neighborhood around the Galactic center is $V_0=227pm4$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.0pm0.15$ kpc.
The kinematic properties of young stars that have not yet reached the stage of the main sequence are studied. The selection of these stars was recently carried out by Marton et al. (2019) and Vioque et al. (2020) according to the Gaia DR2 catalog using a number of photometric infrared surveys. We have determined the rotation parameters of the Galaxy and the parameters of the ellipsoids of the residual velocities. The linear velocity of the circular rotation of a solar region around the center of the Galaxy, found using 4431 stars, is equal to V_0=229.1+-4.4 km/s. The following ellipsoid parameters of their residual velocities are found from low-mass stars (of type T Tau): $sigma_{1,2,3}=(9.45,6.99,6.61)pm(0.94,0.43,0.32)$ km/s. For stars of intermediate masses (Herbig Ae/Be stars), their values turned out to be somewhat larger $sigma_{1,2,3}=(13.67,9.25,7.26)pm(2.40,2.44,0.88)$ km/s. Distant stars from both Catalogs trace the local spiral arm well. For 1212 stars, a new estimate of the pitch angle of the Local spiral arm is equal to i=-8.9+-0.1 deg.
We apply a simple axisymmetric disc model to 218 Galactic Cepheids whose accurate measurements of the distance and velocities are obtained by cross-matching an existing Cepheids catalogue with the Gaia DR2 data. Our model fit determines the local centrifugal speed, $V_mathrm{c}$ $-$ defined as the rotation speed required to balance the local radial gravitational force $-$ at the Suns location to be $V_{c}(R_0)=236pm 3$ km s$^{-1}$ and the Suns azimuthal and radial peculiar motions to be $V_{odot}=12.4pm0.7$ km s$^{-1}$ and $U_{odot}=7.7pm0.9$ km s$^{-1}$, respectively. These results are obtained with strong priors on the solar radius, $R_0=8.2pm0.1$ kpc, and Suns angular rotation velocity, $Omega_{odot}=30.24pm0.12$ km s$^{-1}$ kpc$^{-1}$. We also applied the axisymmetric model to mock data from an N-body/hydrodynamic simulation of a Milky Way-like galaxy with a bar and spiral arms. We find that our axisymmetric model fit to the young stars recovers the local centrifugal speed reasonably well, even in the face of significant non-axisymmetry. However, the local centrifugal speed determined from our Cepheid sample could suffer from systematic uncertainty as large as 6 km s$^{-1}$.
Using Gaia DR2 astrometry, we map the kinematic signature of the Galactic stellar warp out to a distance of 7 kpc from the Sun. Combining Gaia DR2 and 2MASS photometry, we identify, via a probabilistic approach, 599 494 upper main sequence stars and 12 616 068 giants without the need for individual extinction estimates. The spatial distribution of the upper main sequence stars clearly shows segments of the nearest spiral arms. The large-scale kinematics of both the upper main sequence and giant populations show a clear signature of the warp of the Milky Way, apparent as a gradient of 5-6 km/s in the vertical velocities from 8 to 14 kpc in Galactic radius. The presence of the signal in both samples, which have different typical ages, suggests that the warp is a gravitationally induced phenomenon.
We use Gaia DR2 astrometric and line-of-sight velocity information combined with two sets of distances obtained with a Bayesian inference method to study the 3D velocity distribution in the Milky Way disc. We search for variations in all Galactocentric cylindrical velocity components ($V_{phi}$, $V_R$ and $V_z$) with Galactic radius, azimuth, and distance from the disc mid-plane. We confirm recent work showing that bulk vertical motions in the $Rtext{-}z$ plane are consistent with a combination of breathing and bending modes. In the $xtext{-}y$ plane, we show that, although the amplitudes change, the structure produced by these modes is mostly invariant as a function of distance from the plane. Comparing to two different Galactic disc models, we demonstrate that the observed patterns can drastically change in short time intervals, showing the complexity of understanding the origin of vertical perturbations. A strong radial $V_R$ gradient was identified in the inner disc, transitioning smoothly from $16$ km s$^{-1}$ kpc$^{-1}$ at an azimuth of $30^circ<phi<45^circ$ ahead of the Sun-Galactic centre line, to $-16$ km s$^{-1}$ kpc$^{-1}$ at an azimuth of $-45^circ<phi<-30^circ$ lagging the solar azimuth. We use a simulation with no significant recent mergers to show that exactly the opposite trend is expected from a barred potential, but overestimated distances can flip this trend to match the data. Alternatively, using an $N$-body simulation of the Sagittarius dwarf-Milky Way interaction, we demonstrate that a major recent perturbation is necessary to reproduce the observations. Such an impact may have strongly perturbed the existing bar or even triggered its formation in the last $1text{-}2$ Gyr.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
