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, & PyAutoLens makes it simple to model strong gravitational lenses, like this one:
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 Isothermal mass profile lenses a background source at redshift 1.0 with an Exponential light profile.
import autolens as al
import autolens.plot as aplt
"""
To describe the deflection of light by mass, two-dimensional grids of (y,x) Cartesian
coordinates are used.
"""
grid = al.Grid.uniform(
shape_2d=(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."""
sie = 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=sie)
"""The source galaxy has an EllipticalExponential LightProfile and is at redshift 1.0."""
exponential = 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, light=exponential)
"""
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 Grid and Tracer to perform many lensing calculations, for example
plotting the image of the lensed source.
"""
aplt.Tracer.image(tracer=tracer, grid=grid)With PyAutoLens, you can begin modeling a lens in just a couple of minutes. The example below demonstrates a simple analysis which fits the foreground lens galaxy's mass & the background source galaxy's light.
import autofit as af
import autolens as al
import autolens.plot as aplt
"""In this example, we'll fit a simple lens galaxy + source galaxy system."""
dataset_path = "/path/to/dataset"
lens_name = "example_lens"
"""Use the dataset path and lens name to load the imaging data."""
imaging = al.Imaging.from_fits(
image_path=f"{dataset_path}/{lens_name}/image.fits",
noise_map_path=f"{dataset_path}/{lens_name}/noise_map.fits",
psf_path=f"{dataset_path}/{lens_name}/psf.fits",
pixel_scales=0.1,
)
"""Create a mask for the data, which we setup as a 3.0" circle."""
mask = al.Mask.circular(
shape_2d=imaging.shape_2d, pixel_scales=imaging.pixel_scales, radius=3.0
)
"""
We model our lens galaxy using an EllipticalIsothermal MassProfile &
our source galaxy as an EllipticalSersic LightProfile.
"""
lens_mass_profile = al.mp.EllipticalIsothermal
source_light_profile = al.lp.EllipticalSersic
"""
To setup our model galaxies, we use the GalaxyModel class, which represents a
galaxy whose parameters are free & fitted for by PyAutoLens.
"""
lens_galaxy_model = al.GalaxyModel(redshift=0.5, mass=lens_mass_profile)
source_galaxy_model = al.GalaxyModel(redshift=1.0, light=source_light_profile)
"""
To perform the analysis we set up a phase, which takes our galaxy models & fits
their parameters using a non-linear search (in this case, Dynesty).
"""
phase = al.PhaseImaging(
galaxies=dict(lens=lens_galaxy_model, source=source_galaxy_model),
phase_name="example/phase_example",
search=af.DynestyStatic(n_live_points=50),
)
"""
We pass the imaging data and mask to the phase, thereby fitting it with the lens
model & plot the resulting fit.
"""
result = phase.run(dataset=imaging, mask=mask)
aplt.FitImaging.subplot_fit_imaging(fit=result.max_log_likelihood_fit)To get started go to our readthedocs, where you'll find our installation guide, a complete overview of PyAutoLens's features, examples scripts and tutorials and detailed API documentation.
We're building a PyAutoLens community on Slack, so you should contact us on our Slack channel before getting started. Here, I will give you the latest updates on the software & discuss how best to use PyAutoLens for your science case.
Unfortunately, Slack is invitation-only, so first send me an email requesting an invite.