Bibcode
Beckman, J. E.; Casuso, E.; Zurita, A.; Relaño, M.
Bibliographical reference
Penetrating bars through masks of cosmic dust : the Hubble tuning fork strikes a new note, Proceedings of a conference held at Pilanesburg National Park (South Africa). Edited by D. L. Block, I. Puerari, K. C. Freeman, R. Groess, and E. K. Block. Astrophysics and space science library (ASSL) vol. 319. Dordrecht: Kluwer Academic Publishers, 2004, p.119
Advertised on:
1
2004
Citations
2
Refereed citations
2
Description
In the first part of this article we show how observations of the
chemical evolution of the Galaxy: G- and K-dwarf numbers as functions of
metallicity, and abundances of the light elements, D, Li, Be and B, in
both stars and the interstellar medium (ISM), lead to the conclusion
that metal poor HI gas has been accreting to the Galactic disc during
the whole of its lifetime, and is accreting today at a measurable rate,
~2 Msun per year across the full disc. Estimates of the local star
formation rate (SFR) using methods based on stellar activity, support
this picture. The best fits to all these data are for models where the
accretion rate is constant, or slowly rising with epoch. We explain here
how this conclusion, for a galaxy in a small bound group, is not in
conflict with graphs such as the Madau plot, which show that the
universal SFR has declined steadily from z=1 to the present day. We also
show that a model in which disc galaxies in general evolve by accreting
major clouds of low metallicity gas from their surroundings can explain
many observations, notably that the SFR for whole galaxies tends to show
obvious variability, and fractionally more for early than for late
types, and yields lower dark to baryonic matter ratios for large disc
galaxies than for dwarfs. In the second part of the article we use NGC
1530 as a template object, showing from Fabry-Perot observations of its
Halpha emission how strong shear in this strongly barred galaxy acts to
inhibit star formation, while compression acts to stimulate it.