On the nature of the luminous Lya emitter CR7 and its UV components: physical conditions and JWST predictions. Sobral, D., Matthee, J., Brammer, G., Ferrara, A., Alegre, L., Rottgering, H., Schaerer, D., Mobasher, B., & Darvish, B. ArXiv e-prints, 1710:arXiv:1710.08422, October, 2017.
On the nature of the luminous Lya emitter CR7 and its UV components: physical conditions and JWST predictions [link]Paper  abstract   bibtex   
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{\textbackslash}pm0.7){\textbackslash}times10{\textasciicircum}\{-17\}\$erg s\${\textasciicircum}\{-1\}\$cm\${\textasciicircum}\{-2\}\$ and we identify the signal (\textasciitilde2.6\${\textbackslash}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 \${\textbackslash}beta=-2.4{\textbackslash}pm0.4\$ and \$M_\{UV\}=-21.7{\textbackslash}pm0.3\$, consistent with no variability. HST grism data fail to detect any rest-frame UV line in clump A above 3\${\textbackslash}sigma\$, yielding F(HeII)\textless\$0.5{\textbackslash}times10{\textasciicircum}\{-17\}\$erg s\${\textasciicircum}\{-1\}\$cm\${\textasciicircum}\{-2\}\$ (EW\$_0\$\textless10A) at a 95% confidence level. Clump C is tentatively identified as a potential variable and high ionisation source with F(HeII)=\$(1.0{\textbackslash}pm0.4){\textbackslash}times10{\textasciicircum}\{-17\}\$erg s\${\textasciicircum}\{-1\}\$cm\${\textasciicircum}\{-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 \textasciitilde0.05-0.2 Z\$_\{{\textbackslash}odot\}\$ 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.
@article{sobral_nature_2017,
	title = {On the nature of the luminous {Lya} emitter {CR7} and its {UV} components: physical conditions and {JWST} predictions},
	volume = {1710},
	shorttitle = {On the nature of the luminous {Lya} emitter {CR7} and its {UV} components},
	url = {http://adsabs.harvard.edu/abs/2017arXiv171008422S},
	abstract = {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{\textbackslash}pm0.7){\textbackslash}times10{\textasciicircum}\{-17\}\$erg s\${\textasciicircum}\{-1\}\$cm\${\textasciicircum}\{-2\}\$ and we identify
the signal ({\textasciitilde}2.6\${\textbackslash}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 \${\textbackslash}beta=-2.4{\textbackslash}pm0.4\$ and \$M\_\{UV\}=-21.7{\textbackslash}pm0.3\$, consistent
with no variability. HST grism data fail to detect any rest-frame UV
line in clump A above 3\${\textbackslash}sigma\$, yielding
F(HeII){\textless}\$0.5{\textbackslash}times10{\textasciicircum}\{-17\}\$erg s\${\textasciicircum}\{-1\}\$cm\${\textasciicircum}\{-2\}\$ (EW\$\_0\${\textless}10A) at a
95\% confidence level. Clump C is tentatively identified as a potential
variable and high ionisation source with
F(HeII)=\$(1.0{\textbackslash}pm0.4){\textbackslash}times10{\textasciicircum}\{-17\}\$erg s\${\textasciicircum}\{-1\}\$cm\${\textasciicircum}\{-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 {\textasciitilde}0.05-0.2 Z\$\_\{{\textbackslash}odot\}\$ 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.},
	journal = {ArXiv e-prints},
	author = {Sobral, David and Matthee, Jorryt and Brammer, Gabriel and Ferrara, Andrea and Alegre, Lara and Rottgering, Huub and Schaerer, Daniel and Mobasher, Bahram and Darvish, Behnam},
	month = oct,
	year = {2017},
	keywords = {Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics},
	pages = {arXiv:1710.08422},
}

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