Background generation

Background generation#

streamobs models two background populations: stars (field stars passing stellar selection) and misclassified galaxies (galaxies passing a star–galaxy separator). Both can be generated together or independently via source_type.

Two methods are available:

Method

Speed

What you need

Page

'light' (default)

Fast

Precomputed CMD resource files (included with other StreamObs data)

background_light

'injection'

Slow

True background catalogs

background_injection

Quick start — single survey#

from streamobs.surveys import Survey
from streamobs.background import Background

survey = Survey.load('lsst', release='yr4')
bg = Background(survey, source_type='both', method='light', bands=('g', 'r'))

catalog, meta = bg.generate(
    phi1_limits=(-20, 20),
    phi2_limits=(-2, 2),
    gc_frame=frame,   # gala GreatCircleICRSFrame
)

Use source_type='stars' or source_type='galaxies' to restrict to one population.

Quick start — multi-survey#

Two different surveys can cover the two CMD bands (one band each). Pass them as a list; streamobs sorts them into canonical order internally.

from streamobs.surveys import Survey
from streamobs.background import Background

lsst  = Survey.load('lsst',  release='yr4')
roman = Survey.load('roman', release='dc2')

bg = Background(
    surveys=[lsst, roman],
    source_type='stars',
    method='light',
    bands=('g', 'F158'),   # lsst covers g, roman covers F158
)

catalog, meta = bg.generate(
    phi1_limits=(-20, 20),
    phi2_limits=(-2, 2),
    gc_frame=frame,
)

The resource files must be built for each survey combination before use. See build_background_resources for details.

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