Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998larm.confe.136g&link_type=abstract
"IX Latin American Regional IAU Meeting, "Focal Points in Latin American Astronomy", held in Tonantzintla, Mexico, Nov 9-13, 199
Astronomy and Astrophysics
Astronomy
Scientific paper
The classical model of spiral galaxy formation predicts that the bulge and disk formation occurs in two distinct phases, being the bulge formation much faster. Nevertheless, recent observational results, relative to the nature of the bulge in spiral galaxies, suggest the possibility that this component may have been built, in some cases, by secular evolutionary processes in barred galaxies, i.e., inflows of gas, driven by the bar, and star transport from disk to bulge by bar-driven vertical disk heating. Some of these results are: (1) - the detection of metal-rich stars with bar kinematics near the Galactic center, while metal-poor stars in this region do not have this property (Rich & Terndrup 1997,PASP,109,571); (2) - the more rapid rotation of triaxial bulges, which are associated with bars, compared to bulges of non-barred galaxies (Kormendy 1982, ApJ,257,75); (3) - the similar broadband colors of inner disk and bulge (Peletier & Balcells 1996,AJ,111,2238), and the correlation between the scale lengths of disk and bulge (Courteau et al. 1996,ApJL,457,L73) in spiral galaxies. These results are consistent with N-body simulations and theoretical developments that also suggest that bar formation, dissolution, and bulge building may even be a recurrent process (Norman, Sellwood & Hasan 1996, ApJ,462,114 and references therein). The goal of this project consists in exploring the origin of the observed diversities on the properties of bulges, like luminosity and color index, concerning the predictions of bulge building from disk material. With this aim, we have selected a sample of 257 Sbc galaxies (barred and ordinary) with color index measurements along each of them (Longo & de Vaucouleurs 1983, 1985 - University of Texas Astronomy Monographs, No. 3 - 3A). These data are being used to test the existence of correlations that can corroborate, or not, the possible scenario of bulge building. The main preliminary result we have obtained so far is: the majority (~70%) of galaxies have negative color gradients; however, 83% of the galaxies with negligible (B-V) gradients (i.e., -0.10 < grad < 0.10) are barred, while this number drops to 75% when the (U-B) gradient is considered. This result may indicate that the bar acts unifying the stellar populations of bulge and disk, in agreement with the secular evolutionary scenario, and is homologous to the finding of Zaritsky, Kennicutt & Huchra (1994,ApJ,420,87) that barred spirals have flatter abundance gradients than unbarred spirals.
Dos Anjos S.
Gadotti Dimitri A.
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