Mg II Absorber Catalog¶
Overview¶
This value-added catalog contains summarized information regarding the detection and characterization of Mg II absorption systems detected in DESI QSO spectra. The parent QSO catalog utilized is the afterburner catalog produced by the Large Scale Structuring group and Edmond Chaussidon. The code used to generate this catalog can be found on GitHub. For more information about the methods by which this catalog has been generated and its statistics verified see Napolitano et al. (2023).
Data Access¶
Data URL: https://data.desi.lbl.gov/public/dr1/vac/dr1/mgii-absorber/v1.0/
NERSC access:
/global/cfs/cdirs/desi/public/dr1/vac/dr1/mgii-absorber/v1.0/
Documentation¶
Workflow¶
MgII_NMF_HPiterates through HEALpixels and generates .hdf5 files containing the full MCMC chains of succesfully fit absorbersWrite_Abs_Catalogswrites individual HEALPixel-based Mg II absorber catalogs. Indiviudal catalogs are then combined into a per-release catalog.Eval_MgII_Catsgenerates a series of plots by which to evaluate the catalogs.
List of files¶
MgII-Absorbers-DR1.fits: Catalog file. One HDU with data namedMGII_ABSORBERS. 270,529 entries, each having the columns described in the data model below. Note that entries are not unique inTARGETID, as multiple absorbers can be found in the line-of-sight to a single target. Because of this TARGETID & Z_MGII are needed to specify a unique entry.MgII-Absorbers-DR1-PI.fits: Catalog file. One HDU with data namedMGII_ABSORBERS. 392 entries, each having the columns described in the datamodel below. This catalog contains entries that have physically impossible (PI) absorption redshifts, i.e. those with a postive delta_v of greater than 5000 km/s relative to the ‘background’ QSO. This sample has a noticeably lower purity, however does present opportunities to improve QSO classifications/redshifts as described in section 4.1 of the paper linked above
Example of reading the catalog (python using fitsio):
import fitsio
Mgii_fp = '/global/cfs/cdirs/desi/public/dr1/vac/dr1/mgii-absorber/v1.0/MgII-Absorbers-EDR.fits'
MgII_cat = fitsio.read(Mgii_fp, 'MGII_ABSORBERS')
Data model¶
| Name | Type | Units | Description |
|---|---|---|---|
| TARGETID | int64 | – | Unique 64-bit identifier for each object observed by DESI |
| RA | float64 | deg | Right Ascension in decimal degrees (J2000) |
| DEC | float64 | deg | Declination in decimal degrees (J2000) |
| SURVEY | str | – | Survey validation stage (sv1, sv2, or sv3) |
| ZWARN | int64 | – | Redshift redshift warning bitmask |
| TSNR2_QSO | float64 | – | QSO weighted (S/N)2 sum over B, R, Z |
| TSNR2_LYA | float64 | – | LYA weighted (S/N)2 sum over B, R, Z |
| TSNR2_LRG | float64 | – | LRG weighted (S/N)2 sum over B, R, Z |
| Z_QSO | float64 | – | Redshift value from input QSO catalog (following afterburners) |
| EW_2796 | float64 | Angstrom | Central posterior value for the equivalent width of the 2796Å line of the MgII doublet |
| EW_2803 | float64 | Angstrom | Central posterior value for the equivalent width of the 2803Å line of the MgII doublet |
| EW_2796_ERR_LOW | float64 | Angstrom | Low error bar for the equivalent width of the 2796Å line of the Mg II doublet |
| EW_2803_ERR_LOW | float64 | Angstrom | Low error bar for the equivalent width of the 2803Å line of the Mg II doublet |
| EW_2796_ERR_HIGH | float64 | Angstrom | High error bar for the equivalent width of the 2796Å line of the Mg II doublet |
| EW_2803_ERR_HIGH | float64 | Angstrom | High error bar for the equivalent width of the 2803Å line of the Mg II doublet |
| Z_MGII | float64 | – | Central posterior value for the redshift of the Mg II absorption feature |
| AMP_2796 | float64 | 1e-17 erg / (Å cm2 s) | Central posterior value for the amplitude of the 2796Å line of the Mg II doublet |
| AMP_2803 | float64 | 1e-17 erg / (Å cm2 s) | Central posterior value for the amplitude of the 2803Å line of the Mg II doublet |
| STDDEV_2796 | float64 | Angstrom | Central posterior value for the standard deviation of the 2796Å line of the Mg II doublet |
| STDDEV_2803 | float64 | Angstrom | Central posterior value for the standard deviation of the 2803Å line of the Mg II doublet |
| Z_MGII_ERR_LOW | float64 | – | Low error bar for the redshift of the Mg II absorption feature |
| AMP_2796_ERR_LOW | float64 | 1e-17 erg / (Å cm2 s) | Low error bar for the amplitude of the 2796Å line of the Mg II doublet |
| AMP_2803_ERR_LOW | float64 | 1e-17 erg / (Å cm2 s) | Low error bar for the amplitude of the 2803Å line of the Mg II doublet |
| STDDEV_2796_ERR_LOW | float64 | Angstrom | Low error bar for the standard deviation of the 2796Å line of the Mg II doublet |
| STDDEV_2803_ERR_LOW | float64 | Angstrom | Low error bar for the standard deviation of the 2796Å line of the Mg II doublet |
| Z_MGII_ERR_HIGH | float64 | – | High error bar for the redshift of the Mg II absorption feature |
| AMP_2796_ERR_HIGH | float64 | 1e-17 erg / (Å cm2 s) | High error bar for the amplitude of the 2796Å line of the Mg II doublet |
| AMP_2803_ERR_HIGH | float64 | 1e-17 erg / (Å cm2 s) | High error bar for the amplitude of the 2803Å line of the Mg II doublet |
| STDDEV_2796_ERR_HIGH | float64 | Angstrom | High error bar for the standard deviation of the 2796Å line of the Mg II doublet |
| STDDEV_2803_ERR_HIGH | float64 | Angstrom | High error bar for the standard deviation of the 2796Å line of the Mg II doublet |
| CONTINUUM_METHOD | str | – | Method by which QSO continuum was determined while fitting (NMF or Medianfilter) |
| LINE_SNR_MIN | float64 | – | Minimum SNR value of the two Mg II line (used in initial detection; higher values equate to higher catalog purity) |
| LINE_SNR_MAX | float64 | – | Maximum SNR value of the two Mg II lines (used in initial detection; higher values equate to higher catalog purity) |