LVM color HiPS map

The LVM RGB HiPS map is an SDSS-V visualization-only Value Added Product whose observational coverage extends beyond the DR20 spectroscopic release. It provides a fast, browser-based preview of LVM sky coverage and emission-line morphology before users work with released spectra or pipeline products. Explore the map through the LVMvis DR20 interface; additional usage guidance is available on the LVMvis documentation page. In LVMvis, the layer is listed as LVM RGB Halpha – [SII] – [OIII] and can be displayed together with LVM pointings, tile footprints, and individual fiber positions.

Important note: The RGB HiPS map is a visualization preview, not a quantitative science product. It should not be used for measurements or standalone physical classification. Individual emission-line fluxes are mapped into color channels using flux cuts and an asinh stretch to preserve visibility across a wide dynamic range, from faint diffuse emission to bright nebular regions. Displayed colors should therefore be interpreted only as a qualitative guide to morphology and relative line structure.

Some regions of the RGB map show artifacts associated with known limitations in the underlying observations or data processing. These artifacts are especially visible in faint or sparsely sampled regions, where the adopted intensity stretch emphasizes low-level background variations and gaps in the sampling. They should not be interpreted as astrophysical structures; see the LVM Caveats page for relevant data-quality caveats.

HiPS Format

HiPS, or Hierarchical Progressive Survey, is an astronomical data format and IVOA standard for serving sky maps as multi-resolution tiles. A HiPS dataset is organized on the sphere using the HEALPix pixelization scheme, allowing compatible clients to progressively load only the tiles needed for the current field of view and zoom level. This makes it possible to browse very large astronomical maps interactively, from wide-area survey context down to local structure, without downloading the full dataset at once.

For the technical description of the format, see Fernique et al. (2015), Hierarchical Progressive Surveys.

Color Mapping

The LVM RGB HiPS map combines three optical nebular emission-line maps from three ions into a color composite:

Together, the three channels highlight shells, filaments, ionization fronts, and other large-scale variations in emission-line morphology. Because the displayed colors depend on the underlying line ratios, flux cuts, and stretch, they should guide visual exploration rather than physical classification.

Access and Interoperability

The recommended way to explore the map is through LVMvis, where the RGB HiPS layer can be viewed alongside LVM pointings, tile footprints, and individual fiber sky positions. This provides survey-level context for identifying observed regions, inspecting fiber locations, and selecting spectra associated with visually interesting emission-line structures. Additional guidance is available on the LVMvis documentation page.

Although the map is primarily presented through LVMvis, it is a standard HiPS image layer and can also be loaded by compatible HiPS clients such as Aladin Lite, Aladin Desktop, or other HiPS-aware visualization tools, provided that the LVM RGB HiPS root on the SDSS Science Archive Server (SAS) is accessible.

As part of the broader HiPS ecosystem, the LVM RGB map can be compared directly with imaging surveys at other wavelengths available through the CDS public HiPS list aggregator, and Aladin clients.

Data Coverage and Status

The current RGB HiPS map is based on LVM observations obtained before MJD 61086, corresponding to 2026-02-15. This temporal coverage extends significantly beyond the dataset released as part of SDSS-V DR20. The spectra observed in the HiPS map footprint will be released in future data releases (see the Collaboration page for information on joining SDSS-V and gaining early access).

Future SDSS-V data releases are expected to include quantitative HiPS maps in FITS format based on LVM Data Analysis Pipeline (DAP) products. Those released products will support measurements from individual emission-line maps; the current RGB visualization does not.

A detailed description of the HiPS construction — from the aggregation of emission-line measurements and treatment of overlapping fiber coverage through HiPS tiling and final RGB rendering — will be presented in Katkov et al. (in prep.).

Further Reading

For more information about LVM, see the LVM page and the LVM overview paper by Drory et al. (2024). For broader context on SDSS-V as a whole, see the SDSS-V overview paper by Kollmeier et al. (2026).