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cschreib / slinefit

Measure redshifts and emission/absorption lines in 1D galaxy spectra.
MIT License
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Redshift Estimation from Absorption lines ? #9

Open dharmender213 opened 6 months ago

dharmender213 commented 6 months ago

Hi Corentin,

I am using this package to find out the corrected redshift using the metal absorption lines. Can you give some idea how the code measures the redshift. Because when I plot the measured redshift and real readshift in the velocity space, the redshift measured from this code is very far from the absorption. Thank you for this code, really save me a lot.

cschreib commented 6 months ago

Hi! The methods are described in my 2018 paper, you can read it here: https://www.aanda.org/articles/aa/full_html/2018/10/aa33070-18/aa33070-18.html#S11

Let me know if you have more questions.

cschreib commented 6 months ago

The tutorial also contains information that could help you.

dharmender213 commented 6 months ago

Actually I am using it for constraining the redshift of Damped Lyman alpha sources, and it is giving the redshift with some offset from the actual metal absorption. Like : lines=[abs_c2_1335,abs_o1_1302,abs_o4_1342,abs_si2_1304,abs_si2_1526,abs_al2_1671,abs_fe2_1608]. And I used the three components.

cschreib commented 6 months ago

Have the links above been any useful?

I cannot really help unless you can tell me more specifically what it is you're after, or what is specifically not working as you expect (ideally with plots to demonstrate the issue).

One of the main take away point of the tutorial is that the quality of the output of the code depends strongly on the quality of the input data. You may need to check that your error spectrum is accurate, and that the flux spectrum doesn't contain weird values or data extraction errors (often at the edges) that should be blanked out before fitting. Have you done any of this?

I know very little about damped Lyman alpha galaxies, but if the Lyman alpha line is weird, you may have to mask it out and let the fit anchor itself onto the other lines. Once you have the redshift figured out, you can freeze it and fit for the line fluxes.

dharmender213 commented 6 months ago

Hi Corentin, yeah I checked the link you provide thanks for that, from that I found out that this is only the good for the galaxies. But I want to use it for damped Lyman alpha system ? Is it possible to use it for those systems ? the velow is the spectrum plot with continuum fit and model fit. J000136.31+272635.4_boss_fixed.fits_velocity.pdf

cschreib commented 6 months ago

I don't think slinefit has been used for DLAs yet, so unless you do some testing to show it works, I would say it is not supported yet. I am sorry I cannot recommend an alternative, I know too little about these systems.