Open-Source Strong Lensing
Project description
PyAutoLens: Open-Source Strong Lensing
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Installation Guide <https://pyautolens.readthedocs.io/en/latest/installation/overview.html>
_ |
readthedocs <https://pyautolens.readthedocs.io/en/latest/index.html>
_ |
Introduction on Binder <https://mybinder.org/v2/gh/Jammy2211/autolens_workspace/3b48dbc1b0ee85e68a24394895702df78e465323?filepath=introduction.ipynb>
_ |
HowToLens <https://pyautolens.readthedocs.io/en/latest/howtolens/howtolens.html>
_
When two or more galaxies are aligned perfectly down our line-of-sight, the background galaxy appears multiple times. This is called strong gravitational lensing and PyAutoLens makes it simple to model strong gravitational lenses, like this one:
.. image:: https://github.com/Jammy2211/PyAutoLens/blob/master/files/imageaxis.png
Getting Started
The following links are useful for new starters:
-
The introduction Jupyter Notebook on Binder <https://mybinder.org/v2/gh/Jammy2211/autolens_workspace/3b48dbc1b0ee85e68a24394895702df78e465323?filepath=introduction.ipynb>
_, where you can try PyAutoLens in a web browser (without installation). -
The PyAutoLens readthedocs <https://pyautolens.readthedocs.io/en/latest>
, which includesan installation guide <https://pyautolens.readthedocs.io/en/latest/installation/overview.html>
and an overview of PyAutoLens's core features. -
The autolens_workspace GitHub repository <https://github.com/Jammy2211/autolens_workspace>
, which includes example scripts and theHowToLens Jupyter notebook tutorials <https://github.com/Jammy2211/autolens_workspace/tree/master/notebooks/howtolens>
which give new users a step-by-step introduction to PyAutoLens.
API Overview
Lensing calculations are performed in PyAutoLens by building a Tracer
object from LightProfile
,
MassProfile
and Galaxy
objects. Below, we create a simple strong lens system where a redshift 0.5
lens Galaxy
with an EllipticalIsothermal
MassProfile
lenses a background source at redshift 1.0 with an
EllipticalExponential
LightProfile
representing a disk.
.. code-block:: python
import autolens as al
import autolens.plot as aplt
from astropy import cosmology as cosmo
"""
To describe the deflection of light by mass, two-dimensional grids of (y,x) Cartesian
coordinates are used.
"""
grid = al.Grid2D.uniform(
shape_native=(50, 50),
pixel_scales=0.05, # <- Conversion from pixel units to arc-seconds.
)
"""
The lens galaxy has an EllipticalIsothermal MassProfile and is at redshift 0.5.
"""
mass = al.mp.EllipticalIsothermal(
centre=(0.0, 0.0), elliptical_comps=(0.1, 0.05), einstein_radius=1.6
)
lens_galaxy = al.Galaxy(redshift=0.5, mass=mass)
"""
The source galaxy has an EllipticalExponential LightProfile and is at redshift 1.0.
"""
disk = al.lp.EllipticalExponential(
centre=(0.3, 0.2),
elliptical_comps=(0.05, 0.25),
intensity=0.05,
effective_radius=0.5,
)
source_galaxy = al.Galaxy(redshift=1.0, disk=disk)
"""
We create the strong lens using a Tracer, which uses the galaxies, their redshifts
and an input cosmology to determine how light is deflected on its path to Earth.
"""
tracer = al.Tracer.from_galaxies(
galaxies=[lens_galaxy, source_galaxy], cosmology=cosmo.Planck15
)
"""
We can use the Grid2D and Tracer to perform many lensing calculations, for example
plotting the image of the lensed source.
"""
tracer_plotter = aplt.TracerPlotter(tracer=tracer, grid=grid)
tracer_plotter.figures(image=True)
With PyAutoLens, you can begin modeling a lens in just a couple of minutes. The example below demonstrates
a simple analysis which fits the lens galaxy's mass with an EllipticalIsothermal
and the source galaxy's light
with an EllipticalSersic
.
.. code-block:: python
import autofit as af
import autolens as al
import autolens.plot as aplt
"""
Load Imaging data of the strong lens from the dataset folder of the workspace.
"""
imaging = al.Imaging.from_fits(
image_path="/path/to/dataset/image.fits",
noise_map_path="/path/to/dataset/noise_map.fits",
psf_path="/path/to/dataset/psf.fits",
pixel_scales=0.1,
)
"""
Create a mask for the data, which we setup as a 3.0" circle.
"""
mask = al.Mask2D.circular(
shape_native=imaging.shape_native, pixel_scales=imaging.pixel_scales, radius=3.0
)
"""
We model the lens galaxy using an EllipticalIsothermal MassProfile and
the source galaxy using an EllipticalSersic LightProfile.
"""
lens_mass_profile = al.mp.EllipticalIsothermal
source_light_profile = al.lp.EllipticalSersic
"""
To setup these profiles as model components whose parameters are free & fitted for
we use the GalaxyModel class.
"""
lens_galaxy_model = al.GalaxyModel(redshift=0.5, mass=lens_mass_profile)
source_galaxy_model = al.GalaxyModel(redshift=1.0, disk=source_light_profile)
"""
To perform the analysis we set up a phase, which takes our galaxy models & fits
their parameters using a NonLinearSearch (in this case, Dynesty).
"""
phase = al.PhaseImaging(
search=af.DynestyStatic(name="phase[example]",n_live_points=50),
galaxies=dict(lens=lens_galaxy_model, source=source_galaxy_model),
)
"""
We pass the imaging dataset and mask to the phase's run function, fitting it
with the lens model & outputting the results (dynesty samples, visualization,
etc.) to hard-disk.
"""
result = phase.run(dataset=imaging, mask=mask)
"""
The results contain information on the fit, for example the maximum likelihood
model from the Dynesty parameter space search.
"""
print(result.samples.max_log_likelihood_instance)
Support
Support for installation issues, help with lens modeling and using PyAutoLens is available by
raising an issue on the GitHub issues page <https://github.com/Jammy2211/PyAutoLens/issues>
_.
We also offer support on the PyAutoLens Slack channel <https://pyautolens.slack.com/>
, where we also provide the
latest updates on PyAutoLens. Slack is invitation-only, so if you'd like to join send
an email <https://github.com/Jammy2211>
requesting an invite.
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