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

Abstract

view Abstract Citations (59) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The brightest superassociations in spiral and irregular galaxies as extragalactic distance indicators Wray, J. D. ; de Vaucouleurs, G. Abstract 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. Publication: The Astronomical Journal Pub Date: January 1980 DOI: 10.1086/112625 Bibcode: 1980AJ.....85....1W Keywords: Astrometry; Galactic Structure; Luminous Intensity; Spiral Galaxies; Stellar Luminosity; Hydrogen Clouds; Magnitude; Star Clusters; Stellar Spectrophotometry; Astrophysics full text sources ADS | data products NED (81)