Anisotropy of gas Anisotropy of gas random motions random motions - - PowerPoint PPT Presentation
Anisotropy of gas Anisotropy of gas random motions random motions in galactic disks in galactic disks Laurent Chemin Laurent Chemin Universidad de Antofagasta (Chile) Franoise Combes Franoise Combes Observatoire de Paris-LERMA (F)
Universidad de Antofagasta (Chile)
Françoise Combes Françoise Combes
Observatoire de Paris-LERMA (F)
Erwin de Blok Erwin de Blok
ASTRON (NL)
Many applications for gas velocity dispersion Many applications for gas velocity dispersion
✔ Gas pressure, mass distribution (Dalcanton+2010, Oh et al. 2015, Genzel+2017) ✔ Noncircular motions (e.g. Kuzio de Naray+2006) ✔ Disk thickness, vertical equilibrium (e.g. van der Kruit 1981, Combes+1997)
isotropy of gas dispersion ellipsoid is isotropy of gas dispersion ellipsoid is always always assumed σ assumed σR
R =σ
=σΦ
Φ=σ
=σz
z =
= σ σlos
los (observed line-of-sight dispersion)
(observed line-of-sight dispersion)
i= inclination
Spiral and ring-like features in dispersion maps Signs of anisotropy
Lower σ Lower σlos
los
Lower σ Lower σlos
los
Higher σ Higher σlos
los
Higher σ Higher σlos
los
THINGS velocity dispersion map of NGC2903 THINGS velocity dispersion map of NGC2903 (Walter+08)
Measure the dispersion ellipsoid of gas: Measure the dispersion ellipsoid of gas:
σ σR
R ,σ
,σΦ
Φ,σ
,σz
z
Assess the assumption of isotropy Assess the assumption of isotropy Study the properties of ellipsoid & anisotropy Study the properties of ellipsoid & anisotropy
σ σinstrumental
instrumental = 2.6-5.2 km/s
= 2.6-5.2 km/s Angular resolution = 150-800 pc Angular resolution = 150-800 pc
NGC7793 NGC3521 DDO154 NGC7331 NGC2903 NGC3031 NGC925 NGC925 NGC6946 NGC6946 NGC5055 NGC3621 NGC2841 NGC3198 NGC2366 NGC2976 NGC4736
THINGS velocity dispersion maps THINGS velocity dispersion maps
R(R)
(R)= σ
Φ(R)
(R)= σ
z(R)
(R)= σ
los(R)
(R)
σz = 0.71σP = 0.71(σR
2+σΦ 2)1/2
Fixed σR = σlos Free σΦ
Anisotropy parameters
β →1 more radial orbits β = 0 isotropy βΦ < 0 more tangential orbits
σR σP σΦ σtot=(σR
2+σΦ 2+σz 2)1/2
σz
NGC925 NGC925
Closest galaxies to isotropy Closest galaxies to isotropy
DDO154
(i=65°, vmax=45 km/s)
NGC6946
(i=33°, vmax=200 km/s) σR σΦ σz σP σtotal
Isotropy is never verified Isotropy is never verified
σz = 0.5σP
(hydrodynamical simulations, Agertz+ 2009)
Free σR and σΦ
NGC3521
σR σΦ σz σP σtotal
More radial orbits More radial orbits More tangential orbits More tangential orbits
NGC3031 NGC3621
Identification of two classes of disks Identification of two classes of disks
No clear trend No clear trend
More radial More tangential
Anisotropy vs mass Anisotropy vs mass
NGC3521
Disagreement with theory Disagreement with theory
(epicyclic approximation) (epicyclic approximation)
(Binney & Tremaine 2008)
gas in galactic disks
Summary & Future work Summary & Future work
σ σR
R ≠
≠ σ σΦ
Φ≠
≠ σ σz
z
HI disks have more HI disks have more radial radial/ /tangential tangential orbits
Analysis and Analysis and
implications of anisotropy
implications of anisotropy
✔ Increase galaxy sample(s)
Increase galaxy sample(s)
✔ Atomic vs molecular vs ionized gas
Atomic vs molecular vs ionized gas
✔ Dwarf galaxies
Dwarf galaxies
thickness density of dark matter disk
DDO154