Andrew Wetzel edited quiescent_fraction.tex  about 9 years ago

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\subsection{Observed Quiescent Fractions for Satellites}  %Based on our above definitions of ``satellite'' and ''quiescent'' dwarf galaxies.  We group Figure~\ref{fig:quiescent_fraction} shows, for  all satellite dwarf galaxiesin the LG into 1-dex bins  of $\mstar$ and compute the MW and/or M31,  the fraction that are quiescent in each bin. 1-dex bins of $\mstar$ \citep[see also][]{Phillips2014, SlaterBell2014}.  We do not attempt any correction for observational completeness as a function of $\mstar$, because we measure the \emph{relative fraction}that are quiescent  in each bin, which is likely an unbiased metric. metric at these satellites' distances.  %absent significant differential completeness as a function of recent star formation, which is unlikely because star-forming galaxies are generally brighter, but the quiescent fraction is near unity across almost all $\mstar$.  Figure~\ref{fig:quiescent_fraction} shows the quiescent fraction for all satellite dwarf galaxies of the MW and/or M31 versus $\mstar$ \citep[see also][]{Phillips2014, SlaterBell2014}.  We show fractions for all such satellites (blue circles) as well as separately for those in the MW (violet squares) and M31 (green triangles) halos.  Error bars show the 68\% uncertainty for the binomial counts in each bin via using  a beta distribution \citep{Cameron2011}. Of the 56 satellites, only 4 (7\%) are star-forming/gas-rich: LMC and SMC around of  the MW, LGS 3 and IC 10 around of  M31. Moreover, at $\mstar<8\times10^7\msun$, only 1 (LGS 3) of the 51 satellites is star-forming, and at $\mstar<9\times10^5\msun$ \emph{all} 40 satellites are quiescent.  These near-unity quiescent fractions for satellites in of  the LG MW/M31  contrast strongly with the effectively \emph{zero} quiescent fraction for isolated (non-satellite) dwarf galaxies \citep{Geha2012, Phillips2014}, as outlined in the Introduction. (The only known exception is KKR 25, a quiescent dwarf spheroidal with $\mstar=1.4\times10^6\msun$ that is $1853\kpc$ from M31.)