Visualization and Outreach Catalog¶
Overview¶
This is a catalog of galaxy and quasar positions measured by the Dark Energy Spectroscopic Instrument (DESI) and included in the Early Data Release.
This catalog lists the 3D coordinates of about 700,000 objects, which represent roughly 1% of the total final volume that DESI will study. They are arranged into 20 separate cones that radiate out from earth. Each cone contains the objects observed in one direction.
The primary purpose of this catalog is to support visualization and educational outreach activities without requiring expert knowledge of DESI or astronomical data. There is an example visualization here.
Data Access¶
Data URL: https://data.desi.lbl.gov/public/edr/vac/edr/epoviz/
NERSC access for DESI collaborators:
/global/cfs/cdirs/desi/public/edr/vac/edr/epoviz/
Documentation¶
Catalog Creation¶
An accompanying jupyter notebook documents the steps used to create this catalog (view it as a webpage here). To run it, you will need the following packages installed:
The last package is needed to read files in the FITS astronomical data format and can be installed using either pip or conda.
Example Usage¶
The easiest way to open and inspect the catalog is with pandas:
import pandas as pd
catalog = pd.read_csv('EDR-Viz-Outreach-VAC.csv.gz')
Data Model¶
The data is stored as a compressed CSV file with the following columns:
| Column Name | Unit | Description |
|---|---|---|
| TARGETID | Unique identifier of the object | |
| RA | degrees | Right ascension angle of the object |
| DEC | degrees | Declination angle of the object |
| REDSHIFT | Fractional increase in wavelength which serves as an observational proxy of cosmological distance | |
| ROSETTE | Integer code (0-19) identifying which cone-shaped “rosette” this target belongs to | |
| TRACER | Integer code for tracer type (0=QSO, 1=ELG, 2=LRG, 3=BGS) | |
| X | Glyr | X coordinate of the object relative to earth measured today |
| Y | Glyr | Y coordinate of the object relative to earth measured today |
| Z | Glyr | Z coordinate of the object relative to earth measured today |
Notes¶
- The TARGETID can be used to locate further details about each object here, including its optical spectrum.
- To see the 20 different rosettes in 3D watch this video.
- For details on the different tracer types (QSO, ELG, LRG, BGS), see this introduction to DESI target selection.
- 1 Glyr equals 1 billion light years or approximately 307 million parsecs.
- The XY plane corresponds to DEC=0 and the +Z axis corresponds to DEC=90 deg. The +X axis corresponds to DEC=0 and RA=0. The +Y axis corresponds to DEC=0 and RA=90 deg.
- XYZ values are truncated to 5 decimal places to limit the size of the CSV file.
- Since the universe is expanding, XYZ coordinates are time dependent. These values are specified at the present time.
Contact¶
Contact David Kirkby with any questions.