Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userWhich Milky Way masses are consistent with the slightly declining 5-25 kpc rotation curve?
102
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Discoveries of extended rotation curves have suggested the presence of dark matter in spiral galaxy haloes. It has led to many studies that estimated the galaxy total mass, mostly by using the Navarro Frenk and White (NFW) density profile. We aim at verifying how the choice of the dark-matter profile may affect the predicted values of extrapolated total masses. We have considered the recent Milky Way (MW) rotation curve, firstly because of its unprecedented accuracy, and secondly because the Galactic disk is amongst the least affected by past major mergers having fully reshaped the initial disk. We find that the use of NFW profile (or its generalized form, gNFW) for calculating the dark-matter contribution to the MW rotation curve generates apparently inconsistent results, e.g., an increase of the baryonic mass leads to increase of the dark matter mass. Furthermore we find that NFW and gNFW profile narrow the total mass range, leading to a possible methodological bias particularly against small MW masses. By using the Einasto profile that is more appropriate to represent cold dark matter haloes, we finally find that the Milky Way slightly decreasing rotation curve favors total mass that can be as small as 2.6 $times 10^{11}$ $M_{odot}$, disregarding any other dynamical tracers further out in the MW. It is inconsistent with values larger than 18 $times 10^{11}$ $M_{odot}$ for any kind of CDM dark-matter halo profiles, under the assumption that stars and gas do not influence the predicted dark matter distribution in the MW. This methodological paper encourages the use of the Einasto profile for characterizing rotation curves with the aim of evaluating their total masses.
rate research
Read More
We present central velocity dispersions, masses, mass to light ratios ($M/L$s), and rotation strengths for 25 Galactic globular clusters. We derive radial velocities of 1951 stars in 12 globular clusters from single order spectra taken with Hectochelle on the MMT telescope. To this sample we add an analysis of available archival data of individual stars. For the full set of data we fit King models to derive consistent dynamical parameters for the clusters. We find good agreement between single mass King models and the observed radial dispersion profiles. The large, uniform sample of dynamical masses we derive enables us to examine trends of $M/L$ with cluster mass and metallicity. The overall values of $M/L$ and the trends with mass and metallicity are consistent with existing measurements from a large sample of M31 clusters. This includes a clear trend of increasing $M/L$ with cluster mass, and lower than expected $M/L$s for the metal-rich clusters. We find no clear trend of increasing rotation with increasing cluster metallicity suggested in previous work.
In the fundamental quest of the rotation curve of the Milky Way, the tangent-point (TP) method has long been the simplest way to infer velocities for the inner, low latitude regions of the Galactic disk from observations of the gas component. We test the validity of the method on realistic gas distribution and kinematics of the Milky Way, using a numerical simulation of the Galaxy. We show that the resulting velocity profile strongly deviates from the true rotation curve of the simulation, as it overstimates it in the central regions, and underestimates it around the bar corotation. Also, its shape strongly depends on the orientation of the stellar bar. The discrepancies are caused by highly non-uniform azimuthal velocities, and the systematic selection by the TP method of high-velocity gas along the bar and spiral arms, or low-velocity gas in less dense regions. The velocity profile is in good agreement with the rotation curve only beyond corotation, far from massive asymmetric structures. Therefore the observed velocity profile of the Milky Way inferred by the TP method is expected to be very close to the true Galactic rotation curve for 4.5<R<8 kpc. Another consequence is that the Galactic velocity profile for R<4-4.5 kpc is very likely flawed by the non-uniform azimuthal velocities, and does not represent the true Galactic rotation curve, but instead local motions. The real shape of the innermost rotation curve is probably shallower than previously thought. Using a wrong rotation curve has a dramatic impact on the modelling of the mass distribution, in particular for the bulge component of which derived enclosed mass within the central kpc and scale radius are, respectively, twice and half of the actual values. We thus strongly argue against using terminal velocities or the velocity curve from the TP method for modelling the mass distribution of the Milky Way. (abridged)
Flat rotation curves of spiral galaxies are considered as an evidence for dark matter, but the rotation curve of the Milky Way is difficult to measure. Various objects were used to track the rotation curve in the outer parts of the Galaxy, but most studies rely on incomplete kinematical information and inaccurate distances. Here, we use a sample of 773 Classical Cepheids with precise distances based on mid-infrared period-luminosity relations coupled with proper motions and radial velocities from Gaia to construct the accurate rotation curve of the Milky Way up to the distance of ~20 kpc from the Galactic center. We use a simple model of Galactic rotation to measure the rotation speed of the Sun Theta_0 = 233.6 +/- 2.8 km/s, assuming a prior on the distance to the Galactic center R_0 = 8.122 +/- 0.031 kpc from the Gravity Collaboration. The rotation curve at Galactocentric distances 4 < R < 20 kpc is nearly flat with a small gradient of -1.34 +/- 0.21 km/s/kpc. This is the most accurate Galactic rotation curve at distances R > 12 kpc constructed so far.
We review the~current status of the~study of rotation curve (RC) of the~Milky Way, and~present a~unified RC from the~Galactic Center to the galacto-centric distance of about 100 kpc. The~RC is used to directly calculate the~distribution of the~surface mass density (SMD). We then propose a~method to derive the~distribution of dark matter (DM) density in the~in the~Milky Way using the~SMD distribution. The~best-fit dark halo profile yielded a local DM density of $rho_odot = 0.36pm 0.02$ GeV/cc. We also review the~estimations of the~local DM density in the~last decade, and~show that the~value is converging to a~value at $rho_odot=0.39pm 0.09$ GeV/cc.
We present $texttt{galkin}$, a novel compilation of kinematic measurements tracing the rotation curve of our Galaxy, together with a tool to treat the data. The compilation is optimised to Galactocentric radii between 3 and 20 kpc and includes the kinematics of gas, stars and masers in a total of 2780 measurements carefully collected from almost four decades of literature. A simple, user-friendly tool is provided to select, treat and retrieve the data of all source references considered. This tool is especially designed to facilitate the use of kinematic data in dynamical studies of the Milky Way with various applications ranging from dark matter constraints to tests of modified gravity.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
