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 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.

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 Revealing the relation between black hole growth and host-galaxy compactness among star-forming galaxies

2020 ◽  
Vol 500 (4) ◽  
pp. 4989-5008
Author(s):  
Q Ni ◽  
W N Brandt ◽  
G Yang ◽  
J Leja ◽  
C-T J Chen ◽  
...  
Keyword(s):  
Black Hole ◽  
Mass Density ◽  
Formation Rate ◽  
Gas Content ◽  
Host Galaxy ◽  
Universal Relation ◽  
Host Galaxies ◽  
Surface Mass ◽  
Star Forming ◽  
Central Surface

ABSTRACT Recent studies show that a universal relation between black hole (BH) growth and stellar mass (M⋆) or star formation rate (SFR) is an oversimplification of BH–galaxy coevolution, and that morphological and structural properties of host galaxies must also be considered. Particularly, a possible connection between BH growth and host-galaxy compactness was identified among star-forming (SF) galaxies. Utilizing ≈6300 massive galaxies with I814W  <  24 at z < 1.2 in the Cosmic Evolution Survey (COSMOS) field, we perform systematic partial correlation analyses to investigate how sample-averaged BH accretion rate ($\rm \overline{BHAR}$) depends on host-galaxy compactness among SF galaxies, when controlling for morphology and M⋆ (or SFR). The projected central surface mass density within 1 kpc, Σ1, is utilized to represent host-galaxy compactness in our study. We find that the $\rm \overline{BHAR}$–Σ1 relation is stronger than either the $\rm \overline{BHAR}$–M⋆ or $\rm \overline{BHAR}$–SFR relation among SF galaxies, and this $\rm \overline{BHAR}$–Σ1 relation applies to both bulge-dominated galaxies and galaxies that are not dominated by bulges. This $\rm \overline{BHAR}$–Σ1 relation among SF galaxies suggests a link between BH growth and the central gas density of host galaxies on the kpc scale, which may further imply a common origin of the gas in the vicinity of the BH and in the central ∼kpc of the galaxy. This $\rm \overline{BHAR}$–Σ1 relation can also be interpreted as the relation between BH growth and the central velocity dispersion of host galaxies at a given gas content (i.e. gas mass fraction), indicating the role of the host-galaxy potential well in regulating accretion on to the BH.

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.

scholarly journals The MUSE Atlas of Discs (MAD): Ionized gas kinematic maps and an application to diffuse ionized gas

2019 ◽  
Vol 491 (3) ◽  
pp. 4089-4107 ◽  
Author(s):  
Mark den Brok ◽  
C Marcella Carollo ◽  
Santiago Erroz-Ferrer ◽  
Martina Fagioli ◽  
Jarle Brinchmann ◽  
...  
Keyword(s):  
Velocity Dispersion ◽  
Rotation Velocity ◽  
Scale Height ◽  
Molecular Gas ◽  
Ionized Gas ◽  
Nearby Star ◽  
Stellar Disc ◽  
Star Forming ◽  
Gas Kinematics ◽  
Diffuse Ionized Gas

ABSTRACT We have obtained data for 41 star forming galaxies in the MUSE Atlas of Discs (MAD) survey with VLT/MUSE. These data allow us, at high resolution of a few 100 pc, to extract ionized gas kinematics (V, σ) of the centres of nearby star forming galaxies spanning 3  dex in stellar mass. This paper outlines the methodology for measuring the ionized gas kinematics, which we will use in subsequent papers of this survey. We also show how the maps can be used to study the kinematics of diffuse ionized gas for galaxies of various inclinations and masses. Using two different methods to identify the diffuse ionized gas, we measure rotation velocities of this gas for a subsample of six galaxies. We find that the diffuse ionized gas rotates on average slower than the star forming gas with lags of 0–10 km s−1 while also having higher velocity dispersion. The magnitude of these lags is on average 5 km s−1 lower than observed velocity lags between ionized and molecular gas. Using Jeans models to interpret the lags in rotation velocity and the increase in velocity dispersion we show that most of the diffuse ionized gas kinematics are consistent with its emission originating from a somewhat thicker layer than the star forming gas, with a scale height that is lower than that of the stellar disc.

scholarly journals A Dependence of the Tidal Disruption Event Rate on Global Stellar Surface Mass Density and Stellar Velocity Dispersion

2018 ◽  
Vol 853 (1) ◽  
pp. 39 ◽  
Author(s):  
Or Graur ◽  
K. Decker French ◽  
H. Jabran Zahid ◽  
James Guillochon ◽  
Kaisey S. Mandel ◽  
...  
Keyword(s):  
Velocity Dispersion ◽  
Event Rate ◽  
Mass Density ◽  
Stellar Surface ◽  
Tidal Disruption ◽  
Surface Mass ◽  
Stellar Velocity ◽  
Surface Mass Density ◽  
Disruption Event
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