Brightest superassociations in spiral and irregular galaxies as extragalactic distance indicators

Journal Article · Tue Jan 01 00:00:00 EST 1980 · Astron. J.; (United States)

DOI:https://doi.org/10.1086/112625· OSTI ID:5636808

Wray, J D; De Vaucouleurs, G

The brightest blue knots (superassociations) detected by composite U,B,V color photography in spiral and irregular galaxies have absolute magnitudes B/sub 1/ ranging from -10 to -15, which are from 3 to 5 magnitudes brighter than the brightest single stars. The absolute magnitude of the brightest blue knot M/sub 1//sup 0/ (corrected for galactic extinction) depends on the corrected color index (B-V)/sub T//sup 0/ and luminosity index ..lambda../sub c/ of the galaxy, being brighter in the bluer and most luminous galaxies. In a first approximation a two-parameter solution gives M/sub 1//sup 0/=M/sub 1//sup C/+2(..lambda../sub c/-1)+2.5((B-V)/sub T//sup 0/-0.5) where =-13.4 +- 0.2 from a sample of 78 galaxies having known distance moduli 18.3<..mu../sub 0//sup W/<32.0. In a second approximation allowing for internal extinction a three parameter solution gives M/sub 1//sup 0/=M/sub 1//sup asterisk/+2(..lambda../sub c/-0.8)+2.8((B-V)/sub T//sup 0/-0.5)+0.7 (log R/sub 25/-0.2) where R/sub 25/ is the isophotal axis ratio of the galaxy and =-13.0 +- 0.2. Distances derived from B/sub 1/ and M/sub 1//sup c/ or M/sub 1//sup asterisk/ are in good systematic agreement with distances derived from primary, secondary and tertiary indicators, but with a rather large dispersion (sigmaapprox. =0.55 mag) due in part to errors in the preliminary photometry (sigmaapprox. =0.4 mag). With some refinements and better photometry this new distance indicator appears capable of providing distance moduli with mean errors < or approx. =0.5 mag out to distances in excess of 100 megaparsecs.

• Research Organization: Department of Astronomy and McDonald Observatory, The University of Texas at Austin, Texas 78712
• OSTI ID: 5636808
• Journal Information: Astron. J.; (United States), Vol. 85:1
• Country of Publication: United States
• Language: English

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71 CLASSICAL AND QUANTUM MECHANICS
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DISTANCE
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LUMINOSITY
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COSMIC RADIO SOURCES
OPTICAL PROPERTIES
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640105* - Astrophysics &amp; Cosmology- Galaxies
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