Mid infrared polarisation of Ultraluminous Infrared Galaxies
R. Siebenmorgen, A. Efstathiou;
AaA, 2001, 376, L35
ABSTRACT:The mid infrared polarisation properties of four Ultraluminous Infrared Galaxies (ULIRGs) have been investigated by broad band filter
observations with the ISOCAM instrument on board the Infrared Space Observatory
(ISO).
The wavelength region from 5 to 18 mu m was selected where the emission from
the putative torus peaks.
We report detection of polarisation for all
ULIRGs studied.
The fractional polarisation ranges from ~ 3% up to 8%.
The
highest polarisation is recorded in Mrk 231 which has a clear AGN signature,
whereas the lowest is for Arp 220, which is generally thought to be powered
predominantly by star formation.
We discuss the various mechanisms that could give
rise to the polarisation and conclude that the most likely interpretation
is that it is due to magnetically aligned elongated dust grains.
This is
the same mechanism believed to be operating in a number of galactic
sources.
The position angle of polarisation could give the projected magnetic
field direction and therefore constrain models for the formation of the
tori.
Based on observations with ISO, an ESA project with instruments funded by ESA
Member States (especially the PI countries: France, Germany, The
Netherlands and the UK) with the participation of ISAS and NASA.
KEYWORDS: polarisation, infrared: galaxies, galaxies: ism, galaxies: individual: mrk 231, arp 220, iras 15250+3609, mrk 273
PERSOKEY:polarisation, mir, iso, galaxies, dust, magnetic field, pah, ,
CODE: siebenmorgen2001