Marta Gavil

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Gas and Metalliciy in Dwarf Galaxies

• Marta Gavilán Bouzas
• Mercedes Mollá Lorente

Estallidos IV, Granada 2-04-07
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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.

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A short review

• Galactic Chemical Evolution Model
• Grid of models

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Galactic Chemical Evolution Model

• The free parameters are
• the collapse time Tcol
• the efficiency in forming molecular clouds em
• the efficiency in transform the clouds into
  stars eh
• The SFR is a RESULT not an INPUT
• There are no STAR BURSTS the star forming
  process is continuous, but not constant

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Grid of Models

• Mass interval Six values
• From 8 106 M to 3 109M
• Collapse time Four values
• From 8 Gyr to 60 Gyr
• Star Formation Parameters Four values
• S, M, L, XL

TOTAL GRID 96 Models
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SFR HISTORIES

• Lower Tcol and Higher em and eh è e 0.9
• Higher Tcol and Lower em and eh è e 0.1

Efficiency0.88 Efficiency0.40 Efficiency0.17
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Effective Yield
p 0.0034
The gas fraction estimation
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Oxygen Effective Yield
f Mgas/f Yo
6 0.0017
25 0.001
35 0.0009
Mgasf Yo
2 0.0017
4 0.0013
8 0.0008
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Oxygen Abundance
Ln(1/m) Tot
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IIZw70
Kherig and col 2007
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Other observations
M(HI) Observations M(HI) Observations
Kong 2004 3.28 108M
Cox et al 2001 1.0 108M
Larsen et al 2000 5.88 108M
Mas-Hesse Kunth 99 3.4 108M
MB Observations MB 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
What's happening?
Our Model
5.2 107M lt M(HI) lt 1.0 108M
Our Model
-18.7 lt MB lt-16.7
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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.