Fitting balmer lines with emission+absorption

Myrddin wrote on Jun 26, 2017

Hi everyone,

I am dealing with a high S/N calibrated 1D spectrum of a star-forming galaxy. I can see the emission in the balmer lines (typical from SF galaxies) together with the absorption in the same wavelength from the underlying stellar population.

I need separate both contributions and measure their equivalent widths. I guess the correct way to do this is: First, fit a voigt profile to the absorption line and obtain its EW and substract the fit to restore the continuum, and second, measure the emission line, i.e flux and EW.

I have used SPLOT for fitting single emission or absorption lines before, but when I try to fit the absorption line FIRST to substract it, the task always fit the emission line in the center of the absorption. You can see the problem in this image, trying to fit H_gamma.

I don't know how to proceed in order to measure the absorption (voigt profile) and get rid of it before fitting the gaussian to the emission line profile. Any idea?

Thanks in advance

---

Francisco Valdes wrote on Jul 06, 2017

I understand the problem though the graphic showing the line region did not make it. I think to best help you could you send me the spectrum (with info about where in the spectrum is the feature of interest) and I figure out an answer. Ideally it would be nice to simultaneously fit absorption and emission but that is likely beyond the normal capabilities of SPLOT.

You send me an attachment to valdes@noao.edu.

Yours,

Frank

PS I will be away for a couple of weeks so a response will be delayed.

---

Last post on Jul 06, 2017