[galaxy] compute sfr in a more consitent way

galaxy.py

@@ -80,7 +80,11 @@ def get_sfr(pp, stars):
         epoch *= pp.info["unit_time"].express(U.year)
         mass = stars["mass"].copy()
         mass *= pp.info["unit_mass"].express(U.Msun)
-        masstot, time = np.histogram(epoch, weights=mass, bins=100)
+        mask = epoch > 0
+        t_tot = np.max(epoch[mask]) - np.min(epoch[mask])
+        masstot, time = np.histogram(
+            epoch[mask], weights=mass[mask], bins=int(t_tot / 100)
+        )
         dtime = np.diff(time)
         sfr = masstot[-1] / dtime[-1]
     except KeyError:
@@ -95,7 +99,6 @@ def get_coldens(pp):
     pp.coldens("z")
     pp.coldens_map = pp.get_value("/maps/coldens_z", unit=U.coldens)
 
-
     im_extent = np.array(pp.get_attribute("/maps", "im_extent"))
     im_extent *= pp.info["unit_length"].express(U.kpc)
     map_size = pp.pp_params.pymses.map_size
@@ -179,7 +182,6 @@ def ring_analysis(pp, r=4, dr=0.5, dphi=0.125, z=0, dz=0.5):
     return res
 
 
-
 def get_time_from_relax(pp):
     try:
         epoch = pp.parts["epoch"].copy()