EVIDENCE FOR PopIII-LIKE STELLAR POPULATIONS IN THE MOST LUMINOUS Lyα EMITTERS AT THE EPOCH OF REIONIZATION: SPECTROSCOPIC CONFIRMATION

By D. Sobral, J. Matthee, B. Darvish, Daniel Schaerer, B. Mobasher, H. Röttgering, S. Santos, S. Hemmati. 2015

220 citations recorded by the source corpus.

Faint Lyα emitters become increasingly rarer toward the reionization epoch (z ∼ 6–7). However, observations from a very large (∼5 deg2) Lyα narrow-band survey at z = 6.6 show that this is not the case for the most luminous emitters, capable of ionizing their own local bubbles. Here we present follow-up observations of the two most luminous Lyα candidates in the COSMOS field: “MASOSA” and “CR7.” We used X-SHOOTER, SINFONI, and FORS2 on the Very Large Telescope, and DEIMOS on Keck, to confirm both candidates beyond any doubt. We find redshifts of z = 6.541 and z = 6.604 for “MASOSA” and “CR7,” respectively. MASOSA has a strong detection in Lyα with a line width of 386 ± 30 km s−1 (FWHM) and with very high EW0 (>200 Å), but undetected in the continuum, implying very low stellar mass and a likely young, metal-poor stellar population. “CR7,” with an observed Lyα luminosity of 1043.92±0.05 erg s−1 is the most luminous Lyα emitter ever found at z > 6 and is spatially extended (∼16 kpc). “CR7” reveals a narrow Lyα line with 266 ± 15 km s−1 FWHM, being detected in the near-infrared (NIR) (rest-frame UV; β = −2.3 ± 0.1) and in IRAC/Spitzer. We detect a narrow He ii 1640 Å emission line (6σ, FWHM = 130 ± 30 km s−1) in CR7 which can explain the clear excess seen in the J-band photometry (EW0 ∼ 80 Å). We find no other emission lines from the UV to the NIR in our X-SHOOTER spectra (He ii/O iii] 1663 Å > 3 and He ii/C iii] 1908 Å > 2.5). We conclude that CR7 is best explained by a combination of a PopIII-like population, which dominates the rest-frame UV and the nebular emission, and a more normal stellar population, which presumably dominates the mass. Hubble Space Telescope/WFC3 observations show that the light is indeed spatially separated between a very blue component, coincident with Lyα and He ii emission, and two red components (∼5 kpc away), which dominate the mass. Our findings are consistent with theoretical predictions of a PopIII wave, with PopIII star formation migrating away from the original sites of star formation.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/24757bb556cf4c6c40d9a4fa1b74d6a9a505d9ac

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

Citations in the corpus

Systematic Identification of LAEs for Visible Exploration and Reionization Research Using Subaru HSC (SILVERRUSH). I. Program strategy and clustering properties of ∼2000 Lyα emitters at z = 6–7 over the 0.3–0.5 Gpc2 survey area (2017, background): “Because LAEs are low stellar mass galaxies with strong Lyα indicative of a starburst with young massive stars producing a large amount of ionizing photons (Ouchi et al. 2013; Sobral et al. 2015; Stark et al. 2015), LAEs are used as probes of young galaxies.”
Hyper-Eddington accretion flows on to massive black holes (2015, background): “Spectroscopic observation by Sobral et al. (2015) suggests the existence of a Pop III stellar population with a top-heavy initial mass function.”
Binary Population and Spectral Synthesis Version 2.1: Construction, Observational Verification, and New Results (2017, background): “While none of the model sets explored in that work provide an unambiguous interpretation for CR7, BPASS low metallicity, young starburst models are broadly consistent with the colours of the source in question (particularly if some degree of enhancement in α-elements is assumed) suggesting a stellar”
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, unknown): “…Sc12: Schenker et al. (2012), Sh12: Shibuya et al. (2012), W13: Willott et al. (2013), Maio15: Maiolino et al. (2015), W15: Willott et al. (2015), So15: Sobral et al. (2015), St15a: Stark et al. (2015b), St15b: Stark et al. (2015a), K16: Knudsen et al. (2016), P16: Pentericci et al. (2016),…”
Building up the Population III initial mass function from cosmological initial conditions (2016, background): “It has no detected metal emission lines, and it also has a very high HeII line emission of 2× 1043 erg s−1, indicating that the source has a very hard spectrum (e.g. Sobral et al. 2015; Pallottini et al. 2015, Hartwig et al 2015c, Smith et al. 2016).”
SUBARU HIGH-z EXPLORATION OF LOW-LUMINOSITY QUASARS (SHELLQs). I. DISCOVERY OF 15 QUASARS AND BRIGHT GALAXIES AT 5.7 < z < 6.9 (2016, unknown): “The measured L (Lyα) and vFWHM(Lyα) are similar to those of the high-z galaxy “CR7”, which is suggested to contain PopulationIII-like stars (Sobral et al. 2015, based on the very strong nebular lines including He II λ1640), while W0(Lyα) is less than half that of CR7.”
Titans of the early Universe: The Prato statement on the origin of the first supermassive black holes (2018, methodology): “Sobral et al. (2015) indeed found that the SED of the complete system could only be reproduced when including a young (<5Myr) population of massive metal-free stars, with a total stellar mass of at least 107 M for one of the three clumps.”
An extreme [O III] emitter at z = 3.2: a low metallicity Lyman continuum source (2015, background): “The origin of He iiλ1640 emission in galaxies has been matter of investigation, possibly produced by massive stars both in the local Universe (e.g., Szécsi et al. 2015; Gräfener & Vink 2015) and at high-redshift (e.g., Cassata et al. 2013; Sobral et al. 2015; Pallottini et al. 2015).”
Formation of Supermassive Black Hole Seeds (2016, background): “Recent detection of the brightest Lyman alpha emitter at z = 6.6 (CR7) by Sobral et al. (2015) shows strong Lyman alpha and He-1640Å line luminosities and no metal line emission.”
Modelling the nebular emission from primeval to present-day star-forming galaxies (2016, background): “…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).”
Observational evidence for intermediate-mass black holes (2017, methodology): “11; Sobral et al. 2015; Pallottini et al. 2015; Agarwal et al. 2016; Dijkstra et al. 2016; Hartwig et al. 2016; Smith et al. 2016).”
J-PLUS: The Javalambre Photometric Local Universe Survey (2015, background): “Sobral et al. (2015) have confirmed spectroscopically an extremely luminous LAE at z = 6.604, named CR7, with Lyα luminosity of 8.3 × 1043 erg s−1.”
SILVERRUSH. IV. Lyα luminosity functions at z = 5.7 and 6.6 studied with ∼1300 Lyα emitters on the 14–21 deg2 sky (2017, background): “In fact, our bright-end LAEs include well-studied Himiko and CR7, whose morphologies in the Hubble WFC3 images show possible signatures of galaxy mergers (Ouchi et al. 2013; Sobral et al. 2015).”