Three-Dimensional Cube

The main task of three-dimensional cube generation is to arrange and integrate one-dimensional spectra according to the spatial positions provided by the two-dimensional map. This is achieved via the cube3d module, which constructs mock IFS data cubes for galaxies and other extended sources.

Core Principle

Given a set of two-dimensional physical parameter maps \(\mathcal{M}(x, y)\), the cube3d module generates a one-dimensional spectrum \(\mathcal{S}(\lambda)\) at each spatial position \((x_i, y_i)\) by calling the appropriate spectral synthesis modules (e.g., StellarContinuum, HII_Region, AGN). The resulting spectrum is then stored as the voxel \(\mathcal{C}(x_i, y_i, \lambda)\) in the final data cube:

\[\mathcal{C}(x, y, \lambda) = \mathcal{S}(\lambda; \mathcal{M}(x, y))\]

By looping over all valid pixels, the full three-dimensional mock cube \(\mathcal{C}(x, y, \lambda)\) is assembled.

The cube3d module automatically distinguishes the type of input (stellar or gas component) based on the input map classes (StellarPopulationMap, IonizedGasMap, etc.), and calls the corresponding model to simulate the spectrum. The wavelength grid is shared across all components and defined by the configuration object.

../../_images/gehong_framework.png

Component Combination

The spectrum of a galaxy typically includes both stellar continuum and nebular emission lines. The final data cube is constructed by adding the simulated stellar and gas components:

\[\mathcal{C}_\text{total} = \mathcal{C}_\text{stars} + \mathcal{C}_\text{gas} + \mathcal{C}_\text{AGN}\]

This modular design allows each component to be simulated separately, ensuring physical consistency and interpretability. The relative contributions of different components can be controlled via the corresponding 2D maps (e.g., Hα flux, magnitude, star formation rate).

Supported Use Cases

Depending on the input maps provided, the cube simulation supports a wide range of scenarios:

  • Stellar-only galaxies: e.g., early-type galaxies, use only StellarPopulationMap.

  • Emission-line dominated sources: e.g., HII regions, star-forming blobs, provide only IonizedGasMap.

  • Full galaxy systems: include both StellarPopulationMap and IonizedGasMap for realistic disk galaxies.

  • AGN-hosting galaxies: add AGN_PhysicalModel or AGN component to simulate central AGN emission.

Complex Structures and Composite Sources

For more complex systems (e.g., galaxies with outflows, mergers, or superposed sources), the simulation can be decomposed into multiple independent components. Each component is modeled and simulated individually, and the resulting cubes are combined to form the final datacube:

\[\mathcal{C}_\text{final} = \sum_i \mathcal{C}_i\]

This approach allows users to simulate:

  • AGN outflows as an additional ionized gas cube with custom velocity and metallicity;

  • Merging galaxies as two distinct sources with independent dynamics and populations;

  • Background or foreground sources in the same field of view.

Each individual cube is aligned on the same spatial and spectral grid and added voxel-by-voxel. This structure provides maximum flexibility for constructing realistic IFS datasets.