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Mission Overview

Cosmic Origins Spectrograph Quasar Database for Galactic Absorption Lines (COS-GAL)

Primary Investigator: Yong Zheng
HLSP Authors: Yong Zheng
Released: 2019-03-12
Updated: 2019-03-12
Primary Reference(s): Zheng et al. (2019)

Citations: See ADS Statistics


A selection of QSO Si IV doublets, from Zheng et al. (2019).


COS-GAL provides continuum normalized spectra for 401 QSOs that were made publicly available by the Hubble Spectroscopic Legacy Archive (HSLA; Peeples et al. 2017) as of February 2017. It focuses on a number of Milky Way absorption lines, including SII 1250/1253/1259, SiII 1190/1193/1260/1526, SiIII 1206, SiIV 1393/1402, CIV 1548/1550, PII1152, FeII1142/1143/1144/1608, and CII 1334. The spectra are observed using HST G130M and/or G160M gratings by various COS programs on MAST. When available, COS-GAL also provides corresponding HI 21 cm emission lines from HI4PI (HI4PI Collaboration), LAB (Kalberla et al. 2005), and GALFA-HI (Peek et al. 2018).  A catalog of QSO IDs, coordinates, and redshifts based on SIMBAD is also included. For each target, COS-GAL provides FITS files and PDF previews of continuum normalized lines (see files under "FullSpec" category) as well as corresponding continuum normalization process for each line (see files under "Preview Plots" category). COS-GAL is useful for preliminary studies of absorption lines from Milky Way interstellar and circumgalactic media. Users interested in detailed analyses of the provided spectra should inspect the continuum normalization file of each line before use. Any questions or feedback on COS-GAL are welcome. The PI can be reached at

Description Of Data Products

With the exception of the QSO catalog, each file is located under a subdirectory called "spectra/<target>/", where <target> is the object name in lowercase.  Each file is named with the following convention:



  • <tel> = telescope(s) used, can be "hst", "galfahi", "hi4pi", or "lab", if multiple used they are combined with a hyphen (e.g., "lab-hi4pi-galfahi")
  • <ins> = instrument(s) used, can be "cos", "galfahi", "hi4pi", or "lab", if multiple used they are combined with a hyphen (e.g., "lab-hi4pi-galfahi")
  • <target> = name of the target, e.g., "pg-1407+265"
  • <filter> = filter(s) used, can be "21cm", "g130m", or "g160m", if multiple used they are combined with a hyphen (e.g., "g130m-g160m")
  • <exten> = product type, can be one of:
    • <line>-spec.fits = spectrum FITS file for this line, e.g., "c-ii-1334-spec.fits"
    • <line>-spec.pdf = spectrum preview file for this line, e.g., "c-ii-1334-spec.pdf", a png version is also available
    • h-i-21cm-spec-beam<size>deg.fits = spectrum FITS file for the HI 21cm line at a beam size specified by <size>, which is one of "0.067", "0.270", or "1.000".
    • h-i-21cm-spec-beam<size>deg.pdf = spectrum preview file for the HI 21 cm line at a 1-degree beam size, a png version is also available
    • h-i-21cm-spec-multibeam.pdf = spectrum preview file for the HI 21 cm line combining all beam sizes
    • fullspec.fits = FITS file containing the full spectrum, including original coadded spectrum from HSLA, and continuum normalized spectrum that prioritize particular absorption line regions in this database
    • stackspec.pdf = preview of full spectrum, including multiple spectral line regions

The QSO catalog is named "hlsp_cos-gal_hst_cos_qsos_multi_v1_list.fits" and resides at the same level as the "spectra/" directory.

Data Access

Visit the data table to access the COS-GAL spectra and plots.  You can also download the QSO catalog from there, or directly from this link.


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.

Additional References