Marta Gavilán BouzasMercedes Mollá Lorente

Estallidos IV, Granada 2-04-07

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.

A short review

Galactic Chemical Evolution Model

Grid of models

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

Grid of ModelsMass interval: Six values

From 8 106 M to 3 109M

Collapse time: Four values

From 8 Gyr to 60 Gyr

Star Formation Parameters: Four valuesS, M, L, XL

TOTAL GRID: 96 Models

SFR HISTORIES

Lower Tcol and Higher and h

Higher Tcol and Lower and h

SFR para 9 108 Msun

0

0.2

0.4

0.6

0.8

1

0 5 10 15

Tiempo (Gyr)

SF

R (

Msu

n/y

r)

Eficiencia = 0.88

Eficiencia = 0.40

Eficiencia = 0.17

Efficiency=0.88

Efficiency=0.40

Efficiency=0.17

Effective Yieldp = 0.0034

The gas fraction estimation

<Z> = 0.0034ln(1/) + 0.0008

0

0.005

0.01

0.015

0.02

0.025

0 0.5 1 1.5 2 2.5ln(1/)

<Z

>

CBM

Zo = 0,0025ln(1/) + 0,0007

0

0,002

0,004

0,006

0,008

0 0,5 1 1,5 2 2,5ln(1/)

Zo

CBM

LR

Oxygen Effective Yield

0

0,002

0,004

0,006

0,008

0,01

0 0,2 0,4 0,6 0,8 1

Ye

ff(O

)Garnett02 DwGx

Garnett02 SGx

f Mgas/f Yo

6 0.0017

25 0.001

35 0.0009

Mgas*f Yo

2 0.0017

4 0.0013

8 0.0008

Oxygen Abundance

Models

Garnett 02 DwGx

Van Zee 06

Garnett 02 S

0

0.002

0.004

0.006

0.008

0 0.5 1 1.5 2 2.5

ln(1/) Dyn

Zo

Zo = 0,0022ln(1/) + 0,0004

0

0,002

0,004

0,006

0,008

0 0,5 1 1,5 2 2,5

ln(1/)Z

o

CBM

LR

=1.33*M(HI)/1.33*M(HI)+MestrellasLn(1/) Tot

IIZw70

7.27.4

7.67.8

88.2

8.48.6

8.8

-7 -5 -3 -1

Log(SFR)

12

+L

og

(O/H

)

7.27.4

7.67.8

8

8.28.4

8.68.8

-7 -5 -3 -1

Log(SFR)

12

+L

og

(O/H

)

Historia de la Formación Estelar

0

0.01

0.02

0.03

0.04

0 5 10 15Tiempo (Gyr)

SF

R (

Msu

n/y

r)

Tcol = 8 Gyr Tcol = 20 GyrTcol = 40 Gyr Tcol = 60 Gyr

-2

-1.5

-1

-0.5

0

-7 -5 -3 -1

Log(SFR)

Lo

g(N

/O)

Kherig and col 2007

= 0.30

= 0.24

= 0.21

= 0.40

Other observationsM(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

Our Model

5.2 107M< M(HI) < 1.0 108M

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

Our Model

-18.7 < MB <-16.7

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.