%0 Generic %1 sobral2017nature %A Sobral, David %A Matthee, Jorryt %A Brammer, Gabriel %A Ferrara, Andrea %A Alegre, Lara %A Rottgering, Huub %A Schaerer, Daniel %A Mobasher, Bahram %A Darvish, Behnam %D 2017 %K Lya emitter high-z lines %T On the nature of the luminous Lya emitter CR7 and its UV components: physical conditions and JWST predictions %U http://arxiv.org/abs/1710.08422 %X 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.

@misc{sobral2017nature, 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)=$(1.8\pm0.7)\times10^{-17}$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$_{\odot}$ 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.}, added-at = {2017-10-25T10:07:11.000+0200}, 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}, biburl = {https://www.bibsonomy.org/bibtex/22ef436f9787e70cfc9fa888f620fd4d1/miki}, description = {[1710.08422] On the nature of the luminous Lya emitter CR7 and its UV components: physical conditions and JWST predictions}, interhash = {5063b9c53ff93c7b244410efb3181adb}, intrahash = {2ef436f9787e70cfc9fa888f620fd4d1}, keywords = {Lya emitter high-z lines}, note = {cite arxiv:1710.08422Comment: Submitted to MNRAS, comments welcomed. 19 pages, 11 figures}, timestamp = {2017-10-25T10:07:11.000+0200}, title = {On the nature of the luminous Lya emitter CR7 and its UV components: physical conditions and JWST predictions}, url = {http://arxiv.org/abs/1710.08422}, year = 2017 }