The redshift-distance relation. VII. Absolute magnitudes of the first three ranked cluster galaxies as functions of cluster richness and Bautz--Morgan cluster type: the effect on q$sub 0$

Journal Article · Wed Aug 01 04:00:00 EDT 1973 · Astrophys. J., v. 183, no. 3, pp. 743-757

OSTI ID:4322932

Sandage, A; Hardy, E

The ratio of angular diameters of the first three ranked galaxies in E and SO aggregates defines contrast paratmeters that correlate well with Bautz- Morgan (BM) cluster types. Interpreted as an apparent maginitude difference, 5 log theta /sub 1// theta /sub 2/ varies from 1.3 mag for Bautz-Morgan cla ss I clusters to 0.4 mag for class III. The absolute magnitudes also change with BM class. Magnitude residuals from the Hubble diagram show that the first-ranked galaxy is absolutely brighter in claas I clusters than in class III by < DELTA M/ sub nu / =0.6 mag. However, the second and third ranked are fainter by 0.5 mag in class I compared to class II clusters. This startling, but well-determined, inverse effect suggests that the dominance of first-ranked galaxies in clusters occurs at the expense of the fainter members. Because both the Bautz-Morgan class and the first-ranked are independent of cluster richness, we argue that the Bautz-Morgan effect is more likely to be related to an initial condition of cluster formation than to later evolution by process that depend on the rate of interaction of cluster members. New data, obtained by extensive counting, are given for the galaxy population (N) of all groups and clusters in our sample. There is no correlation of first-ranked absolute magnitudes with N at a level more significant than I sigma , but a significant correlation does exist for second- and third-ranked galaxies. The Hubble diagram using the V magnitudes of first-ranked galaxies is 98 E and SO groups, corrected for aperture effect, K- dimming, galactic absorption, Bautz-Morgan effect, and cluster a linerar redshift- distance relation, and has the small dispersion of sigma (M/sub nu ) = 0.28 mag for the distribution of horizontal residuals. The effect of the BM and the richness corrections on the value of 90 in our sample is negligible compared with the large errors of the current detertninations. Only the grossest altenatives to q/sub o/ (apparent) =1 plus or minus 1 (such as q/sub o/=-1 or q/sub o/ > 3 ) can be discarded from the data now available, no matter how the material is analyzed. New data for many clusters with large redshift (z>0.4) are needed for a finer solution. However, the prediction of steady-state cosmology (q/sub o/=- 1) is clearly at variance even with the present data. (auth)

• Research Organization: Hale Observatories, Carnegie Institution of Washington, California Institute of Technology
• NSA Number: NSA-29-022079
• OSTI ID: 4322932
• Journal Information: Astrophys. J., v. 183, no. 3, pp. 743-757, Journal Name: Astrophys. J., v. 183, no. 3, pp. 743-757; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

*GALAXIES-- PHOTOMETRY
*GALAXY CLUSTERS-- LUMINOSITY
ABSORPTION
DISTANCE
DOPPLER EFFECT
ENERGY SPECTRA
N56600* --Physics (Astrophysics &amp; Cosmology)--Cosmology
RADIO GALAXIES GALAXY CLUSTERS