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Constraining the star formation histories of spiral bulges

Proctor, R. N. and Sansom, A. E. and Reid, I. N. (2000) Constraining the star formation histories of spiral bulges. Monthly Notices of the Royal Astronomical Society, 311 (1). pp. 37-49. ISSN 0035-8711. doi:10.1046/j.1365-8711.2000.03018.x.

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Stellar populations in spiral bulges are investigated using the Lick system of spectral indices. Long-slit spectroscopic observations of line strengths and kinematics made along the minor axes of four spiral bulges are reported. Comparisons are made between central line strengths in spiral bulges and those in other morphological types [elliptical, spheroidal (Sph) and S0]. The bulges investigated are found to have central line strengths comparable to those of single stellar populations of approximately solar abundance or above. Negative radial gradients are observed in line strengths, similar to those exhibited by elliptical galaxies. The bulge data are also consistent with correlations between Mg_2, Mg_2 gradient and central velocity dispersion observed in elliptical galaxies. In contrast to elliptical galaxies, central line strengths lie within the loci defining the range of 〈Fe〉 and Mg_2 achieved by Worthey’s solar abundance ratio, single stellar populations (SSPs). The implication of solar abundance ratios indicates significant differences in the star formation histories of spiral bulges and elliptical galaxies. A ‘single zone with infall’ model of galactic chemical evolution, using Worthey’s SSPs, is used to constrain the possible star formation histories of our sample. We show that the 〈Fe〉, Mg_2 and Hβ line strengths observed in these bulges cannot be reproduced using primordial collapse models of formation but can be reproduced by models with extended infall of gas and star formation (2–17 Gyr) in the region modelled. One galaxy (NGC 5689) shows a central population with a luminosity-weighted average age of ~5 Gyr, supporting the idea of extended star formation. Kinematic substructure, possibly associated with a central spike in metallicity, is observed at the centre of the Sa galaxy NGC 3623.

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Additional Information:© 2000 Royal Astronomical Society. Accepted 1999 July 27. Received 1999 July 22; in original form 1999 March 22. Article first published online: 6 Apr. 2002. We thank our referee D. Friedli for his constructive comments. The authors acknowledge the data analysis facilities provide by the Starlink Project which is run by CCLRC on behalf of PPARC. In addition, the iraf software package was used. iraf is distributed by the National Optical Astronomy Observatories, which is operated by AURA, Inc., under cooperative agreement with the National Science Foundation. This work is based on observations obtained at Palomar observatory, which is owned and operated by the California Institute of Technology.
Subject Keywords:galaxies: abundances; galaxies: evolution; galaxies: formation; galaxies: spiral; galaxies: stellar content
Issue or Number:1
Record Number:CaltechAUTHORS:20111201-093749975
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Official Citation:Proctor, R. N., Sansom, A. E. and Reid, I. N. (2000), Constraining the star formation histories of spiral bulges. Monthly Notices of the Royal Astronomical Society, 311: 37–49. doi: 10.1046/j.1365-8711.2000.03018.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:28271
Deposited On:01 Dec 2011 21:07
Last Modified:09 Nov 2021 16:55

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