Multiwavelength analysis of the Lyman alpha emitting galaxy Haro 2:
  relation between the diffuse Lyman alpha and soft X-ray emissions
  In order to use Lyman alpha (Lya) emission as star formation tracer in
cosmological studies, we must understand how the resonant scattering affects
the escape fraction of the Lya photons. Thus, high spatial resolution
multiwavelength studies of nearby Lya emitters, like Haro 2, are highly needed.
For that purpose, we have used Chandra X-ray and HST (UV, optical and NIR)
images of Haro 2, and STIS and ground-based spectral images along its major and
minor axes, to characterize the Lya emission and the properties of the stellar
population. The UV, Ha (Halpha) and FIR luminosities of the Haro 2 nuclear
starburst are reproduced using evolutionary synthesis models assuming a young
stellar population with ages ~3.5-5.0 Myr, affected by differential
interstellar extinctions. The observed X-ray emission is attributed to gas
heated by the mechanical energy released by the starburst (soft component) and
a Ultra-Luminous X-ray source candidate (hard). Both compact and diffuse Lya
components are observed. Whereas Lya is spatially decoupled from Balmer lines
emission, Balmer decrement and UV continuum, the diffuse Lya component is
spatially correlated with the diffuse soft X-ray emission. Moreover, unlike the
compact one, diffuse Lya shows luminosities larger than predicted from Ha,
assuming case B recombination and dust extinction as derived from Ha/Hbeta. We
propose that, whereas the compact Lya emission is associated to the massive
stellar clusters and is affected by outflows and dust extinction, the diffuse
Lya originates in gas ionized by the hot plasma responsible for the soft X-ray
radiation, as suggested by their spatial correlation and by the measured
L(Ha)/LsoftX ratios. Calibration of Lya as star formation rate tracer should
therefore include both effects (destruction vs. enhancement) to avoid biases in
the study of galaxies at cosmological distances.
