Spectroscopic detections of C iii] λ1909 Å at z ≃ 6–7: a new probe of early star-forming galaxies and cosmic reionization

By D. Stark, J. Richard, S. Charlot, B. Clément, Richard S. Ellis, B. Siana, Brant Robertson, M. Schenker, Julia Gutkin, A. Wofford. 2014

150 citations recorded by the source corpus.

Deep spectroscopic observations of z ≳ 6.5 galaxies have revealed a marked decline with increasing redshift in the detectability of Ly α emission. While this may offer valuable insight into the end of the reionization process, it presents a challenge to the detailed spectroscopic study of bright photometrically-selected distant sources now being found via deep Hubble Space Telescope imaging, and particularly those highly magnified sources viewed through foreground lensing clusters. In this paper, we demonstrate the validity of a new way forward via the detection of an alternative diagnostic line, C iii] λ1909 A, seen in spectroscopic exposures of a star-forming galaxy at zLyα = 6.029. We also report tentative detection of C iii] λ1909 A in a galaxy at z_Lyα = 7.213. The former 3.3σ detection is based on a 3.5 h XShooter spectrum of a bright (J125 = 25.2) gravitationally-lensed galaxy behind the cluster Abell 383. The latter 2.8σ detection is based on a 4.2 h MOSFIRE spectra of one of the most distant spectroscopically confirmed galaxies, GN-108036, with J140 = 25.2. Both targets were chosen for their continuum brightness and previously-known redshift (based on Ly α), ensuring that any C iii] emission would be located in a favourable portion of the near-infrared sky spectrum. Since the availability of secure Ly α redshifts significantly narrows the wavelength range where C iii] is sought, this increases confidence in these, otherwise, low-signal-to-noise ratio detections. We compare our C iii] and Ly α equivalent widths in the context of those found at z ≃ 2 from earlier work and discuss the motivation for using lines other than Ly α to study galaxies in the reionization era.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/735604d89de0fda391d339635d620a735d5795fb

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In Astronomy and Astrophysics

1. Richard S. Ellis
2. R. Bouwens
3. P. Oesch
4. C. Conroy
5. G. Illingworth
6. M. Franx
7. P. V. van Dokkum
8. I. Labbé

In Instrumentation

1. Richard S. Ellis
2. R. Bouwens
3. P. Oesch
4. G. Illingworth
5. C. Conroy
6. M. Franx
7. I. Labbé
8. P. V. van Dokkum

Citations in the corpus

• Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “…the strong nebular fluxes, high ionization lines, and extreme line widths that are now known to be ubiquitous at z∼2.5–3.5 (e.g., Holden et al. 2016; Steidel et al. 2016; Reddy et al. 2018b) and also commonly seen at z>6 (e.g., Stark et al. 2015; RobertsBorsani et al. 2016; Mainali et al. 2017).”
• Big Three Dragons: A z = 7.15 Lyman-break galaxy detected in [O iii] 88 μm, [C ii] 158 μm, and dust continuum with ALMA (2018, background): “1-1145 [Cii] 6.77 20+140 −40 −20.8 + 2.5 log(µ) b 26± 4 7.0+1.0 −1.5/µ b 5.0± 0.3 B17 NTTDF6345 [Cii] 6.70 110 −21.6 15 17.7 - P16 UDS16291 [Cii] 6.64 110 −21.0 6 7.15 - P16 COSMOS24108 [Cii] 6.62 240 −21.7 27 10.0 - P16 CR7 (full) [Cii] 6.60 167± 22 −22.2 211± 20 21.7± 3.6c - S15, Mat17 Himiko (Tot”
• Detection of the Far-infrared [O iii] and Dust Emission in a Galaxy at Redshift 8.312: Early Metal Enrichment in the Heart of the Reionization Era (2018, background): “These lines, in addition to the restframe optical oxygen and nitrogen lines, are also useful for characterizing the metal enrichment of the interstellar medium (ISM) and stellar components of the galaxies (e.g., Stark et al. 2015a, 2015b, 2017; Mainali et al. 2018).”
• RELICS: Reionization Lensing Cluster Survey (2019, background): “C iii] detections may be powered by low metallicity massive stars (Stark et al. 2015, 2017) or may require AGNs (Nakajima et al. 2018).”
• Evolution of the AGN UV luminosity function from redshift 7.5 (2018, background): “…may also be consistent with the shallow bright-end slopes of the z ∼ 7 UV luminosity function of galaxies relative to a Schechter function (Bowler et al. 2012, 2014; Bradley et al. 2014; Bowler et al. 2015) and the hard spectra of these galaxies (Stark et al. 2015a,b, 2017; Laporte et al. 2017).”
• Spectroscopic detection of C iv λ1548 in a galaxy at z = 7.045: implications for the ionizing spectra of reionization-era galaxies (2015, methodology): “We use a comprehensive model grid similar to that adopted by Stark et al. (2015) As in Stark et al. (2014a), we consider models with 2- component star formation histories: a ‘starburst’ component (represented here by a 3 Myr-old stellar population with constant SFR) and an ‘old’ component…”
• Lyα EMISSION FROM A LUMINOUS z = 8.68 GALAXY: IMPLICATIONS FOR GALAXIES AS TRACERS OF COSMIC REIONIZATION (2015, background): “Evidence for stronger than usual ionizing spectra in z > 7 dropouts with known Lyα emission is provided by the prominent detection of CIV 1548 Å emission in the lensed galaxy at z = 7.047 (Stark et al. 2015a).”
• CONTRASTING GALAXY FORMATION FROM QUANTUM WAVE DARK MATTER, ψDM, WITH ΛCDM, USING PLANCK AND HUBBLE DATA (2015, background): “5 7.0 from the statistical absence of strong Lyα emission from the most distant galaxies amenable to spectroscopy (Pentericci et al. 2014; Stark et al. 2015).”
• Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction (2019, background): “Stark et al. (2015b, 2016) measured ξion via ionized carbon emission, finding ξion= - +25.68 0.19 0.27 erg−1 Hz in a lensed galaxy at z=7.045 with an intrinsic MUV=−19.3 and ξion=25.6 for three luminous (MUV=−22) galaxies at z=7.15, 7.48, and 7.73.”
• Binary Population and Spectral Synthesis Version 2.1: Construction, Observational Verification, and New Results (2017, background): “A number of recent publications have suggested that starforming galaxies in the distant (z > 2) Universe may show signs of a harder typical ultraviolet radiation field than is common in the local Universe (e.g. Steidel et al. 2016; Stark et al. 2015; Stanway et al. 2014).”
• Modelling the nebular emission from primeval to present-day star-forming galaxies (2016, methodology): “…to the epoch of cosmic reionization, rapid progress is being accomplished in the observation of fainter emission lines in the rest-frame ultraviolet spectra of galaxies in this redshift range (e.g., Shapley et al. 2003; Erb et al. 2010; Stark et al. 2014, 2015a,b, 2016; Sobral et al. 2015).”
• Lyα and C iii] emission in z = 7–9 Galaxies: accelerated reionization around luminous star-forming systems? (2016, methodology): “Yet owing to the lack of strong nebular lines in reionization-era galaxies, there are currently only a handful of ∆vLyα measurements at z > 6 (Willott et al. 2015; Stark et al. 2015a).”
• REIONIZATION AFTER PLANCK: THE DERIVED GROWTH OF THE COSMIC IONIZING EMISSIVITY NOW MATCHES THE GROWTH OF THE GALAXY UV LUMINOSITY DENSITY (2015, background): “Not only do the observational inferences depend on the intrinsic velocity offset of Lyα emission (e.g., Mesinger et al. 2015; Stark et al. 2015), but it is dependent on details of the radiative transfer, inhomogeneities in the IGM, the ionizing background, all of which rely on high-quality…”
• Nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths (2015, methodology): “Thus, emission lines associated with ion species requiring ionization energies greater than 50 eV should be the most promising indicators of the presence of an AGN, as we shall see in the following sections (see also Steidel et al. 2014; Stark et al. 2015b).”