Astron. Astrophys. 364, 26-42 (2000)

The morphology of extremely red objects

G. Moriondo ¹, A. Cimatti ¹ and E. Daddi <sup>2

1</sup> Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
² Università degli Studi di Firenze, Dipartimento di Astronomia e Scienza dello Spazio, Largo E. Fermi 5, 50125 Firenze, Italy

Received 17 April 2000 / Accepted 6 October 2000

Abstract

We present a quantitative study of the morphology of 41 Extremely Red Objects (EROs). The analysis is based on deep otical and near-infrared images from the Hubble Space Telescope public archive, and performed by fitting to each galaxy image a PSF-convolved bi-dimensional model brightness distribution. Relying both on the visual inspection of the data and on the results of the fitting procedure, we are able to determine the fraction of irregular and/or interacting EROs, and to identify those that more closely resemble local ellipticals. To the former class, whose members are probably high-redshift dusty starburst, belongs about 15% of the whole sample, whereas the elliptical-like objects are between 50 and 80% of the total. A few galaxies, although characterized by a compact morphology, are best fitted by an exponential distribution, more typical of local spirals. Our data also suggest that irregular EROs are found predominantly in the field, and that - on average - they tend to be characterized by the reddest colors. Finally, we plot the rest-frame Kormendy Relation ( vs. ) for a sample of 6 EROs with spectroscopic redshifts (), and estimate its evolution with respect to the local relation.

Key words: galaxies: distances and redshifts galaxies: elliptical and lenticular, cD galaxies: evolution galaxies: fundamental parameters galaxies: photometry

Send offprint requests to: gmorio@arcetri.astro.it

SIMBAD Objects

Contents

• 1. Introduction
• 2. The sample
• 3. Data reduction and analysis
• 4. Fitting the surface brightness distributions
  • 4.1. The point spread function
  • 4.2. The model
• 5. Simulations of faint galaxies
  • 5.1. Disentangling the and distributions
  • 5.2. Systematic errors
  • 5.3. Mapping the parameter space
• 6. Results
  • 6.1. Irregular and compact objects
  • 6.2. Structural parameters
  • 6.3. The shape index n and the fraction of ellipticals
• 7. Discussion
  • 7.1. Field and cluster objects
  • 7.2. Red exponential galaxies
  • 7.3. Morphology and colors
  • 7.4. The distribution of n
  • 7.5. The Kormendy relation
• 8. Summary and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000
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