We discuss new Keck/MOSFIRE spectroscopic observations of four luminous galaxies at z ... 7-9 selected to have intense optical line emission by Roberts-Borsani et al. Previous follow-up has revealed ...Ly... in two of the four galaxies. Our new MOSFIRE observations confirm that Ly... is present in the entire sample. We detect Ly... emission in the galaxy COS-zs7-1, confirming its redshift as z^sub Ly...^ = 7.154, and we detect Ly... in EGS-zs8-2 at z^sub Ly...^ = 7.477, verifying an earlier tentative detection. The ubiquity of Ly... in this sample is puzzling given that the IGM is expected to be significantly neutral over 7 < z < 9. To investigate this result in more detail, we have initiated a campaign to target UV metal lines in the four Ly... emitters as a probe of both the ionizing field and the Ly... velocity offset at early times. Here we present the detection of C iii emission in the z = 7.73 galaxy EGS-zs8-1, requiring an intense radiation field and moderately low metallicity. We argue that the radiation field is likely to affect the local environment, increasing the transmission of Ly... through the galaxy. Moreover, the centroid of C...iii indicates that Ly... is redshifted by 340 km s^sup -1^. This velocity offset is larger than that seen in less luminous systems, providing an explanation for the transmission of Ly... emission through the IGM. Since the transmission is further enhanced by the likelihood that such systems are also situated in large ionized bubbles, the visibility of Ly... at z > 7 is expected to be strongly luminosity-dependent, with transmission accelerated in systems with intense star formation. (ProQuest: ... denotes formulae/symbols omitted.)
We present Keck/MOSFIRE observations of UV metal emission 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 Lya redshift of z = 7.045, reveals a confident detection of the nebular Civ ...1548 emission line (unresolved with full width at half-maximum<125 km s...). UV metal emission lines are not detected in the three other galaxies. At z ... 2-3, nebular Civ emission is observed in just 1 per cent of UV-selected galaxies. The presence of strong Civ emission in one of the small sample of galaxies targeted in this paper may indicate that hard ionizing spectra are more common at z ... 7. The total estimated rest-frame equivalent width of the C iv doublet and C iv/Lya flux ratio 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 1500 A luminosity (log(.../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 Lya 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 Lya detections will help clarify whether hard ionizing spectra are common in the reionization era. (ProQuest: ... denotes formulae/symbols omitted.)
We present Keck/MOSFIRE observations of UV metal emission 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 Lya redshift of z = 7.045, reveals a confident detection of the nebular Civ ...1548 emission line (unresolved with full width at half-maximum<125 km s...). UV metal emission lines are not detected in the three other galaxies. At z ... 2-3, nebular Civ emission is observed in just 1 per cent of UV-selected galaxies. The presence of strong Civ emission in one of the small sample of galaxies targeted in this paper may indicate that hard ionizing spectra are more common at z ... 7. The total estimated rest-frame equivalent width of the C iv doublet and C iv/Lya flux ratio 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 1500 A luminosity (log(.../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 Lya 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 Lya detections will help clarify whether hard ionizing spectra are common in the reionization era. (ProQuest: ... denotes formulae/symbols omitted.)
We present new observations of sixteen bright ($r=19-21$) gravitationally
lensed galaxies at $z\simeq 1-3$ selected from the CASSOWARY survey. Included
in our sample is the $z=1.42$ galaxy CSWA-141, ...one of the brightest known
reionization-era analogs at high redshift (g=20.5), with a large sSFR (31.2
Gyr$^{-1}$) and an OIII+H$\beta$ equivalent width
(EW$_{\rm{OIII+H\beta}}$=730~\r{A}) that is nearly identical to the average
value expected at $z\simeq 7-8$. In this paper, we investigate the rest-frame
UV nebular line emission in our sample with the goal of understanding the
factors that regulate strong CIII emission. Whereas most of the sources in our
sample show weak UV line emission, we find elevated CIII in the spectrum of
CSWA-141 (EW$_{\rm{CIII}}$=4.6$\pm1.9$~\r{A}) together with detections of
other prominent emission lines (OIII, Si III, Fe II$^\star$, Mg II). We
compare the rest-optical line properties of high redshift galaxies with strong
and weak CIII emission, and find that systems with the strongest UV line
emission tend to have young stellar populations and nebular gas that is
moderately metal-poor and highly ionized, consistent with trends seen at low
and high redshift. The brightness of CSWA-141 enables detailed investigation of
the extreme emission line galaxies which become common at $z>6$. We find that
gas traced by the CIII doublet likely probes higher densities than that traced
by OII and SII. Characterisation of the spectrally resolved Mg II emission
line and several low ionization absorption lines suggests neutral gas around
the young stars is likely optically thin, potentially facilitating the escape
of ionizing radiation.
JWST has recently discovered a subset of reionization era galaxies with ionized gas that is metal poor in oxygen and carbon but heavily-enriched in nitrogen. This abundance pattern is almost never ...seen in lower redshift galaxies but is commonly observed in globular cluster stars. We have recently demonstrated that this peculiar abundance pattern appears in a compact (\(\simeq 20\) pc) metal-poor galaxy undergoing a strong burst of star formation. This galaxy was originally selected based on strong CIV emission, indicating a hard radiation field rarely seen locally. In this paper, we present JWST/NIRSpec observations of another reionization-era galaxy known to power strong CIV emission, the \(z=7.04\) gravitationally-lensed galaxy A1703-zd6. The emission line spectrum reveals this is a metal poor galaxy (\(12+\log(\rm O/H) = 7.47\pm0.19\)) dominated by a young stellar population (\(1.6^{+0.5}_{-0.4}\) Myr) that powers a very hard ionizing spectrum (CIV EW = 19.4 \(\unicode{x212B}\), He II EW = 2.2 \(\unicode{x212B}\)). The ISM is highly-enriched in nitrogen (\(\log(\rm N/O)=-0.6\)) with very high electron densities (\(8-19\times10^4\) cm\(^{-3}\)) and extreme ionization conditions rarely seen at lower redshift. We also find intense CIV emission (EW\(\gtrsim20\) \(\unicode{x212B}\)) in two new \(z\gtrsim 6\) metal poor galaxies. To put these results in context, we search for UV line emission in a sample of 737 \(z\gtrsim 4\) galaxies with NIRSpec spectra, establishing that 40(30)% of systems with OIII+H\(\beta\) EW \(>2000\unicode{x212B}\) have NIV (CIV) detections with EW\(>5\) \(\unicode{x212B}\) (\(>10\) \(\unicode{x212B}\)). These results suggest high N/O ratios and hard ionizing sources appear in a brief phase following a burst of star formation in compact high density stellar complexes.
Nearly a decade ago, we began to see indications that reionization-era
galaxies power hard radiation fields rarely seen at lower redshift. Most
striking were detections of nebular CIV emission in ...what appeared to be typical
low mass galaxies, requiring an ample supply of 48 eV photons to triply ionize
carbon. The nature of this population has long remained unclear owing to
limitations of ground-based spectroscopy. We have obtained deep JWST/NIRSpec
R=1000 spectroscopy of the two z>6 CIV-emitting galaxies known prior to JWST.
Here we present a rest-UV to optical spectrum of one of these two systems, the
multiply-imaged z=6.1 lensed galaxy RXCJ2248-ID. NIRCam imaging reveals two
compact (<22pc) clumps separated by 220pc, with one comprising a dense
concentration of massive stars ($>10,400M_{\odot}$/yr/kpc$^2$) formed in a
recent burst. We stack spectra of 3 images of the galaxy (J=24.8-25.9),
yielding a very deep spectrum providing a high S/N template of strong emission
line sources at z>6. The spectrum reveals narrow high ionization lines (HeII,
CIV, NIV) with line ratios consistent with powering by massive stars. The
rest-optical spectrum is dominated by very strong emission lines (OIII
EW=2800\AA), albeit with weak emission from low-ionization transitions
(OIII/OII=184). The electron density is found to be very
high($6.4-31\times10^4$cm$^{-3}$) based on three UV transitions. The ionized
gas is metal poor ($12+\log(\rm O/H)=7.43^{+0.17}_{-0.09}$), yet highly
enriched in nitrogen ($\log(\rm N/O)=-0.39^{+0.11}_{-0.10}$). The spectrum
appears broadly similar to that of GNz11 at z=10.6, without showing the same
AGN signatures. We suggest that the hard radiation field and rapid nitrogen
enrichment may be a short-lived phase that many z>6 galaxies go through as they
undergo strong bursts of star formation. We comment on the potential link of
such spectra to globular cluster formation.
Extreme, young stellar populations are considered the primary contributor to cosmic re-ionization. How Lyman-continuum (LyC) escapes these galaxies remains highly elusive, and it is challenging to ...observe this process in actual LyC emitters without resolving the relevant physical scales. We investigate the Sunburst Arc: a strongly lensed, LyC emitter at \(z =2.37\) that reveals an exceptionally small scale (tens of parsecs) region of high LyC escape. The small (\(<\) 100 pc) LyC leaking region has extreme properties: a very blue UV slope (\(\beta = -2.9 \pm 0.1\)), high ionization state (O III\(\lambda 5007\)/O II\(\lambda 3727 \) \(= 11 \pm 3\) and O III\(\lambda 5007\)/H\(\beta\) \(=6.8 \pm 0.4\)), strong oxygen emission (EW(O III) \(= 1095 \pm 40 \ Å\)), and high Lyman-\(\alpha\) escape fraction (\(0.3 \pm 0.03\)), none of which are found in non-leaking regions of the galaxy. The leaking region's UV slope is consistent with approximately ``pure'' stellar light that is minimally contaminated by surrounding nebular continuum emission or extinguished by dust. These results suggest a highly anisotropic LyC escape process such that LyC is produced and escapes from a small, extreme starburst region where the stellar feedback from an ionizing star cluster creates one or more ``pencil beam'' channels in the surrounding gas through which LyC can directly escape. Such anisotropic escape processes imply that random sightline effects drive the significant scatters between measurements of galaxy properties and LyC escape fraction, and that strong lensing is a critical tool for resolving the processes that regulate the ionizing budget of galaxies for re-ionization.
We analyze spectra of a gravitationally lensed galaxy, known as the Sunburst Arc, that is leaking ionizing photons, also known as the Lyman continuum (LyC). Magnification from gravitational lensing ...permits the galaxy to be spatially resolved into one region that leaks ionizing photons, and several that do not. Rest-frame ultraviolet and optical spectra from Magellan target ten different regions along the lensed Arc, including six multiple images of the LyC leaking region, as well as four regions that do not show LyC emission. The rest-frame optical spectra of the ionizing photon emitting regions reveal a blue-shifted (\(\Delta V\)=27 km s\(^{-1}\)) broad emission component (FWHM=327 km s\(^{-1}\)) comprising 55% of the total OIII line flux, in addition to a narrow component (FWHM = 112 km s\(^{-1}\)), suggesting the presence of strong highly ionized gas outflows. This is consistent with the high-velocity ionized outflow inferred from the rest-frame UV spectra. In contrast, the broad emission component is less prominent in the non-leaking regions, comprising \(\sim\)26% of total OIII line flux. The high ionization absorption lines are prominent in both leaker and non-leaker but low ionization absorption lines are very weak in the leaker, suggesting that the line of sight gas is highly ionized in the leaker. Analyses of stellar wind features reveal that the stellar population of the LyC leaking regions is considerably younger (\(\sim\)3 Myr) than the non-leaking regions (\(\sim\)12 Myr), highlighting that stellar feedback from young stars may play an important role in ionizing photon escape.
![Ly[alpha] and C III] emissi...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0035-8711/small "Ly[alpha] and C III] emission in z = 7-9 Galaxies: accelerated reionization around luminous star-forming systems?")
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