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|Morphology of star formation regions in irregular galaxies|
The location of HII regions, which indicates the locus of present starformation in galaxies, is analysed for a large collection of 110irregular galaxies (Irr) imaged in Hα and nearby continuum. Theanalysis is primarily by visual inspection, although a two-dimensionalquantitative measure is also employed. The two different analyses yieldessentially identical results. HII regions appear preferentially at theedges of the light distribution, predominantly on one side of thegalaxy, contrary to what is expected from stochastic self-propagatingstar formation scenarios. This peculiar distribution of star-formingregions cannot be explained by a scenario of star formation triggered byan interaction with extragalactic gas, or by a strong one-armed spiralpattern.
|The Kinematics and Distribution of H I in IC 10|
We present the results of an extensive study of the neutral hydrogencontent of IC 10, a dwarf irregular in the Local Group that is rightlyconsidered a starburst. The H I content of IC 10 is characterized by aregularly rotating disk embedded within an extended and complexdistribution of gas. The distribution of gas within the disk isdominated by holes and shells and has been and continues to be shaped bystellar winds associated with the numerous Wolf-Rayet and O stars. Thestellar winds have likely triggered secondary generations of starformation within the shells surrounding many of the holes. We havedetected the kinematic signature of the previously reported youngsuperbubble in a large H I cloud at the southeastern tip of the opticalgalaxy. Finally, the complex distribution and kinematics of the extendedgas around IC 10 suggest that this is a galaxy that is still forming viathe accretion of the surrounding gas.
|An image database. II. Catalogue between δ=-30deg and δ=70deg.|
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
|Turbulent gas motions in giant H II regions. II - The luminosity-velocity dispersion relation|
The relation between luminosity L(H-alpha) and velocity dispersion sigmais reinvestigated in view of H-alpha and O III 5007-A forbidden linemeasurements of the velocity dispersion for 43 giant, extragalactic H IIregions. A correlation of L(H-alpha) that varies as sigma (H-alpha) tothe 6.6th power is obtained; O III-line velocity dispersions are notedto obey a similar relation, but are somewhat smaller, and the slope ofboth relations is steeper than expected for gravitationally boundsystems.
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