Available Catalogs

Release	LRG: Mg < -21.8	LRG: Mg < -21.2	Mr < -22	Mr < -21	Mr < -20	Mr < -19	Mr < -18
	(from Oriana)	(Oriana)	(Oriana)	(Carmen)	(Esmeralda)	(Consuelo)	(Consuelo)
beta	-	-	-	82	30	-	-
gamma	80 / 160	80 / 160	80 / 160	82 / 164	60 / 120	-	-

Descriptions of the release are included below. The mocks themselves can be obtained from the following page: Download.

We recommend using the latest release: gamma . The two numbers in the above table show the available mocks using two and four mocks per simulation box respectively (2x/4x). The full “North + South” SDSS footprint can be reproduced twice from each box without any repeated galaxies. If the southern stripes are neglected, four “North Only” mocks can be produced without overlap. The preferred version might vary depending on the science application, so we make both available. We make it clear which galaxy mock comes from which simulation in the filenames, so it should be easy to select appropriately.

SDSS Gamma Release

Properties of the gamma release of galaxy mock catalogs:

designed to match SDSS DR7 clustering
modeled after volume-limited samples
reproduce the SDSS DR7 geometry
include redshift space distortions from velocities
include no modeling of fiber collisions

This release includes mocks modeled after five volume-limited SDSS galaxy samples.

Three Main SDSS galaxy samples:

Sample	z_median	z_mean	z_min	z_max
Main Mr < -20	0.082	0.079	0.02	0.106
Main Mr < -21	0.130	0.122	0.02	0.165
Main Mr < -22	0.188	0.180	0.02	0.247

Two LRG samples:

Sample	z_median	z_mean	z_min	z_max
LRG Mg < -21.2	0.286	0.277	0.16	0.36
LRG Mg < -21.8	0.350	0.337	0.16	0.44

General Description

From our simulations (see Simulations for more details), we identify DM halos using FOF with a linking length of b=0.2 in units of the mean inter-particle separation. Using a halo model approach, we apply HOD parameters to populate dark matter halos with mock galaxies. We place a central galaxy using the position of the deepest potential particle (think most-bound particle but neglecting velocity information) and assign the mean velocity of the halo to it. We populate satellite galaxies by randomly selecting dark matter particles from the halo and use their positions and velocities. We choose specific HOD parameters so that the mocks reproduce the galaxy number density and projected correlation function of observed SDSS samples. We find one set of HOD parameters for each galaxy sample, and apply this one set of parameters to each simulation box to produce the number of available mock catalogs.

Improvements on the “beta” release include:

larger number of simulations
more SDSS galaxy samples: two LRG samples and a brighter Main galaxy sample
using the final SDSS-II data (DR7) to match observed clustering
DM halo centers use deepest potential particle rather than center-of-mass
a “North Only” version that makes four mocks from each simulation box

This is not yet the “version 1” release due mainly to two factors:

we do not yet have mocks for the two faint Main galaxy samples from Consuelo
we have not yet modeled fiber collisions in the galaxy mocks

We expect the above limitations to be addressed in the release following “gamma”.

Random Catalogs

Random catalogs are generated using the same SDSS DR7 geometry as the mocks. They have uniform density, which is at least 10 times the number density of the galaxy mocks and include redshifts. One random for each sample is provided.

Downloading

Please see the download page for directions in obtaining the galaxy mock files.

Additional Notes

Where appropriate, the LasDamas cosmology (see simulations) was used in standard units of the dimension-less Hubble constant.

The footprint is applied using SDSSPix versions of the ‘lss_geometry’ file found in the NYU Value-Added Galaxy Catalog . We do not trim by the bright star mask, which makes the mocks slightly more contiguous than the SDSS data. Please note, this is a slightly different footprint than the “beta” release.

The total area of these galaxy mocks:

North + South	7961.26 square degrees
North Only	7214.34 square degrees

Example of 2 mocks from SDSS North + South footprint Example of 4 mocks from SDSS North Only footprint

The above figures are examples of the rotation angles used to obtain 2 “North + South” and 4 “North Only” mocks from each simulation box without overlap. The red is the unrotated SDSS geometry. Both the red and the blue rotations are consistent between footprints.

SDSS Beta Release

Properties of the Beta release mocks:

designed to match SDSS DR6 clustering
geometry defined by SDSS DR7 (final)
volume-limited samples
include redshift space distortions using velocity information
include no modeling of fiber collisions

Using a halo model approach, HOD parameters are applied to FOF halos with a linking length of b=0.2 times the mean inter-particle separation. A central galaxy is always placed at the center-of-mass of each halo and is given the mean velocity of the halo. Satellite galaxies are placed by randomly selecting dark matter particles from the halo, and are given their positions and velocities. The HOD parameters themselves are chosen to match the clustering of SDSS galaxies. One set of HOD parameters is found for each galaxy sample, and this one set of parameters is applied to each simulation box to produce the number of available mock catalogs. For this release, no light-cones were used. The galaxy mocks used snapshots at the median redshift of the corresponding SDSS galaxy samples.

Sample	z_median	z_mean	z_min	z_max
Main Mr < -20	0.082	0.079	0.02	0.1061
Main Mr < -21	0.132	0.126	0.02	0.1697

This beta release used the galaxy number density, n_g, and the projected 2pt correlation function, wp(rp), for fitting to SDSS samples. As a sanity check, the large scale power spectrum, P(k), was verified to look reasonable with the final catalogs — but was not used explicitly in the fitting pipeline.

Projected 2pt for Mr < -20 mocks Projected 2pt for Mr < -21 mocks

These plots depict the projected two-point correlation function of the two beta samples, Mr < -20 and Mr < -21, with the SDSS DR6 measurement (colored points with errors) and the 30 and 82 mocks (gray lines) respectively.