To be published in Seychelles conference on galaxy evolution, "Lessons from the Local Group", ed. K. C. Freeman, B. G. Elmegreen, D. L. Block, and M. Woolway (Dordrecht: Springer), in press, 2014
http://arxiv.org/abs/1405.1421

For a PDF version of the article, click here.

STRUCTURE AND EVOLUTION OF DWARF GALAXIES

John Kormendy


Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USA;
Max-Planck-Institut für Extraterrestrische Physik, Gießenbachstraße, 85748 Garching bei München, Germany;
Universitäts-Sternwarte München, Ludwig-Maximilians-Universität, Scheinerstraße 1, 81679 München, Germany


Abstract: Different structural parameter correlations show how classical bulge components and elliptical galaxies are different from spiral and S0 galaxy disks, irregular (Im) galaxies, and spheroidal (Sph) galaxies. In contrast, the latter, apparently diverse galaxies or galaxy components have almost identical parameter correlations. This shows that they are related. A review of galaxy transformation processes suggests that S0 and spheroidal galaxies are star-formation-quenched, "red and dead" versions of spiral and Im galaxies. In particular, Sph galaxies are bulgeless S0s. This motivates a parallel sequence galaxy classification in which an S0a-S0b-S0c-Sph sequence of decreasing bulge-to-total ratios is juxtaposed to an Sa-Sb-Sc-Im sequence of star-forming galaxies. All parameter sequences show a complete continuity from giant galaxies to the tiniest dwarfs. Dwarfs are not a new or different class of galaxies. Rather, they are the extreme products of transformation processes that get more important as gravitational potential wells get more shallow. Smaller Sph and S+Im galaxies have lower stellar densities because they retain fewer baryons. Comparison of the baryonic parameter correlations with those for dark matter halos allows us to estimate baryon loss as a function of galaxy mass. Extreme dwarfs are almost completely dominated by dark matter.


Table of Contents

A PARALLEL SEQUENCE GALAXY CLASSIFICATION

S0+Sph GALAXIES AS TRANSFORMED SPIRAL+IRREGULAR GALAXIES

S+Im → S0+Sph GALAXY TRANSFORMATION PROCESSES

VISIBLE MATTER AND DARK MATTER PARAMETER CORRELATIONS

CONCLUSIONS

REFERENCES

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