The source of leaking ionizing photons from Haro11 -- Clues from HST/COS spectroscopy of knots A, B and C

Abstract

Understanding the escape of ionizing (Lyman continuum) photons from galaxies is vital for determining how galaxies contributed to reionization in the early universe. While directly detecting Lyman continuum from high redshift galaxies is impossible due to the intergalactic medium, low redshift galaxies in principle offer this possibility, but requirie observations from space. The first local galaxy for which Lyman continuum escape was found is Haro11 , a luminous blue compact galaxy at z=0.02, where observations with the FUSE satellite revealed an escape fraction of 3.3 %. However the FUSE aperture covers the entire galaxy, and it is not clear from where the Lyman continuum is leaking out. Here we utilize HST/COS spectroscopy in the wavelength range 1100-1700 A of the three knots (A, B, and C) of Haro11 to study the presence of Ly-$\alpha$ emission and the properties of intervening gas. We find that all knots have bright Ly-$\alpha$ emission. UV absorption lines, originating in the neutral interstellar medium, as well as lines probing the ionized medium, are seen extending to blue shifted velocities of 500 km/s in all three knots, demonstrating the presence of an outflowing multiphase medium. We find that knots A and B have large covering fractions of neutral gas, making LyC escape along these sightlines improbable, while knot C has a much lower covering fraction ($\lesssim 50$%). Knot C also has the the highest Ly-$\alpha$ escape fraction and we conclude that it is the most likely source of the escaping Lyman continuum detected in Haro11.

19 pages, 7 figures, accepted for publication in ApJ

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• The molecular gas resolved by ALMA in the low-metallicity dwarf merging galaxy Haro 11
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• Extended far-ultraviolet emission in distant dwarf galaxies
• KMTNet Nearby Galaxy Survey III. Deficient H$\alpha$ flux in the Extended Disks of Spiral Galaxies
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• Ionizing Radiation Escape from Low-Redshift Galaxies and Its Connection to Cosmic Reionization
• Disentangling the X-ray variability in the Lyman continuum emitter Haro 11
• Forming the local starburst galaxy Haro 11 through hydrodynamical merger simulations
• The Lyman Alpha Reference Sample. XVI. Global 21cm HI properties of Lyman-$\alpha$ emitting galaxies
• Power-law Emission-line Wings and Radiation-Driven Superwinds in Local Lyman Continuum Emitters