HETDEX-LOFAR Spectroscopic Redshift Catalog

We combine the power of blind integral field spectroscopy from the Hobby-Eberly Telescope (HET) Dark Energy Experiment (HETDEX) with sources detected by the Low Frequency Array (LOFAR) to construct the HETDEX-LOFAR Spectroscopic Redshift Catalog. Starting from the first data release of the LOFAR Two-metre Sky Survey (LoTSS), including a value-added catalog with photometric redshifts, we extracted 28,705 HETDEX spectra. Using an automatic classifying algorithm, we assigned each object a star, galaxy, or quasar label along with a velocity/redshift, with supplemental classifications coming from the continuum and emission line catalogs of the internal, fourth data release from HETDEX (HDR4). We measured 9,087 new redshifts; in combination with the value-added catalog, our final spectroscopic redshift sample is 9,710 sources. This new catalog contains the highest substantial fraction of LOFAR galaxies with spectroscopic redshift information; it improves archival spectroscopic redshifts, and facilitates research to determine the [O II] emission properties of radio galaxies from 0.0 < z < 0.5, and the Lyα emission characteristics of both radio galaxies and quasars from 1.9 < z < 3.5. Additionally, by combining the unique properties of LOFAR and HETDEX, we are able to measure star formation rates (SFR) and stellar masses. Using the Visible Integral-field Replicable Unit Spectrograph (VIRUS), we measure the emission lines of [O III], [Ne III], and [O II] and evaluate line-ratio diagnostics to determine whether the emission from these galaxies is dominated by AGN or star formation.

The catalog is comprised of one FITS file with two extensions:

• No. 0 (1036, 28705): The first extension contains the spectrum, of length 1036, for each object. The corresponding wavelength values range from 3470 - 5540 angstroms.
• No. 1 (28705 rows x 13 columns): The second extension contains the derived values found for each source. The table below describes each column:

  COLUMN NAME	DESCRIPTION	DATA TYPE
  objID	LoTSS Object ID	string
  source_name	Source Name	string
  RA	PanSTARRS1 Right Ascension (J2000)	float
  Dec	PanSTARRS1 Declination (J2000)	float
  z_diagnose	Best fit redshift from Diagnose	float
  z_hdr4	Best fit redshift from ELiXer	float
  z_archive	Spectroscopic redshift from value-added LoTSS catalog	float
  z_best	HETDEX-LOFAR redshift	float
  z_best_src	1 = Diagnose, 2 = HDR4, 3 = Archive	integer
  classification	STAR, AGN, LOWZGAL, HIGHZGAL, or ARCHIVE	string
  log_mass	MCSED derived stellar mass	float
  log_SFR	MCSED derived star formation rate	float
  log_L150	MCSED derived 150 MHz luminosity	float

We request that the following acknowledgement be included in any paper using HETDEX-LOFAR data:

HETDEX is led by the University of Texas at Austin McDonald Observatory and Department of Astronomy with participation from the Ludwig-Maximilians-Universität München, Max-Planck-Institut für Extraterrestrische Physik (MPE), Leibniz-Institut für Astrophysik Potsdam (AIP), Texas A&M University, Pennsylvania State University, Institut für Astrophysik Göttingen, The University of Oxford, Max-Planck-Institut für Astrophysik (MPA), The University of Tokyo and Missouri University of Science and Technology.

Observations for HETDEX were obtained with the Hobby-Eberly Telescope (HET), which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly. The Visible Integral-field Replicable Unit Spectrograph (VIRUS) was used for HETDEX observations. VIRUS is a joint project of the University of Texas at Austin, Leibniz-Institut für Astrophysik Potsdam (AIP), Texas A&M University, Max-Planck-Institut fürExtraterrestrische Physik (MPE), Ludwig-Maximilians-Universität München, Pennsylvania State University, Institut für Astrophysik Göttingen, University of Oxford, and the Max-Planck-Institut fur Astrophysik (MPA).

Funding for HETDEX has been provided by the partner institutions, the National Science Foundation, the State of Texas, the US Air Force, and by generous support from private individuals and foundations.

We request that the following papers are cited when using any HETDEX-LOFAR data:

Debski, M. H., Zeimann, G. R., Hill, G. J., et al. 2024, arXiv e-prints, arXiv:2411.08974, doi: 10.48550/arXiv.2411.08974