Neutral gas in Lyman-alpha emitting galaxies Haro 11 and ESO 338-IG04 measured through sodium absorption

Abstract

Context. The Lyman alpha emission line of galaxies is an important tool for finding galaxies at high redshift, and thus probe the structure of the early universe. However, the resonance nature of the line and its sensitivity to dust and neutral gas is still not fully understood. Aims. We present measurements of the velocity, covering fraction and optical depth of neutral gas in front of two well known local blue compact galaxies that show Lyman alpha in emission: ESO 338-IG 04 and Haro 11. We thus test observationally the hypothesis that Lyman alpha can escape through neutral gas by being Doppler shifted out of resonance. Methods. We present integral field spectroscopy from the GIRAFFE/Argus spectrograph at VLT/FLAMES in Paranal, Chile. The excellent wavelength resolution allows us to accurately measure the velocity of the ionized and neutral gas through the H-alpha emission and Na D absorption, which traces the ionized medium and cold interstellar gas, respectively. We also present independent measurements with the VLT/X-shooter spectrograph which confirm our results. Results. For ESO 338-IG04, we measure no significant shift of neutral gas. The best fit velocity is -15 (16) km/s. For Haro 11, we see an outflow from knot B at 44 (13) km/s and infalling gas towards knot C with 32 (12) km/s. Based on the relative strength of the Na D absorption lines, we estimate low covering fractions of neutral gas (down to 10%) in all three cases. Conclusions. The Na D absorption likely occurs in dense clumps with higher column densities than where the bulk of the Ly-alpha scattering takes place. Still, we find no strong correlation between outflowing neutral gas and a high Lyman alpha escape fraction. The Lyman alpha photons from these two galaxies are therefore likely escaping due to a low column density and/or covering fraction.

9 pages, 3 figures

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Cited by in corpus (12)

• Using Lyman-alpha to detect galaxies that leak Lyman continuum
• Escape of Lyman continuum radiation from local galaxies - Detection of leakage from the young starburst Tol 1247-232
• The Lyman Alpha Reference Sample: V. The impact of neutral ISM kinematics and geometry on Lyman Alpha escape
• The molecular gas reservoir of 6 low-metallicity galaxies from the Herschel Dwarf Galaxy Survey: A ground-based follow-up survey of CO(1-0), CO(2-1), and CO(3-2)
• Super star cluster feedback driving ionization, shocks and outflows in the halo of the nearby starburst ESO 338-IG04
• Kinematics of Haro11 - the miniature Antennae
• Neutral ISM, Lyman-Alpha and Lyman-continuum in the nearby starburst Haro 11
• VLT/MUSE view of the highly ionized outflow cones in the nearby starburst ESO338-IG04
• The Lyman alpha Reference Sample VI: Lyman alpha escape from the edge-on disk galaxy Mrk1486
• Detection of HI in Emission in the Lyman Alpha Emitting Galaxy Haro 11
• HI Lyman-alpha equivalent widths of stellar populations
• Disentangling the X-ray variability in the Lyman continuum emitter Haro 11