A measurement of the optical depth through a galaxy disk
Article Abstract:
Scientists White and Keel have used measurements of broadband colors from an overlapping pair of galaxies to determine the optical depth of spiral galaxy disks. Their method, however, did not offer a way of separating contributions from each galaxy unambiguously. In the present study, this source of ambiguity was separated using individual emission lines, which are fully separated when both galaxies possess a sufficiently large redshift as in the case of NGC3314a and b. The Balmer decrement of emissions from HII regions in the background galaxy was used to measure the degree of dust obscuration through NGC3314a, which was found to have substantial optical depths along three lines of sight.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1993
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An ultraviolet flare at the centre of the elliptical galaxy NGC4552
Article Abstract:
Imaging of NGC1399 and NGC4552 elliptical galaxies by the pre-COSTAR Hubble Space Telescope Faint Object Camera reveals that the ultraviolet central spike in NGC4552 is a flare. Ultraviolet flares at the core of galaxies may occur consistently and facilitate an opportunity to analyze black-hole activities. A comparison of images obtained in 1991 and 1993 indicates an increased in brightness by 7 plus or minus 1.5. Four possible mechanisms exist for the NGC4552 flare namely: nova/supernova outburst, gravitational lensing, transient accretion on a black hole and stellar collision.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1995
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Magnetic spiral arms in the galaxy NGC6946
Article Abstract:
Two magnetic spiral arms have been observed in the galaxy NGC6946, lying between the optical spiral arms. The arms are about 500 to 1,000 parsecs wide and more than 12 kiloparsecs long. The magnetic arms have greater symmetry than the optical arms, indicating the presence of global mechanisms that produce magnetic fields despite the unlikely position for star formation activity. However, neither the dynamo theory nor any current theory are sufficient to explain the event.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1996
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