On the Structure and Kinematics of the Gas in Leo A

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Session 108 -- Dwarf and Irregular Galaxies
Display presentation, Saturday, January 15, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[108.09] On the Structure and Kinematics of the Gas in Leo A

L. Norton, K. Y. Lo (U. Illinois), D. Westpfahl (NMIMT)

We have obtained new VLA observations of the HI in the Local Group dwarf irregular galaxy Leo A in order to study the structure of its interstellar medium and its interaction with the stars in the galaxy. The new data have much higher frequency resolution and sensitivity than before (Lo et. al. 1993, A.J., 106, 337). Previous images have shown that the HI in Leo A is distributed in a clumpy, squashed ring, with current or recent star formation apparently concentrated on the brighter side of the ring. These new data also reveal the presence of a lower column density envelope, which contains about 1/3 of the galaxy's HI mass and extends out to twice the previously known HI radius. Line profiles in Leo A imply that there are two components of the HI: one is a smooth, low brightness temperature component which may be identified with the envelope, and the other consists of small, high brightness temperature clumps of gas which are moving with random velocities comparable in magnitude to the total linewidth of the galaxy. The velocity field of the galaxy shows a significant gradient; multipole analysis of the velocity field and gas distribution implies that the gradient is probably due to a combination of rotation and expansion of the galaxy. Thus, the HI gas is better supported against gravity than was previously thought, which may help explain why the current star formation rate in Leo A is so low. It is clear that the HI in Leo A is not in a relaxed, steady state configuration; indeed, there has been a considerable amount of recent activity (presumably stellar in origin) transferring kinetic energy to the gas.

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