Andrew Wetzel edited quiescent_fraction.tex  about 9 years ago

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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.  This is likely an unbiased metric, 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 or 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.  The error bars show 68\% uncertainty for a beta distribution \citep{Cameron2011} based on the counts in each bin.  Of the 56known  satellites, only 4 (7\%) are star-forming/gas-rich: the LMC and SMC around the MW, LGS 3 and IC 10 around M31. Moreover, at $\mstar<8\times10^7\msun$, only 1 (LGS 3) of the 51 satellites are star-forming, and at $\mstar<9\times10^5\msun$ \emph{all} 40 satellites are quiescent.  These near-unity quiescent fractions for satellite dwarf galaxies dwarfs in the LG  contrast strongly with the effectively \emph{zero} quiescent fraction for dwarf galaxies that are isolated ($>1500\kpc$ from a more massive host) \citep{Geha2012, Phillips2014}  and thus not satellites \citep{Geha2012, Phillips2014}. are not/were never satellites.  The only known exception is KKR 25, a quiescent  dwarf spheroidal with $\mstar=1.4\times10^6\msun$ that is $1853\kpc$ from M31.