The Lyman alpha Reference Sample VI: Lyman alpha escape from the edge-on
  disk galaxy Mrk1486
  While numerical simulations suggest that the strength of the Lyman alpha
(Lya) line of star-forming disk galaxies strongly depends on the inclination at
which they are observed (i.e. from edge-on to face-on, we expect to see a
change from an attenuated Lya line to a strong Lya emission line), recent
observations with the Hubble space telescope (HST) have highlighted few
low-redshift highly inclined (edge-on) disk galaxies that breaks this trend. We
aim to understand how a strong Lya emission line is able to escape from one of
those inclined disk galaxies, named Mrk1486 (z=0.0338). For that purpose we
used a large set of HST imaging and spectroscopic data to investigate both the
ISM structure and the dominant source of Lya radiation inside Mrk1486.
Moreover, we used a 3D Monte Carlo Lya radiation transfer code to study the
radiative transfer of Lya and UV continuum photons inside a 3D geometry of
neutral hydrogen (HI) and dust that models the ISM structure at the galaxy
center. The analysis of IFU Halpha spectroscopic data of Mrk1486 indicates the
presence of two bipolar galactic winds of HI gas above and bellow the disk
plane of Mrk1486. Furthermore, comparing different diagnostic diagrams (such as
[OIII]5007/Hbeta versus [OI]6300/Halpha) to photo- and shock-ionization models,
we find that the Lya production of Mrk1486 is dominated by photoionization
inside the galaxy disk. From this perspective, our numerical simulations
succeed in reproducing the strength and spectral shape of the observed Lya line
of Mrk1486 by assuming a scenario in which the Lya photons are produced inside
the disk, travel along the galactic winds and scatter on cool HI materials
toward the observer. As bipolar galactic winds are ubiquitous in star-forming
disk galaxies, this mechanism may explain the origin of strong Lya emission
lines recently observed from highly inclined galaxies at high-redshift.
