Lyman-alpha Catalog¶
Overview¶
This value-added catalog contains the measured Lyman-alpha forest fluctuations from the DESI Early Data Release (EDR). For additional information see Ramírez-Pérez et al. (2023).
Data Access¶
Data URL: https://data.desi.lbl.gov/public/edr/vac/edr/lya/fuji/v0.3/
NERSC access:
/global/cfs/cdirs/desi/public/edr/vac/edr/lya/fuji/v0.3/
Documentation¶
The full data model can be accessed with the picca documentation on GitHub.
Reproduction¶
To reproduce this catalog, the software picca is needed. Instructions to install it can be found in its GitHub repository (a tagged version will be included when the final catalog is released).
Once the code is installed, the catalog can be easily reproduced with picca_delta_extraction.py and the configuration files located under configs/:
continuum_fitting_mask.txt: mask used in our runsdelta_extraction_ciii_calib_step_1.ini: configuration used for the calibration rundelta_extraction_lya.ini: configuration used for the actual run
First the calibration:
picca_delta_extraction.py configs/delta_extraction_ciii_calib_step_1.ini
Then the actual Lyman-alpha run:
picca_delta_extraction.py configs/delta_extraction_lya.ini
These two scripts should be run using slurm jobs with about two hours of walltime.
Flux-transmission field data model¶
The flux-transmission field is stored under Delta/. This folder contains per-HEALPixel files, which contain the main output from the picca delta extraction: the Lyman-alpha transmission fluctuations for all analysed quasars in a given HEALPixel. Each file contains the mentioned flux-transmission field, metadata, and quasar continua.
- Naming convention:
delta-HEALPIX.fits, whereHEALPIXis the HEALPixel ID - File type: FITS
| HDU Number | EXTNAME | Type | Contents |
|---|---|---|---|
| HDU0_ | PRIMARY | PRIMARY | — |
| HDU1_ | LAMBDA | IMAGE | Wavelength grid |
| HDU2_ | METADATA | BINTABLE | Per-forest metadata |
| HDU3_ | DELTA_BLIND | IMAGE | Flux-transmission field in wavelength bins |
| HDU4_ | WEIGHT | IMAGE | Weights in wavelength bins |
| HDU5_ | CONT | IMAGE | Quasar continua in wavelength bins |
Wavelength grid¶
EXTNAME = LAMBDA
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 1 | int | Number of array dimensions |
| NAXIS1 | 2716 | int | Number of wavelength pixels |
| WAVE_SOLUTION | lin | str | Chosen wavelength solution |
| DELTA_LAMBDA | 0.8 | float | Pixel step |
| BUNITS | Angstrom | str | Wavelength units |
Per-forest metadata¶
EXTNAME = METADATA
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 2 | int | Number of array dimensions |
| NAXIS1 | 84 | int | Table width |
| NAXIS2 | 340 | int | Number of forests |
| BLINDING | none | char[12] | Blinding scheme used |
Column descriptions:
| Column Name | Type | Units | Description |
|---|---|---|---|
| LOS_ID | int64 | — | PICCA unique target ID |
| RA | float64 | degrees | Target Right Ascension (J2000) |
| DEC | float64 | degrees | Target Declination (J2000) |
| Z | float64 | — | Redshift |
| MEANSNR | float64 | — | Mean signal-to-noise ratio |
| TARGETID | int64 | — | Unique 64-bit identifier for each object observed by DESI |
| NIGHT | char[12] | — | Observation night(s) |
| PETAL | char[12] | — | Observation petal(s) |
| TILE | char[12] | — | Observation tile(s) |
Flux-transmission field¶
EXTNAME = DELTA_BLIND
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 2 | int | Number of array dimensions |
| NAXIS1 | 2716 | int | Number of wavelength pixels |
| NAXIS2 | 340 | int | Number of forests |
| BUNITS | — | str | Delta units (unitless) |
Weights¶
EXTNAME = WEIGHT
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 2 | int | Number of array dimensions |
| NAXIS1 | 2716 | int | Number of wavelength pixels |
| NAXIS2 | 340 | int | Number of forests |
| BUNITS | — | str | Weight units (unitless) |
Quasar continua¶
EXTNAME = CONT
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 2 | int | Number of array dimensions |
| NAXIS1 | 2716 | int | Number of wavelength pixels |
| NAXIS2 | 340 | int | Number of forests |
| BUNITS | — | str | Quasar continuum units (unitless) |
Data model for auxiliary files¶
Under Log/ there are complementary output files:
The files delta_attributes(_iteration*).fits.gz contain information about the fits performed in the analysis, for variance functions and forest continua, as well as delta statistics at each iteration.
- Naming convention:
delta-attributes.fits.gzordelta-attributes_iterationITERATION.fits.gz, whereITERATIONis the iteration step - File type: FITS
| HDU Number | EXTNAME | Type | Contents |
|---|---|---|---|
| HDU0_ | PRIMARY | PRIMARY | — |
| HDU1_ | STACK_DELTAS | BINTABLE | Delta mean properties |
| HDU2_ | VAR_FUNC | BINTABLE | Variance fitted functions |
| HDU3_ | CONT | BINTABLE | Mean quasar continuum |
| HDU4_ | FIT_METADATA | BINTABLE | Extra fit metadata |
Delta mean properties¶
EXTNAME = STACK_DELTAS
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 2 | int | Number of array dimensions |
| NAXIS1 | 24 | int | Table width |
| NAXIS2 | 2716 | int | Number of wavelength pixels |
Column descriptions:
| Column Name | Type | Units | Description |
|---|---|---|---|
| LOGLAM | float64 | — | log(Angstrom) log(wavelength) |
| STACK | float64 | — | mean(1 + delta) |
| WEIGHT | float64 | — | Mean weight |
Variance fitted functions¶
EXTNAME = VAR_FUNC
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 2 | int | Number of array dimensions |
| NAXIS1 | 48 | int | Table width |
| NAXIS2 | 20 | int | Number of wavelength pixels |
Column descriptions:
| Column Name | Type | Units | Description |
|---|---|---|---|
| LOGLAM | float64 | log(Angstrom) | log(wavelength) |
| ETA | float64 | — | Intrinsic variace of fluctuations |
| VAR_LSS | float64 | — | Mean weight |
| NUM_PIXELS | int32 | — | Number of pixels in the fit |
| VALID_FIT | bool | — | Indicates valid fit |
Mean quasar continuum¶
EXTNAME = CONT
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 2 | int | Number of array dimensions |
| NAXIS1 | 84 | int | Table width |
| NAXIS2 | 206 | int | Number of rest-frame pixels |
Column descriptions:
| Column Name | Type | Units | Description |
|---|---|---|---|
| LOGLAM_REST | float64 | log(Angstrom) | Logarithm of rest-frame wavelength |
| MEAN_CONT | float64 | — | Mean quasar continuum |
| WEIGHT | float64 | — | Mean weight |
Extra fit metadata¶
EXTNAME = FIT_METADATA
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 2 | int | Number of array dimensions |
| NAXIS1 | 43 | int | Table width |
| NAXIS2 | 23168 | int | Number of forests |
Column descriptions:
| Column Name | Type | Units | Description |
|---|---|---|---|
| LOS_ID | int64 | — | PICCA unique target ID |
| ZERO_POINT | float64 | — | Continuum zero-point parameter |
| SLOPE | float64 | — | Continuum slope parameter |
| CHI2 | float64 | — | Continuum fit \(\chi\)2 |
| NUM_DATAPOINTS | int64 | — | Number of wavelenth pixels |
| ACCEPTED_FIT | bool | — | Fit acceptance |
The file rejection_log.fits.gz contains the rejection reason for each instance of a forest being rejected during the picca delta extraction.
| HDU Number | EXTNAME | Type | Contents |
|---|---|---|---|
| HDU0_ | PRIMARY | PRIMARY | — |
| HDU1_ | REJECTION_LOG | BINTABLE | Rejected forest statistics |
Rejected forest statistics¶
EXTNAME = REJECTION_LOG
| Header Keyword | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS | 2 | int | Number of array dimensions |
| NAXIS1 | 104 | int | Table width |
| NAXIS2 | 24719 | int | Number of rejected forests |
Column descriptions:
| Column Name | Type | Units | Description |
|---|---|---|---|
| LOS_ID | int64 | — | PICCA unique target ID |
| RA | float64 | degrees | Target Right Ascension (J2000) |
| DEC | float64 | degrees | Target Declination (J2000) |
| Z | float64 | — | Redshift |
| MEANSNR | float64 | — | Mean signal-to-noise ratio |
| TARGETID | int64 | — | Unique identifier for each object observed by DESI |
| NIGHT | char[12] | — | Observation night(s) |
| PETAL | char[12] | — | Observation petal(s) |
| TILE | char[12] | — | Observation tile(s) |
| FOREST_SIZE | int64 | — | Number of pixels in the forest |
| REJECTION_STATUS | char[12] | — | Rejection status of forest |