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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: 2023-07-13
Primary Reference(s): Zheng et al. (2019)

Citations: See ADS Statistics


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


July 13, 2023

A list of QSOs below had incorrect grating information in their FITS header with two gratings (G130M and G160M), while their filename represents a single grating. They are now appropriately fixed with a single grating corresponding to the grating in the filename.

2XMM-J141348.3+440014,  J110631.05+351051.3,  MRK304,  PG1435-067,  Q2135-145,  SDSSJ085259.22+031320.6, H1821+643, J142127.85+473011.7, PG1126-041, Q0850+440, QSO-B1124+271


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 PNG previews of continuum normalized lines as well as the corresponding continuum normalization process for each line. 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. 

Description Of Data Products

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-p265" or sdssj004222.29-m103743.8. Note that '+' is replaced with 'p' and '-' is replaced with 'm' in the middle of numbers in the file name.
  • <filter> = filter(s) used, can be "21cm", "g130m", or "g160m", if multiple used, they are combined with a hyphen (e.g., "g130m-g160m")
  • <ext> = product type, can be one of:
    • <line>-spec.fits = spectrum FITS file for this line, e.g., "c-ii-1334-spec.fits"
    • <line>-spec.png = spectrum preview file for this line, e.g., "c-ii-1334-spec.png"
    • 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.png = spectrum preview file for the HI 21 cm line at a 1-degree beam size
    • h-i-21cm-spec-multibeam.png = 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 prioritizes particular absorption line regions in this database
    • stackspec.png = preview of full spectrum, including multiple spectral line regions

The QSO catalog is named "hlsp_cos-gal_hst_cos_qsos_multi_v1_list.fits".

Data Access

The QSO catalog can be downloaded directly: hlsp_cos-gal_hst_cos_qsos_multi_v1_list.fits

Individual QSO spectra are 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) and via the direct download table below. Set the Provenance Name filter to COS-GAL in the Portal Advanced Search to find all or individual spectra. Each Portal observation contains COS UV data and 21 cm emission line data as minimum recommended products (MRP). To retrieve the preview spectral images of QSOs, select the observations of interest, add them to the download basket, and uncheck MRP in the Download Manager. The spectra can also be retrieved programmatically using the astroquery—mast module. See the code example below for retrieving and downloading all files. 

from astroquery.mast import Observations
all_obs = Observations.query_criteria(provenance_name="cos-gal")
data_products = Observations.get_product_list(all_obs)



  • A web-based interface for cross-mission searches of data at MAST or the Virtual Observatory
  • Search for and retrieve COS-GAL 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.

Additional References