of Supernova Driven Turbulent MHD Simulations of the Diffuse Ionised Gas Jo Barnes 1 Kenny Wood 1 Alex Hill 2 1University of St Andrews 2 CSIRO Astronomy and Space Science ID: 322660
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Slide1
Photoionisation of Supernova Driven, Turbulent, MHD Simulations of the Diffuse Ionised Gas
Jo Barnes1, Kenny Wood1, Alex Hill2
[1]University of
St Andrews
,
[2]
CSIRO Astronomy and Space
ScienceSlide2
OutlineObservations of the ISMMHD and
radiative transfer simulations Fractal models of the ISMScattered LightHow far can photons travel in the DIG? ConclusionsSlide3
Observations: WHAM SurveyAll sky survey of Hα
(Haffner et al. 2003,2010)Wide area surveys of [NII] λ6584 and [SII]λ6716 (Reynolds et al 1998, Hausen et al, 2002)Filaments, loops and HII regions
[NII]/Hα and [SII]/Hα increase with height above midplane
(
Haffner
1999)
Additional heating mechanism (Reynolds 1999)
H
[S II]/H
[S II]/[N II]
[N II]/H
Slide4
MHD simulationsMHD simulations of ISM from Hill et al. 2012Include type
Ia and core collapse supernovae, set off at galactic supernova rate3/5 of core collapse distributed to simulate superbubbles in the gas.Do not include photoionisation heating Slide5
Monte Carlo Radiative TransferMonte Carlo radiation transfer code of Wood et al. 2004.
Includes ions of H, He, C, N, O, Ne, SOutputs 3D temperature and ionisation structureInclude additional heating sources for diffuse ionised
gas in the Milky Way. Slide6
Simulation SetupSubsection of MHD simulations with z = ±2kpc24
ionising sources with scaleheight 63 pc (Maiz-Apellaniz 2001)I
onizing luminosity 0.5<Q<10 x 1049 s
-1
kpc
-2
.
Repeating boundary conditions to simulate semi-infinite simulation box
N (cm
-2
)
MHD
DL
DL+DIGSlide7
Hα and HISlide8
Hα Scale height
Perseus Arm, H = 500 pcQ=10 x 10 49s-1
kpc-2, H = 150 pcSlide9
Fractal models of the ISMMHD simulations have a lower density above the plane than observed in the Galaxy.
Average Column densities above 1kpc: MHD = 2.4 x 1018cm-2
DL+WIM= 2.4 x 10
19
cm
-2
Fractal
= 3.0x 1019
cm-2Q=
16 x 10
49 s-1 kpc
-
2Additional heating: G = 4 x 10-
26 ne ergs cm-3s-1
+ Perseus Arm+ Simulation: 2<z<2kpc+simulation: 1.8<z<1.8 kpcSlide10
Fractal Models
Additional heating G = 4 x 10-26 ergs cm-3s
-1, Q
49
=
16Slide11
Scattered LightMonte Carlo scattered light code.
Look at scattering of photons from HII regionsInclude effects of dust scattering and absorptions in the DIGSlide12
Scattered Light Maps
+
=
HII region
Diffuse gas
TotalSlide13
Scattered LightSlide14
Distance Travelled by Ionising Photons
Ionising photons travel through low density ‘bubbles’ close to the midplane Need very few photons to travel to the top of the simulation box. Higher
ionising luminosity = larger distance
Photons with higher energy travel further than those with low energy
Total distance
Reprocessed photons Slide15
ConclusionsPhotoionisation of MHD simulations produces general Hα and HI with different scale heights
Able to reproduce general trends that we see in the Milky WayFractal models produce line ratios and scale heights similar to those in the Perseus ArmBut structure not the same as observedAlong many sightlines scattered light has a very small impact on the observed light. Along other sight lines, particularly close to the midplane, scattered light may have a significant effect on the intensity of light observed
.Only
a small number of photons are required to travel large distances to
ionise
the DIG, but enough are able to reach the top of the simulation box and
ionise
the gasSlide16
Distance Travelled by Ionising Photons
Q = 10 x10
49 s-1 kpc-2
Q = 1 x10
49
s
-1
kpc-2
Q = 0.5 x1049 s-1
kpc-2Slide17