http://arxiv.org/abs/1709.06569
We present spectroscopic follow-up observations of CR7 with ALMA, targeted at constraining the infrared (IR) continuum and [CII]${158 \mu \rm m}$ line-emission at high spatial resolution matched to the HST/WFC3 imaging. CR7 is a luminous Ly$\alpha$ emitting galaxy at $z=6.6$ that consists of three separated UV-continuum components. Our observations reveal several well-separated components of [CII] emission. The two most luminous components in [CII] coincide with the brightest UV components (A and B), blue-shifted by $\approx 150$ km s$^{-1}$ with respect to the peak of Ly$\alpha$ emission. Other [CII] components are observed close to UV clumps B and C and are blue-shifted by $\approx300$ and $\approx80$ km s$^{-1}$ with respect to the systemic redshift. We do not detect FIR continuum emission due to dust with a 3$\sigma$ limiting luminosity L${\rm IR} (T_d = 35 \rm \, K) < 3.1\times10^{10}$ L${\odot}$. This allows us to mitigate uncertainties in the dust-corrected SFR and derive SFRs for the three UV clumps A, B and C of 29, 6 and 7 M${\odot}$ yr$^{-1}$. All clumps have [CII] luminosities consistent within the scatter observed in the local relation between SFR and L${\rm [CII]}$, implying that strong Ly$\alpha$ emission does not necessarily anti-correlate with [CII] luminosity. Combining our measurements with the literature, we show that galaxies with blue UV slopes have weaker [CII] emission at fixed SFR, potentially due to their lower metallicities and/or higher photoionisation. Comparison with hydrodynamical simulations suggests that CR7’s clumps have metallicities of $0.1<\rm Z/Z{\odot}<0.2$. The observed ISM structure of CR7 indicates that we are likely witnessing the build up of a central galaxy in the early Universe through complex accretion of satellites.
J. Matthee, D. Sobral, F. Boone, et. al.
Thu, 21 Sep 17
25/50
Comments: 17 pages, submitted to ApJ, comments welcome