NYU Value-Added Galaxy Catalog
K-corrections
We include K-corrections for each object; if there is no measured redshift,
zero redshift is assumed, and the K-correction value should be
ignored. The files are in the $VAGC_REDUX/kcorrect subdirectory with
the naming convention:
kcorrect.[collision_type].[flux_type].z[band_shift].fits
where:
- collision_type: What is done with redshifts that are
not obtained due to fiber collisions. Options are
- "none": nothing, they are left unfixed
- "nearest": the nearest galaxy neighbor with a redshift (within
groups defined with a 55'' linking length)
- "photoz": the nearest galaxy neighbor, but only if the photo-z of
the fixed galaxy is within 0.05 of the neighbor
- flux_type: Which flux is used. Possibilities are:
- "petro": SDSS Petrosian magnitudes
- "model": SDSS model magnitudes
- band_shift: Blue-shift of band-passes that K-corrections
correct to.
The K-corrections are performed using the kcorrect
product version v4_1_4.
Note that the AB magnitudes referred to here differ from the
pipeline magnitudes output by the SDSS pipelines, as described at the
kcorrect page (look under "A Note on the Absolute Calibration of
SDSS Magnitudes").
The FITS file contains 5 columns:
- RA, DEC: J2000 coordinates
- ABMAGGIES[8]: extinction-corrected AB fluxes in maggies for
ugrizJHK
- ABMAGGIES_IVAR[8]: inverse variances for the fluxes
- Z: redshift used
- KCORRECT[8]: ugrizJHK K-corrections
- ABSMAG[8]: ugrizJHK absolute magnitudes (uses h=1)
- ABSMAG_IVAR[8]: ugrizJHK absolute magnitude inverse
variancess
- COEFFS[5]: best fit coefficients for templates from
kcorrect.
- MTOL[8]: mass-to-light ratios in all 8 bands
- MASS: estimate of current stellar mass (uses h=1)
- INTSFH: integral of star-formation history (uses h=1)
- METS: average metallicity from template fits
- B300: specific star-formation rate over pass 300 Myrs
- B1000: specific star-formation rate over pass Gyr
Please take the metallicities and specific star-formation rates
with a grain of salt, as explained in the kcorrect paper.
Maggies are the ratio of the
source to the AB standard source in each band. To relate these
quantities to magnitudes, an object with total flux f in nMgy
has magnitude
m = − 2.5 log
10 f .
Note that in DR4 and previous, the units in this file were
in nMgy (nano-maggies), and the K-corrections were calculated with
version v3_4.
The K-corrections are defined such that the following formula
holds:
m = M + 5 log
10 [DL/10 pc] +K .
The absolute magnitudes in the file use a distance modulus
assuming H_0 = 100 km/s/Mpc, a matter density of 0.3, and a
cosmological constant of 0.7.
NYU Value-Added Galaxy Catalog