Background Sky

Background Sky

This page describes ALMASim’s additive background-sky simulation.

Purpose

ALMASim can now add an astrophysical background sky to the clean cube before interferometric simulation.

This is separate from thermal or atmospheric noise.

Default Behavior

The default background mode is none.

That means:

• the science target is centered at the phase center

• no additive background sky is injected

Background Modes

blank_field_dsfg

Adds a sparse field of faint dusty star-forming galaxies.

This is intended to approximate blank-field extragalactic confusion in the ALMA band regime.

dusty_diffuse

Adds a correlated low-spatial-frequency dusty background field.

This is useful as a first approximation to diffuse mm/sub-mm background structure.

combined

Adds both of the above.

Controls

ALMASim exposes:

• background_mode

• background_level

• background_seed

background_seed makes the background reproducible.

Current Physical Intent

The current background implementation is a pragmatic first step for ALMA-band simulations:

• faint unresolved dusty galaxies

• diffuse dusty structure with smooth spectral dependence

It is not yet a full cosmological sky model.

Outputs

When a background is generated:

• it is added to the clean sky cube

• its total injected flux is recorded in metadata

• a background-cube_* product is exported when outputs are persisted

Scope Notes

This is an astrophysical background, not:

• atmospheric emission

• calibration error

• correlator noise

Those belong elsewhere in the simulation chain.