Is the Local Fluff Typical

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Is the Local Fluff Typical ?
John M. Dickey University of Minnesota
COSPAR 17 October 2002
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The Local Fluff is now called the Complex of
Local Interstellar Clouds.
It has... Temperature T 7000
K density (neutrals) nH 0.25 cm-3
(electrons) ne 0.1 cm-3 velocity vsun
25 km s-1
And... it only extends 2 to 4 pc from the sun !
Slavin and Frisch, 2002, Ap. J. 565, 364 and
references therein.
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Where does this fit among the phases of the
interstellar medium ?
WIM
Molecular clouds
WNM
PDRs
Log HI Column Density
The Local Fluff is WNM (Warm Neutral Medium).
Diffuse clouds
1 2 3
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Log Temperature (K)
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5 pc
100 pc ?
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A nearby interstellar shell similar to the local
bubble from the SGPS (Southern Galactic Plane
Survey)
Dickey 2001, ASP Conf. Ser. 231, p. 318.
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The Southern Galactic Plane Survey

• Project Team
• Naomi McClure-Griffiths
• ATNF
• John Dickey
• University of Minnesota
• Bryan Gaensler
• Harvard University
• Anne Green
• Sydney University

A survey of l21-cm line and continuum emission
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The Australia Telescope
Compact Array
The Parkes Telescope
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Combining data from the single dish and the
interferometer
Vela supernova remnant with nearby HII region
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Parkes
Compact Array
Combined data
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Combined HI Cube
ATCA
Combined
Parkes
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Atomic hydrogen data cube
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DRAO
The International Galactic Plane Survey
NRAO VLA
ATNF Compact Array
ATNF Parkes
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Figure courtesy CGPS consortium
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The Multiwavelength Milky Way
Optical (6520 Å)
Infrared (12, 60, 100 ?m)
HI (21 cm)

• HI is much more extended than optical
• Warped, flared, scale height changes
• HI is largely transparent so its a brilliant way
  to study all of the Galaxy, not just the nearest
  bits

Stars obscured by dust
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A Galactic chimney from the Canadian Galactic
Plane Survey (CGPS) Normandeau et al. 1997, Ap.
J. Supp, 108, 279.
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McClure-Griffiths et al. 2002 in prep.
McClure-Griffiths, et al. 2000 A.J. 119,
2828. Parkes plus ATCA 1000 field mosaic.
An HI bubble that blows out of the disk into the
halo above and below.
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A less dramatic, more typical area, the SGPS
test region...
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SGPS test region Radio Continuum
Extragalactic sources
H II regions
SNRs
Stokes I total power
Gaensler et al., 2001, Ap. J. 549, 959.
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SGPS test region Radio Continuum
Point sources
Gaensler et al., 2001, Ap. J. 549, 959.
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SGPS test region Radio Continuum
Diffuse emission
Gaensler et al., 2001, Ap. J. 549, 959.
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SGPS test region Radio continuum
Voids
Gaensler et al., 2001, Ap. J. 549, 959.
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SGPS test region Spectral Line Cube
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Large structures like shells and chimneys stand
out, but most of the interstellar medium
has structure in density and velocity that is
stochastic (turbulent).
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In the ionized gas (the WIM) we see a turbulence
spectrum over many orders of magnitude in scale
size.
Figure from Armstrong, Rickett, and Spangler
1995, Ap. J. 443, 209.
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In the neutral gas we also see a power law
distribution of column densities.
Figure from Dickey et al., 2001, Ap.J. 561, 264.
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The power law slope changes with velocity
averaging.
See also Lazarian and Pogosian, 2000, Ap. J. 537,
720, and Lazarian and Stanimirovic, 2001 Ap. J.
551, 53.
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The slope change shows that this is a dynamical
process, i.e. turbulence, not just a
statistical distribution of density irregularities
.
Figure from Dickey et al., 2001, Ap.J. 561, 264.
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Tiny scale structure in the neutral ISM
4 AU
Figure from Faison et al. 1998, A.J. 116, 2916.
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Deshpande, 2000, MNRAS 543, 227.
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Deshpande, 2000, MNRAS 543, 227.
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peak variations
typical variations
The heliosphere moves through the local WNM at 25
km/s 5 AU/year. How much variation can we
expect to see in a few years ?
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What can we expect to see in the Local
Interstellar Cloud ?

• density fluctuations
• velocity fluctuations
• - magnitude
• - direction
• temperature changes ?
• ionization fraction changes ?
• magnetic field changes ???

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We might also see a linear variation of velocity
with time, if we move from the LIC (local
interstellar cloud) to the BC (blueshifted cloud).
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Conclusions Studying the properties of the
local interstellar clouds is very useful for
understanding the physical conditions in the
WNM. We may hope to see variations in the
velocity and density that will show us how
interstellar turbulence works !