Data Release 20 includes Local Volume Mapper (LVM) optical integral-field spectroscopic data products for six representative targets. These targets span three Galactic H II regions, one planetary nebula, and two nearby galaxies, and are intended to demonstrate the range of LVM science cases enabled by the survey.
DR20 substantially expands the LVM data released in DR19. DR19 included a single LVM optical IFU observation of the Helix Nebula. DR20 includes this target again, now as an updated version of the dataset, together with five additional targets: the Rosette Nebula, the Trifid Nebula, the Flame Nebula/Horsehead Nebula region, NGC 4945, and M33/NGC 598.
The DR20 LVM release includes data products from both the LVM Data Reduction Pipeline (DRP) (Mejía-Narváez et al., in prep.) and the LVM Data Analysis Pipeline (DAP) (Sánchez et al. 2025). The DRP products provide fully reduced, wavelength-calibrated, flux-calibrated, and sky-subtracted spectra for individual LVM exposures. The DAP products provide higher-level measurements derived from those spectra, including stellar-continuum modeling and emission-line measurements.
For DR20, LVM releases per-exposure DRP and DAP products, together with three summary files: drpall, dapall, and the LVM quality-control summary file. These summary files are the recommended starting point for identifying observations, locating data products, and selecting data according to quality information.
Access Options
LVM data products are available as flat files through the SDSS Science Archive Server (SAS). Each file type is described by an SDSS Data Model, which documents the FITS extensions, metadata, columns, units, and data-quality information.
Users planning to download large numbers of LVM files should begin with the summary files described below, and then use the corresponding SAS directories to retrieve the individual DRP or DAP products.
Per-exposure DRP Products
The LVM Data Reduction Pipeline produces the primary reduced spectroscopic products for each delivered exposure. The main DRP science product is the row-stacked spectrum file with datamodel lvm_sframe:
lvmSFrame-EXPNUM.fitswhere EXPNUM is the exposure number. Each lvmSFrame file contains the fully reduced spectra for the LVM science fibers, preserving the native fiber sampling of the instrument.
The DRP products released in DR20 were produced with DRP version 1.2.0. The individual DRP files and the corresponding DRP summary file are available from:
https://dr20.sdss.org/sas/dr20/spectro/lvm/redux/1.2.0
The DRP release includes 169 individual lvmSFrame files, one for each delivered exposure, together with the DRP summary file with datamodel drpall:
drpall-drpver.fitswith drpver = 1.2.0 for DR20.
The lvmSFrame files contain the sky-subtracted and flux-calibrated spectra, inverse variances, data-quality masks, wavelength information, line-spread function information, sky models, flux-calibration information, and the fiber mapping table.
Per-exposure DAP Products
The LVM Data Analysis Pipeline analyzes the reduced DRP spectra on a fiber-by-fiber basis. The DAP products provide measurements of the stellar continuum and ionized gas emission lines for each analyzed exposure.
The main per-exposure DAP file, with datamodel dap, follows the naming convention:
dap-rsp{#RSP}-sn{SN}-{EXPNUM}.dap.fitsFor example:
dap-rsp108-sn20-00030199.dap.fitscorresponds to an analysis using an RSP library with 108 templates, a minimum signal-to-noise threshold of 20, and the LVM exposure identified by the exposure number in the filename.
The DAP products released in DR20 use DAP version 1.2.0.251218. The individual DAP files and the corresponding DAP summary file are available from:
https://dr20.sdss.org/sas/dr20/spectro/lvm/analysis/1.2.0/1.2.0.251218
The DR20 LVM release includes 172 DAP files: 169 standard DAP files corresponding to the delivered DRP exposures, and three additional DAP files associated with the Local Volume galaxy analyses.
The DAP files include tables with the fiber positions, continuum-modeling results, RSP decomposition coefficients, parametric emission-line measurements, non-parametric emission-line measurements, quality metrics, and processing information.
In addition to the DAP-files, DR20 includes a corresponding spectral model file for each exposure. Model files, with datamodel dap_model, follow a similar naming convention as the DAP files:
dap-rsp{#RSP}-sn{SN}-{EXPNUM}.model.fits
For example:
dap-rsp108-sn20-00030199.model.fits
corresponds to the spectral models derived from the analysis of the same LVM exposure, using the same RSP library and signal-to-noise threshold. The model files are stored in the same directory as the DAP files.
Each model file is a 3D FITS cube containing 9 RSS slices distributed along the z-axis, each one covering the full LVM wavelength range (3600–9800 Å at 0.5 Å/pixel) for each of the 1754 good-quality science fibers. The 9 RSS slices store the observed spectrum, the best-fitting stellar continuum model, the joint stellar and emission-line models from both parametric fitting iterations, the gas-pure and gas-free spectra, and the non-parametric emission-line model, as described in the header and the DR20 article.
Summary Files
The LVM DR20 release includes summary files that provide convenient entry points to the DRP, DAP, and quality-control information. Users should consult these files before downloading large numbers of individual exposure products.
drpall
The drpall file, with datamodel drpall, summarizes the DRP products included in the release. It collects metadata for all reduced exposures and should be used to identify available lvmSFrame files.
drpall-drpver.fitsFor DR20, drpver = 1.2.0. The file is distributed with the DRP products at:
https://dr20.sdss.org/sas/dr20/spectro/lvm/redux/1.2.0
dapall
The dapall file, with datamodel dapall, summarizes the DAP products included in the release. It collects information for each analyzed science exposure, together with selected average properties across the LVM science field of view extracted from the individual DAP files.
dapall-drpver-dapver.fitsFor DR20, drpver = 1.2.0 and dapver = 1.2.0.251218. The file is distributed with the DAP products at:
https://dr20.sdss.org/sas/dr20/spectro/lvm/analysis/1.2.0/1.2.0.251218
Quality-control summary file
The LVM quality-control summary file, with datamodel qa_bitmasks, provides quality flags for the released exposures. These flags are distributed as a bitmask and are intended to help users identify potential issues before performing quantitative analysis.
qcall-drpver-dapver.fitsThe quality-control summary file is distributed with the DAP products at:
https://dr20.sdss.org/sas/dr20/spectro/lvm/analysis/1.2.0/1.2.0.251218
Users are strongly encouraged to consult these quality flags before performing quantitative analysis of the released LVM data products.
Local Volume Galaxy Products
For the Local Volume galaxy targets, the released DRP files preserve the foreground Milky Way contribution, as in the full LVM dataset. This foreground includes both stars and diffuse Galactic emission-line flux. Because the Milky Way interstellar medium is itself a primary science target of LVM, this component is not removed from the standard DRP products.
For the Local Volume targets, DR20 also includes experimental products in which a Milky Way foreground-subtraction procedure has been applied. These products with datamodels LV_dap and LV_dap_model, are distributed in the same analysis directories as the standard DAP products and follow the naming convention:
LV_dap-rsp108-sn20-EXPNUM.fitsThese experimental products are provided to allow users to evaluate the effect of the Milky Way foreground and to explore the intrinsic properties of the extragalactic targets.
Visual Access with LVMvis
LVMvis is an interactive, browser-based visualization tool for exploring LVM data products. It provides access to both DRP and DAP outputs through a unified interface, helping users identify available observations, inspect spectra, and assess data quality before downloading files for further analysis.
LVMvis is available at:
LVMvis can also be linked directly to a specific exposure and fiber. For example:
https://dr20.sdss.org/lvmvis/?expnum=4297&fiber=990
The interface includes a sky view of the LVM survey footprint, a pointings table with exposure metadata, and a spectral viewer showing the DRP spectrum together with DAP model components and residuals.
Getting Started
- Use
drpallto identify the reduced DRP exposures and correspondinglvmSFramefiles. - Use
dapallto identify the available DAP products and selected DAP-level measurements. - Consult the LVM quality-control summary file before selecting data for quantitative analysis.
- Download the individual DRP and DAP files from the SAS directories linked above.
- Use the SDSS Data Models to inspect the FITS structure, extensions, columns, and units.
- Use LVMvis for interactive exploration of the observations and spectra.