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UCHUU-DESI Catalog

Overview

This VAC includes the 102 lightcones generated from the Uchuu simulation for the four DESI tracers observed in the One-Percent Survey. This includes the Bright Galaxy Survey (BGS) BRIGHT sample, Luminous Red Galaxies (LRG), Emission Line Galaxies (ELG) and quasars (QSO).

For more information about these lightcones can be found here
More information about Uchuu simulation can be found here

The lightcones available here are given for both hemispheres of the One-Percent Survey separately (North-N- and South-S-).

Our lightcones cover a redshift range between

  • Z=0.0 and Z=0.6 (BGS-BRIGHT)
  • Z=0.4 and Z=1.1 (LRG)
  • Z=0.88 and Z=1.34 (ELG)
  • Z=0.9 and Z=2.1 (QSO)

The total effective area for all tracers is 191.4 deg2 (95.7 deg2 for each hemisphere).

If you use these catalogs in your paper, please cite Prada et al. (2023)

Data Access

Data URL: https://data.desi.lbl.gov/public/edr/vac/edr/uchuu/

NERSC access for DESI collaborators: 

/global/cfs/cdirs/desi/public/edr/vac/edr/uchuu/

Documentation

Files

Lightcone files:

  • BGS_BRIGHT_[N/S]_[i]_uchuu.dat.fits: 102 BGS Uchuu lightcones, split into North and South
  • LRG_main_[N/S]_[i]_uchuu.dat.fits: 102 LRG Uchuu lightcones, split into North and South
  • ELG_[N/S]_[i]_uchuu.dat.fits: 102 ELG Uchuu lightcones, split into North and South
  • QSO_[N/S]_[i]_uchuu.dat.fits: 102 QSO Uchuu lightcones, split into North and South

Random files:

  • BGS_BRIGHT_[N/S]_[i]_uchuu.ran.fits: 18 BGS Uchuu random files, split into North and South. Each file contains 3x the number of galaxies as the BGS Uchuu lightcones
  • LRG_main_[N/S]_uchuu.ran.fits: 1 LRG Uchuu random file, split into North and South. Each file contains 40x the number of galaxies as the LRG Uchuu lightcones
  • ELG_[N/S]_[i]_uchuu.ran.fits: 102 ELG Uchuu random files, split into North and South. Each file contains 1x the number of galaxies as the ELG Uchuu lightcones
  • QSO_[N/S]_uchuu.ran.fits: 1 QSO Uchuu random file, split into North and South. Each file contains 20x the number of galaxies as the QSO Uchuu lightcones

Data model

The following columns are provided for all tracers

Column Type Description Units
RA float64 Right Ascension of the galaxy deg
DEC float64 Declination of the galaxy deg
Z float64 Redshift, including the effect of peculiar velocity
NZ float64 Number density, n(z), at the redshift of the galaxy h3 Mpc-3
WEIGHT_FKP float64 FKP weight of the galaxy

The following columns are provided for BGS-BRIGHT only

Column Type Description Units
ABSMAG_R float64 Absolute magnitude in the r-band, k-corrected to a reference redshift Z=0.1, with h=1. There is no evolutionary correction applied
APPMAG_R float64 Apparent r-band magnitude
EQ_ALL_0P1 float64 Evolutionary correction, to a reference redshift Z=0.1
KCORR_G0P1 float64 K-correction in the g-band
KCORR_R0P1 float64 K-correction in the r-band
REST_GMR_0P1 float64 Rest-frame g-r color

The following columns are provided for LRGs only

Column Type Description Units
M_STAR float64 Stellar mass of the galaxy Msun

FAQs

A) Why are there 102 lightcone .dat.fits files?

We cut the full-sky lightcone to 102 copies of the One-Percent Survey footprint, without any overlapping area. For more information about how this process is performed, see Section 3.3.6 of Prada et al. (2023)

B) Which one of the 102 lightcone .dat.fits should I use?

The 102 lightcones are (almost) independent, therefore any of them can be used individually. However, due to the small size of the SV3 footprint, we recommend using all the 102 lightcones in order to obtain the mean and standard deviation of each measurement.

C) How have the FKP weights been calculated?

The WEIGHT_FKP has been calculated using the following formula:
1 / (1 + NZ*P0)
where NZ is the number density of each tracer, as a function of redshift. P0 is the value of the power spectrum at the scale where we wish to minimize the variance.

For the four tracers, we use a value of P0 of:

  • BGS: P0=7000 (Mpc/h)3
  • LRG: P0=10000 (Mpc/h)3
  • ELG: P0=4000 (Mpc/h)3
  • QSO: P0=6000 (Mpc/h)3

See FAQ D for when the NZ and WEIGHT_FKP need to be recalculated

D) Which NZ and WEIGHT_FKP columns should I use?

For all tracers: if you are using the full sample split into North and South, you can use the NZ and WEIGHT_FKP columns provided.

The NZ and WEIGHT_FKP columns will need to be recalculated if: - Combining North+South - Splitting the lightcone (and randoms) into subsamples, e.g. with magnitude cuts for BGS, or stellar mass cuts for LRG

E) What are the columns stored in the random .ran.fits files?

The columns in the random file are the same as in the lightcone .dat.fits files. This allows the same cut (e.g. magnitude, stellar mass) to be applied to both the data and random files, and the random catalog will have the correct n(z). Note that the NZ and WEIGHT_FKP need to be recalculated (see FAQ D)

F) Which random .ran.fits files should I use?

Random files are provided separately for North and South. Any number of random files can be used. If cutting the mock into subsamples (e.g. based on magnitude, stellar mass), the same cuts should be applied to the random catalogs. Note that the NZ and WEIGHT_FKP must be recalculated (see FAQ D).

G) How do I use the BGS k-corrections?

For the BGS-BRIGHT lightcone, we provide r-band and g-band k-corrections, which corrects for the shift in the bandpass with redshift.

Absolute magnitudes in the mock are k-corrected to a reference redshift Z=0.1, using a set of color-dependent polynomial k-corrections from the GAMA survey. The ABSMAG_R column provided already has the k-correction included.

The relation between absolute and apparent magnitude is
ABSMAG_R = APPMAG_R - 5log10(D_L) - 25 - KCORR_R0P1
where D_L is the luminosity distance, in Mpc/h.

The rest-frame g-r color REST_GMR_0P1 is also already k-corrected to Z=0.1. The observed g-r color can be obtained from
Observed g-r color = REST_GMR_0P1 + KCORR_G0P1 - KCORR_R0P1

H) How do I use the BGS E-corrections?

For the BGS-BRIGHT lightcone, we provide an evolutionary correction.

An E-correction can be applied to the absolute magnitudes to correct for evolution of the luminosity function with redshift. We provide the column EQ_ALL_0P1, which is a E-correction of the form
E(Z) = Q*(Z-Z0), where Q=0.97 and Z0=0.1

The absolute magnitudes in the ABSMAG_R column are not E-corrected. To apply the E-correction,
E-corrected absolute magnitude = ABSMAG_R - EQ_ALL_0P1

Contact

For questions about the lightcones please contact