{
  "name": "Optical Spectroscopic Galaxy Classification Rules",
  "description": "Rules for classifying galaxies using BPT diagnostics and spectral indices (Dn4000, Hδ) from optical spectroscopy.",
  "version": "1.0",
  "input_parameters": {
    "helpha_flux": "Hα emission line flux (erg/s/cm²)",
    "nii_6584_flux": "[N II] λ6584 emission line flux",
    "hbeta_flux": "Hβ emission line flux",
    "oiii_5007_flux": "[O III] λ5007 emission line flux",
    "dn4000": "4000 Å break index; >1.6 indicates old stellar population",
    "hdelta_ew": "Hδ_A equivalent width in absorption (Å); high values indicate recent star formation cessation",
    "vdisp": "Stellar velocity dispersion (km/s); proxy for bulge mass",
    "z": "Redshift; used to correct line ratios if needed"
  },
  "bpt_classification_rules": [
    {
      "type": "Star-forming",
      "condition": "log10([OIII]/Hβ) <= 0.61 / (log10([NII]/Hα) - 0.47) + 1.19",
      "reference": "Kauffmann et al. (2003)"
    },
    {
      "type": "Seyfert",
      "condition": "log10([OIII]/Hβ) > 0.61 / (log10([NII]/Hα) - 0.47) + 1.19 AND log10([NII]/Hα) > 0.0",
      "reference": "Kewley et al. (2001)"
    },
    {
      "type": "LINER",
      "condition": "log10([OIII]/Hβ) <= 0.61 / (log10([NII]/Hα) - 0.47) + 1.19 AND log10([NII]/Hα) > 0.0",
      "reference": "Cid Fernandes et al. (2010)"
    },
    {
      "type": "Composite",
      "condition": "Between Kauffmann and Kewley lines",
      "reference": "Kewley et al. (2006)"
    }
  ],
  "stellar_population_rules": [
    {
      "population_type": "Old/quiescent",
      "condition": "dn4000 > 1.6 AND hdelta_ew < 2.0",
      "reasoning": "Strong 4000 Å break and weak Hδ absorption → no recent star formation"
    },
    {
      "population_type": "Post-starburst (recently quenched)",
      "condition": "dn4000 > 1.4 AND hdelta_ew > 4.0",
      "reasoning": "Strong Hδ absorption from A-stars + moderate Dn4000 → star formation ceased ～0.1–1 Gyr ago"
    },
    {
      "population_type": "Ongoing star formation",
      "condition": "dn4000 < 1.4 AND strong nebular emission (e.g., Hα, [OIII])",
      "reasoning": "Young stellar population dominates spectrum"
    }
  ],
  "quality_checks": [
    {
      "check": "All emission lines must have S/N > 3",
      "fallback": "Classification uncertain due to low line significance"
    },
    {
      "check": "helpha_flux > 0, hbeta_flux > 0, etc.",
      "fallback": "Invalid flux values; skip classification"
    }
  ],
  "references": [
    {
      "citation": "Baldwin, Phillips & Terlevich (1981, PASP, 93, 5)",
      "role": "Original BPT diagnostic diagram"
    },
    {
      "citation": "Kauffmann et al. (2003, MNRAS, 346, 1055)",
      "role": "Empirical SF separation line"
    },
    {
      "citation": "Kewley et al. (2001, ApJ, 556, 121)",
      "role": "Theoretical maximum starburst line"
    },
    {
      "citation": "Cid Fernandes et al. (2010, MNRAS, 406, 1471)",
      "role": "Refined LINER/Seyfert separation"
    },
    {
      "citation": "Worthey (1994), Balogh et al. (1999)",
      "role": "Dn4000 and Hδ as age indicators"
    }
  ]
}