Astronomy & Astrophysics

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$\begin{figure} \par\includegraphics[width=5.9cm,clip]{1585fig1.eps}\includegraph... ...,clip]{1585fig2.eps}\includegraphics[width=5.9cm,clip]{1585fig3.eps}\end{figure}$ Figure 1: The temporal evolution of B-i vs. V-J predicted by Z01 (solid) and PÉGASE.2 (dashed). Both models assume a metallicity of Z=0.001, a Salpeter IMF throughout the mass range 0.08-120 $M_\odot$ , a redshift of z=0 and an exponential star formation history with a) $\tau =1$ Gyr; b) $\tau =6$ Gyr; and c) $\tau =-2$ Gyr. The additional parameter values for Z01 are a filling factor 0.1 and a total gas mass of $10^{10}~M_\odot$ available for star formation. Markers indicate ages of 1 Myr (circle), 100 Myr (triangle), 1 Gyr (square), 5 Gyr (pentagram, omitted from rightmost plot to avoid cluttering) and 15 Gyr (asterisk) along the model sequences. The colours of the eight objects (corrected for intrinsic extinction using c=0.15), for which data exist in all four filters required, are indicated by crosses representing $1\sigma$ error bars.
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In the text

$\begin{figure} \includegraphics[width=5.9cm,clip]{1585fig4.eps}\includegraphics[... ...,clip]{1585fig5.eps}\includegraphics[width=5.9cm,clip]{1585fig6.eps}\end{figure}$ Figure 2: The temporal evolution of EW(H $\alpha$ ) predicted by Z01 (solid lines) and PÉGASE.2 (dashed) for various SFHs compared to the range observed among the bluest LSBGs (gray area). Both models assume Z=0.001. Z01 furthermore assumes a filling factor of 0.1 and $M_{\rm tot}=10^{10}~M_\odot$ . The three panels represent different assumptions about the IMF. a) A Salpeter IMF with $M_{\rm up}=120~M_\odot$ . b) An IMF slope of $\alpha =2.85$ with $M_{\rm up}=120~M_\odot$ . c) A Salpeter IMF with an upper mass limit of 40 $M_\odot$ . From top to bottom in the right half of each panel, the different lines indicate star formation histories with $\tau =-2$ Gyr, -15 Gyr, constant SFR, $\tau =15$ Gyr, 6 Gyr, 3 Gyr, 1 Gyr and 500 Myr. The line dropping rapidly at an age of 100 Myr corresponds to the short burst scenario. The dash-dotted line running up to 1 Gyr in a) represents the predictions of Starburst99 for a constant SFR.
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In the text

$\begin{figure} \par\includegraphics[width=8.85cm,clip]{1585fig7.eps}\includegraphics[width=8.85cm,clip]{1585fig8.eps}\end{figure}$ Figure 3: Diagrams of B-V vs. V-J, showing the predicted positions of stellar populations at absolute ages of 3 Gyr ( left panel) and 13 Gyr ( right panel). In each panel, lines corresponding to metallicities of Z=0.001 (thick solid) and Z=0.004 (thin solid) connect the colours predicted for different star formation histories, parametrized by $\tau$ in ${\rm SFR}(t)\propto \exp{(-t/\tau)}$ . Each combination of absolute age and $\tau$ corresponds to the listed average stellar population ages, $\langle$ Age $\rangle$ . Dashed lines connect predicted populations with the same SFH but different Z. The colours (corrected for intrinsic extinction using c=0.15) of the eight objects for which data exists in all three filters are indicated by crosses representing $1\sigma$ error bars. A Salpeter IMF with $M_{\rm up}=120~M_\odot$ is assumed.
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In the text

$\begin{figure} \par\includegraphics[width=5.9cm,clip]{1585fig9.eps}\includegraph... ...lip]{1585fig13.eps}\includegraphics[width=5.9cm,clip]{1585fig14.eps}\end{figure}$ Figure 4: The allowed ages and M/L_V of acceptable fits (markers) for both Z01 and PÉGASE.2 at the 1 $\sigma$ level, under various assumption about the IMF: a) $M_{\rm up}=120~M_\odot$ , $\alpha =2.35$ for Z01; b) $M_{\rm up}=120~M_\odot$ , $\alpha =1.85$ -2.85 for Z01; c) $M_{{\rm up}}=40~M_\odot$ , $\alpha =2.35$ for Z01; d) $M_{{\rm up}}=40~M_\odot$ , $\alpha =1.85$ -2.85 for Z01; e) $M_{\rm up}=120~M_\odot$ , $\alpha =2.35$ for PÉGASE.2; f) $M_{\rm up}=120~M_\odot$ , $\alpha =1.85$ -2.85 for PÉGASE.2.
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In the text