Tests of ELG target selection algorithms
Pilot study of emission line galaxies based on selection from multiple imaging programs.
Contact
| Anand Raichoor |
|---|
| Ecole polytechnique federale de Lausanne (EPFL) |
| anand.raichoor@epfl.ch |
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
