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Mission Overview

Plane Quasar Survey (PQS)


Primary Investigator: Jessica Werk

HLSP AuthorsJessica Werk, Kirill Tchernyshyov, Hannah V. Bish, Yong Zheng, Mary Putman, David Schiminovich, Joshua E. G. Peek

Released: 2024-06-10

Updated: 2024-06-10

Primary Reference(s): Werk et al. 2024

DOI: 10.17909/86my-mr86

Citations: See ADS Metrics
UV-bright QSO All-Sky Distribution:  An all-sky Aitoff projection in Galactic coordinates, centered at b = 0 degrees, l = 180 degrees showing the distribution of different UV-bright QSO samples, including the Plane QSO candidates (dark and light purple shapes).  For orientation within this frame of reference, the underlying gray map shows high-velocity |vLSR| > 80 km/s HI detected in 21-cm emission from the HI4PI Survey, generally with NHI > 10^18 cm^-2.  The black circles show the 401 archival QSO sightlines with high-resolution HST/COS spectra from the COS-GAL database, and the gray plusses show all the confirmed AGN from the UVQS Survey, including those that were previously identified by the Milliquas Survey. Purple diamonds highlight the spectroscopically-confirmed low-latitude QSOs, which fill a gap in the existing datasets. The 12 purple stars show objects in our candidate list that were confirmed stellar sources, and the light purple x's are targets from our candidate list that have not yet been observed.


The Plane Quasar Survey (PQS) is a sample of 305 QSO candidates having |b| < 30 degrees, the majority with GALEX magnitudes NUV < 18.75. To generate this sample, the team applies a UV-IR color selection criteria to photometric data from the Ultraviolet GAlactic Plane Survey (UVGAPS) as part of GALEX-CAUSE, the Million Quasars Catalog, Gaia DR2, and Pan-STARRS DR1. 165 of these 305 candidate UV-bright AGN (54%) have published  spectroscopic redshifts from 45 different surveys, confirming them as AGN. The team further obtained low-dispersion, optical, longslit spectra with the APO 3.5-m, MDM 2.4-m, and MDM 1.3-m telescopes for 84 of the candidates, and confirm 86% (N = 72) as AGN, generally with z < 0.6. These sources fill a gap in the Galactic latitude coverage of the available samples of known UV-bright QSO background probes.   Along with a description of the confirmed QSO properties, the team provides the fully-reduced, flux and wavelength-calibrated spectra of 84 low-latitude QSOs through the Mikulski Archive for Space Telescopes.  Future HST/COS spectroscopy of these low-Galactic-latitude QSOs has the potential to transform our view of the Milky Way and Local Group circumgalactic medium. 

Data Products

The full PQS collection consists of 1 summary catalog and 82 spectra files. 

Data file types:

_1dspec.fits The 1D reduced, wavelength and flux-calibrated spectra are provided for each PQS target we observed with the APO 3.5-m, the MDM 2.4-m, or the MDM 1.3-m. All wavelengths are corrected to a vacuum, heliocentric rest frame.
_catalog.fits The summary catalog containing metadata for each source


Spectrum Files

Each spectrum file is provided with the following file naming convention:



  • <telescope> is the telescope used for observations (APO or MDM)
  • <instrument> is the corresponding instrument used (DIS or OSMOS) 
  • <target_name> is the identifier for each target
  • <filter> is the name of the filter used in observations.

Summary Catalog

The summary catalog named hlsp_pqs_multi_multi_alltargets_spectral_v1_catalog.fits contains the full PQS catalog, with the following columns. These fields are described in full text of the PQS First Data Release Paper

  • RAJ2000: Right ascension coordinate in J2000
  • DECJ2000: Declination coordinate in J2000
  • GLON: Galactic Longitude
  • GLAT: Galactic Latitude
  • NUVMAG: GALEX NUV magnitude
  • NICKNAME: Alternate target name
  • W1MAG: WISE W1 magnitude
  • W2MAG: WISE W2 magnitude
  • SPECTYPE: Spectrally determined source type: star, AGN, etc.
  • TELESCOPE: Telescope used for observation
  • ZNARROW: Redshift estimated by narrow emission lines
  • SAMPLE: Identifier for the photometric selection technique
  • SPECFILE: File name of spectrum
  • HLSPTARG: Target name
  • ZARCHIVAL: Redshift from previous literature
  • SIMBADNAME: Alternate target name from SIMBAD


Data Access

The summary catalog and spectral files can be downloaded directly from the table below. The spectra bundle contains 82 files which are 50-100 KB each.

Description Files Size
Summary Catalog


76 KB
Spectra Bundle


3.0 MB

MAST Portal and Astroquery

The PQS data products are also available in the MAST Portal (web-based, cross-mission search interface) and Astroquery (Python package to search for and download files from Python scripts you write). In the MAST Portal, set the Provenance Name filter to "PQS" in an Advanced Search to find these data. In Astroquery, the following example code demonstrates how to search for and download these products:

from astroquery.mast import Observations
# Search for all PQS products
all_obs = Observations.query_criteria(provenance_name="pqs")
data_products = Observations.get_product_list(all_obs)
# Download data
  • A web-based interface for cross-mission searches of data at MAST or the Virtual Observatory
  • Search for and retrieve PQS data products programmatically.


Please remember to cite the appropriate paper(s) below and the DOI if you use these data in a published work. 

Note: These HLSP data products are licensed for use under CC BY 4.0.