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Astron. Astrophys. 318, 729-740 (1997)

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Studies of the association of faint blue and luminous galaxies using the Hitchhiker parallel camera

J.B. Jones 1, S.P. Driver 2, S. Phillipps 3, J.I. Davies 1, I. Morgan 1 and M.J. Disney 1

1 Department of Physics and Astronomy, University of Wales College of Cardiff, P.O. Box 913, Cardiff, CF2 3YB, Wales, UK (jbj@astro.cf.ac.uk)
2 School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
3 Astrophysics Group, Department of Physics, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, England, UK

Received 12 September 1995 / Accepted 11 June 1996


At B magnitudes [FORMULA] there is a well-known excess of galaxies (compared to standard models) which is probably due to an (evolving) population of sub- [FORMULA] galaxies at moderate redshifts ([FORMULA]). One particular hypothesis which is hard to test directly via number counts or even redshift surveys is the possibility that the faint blue galaxies are in fact sub-galactic objects destined to merge by the present day to form current giant galaxies. If this were the case we might expect to find the faint blue galaxies in the vicinity of [FORMULA] galaxies (at redshifts [FORMULA] to 0.4) with which they can merge (the blue galaxies are already known to be weakly clustered among themselves, limiting the possibility for multiple mergers of small fragments).

In the present paper we look for evidence of such clustering of faint blue galaxies around larger systems using candidates chosen photometrically from deep multicolour CCD images using the Hitchhiker parallel CCD camera. A sample of candidate [FORMULA] galaxies expected to lie at redshifts [FORMULA] to 0.4 has been selected on the basis of apparent magnitude (B [FORMULA] to [FORMULA]) and colours typical of early-type spirals. The distribution of 152 blue galaxies having [FORMULA] [FORMULA] around 13 candidate [FORMULA] galaxies has been determined. No evidence has been found for any preferential clustering of blue galaxies about the [FORMULA] candidates; the observed overdensity within 60 arcsec of the [FORMULA] candidates is [FORMULA] per candidate. We have also looked for clustering between other photometrically selected samples (such as faint blue and faint red objects). Null results have been found in all cases, placing significant limits on the scenarios wherein dwarfs at medium redshifts are removed via mergers with larger objects.

Key words: galaxies: interactions – galaxies: evolution – galaxies: photometry – galaxies: statistics – cosmology: observations

Send offprint requests to: J.B. Jones


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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998