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)

All-sky Total HI -450 to +450 km/s

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

Orienting us in galactic space

Low-velocity gas

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

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Galactic longitude (°)

Galactic latitude (°)

V = -82 km/s

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Galactic longitude (°)

Galactic latitude (°)

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Galactic longitude (°)

Galactic latitude (°)

0 5 10K.km/s

Corkscrew

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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

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0 5 10 15 20HI_integ__95kms_rs

HI integrated -90 to -100 km/s

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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

Two position-velocity plots across the major anomalous-

velocity filament

-150 -125 -100 -75 -50 -25 0 25

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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

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Velocity (km/s)

Galactic latitude (°)

b = 60° rs & sm 1x (0.1 : 2.1 @ 0.2, 3 : 7 @ 1 K)

SH

Southern Galactic hemisphere data

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

Accounting for velocity gradientsStreaming motions

Clouds versus filaments in detail

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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

Structure in maps of the “cloud” MII could be interpreted as rotation

However:

MII area showing wave patterns MII

“Twisted” in color

The ridge lines of “Twisted” overlain on a continuum radio map

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?

The End

• For now!

The associations between the absence of low-velocity gas and the presence of anomalous

velocity HI

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Velocity (km/s)

Galactic longitude (°)

= +65° (contours 0.3 : 4.2 @ 0.3 , 5 :9 @ 1 K)

Longitude-velocity plot

Implications for distance

• Anomalous velocity gas must be very local