Calculate birth halo catalogue index

SOAP/particle_selection/aperture_properties.py

@@ -760,6 +760,24 @@ def TotalSNIaRate(self) -> unyt.unyt_quantity:
             self.star_mask_ap
         ].sum()
 
+    @lazy_property
+    def ExSituFraction(self) -> unyt.unyt_quantity:
+        """
+        Mass fraction of bound stars that formed in a different subhalo.
+        """
+        if self.Nstar == 0:
+            return None
+
+        group_nr = self.get_dataset("PartType4/GroupNr_bound")[self.star_mask_all][
+            self.star_mask_ap
+        ]
+        birth_group_nr = self.get_dataset("PartType4/BirthHaloCatalogueIndex")[
+            self.star_mask_all
+        ][self.star_mask_ap]
+        ex_situ = group_nr != birth_group_nr
+
+        return self.star_mass_fraction[ex_situ].sum()
+
     @lazy_property
     def bh_mask_all(self) -> NDArray[bool]:
         """
@@ -3788,6 +3806,7 @@ class ApertureProperties(HaloProperty):
         "stellar_age_mw": False,
         "stellar_age_lw": False,
         "TotalSNIaRate": False,
+        "ExSituFraction": False,
         "HydrogenMass": False,
         "HeliumMass": False,
         "MolecularHydrogenMass": False,

SOAP/property_table.py

@@ -1905,6 +1905,22 @@ class PropertyTable:
             output_physical=True,
             a_scale_exponent=0,
         ),
+        "ExSituFraction": Property(
+            name="ExSituFraction",
+            shape=1,
+            dtype=np.float32,
+            unit="dimensionless",
+            description="Mass fraction of bound stars that formed in a different subhalo",
+            lossy_compression_filter="FMantissa9",
+            dmo_property=True,
+            particle_properties=[
+                "PartType4/Masses",
+                "PartType4/BirthHaloCatalogueIndex",
+                "PartType4/GroupNr_bound",
+            ],
+            output_physical=True,
+            a_scale_exponent=0,
+        ),
         "Mgas": Property(
             name="GasMass",
             shape=1,
@@ -5134,7 +5150,7 @@ def generate_tex_files(self, output_dir: str):
         # standalone table file footer
         tailstr = "\\end{document}"
 
-        # generate the auxilary documentation files
+        # generate the auxiliary documentation files
         with open(f"{output_dir}/timestamp.tex", "w") as ofile:
             ofile.write(get_version_string())
         with open(f"{output_dir}/table.tex", "w") as ofile: