galfits-manual

name: galfits-manual description: Galaxy imaging spectra fitting tool for multi-band image decomposition, SED modeling, and joint analysis. Covers .lyric config files, command-line arguments, and MCP interface.

GalfitS Configuration Guide

This skill provides comprehensive guidance for writing GalfitS configuration files (.lyric format). GalfitS extends GALFIT to simultaneously fit multiple photometric bands with SED constraints.

Quick Start

To create a new GalfitS config file:

1. Identify your fitting phase:

   • Phase 1: Image-only fitting (spatial parameters free, SED fixed)
   • Phase 2: SED-only fitting (spatial fixed, SED free)
   • Phase 3: Joint optimization (all parameters free)

2. Configure data input (Region → Images → Spectra → Atlas)

3. Define model components:

   • Profile components (P): Galaxy structural components with types specified by Pa2 parameter
     • sersic - Standard bulge/disk profile
     • sersic_f - Fourier mode profile (spiral arms, bars, etc.)
     • ferrer, edgeondisk, GauRing, const, Gaussian - Other profiles
   • Nuclei/AGN components (N): AGN with full SED model
   • Foreground stars (F): Stellar sources with blackbody SED
   • Galaxy components (G): Combine multiple Profile (P) components

4. Set parameter constraints (optional)

5. Run GalfitS with appropriate command-line options

Navigation

Component Type Quick Reference

GalfitS has TWO main categories of components. Understanding which category you need is the first step.

📊 Category 1: Data Components (Input Configuration)

Purpose: Define your observational data (images, spectra) before fitting.

🌌 Category 2: Model Components (What You're Fitting)

Purpose: Define the physical components that make up your source.

Component Hierarchy

Model Components
│
├── 🔹 Galaxy (G) ──────────────► Combines Profiles into ONE physical galaxy
│    └── contains Profile (P) components
│
├── 🔹 Profile (P) ─────────────► Galaxy structural component (bulge, disk, bar...)
│    └── Type determined by Pa2 parameter
│
├── 🔹 Nuclei/AGN (N) ──────────► AGN with full SED model (independent component)
│
└── 🔹 Foreground Star (F) ────► Star in Milky Way (independent component)

Detailed Model Component Reference

Profile (P) Sub-Types (determined by Pa2 parameter)

🎯 Quick Decision Guide

What do you want to model?

📝 Component Letter Rules

Important: Letters (a, b, c...) are user-defined, NOT fixed to types.

Example:

# All three are Sersic profiles, just with different parameters
Pa1) bulge    Pa2) sersic
Pb1) disk     Pb2) sersic     ← Same type!
Pc1) bar      Pc2) sersic_f   ← Different type (Fourier)

# AGN is a DIFFERENT component type (N prefix, not P)
Na1) AGN      (not Pa1)       ← Separate component type

Parameter Format Reminder

All parameters use: [value, min, max, step, vary]

Phase-Specific Configuration

Running GalfitS

Basic Command

galfits config.lyric --work ./output

For detailed command-line arguments, fitting methods, and usage examples, see running-galfits.md.

Quick Reference

Common Issues & Solutions

File Structure

your-config/
├── SKILL.md                    # This file - main entry point
├── running-galfits.md          # Command-line arguments & usage
├── data-config.md              # Data input configuration
├── model-components/           # Model component documentation
│   ├── index.md                # Component overview
│   ├── galaxy.md               # Galaxy configuration
│   ├── profile-sersic.md       # Sersic profile
│   ├── profile-fourier.md      # Fourier Sersic profile
│   ├── profile-other.md        # Other profile types
│   ├── nuclei-agn.md           # Nuclei/AGN configuration
│   ├── foreground-star.md      # Foreground star configuration
│   └── parameter-format.md     # Parameter format and combining
├── constraints/                # Parameter constraints & priors
│   ├── index.md                # Constraints overview
│   ├── parameter-files.md      # .params and .constrain file usage
│   ├── mass-size-relation.md   # MSR prior for size-mass correlation
│   ├── mass-metallicity-relation.md  # MMR prior for stellar mass-metallicity
│   ├── sfh-constraints.md      # Star formation history priors
│   ├── agn-constraints.md      # AGN-specific constraints
│   ├── gaussian-priors.md      # GP parameter for Gaussian priors
│   └── energy-balance.md       # EB parameter for dust-stellar energy balance
├── examples/                   # Configuration examples
│   ├── index.md                # Examples overview
│   ├── multi-band-imaging.md   # Multi-band bulge-disk decomposition
│   ├── pure-sed-fitting.md     # Photometric SED fitting
│   ├── spectrum-fitting.md     # AGN/host spectrum decomposition
│   ├── imaging-spectrum-joint.md  # Joint imaging+spectra fitting
│   └── grism-imaging.md        # Grism data analysis (placeholder)
└── templates/                  # Config templates (optional)

Usage

To use this configuration guide, refer to the detailed documentation files:

• Data Configuration: data-config.md - Region, Images, Spectra, Atlas
• Model Components: model-components/ - Galaxy, Profile, Nuclei/AGN, Foreground Star
• Parameter Constraints: constraints/ - Parameter files, MSR, MMR, SFH, AGN, priors
• Configuration Examples: examples/ - Multi-band, SED-only, spectrum fitting
• Running GalfitS: running-galfits.md - Command-line options, fitting methods

Model Components Quick Links

• Galaxy - Combine profile components into galaxies
• Sersic Profile - Standard bulge/disk profile
• Fourier Sersic - Bars and spiral arms
• Other Profiles - Ferrer, edge-on, ring, Gaussian
• Nuclei/AGN - AGN with full SED model
• Foreground Star - Stellar sources
• Parameter Format - Parameter combining and format

Constraints Quick Links

• Parameter Files - .params and .constrain file usage
• Mass-Size Relation - MSR prior for galaxy size-mass correlation
• Mass-Metallicity Relation - MMR prior for stellar mass-metallicity
• SFH Constraints - Star formation history priors
• AGN Constraints - Black hole mass, emission line relations
• Gaussian Priors - GP parameter for Gaussian priors
• Energy Balance - EB parameter for dust-stellar energy balance