We present Keck/MOSFIRE observations of UV metal lines in four bright (H=23.9-25.4) gravitationally-lensed z 6 − 8 galaxies behind the cluster Abell 1703. The spectrum of A1703-zd6, a highly-magnified star forming galaxy with a Lyα redshift of z = 7.045, reveals a confident (S/N=5.1) detection of the nebular CIVλ1548 emission line (unresolved with FWHM<125 km s −1 ). UV metal lines are not detected in the three other galaxies. At z 2 − 3, nebular CIV emission is observed in just 1% of UV-selected galaxies. The presence of strong CIV emission in one of the small sample of galaxies targeted in this paper may indicate hard ionizing spectra are more common at z 7. The total estimated equivalent width of the CIV doublet (W CIV 38Å) and CIV/Lyα flux ratio (f CIV /f Lyα 0.3) are comparable to measurements of narrow-lined AGNs. Photoionization models show that the nebular CIV line can also be reproduced by a young stellar population, with very hot metal poor stars dominating the photon flux responsible for triply ionizing carbon. Regardless of the origin of the CIV, we show that the ionizing spectrum of A1703-zd6 is different from that of typical galaxies at z 2, producing more H ionizing photons per unit 1500Å luminosity (log(ξ ion /erg −1 Hz)=25.68) and a larger flux density at 30-50 eV. If such extreme radiation fields are typical in UV-selected systems at z ∼ > 7, it would indicate that reionization-era galaxies are more efficient ionizing agents than previously thought. Alternatively, we suggest that the small sample of Lyα emitters at z ∼ > 7 may trace a rare population with intense radiation fields capable of ionizing their surrounding hydrogen distribution. Additional constraints on high ionization emission lines in galaxies with and without Lyα detections will help clarify whether hard ionizing spectra are common in the reionization era.

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.

We use the first data release from the SINGG H survey of H iYselected galaxies to study the quantitative behavior of the diffuse, warm ionized medium ( WIM ) across the range of properties represented by these 109 galaxies. The mean fraction f WIM of diffuse ionized gas in this sample is 0:59 AE 0:19, slightly higher than found in previous samples. Since lower surface brightness galaxies tend to have higher f WIM , we believe that most of this difference is due to selection effects favoring large, optically bright, nearby galaxies with high star formation rates. As found in previous studies, there is no appreciable correlation with Hubble type or total star formation rate. However, we find that starburst galaxies, defined here by an H surface brightness >2:5 ; 10 39 erg s À1 kpc À2 within the H half-light radius, do show much lower fractions of diffuse H emission. The cause apparently is not dominated by a lower fraction of field OB stars. However, it is qualitatively consistent with an expected escape of ionizing radiation above a threshold star formation rate, predicted from our model in which the ISM is shredded by pressure-driven supernova feedback. The H i gas fractions in the starburst galaxies are also lower, suggesting that the starbursts are consuming and ionizing all the gas, and thus promoting regions of density-bounded ionization. If true, these effects imply that some amount of Lyman continuum radiation is escaping from most starburst galaxies, and that WIM properties and outflows from mechanical feedback are likely to be pressure-driven. However, in view of previous studies showing that the escape fraction of ionizing radiation is generally low, it is likely that other factors also drive the low fractions of diffuse ionized gas in starbursts.

It is generally believed that expanding superbubbles and mechanical feedback from massive stars trigger star formation, because there are numerous examples of superbubbles showing secondary star formation at their edges. However, although these systems show an age sequence, they do not provide strong evidence of a causal relationship. The W3/ W4 Galactic star-forming complex suggests a three-generation hierarchy: the supergiant shell structures correspond to the oldest generation; these triggered the formation of IC 1795 in W3, the progenitor of a molecular superbubble that in turn triggered the current star-forming episodes in the embedded regions W3-North, W3-Main, and W3-OH. We present UBV photometry and spectroscopic classifications for IC 1795, which show an age of 3-5 Myr. This age is intermediate between the reported 6-20 Myr age of the supergiant shell system and the extremely young ages (10 4 -10 5 yr) for the embedded knots of the ultracompact H ii regions, W3-North, W3-Main, and W3-OH. Thus, an age sequence is indeed confirmed for the entire W3/ W4 hierarchical system. This therefore provides some of the first convincing evidence that superbubble action and mechanical feedback are indeed a triggering mechanism for star formation.

Citation for published item:wleD FhF nd igmiD iF nd fussmnnD FF nd qurwellD wF nd svisonD FtF nd fooneD pF nd gomesD pF nd hnielsonD eFvFF nd exD wF nd ihrdD tF nd milD sF nd winnkD eFwF nd eltieriD fF nd flinD eFF nd glementD fF nd hessugesEvdskyD wF nd idgeD eFgF nd pzioD qFqF nd tonesD F nd uneiD tFEF nd ymontD eF nd ¡ erezEqonz¡ lezD FqF nd hererD hF nd lthnovD sF nd vn der erfD FF nd lthD qF nd mojskiD wF nd emovD wF @PHIRA 9g ss nd IPgy@IEHA emission mps in rvtHWIVPVFTCSIRPPQ X strongly lensed interting system t z a SFPRF9D estrophysil journlFD UVQ @IAF pF SWF Further information on publisher's website: Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT We present Submillimeter Array [C ii] 158 μm and Karl G. Jansky Very Large Array 12 CO(1-0) line emission maps for the bright, lensed, submillimeter source at z = 5.2430 behind A 773: HLSJ091828.6+514223 (HLS0918). We combine these measurements with previously reported line profiles, including multiple 12 CO rotational transitions, [C i], water, and [N ii], providing some of the best constraints on the properties of the interstellar medium in a galaxy at z > 5. HLS0918 has a total far-infrared (FIR) luminosity L FIR(8-1000 μm) = (1.6 ± 0.1) × 10 14 L μ −1 , where the total magnification μ total = 8.9 ± 1.9, via a new lens model from the [C ii] and continuum maps. Despite a HyLIRG luminosity, the FIR continuum shape resembles that of a local LIRG. We simultaneously fit all of the observed spectral line profiles, finding four components that correspond cleanly to discrete spatial structures identified in the maps. The two most redshifted spectral components occupy the nucleus of a massive galaxy, with a source-plane separation <1 kpc. The reddest dominates the continuum map (demagnified L FIR,component = (1.1 ± 0.2) × 10 13 L ) and excites strong water emission in both nuclear components via a powerful FIR radiation field from the intense star formation. A third star-forming component is most likely a region of a merging companion (ΔV ∼ 500 km s −1 ) exhibiting generally similar gas properties. The bluest component originates from a spatially distinct region and photodissociation region analysis suggests that it is lower density, cooler, and forming stars less vigorously than the other components. Strikingly, it has very strong [N ii] emission, which may suggest an ionized, molecular outflow. This comprehensive view of gas properties and morphology in HLS0918 previews the science possible for a large sample of high-redshift galaxies once ALM...