1. School of Physics & Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3AA, UK
2. Department of Physics and Astronomy, The University of Texas at Brownsville, 80 Fort Brown, Brownsville, Texas 78520, USA
3. European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
4. Astronomy Department, University of California, 601 Campbell Hall, Berkeley, California 94720-3411, USA
5. Department of Astronomy, Physics-Astronomy Building C309, University of Washington, Box 351580, Seattle, Washington 98195, USA

Correspondence to: M. J. Disney¹ Correspondence and requests for materials should be addressed to M.J.D. (Email: mjd@astro.cf.ac.uk).

Abstract

Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment and feedback from supernova explosions and supermassive black holes¹. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter^{2, 3, 4}. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular momentum, baryon fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free from optical selection effects⁵, shows five independent correlations among six independent observables, despite having a wide range of properties. This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our data set. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter model in cosmology⁶.

1. School of Physics & Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3AA, UK
2. Department of Physics and Astronomy, The University of Texas at Brownsville, 80 Fort Brown, Brownsville, Texas 78520, USA
3. European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
4. Astronomy Department, University of California, 601 Campbell Hall, Berkeley, California 94720-3411, USA
5. Department of Astronomy, Physics-Astronomy Building C309, University of Washington, Box 351580, Seattle, Washington 98195, USA

Correspondence to: M. J. Disney¹ Correspondence and requests for materials should be addressed to M.J.D. (Email: mjd@astro.cf.ac.uk).

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