Galaxy chemical evolution models: The role of molecular gas formation

In our classical grid of multiphase chemical evolution models, star formation in the disc occurs in two steps: first, molecular gas forms, and then stars are created by cloud-cloud collisions or interactions of massive stars with the surrounding molecular clouds. The formation of both molecular clouds and stars are treated through the use of free parameters we refer to as efficiencies. In this work, we modify the formation of molecular clouds based on several new prescriptions existing in the literature, and we compare the results obtained for a chemical evolution model of theMilkyWay Galaxy regarding the evolution of the Solar region, the radial structure of the Galactic disc and the ratio between the diffuse and molecular components, H I /H 2 . Our results show that the six prescriptions we have tested reproduce fairly consistent most of the observed trends, differing mostly in their predictions for the (poorly constrained) outskirts of the Milky Way and the evolution in time of its radial structure. Among them, the model proposed by Ascasibar et al. (in preparation), where the conversion of diffuse gas into molecular clouds depends on the local stellar and gas densities as well as on the gas metallicity, seems to provide the best overall match to the observed data

A photometric comprehensive study of circumnuclear star forming rings: the sample

We present photometry in U, B, V, R and I continuum bands and in H$\alpha$ and H$\beta$ emission lines for a sample of 336 circumnuclear star forming regions (CNSFR) located in early type spiral galaxies with different levels of activity in their nuclei. They are nearby galaxies, with distances less than 100 Mpc, 60\% of which are considered as interacting objects. This survey of 20 nuclear rings aims to provide insight into their star formation properties as age, stellar population and star formation rate. Extinction corrected H$\alpha$ luminosities range from $1.3\times 10^{38}$ to $4\times 10^{41} erg s^{-1}$, with most of the regions showing values between 39.5 $\leq log L(H\alpha) \leq$ 40, which implies masses for the ionizing clusters higher than $2\times 10^{5} M_\odot$. H$\alpha$ and H$\beta$ images have allowed us to obtain an accurate measure of extinction. We have found an average value of A$_V$ = 1.85 magnitudes. (U-B) colour follows a two maximum distribution around (U-B)$\simeq$ -0.7, and -0.3; (R-I) also presents a bimodal behaviour, with maximum values of 0.6 and 0.9. Reddest (U-B) and (R-I) regions appear in non-interacting galaxies. Reddest (R-I) regions lie in strongly barred galaxies. For a significant number of HII regions the observed colours and equivalent widths are not well reproduced by single burst evolutionary theoretical models.Comment: Accepted for publication in MNRAS. Accepted 15 May 2015. Received, 21 April 201

Radial gradients of abundances

The final publication is available at link.springer.co

The impact of the visibility of the [O III]λ4363 line on the general properties of H II galaxies in the Local Universe

This is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. Hoyos, C. and A.I. Díaz. The impact of the visibility of the [O III]λ4363 line on the general properties of H II galaxies in the Local Universe. Monthly Notices of the Royal Astronomical Society 365 (2006): 454-46

The nature of the Wolf-Rayet galaxy Mrk 209 from photoionization models

This is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. Pérez-Montero, E. and A.I. Díaz. The nature of the Wolf-Rayet galaxy Mrk 209 from photoionization models. Monthly Notices of the Royal Astronomical Society 377 (2007): 1195-120

Damped Lyα systems as spiral galaxies

This is an electronic version of an article published in The Astrophysical Journal. Clavel, J. et al. Damped Lyα systems as spiral galaxies. The Astrophysical Journal 487 (1997): 29-3

Evolution of spiral galaxies. VII. Time evolution of the radial distributions of abundances

This is an electronic version of an article published in The Astrophysical Journal. Mollá, M., Ferrini, F. and A.I. Díaz. Evolution of spiral galaxies. VII. Time evolution of the radial distributions of abundances. The Astrophysical Journal 475 (1997): 519-53