\begin{table}%t3
\caption{\label{valorigrad}Current values for the oxygen abundance gradient from the models for the galaxies in study.} 
\par
%\centerline
{\small
\begin{tabular}{cccc} 
  \hline\hline 
\multicolumn{4}{c}{Milky Way}  \\  
& MW-A1 & MW-A2 & MW-B  \\  
Disk range & $\Delta$(O/H)/$\Delta R$ & $\Delta$(O/H)/$\Delta R$ & $\Delta$(O/H)/$\Delta R$ \\ 
kpc & dex/kpc & dex/kpc & \\  
\noalign{\smallskip} 
  \hline 
4 to 14 & $-0.059$ & $-0.025$ & $-0.029$ \\ 
4 to 12 & $-0.033$ & $-0.019$ & $-0.024$ \\ 
4 to 10 & $-0.024$ & $-0.017$ & $-0.026$ \\ 
6 to 12 & $-0.073$ & $-0.027$ & $-0.029$ \\ 
\hline 
\noalign{\smallskip} 
\multicolumn{4}{c} {M~31} \\ 
& M~31-A1 & M~31-A2 & M~31-B (k~=~1.25)\\   
Disk range & $\Delta$(O/H)/$\Delta R$ & $\Delta$(O/H)/$\Delta R$& $\Delta$(O/H)/$\Delta R$\\ 
dex/kpc & dex/kpc & dex/kpc & dex/kpc\\  
  \hline 
4 to 20 & $-0.016$ & $-0.018$ & $­0.020$  ($-0.031$)\\ 
4 to 18 & $-0.013$ & $-0.015$ & $-0.018$  ($-0.023$) \\ 
4 to 16 & $-0.011$ & $-0.014$ & $-0.019$  ($-0.017$)\\ 
4 to 14 & $-0.011$ & $-0.013$ & $-0.021$  ($-0.019$)\\ 
6 to 16 & $-0.010$ & $-0.012$ & $-0.017$  ($-0.015$)\\ 
\hline 
\multicolumn{4}{c}{M~33}\\ 
& M~33-A05 & M~33-A01 & M~33-B \\ 
Disk range & $\Delta$(O/H)/$\Delta R$ & $\Delta$(O/H)/$\Delta R$ & $\Delta$(O/H)/$\Delta R$ \\ 
kpc & dex/kpc & dex/kpc & dex/kpc \\  
  \hline 
2 to 6 & $-0.015$ & $-0.015$ & $-0.063$ \\ 
\hline 
\multicolumn{4}{c}{Observed Values} \\  
Galaxy & $\Delta$(O/H)/$\Delta R$ & References* & \\ 
 & dex/kpc & & \\ 
  \hline 
 MW & $-0.040$ to $-0.060$ & 1, 2 & \\ 
 M~31 & $-0.013$ to $-0.027$ & 3 & \\ 
 M~33 & $-0.012$ to $-0.054$ & 4, 5, 6& \\ 
\hline
\end{tabular}} 
\tablebib{(1)~Deharveng et~al. (\cite{Deharveng2000}); (2)~Rudolph et~al. (\cite{Rudolph2006}); (3)~Trundle et~al. (\cite{Trundle2002}); (4)~Crockett et~al. (2006); (5)~Magrini et~al. (\cite{Magrini2007}); (6)~Rosolowsky et~al. (\cite{Rosolowsky2008}).} 
\end{table}