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bpt_line_ratios

Measure BPT line ratios + classify a galaxy (HII / Composite / Seyfert / LINER).
Category Nebular diagnostics
Backend scipy - implemented here on top of scipy primitives
Version 1.1.0
Reads ctx.spectrum (a Spectrum1D)
Writes metrics.log_nii_ha, metrics.log_oiii_hb, metrics.log_sii_ha, metrics.log_oii_hb, extras.bpt_classification, extras.line_fluxes, extras.rest_wavelengths, extras.fit_details, extras.method, extras.bpt_line_fluxes, extras.bpt_rest_wavelengths, extras.bpt_fit_details, extras.bpt_method

BPT classification uses the [N II]/Hα plane only (the most-cited standard). Auxiliary log ratios log_oii_hb (3727/Hβ) and log_sii_ha ((6716+6731)/Hα) are reported for downstream analysis but not used for the class label. Override the default rest wavelengths via params['lines'] (dict). v1.1.0: extras['method'] (shared with the other nebular bricks) is also written as extras['bpt_method'], and line_fluxes / rest_wavelengths / fit_details as bpt_line_fluxes / bpt_rest_wavelengths / bpt_fit_details, so a pipeline keeps unambiguous provenance.

Parameters

Parameter Default Required Description
window 8.0 - Half-width (Å) of the fit window around each line.
lines {'ha': 6562.82, 'hb': 4861.33, 'oiii_5007': 5006.84, 'nii_6583': 6583.45, 'sii_6716': 6716.44, 'sii_6731': 6730.82, 'oii_3727': 3727.42} - Mapping of line keys to rest wavelengths (Å). Keys: ha, hb, oiii_5007, nii_6583, sii_6716, sii_6731, oii_3727.

Use it

from spectro_kernel import run_algorithm

output = run_algorithm("bpt_line_ratios", ctx, {
    "window": 8.0,
    "lines": {
        "ha": 6562.82,
        "hb": 4861.33,
        "oiii_5007": 5006.84,
        "nii_6583": 6583.45,
        "sii_6716": 6716.44,
        "sii_6731": 6730.82,
        "oii_3727": 3727.42
    }
})

spectro run bpt_line_ratios --input spectrum.fits \
  --param window=8.0 \
  --param lines={"ha":6562.82,"hb":4861.33,"oiii_5007":5006.84,"nii_6583":6583.45,"sii_6716":6716.44,"sii_6731":6730.82,"oii_3727":3727.42}

{
  "tool": "bpt_line_ratios",
  "arguments": {
    "session_id": "<session_id>",
    "params": {
      "window": 8.0,
      "lines": {
        "ha": 6562.82,
        "hb": 4861.33,
        "oiii_5007": 5006.84,
        "nii_6583": 6583.45,
        "sii_6716": 6716.44,
        "sii_6731": 6730.82,
        "oii_3727": 3727.42
      }
    }
  }
}

Every algorithm is an MCP tool of the same name; describe_algorithm returns this page's metadata as JSON.

References

  • Baldwin, Phillips & Terlevich 1981, PASP 93, 5 — original BPT.
  • Kewley & Dopita 2001, ApJ 556, 121 — maximum-starburst line.
  • Kauffmann et al. 2003, MNRAS 346, 1055 — HII/AGN empirical split.
  • Cid Fernandes et al. 2010, MNRAS 403, 1036 — Seyfert/LINER cut.
  • Kewley et al. 2006, MNRAS 372, 961 — [S II], [O I] variants.