scholarly journals Resolving the Disk-Halo Degeneracy: A look at M74

2016 ◽  
Vol 11 (S321) ◽  
pp. 267-267
Author(s):  
S. Aniyan ◽  
K. C. Freeman ◽  
M. Arnaboldi ◽  
O. Gerhard ◽  
L. Coccato ◽  
...  
Keyword(s):  
Surface Density ◽  
Rotation Curve ◽  
Velocity Dispersion ◽  
Mass Density ◽  
Disk Surface ◽  
Scale Height ◽  
Dark Halo ◽  
Conceptual Problem ◽  
Surface Mass ◽  
Surface Mass Density

AbstractThe decomposition of the 21 cm rotation curve of galaxies into contribution from the disk and dark halo depends on the adopted mass to light ratio (M/L) of the disk. Given the vertical velocity dispersion (σz) of stars in the disk and its scale height (h), the disk surface density and hence the M/L can be estimated. Earlier works have used this technique to conclude that galaxy disks are submaximal. Here we address an important conceptual problem: σz and h must pertain to the same population. Our analysis concludes that previous studies underestimate the disk surface mass density by ~ 2, sufficient to make a maximal disk for M74 appear like a submaximal disk.

scholarly journals Resolving the Disk-Halo Degeneracy using Planetary Nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 284-287
Author(s):  
S. Aniyan ◽  
K. C. Freeman ◽  
M. Arnaboldi ◽  
O. Gerhard ◽  
L. Coccato ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Velocity Dispersion ◽  
Mass Density ◽  
Planetary Nebulae ◽  
Disk Surface ◽  
Scale Height ◽  
Dark Halo ◽  
Surface Mass ◽  
Star Forming ◽  
Light Spectra

AbstractThe decomposition of the 21 cm rotation curve of galaxies into contribution from the disk and dark halo depends on the adopted mass to light ratio (M/L) of the disk. Given the vertical velocity dispersion (σz) of stars in the disk and its scale height (hz), the disk surface density and hence the M/L can be estimated. Earlier works have used this technique to conclude that galaxy disks are submaximal. Here we address an important conceptual problem: star-forming spirals have an old (kinematically hot) disk population and a young cold disk population. Both of these populations contribute to the integrated light spectra from which σz is measured. The measured scale height hz is for the old disk population. In the Jeans equation, σz and hz must pertain to the same population. We have developed techniques to extract the velocity dispersion of the old disk from integrated light spectra and from samples of planetary nebulae. We present the analysis of the disk kinematics of the galaxy NGC 628 using IFU data in the inner regions and planetary nebulae as tracers in the outer regions of the disk. We demonstrate that using the scale height of the old thin disk with the vertical velocity dispersion of the same population, traced by PNe, results in a maximal disk for NGC 628. Our analysis concludes that previous studies underestimate the disk surface mass density by ~ 2, sufficient to make a maximal disk for NGC 628 appear like a submaximal disk.

scholarly journals Resolving the Disc–Halo Degeneracy – II: NGC 6946

2020 ◽  
Vol 500 (3) ◽  
pp. 3579-3593
Author(s):  
S Aniyan ◽  
A A Ponomareva ◽  
K C Freeman ◽  
M Arnaboldi ◽  
O E Gerhard ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Velocity Dispersion ◽  
Mass Density ◽  
Scale Height ◽  
Galactic Rotation ◽  
Dark Halo ◽  
Surface Mass ◽  
Ngc 6946 ◽  
Stellar Velocity ◽  
Surface Mass Density

ABSTRACT The mass-to-light ratio (M/L) is a key parameter in decomposing galactic rotation curves into contributions from the baryonic components and the dark halo of a galaxy. One direct observational method to determine the disc M/L is by calculating the surface mass density of the disc from the stellar vertical velocity dispersion and the scale height of the disc. Usually, the scale height is obtained from near-IR studies of edge-on galaxies and pertains to the older, kinematically hotter stars in the disc, while the vertical velocity dispersion of stars is measured in the optical band and refers to stars of all ages (up to ∼10 Gyr) and velocity dispersions. This mismatch between the scale height and the velocity dispersion can lead to underestimates of the disc surface density and a misleading conclusion of the submaximality of galaxy discs. In this paper, we present the study of the stellar velocity dispersion of the disc galaxy NGC 6946 using integrated star light and individual planetary nebulae as dynamical tracers. We demonstrate the presence of two kinematically distinct populations of tracers that contribute to the total stellar velocity dispersion. Thus, we are able to use the dispersion and the scale height of the same dynamical population to derive the surface mass density of the disc over a radial extent. We find the disc of NGC 6946 to be closer to maximal with the baryonic component contributing most of the radial gravitational field in the inner parts of the galaxy (Vmax(bar) = 0.76(±0.14)Vmax).

scholarly journals Rotation Curve of the Milky Way and the Dark Matter Density

Galaxies ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 37 ◽  
Author(s):  
Yoshiaki Sofue
Keyword(s):  
Dark Matter ◽  
Rotation Curve ◽  
Milky Way ◽  
Galactic Center ◽  
Mass Density ◽  
Current Status ◽  
Dark Halo ◽  
Surface Mass ◽  
A Value ◽  
Surface Mass Density

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 ρ ⊙ = 0.36 ± 0.02 GeV cm − 3 . 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 ρ ⊙ = 0.39 ± 0.09 GeV cm − 3 .

The surface mass density in the solar neighbourhood using red clumps stars in TGASxRAVE

2017 ◽  
Vol 13 (S334) ◽  
pp. 304-305
Author(s):  
Jorrit H. J. Hagen ◽  
Amina Helmi
Keyword(s):  
Vertical Velocity ◽  
Velocity Dispersion ◽  
Mass Density ◽  
Solar Neighbourhood ◽  
Local Distribution ◽  
Surface Mass ◽  
Preliminary Results ◽  
Combining Data ◽  
Surface Mass Density ◽  
Red Clump

AbstractWe investigate the kinematics of red clump stars in the Solar neighbourhood by combining data from the RAVE survey with the TGAS dataset presented in Gaia DR1. Our goal is to put new constraints on the (local) distribution of mass using the Jeans Equations. Here we show the variation of the vertical velocity dispersion as function of height above the mid-plane for both a thin and a thick disk tracer sample and present preliminary results.

scholarly journals IMF radial gradients in most massive early-type galaxies

2019 ◽  
Vol 489 (3) ◽  
pp. 4090-4110 ◽  
Author(s):  
F La Barbera ◽  
A Vazdekis ◽  
I Ferreras ◽  
A Pasquali ◽  
C Allende Prieto ◽  
...  
Keyword(s):  
Stellar Population ◽  
Velocity Dispersion ◽  
Mass Density ◽  
Initial Mass Function ◽  
Early Type ◽  
Low Mass Stars ◽  
Surface Mass ◽  
Low Mass ◽  
Surface Mass Density ◽  
The Imf

ABSTRACT Using new long-slit spectroscopy obtained with X-Shooter at ESO-VLT, we study, for the first time, radial gradients of optical and near-infrared initial mass function (IMF)-sensitive features in a representative sample of galaxies at the very high mass end of the galaxy population. The sample consists of seven early-type galaxies (ETGs) at z ∼ 0.05, with central velocity dispersion in the range 300 ≲ σ ≲ 350 km s−1. Using state-of-the-art stellar population synthesis models, we fit a number of spectral indices, from different chemical species (including TiO and Na indices), to constrain the IMF slope (i.e. the fraction of low-mass stars), as a function of galactocentric distance, over a radial range out to ∼4 kpc. ETGs in our sample show a significant correlation of IMF slope and surface mass density. The bottom-heavy population (i.e. an excess of low-mass stars in the IMF) is confined to central galaxy regions with surface mass density above $\rm \sim 10^{10}\, M_\odot \, kpc^{-2}$, or, alternatively, within a characteristic radius of ∼2 kpc. Radial distance, in physical units, and surface mass density are the best correlators to IMF variations, with respect to other dynamical (e.g. velocity dispersion) and stellar population (e.g. metallicity) properties. Our results for the most massive galaxies suggest that there is no single parameter that fully explains variations in the stellar IMF, but IMF radial profiles at z ∼ 0 rather result from the complex formation and mass accretion history of galaxy inner and outer regions.

scholarly journals Gravitational Microlensing By Random Motion Of Stars: Movie and Analysis of Light Curves

1996 ◽  
Vol 173 ◽  
pp. 287-288
Author(s):  
Joachim Wambsganss ◽  
Tomislav Kundić
Keyword(s):  
Velocity Dispersion ◽  
Mass Density ◽  
Random Motion ◽  
Light Curves ◽  
Short Version ◽  
Full Paper ◽  
Surface Mass ◽  
Bulk Motion ◽  
The Galaxy ◽  
Surface Mass Density

We present a quantitative analysis of the effect of microlensing caused by random motion of individual stars in a galaxy lensing a background quasar. We calculate a large number of magnification patterns for positions of the stars slightly offset from one frame to the next, and thus obtain light curves for fixed quasar and galaxy positions, only due to the change in the relative star positions. These light curves are analyzed to identify microlensing events, which are then classified with respect to height, duration, and slope. These random motion microlensing events are compared with the corresponding ones caused by the bulk motion of the galaxy.We find that microlensing events produced by random motion of stars are shorter, steeper, and more frequent than bulk motion events, assuming the velocity dispersion of the stars equals the bulk velocity of the galaxy. The reason for this difference is that in the case of random motion, caustics can move with an arbitrarily high velocity, producing very short events, whereas in the comparison case for bulk motion a microlensing event can never be shorter than it takes a fold caustic, which moves with the velocity of the lensing galaxy projected onto the quasar plane, to cross the quasar. An accompanying video illustrates these results. For three different values of the surface mass density κ, it shows time sequences of 1000 magnification patterns for slowly changing lens positions, together with the positions and velocity vectors of the microlensing stars. The full paper including the video can be found in Wambsganss & Kundić (1995). A short version of the video is available as an MPEG movie under anonymous ftp at astro.princeton.edu, in the directory jkw/microlensing/moving_stars.

Numerical computation of gravitational field of infinitely-thin axisymmetric disc with arbitrary surface mass density profile and its application to preliminary study of rotation curve of M33

2018 ◽  
Vol 14 (S344) ◽  
pp. 276-279
Author(s):  
Toshio Fukushima
Keyword(s):  
Gravitational Field ◽  
Power Law ◽  
Density Profile ◽  
Rotation Curve ◽  
Mass Density ◽  
Power Law Distribution ◽  
Surface Mass ◽  
Double Exponential ◽  
Surface Mass Density ◽  
Mass Density Profile

AbstractWe developed a numerical method[-70pt] to compute the gravitational field of an infinitely-thin axisymmetric disc with an arbitrary surface mass density profile. We evaluate the gravitational potential by a split quadrature using the double exponential rule and obtain the acceleration vector by numerically differentiating the potential by Ridders’ algorithm. By using the new method, we show the rotation curves of some non-trivial discs: (i) truncated power-law discs, (ii) discs with a non-negligible center hole, (iii) truncated Mestel discs with edge-softening, (iv) double power-law discs, (v) exponentially-damped power-law discs, and (vi) an exponential disc with a sinusoidal modulation of the density profile. Also, we present a couple of model fittings to the observed rotation curve of M33: (i) the standard deconvolution by assuming a spherical distributin of the dark matter and (ii) a direct fit of infinitely-thin disc mass with a double power-law distribution of the surface mass density.

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