The oxygen abundance deficiency in irregular galaxies

The observed oxygen abundances in a number of irregular galaxies have been compared with predictions of the closed-box model of chemical and photometric evolution of galaxies. Oxygen is found to be deficient with respect to the predicted abundances. This is an indicator in favor of loss of heavy elements via galactic winds or/and of infall of low--abundance gas onto the galaxy. The oxygen abundance deficiency observed within the optical edge of a galaxy cannot be explained by mixing with the gas envelope observed outside the optical limit. We confirm the widespread idea that a significant part of the heavy elements is ejected by irregular galaxies in the intergalactic medium.Comment: 8 pages, 7 figures, accepted for publication in Astronomy and Astrophysic

Bulges

We model the evolution of the galactic bulge and of the bulges of a selected sample of external spiral galaxies, via the multiphase multizone evolution model. We address a few questions concerning the role of the bulges within galactic evolution schemes and the properties of bulge stellar populations. We provide solutions to the problems of chemical abundances and spectral indices, the two main observational constraints to bulge structure.Comment: 15 pages, 10 figures, to be published in MNRA

Physical constraints on the halo mass function

We analyse the effect of two relevant physical constraints on the mass multiplicity function of dark matter halos in a Press--Schechter type algorithm. Considering the random--walk of linear Gaussian density fluctuations as a function of the smoothing scale, we simultaneously i) account for mass semi--positivity and ii) avoid the cloud--in--cloud problem. It is shown that the former constraint implies a severe cutoff of low--mass objects, balanced by an increase on larger mass scales. The analysis is performed both for scale--free power--spectra and for the standard cold dark matter model. Our approach shows that the well--known ``infrared" divergence of the standard Press--Schechter mass function is caused by unphysical, negative mass events which inevitably occur in a Gaussian distribution of density fluctuations.Comment: Revised version (accepted for publication in MNRAS) including a new comparison with numerical results, a new appendix and new references. uuencoded gzip'ed tar archive containing many LaTex files (the main file is mass.tex). 16 pages with 6 figures (all included

Climate is changing: are we changing too?

Many problems in the urban landscape can be reduced or eliminated by proper plant selection and by maintaining trees healthy so that they can fully provide their benefits. In a climate change scenario possible adaptation measures include changes to establishment practices and tree management, better matching of species to site, both under current and future climates, and the planting of non-native species and provenances in anticipation of climate change. Current opinion is to encourage the planting of local provenances of native species, citing adaptation of provenances to local conditions, and the requirement to maintain biodiversity and a native genetic base. However, local provenances may not be able to adapt to a changing climate, particularly given the rate of change predicted. Sourcing planting stock from regions with a current climate similar to that predicted for the future may provide one option, although care must be taken to ensure that suitable provenances are selected which are not at risk from, for example, spring frost damage as a result of early flushing. In this paper we'll focused on the technical and practical solutions for the selection of trees that might be the best choice in urban environments for the next future, given differences in urban sites (infrastructures, climate, soils etc), species attributes, management requirements and climate