SDSS

The kszx.sdss module contains functions for downloading/parsing SDSS data products.

References

kszx.sdss.read_galaxies(survey, dr=12, download=False)

Reads SDSS galaxy catalog, and returns a Catalog object.

After calling this function, you’ll probably want to call Catalog.apply_redshift_cut() to retrict to an appropriate redshift range.

Function arguments:

  • survey (str): either ‘CMASS_North’, ‘CMASS_South’, ‘LOWZ_North’, ‘LOWZ_South’, ‘CMASSLOWZTOT_North’, ‘CMASSLOWZTOT_South’, ‘CLASSLOWZE2_North’, or ‘CMASSLOWZE3_North’.

  • dr (integer): either 11 or 12.

  • download (boolean): if True, then all needed data files will be auto-downloaded.

Returns a kszx.Catalog object, with the following columns:

ra_deg, dec_deg, z,    # sky location, redshift
wfkp,                  # FKP weight
wcp, wzf, wsys,        # systematic weights
cboss,                 # completeness (denoted C_BOSS in papers and COMP in the FITS file)
id                     # unique identifier

Reminder: SDSS galaxies are usually weighted by (wzf + wcp − 1) * wsys * wkp.

Example usage:

# kszx.sdss.read_galaxies() returns a kszx.Catalog.
gcat = kszx.sdss.read_galaxies('CMASS_North')
gcat.apply_redshift_cut(0.43, 0.7)
kszx.sdss.read_randoms(survey, dr=12, download=False)

Reads SDSS random catalog, and returns a Catalog object.

After calling this function, you’ll probably want to call Catalog.apply_redshift_cut() to retrict to an appropriate redshift range.

Function arguments:

  • survey (str): either ‘CMASS_North’, ‘CMASS_South’, ‘LOWZ_North’, ‘LOWZ_South’, ‘CMASSLOWZTOT_North’, ‘CMASSLOWZTOT_South’, ‘CLASSLOWZE2_North’, or ‘CMASSLOWZE3_North’.

  • dr (integer): either 11 or 12.

  • download (boolean): if True, then all needed data files will be auto-downloaded.

Returns a kszx.Catalog object, with the following columns:

ra_deg, dec_deg, z   # sky location, redshift
wfkp                 # FKP weight

Example usage:

# kszx.sdss.read_randoms() returns a kszx.Catalog.
rcat = kszx.sdss.read_randoms('CMASS_North')
rcat.apply_redshift_cut(0.43, 0.7)
kszx.sdss.read_mock(survey, mock_type, ix, dr=12, download=False)

Reads SDSS mock galaxy catalog, and returns a Catalog object.

Note that the qpm mocks are already restricted to an appropriate redshift range, i.e. there should be no need to call Catalog.apply_redshift_cut() (unlike the “core” SDSS galaxy/random catalogs).

Function arguments:

  • survey (str): either ‘CMASS_North’, ‘CMASS_South’, ‘LOWZ_North’, ‘LOWZ_South’.

  • mock_type (str): currently ‘qpm’ (DR12 only) and ‘pthalos’ (DR11 only) are implemented.

  • ix (integer): index of mock, in the range 0 <= ix < 1000, except for CMASS PTHALOS where the range is 0 <= ix < 600.

  • dr (integer): either 11 or 12.

  • download (boolean): if True, then all needed data files will be auto-downloaded.

Returns a kszx.Catalog object, with the following columns:

ra_deg, dec_deg, z,    # sky location, redshift
wveto                  # systematic weights
wfkp                   # FKP weight (available for QPM but not PTHALOS)
cboss, wcp, wzf        # PTHALOS only: completeness/systematics weights
ztrue                  # PTHALOS only: true redshift, removing peculiar velocities

Example usage:

# kszx.sdss.read_mock() returns a kszx.Catalog.
mcat = kszx.sdss.read_mock('CMASS_North', 'qpm', 0)   # index can be 0 <= ix < 1000
# mcat.apply_redshift_cut(0.43, 0.7) not needed!
kszx.sdss.read_mock_randoms(survey, mock_type, dr=12, download=False)

Reads SDSS mock random catalog, and returns a Catalog object.

Note that the qpm mocks are already restricted to an appropriate redshift range, i.e. there should be no need to call Catalog.apply_redshift_cut() (unlike the “core” SDSS galaxy/random catalogs).

Function arguments:

  • survey (str): either ‘CMASS_North’, ‘CMASS_South’, ‘LOWZ_North’, ‘LOWZ_South’.

  • mock_type (str): currently ‘qpm’ (DR12 only) and ‘pthalos’ (DR11 only) are implemented.

  • dr (integer): either 11 or 12.

  • download (boolean): if True, then all needed data files will be auto-downloaded.

Returns a kszx.Catalog object, with the following columns:

ra_deg, dec_deg, z   # sky location, redshift
wfkp                 # FKP weight

Example usage:

# kszx.sdss.read_mock_randoms() returns a kszx.Catalog.
mrcat = kszx.sdss.read_mock_randoms('CMASS_North', 'qpm')
# mrcat.apply_redshift_cut(0.43, 0.7) not needed!
kszx.sdss.read_mask(survey, dr=12, download=False)

Reads SDSS mangle mask, and returns a pymangle object. Rarely needed!

Function arguments:

  • survey (str): either ‘CMASS_North’, ‘CMASS_South’, ‘LOWZ_North’, ‘LOWZ_South’, ‘CMASSLOWZTOT_North’, ‘CMASSLOWZTOT_South’, ‘CLASSLOWZE2_North’, or ‘CMASSLOWZE3_North’.

  • dr (integer): either 11 or 12.

  • download (boolean): if True, then all needed data files will be auto-downloaded.

Returns a pymangle object that can be evaluated with mask.weight(ra_deg, dec_deg). The return value is either 0, or close to 1 (e.g. 0.98).

Note: requires pymangle! (Not a dependency by default.)

kszx.sdss.read_fits_catalog(filename, is_randcat, name=None, extra_columns=[])

Reads FITS file in SDSS catalog format.

Intended as a helper for read_galaxies() or read_randoms(), but may be useful elsewhere.

Function arguments:

  • filename (string): should end in .fits.

  • is_randcat (boolean): True for a random catalog, False for a galaxy catalog. (Determines which column names are expected).

  • name (str, optional): name of Catalog, passed to kszx.Catalog constructor.

  • extra_columns (list of string): extra columns to read (if any).

Returns a kszx.Catalog object.

kszx.sdss.download(survey, dr=12, mask=False, qpm=False, pthalos=False)

Downloads SDSS data products (galaxies, randoms, and optionally mocks + mangle mask) for a given survey.

Can be called from command line: python -m kszx download_sdss.

Function arguments:

  • survey (str): either ‘CMASS_North’, ‘CMASS_South’, ‘LOWZ_North’, ‘LOWZ_South’, ‘CMASSLOWZTOT_North’, ‘CMASSLOWZTOT_South’, ‘CLASSLOWZE2_North’, or ‘CMASSLOWZE3_North’.

  • dr (integer): either 11 or 12.

  • mask (boolean): if True, then mangle mask will be downloaded (in addition to galaxies and randoms).

  • qpm (boolean): if True, then QPM mocks will be downloaded (DR12 only).

  • pthalos (boolean): if True, then PTHALOS mocks will be downloaded (DR11 only).