BHM Ancillary Programs

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Summary

The BHM project has a number of ancillary spectroscopic programs, which provide scientifically interesting targets when BOSS fibers are not assigned to core science projects. These have the goal of obtaining redshifts and classifications for candidate QSOs and bright galaxies selected via wide-area optical/IR surveys. These supplementary programs do not affect the overall SDSS-V MOS survey plan (allocation of exposure resources across the sky).

Gaia-unWISE AGN survey

Sky map of Gaia-unWISE QSO target density
Sky density of Gaia unWISE QSO targets selected as candidates for observation in dark time (v0.5.3 targeting)

This BHM-led program collects BOSS spectroscopy for a large sample of candidate QSOs. We downselect targets suitable for SDSS-V spectroscopy from the parent sample presented by Shu et al. (2019), who used applied a machine-learning approach to a combination of the Gaia DR2 and unWISE catalogues. The Gaia-unWISE AGN targets are distributed across almost the entire sky (except for the innermost Galactic plane and regions around the Magellanic Clouds), and so are well matched to the SDSS-V all-sky survey strategy. This is primarily a discovery program, and so we have excluded AGN targets having existing good quality optical spectroscopy in earlier SDSS iterations.

Bright Low-Redshift Galaxy Survey

This program seeks to measure redshifts and provide classifications for a sample of optically bright, low-redshift, morphologically resolved galaxies, initially selected from LegacySurvey DR8 optical/IR catalogues, later updated to LegacySurvey DR10. This program is primarily intended as a filler, with no expectation of a high degree of spectroscopic completeness.

BHM Cartons for FPS Commissioning

In order to support FPS commissioning tests, we defined two cartons (manual_bhm_spiders_comm, manual_bhm_spiders_comm_lco) of X-ray selected targets having known redshifts. These targets were drawn from the eFEDS/SDSS-V sample presented by Aydar, et al (2025). This carton was used to check the ability of the whole SDSS-V system (telescope, FPS, spectrograph and data reduction pipelines) to collect reliable redshifts for SPIDERS-like targets.

Observational goals and requirements

The SDSS-V/BHM Ancillary projects seek to gather spectroscopic redshifts and classifications for large samples of candidate QSOs and galaxies.

These samples generally have only moderate surface density on the sky, and so benefit most from the widest area components of the SDSS-V survey.

Target selection and survey implementation

Further details of the algorithms and criteria used to select BHM ancillary target cartons are provided via the links below.

Targeting generations used in early FPS operations

The ‘v0.5.epsilon-7-core-0’, ‘v0.5.2’, ‘v0.5.3’, and ‘v0.5.5’ targeting generations were used during SDSS-V/FPS operations (2022-2023). These generations are identical from the point of view of BHM Ancillary program targeting. The ‘v1.0.2’, ‘v1.0.3’, ‘v1.0.4’, ‘v1.0.5’, ‘v1.0.5-boss-only’, and ‘dr20.manual’ targeting generations were used for SDSS-V/FPS operations (2023-2025). These generations are identical from the point of view of BHM Ancillary program targeting.

Below is a list of BHM Ancillary cartons that were considered (the carton names link to detailed descriptions):

Targeting generations used during the bulk of FPS operations

The ‘v1.0.2’, ‘v1.0.3’, ‘v1.0.4’, ‘v1.0.5’, and ‘v1.0.5-boss-only’ targeting generations were used during the bulk of SDSS-V/FPS operations (2023-2025) that are being released in DR20. The first three of these targeting generations are identical from the point of view of BHM Ancillary targeting. In the ‘v1.0.5’ and ‘v1.0.5-boss-only’ targeting generations we introduced additional shallower “*_d3” versions of GUA and Bright Galaxy cartons (where faint targets have lower exposure time requests). Below is a list of BHM Ancillary cartons that were considered during this phase:

Targeting generation used during SDSS-V plate operations

The ‘v0.plates’ targeting generation was used during the first year of SDSS-V operations at APO when the old plug plate system was still in place. We included early versions of the Gaia/unWISE AGN cartons during this phase.

Below is a list of BHM Ancillary cartons that were considered (the carton names link to detailed descriptions):

BHM-centric open fiber programs

A subset of the SDSS-V Open Fiber Program focus on BOSS (re-)observations of optical/IR/X-ray selected QSOs/AGN or other extragalactic targets, and so have strong overlap with BHM’s core science themes.

An initial set of six open fiber programs used from the start of FPS operations are listed below.

A further call for targets in June 2024 led to the following seven BHM-related openfiber cartons:

The Open Fiber programs were not used during the SDSS-V plate program.

Spectroscopic data released in DR20

The sky density of BHM GUA targets having at least one spectrum in DR20.
The sky density of BHM bright low-z galaxy targets having at least one spectrum in DR20.
The sky density of BHM-related openfiber targets having at least one spectrum in DR20.

The number of BHM Ancillary and BHM-centric open fiber program spectra in DR20 are given in the table below.

(First)Carton nameNdailyNepochNallepoch Unique targets
bhm_gua_dark1581191431218173484809
bhm_gua_bright53875508283158933020
bhm_colr_galaxies_lsdr828655237431630816893
openfibertargets_bhm_quaia_boss24920248892295723905
bhm_colr_galaxies_lsdr1019673188931411114137
bhm_gua_dark_d318475182831759317736
openfibertargets_nov2020_277373708745216563
openfibertargets_bhm_lofarradio_boss6000599838165913
openfibertargets_bhm_racsradio_boss3487347723633370
openfibertargets_nov2020_332338232117622136
openfibertargets_bhm_morexray_boss182217999031749
openfibertargets_nov2020_1810801046490940
openfibertargets_nov2020_1168267277649
bhm_colr_galaxies_lsdr10_d3230224214214
openfibertargets_bhm_hightderates_qbs_boss13212844127
openfibertargets_bhm_varagn_boss3030730
openfibertargets_bhm_hightderates_psb_boss2525725
openfibertargets_nov2020_261616816
Number of SDSS DR20 BOSS BHM Ancillary and Open Fiber spectra (per coadding scheme) associated with each carton (considering only the FIRSTCARTON label for each spectrum). Target uniqueness is determined via SDSS_ID.

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