Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998larm.confe.188r&link_type=abstract
"IX Latin American Regional IAU Meeting, "Focal Points in Latin American Astronomy", held in Tonantzintla, Mexico, Nov 9-13, 199
Astronomy and Astrophysics
Astronomy
Scientific paper
We present optical spectroscopy and B,V,R and I CCD photometry, as well as VLA neutral hydrogen (HI) observations of the interacting system NGC6845. This system appears as a quartet on the sky of which two components, NGC6845-A and NGC6845-B are interacting. Components C and D show no obvious signs, neither in the optical nor in the HI. The kinematical mass of NGC6845-A, from the optical rotation curve, is 4.4E11 Msun. Model fitting of the rotation curve reveals that NGC6845-A has a prominent bulge and a thick disk. There is strong HI emission distributed in a SW-NE direction, along the line determined by the four galaxies. The total amount of HI is 1.5E10Msun. The HI kinematics, as well as the group differential velocities, indicates a group mass of 1-2E12 Msun inside the outermost HI isodensity contour at 3-4 galaxy radii, indicating that dark matter represents ~3/4 of the group mass. NGC6845-A, the dominant object, supports a broad and bright tidal tail, connecting up to NGC6845-B. Comparison with existing simulations suggest that the closest encounter occurred ~200 Myr ago. At the place where the tidal arm joins the disk of NGC6845-A we find 2 giant HII regions comparable or larger than 30 Dor. 5 HII regions brighter than the britest known one in our galaxy are present all along the robust tidal tail, with the two most luminous ones located at its tip. Since the age of the HII regions is 3-8 Myr, strong processes of star formation is occurring well after the perigalacticum. That points to the presence of deep potential well inside the tidal arm able to retain the pre-stellar gas during the colision development. The tidal arm has a (B-I) color similar to that of the disk of NGC6845-A.
Brinks Elias
Dottori Horacio
Mirabel Felix
Rodrigues Irapuan
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