Extended ionised and clumpy gas in a normal galaxy at z = 7.1 revealed by ALMA

Abstract

We present new ALMA observations of the [Oiii]88µm line and high angular resolution observations of the [Cii]158µm line in a normal star forming galaxy at z=7.1. Previous [Cii] observations of this galaxy had detected [Cii] emission consistent with the Lyα redshift but spatially slightly offset relative to the optical (UV-rest frame) emission. The new [Cii] observations reveal that the [Cii] emission is partly clumpy and partly diffuse on scales larger than about 1kpc.[Oiii] emission is also detected at high significance, offset relative to the optical counterpart in the same direction as the [Cii] clumps, but mostly not overlapping with the bulk of the [Cii] emission. The offset between different emission components (optical/UV and different far-IR tracers) is similar to that which is observed in much more powerful starbursts at high redshift. We show that the [Oiii] emitting clump cannot be explained in terms of diffuse gas excited by the UV radiation emitted by the optical galaxy, but it requires excitation by in-situ (slightly dust obscured) star formation, at a rate of about 7 M yr −1 . Within 20 kpc from the optical galaxy the ALMA data reveal two additional [Oiii] emitting systems, which must be star forming companions. We discuss that the complex properties revealed by ALMA in the z∼7.1 galaxy are consistent with expectations by recent models and cosmological simulations, in which differential dust extinction, differential excitation and different metal enrichment levels, associated with different subsystems assembling a galaxy, are responsible for the various appearance of the system when observed with distinct tracers.

ALMA Reveals Metals yet No Dust within Multiple Components in CR7

“…Clump A is blueshifted by 146±27 km s −1 with respect to Lyα. This is slightly smaller than typical offsets between Lyα and nebular lines for sources with similar UV luminosities (e.g., Stark et al 2017), although Carniani et al (2017) shows a wide spread of velocity offsets in a compilation of ALMA detections (i.e., v 150 400 -< D < + km s −1 for galaxies with M 10 SFR 100…”

“…direction (see also Carniani et al 2017 and references therein for offsets in z 6 7 -galaxies). For the rest of the analysis, we align the ALMA data with HST and Subaru narrowband data by applying an offset of 0.…”

“…Combining measurements of emission lines in the far-infrared such as the [ ] allows us to constrain the star formation rate (SFR), metallicity, density, and ionization state of the gas, both at low redshift (e.g., Ferkinhoff et al 2010;De Looze et al 2014;HerreraCamus et al 2015) and at high-redshift (e.g., Inoue et al 2016;Carniani et al 2017). Furthermore, spatially resolved emissionline measurements can probe the dynamical structure of the gas (e.g., Jones et al 2017;Smit et al 2017).…”

RELICS: Reionization Lensing Cluster Survey

“…While [C ii] is associated with neutral H i gas in photodissociation regions (PDRs), [O iii] is associated with ionized H ii gas, more prevalent in higher redshift, lower metallicity galaxies with higher ionization states (Harikane et al 2018). As predicted, ALMA's highest-redshift spectroscopic confirmations have come from [O iii], and the six z > 6 galaxies targeted to date have all yielded [O iii] detections at z = 6.900 (Marrone et al 2018); z = 7.107 (Carniani et al 2017); z = 7.212 (Inoue et al 2016); z = 8.312 (Tamura et al 2018); z = 8.382 (Laporte et al 2017a); and z = 9.11 (Hashimoto et al 2018b). The two highest redshift detections are lensed galaxies.…”

A dense, solar metallicity ISM in the z = 4.2 dusty star-forming galaxy SPT 0418−47

“…Both single dish submillimetre telescopes and interferometers have also detected the [NII] 122 µm and 205 µm lines at high redshift (Ferkinhoff et al 2011(Ferkinhoff et al , 2015Combes et al 2012;Nagao et al 2012;Decarli et al 2012Decarli et al , 2014Béthermin et al 2016;Pavesi et al 2016;Lu et al 2017;Tadaki et al 2019;Novak et al 2019). After a slow start, the [OIII] 88 µm line is quickly becoming a popular line to confirm redshifts of galaxies in the epoch of reionization (z 6), where it shifts into the submillimetre atmospheric windows below 500 GHz Inoue et al 2016;Carniani et al 2017;Marrone et al 2018;Vishwas, et al 2018;Hashimoto, et al 2018;Walter et al 2018;Tamura et al 2019;Tadaki et al 2019;Hashimoto et al 2019;Novak et al 2019). Deep Herschel/SPIRE spectroscopy has also revealed a number of FSL detections, either in individual objects (Valtchanov et al 2011;Coppin et al 2012;George et al 2013;Uzgil et al 2016;Rigopoulou et al 2018;Zhang et al 2018), or in stacked spectra (Wardlow et al 2017;Wilson et al 2017;Zhang et al 2018).…”