The brightest superassociations in spiral and irregular galaxies as extragalactic distance indicators

Details The brightest superassociations in spiral and irregular galaxies as extragalactic distance indicators The brightest superassociations in spiral and irregular galaxies as extragalactic distance indicators

Jan 1980

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980aj.....85....1w&link_type=abstract

Astronomical Journal, vol. 85, Jan. 1980, p. 1-8.

Astronomy and Astrophysics

Astronomy

57

Astrometry, Galactic Structure, Luminous Intensity, Spiral Galaxies, Stellar Luminosity, Hydrogen Clouds, Magnitude, Star Clusters, Stellar Spectrophotometry

Scientific paper

The brightest blue knots (superassociations) detected by composite U,B,V color photography in spiral and irregular galaxies have absolute magnitudes B1 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 M10 (corrected for galactic extinction) depends on the corrected color index (B-V)T0 and luminosity index Λc of the galaxy, being brighter in the bluer and most luminous galaxies. In a first approximation a two-parameter solution gives
M10 = M1C + 2(Λc -1)+2.5 [(B-V)T0-0.5]
where 1C = -13.4 ± 0.2 from a sample of 78 galaxies having known distance moduli 18.3 < μ0 < 32.0. In a second approximation allowing for internal extinction a three parameter solution gives
M10 = M1* +2(Λc -0.8)+2.8 [(B-V)T0 -0.5] +0.7 (log R25 -0.2)
where R25 is the isophotal axis ratio of the galaxy and 1* > = -13.0 ± 0.2. Distances derived from B1 and M1C or M1* are in good systematic agreement with distances derived from primary, secondary and tertiary indicators, but with a rather large dispersion (σ ≅ 0.55 mag) due in part to errors in the preliminary photometry (σ ≅ 0.4 mag). With some refinements and better photometry this new distance indicator appears capable of providing distance moduli with mean errors ≲0.5 mag out to distances in excess of 100 megaparsecs.

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