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Date and Time of the Query: 2019-03-26 T05:36:34 PDT
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For refcode 2001A&A...366...68P:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2001A&A...366...68P The formation of galaxy bulges: Spectrophotometric constraints. PRUGNIEL P., MAUBON G., SIMIEN F. Received 23 May 2000/Accepted 24 October 2000 Abstract. We have measured Mg_2_, Fe 5270 and Fe 5335 spectrophotometric indices (LICK system) in the bulge of 89 galaxies, mostly spirals from the Heraudeau (1996) sample. The indices are reduced to a null velocity dispersion and normalized to an aperture of 0.2 h^-1^ kpc. The mean errors are 0.009 mag on Mg_2_, and 0.3A on the iron indices. These measurements almost double the amount of similar data already available on spiral galaxies. Our data confirm the existence of the relation between Mg_2_ and {sigma}0, the central stellar velocity dispersion; we find an even tighter relation between Mg_2_ and V_rot_^m^, the maximum rotational velocity of the galaxy, deduced from HI observations. For the most massive bulges, these correlations may be interpreted as a mass-metallicity relation. However, the presence of young stellar populations, traced by the detection of [OIII] {lambda} 5007A emission, provides clear evidence that age effects do play a role. Since the contribution of the young population is anti- correlated to the mass of the galaxy, it continues the Mg_2_ vs. {sigma}_0_ relation toward the low-{sigma}0 region and globally increases its slope. We also present evidence for a new positive correlation between Fe indices and {sigma}0, and for a significant correlation between the line-strength indices and the total or disk luminosity. We propose to model the whole sequence of bulges within the following framework: bulges are composed of a primary population formed prior to the disk, during the initial collapse, and of a secondary population formed during its evolution. The whole family of bulges can be classified into three classes: (A) the bulges dominated by young populations are generally small, have ionized gas, low velocity dispersion and low line strengths; (B) the bulges dominated by the primary population lie along the mass-metallicity sequence defined for elliptical galaxies; and (C) the bulges where the secondary population is significant are less Mg-over-abundant than (B)-type bulges and deviate from the Mg_2_ vs. {sigma}_0_ relation of elliptical galaxies. Key words: galaxies: general - galaxies: spiral - galaxies: fundamental parameters - galaxies: stellar content - galaxies: evolution
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