Misc,
Escape of Lyman continuum radiation from local galaxies - Detection of leakage from the young starburst Tol 1247-232
(2013)cite arxiv:1302.6971Comment: 16 pages, 7 pictures, submitted to A&A.
Abstract
The escape fraction of hydrogen ionizing photons (f_esc) from galaxies has
been suggested to be evolving with time, but the picture is far from clear.
While evidence for significant escape fractions has been found at high
redshifts in several studies, the picture looks different in the more nearby
universe. Here, we apply a new background subtraction routine on archival data
from the Far Ultraviolet Spectroscopic Explorer (FUSE), in order to study local
galaxies in search for possible Lyman Continuum (LyC) leakage. In the process,
for the first time a stacked spectrum in the LyC is produced for local
galaxies. With this small sample, we also make a more tentative approach to
look for possible correlations between f_esc and physical parameters such as
internal absorption E(B-V)_i, mass, H I mass, specific star formation rate
(SSFR), metallicity, and Ly-alpha emission. Eight star forming galaxies with
redshifts z > 0.015 from the FUSE archive were re-examined. Also, a sub-sample
of an additional four galaxies with lower redshifts were included, for which
the escape fraction was estimated from residual flux in the low ionization
interstellar C II(1036\AA) line. Out of the eight galaxies, only one was
found to have significant LyC leakage, Tol 1247-232 (S/N=5.2). This is the
second detection of a leaking galaxy in the local universe. We find an absolute
escape fraction for Tol 1247-232 of f_esc = 2.4(+0.9/-0.8) %. The stacked
sample show an excess in the LyC with f_esc = 1.4(+0.6/-0.5) %, but we note
that there might be important selection biases involved. With the small sample,
we suggest a possible trend for higher f_esc with lower mass and with enhanced
SSFR. None of the galaxies with high values of E(B-V)_i were found to show any
sign of leakage.
