Testing for interaction between the galaxies NGC 450 and UGC 807

Publication date: 
Main author: 
Moles M.
IAA authors: 
Moles, M.;Márquez, I.;Masegosa, J.;Del Olmo, A.;Perea, J.
Moles M., Márquez I., Masegosa J., Del Olmo A., Perea J., Arp H.
Astrophysical Journal
Publication type: 
The Sc spiral, NGC 450 (ν0 = 1863 km s-1) has conspicuously brighter H II regions at just the point of projected contact with the spiral UGC 807 (ν0 = 11,600 km s-1). New spectra and photometry are reported which show the following: 1. The rotation curve of the low-redshift spiral has asymmetries and large discontinuities. 2. The brightest H II regions show differences between them of the order of 100 km s-1, and one knot shows a discrepancy of 400 km s-1, well in excess of escape velocity. 3. The distribution of neutral hydrogen in NGC 450 is heavily overbalanced to the side of the bright knots and the position of UGC 807. 4. The rotation curve of the high-redshift spiral shows a shallow increase to maximum rotational velocity (νmax = 171 km s-1) which is characteristic of lower luminosity spirals. The rotation curve is also asymmetric and shows irregularities. 5. The relative Hα surface brightness, a distance-independent quantity, signifies currently enhanced star formation in UGC 807. The Hα luminosity of the higher redshift spiral is unprecedentedly large if placed at its redshift distance. 6. The morphology of the higher redshift spiral is more extended on the side toward NGC 450 than on the side away and the color index isocontour lines indicate a discontinuity where the UGC 807 image merges well that of NGC 450. The conclusion from the extensive analysis is that one would have to invoke an enormous conspiracy of accidents in order to avoid the conclusion that UGC 807 is a moderately low luminosity galaxy interacting with NGC 450.
Galaxies: individual (NGC 450, UGC 807); Galaxies: interactions; Galaxies: kinematics and dynamics; Galaxies: photometry; H II regions; Radio lines: galaxies