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"""
SDSS Line-ratio Diagrams
------------------------
This shows how to plot line-ratio diagrams for the SDSS spectra. These
diagrams are often called BPT plots [1]_, Osterbrock diagrams [2]_,
or Kewley diagrams [3]_. The location of the dividing line is taken from
from Kewley et al 2001.
References
~~~~~~~~~~
.. [1] Baldwin, J. A.; Phillips, M. M.; Terlevich, R. (1981)
http://adsabs.harvard.edu/abs/1981PASP...93....5B
.. [2] Osterbrock, D. E.; De Robertis, M. M. (1985)
http://adsabs.harvard.edu/abs/1985PASP...97.1129O
.. [3] Kewley, L. J. `et al.` (2001)
http://adsabs.harvard.edu/abs/2001ApJ...556..121K
"""
# Author: Jake VanderPlas <vanderplas@astro.washington.edu>
# License: BSD
# The figure is an example from astroML: see http://astroML.github.com
import numpy as np
from matplotlib import pyplot as plt
from astroML.datasets import fetch_sdss_corrected_spectra
from astroML.datasets.tools.sdss_fits import log_OIII_Hb_NII
data = fetch_sdss_corrected_spectra()
i = np.where((data['lineindex_cln'] == 4) | (data['lineindex_cln'] == 5))
plt.scatter(data['log_NII_Ha'][i], data['log_OIII_Hb'][i],
c=data['lineindex_cln'][i], s=9, lw=0)
NII = np.linspace(-2.0, 0.35)
plt.plot(NII, log_OIII_Hb_NII(NII), '-k')
plt.plot(NII, log_OIII_Hb_NII(NII, 0.1), '--k')
plt.plot(NII, log_OIII_Hb_NII(NII, -0.1), '--k')
plt.xlim(-2.0, 1.0)
plt.ylim(-1.2, 1.5)
plt.xlabel(r'$\mathrm{log([NII]/H\alpha)}$', fontsize='large')
plt.ylabel(r'$\mathrm{log([OIII]/H\beta)}$', fontsize='large')
plt.show()
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