From 07d2312bcea7971ff30229fa04d27c87dc1b297c Mon Sep 17 00:00:00 2001
From: Aaron LI <aly@aaronly.me>
Date: Sat, 30 Dec 2017 20:23:02 +0800
Subject: clusters/halo: Add virial_speed() helper function
---
fg21sim/extragalactic/clusters/helper.py | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
(limited to 'fg21sim/extragalactic/clusters')
diff --git a/fg21sim/extragalactic/clusters/helper.py b/fg21sim/extragalactic/clusters/helper.py
index 10c4f12..e751bbe 100644
--- a/fg21sim/extragalactic/clusters/helper.py
+++ b/fg21sim/extragalactic/clusters/helper.py
@@ -297,6 +297,18 @@ def speed_sound(kT):
return cs * AUC.cm2km # [km/s]
+def velocity_virial(mass, z=0.0):
+ """
+ Calculate the virial velocity, i.e., free-fall velocity.
+
+ Unit: [km/s]
+ """
+ R_vir = radius_virial(mass, z) * AUC.kpc2cm # [cm]
+ vv = np.sqrt(AC.G * mass*AUC.Msun2g / R_vir) # [cm/s]
+ vv /= AUC.km2cm # [km/s]
+ return vv
+
+
def velocity_impact(M_main, M_sub, z=0.0):
"""
Estimate the relative impact velocity between the two merging
@@ -354,8 +366,7 @@ def time_crossing(M_main, M_sub, z=0.0):
"""
R_vir = radius_virial(M_main, z) # [kpc]
vi = velocity_impact(M_main, M_sub, z) # [km/s]
- # Unit conversion coefficient: [s kpc/km] => [Gyr]
- uconv = AUC.kpc2km * AUC.s2Gyr
+ uconv = AUC.kpc2km * AUC.s2Gyr # [s kpc/km] => [Gyr]
time = uconv * R_vir / vi # [Gyr]
return time
--
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