# README file describing Lyman alpha related SNR files and programs
#
# by Andreu Font-Ribera (LBNL), May 7th 2015

spec-lya.dat
------------

spec-lya.dat is a file (generated by Anze Slosar in July 2014) with the typical lya quasar spectrum at 
several redshifts (2.0, 2.25, 2.50, ..., 4.75). 

The first column is the wavelength in Angstroms, and the remaining 12 columns correspond to the 12 redshifts.

Note that these are not only rescaled with redshifts, but the mean level of lyman alpha absorption also 
evolves with redshift.

This file is used as an input for desi_quicklya.pro and desi_quicklya.py.


quickstudy.py
-------------

Python program by David Kirkby, with a --lya option.

It will compute median and total SNR in the forest of a given quasar as a funcion of magnitude and redshift, 
and similar, and optionaly generate plots like those in the DESI wiki page (wiki/LyaSNR).


desi_quicklya.py / desi_quicklya.pro
------------------------------------

Tor a series of quasar g magnitudes, generates a file with the SNR per pixel for a quasar of that magnitude, 
and for different redshifts (those in the input file spec-lya.dat).

The outputs are named sn-spec-lya-MAG.dat, where MAG is the g magnitude (22.25, for example), and are also 
available on SVN under data/spectra/.

The old files are obsolete, since they were generated with an older version of the DESI throughput. 

A newer version of these files (computed only with the python script) includes the exposure time in the file 
name, as an example sn-spec-lya-22.75-4000.dat, and are stored under LyaSNR.