Tests of ELG target selection algorithms

Pilot study of emission line galaxies based on selection from multiple imaging programs.

Contact

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Anand Raichoor
Ecole polytechnique federale de Lausanne (EPFL)

Tests of ELG target selection algorithms

To optimize the selection algorithm for the eBOSS emission line galaxy (ELG) program, spectroscopic targets were selected in a series of small pilot surveys based on data from several imaging surveys. A portion of these spectra are found in interpretative catalogs at the CDS here. The pilot program informed the final selection algorithm for the eBOSS ELG cosmological program. The catalog for targets is found in the value-added catalog.

Finding Targets

An object whose EBOSS_TARGET2 value includes one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS bitmasks to learn how to use these values to identify objects in this ancillary target program.

Program (bit name) Bit number Target Description Unique Primary Objects
ELG_SCUSS_TEST1 40 “SCUSS selection for test1 ELG plates” 1107
ELG_DES_TEST1 41 “DES selection for test1 ELG plates” 4021
ELG_DESI_TEST1 42 “DESI selection for test1 ELG plates” 3554
ELG_SDSS_TEST1 43 “SDSS-only selection for test1 ELG plates” 1857
ELG_UGRIZW_TEST1 44 “WISE selection for test1 ELG plates” 892
ELG_UGRIZWbright_TEST1 45 “WISE selection for test1 ELG plates” 183
ELG_GRIW_TEST1 46 “WISE selection for test1 ELG plates” 733
ELG_DECALS_TEST1 47 “DECALS ELG selection” 6235

Description

The first series of observations were designed to test selection algorithms using different imaging samples and different selection techniques. These targets are found on plates 8123-8130, 8355-8356, and 8763-8769. In addition to the EBOSS_TARGET2 values found in the table above, they are generally identified in the EBOSS_TARGET1 bitmask under bit 40 with the name ELG_TEST1. The last set of pilot observations are found on plates 8954-8958 and 9003. They do not have corresponding EBOSS_TARGET2 values and are identified in the EBOSS_TARGET1 mask by either bit 41 (ELG1_EBOSS) or bit 42 (ELG1_EXTENDED). There are 4741 targets that were observed under the ELG1_EBOSS flag and 659 targets observed under the ELG1_EXTENDED flag.

Caveats

None of the plates described above were used to contribute to the final ELG catalog of clustering objects, although much of the area was used in the final ELG footprint and a significant number of targets also satisfy the final ELG selection criteria.
Due to a proper motion bug, the fibers assigned to ELG targets on plates 8763-8769 were offset relative to the guide fibers, thus causing a significant reduction in throughput, flux calibration, and overall data quality.

REFERENCES

Raichoor, A., et al., 2016, A&A, 585, 50
Comparat, J., et al., 2016, A&A, 592, 121
Raichoor, A., et al., 2017, MNRAS, 471, 3955