21 October 19991 Introduction to M4 Science Observe 95 m Polarized Radiation l Map the “Magnetic...
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Transcript of 21 October 19991 Introduction to M4 Science Observe 95 m Polarized Radiation l Map the “Magnetic...
21 October 1999 1
Introduction to M4 Science
Observe 95 m Polarized Radiation Map the “Magnetic Field of the Milky Way”
(Central 100 degrees in l and 10 degrees in b) Technique for Constructing 3-D Field Relies on
FIR/CO Associations Detailed Studies of B in selected
Supershells (Cirrus), Star-forming Regions, and External Galaxies
The 20th Century Magnetic Field of the Milky Way
Serkowski, Mathewson & Ford, et al.
See Heiles for more, later.
21 October 1999 5
Grain Alignment
Role of Radiative Torques (Draine, Weingartner, Lazarian)
Spectral Dependence of Thermal Emission Polarization (Hildebrand et al. 1999; see Dowell)
Global Polarization-Extinction Relation (Arce et al. 1998; Goodman 1999)
Radiative Torques on “Helical” Grains
Non-Davis-Greenstein processes likely dominate (see Draine, Weingartner,Lazarian)
Rapid alignment of grains in less than dim regions
Draine & Weingartner, 1997
21 October 1999
“Go no further than AV~1.3 mag.”
3.0
2.5
2.0
1.5
1.0
0.5
0.0
P R
[%]
43210
43210AV [mag]
Background to Cold Dark Cloud
Arce et al. 1998
Background to General ISM
Elongated Large Coagulate Grain
Round Grainw/Ice Mantle
Very Small Grain
"Not All Grains are Created Equal"
High-Porosity (Fluffy) Grain
21 October 1999 10
Developments in Star-forming Regions
Interferometric Polarimetry of Outflow/Disk Sources (OVRO: Akeson et al. 1996; BIMA: Rao et al. 1998; see Myers)
Polarized Spectral-line Emission (BIMA: Girart et al. 1999)
Sub-mm (SCUBA) Polarimetry of Massive, and now Low-Mass, SFRs (e.g. Matthews & Wilson 1999; see Greaves)
21 October 1999
Zooming on Orion BN/KLSchleuning 1998
Rao et al. 1998
BIMAInterferometer
STOKESon KAO
M4 Beam
21 October 1999 12
On a Galactic Scale
Rand & Lyne (94) Pulsar RM/DM Mapping of B
Reid & Menten update of Galactic B from H2O Masers (in prep.)
Heiles’ Re-analysis of Galactic Plane Background Starlight Polarimetry Surveys (see Heiles)
SCUBA Polarimetry of the Galactic Center (see Greaves)
21 October 1999 15
On a Universal Scale
Connection to CMB Polarimetry (see Lazarian)
Our signal is their “foreground,” and we have MUCH better polarimetric sensitivity and resolution.
MAP launch November 2000
Any light on galactic dynamo issues/origin of galactic fields (ask Zweibel)?
What can we expect?
2
4
6
81
2
4
6
810
2
4
6
8100
2p
max [
%]
0.1 1 10 100 1000EB-V [mag]
0.1 1 10 100 1000 AV
[mag]
0.01 0.1 1 10 100K
PV TheoreticalMaximum
100 m in Massive SFR
pV Cold Dark Clouds
pV Low-Density ISM
BIMA MillimeterOrion ObservationsP100 m Semi-Empirical
Maximum
Figure from Goodman 1999.