Atomic Hydrogen and Hydroxyl spectral line cubes in M82

Spectral line observations of sources are often collected into 'data cubes'. These usually consist two dimensions of space (eg RA & Dec) and one of frequency (Velocity). One way of displaying the data is as a 'movie' showing successive planes of an RA-Dec-Velocity cube.

The atomic hydrogen cube data was obtained on the VLA and has been described in Wills, Pedlar & Muxlow 2002 MNRAS 331, 313 and the OH data was obtained in 2002 by Pedlar, Aalto, Booth, Wills & Muxlow.The angular resolution is ~1 arcsec and the velocity resolution ~10 km/s

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M82 H1 absorption

This sequence shows the original data before the continuum has been subtracted. Discrete continuum sources are supernova remnants superimposed on a diffuse non-thermal background. The H1 absorption is clearly visible as dark clouds passing from left to right as the observing frequency increases and the velocity decreases. Note the excess of absorption to the north of the starburst showing the disk is tilted in this direction. The absorpting H1 clouds move across in velocity roughly consistent with solid body rotation, although more careful study reveals evidence for gas motions due to bar potentials and expanding shells.

M82 H1 optical depth

The second movie shows the H1 optical depth- derived from the first cube by measuring the decrease in continuuum intensity. Note some of the H1 shells which are thought to have been formed by winds from starforming regions.

M82 1665 & 1667 OH lines

The movie below shows the 1665 and 1667 MHz OH lines observed with the VLA. Note that strong maser emission is seen (blue/light dots) as well as OH absorption M82. The sequence starts with the 1665 line and then is followed by 1667 data. Note the absorption is more confined to the plane than the H1, and that 1665 and 1667 Masers do not all occur at the same places. Click on this image to view a larger movie as well as the 1665 and 1667 movies separately.