ALMA reveals metals yet no dust within multiple components in CR7

Abstract

We present spectroscopic follow-up observations of CR7 with ALMA, targeted at constraining the infrared (IR) continuum and [CII]${}_{158\mu \mathrm{m}}$ 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 $\approx 300$ and $\approx 80$ 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${}_{\mathrm{IR}}(T_d=35\mathrm{K})<3.1\times 10^{10}$ 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 28, 5 and 7 M${}_{\odot }$ yr${}^{-1}$. All clumps have [CII] luminosities consistent within the scatter observed in the local relation between SFR and L${}_{[\mathrm{CII}]}$, 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 $0.1<Z/{\mathrm{Z}}_{\odot }<0.2$. 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.

17 pages, accepted for publication in ApJ

References in corpus (27)

• A Dust-Obscured Massive Maximum-Starburst Galaxy at a Redshift of 6.34
• An ALMA survey of Sub-millimeter Galaxies in the Extended Chandra Deep Field South: Physical properties derived from ultraviolet-to-radio modelling
• A dusty, normal galaxy in the epoch of reionization
• Dust in the reionization era: ALMA observations of a $z$=8.38 Galaxy
• Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6
• [CII] 158 $\mu$m Emission as a Star Formation Tracer
• Identification of the brightest Lyα emitters at z=6.6: implications for the evolution of the luminosity function in the re-ionisation era
• Tracing the reionization epoch with ALMA: [CII] emission in z~7 galaxies
• Star formation and the interstellar medium in z>6 UV-luminous Lyman-break galaxies
• Zooming on the internal structure of $z\simeq 6$ galaxies
• The impact of chemistry on the structure of high-z galaxies
• Dust production 680-850 million years after the Big Bang
• On the Detectability of Lyman-alpha Emission in Star-forming Galaxies: The Role of Dust
• The IRX-Beta Dust Attenuation Relation in Cosmological Galaxy Formation Simulations
• ALMA Observation of 158 micron [CII] Line and Dust Continuum of a z=7 Normally Star-forming Galaxy in the Epoch of Reionization
• A Hard Ionizing Spectrum in z=3-4 Ly-alpha Emitters with Intense [OIII] Emission: Analogs of Galaxies in the Reionization Era?
• ALMA [CII] detection of a redshift 7 lensed galaxy behind RXJ1347.1-1145
• The Rest-Frame Optical Spectroscopic Properties of Ly$\alpha$-Emitters at $z\sim 2.5$: The Physical Origins of Strong Ly$\alpha$ Emission
• New constraints on dust emission and UV attenuation of z=6.5-7.5 galaxies from millimeter observations
• Spectroscopic properties of luminous Lyman-α emitters at $z\approx 6-7$ and comparison to the Lyman-break population
• First Detection of the [OIII] 88 micron Line at High Redshifts: Characterizing the Starburst and Narrow Line Regions in Extreme Luminosity Systems
• Dust Properties of [CII] Detected z $\sim$ 5.5 Galaxies: New HST/WFC3 Near-IR Observations
• Interpreting the evolution of galaxy colours from $z=8$ to $z=5$
• Constraining dust formation in high-redshift young galaxies
• The Local [CII] 158 um Emission Line Luminosity Function
• Galaxy Formation Through Filamentary Accretion at z=6.1
• Molecular clumps photoevaporation in ionized regions