A Brief discussion of interstellar HI structure with special reference to filaments • Gerrit Verschuur Physics Department, University of Memphis
Dec 13, 2015
A Brief discussion of interstellar HI structure with special
reference to filaments
• Gerrit Verschuur Physics Department, University of Memphis
Goals for the talk
• To demonstrate the essentially filamentary nature of the anomalous velocity HI, in particular.
• Zoom in one some of the areas within the larger filamentary features.
• Raise questions about the origin of such structures.
• Seek directions in which answers may be found.
Data used
• Leiden-Argentina-Bonn HI survey: LAB survey• All-sky• 36’ resolution• 1.03 km/s bandwidth• Side-lobe corrected
• Kalberla et al. (2005)
The area of sky under consideration
• High northern galactic latitudes from b= +30° to +70°
• Also southern latitude data in same intervals• Then focus on some details
Northern Galactic hemisphere HI data
The sequences that follow show HI area maps that reveal HI features changing position as the line-of-sight velocity shifts.
Some of these can be understood as flow along filaments but other features show large scale “winds”perhaps.
NH
220 200 180 160 140 120 100 80 60
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Galactic longitude (°)
Galactic latitude (°)
V = -82 km/s
220 200 180 160 140 120 100 80 60
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Galactic longitude (°)
Galactic latitude (°)
220 200 180 160 140 120 100 80 60
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Galactic longitude (°)
Galactic latitude (°)
0 5 10K.km/s
Corkscrew
170 160 150 140 130 120 110
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col
row
0 5 10 15 20HI_integ__85kms_rs
HI integrated from -80 to -90 km/s
Corkscrew close-up
170 160 150 140 130 120 110
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col
row
0 5 10 15 20HI_integ__95kms_rs
HI integrated -90 to -100 km/s
220 200 180 160 140 120 100 80 60
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Galactic longitude (°)
Galactic latitude (°)
Combination of v = -120, -100 @ -82 km/s(1:4@1, 5:17 @2 K. km/s)
Filamentary features can be followed through velocity space
MIMII
Complex C
“Twisted”
Corkscrew
-150 -125 -100 -75 -50 -25 0 25
0
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Velocity (km/s)
Galactic longitude (°)
= +65° (contours 0.3 : 4.2 @ 0.3 , 5 :9 @ 1 K)
In the northern galactic hemisphere the low-velocity HI is severely disturbed. Its l.o.s. velocity has shifted.
MI (no LV gas)
MII
Longitude-velocity plot
Baseline structure“normal”
Baseline structure“normal”
Southern galactic hemisphereb = -65°
For comparison, this plot shows “normal” low velocity HI emission due to local gas
-150 -125 -100 -75 -50 -25 0 25
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Velocity (km/s)
Galactic longitude (°)
b = +65° ( 0.3 : 3 @ 0.4, 4 :10.0@2 K)
Longitude-velocity plot
-150 -125 -100 -75 -50 -25 0 25
0
30
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Velocity (km/s)
Galactic latitude (°)
b = 60° rs & sm 1x (0.1 : 2.1 @ 0.2, 3 : 7 @ 1 K)
Similarities and differences w.r.t NH data
• The “moving” shell-like feature in the SH is diametrically opposite the feature in the NH.
• The velocity vectors are confusing
“Clouds” may be illusions created by enhancements of emission where segments of filaments twist into the line-of-sight
Clouds versus filaments in detail
48
1216
8
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28
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4
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8 84
4
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4
12
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16
210 205 200 195 190 185 180
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Velocity (km/s)
Galactic latitude (°)
MII Area -40 to -30 km/s 4 : 56 @ 4
MII
Filamentary structures at all velocities
What is lacking
• All theoretical discussions of diffuse interstelllar HI are based on the “cloud” concept.
• What is needed is a comprehensive theory to account for high complex, twisted filaments controlled by magnetic fields.
• Only then can be begin to understand the earliest stages of star formation!
Summary
• A physics of interstellar filaments is needed that brings in:
• Plasma phenomena• Motions along filaments - currents• Plasma instabilities• Are these filaments all at the surfaces of old
shells?• And/or is gas “blowing” along field lines from
regions of recent star formation?
-150 -125 -100 -75 -50 -25 0 25
0
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Velocity (km/s)
Galactic longitude (°)
= +65° (contours 0.3 : 4.2 @ 0.3 , 5 :9 @ 1 K)
Longitude-velocity plot