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Register a new userDiscovery of a z = 7.452 High Equivalent Width Lyman-{alpha} Emitter from the Hubble Space Telescope Faint Infrared Grism Survey
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We present the results of an unbiased search for Ly{alpha} emission from continuum-selected 6 < z < 8 galaxies. Our dataset consists of 160 orbits of G102 slitless grism spectroscopy obtained with the Hubble Space Telescope (HST) Wide Field Camera 3 as part of the Faint Infrared Grism Survey (FIGS; PI: Malhotra), which obtains deep slitless spectra of all sources in four fields, and was designed to minimize contamination in observations of previously-identified high-redshift galaxy candidates. The FIGS data can potentially spectroscopically confirm the redshifts of galaxies, and as Ly{alpha} emission is resonantly scattered by neutral gas, FIGS can also constrain the ionization state of the intergalactic medium (IGM) during the epoch of reionization. These data have sufficient depth to detect Ly{alpha} emission in this epoch, as Tilvi et al. (2016) have published the FIGS detection of previously known (Finkelstein et al. 2013) Ly{alpha} emission at z = 7.51. The FIGS data use five separate roll-angles of HST to mitigate the contamination by nearby galaxies. We created a method that accounts for and removes the contamination from surrounding galaxies, and also removes any dispersed continuum light from each individual spectrum (Pirzkal et al. 2017). We searched for significant (> 4{sigma}) emission lines using two different automated detection methods, free of any visual inspection biases. Applying these methods on photometrically-selected high-redshift candidates between 6 < z < 8 we find two emission lines, one previously published by Tilvi et al. (2016), and a new line at 1.028{mu}m. We identify this lines as Ly{alpha} at z = 7.452 +/- 0.003. This newly spectroscopically confirmed galaxy has the highest Ly{alpha} rest-frame equivalent width (EW Ly{alpha}) yet published at z > 7 (140.3 +/- 19.0{AA}).
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Galaxies at high redshifts provide a valuable tool to study cosmic dawn, and therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyman-alpha emission and the Lyman break from a z = 7.512+/- 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with G102 grism on Hubble Space Telescope (HST), show a significant emission line detection (6 sigma) in multiple observational position angles (PA), with total integrated Ly{alpha} line flux of 1.06+/- 0.12 e10-17erg s-1cm-2. The line flux is nearly a factor of four higher than the previous MOSFIRE spectroscopic observations of faint Ly{alpha} emission at {lambda} = 1.0347{mu}m, yielding z = 7.5078+/- 0.0004. This is consistent with other recent observations implying that ground-based near-infrared spectroscopy underestimates total emission line fluxes, and if confirmed, can have strong implications for reionization studies that are based on ground-based Lyman-{alpha} measurements. A 4-{sigma} detection of the NV line in one PA also suggests a weak Active Galactic Nucleus (AGN), potentially making this source the highest-redshift AGN yet found. Thus, this observation from the Hubble Space Telescope clearly demonstrates the sensitivity of the FIGS survey, and the capability of grism spectroscopy to study the epoch of reionization.
We present the highest redshift detections of resolved Lyman alpha emission, using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyman alpha emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyman alpha photons at high redshift. While our data do not support a positional offset between the Lyman alpha and rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out of the three galaxies are significantly larger in Lyman alpha than in the rest-frame UV continuum. This result is confirmed when comparing object sizes in a stack of all objects in both bands. Additionally, the narrowband flux detected with HST is significantly less than observed in similar filters from the ground. These results together imply that the Lyman alpha emission is not strictly confined to its indigenous star-forming regions. Rather, the Lyman alpha emission is more extended, with the missing HST flux likely existing in a diffuse outer halo. This suggests that the radiative transfer of Lyman alpha photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.
We present a flux-limited sample of $zsim0.3$ Ly$alpha$ emitters (LAEs) from Galaxy Evolution Explorer (GALEX) grism spectroscopic data. The published GALEX $zsim0.3$ LAE sample is pre-selected from continuum-bright objects and thus is biased against high equivalent width (EW) LAEs. We remove this continuum pre-selection and compute the EW distribution and the luminosity function of the Ly$alpha$ emission line directly from our sample. We examine the evolution of these quantities from $zsim0.3$ to $2.2$ and find that the EW distribution shows little evidence for evolution over this redshift range. As shown by previous studies, the Ly$alpha$ luminosity density from star-forming galaxies declines rapidly with declining redshift. However, we find that the decline in Ly$alpha$ luminosity density from $z=2.2$ to $z=0.3$ may simply mirror the decline seen in the H$alpha$ luminosity density from $z=2.2$ to $z=0.4$, implying little change in the volumetric Ly$alpha$ escape fraction. Finally, we show that the observed Ly$alpha$ luminosity density from AGNs is comparable to the observed Ly$alpha$ luminosity density from star-forming galaxies at $z=0.3$. We suggest that this significant contribution from AGNs to the total observed Ly$alpha$ luminosity density persists out to $zsim2.2$.
We present Hubble WFC3/IR slitless grism spectra of a remarkably bright $zgtrsim10$ galaxy candidate, GN-z11, identified initially from CANDELS/GOODS-N imaging data. A significant spectroscopic continuum break is detected at $lambda=1.47pm0.01~mu$m. The new grism data, combined with the photometric data, rule out all plausible lower redshift solutions for this source. The only viable solution is that this continuum break is the Ly$alpha$ break redshifted to ${z_mathrm{grism}=11.09^{+0.08}_{-0.12}}$, just $sim$400 Myr after the Big Bang. This observation extends the current spectroscopic frontier by 150 Myr to well before the Planck (instantaneous) cosmic reionization peak at z~8.8, demonstrating that galaxy build-up was well underway early in the reionization epoch at z>10. GN-z11 is remarkably and unexpectedly luminous for a galaxy at such an early time: its UV luminosity is 3x larger than L* measured at z~6-8. The Spitzer IRAC detections up to 4.5 $mu$m of this galaxy are consistent with a stellar mass of ${sim10^{9}~M_odot}$. This spectroscopic redshift measurement suggests that the James Webb Space Telescope (JWST) will be able to similarly and easily confirm such sources at z>10 and characterize their physical properties through detailed spectroscopy. Furthermore, WFIRST, with its wide-field near-IR imaging, would find large numbers of similar galaxies and contribute greatly to JWSTs spectroscopy, if it is launched early enough to overlap with JWST.
The CIII] and CIV rest-frame UV emission lines are powerful probes of the ionizations states of galaxies. They have furthermore been suggested as alternatives for spectroscopic redshift confirmation of objects at the epoch of reionization ($z>6$), where the most frequently used redshift indicator, Ly$alpha$, is attenuated by the high fraction of neutral hydrogen in the inter-galactic medium. However, currently only very few confirmations of carbon UV lines at these high redshifts exist, making it challenging to quantify these claims. Here, we present the detection of CIV$lambdalambda$1548,1551AA in HST slitless grism spectroscopy obtained by GLASS of a Ly$alpha$ emitter at $z=6.11$ multiply imaged by the massive foreground galaxy cluster RXJ2248. The CIV emission is detected at the 3--5$sigma$ level in two images of the source, with marginal detection in two other images. We do not detect significant CIII]$lambdalambda$1907,1909AA emission implying an equivalent width EW$_textrm{CIII]}<20$AA (1$sigma$) and $textrm{CIV/CIII}>0.7$ (2$sigma$). Combined with limits on the rest-frame UV flux from the HeII$lambda$1640AA emission line and the OIII]$lambdalambda$1661,1666AA doublet, we put constraints on the metallicity and the ionization state of the galaxy. The estimated line ratios and equivalent widths do not support a scenario where an AGN is responsible for ionizing the carbon atoms. SED fits including nebular emission lines imply a source with a mass of log(M/M$_odot)sim9$, SFR of around 10M$_odot$/yr, and a young stellar population $<50$Myr old. The source shows a stronger ionizing radiation field than objects with detected CIV emission at $z<2$ and adds to the growing sample of low-mass (log(M/M$_odot)lesssim9$) galaxies at the epoch of reionization with strong radiation fields from star formation.
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