1. Marta Gavilán Bouzas Mercedes Mollá Lorente Estallidos IV, Granada 2-04-07

2. What are we looking for? We are looking for some signs to know if dwarf galaxies lose some of their gas or not. How do we looking for it? Our aim is to have a large amount of model results (in an autoconsistent way) to obtain the maximum number of clues. We analized: gas content, metallicity and photometry and compare them with observations.

3. A short review Galactic Chemical Evolution Model Grid of models

4. Galactic Chemical Evolution Model The free parameters are: the collapse time: Tcol the efficiency in forming molecular clouds:   the efficiency in transform the clouds into stars:  h The SFR is a RESULT not an INPUT There are no STAR BURSTS: the star forming process is continuous, but not constant

5. Grid of Models Mass interval: Six values From 8 10 6 M  to 3 10 9 M  Collapse time: Four values From 8 Gyr to 60 Gyr Star Formation Parameters: Four values S, M, L, XL TOTAL GRID: 96 Models

6. SFR HISTORIES Lower Tcol and Higher   and  h    Higher Tcol and Lower   and  h    Efficiency=0.88 Efficiency=0.40 Efficiency=0.17

7. Effective Yield p = 0.0034 The gas fraction estimation

8. Oxygen Effective Yield f Mgas/fYo 60.0017 250.001 350.0009 Mgas*fYo 20.0017 40.0013 80.0008

9. Oxygen Abundance Models Garnett 02 DwGx Van Zee 06 Garnett 02 S Ln(1/  ) Tot

10. IIZw70 Kherig and col 2007  = 0.30  = 0.24  = 0.21  = 0.40

11. Other observations M(HI) Observations Kong 2004 3.28 10 8 M  Cox et al 2001 1.0 10 8 M  Larsen et al 2000 5.88 10 8 M  Mas-Hesse & Kunth 99 3.4 10 8 M  Our Model 5.2 10 7 M  < M(HI) < 1.0 10 8 M  M B Observations Kong 2004 -17.23 Gil de Paz et al 2003 -16.52 Cairós et al 2001 -16.31 Cox et al 2001 -16.53 Larsen et al 2000 -17.49 Our Model -18.7 < M B <-16.7

12. CONCLUSIONS Our models present an effective yield without gas outflow according with most observations. The models with high efficiency give too much high abundances. It is possible that they do not match with any observations. In the case of IIZw70 we reproduce the SFR and the (O/H) value with no star burst. …but the gas content needs additional explanation.