The Lyman Continuum Escape and ISM properties in Tololo 1247-232 – New Insights from HST and VLA [GA]

Low- and intermediate mass galaxies are widely discussed as cause of reionization at redshift $z\sim10-6$. However, observational proof of galaxies that are leaking ionizing radiation (Lyman continuum; LyC) is a currently ongoing challenge and the list of LyC emitting candidates is still short. Tololo 1247-232 is among those very few galaxies with recently reported leakage. We performed intermediate resolution ultraviolet (UV) spectroscopy with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope and confirm ionizing radiation emerging from Tololo 1247-232. Adopting an improved data reduction procedure, we find that LyC escapes from the central stellar clusters, with an escape fraction of 1.5$\pm$0.5% only, i.e. the lowest value reported for the galaxy so far. We further make use of FUV absorption lines of Si II and Si IV as a probe of the neutral and ionized interstellar medium. We find that most of the ISM gas is ionized, likely facilitating LyC escape from density bounded regions. Neutral gas covering as a function of line-of-sight velocity is derived using the apparent optical depth method. The ISM is found to be sufficiently clumpy, supporting the direct escape of LyC photons. We further report on broadband UV and optical continuum imaging as well as narrowband imaging of Ly$\alpha$, H$\alpha$ and H$\beta$. Using stellar population synthesis, a Ly$\alpha$ escape fraction of 8% was derived. We also performed VLA 21cm imaging. The hydrogen hyperfine transition was not detected, but a deep upper limit atomic gas mass of $\lesssim10^9 M_{\odot}$ could be derived. The upper limit gas fraction defined as $\frac{M_{H I}}{M_*}$ is only 20%. Evidence is found that the H I gas halo is relatively small compared to other Lyman Alpha emitters.

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J. Puschnig, M. Hayes, G. Ostlin, et. al.
Fri, 21 Apr 17

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