SDSS-V: Pioneering Panoptic Spectroscopy

TL;DR

SDSS-V introduces a pioneering panoptic spectroscopic framework to map the Milky Way, Local Volume, and black hole populations through all-sky, multi-epoch MOS and wide-field IFU capabilities. By leveraging dual-hemisphere infrastructure and novel robotics, it enables continuous time-domain observations and high-resolution ISM mapping, integrating near-IR and optical data with existing missions like Gaia, TESS, and eROSITA. The project emphasizes open data, global collaboration, and a scalable path toward future LSST-like spectroscopic surveys. Its three mapper programs—Milky Way, Black Hole, and Local Volume—address core questions in stellar, galactic, and extragalactic astrophysics, providing transformative datasets for the coming decade.

Abstract

SDSS-V will be an all-sky, multi-epoch spectroscopic survey of over six million objects. It is designed to decode the history of the Milky Way, trace the emergence of the chemical elements, reveal the inner workings of stars, and investigate the origin of planets. It will also create an integral-field spectroscopic map of the gas in the Galaxy and the Local Group that is 1,000x larger than the current state of the art and at high enough spatial resolution to reveal the self-regulation mechanisms of galactic ecosystems. SDSS-V will pioneer systematic, spectroscopic monitoring across the whole sky, revealing changes on timescales from 20 minutes to 20 years. The survey will thus track the flickers, flares, and radical transformations of the most luminous persistent objects in the universe: massive black holes growing at the centers of galaxies. The scope and flexibility of SDSS-V will be unique among extant and future spectroscopic surveys: it is all-sky, with matched survey infrastructures in both hemispheres; it provides near-IR and optical multi-object fiber spectroscopy that is rapidly reconfigurable to serve high target densities, targets of opportunity, and time-domain monitoring; and it provides optical, ultra-wide-field integral field spectroscopy. SDSS-V, with its programs anticipated to start in 2020, will be well-timed to multiply the scientific output from major space missions (e.g., TESS, Gaia, eROSITA) and ground-based projects. SDSS-V builds on the 25-year heritage of SDSS's advances in data analysis, collaboration infrastructure, and product deliverables. The project is now refining its science scope, optimizing the survey strategies, and developing new hardware that builds on the SDSS-IV infrastructure. We present here an overview of the current state of these developments as we seek to build our worldwide consortium of institutional and individual members.

Figures (11)

• Figure 1: A schematic representation of SDSS-V: an all-sky, multi-epoch spectroscopic facility and its science programs. Survey operations will be carried out in two hemispheres, at Apache Point Observatory (APO) and Las Campanas Observatory (LCO). Multi-object fiber spectroscopy will be obtained with two 2.5m telescopes, each feeding a near-IR APOGEE spectrograph (300 fibers, $R \sim 22,000$) and an optical BOSS spectrograph (500 fibers, $R \sim 2,000$); this configuration enables a sky-survey rate of $\sim$40 deg$^2$ hr$^{-1}$. Ultra-wide field integral field spectroscopy will be performed mostly with smaller telescopes at these observatories, with $\sim$2,000-fiber bundles feeding three optical spectrographs in each hemisphere. This schematic also outlines the three primary science programs: the Milky Way Mapper, drawing on both APOGEE (red) and BOSS (blue) spectra; the Black Hole Mapper, acquiring BOSS spectra of fainter targets; and the Local Volume Mapper, performing IFU mapping of the ionized ISM in the MW and nearby galaxies.
• Figure 2: Evolution of SDSS on-sky target density: Left: SDSS-IV field map, in Galactic coordinates. The colored dots show regions of the sky targeted by SDSS-IV's MaNGA, eBOSS, and APOGEE-2 (orange) and APOGEE-2 only (yellow, green, and blue). There are no data where the background image is visible. Right: Density map of SDSS-V's spectroscopic targets (objects per square degree). The analysis of the data from the sparse but deep sampling provided by earlier generations of SDSS allows us to exploit new technologies and analysis techniques to cover the entire sky contiguously with spectra in SDSS-V.
• Figure 3: Evolution of SDSS in-plane Galactic target density: Midplane target surface density of the recent APOGEE DR14 catalog (left) and MWM's Galactic Genesis Survey (GGS; right). The maps show a face-on schematic of the Milky Way ( credit: NASA/JPL-Caltech/R. Hurt) beneath target density contours. The Sun is located 8 kpc from the center of the Galaxy, at ($X, Y = -8.0, 0.0$). Light gray contours show areas with observed/anticipated stars at surface densities $<$10 per (100 pc)$^2$; colored contours follow the colorbar. These contours only contain stars within 500 pc of the midplane, summing to $1.5 \times 10^5$ in APOGEE DR14 and $3.6 \times 10^6$ stars in GGS. For APOGEE, we show stars with distances reported in the APOGEE DR14 Distance Value Added Catalog, which represent $\sim$95% of all main survey targets. We note that ongoing APOGEE-2 observations will fill in the fourth quadrant of the Galaxy. Distance distributions for SDSS-V targets were calculated using a mock GGS observation of the Galaxia model of the MW Sharma2011 and a 3D extinction map Bovy2016.
• Figure 4: Stellar astrophysical targets in the MWM: The $(J-K)$ color and absolute $J$ magnitude of 0.001% of the $\sim$1 billion stars that Gaia will observe, color-coded by their expected ages based on a Besançon Galaxy model robinetal2003. The wide range of ages of the red giants provides a perfectly-suited exploration space for the MWM (Section \ref{['sec:mwm']}), given that we can determine their asteroseismic-calibrated ages. The luminous hot stars in the upper left ionize the gas seen by the LVM in the Milky Way (Section \ref{['sec:lvm']}), and the cool dwarfs on the lower right yield prime hunting ground for rocky planets in the habitable zone, whose host stars must be carefully characterized. The stars marked in bright colors represent those that are within 100 pc of the Sun and therefore part of the MWM's solar neighborhood census. The lowest-mass stars will be a major component of this census, especially since subsequent Gaia catalogs will have distances for much fainter stars than Data Release 1 does. The gray points with $M_J>10$ mark white dwarfs with Gaia DR1 distances; the number of these "cinders" of low-mass stars will increase by a factor of 10$^5$ as Gaia continues. With knowledge of the white dwarf initial mass-final mass relation, ages can determined for these as well.
• Figure 5: SDSS-V's stellar companion mass sensitivity: The minimum companion mass SDSS-V can detect in systems with a range of periods and primary masses, in the context of several scientifically interesting regimes. For example, the left-most region has a high minimum mass because systems there have undergone common envelope evolution, and there must be at least one white dwarf to survive. We have indicated the area where stars becoming red giants swallow their closest companions. Faint white dwarfs will need to have $\sim$15 km s$^{-1}$ RV variability to be detected by the optical BOSS spectrographs. This precision is well matched to the RV amplitudes of several 100 km s$^{-1}$ in double-white dwarf binaries. The "WD Line" shows the minimum mass of an unseen companion around a WD, and we can clearly detect neutron star and black hole companions out to a period of many months. The " Gaia Line" shows the minimum secondary mass detectable by Gaia around a 0.2 M$_{\odot}$ star at a distance of 250 pc. This illustrates how Gaia and SDSS-V complement each other: astrometry becomes increasingly powerful at long periods, spectra at short periods. Gray areas will be explored statistically, but we will not have full orbital information for systems in these regions.