Query : 2017ApJ...836L..14M

2017ApJ...836L..14M - Astrophys. J., 836, L14-L14 (2017/February-2)

Evidence for a hard ionizing spectrum from a z = 6.11 stellar population.


Abstract (from CDS):

We present the Magellan/FIRE detection of highly ionized C ivλ1550 and O III]λ1666 in a deep infrared spectrum of the z = 6.11 gravitationally lensed low-mass galaxy RXC J2248.7-4431-ID3, which has previously known Lyα. No corresponding emission is detected at the expected location of He IIλ1640. The upper limit on He II, paired with detection of O III] and C iv, constrains possible ionization scenarios. Production of C iv and O III] requires ionizing photons of 2.5-3.5 Ryd, but once in that state their multiplet emission is powered by collisional excitation at lower energies (∼0.5 Ryd). As a pure recombination line, He II emission is powered by 4 Ryd ionizing photons. The data therefore require a spectrum with significant power at 3.5 Ryd but a rapid drop toward 4.0 Ryd. This hard spectrum with a steep drop is characteristic of low-metallicity stellar populations, and less consistent with soft AGN excitation, which features more 4 Ryd photons and hence higher He II flux. The conclusions based on ratios of metal line detections to helium non-detection are strengthened if the gas metallicity is low. RXJ2248-ID3 adds to the growing handful of reionization-era galaxies with UV emission line ratios distinct from the general z=2–3 population in a way that suggests hard ionizing spectra that do not necessarily originate in AGNs.

Abstract Copyright: © 2017. The American Astronomical Society. All rights reserved.

Journal keyword(s): cosmology: observations - galaxies: evolution - galaxies: formation - galaxies: high-redshift - galaxies: high-redshift

Simbad objects: 3

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Number of rows : 3
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 [MSG2014] Lensed G G 22 48 44.1 -44 31 51           ~ 3 0
2 ACO S 1063 ClG 22 48 45.4 -44 31 42           ~ 313 0
3 CLASH RXJ2248-4431 1291 LeG 22 48 45.810 -44 32 14.86         25.9 ~ 25 0

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