Store the last redshift at which a BH has had its last minor or major merger.

examples/EAGLE_ICs/EAGLE_12/eagle_12.yml

@@ -182,4 +182,6 @@ EAGLEAGN:
   coupling_efficiency:              0.15       # Fraction of the radiated energy that couples to the gas in feedback events.
   AGN_delta_T_K:                    3.16228e8  # Change in temperature to apply to the gas particle in an AGN feedback event in Kelvin.
   AGN_num_ngb_to_heat:              1.         # Target number of gas neighbours to heat in an AGN feedback event.
-  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
\ No newline at end of file
+  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
+  threshold_major_merger:           0.333      # Mass ratio threshold to consider a BH merger as 'major'
+  threshold_minor_merger:           0.1        # Mass ratio threshold to consider a BH merger as 'minor'

examples/EAGLE_ICs/EAGLE_25/eagle_25.yml

@@ -183,4 +183,6 @@ EAGLEAGN:
   coupling_efficiency:              0.15       # Fraction of the radiated energy that couples to the gas in feedback events.
   AGN_delta_T_K:                    3.16228e8  # Change in temperature to apply to the gas particle in an AGN feedback event in Kelvin.
   AGN_num_ngb_to_heat:              1.         # Target number of gas neighbours to heat in an AGN feedback event.
-  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
\ No newline at end of file
+  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
+  threshold_major_merger:           0.333      # Mass ratio threshold to consider a BH merger as 'major'
+  threshold_minor_merger:           0.1        # Mass ratio threshold to consider a BH merger as 'minor'

examples/EAGLE_ICs/EAGLE_50/eagle_50.yml

@@ -184,3 +184,5 @@ EAGLEAGN:
   AGN_delta_T_K:                    3.16228e8  # Change in temperature to apply to the gas particle in an AGN feedback event in Kelvin.
   AGN_num_ngb_to_heat:              1.         # Target number of gas neighbours to heat in an AGN feedback event.
   max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
+  threshold_major_merger:           0.333      # Mass ratio threshold to consider a BH merger as 'major'
+  threshold_minor_merger:           0.1        # Mass ratio threshold to consider a BH merger as 'minor'

examples/EAGLE_low_z/EAGLE_12/eagle_12.yml

@@ -177,4 +177,6 @@ EAGLEAGN:
   coupling_efficiency:              0.15       # Fraction of the radiated energy that couples to the gas in feedback events.
   AGN_delta_T_K:                    3.16228e8  # Change in temperature to apply to the gas particle in an AGN feedback event in Kelvin.
   AGN_num_ngb_to_heat:              1.         # Target number of gas neighbours to heat in an AGN feedback event.
-  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
\ No newline at end of file
+  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
+  threshold_major_merger:           0.333      # Mass ratio threshold to consider a BH merger as 'major'
+  threshold_minor_merger:           0.1        # Mass ratio threshold to consider a BH merger as 'minor'

examples/EAGLE_low_z/EAGLE_25/eagle_25.yml

@@ -185,4 +185,6 @@ EAGLEAGN:
   coupling_efficiency:              0.15       # Fraction of the radiated energy that couples to the gas in feedback events.
   AGN_delta_T_K:                    3.16228e8  # Change in temperature to apply to the gas particle in an AGN feedback event in Kelvin.
   AGN_num_ngb_to_heat:              1.         # Target number of gas neighbours to heat in an AGN feedback event.
-  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
\ No newline at end of file
+  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
+  threshold_major_merger:           0.333      # Mass ratio threshold to consider a BH merger as 'major'
+  threshold_minor_merger:           0.1        # Mass ratio threshold to consider a BH merger as 'minor'

examples/EAGLE_low_z/EAGLE_50/eagle_50.yml

@@ -176,4 +176,6 @@ EAGLEAGN:
   coupling_efficiency:              0.15       # Fraction of the radiated energy that couples to the gas in feedback events.
   AGN_delta_T_K:                    3.16228e8  # Change in temperature to apply to the gas particle in an AGN feedback event in Kelvin.
   AGN_num_ngb_to_heat:              1.         # Target number of gas neighbours to heat in an AGN feedback event.
-  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
\ No newline at end of file
+  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
+  threshold_major_merger:           0.333      # Mass ratio threshold to consider a BH merger as 'major'
+  threshold_minor_merger:           0.1        # Mass ratio threshold to consider a BH merger as 'minor'

examples/EAGLE_low_z/EAGLE_6/eagle_6.yml

@@ -186,4 +186,6 @@ EAGLEAGN:
   coupling_efficiency:              0.15       # Fraction of the radiated energy that couples to the gas in feedback events.
   AGN_delta_T_K:                    3.16228e8  # Change in temperature to apply to the gas particle in an AGN feedback event in Kelvin.
   AGN_num_ngb_to_heat:              1.         # Target number of gas neighbours to heat in an AGN feedback event.
-  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
\ No newline at end of file
+  max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
+  threshold_major_merger:           0.333      # Mass ratio threshold to consider a BH merger as 'major'
+  threshold_minor_merger:           0.1        # Mass ratio threshold to consider a BH merger as 'minor'

examples/parameter_example.yml

@@ -435,3 +435,5 @@ EAGLEAGN:
   AGN_delta_T_K:                    3.16228e8  # Change in temperature to apply to the gas particle in an AGN feedback event in Kelvin.
   AGN_num_ngb_to_heat:              1.         # Target number of gas neighbours to heat in an AGN feedback event.
   max_reposition_mass:              2e8        # Maximal BH mass considered for BH repositioning in solar masses.
+  threshold_major_merger:           0.333      # Mass ratio threshold to consider a BH merger as 'major'
+  threshold_minor_merger:           0.1        # Mass ratio threshold to consider a BH merger as 'minor'

src/black_holes/Default/black_holes.h

@@ -163,9 +163,14 @@ __attribute__((always_inline)) INLINE static void black_holes_swallow_part(
  * @param bpi The #bpart to update.
  * @param bpj The #bpart that is swallowed.
  * @param cosmo The current cosmological model.
+ * @param time Time since the start of the simulation (non-cosmo mode).
+ * @param with_cosmology Are we running with cosmology?
+ * @param props The properties of the black hole scheme.
  */
 __attribute__((always_inline)) INLINE static void black_holes_swallow_bpart(
-    struct bpart* bpi, const struct bpart* bpj, const struct cosmology* cosmo) {
+    struct bpart* bpi, const struct bpart* bpj, const struct cosmology* cosmo,
+    const double time, const int with_cosmology,
+    const struct black_holes_props* props) {
 
   /* Nothing to do here: No merging in the default model */
 }

src/black_holes/EAGLE/black_holes.h

@@ -63,6 +63,8 @@ __attribute__((always_inline)) INLINE static void black_holes_first_init_bpart(
   bp->cumulative_number_seeds = 1;
   bp->number_of_mergers = 0;
   bp->last_high_Eddington_fraction_scale_factor = -1.f;
+  bp->last_minor_merger_time = -1.;
+  bp->last_major_merger_time = -1.;
 
   black_holes_mark_bpart_as_not_swallowed(&bp->merger_data);
 }
@@ -280,14 +282,35 @@ __attribute__((always_inline)) INLINE static void black_holes_swallow_part(
  * @param bpi The #bpart to update.
  * @param bpj The #bpart that is swallowed.
  * @param cosmo The current cosmological model.
+ * @param time Time since the start of the simulation (non-cosmo mode).
+ * @param with_cosmology Are we running with cosmology?
+ * @param props The properties of the black hole scheme.
  */
 __attribute__((always_inline)) INLINE static void black_holes_swallow_bpart(
-    struct bpart* bpi, const struct bpart* bpj, const struct cosmology* cosmo) {
+    struct bpart* bpi, const struct bpart* bpj, const struct cosmology* cosmo,
+    const double time, const int with_cosmology,
+    const struct black_holes_props* props) {
 
   /* Get the current dynamical masses */
   const float bpi_dyn_mass = bpi->mass;
   const float bpj_dyn_mass = bpj->mass;
 
+  /* Is this merger ratio above the threshold for recording? */
+  const double merger_ratio = bpj->subgrid_mass / bpi->subgrid_mass;
+  if (merger_ratio > props->major_merger_threshold) {
+    if (with_cosmology) {
+      bpi->last_major_merger_scale_factor = cosmo->a;
+    } else {
+      bpi->last_major_merger_time = time;
+    }
+  } else if (merger_ratio > props->minor_merger_threshold) {
+    if (with_cosmology) {
+      bpi->last_minor_merger_scale_factor = cosmo->a;
+    } else {
+      bpi->last_minor_merger_time = time;
+    }
+  }
+
   /* Increase the masses of the BH. */
   bpi->mass += bpj->mass;
   bpi->gpart->mass += bpj->mass;
@@ -573,6 +596,10 @@ INLINE static void black_holes_create_from_gas(
   /* Last time this BH had a high Eddington fraction */
   bp->last_high_Eddington_fraction_scale_factor = -1.f;
 
+  /* Last time of mergers */
+  bp->last_minor_merger_time = -1.;
+  bp->last_major_merger_time = -1.;
+
   /* First initialisation */
   black_holes_init_bpart(bp);
 

src/black_holes/EAGLE/black_holes_io.h

@@ -114,7 +114,7 @@ INLINE static void black_holes_write_particles(const struct bpart* bparts,
                                                int with_cosmology) {
 
   /* Say how much we want to write */
-  *num_fields = 15;
+  *num_fields = 17;
 
   /* List what we want to write */
   list[0] = io_make_output_field_convert_bpart(
@@ -191,16 +191,40 @@ INLINE static void black_holes_write_particles(const struct bpart* bparts,
     list[14] = io_make_output_field(
         "LastHighEddingtonFractionScaleFactors", FLOAT, 1, UNIT_CONV_NO_UNITS,
         0.f, bparts, last_high_Eddington_fraction_scale_factor,
-        "Scale-factors at which the black holes last reached an Eddington "
-        "ratio > 0.1. -1 if never reached.");
+        "Scale-factors at which the black holes last reached a large Eddington "
+        "ratio. -1 if never reached.");
   } else {
     list[14] = io_make_output_field(
         "LastHighEddingtonFractionTimes", FLOAT, 1, UNIT_CONV_TIME, 0.f, bparts,
         last_high_Eddington_fraction_time,
-        "Times at which the black holes last reached an Eddington ratio > 0.1. "
+        "Times at which the black holes last reached a large Eddington ratio. "
         "-1 if never reached.");
   }
 
+  if (with_cosmology) {
+    list[15] = io_make_output_field(
+        "LastMinorMergerScaleFactors", FLOAT, 1, UNIT_CONV_NO_UNITS, 0.f,
+        bparts, last_minor_merger_scale_factor,
+        "Scale-factors at which the black holes last had a minor merger.");
+  } else {
+    list[15] = io_make_output_field(
+        "LastMinorMergerScaleTimes", FLOAT, 1, UNIT_CONV_TIME, 0.f, bparts,
+        last_minor_merger_time,
+        "Times at which the black holes last had a minor merger.");
+  }
+
+  if (with_cosmology) {
+    list[16] = io_make_output_field(
+        "LastMajorMergerScaleFactors", FLOAT, 1, UNIT_CONV_NO_UNITS, 0.f,
+        bparts, last_major_merger_scale_factor,
+        "Scale-factors at which the black holes last had a major merger.");
+  } else {
+    list[16] = io_make_output_field(
+        "LastMajorMergerScaleTimes", FLOAT, 1, UNIT_CONV_TIME, 0.f, bparts,
+        last_major_merger_time,
+        "Times at which the black holes last had a major merger.");
+  }
+
 #ifdef DEBUG_INTERACTIONS_BLACK_HOLES
 
   list += *num_fields;

src/black_holes/EAGLE/black_holes_part.h

@@ -121,6 +121,26 @@ struct bpart {
     float last_high_Eddington_fraction_scale_factor;
   };
 
+  /*! Union for the last minor merger point in time */
+  union {
+
+    /*! Last time the BH had a a high Eddington fraction */
+    float last_minor_merger_time;
+
+    /*! Last scale factor the BH had a a high Eddington fraction */
+    float last_minor_merger_scale_factor;
+  };
+
+  /*! Union for the last major merger point in time */
+  union {
+
+    /*! Last time the BH had a a high Eddington fraction */
+    float last_major_merger_time;
+
+    /*! Last scale factor the BH had a a high Eddington fraction */
+    float last_major_merger_scale_factor;
+  };
+
   /*! Properties used in the feedback loop to distribute to gas neighbours. */
   struct {
 

src/black_holes/EAGLE/black_holes_properties.h

@@ -82,6 +82,14 @@ struct black_holes_props {
   /*! Maximal mass of BH to reposition */
   float max_reposition_mass;
 
+  /* ---- Properties of the merger model ---------- */
+
+  /*! Mass ratio above which a merger is considered 'minor' */
+  float minor_merger_threshold;
+
+  /*! Mass ratio above which a merger is considered 'major' */
+  float major_merger_threshold;
+
   /* ---- Common conversion factors --------------- */
 
   /*! Conversion factor from temperature to internal energy */
@@ -151,8 +159,8 @@ INLINE static void black_holes_props_init(struct black_holes_props *bp,
   /* Accretion parameters ---------------------------------- */
 
   bp->f_Edd = parser_get_param_float(params, "EAGLEAGN:max_eddington_fraction");
-  bp->f_Edd_recording =
-      parser_get_param_float(params, "EAGLEAGN:eddington_fraction_for_recording");
+  bp->f_Edd_recording = parser_get_param_float(
+      params, "EAGLEAGN:eddington_fraction_for_recording");
   bp->epsilon_r =
       parser_get_param_float(params, "EAGLEAGN:radiative_efficiency");
   bp->epsilon_f =
@@ -175,6 +183,14 @@ INLINE static void black_holes_props_init(struct black_holes_props *bp,
   /* Convert to internal units */
   bp->max_reposition_mass *= phys_const->const_solar_mass;
 
+  /* Merger parameters ------------------------------------- */
+
+  bp->minor_merger_threshold =
+      parser_get_param_float(params, "EAGLEAGN:threshold_minor_merger");
+
+  bp->major_merger_threshold =
+      parser_get_param_float(params, "EAGLEAGN:threshold_major_merger");
+
   /* Common conversion factors ----------------------------- */
 
   /* Calculate temperature to internal energy conversion factor (all internal

src/runner_black_holes.c

@@ -275,6 +275,8 @@ void runner_do_bh_swallow(struct runner *r, struct cell *c, int timer) {
 
   struct engine *e = r->e;
   struct space *s = e->s;
+  const int with_cosmology = (e->policy & engine_policy_cosmology);
+  const struct black_holes_props *props = e->black_holes_properties;
   struct bpart *bparts = s->bparts;
   const size_t nr_bpart = s->nr_bparts;
 #ifdef WITH_MPI
@@ -349,7 +351,8 @@ void runner_do_bh_swallow(struct runner *r, struct cell *c, int timer) {
             lock_lock(&s->lock);
 
             /* Swallow the gas particle (i.e. update the BH properties) */
-            black_holes_swallow_bpart(bp, cell_bp, e->cosmology);
+            black_holes_swallow_bpart(bp, cell_bp, e->cosmology, e->time,
+                                      with_cosmology, props);
 
             /* Release the space as we are done updating the bpart */
             if (lock_unlock(&s->lock) != 0)