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Published June 10, 2008 | Published
Journal Article Open

The evolutionary history of galactic bulges : photometric and spectroscopic studies of distant spheroids in the GOODS fields

Abstract

We report on the first results of a new study aimed at understanding the diversity and evolutionary history of distant galactic bulges in the context of now well-established trends for pure spheroidal galaxies. To this end, bulges have been isolated for a sample of 137 spiral galaxies within the redshift range 0.1 < z < 1.2 in the GOODS fields. Using proven photometric techniques, we determine the characteristic parameters (size, surface brightness, profile shape) of both the disk and bulge components in our sample. In agreement with earlier work that utilized aperture colors, distant bulges show a broader range of optical colors than would be the case for passively evolving populations. To quantify the amount of recent star formation necessary to explain this result, we used DEIMOS to secure stellar velocity dispersions for a sizeable fraction of our sample. This has enabled us to compare the fundamental plane of our distant bulges with that for spheroidal galaxies in a similar redshift range. Bulges of spiral galaxies with a bulge-to-total luminosity ratio (B/T) >0.2 show similar patterns of evolution to those seen for pure spheroidals such that the stellar populations of all spheroids with M > 10^(11) M⊙ are consistent with a single major burst of star formation at high redshift (z_f ≳ 2), while bulges with M < 10^(11) M⊙ must have had more recent stellar mass growth (~10% in mass since z ~ 1). Although further data spanning a wider range of redshift and mass are desirable, the similarity between the assembly histories of bulges and low-mass spheroidals seems difficult to reconcile with the picture whereby the majority of large bulges form primarily via secular processes within spiral galaxies.

Additional Information

© 2008 The American Astronomical Society. Received 2007 October 31; accepted 2008 February 26. The authors would like to extend their appreciation to Jason Rhodes for running the Tiny Tim PSF simulations and to Stephane Courteau and Michael McDonald for sharing their XVISTA routines. Thanks also to Ignacio Trujillo, David Koo, Mark Dickinson, and Bob Abraham for useful discussions. We also wish to thank the anonymous referee for a careful review and providing constructive comments that greatly improved the presentation and content of the paper. L. A. M. acknowledges financial support from the National Science and Engineering Council of Canada. T. T. acknowledges support from the NSF through CAREER award NSF-0642621, by the Sloan Foundation through a Sloan Research Fellowship, and by the Packard Foundation through a Packard Fellowship. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work is partly based on archival data from the Hubble Space Telescope, obtained from the data archive at the Space Telescope Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS5-26555.

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August 22, 2023
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