HII Region Emission Lines

This section describes how to simulate emission-line spectra from HII regions using the spec1d.HII_Region class in GEHONG.

Emission Line Template

Before simulating spectra, an emission line template must be initialized using the EmissionLineTemplate class. For HII regions, set model='hii'.

Usage Example:

from gehong import spec1d
gas_tem = spec1d.EmissionLineTemplate(config, model='hii')

HII Region Spectrum Simulation

The HII_Region class supports two working modes for generating integrated emission-line spectra.

Flux-calibrated mode** (empirical Hα normalization)

Activated when halpha is provided.

Input Parameters:

  • halpha: Total Hα flux (\(10^{-17}\ \mathrm{erg\ s^{-1}\ cm^{-2}\ Å^{-1}}\))

  • vel: Line-of-sight velocity (km/s)

  • vdisp: Velocity dispersion (km/s)

  • logz: Gas-phase metallicity [Z/H] (dex)

  • ebv: Dust extinction E(B-V)

Usage Example:

gas = spec1d.HII_Region(config, gas_tem,
                        halpha=500, vel=8000, vdisp=80,
                        logz=-0.3, ebv=0.1)
../../_images/example_spec1d_hii1.png

Physically calibrated mode (based on star formation rate)

Activated when halpha is set to None, and sfr and z are provided.

Input Parameters:

  • sfr: Star formation rate (M☉/yr)

  • z: Redshift

  • vpec: Peculiar velocity (km/s)

  • logz: Gas-phase metallicity [Z/H] (dex)

  • vdisp: Velocity dispersion (km/s)

  • ebv: Dust extinction E(B-V)

Usage Example:

gas = spec1d.HII_Region(config, gas_tem,
                        sfr=0.5, z=0.01, vpec=300,
                        logz=-0.2, vdisp=60, ebv=0.2)
../../_images/example_spec1d_hii2.png

Output Attributes

  • gas.wave: 1D wavelength array (Ångströms)

  • gas.flux: Corresponding flux array in units of \(10^{-17}\ \mathrm{erg\ s^{-1}\ cm^{-2}\ Å^{-1}}\)