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Odd behavior with optical emission lines #199
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Pinging @bd-j, who may have suggestions. |
For MIST and MILES here are no nebular models above Z/Z_sol = +0.2, due to limitations in the isochrones and spectral libraries used to create the ionizing spectra. So the nebular lines are nearest-neighbor extrapolation above that. |
I also note that the computed spectra are extrapolated beyond log(Z/Z_sol) > +0.2, and so are less reliable. |
Ok, then this is an expected behavior... I guess though that means that even the IR emission is affected above log(Z/Z_sol) > +0.2 as it is the "reprocessing" of the UV produced by stars. So that means that if I want reliable IR spectra I should not exceed this metalicity limit for MIST and MILES, I am correct? What libraries do you suggest I use for log(Z/Z_sol) > +0.2? |
I noticed a strange behavior where after a logzsol value of 0.2 all points in a standard BPT diagram ([NII]/Hα, [OIII]/Hβ) are stuck to a certain value. I am using default stellar libraries: "mist" and "miles" to get the BPT emission-line ratios ([OIII]/Hβ and [NII]/Hα) for an SSP (sfh=0) observed at tage=1Myr (0.001Gyr) with a constant ionization parameter of logU=-2.5 but for different metallicities (logzsol=[-0.6,0.6]), also I set zcontinuous=1. The models are such that logzsol = gas_logz. I attach the resulted BPT diagram bellow. In an attempt to understand what is happening I have calculated the SEDs in two cases; 1) sfh=0 (SSP), logz=0, dust1=0, dust2=0 for different ages; 2) sfh=0 (SSP), dust1=0, dust2=0 for different metallicities (both with default stellar libraries). The UV produced by the two SSPs (I think that) look normal (attached bellow). Finally I am giving you the result of the [OIII]/Hβ as a function of metallicity (from the calculations of BPT).
Is this expected behavior?
Here is my code for the BPT calculations (the two SED tests are calculated from an other script)
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