Absorbers cookbook

Table of contents

  1. Find lines
  2. Model Ly-a forest
  3. Model metals
  4. Identify unknown lines
  5. Check system list

Find lines

Method CookbookAbsorbers.find_lines
Parameters
  • kind: Kind
  • prominence: Prominence
  • append: Append to existing line list
JSON template 
{
  "cookbook": "cb",
  "recipe": "find_lines",
  "params": {
    "kind": "'abs'",
    "prominence": "null",
    "append": "true"
  }
}

Find absorption or emission lines, based on their prominence.

Lines are found in column y of the spectrum. kind is either abs or em, to find absorption or emission lines respectively. prominence is defined as in scipy.signal.find_peaks; if the user does not specify it, it is defined as 5 times the value in column dy of the spectrum.

Model Ly-a forest

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Model metals

Method CookbookAbsorbers.model_metals
Parameters
  • trans: Transitions
  • zem: Emission redshift
  • no_ly: Exclude Lyman forest
  • use_lines: Use line list to define absorbers @url absorbers_cb.html#model-metals
JSON template 
{
  "cookbook": "cb",
  "recipe": "model_metals",
  "params": {
    "series": "series",
    "zem": "zem",
    "no_ly": "true",
    "use_lines": "false"
  }
}

Model metal absorbers, based on transition and emission redshift.

The spectrum is scanned to identify absorption systems and fit them with Voigt profiles. If series is a doublet or multiplet (recommended), e.g. CIV or MgII_2796,MgII_2803, only absorbers with the right wavelength ratio(s) are modelled as bona fide systems and saved in the system table with their fitting parameters. Only wavelengths up to the emission redshift zem of the chosen series are considered. The user may decide to exclude the Lyman forest with no_ly. If use_lines is True, absorption systems are identified on an existing line list, otherwise they are identified by cross-correlating the flux spectrum with itself, after applying a shift corresponding to the wavelength ratio(s) under consideration.

When the system table is empty, the recipe tries to identify systems using the column y of the spectrum, otherwise it tries on the column deabs (to avoid considering absorbers already identified and modeled). The recommended practice is to use this recipe to identify the most common doublets, and to identify the remaining lines using identify_unknown instead. If the Lyman forest has already been modeled, the user may want to set no_ly to False and tentatively identify metals within the forest too.

Identify unknown lines

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Check system list

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