Volume 658, February 2022
|Number of page(s)||6|
|Section||Letters to the Editor|
|Published online||18 February 2022|
Letter to the Editor
Strong Lyman continuum emitting galaxies show intense C IV λ1550 emission
Observatoire de Genève, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
2 CNRS, IRAP, 14 Avenue E. Belin, 31400 Toulouse, France
3 Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, 14-b Metrolohichna Str., Kyiv 03143, Ukraine
4 Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
5 Department of Astronomy, University of Texas at Austin, Austin, TX 78712, USA
6 Department of Astronomy, Williams College, Williamstown, MA 01267, USA
7 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
8 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
9 Astronomy Department, University of Virginia, PO Box 400325 Charlottesville, VA 22904-4325, USA
Accepted: 7 February 2022
Using the Space Telescope Imaging Spectrograph, we have obtained ultraviolet spectra from ∼1200 to 2000 Å of known Lyman continuum (LyC) emitting galaxies at low redshift (z ∼ 0.3 − 0.4) with varying absolute LyC escape fractions (fesc ∼ 0.01 − 0.72). Our observations include in particular the galaxy J1243+4646, which has the highest known LyC escape fraction at low redshift. While all galaxies are known Lyman alpha emitters, we consistently detect an inventory of additional emission lines, including C IV λ1550, He II λ1640, O III] λ1666, and C III] λ1909, whose origin is presumably essentially nebular. C IV λ1550 emission is detected above 4σ in six out of eight galaxies, with equivalent widths of EW(C IV) = 12 − 15 Å for two galaxies, which exceeds the previously reported maximum emission in low-z star-forming galaxies. We detect C IV λ1550 emission in all LyC emitters with escape fractions fesc > 0.1 and find a tentative increase in the flux ratio C IV λ1550/C III] λ1909 with fesc. Based on the data, we propose a new criterion to select and classify strong leakers (galaxies with fesc > 0.1): C IV λ1550/C III] λ1909 ≳ 0.75. Finally, we also find He II λ1640 emission in all the strong leakers with equivalent widths from 3 to 8 Å rest frame. These are among the highest values observed in star-forming galaxies and are primarily due to a high rate of ionizing photon production. The nebular He II λ1640 emission of the strong LyC emitters does not require harder ionizing spectra at > 54 eV compared to those of typical star-forming galaxies at similarly low metallicity.
Key words: galaxies: starburst / galaxies: high-redshift / dark ages, reionization / first stars / ultraviolet: galaxies
© ESO 2022
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