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Summary of BHM Time-Domain Spectral Programs

The BHM optical (BOSS) repeat spectral time-domain programs emphasize the astrophysics of quasars, including studies of BH masses, binarity, accretion and events, broad line region (BLR) dynamics, outflows, etc., requiring spectral sampling at a broad range of timescales/cadence, ranging from days to decades; this is achieved via several tiers.

AQMES (All-Quasar Multi-Epoch Spectroscopy)

The AQMES core program includes both a wide-area and low-cadence tier, and a modest-area and modest cadence tier, adding new epochs in SDSS-V to quasars/AGN also with at least one previous epoch of SDSS I to IV spectra, e.g., selected mainly from the DR16 quasar catalog (Lyke et al., 2020) :

  • AQMES-WIDE: For >20,000 quasars, ≧ 2 epochs will be added during SDSS-V, and combined with earlier-epoch SDSS spectra, sampling ~1-10 yr timescales, e.g., to probe the BLR dynamics of the most massive BHs, statistics of changing look quasars, broad absoprtion line (BAL) disappearance/emergence, etc. (this is a wide area, but low-cadence time-domain tier; ≳2000 deg2).
  • AQMES-MEDIUM: For >2000 quasars, ~10 epochs added in SDSS-V, probing down to ~1-month to 1-year timescales, adding unfolding BLR structural and dynamical changes (a medium tier in area and cadence; ≳200 deg2).

In addition, non-core programs will repeatedly observe fainter QSOs within the dedicated AQMES-Wide and AQMES-Medium fields, as well as opportunistically targeting known QSOs outside of that area, where fiber-resources permit.

For more details please see the dedicated AQMES page.

RM (Reverberation Mapping)

  • Reverberation Mapping (RM; another core BHM program) aims — for >1000 quasars in 4-5 dedicated fields — to obtain optical (BOSS) repeat spectra with a high-cadence of >102 epochs, sampling down to days to weeks. The lags between the continuum and BLR emission yield BH masses, advancing RM measures to a broad range of luminosity and redshift (a small area, but high-cadence tier; ~30 deg2).

For more details please see the dedicated Reverberation Mapping page.

TierNo. of ~15 min BOSS
exposures per epoch
(mag limits)		Approx no.
of epochs
to be obtained		Approx. no.
of fields		Approx. total
no. of targets
AQMES
WIDE		4 (i<19.1)>2~400-600
(mainly North)		~20,000
AQMES
MEDIUM		4 (i<19.1)>10~35-60
(mainly North)		~2000
RM8 (i<~21)~1744-5
(North+ South)		~1000
The repeat spectroscopy time-domain (TD) component of BHM is mainly in the North, as the AQMES core and AQMES-related ancillary programs rely strongly on the DR16 quasar catalog (latter depicted in the red/magenta regions of the map above). The RM fields (5 small fields shown in dark blue) are mainly North or equatorial, but also in the South. The eROSITA-DE region is South of the green triangles (and the red region highlights the parent overlap region at high-Galactic latitude between DR16 quasars and eROSITA-DE).

Summary of BHM X-ray Source Counterpart Follow-up Programs

BHM optical (BOSS) spectroscopic follow-up of X-ray sources include a large core program (SPIDERS) relying on eROSITA X-ray data , and a more modest program relying on Chandra archival X-ray data.

SPIDERS (SPectroscopic IDentfication of ERosita Sources)

The main goal of the core SPIDERS (more formally the SPIDERS II) program is to provide a complete and homogeneous optical spectroscopic followup of X-ray sources (both point-like and extended) detected by eROSITA (in ~ 10,000 deg2 at high-Galactic latitude, within the German or ‘DE’ half of the sky). SPIDERS uses X-ray data from eROSITA’s first 1.5 years of operation, which began in 2019 (emphasizing eFEDS mini-survey spectroscopic follow-up in DR18, and eRASS:3 all-sky follow-up data later in SDSS-V).

  • SPIDERS in BHM in its wide-area survey, utilizing data through eRASS:3 (first 3 eROSITA all-sky scans), aims to obtain the optical spectroscopic identifications and redshifts, evolution, and astrophysics of ~300,000 X-ray source counterparts, especially AGN (but also including ~104 X-ray emitting clusters of galaxies, and X-ray emitting stars).
  • This program (beginning in SDSS-IV and finishing in SDSS-V) has largely completed BOSS spectroscopy for ~104 candidate counterparts in the eFEDS mini-survey (140 deg2) region of the sky, and these BHM/SPIDERS optical spectra in eFEDS are a centerpiece of the DR18 data release.

There are also several SPIDERS-driven non-core programs, primarily intended to expand the footprint of the SPIDERS survey area, and implemented by exploiting somewhat lower quality optical imaging data.

ComponentNo. of ~15 min BOSS
exposures per epoch
(mag limits)		Approx no.
of epochs
to be obtained		Approx. no.
of fields		Approx. total
no. of targets
SPIDERS
(main)		3-4 (i<21.5)~1~600 (N) +
~2800 (S)		>250,000
eFEDS~4 (i<21.5)~1~37?
(equatorial)		>10,000
For the BHM SPIDERS program of optical follow-up spectroscopy of eROSITA-DE X-ray sources, this equatorial map shows the anticipated density of eRASS: 3 sources at high Galactic latitude. This portion of the sky is mainly in the South, though CSC follow-up is both North and South.

For more details please see the dedicated SPIDERS page.

CSC (Chandra Source Catalog)

A related, more modest, program of mainly optical (BOSS) spectroscopy of X-ray counterparts (but including some IR APOGEE spectra as well), involves tens of thousands of X-ray source counterparts selected from the Chandra Source Catalog.

For more details please see the dedicated CSC page.

BHM Ancillary programs

In order to usefully use spare BOSS fiber-hours, the BHM team have devised two filler programs, targeting optical/IR selected QSOs and low redshift galaxies. These are described in more detail on the Ancillary Programs page.

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