Generating photometry from a Galaxy

If you are working with a Galaxy (or many Galaxy objects) containing multiple spectra, you can use the galaxy level get_photo_lnu and get_photo_fluxes methods to generate photometry for all spectra in the galaxy.

Before we can demonstrate this we firs need to make a parametric galaxy with a Stars and Blackhole component, define an emission model for a whole galaxy and generate their rest–frame and observed spectra.

import numpy as np
from astropy.cosmology import Planck18 as cosmo
from unyt import Myr, kelvin, Msun, Mpc, yr

from synthesizer.emission_models import (
    AttenuatedEmission,
    BimodalPacmanEmission,
    DustEmission,
    EmissionModel,
    UnifiedAGN,
)
from synthesizer.emission_models.attenuation import PowerLaw
from synthesizer.emission_models.dust.emission import Blackbody, Greybody
from synthesizer.filters import FilterCollection
from synthesizer.grid import Grid
from synthesizer.parametric import SFH, ZDist
from synthesizer.parametric import Stars as ParametricStars
from synthesizer.particle import BlackHoles, Galaxy
from synthesizer.particle.stars import sample_sfhz

# Get the grids which we'll need for extraction
grid_dir = "../../../tests/test_grid"
grid_name = "test_grid"
grid = Grid(grid_name, grid_dir=grid_dir)
nlr_grid = Grid("test_grid_agn-nlr", grid_dir="../../../tests/test_grid")
blr_grid = Grid("test_grid_agn-blr", grid_dir="../../../tests/test_grid")

# Define the metallicity history
zh = ZDist.DeltaConstant(metallicity=0.01)

# Define the star formation history
sfh_p = {"max_age": 100 * Myr}
sfh = SFH.Constant(**sfh_p)

# Initialise the parametric Stars object
param_stars = ParametricStars(
    grid.log10age,
    grid.metallicity,
    sf_hist=sfh,
    metal_dist=zh,
    initial_mass=10**9 *Msun,
)

# Define the number of stellar particles we want
n = 500

# Sample the parametric SFZH, producing a particle Stars object
# we will also pass some keyword arguments for some example attributes
part_stars = sample_sfhz(
    sfzh=param_stars.sfzh,
    log10ages=param_stars.log10ages,
    log10metallicities=param_stars.log10metallicities,
    nstar=n,
    current_masses=np.full(n, 10**8.7 / n) * Msun,
    redshift=1,
    coordinates=np.random.normal(0, 0.01, (n, 3)) * Mpc,
    centre=np.zeros(3) * Mpc,
)

# Make fake properties
n = 4
masses = 10 ** np.random.uniform(low=7, high=9, size=n) * Msun
coordinates = np.random.normal(0, 0.01, (n, 3)) * Mpc
accretion_rates = 10 ** np.random.uniform(
    low=-2, high=1, size=n
)  * Msun / yr
metallicities = np.full(n, 0.01)

# And get the black holes object
blackholes = BlackHoles(
    masses=masses,
    coordinates=coordinates,
    accretion_rates=accretion_rates,
    metallicities=metallicities,
)

# And create the galaxy
gal = Galaxy(
    stars=part_stars,
    black_holes=blackholes,
    redshift=1,
)

# Get the stellar pacman model
pc_model = BimodalPacmanEmission(
    grid=grid,
    tau_v_ism=1.0,
    tau_v_birth=0.7,
    dust_curve_ism=PowerLaw(slope=-1.3),
    dust_curve_birth=PowerLaw(slope=-0.7),
    dust_emission_ism=Blackbody(temperature=100 * kelvin),
    dust_emission_birth=Blackbody(temperature=30 * kelvin),
    fesc=0.2,
    fesc_ly_alpha=0.9,
    label="stellar_total",
)

# Get the UnifiedAGN model
uni_model = UnifiedAGN(
    nlr_grid,
    blr_grid,
    covering_fraction_nlr=0.1,
    covering_fraction_blr=0.1,
    torus_emission_model=Blackbody(1000 * kelvin),
    label="agn_intrinsic",
)

# Define an emission model to attenuate the intrinsic AGN emission
att_uni_model = AttenuatedEmission(
    dust_curve=PowerLaw(slope=-1.0),
    apply_dust_to=uni_model,
    tau_v=0.7,
    emitter="blackhole",
    label="agn_attenuated",
)

gal_intrinsic = EmissionModel(
    label="total_intrinsic",
    combine=(uni_model, pc_model["intrinsic"]),
    emitter="galaxy",
)

gal_attenuated = EmissionModel(
    label="total_attenuated",
    combine=(att_uni_model, pc_model["attenuated"]),
    related_models=(gal_intrinsic,),
    emitter="galaxy",
)

# And now include the dust emission
gal_dust = DustEmission(
    dust_emission_model=Greybody(30 * kelvin, 1.2),
    dust_lum_intrinsic=gal_intrinsic,
    dust_lum_attenuated=gal_attenuated,
    emitter="galaxy",
    label="dust_emission",
)

gal_total = EmissionModel(
    label="total",
    combine=(gal_attenuated, gal_dust),
    related_models=(gal_intrinsic),
    emitter="galaxy",
)

# Get the spectra
sed = gal.get_spectra(gal_total)

# Get fluxes
gal.get_observed_spectra(cosmo)

We can then combine with a FilterCollection to generate the galaxy-level photometry.

# Get the filter collection
fs = [
    f"JWST/NIRCam.{f}"
    for f in ["F090W", "F150W", "F200W", "F277W", "F356W", "F444W"]
]

filters = FilterCollection(
    filter_codes=fs,
    new_lam=grid.lam,
)

# Get the photometry
gal.get_photo_lnu(filters)
gal.get_photo_fnu(filters)

The photometry produced by these methods are stored in the photo_lnu and photo_fluxes attributes, either at the base galaxy level or the individual components. These attributes are dictionaries containing the photometry for each spectra key.

For example, on the Galaxy.Stars object:

print(gal.stars.photo_lnu)
print(gal.stars.photo_fnu)

{'intrinsic': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fc520>, 'young_intrinsic': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8ffc10>, 'young_reprocessed': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8ff7f0>, 'young_transmitted': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8ff370>, 'young_nebular': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fdea0>, 'young_linecont': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fdcc0>, 'young_nebular_continuum': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fdb10>, 'young_escaped': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fd930>, 'old_intrinsic': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fdb40>, 'old_escaped': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fd5d0>, 'old_reprocessed': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fd480>, 'old_transmitted': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fc430>, 'old_nebular': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8ffee0>, 'old_nebular_continuum': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fd420>, 'old_linecont': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fc580>, 'attenuated': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fff10>, 'old_attenuated': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8ff820>, 'young_attenuated': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fd360>, 'young_attenuated_nebular': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc90ead0>}
{'intrinsic': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc90ec80>, 'young_intrinsic': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fc5b0>, 'young_reprocessed': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc90e8f0>, 'young_transmitted': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fc3a0>, 'young_nebular': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc90e170>, 'young_linecont': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc90e0b0>, 'young_nebular_continuum': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc8fc5e0>, 'young_escaped': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf2e30>, 'old_intrinsic': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf3310>, 'old_escaped': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf34c0>, 'old_reprocessed': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf3670>, 'old_transmitted': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf3820>, 'old_nebular': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf39d0>, 'old_nebular_continuum': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf3b80>, 'old_linecont': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf3d30>, 'attenuated': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf2c80>, 'old_attenuated': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf3160>, 'young_attenuated': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf3d60>, 'young_attenuated_nebular': <synthesizer.photometry.PhotometryCollection object at 0x7f76adaf1660>}

Or on the galaxy level

print(gal.photo_lnu)

{'total': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc90db40>, 'dust_emission': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc90fa00>, 'total_intrinsic': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc90ed70>, 'total_attenuated': <synthesizer.photometry.PhotometryCollection object at 0x7f76fc90e710>}

As before we can print the photometry.

print(gal.photo_fnu["total_attenuated"])

------------------------------------------------------------------
|                       PHOTOMETRY (FLUX)                        |
|------------------------------------|---------------------------|
| JWST/NIRCam.F090W (λ = 9.02e+03 Å) | 2.27e+17 erg/(Hz*cm**2*s) |
|------------------------------------|---------------------------|
| JWST/NIRCam.F150W (λ = 1.50e+04 Å) | 3.14e+16 erg/(Hz*cm**2*s) |
|------------------------------------|---------------------------|
| JWST/NIRCam.F200W (λ = 1.99e+04 Å) | 8.24e+16 erg/(Hz*cm**2*s) |
|------------------------------------|---------------------------|
| JWST/NIRCam.F277W (λ = 2.76e+04 Å) | 2.45e+17 erg/(Hz*cm**2*s) |
|------------------------------------|---------------------------|
| JWST/NIRCam.F356W (λ = 3.57e+04 Å) | 1.12e+18 erg/(Hz*cm**2*s) |
|------------------------------------|---------------------------|
| JWST/NIRCam.F444W (λ = 4.40e+04 Å) | 2.68e+18 erg/(Hz*cm**2*s) |
------------------------------------------------------------------

Or plot them.

gal.photo_fnu["total_attenuated"].plot_photometry(show=True)

(<Figure size 350x500 with 2 Axes>,
 <Axes: xlabel='$\\lambda_\\mathrm{obs}/[\\mathrm{\\AA}]$', ylabel='$F/[\\mathrm{\\rm{erg} \\ / \\ \\rm{Hz \\cdot \\rm{cm}^{2} \\cdot \\rm{s}}}]$'>)

gal.photo_fnu["total_intrinsic"].plot_photometry(show=True)

(<Figure size 350x500 with 2 Axes>,
 <Axes: xlabel='$\\lambda_\\mathrm{obs}/[\\mathrm{\\AA}]$', ylabel='$F/[\\mathrm{\\rm{erg} \\ / \\ \\rm{Hz \\cdot \\rm{cm}^{2} \\cdot \\rm{s}}}]$'>)

gal.photo_fnu["total"].plot_photometry(show=True)

(<Figure size 350x500 with 2 Axes>,
 <Axes: xlabel='$\\lambda_\\mathrm{obs}/[\\mathrm{\\AA}]$', ylabel='$F/[\\mathrm{\\rm{erg} \\ / \\ \\rm{Hz \\cdot \\rm{cm}^{2} \\cdot \\rm{s}}}]$'>)

Calculating light radii

Once we have photometry we can calculate the radius enclosing a given fraction of the light for a component. Here we’ll calculate the half light radius for both the intrinsic emission and the total emission in “F444W” in terms of luminosity, but before we can do that we need to get the particle spectra and call get_particle_photo_lnu to first calculate the per particle photometry (above we used the galaxy level methods to calculate integrated spectra).

# Get the particle spectra
pc_model.set_per_particle(True)
gal.stars.get_spectra(pc_model)

# Get the particle photometry
gal.stars.get_particle_photo_lnu(filters)

int_r50 = gal.stars.get_half_luminosity_radius(
    "intrinsic", "JWST/NIRCam.F444W"
)
tot_r50 = gal.stars.get_half_luminosity_radius(
    "stellar_total", "JWST/NIRCam.F444W"
)
print(int_r50, tot_r50)

0.01632946545296936 Mpc 0.016302480668360934 Mpc

Similarly to the “attr” radii we can compute for any particle component, we can also compute the radius enclosing any fraction of the light for any particle component.

int_r20 = gal.stars.get_luminosity_radius(
    "intrinsic", "JWST/NIRCam.F444W", frac=0.2
)
tot_r20 = gal.stars.get_luminosity_radius(
    "stellar_total", "JWST/NIRCam.F444W", frac=0.2
)
int_r80 = gal.stars.get_luminosity_radius(
    "intrinsic", "JWST/NIRCam.F444W", frac=0.8
)
tot_r80 = gal.stars.get_luminosity_radius(
    "stellar_total", "JWST/NIRCam.F444W", frac=0.8
)
print(int_r20, int_r80, tot_r20, tot_r80)

0.010636757725121977 Mpc 0.022028889161372706 Mpc 0.010634726116008148 Mpc 0.022029954238747096 Mpc