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SWIFT
SWIFTsim
Commits
971c1ed3
Commit
971c1ed3
authored
Mar 08, 2020
by
Matthieu Schaller
Browse files
Clarifications in the documentation of the EAGLE SF model
parent
ae708c04
Changes
1
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doc/RTD/source/SubgridModels/EAGLE/index.rst
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971c1ed3
...
...
@@ -424,9 +424,11 @@ pc^2} \right)^{-n} \times \left(\frac{\gamma}{G_{\rm N}}f_gP\right)^{(n-1)/2}`,
where :math:`n` is the exponent of the Kennicutt-Schmidt relation (typically
:math:`n=1.4`) and :math:`A` is the normalisation of the law (typically
:math:`A=1.515\times10^{-4} {\rm M_\odot}~{\rm yr^{-1}}~{\rm kpc^{-2}}` for a
Cabrier IMF). :math:`m_g` is the gas particle mass, :math:`\gamma` is the
C
h
abrier IMF). :math:`m_g` is the gas particle mass, :math:`\gamma` is the
adiabatic index, :math:`f_g` the gas fraction of the disk and :math:`P` the
total pressure of the gas including any subgrid turbulent terms.
total pressure of the gas including any subgrid turbulent terms. The star
formation rate of the gas particles is stored in the particles and written to
the snapshots.
Once a gas particle has computed its star formation rate, we compute the
probability that this particle turns into a star using :math:`Prob=
...
...
@@ -434,7 +436,7 @@ probability that this particle turns into a star using :math:`Prob=
and convert the gas particle into a star or not depending on our luck.
The density threshold itself has a metallicity dependence. We use the *smoothed*
metallicty (metal mass fraction) of the gas (See :ref:`EAGLE_chemical_tracers`)
metallic
i
ty (metal mass fraction) of the gas (See :ref:`EAGLE_chemical_tracers`)
and apply the relation :math:`n^*_{\rm H} = n_{\rm H,norm}\left(\frac{Z_{\rm
smooth}}{Z_0}\right)^{n_{\rm Z}}`, alongside a maximal value. The model is
designed such that star formation threshold decreases with increasing
...
...
@@ -445,10 +447,10 @@ the figure below.
:width: 400px
:align: center
:figclass: align-center
:alt: Metal-depend
a
nce of the threshold for star formation in the
:alt: Metal-depend
e
nce of the threshold for star formation in the
EAGLE model.
The dependency of the SF threshold density on the metallicty of the gas
The dependency of the SF threshold density on the metallic
i
ty of the gas
in the EAGLE model (black line). The function is described by the four
parameters indicated on the figure. These are the slope of the
dependency, its position on the metallicity-axis and normalisation
...
...
@@ -485,7 +487,7 @@ the relevant YAML parameters defining it is shown on the figure below.
ones assumed in the reference EAGLE model.
In EAGLE, an entropy floor is already in use, so that the pressure of the gas is
m
e
ntained high enough to prvent fragmentation of the gas. In such a scenario,
m
ai
ntained high enough to pr
e
vent fragmentation of the gas. In such a scenario,
there is no need for the internal EoS described above. And, of course, in such a
scenario, the gas can have a pressure above the floor. The code hence uses
:math:`P = \max(P_{\rm gas}, P_{\rm floor}, P_{\rm EoS})`.
...
...
@@ -515,6 +517,25 @@ The code applying this star formation law is located in the directory
``src/star_formation/EAGLE/``. To simplify things, all constants are converted
to the internal system of units upon reading the parameter file.
Snapshots contain an extra field to store the star formation rates of the gas
particles. If a particle was star forming in the past but isn'
t
any
more
,
the
field
will
contain
negative
number
either
corresponding
to
the
last
scale
-
factor
where
the
particle
was
star
forming
(
cosmological
runs
)
or
the
last
time
where
it
was
star
forming
(
non
-
cosmological
runs
).
+------------------------+--------------------------------------+-------------+-------------------------------------+
|
Name
|
Description
|
Units
|
Comments
|
+========================+======================================+=============+=====================================+
|
``
StarFormationRates
``
|
|
Star
formation
rates
of
the
gas
if
|
[
U_M
/
U_t
]
|
|
The
quantity
is
not
drifted
so
|
|
|
|
star
forming
.
Negative
numbers
|
|
|
corresponds
to
the
rate
the
last
|
|
|
|
indicate
the
last
time
the
gas
was
|
|
|
time
the
particle
was
active
.
|
|
|
|
star
-
forming
.
|
|
|
|
+------------------------+--------------------------------------+-------------+-------------------------------------+
Note
that
the
star
formation
rates
are
expressed
in
internal
units
and
not
in
solar
masses
per
year
as
is
the
case
in
many
other
codes
.
This
choice
ensures
consistency
between
all
the
fields
written
to
the
snapshots
.
For
a
normal
EAGLE
run
,
that
section
of
the
parameter
file
reads
:
..
code
::
YAML
...
...
@@ -527,8 +548,8 @@ For a normal EAGLE run, that section of the parameter file reads:
KS_normalisation
:
1.515e-4
#
Normalization
of
the
Kennicutt
-
Schmidt
law
in
Msun
/
kpc
^
2
/
yr
.
KS_exponent
:
1.4
#
Exponent
of
the
Kennicutt
-
Schmidt
law
.
min_over_density
:
57.7
#
Over
-
density
above
which
star
-
formation
is
allowed
.
KS_high_density_threshold_H_p_cm3: 1e3 # Hydrogen number density above which the Kennicut-Schmidt law changes slope in Hydrogen atoms per cm^3.
KS_high_density_exponent: 2.0 # Slope of the Kennicut-Schmidt law above the high-density threshold.
KS_high_density_threshold_H_p_cm3
:
1e3
#
Hydrogen
number
density
above
which
the
Kennicut
t
-
Schmidt
law
changes
slope
in
Hydrogen
atoms
per
cm
^
3.
KS_high_density_exponent
:
2.0
#
Slope
of
the
Kennicut
t
-
Schmidt
law
above
the
high
-
density
threshold
.
EOS_entropy_margin_dex
:
0.5
#
(
Optional
)
Logarithm
base
10
of
the
maximal
entropy
above
the
EOS
at
which
stars
can
form
.
KS_max_density_threshold_H_p_cm3
:
1e5
#
(
Optional
)
Hydrogen
number
density
above
which
a
particle
gets
automatically
turned
into
a
star
in
Hydrogen
atoms
per
cm
^
3.
threshold_norm_H_p_cm3
:
0.1
#
Normalisation
of
the
metal
-
dependant
density
threshold
for
star
formation
in
Hydrogen
atoms
per
cm
^
3.
...
...
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