Zusammenfassung
We present new HST/WFC3 grism observations and re-analyse VLT data to unveil
the continuum, variability and rest-frame UV lines of the three UV components
of the most luminous Ly-alpha (Lya) emitter at z=6.6, COSMOS Redshift 7 (CR7).
Our re-reduced, flux calibrated X-SHOOTER spectra of CR7 reveal a tentative
detection of HeII with F(HeII)=$(1.8\pm0.7)\times10^-17$erg s$^-1$cm$^-2$
and we identify the signal (~2.6$\sigma$) as coming only from observations
obtained along the major axis of Lya emission. There is a change of +0.2-0.5mag
in UltraVISTA J band data for CR7 from DR2 to DR3, which virtually eliminates
the strong J-band excess previously interpreted as being caused by HeII. Our
WFC3 grism spectra provide a significant detection of the UV continuum of CR7's
clump A, yielding an excellent fit to a power law with $\beta=-2.4\pm0.4$ and
$M_UV=-21.7\pm0.3$, consistent with no variability. HST grism data fail to
detect any rest-frame UV line in clump A above 3$\sigma$, yielding
F(HeII)<$0.5\times10^-17$erg s$^-1$cm$^-2$ (EW$_0$<10A) at a 95%
confidence level. Clump C is tentatively identified as a potential variable and
high ionisation source with F(HeII)=$(1.0\pm0.4)\times10^-17$erg
s$^-1$cm$^-2$. We perform CLOUDY modelling to constrain the metallicity and
the ionising nature of CR7, and also make emission-line predictions for
JWST/NIRSpec. CR7 seems to be actively forming stars without any clear AGN
activity in clumps A and B, consistent with a metallicity of ~0.05-0.2
Z$_ødot$ and with component A experiencing the most massive starburst.
Component C may host a high ionisation source/AGN. Our results highlight the
need for spatially resolved information to study the complex formation and
assembly of early galaxies within the epoch of re-ionisation.
Nutzer