{
  "name": "Galaxy Morphological Classification Rules",
  "description": "Rules for classifying galaxies into Hubble types (E, S0, Spiral, Irregular) using quantitative morphology parameters from imaging data, based on Gini-M20, CAS (Concentration-Asymmetry-Smoothness), and Sérsic decomposition.",
  "version": "2.0",
  "parameters": {
    "morph_gini": "Gini coefficient (0–1): measures inequality of light distribution. High in bulge-dominated systems (E/S0).",
    "morph_m20": "Second-order moment of brightest 20% of flux. Low (< -1.5) in relaxed ellipticals; high (> -1.0) in mergers/irregulars.",
    "morph_concentration": "C = 5 * log10(r80/r20). Typical values: E/S0 ≈ 4.4, Spirals ≈ 3.1–3.9, Irregulars ≈ 2.9.",
    "morph_asymmetry": "A: rotational asymmetry (0–1). Low in E/S0 (<0.1), moderate in spirals (0.1–0.3), high in mergers (>0.35).",
    "morph_smoothness": "S: clumpiness (0–1). Low in E/S0 (<0.1), higher in star-forming disks (0.2–0.4), very high in mergers (>0.4).",
    "sersic_n": "Sérsic index: n > 2.5 → E; 1.8–2.5 → S0; 0.8–2.0 → Spiral; <1.0 → Irregular/disk.",
    "dser_BD": "Bulge-to-total luminosity ratio from double Sérsic fit. B/D > 0.5 → early-type spiral (Sa); not defined for pure ellipticals."
  },
  "classification_rules": [
    {
      "type": "Elliptical",
      "conditions": [
        "morph_gini > 0.55",
        "morph_m20 < -1.5",
        "morph_concentration >= 4.1",
        "morph_asymmetry < 0.12",
        "morph_smoothness < 0.08",
        "sersic_n > 2.5"
      ],
      "reasoning": "Based on Gini-M20 (Lotz+2004) and CAS (Conselice+2003): high concentration, low asymmetry/smoothness, and high Sérsic index indicate a smooth, pressure-supported elliptical galaxy."
    },
    {
      "type": "Lenticular (S0)",
      "conditions": [
        "morph_gini > 0.55",
        "morph_m20 < -1.5",
        "3.2 <= morph_concentration <= 3.6",
        "morph_asymmetry < 0.10",
        "morph_smoothness < 0.08",
        "1.8 <= sersic_n <= 2.5"
      ],
      "reasoning": "Bulge-dominated with a smooth disk but no spiral arms: lower concentration than E, very low asymmetry, and intermediate Sérsic index."
    },
    {
      "type": "Spiral",
      "conditions": [
        "(0.4 < morph_gini < 0.55 AND -1.5 < morph_m20 < -1.0) OR (dser_BD > 0.05)",
        "2.7 <= morph_concentration <= 4.4",
        "0.12 <= morph_asymmetry <= 0.35",
        "0.15 <= morph_smoothness <= 0.42",
        "0.8 <= sersic_n <= 2.2"
      ],
      "reasoning": "Disk-dominated systems with spiral arms: moderate Gini/M20, intermediate CAS values, and exponential-like profiles. B/D > 0.05 confirms presence of a disk+bulge structure."
    },
    {
      "type": "Irregular",
      "conditions": [
        "(morph_gini < 0.4 AND morph_m20 > -1.0) OR (morph_asymmetry > 0.35 AND morph_asymmetry > morph_smoothness)",
        "morph_concentration < 3.2",
        "morph_asymmetry > 0.35",
        "morph_smoothness > 0.4",
        "sersic_n < 1.2"
      ],
      "reasoning": "Chaotic or merging systems: low Gini, high M20, high asymmetry and clumpiness, and low concentration—consistent with disturbed or clumpy star-forming galaxies."
    }
  ],
  "fallback_rules": [
    {
      "condition": "morph_flag != 0 OR sersic_flag != 0",
      "action": "Uncertain morphology due to fitting failure or poor data quality."
    },
    {
      "condition": "peak_value is NaN OR effective_radius_Value <= 0 OR isophotal_diameter <= 0",
      "action": "Invalid source; skip classification."
    },
    {
      "condition": "All key morphology parameters (Gini, M20, C, A, S, n) are missing or out of physical range",
      "action": "Classification impossible; label as UNKNOWN."
    }
  ],
  "references": [
    {
      "id": "lotz2004",
      "citation": "Lotz, J. M., Primack, J., & Madau, P. 2004, AJ, 128, 163",
      "description": "Introduces the Gini-M20 non-parametric morphological classification system to distinguish ellipticals, spirals, and merging galaxies in HST imaging.",
      "doi": "https://doi.org/10.1086/421962",
      "ads_url": "https://ui.adsabs.harvard.edu/abs/2004AJ....128..163L"
    },
    {
      "id": "conselice2003",
      "citation": "Conselice, C. J. 2003, ApJS, 147, 1",
      "description": "Establishes the CAS (Concentration, Asymmetry, Smoothness) system for quantitative galaxy morphology, widely used for high-redshift galaxy classification.",
      "doi": "https://doi.org/10.1086/375001",
      "ads_url": "https://ui.adsabs.harvard.edu/abs/2003ApJS..147....1C"
    },
    {
      "id": "simard2011",
      "citation": "Simard, L., Willmer, C. N. A., Vogt, N. P., et al. 2011, ApJS, 196, 11",
      "description": "Provides bulge-disk decompositions and Sérsic profile fits for over 1 million SDSS galaxies, enabling reliable B/D ratio and n measurements.",
      "doi": "https://doi.org/10.1088/0067-0049/196/1/11",
      "ads_url": "https://ui.adsabs.harvard.edu/abs/2011ApJS..196...11S"
    }
  ]
}