The catalog of galaxy shapes measured using the re-Gaussianization technique and the associated weight factors and calibrations derived from image simulations (Mandelbaum et al. 2018b). This shape catalog can be used for weak lensing science cases. The shape catalog is based on the intermediate data release S16a (which is also being made public as part of PDR2). The shape catalog and the associated calibrations consists of a subset of galaxies that satisfy the weak lensing flag as described in the shape catalog paper (Mandelbaum et al. 2018a). The shapes should be cross-matched to the positional catalogs using object_id in the S16a_wide2 database. Note that this catalog uses the Sirius star mask which is the same one as employed in Mandelbaum et al (2018a).
Obtaining a weak lensing shape catalog
Use this sql query to obtain the shape catalogs for the different fields:
select b.*, c.ira, c.idec, a.ishape_hsm_regauss_e1, a.ishape_hsm_regauss_e2 from s16a_wide.meas2 a inner join s16a_wide.weaklensing_hsm_regauss b using (object_id) inner join s16a_wide.meas c using (object_id) -- Uncomment the specific lines depending upon the field to be used -- where s16a_wide.search_xmm(c.skymap_id) -- where s16a_wide.search_wide01h(c.skymap_id) -- where s16a_wide.search_vvds(c.skymap_id) -- where s16a_wide.search_hectomap(c.skymap_id) -- where s16a_wide.search_gama15h(c.skymap_id) -- where s16a_wide.search_gama09h(c.skymap_id)
This should give a list of columns for each field separately:
- ira, idec: RA and DEC of the object
- object_id: object_id to be cross matched to get photometric redshifts.
- ishape_hsm_regauss_e1/2: Galaxy distortion (e1, e2) in sky coordinates
- ishape_hsm_regauss_derived_sigma_e: per-component shape measurement uncertainty
- ishape_hsm_regauss_derived_rms_e: per-component RMS ellipticity estimate
- ishape_hsm_regauss_derived_weight: Weight factor to be used for lensing calculations, corresponding to inverse variance weighting based on shape uncertainty
- ishape_hsm_regauss_derived_shear_bias_m : Multiplicative bias factor effectively averaged over components
- ishape_hsm_regauss_derived_shear_bias_c1/2: Additive bias factor with a value for each component
Computing a weak lensing signal
The shape distortions (with |e| = (1-q^2) / (1+q^2), q denotes the axis ratio) need to be used to construct an ensemble shear estimator. The full process for deriving the ensemble shear estimator is given in appendix A3.1 of the shape catalog paper. The appendix includes equations and the correspondence between the quantities in equations and catalog columns.
Note that, whether you are using point photometric redshift estimates or full photometric redshift PDFs, you should apply corrections for the inaccuracies of the photometric redshifts, or for dilution factors. When using the point estimates, you need to correct the dilution effect following the prescription described in Section 7.1 in Nakajima et al. (2012). When using the full PDFs, you can take into account the dilution effect by following Section 3.1 in Miyatake et al. (2019). You can download the full PDFs for each tract from the following link:
Note that you need to type in your username and password to access these files. For the definition of redshift bins of P(z), you need to use pz_pdf_bins_[photo-z].fits in
The column “BINS” is the center of redshift bins for ephor, mizuki, and mlz, and the point where PDF is evaluated for frankenz.
The publication describing a catalog of COSMOS photometric redshifts reweighted to mimic the weak lensing selected galaxies is in preparation. This catalog can be used to correct for systematic issues with the HSC photometric redshift distributions. This catalog can be found on the page below.
The selection of galaxies used to measure the weak lensing signal is expected to be affected by selection biases. The measured signal can be corrected for these selection biases (see Sec 5.6 from Mandelbaum et al. 2018b).
There is also a correction to the shear responsivity due to the dependence of the intrinsic ellipticity variation on redshift that needs to be applied for galaxies between 1<z<1.5 (see Section 5.3 in Mandelbaum et al. 2018b).
Weak lensing systematics
The systematics of the weak lensing tests have been checked and reported in the shape catalog paper. In short, we have checked that PSF determinations is accurate enough for cosmological constraints either from cosmic shear or from a combined galaxy-galaxy clustering and lensing analysis. We have also checked the shape catalog passed a number of null tests such as the B-mode test, random point test, and mass map test, after the multiplicative and additive bias corrections are applied (see Oguri et al. 2018 as well).
NEW: Shape catalog calibration code
Upon request from the community, we make our code to produce the S16A shape catalog calibrations available here.