Lyman-alpha Research Articles

Lyman continuum leaker candidates at z ∼ 3–4 in the HDUV based on a spectroscopic sample of MUSE LAEs

Context. In recent years, a number of Lyman continuum (LyC) leaker candidates have been found at intermediate redshifts, providing insight into how the Universe was reionised at early cosmic times. There are now around 100 known LyC leakers at all redshifts, which enables us to analyse their properties statistically. Aims. Here, we identify new LyC leaker candidates at z ≈ 3 − 4.5 and compare them to objects from the literature to get an overview of the different observed escape fractions and their relation to the properties of the Lyman α (Lyα) emission line. The aim of this work is to test the indicators (or proxies) for LyC leakage suggested in the literature and to improve our understanding of the kinds of galaxies from which LyC radiation can escape. Methods. We used data from the Hubble Deep Ultraviolet (HDUV) legacy survey to search for LyC emission based on a sample of ≈2000 Lyα emitters (LAEs) detected previously in two surveys with the Multi-Unit Spectroscopic Explorer (MUSE), namely MUSE-Deep and MUSE-Wide. Based on the redshifts and positions of the LAEs, we look for potential LyC leakage in the WFC3/UVIS F336W band of the HDUV survey. The escape fractions are measured and compared in different ways, including spectral energy distribution (SED) fitting performed using the CIGALE software. Results. We add 12 objects to the sample of known LyC leaker candidates (5 highly likely leakers and 7 potential ones), 1 of which was previously known, and compare their Lyα properties to their escape fractions. We find escape fractions of between ∼20% and ∼90%, assuming a high transmission in the intergalactic medium (IGM). We present a method whereby the number of LyC leaker candidates we find is used to infer the underlying average escape fraction of galaxies, which is ≈12%. Conclusion. Based on their Lyα properties, we conclude that LyC leakers are not very different from other high-z LAEs and suggest that most LAEs could be leaking LyC even if this cannot always be detected because of the direction of emission and the transmission properties of the IGM.

Review of recent analytical advances in the spectroscopy of hydrogenic lines in plasmas

Abstract Broadening of hydrogenic spectral lines is an important tool in spectroscopic diagnostics of various laboratory and astrophysical plasmas. We review recent analytical advances in three areas. First, we review the analytical solution for the splitting of hydrogenic lines under the combination of a circularly polarized electromagnetic wave with a strong magnetic field. Practical applications of this solution relate to the spectroscopic diagnostic of the electron cyclotron waves and to the relativistic laser–plasma interactions. Second, we review analytical results concerning the Stark–Zeeman broadening of the Lyman-alpha (Ly-alpha) line in plasmas. These results allow for the Stark width of the Ly-alpha π-component to be used for the experimental determination of the ion density or of the root-mean-square field of a low-frequency electrostatic plasma turbulence in the situation where the Zeeman effect dominates over the Stark effects. Third, we review recent analytical advances in the area of the intra-Stark spectroscopy: three different new methods, based on the emergent phenomenon of the Langmuir-wave-caused structures (“L-dips”) in the line profiles, for measuring super-strong magnetic fields of the GigaGauss range developing during relativistic laser–plasma interactions. We also review the rich physics behind the L-dips phenomenon – because there was a confusion in the literature in this regard.

JADES: The production and escape of ionizing photons from faint Lyman-alpha emitters in the epoch of reionization

We present the properties of 17 faint Lyman-α emitting galaxies (LAEs) at z > 5.8 from the JWST Advanced Deep Extragalactic Survey (JADES) spectroscopic data in the Hubble Ultra Deep Field/GOODS-S. These LAEs span a redshift range z ≈ 5.8 − 8.0 and a UV magnitude range MUV ≈ −17 to −20.6, with the Lyα equivalent width (EW) in the range ≈25 − 350 Å. The detection of other rest-optical emission lines in the spectra of these LAEs enables the determination of accurate systemic redshifts and Lyα velocity offsets, as well as the physical and chemical composition of their stars and interstellar media. These faint LAEs are consistent with metal-poor systems with high ionization parameters, similar to the general galaxy population at z > 6. We measured an average ionizing photon production efficiency, log(ξion/erg−1 Hz) ≈ 25.57 across our LAEs, which does not evolve strongly with redshift. We report an anti-correlation between the Lyα escape fraction and the velocity offset from systemic redshift, consistent with model expectations. We further find that the strength and velocity offset of Lyα are neither correlated with galaxy spectroscopic properties nor with ξion. We find a decrease in Lyα escape fractions with redshift, indicative of decreasing sizes of ionized bubbles around LAEs at high redshifts. We used a range of galaxy properties to predict Lyman continuum escape fractions for our LAEs, finding that the ionizing photon output into the intergalactic medium from our LAEs remains roughly constant across the observed Lyα EW, showing a mild increase at fainter UV magnitudes and at higher redshifts. We derived correlations between the ionizing photon output from LAEs and their UV magnitudes, Lyα strengths and redshifts, which can be used to constrain the ionizing photon contribution of LAEs at z > 6 towards cosmic reionization.

Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium

Ultraviolet (UV) processing in the interstellar medium (ISM) induces the dehydrogenation of hydrocarbons. Aliphatics, including alkanes, are present in different interstellar environments, being prevalently formed in evolved stars; thus, the dehydrogenation by UV photoprocessing of alkanes plays an important role in the chemistry of the ISM, leading to the formation of unsaturated hydrocarbons and eventually to aromatics, the latter ubiquitously detected in the ISM. Here, through combined experimental results and ab initio calculations, we show that UV absorption (mainly at the Lyα emission line of hydrogen at 121.6 nm) promotes an alkane to an excited Rydberg state from where it evolves toward fragmentation, inducing the formation of olefinic C=C bonds, which are necessary precursors of aromatic hydrocarbons. We show that the photochemistry of aliphatics in the ISM does not primarily produce direct hydrogen elimination but preferential C–C photocleavage. Our results provide an efficient synthetic route for the formation of unsaturated aliphatics, including propene and dienes, and suggest that aromatics could be formed in dark clouds by a bottom-up mechanism involving molecular fragments produced by UV photoprocessing of aliphatics.

Polarimetry of the Lyα envelope of the radio-quiet quasar SDSS J124020.91+145535.6

The radio quiet quasar SDSS J1240+1455 lies at a redshift of z = 3.11, is surrounded by a Lyα blob (LAB), and is absorbed by a proximate damped Lyα system. In order to better define the morphology of the blob and determine its emission mechanism, we gathered deep narrow-band images isolating the Lyα line of this object in linearly polarized light. We provide a deep intensity image of the blob, showing a filamentary structure extending up to 16″ (or 122 physical kpc) in diameter. No significant polarization signal could be extracted from the data, but 95% probability upper limits were defined through simulations. They vary between ∼3% in the central 0.75″ disk (after subtraction of the unpolarized quasar continuum) and ∼10% in the 3.8 − 5.5″ annulus. The low polarization suggests that the Lyα photons are emitted mostly in situ, by recombination and de-excitation in a gas largely ionized by the quasar ultraviolet light, rather than by a central source and scattered subsequently by neutral hydrogen gas. This blob shows no detectable polarization signal, contrary to LAB1, a brighter and more extended blob that is not related to the nearby active galactic nucleus (AGN) in any obvious way, and where a significant polarization signal of about 18% was detected.

Super-early JWST galaxies, outflows, and Lyα visibility in the Epoch of Reionization

The overabundance of super-early (redshift z > 10) luminous (MUV < −20) blue galaxies detected by JWST has been explained as being due to negligible dust attenuation in these systems. We show that this model correctly reproduces the UV luminosity function at z > 10 and the star formation rate (SFR) density evolution. The model also predicts, in agreement with data, that the cosmic specific SFR (sSFR) grows as sSFR ∝ (1 + z)3/2. At z ≃ 10, the cosmic sSFR crosses the critical value sSFR⋆ = 25 Gyr−1, and approximately 45% of the galaxies become super-Eddington, driving outflows reaching velocities of ≈830(ϵ⋆/fM)1/2 km s−1, where ϵ⋆ and fM are the star formation efficiency and fraction of the halo gas expelled in the outflow, respectively. This prediction is consistent with the outflow velocities measured in 12 super-Eddington galaxies of the JWST/JADES sample. Such outflows clear the dust, thus boosting the galaxy luminosity. They also dramatically enhance the visibility of the Lyα line from z > 10 galaxies by introducing a velocity offset. The observed Lyα properties in GN-z11 (z = 10.6) are simultaneously recovered by the outflow model if log NHI ≃ 20.1, implying that the outflow is largely ionized. We make analogous predictions for the Lyα visibility of other super-early galaxies, and we compare the model with Lyα surveys at z > 7, finding that essentially all super-Eddington (sub-Eddington) galaxies are (not) detected in Lyα. Finally, the sSFR positively correlates with the LyC escape fraction, as outflows carve ionized transparent channels through which LyC photons leak.

Lyα at Cosmic Dawn with a Simulated Roman Grism Deep Field

The slitless grism on the Nancy Grace Roman Space Telescope will enable deep near-infrared spectroscopy over a wide field of view. We demonstrate Roman's capability to detect Lyα galaxies at z > 7 using a multiple position angle (PA) observational strategy. We simulate Roman grism data using a realistic foreground scene from the COSMOS field. We also input fake Lyα galaxies spanning redshift z = 7.5–10.5 and a line-flux range of interest. We show how a novel data-cube search technique—CUBGRISM—originally developed for the Galaxy Evolution Explorer can be applied to Roman grism data to produce a Lyα flux-limited sample without the need for continuum detections. We investigate the impact of altering the number of independent PAs and exposure time. A deep Roman grism survey with 25 PAs and a total exposure time of 70 hr can achieve Lyα line depths comparable to the deepest z = 7 narrowband surveys (L Lyα ≳ 1043 erg s−1). Assuming a null result, where the opacity of the intergalactic medium (IGM) remains unchanged from z ∼ 7, this level of sensitivity will detect ∼400 deg−2 Lyα emitters from z = 7.25 to 8.75. A decline from this expected number density is the signature of an increasing neutral hydrogen fraction and the onset of reionization. Our simulations indicate that a deep Roman grism survey has the ability to measure the timing and magnitude of this decline, allowing us to infer the ionization state of the IGM and helping us to distinguish between models of reionization.

Large-scale excess H i absorption around z ≈ 4 galaxies detected in a background galaxy spectrum in the MUSE eXtremely deep field

ABSTRACT Observationally mapping the relation between galaxies and the intergalactic medium (IGM) is of key interest for studies of cosmic reionization. Diffuse hydrogen gas has typically been observed in H i Lyman-α (Lyα) absorption in the spectra of bright background quasars. However, it is important to extend these measurements to background galaxies as quasars become increasingly rare at high redshift and rarely probe closely separated sight lines. Here, we use deep integral field spectroscopy in the MUSE eXtremely Deep Field to demonstrate the measurement of the Lyα transmission at z ≈ 4 in absorption to a background galaxy at z = 4.77. The H i transmission is consistent with independent quasar sight lines at similar redshifts. Exploiting the high number of spectroscopic redshifts of faint galaxies (500 between z = 4.0–4.7 within a radius of 8 arcmin) that are tracers of the density field, we show that Lyα transmission is inversely correlated with galaxy density, i.e. transparent regions in the Lyα forest mark underdense regions at z ≈ 4. Due to large-scale clustering, galaxies are surrounded by excess H i absorption over the cosmic mean out to 4 cMpc/h70. We also find that redshifts from the peak of the Lyα line are typically offset from the systemic redshift by +170 km s−1. This work extends results from z ≈ 2–3 to higher redshifts and demonstrates the power of deep integral field spectroscopy to simultaneously measure the ionization structure of the IGM and the large-scale density field in the early Universe.

Galaxy main sequence and properties of low-mass Lyman-α emitters towards reionisation as viewed by VLT/MUSE and JWST/NIRCam

Context. Faint, star-forming galaxies are likely to play a dominant role in cosmic reionisation. Great strides have been made in recent years to characterise these populations at high redshifts (z > 3). Now, for the first time, with JWST photometry beyond 1 μm in the rest frame, we can derive accurate stellar masses and position these galaxies on the galaxy main sequence. Aims. We seek to assess the place of 96 individual Lyman-α emitters (LAEs) selected behind the A2744 lensing cluster with MUSE IFU spectroscopy on the galaxy main sequence. We also compare the derived stellar masses to Lyman-α luminosities and equivalent widths to better quantify the relationship between the Lyman-α emission and the host galaxy. Methods. These 96 LAEs lie in the redshift range of 2.9 < z < 6.7, with their range of masses extending down to 106 M⊙ (over half with M⋆ < 108 M⊙). We used the JWST/NIRCam and HST photometric catalogues from the UNCOVER project, giving us excellent wavelength coverage from 450 nm to 4.5 μm. We also performed an SED fitting using CIGALE, fixing the redshift of the LAEs to the secure, spectroscopic value. This combination of photometric coverage with spectroscopic redshifts allows us to robustly derive stellar masses for these galaxies. Results. We found a main sequence relation for these low-mass LAEs of log SFR = (0.88 ± 0.07 − 0.030 ± 0.027 × t) log M⋆ − (6.31 ± 0.41 − 0.08 ± 0.37 × t). This is in relative agreement with the best-fit results of prior collated studies; however, here we see a steeper slope and a higher normalisation. This indicates that low-mass LAEs towards the epoch of reionisation lie above the typical literature main sequence relations derived at lower redshift and higher masses. In addition, by comparing our results to UV-selected samples, we can see that while low-mass LAEs lie above these typical main sequence relations, they are likely not singular in this respect at these particular masses and redshifts. While low-mass galaxies have been shown to play a significant role in cosmic reionisation, our results point to the likelihood that LAEs hold no special position in this regard.

Eruptive events with exceptionally bright emission in H I Ly-α observed by the Metis coronagraph

Context. Ultraviolet (UV) emission from coronal mass ejections can provide information on the evolution of plasma dynamics, temperature, and elemental composition, as demonstrated by the UV Coronagraph Spectrometer (UVCS) on board the SOlar and Heliospheric Observatory (SOHO). Metis, the coronagraph on board Solar Orbiter, provides for the first time coronagraphic imaging in the UV H I Ly-α line and, simultaneously, in polarized visible light, thus providing a host of information on the properties of coronal mass ejections and solar eruptions such as their overall dynamics, time evolution, mass content, and outflow propagation velocity in the expanding corona. Aims. For this work, we analyzed six coronal mass ejections observed by Metis between April and October 2021, which are characterized by a very strong H I Ly-α emission. We studied in particular the morphology, kinematics, and the temporal and radial evolution of the emission of such events, focusing on the brightest UV features. Methods. The kinematics of the eruptive events under consideration were studied by determining the height-time profiles of the brightest parts on the Metis plane of the sky. Furthermore, the 3D positions in the heliosphere of the coronal mass ejections were determined by employing co-temporal images, when available, from two other coronagraphs: LASCO/C2 on board SOHO, and COR2 on board STEREO-A. In three cases, the most likely source region on the solar surface could be identified. Finally, the radiometrically calibrated Metis images of the bright UV features were analyzed to provide estimates of their volume and density. From the kinematics and radiometric analysis, we obtained indications of the temperatures of the bright UV cores of these events. These results were then compared with previous studies with the UVCS spectrocoronagraph. Results. The analysis of these strong UV-emitting features associated with coronal mass ejections demonstrates the capabilities of the current constellation of space coronagraphs, Metis, LASCO/C2, and COR2, in providing a complete characterization of the structure and dynamics of eruptive events in their propagation phase from their inception up to several solar radii. Furthermore, we show how the unique capabilities of the Metis instrument to observe these events in both the H I Ly-α line and polarized VL radiation allow plasma diagnostics on the thermal state of these events.

Extended Lyman-α emission towards the SPT2349-56 protocluster at z = 4.3

Context. Deep spectroscopic surveys with the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed that some of the brightest infrared sources in the sky correspond to concentrations of submillimeter galaxies (SMGs) at high redshift. Among these, the SPT2349-56 protocluster system is amongst the most extreme examples given its high source density and integrated star formation rate. Aims. We conducted a deep Lyman-α line emission survey around SPT2349-56 using the Multi-Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT) in order to characterize this uniquely dense environment. Methods. Taking advantage of the deep three-dimensional nature of this survey, we performed a sensitive search for Lyman-α emitters (LAEs) toward the core and northern extension of the protocluster, which correspond to the brightest infrared regions in this field. Using a smoothed narrowband image extracted from the MUSE datacube around the protocluster redshift, we searched for possible extended structures. Results. We identify only three LAEs at z = 4.3 in this field. This number is lower than expectations for blank fields, and is significantly lower than the number of previously identified SMGs in this system. We find an extended Lyman-α structure of about 60 × 60 kpc2 in size located 56 kpc east of the protocluster core. Three SMGs coincide spatially with the location of this structure. All the other SMGs are undetected in Lyman-α emission, which is consistent with the conspicuous dust obscuration in these systems. We conclude that either the three co-spatial SMGs or the protocluster core itself are feeding ionizing photons to the Lyman-α structure.

Unveiling Luminous Lyα Emitters at z ≈ 6 through JWST/NIRCam Imaging in the COSMOS Field

We study a sample of 14 spectroscopically confirmed Lyα emitters (LAEs) in the late era of reionization (at redshift z ≈ 6) based on the JWST/NIRCam imaging data set. These LAEs with high Lyα luminosity of L(Lyα) ∼1042.4–1043.4 erg s−1 have been covered by the (ongoing) COSMOS-Web survey over 0.28 deg2 in four NIRCam bands (F115W, F150W, F277W, and F444W). With JWST/NIRCam imaging, we determine the UV continua with M UV ranging from −20.5 to −18.5 mag. The UV slopes have a median value of β ≈ −2.35, and the steepest slopes can reach β < −3. Under the excellent spatial resolution of JWST, we identify three objects in the sample as potential merging/interacting systems. The 14 LAEs (and their components) are compact in morphology, residing substantially below the mass–size relation of high-z galaxies. We further investigate their physical properties, including the stellar mass (M *) and star formation rates (SFRs). Most of the LAEs lie on the SFR–M * main-sequence relation, while two of them, featured as “little red dots,” likely host active galactic nuclei (AGNs), implying a ∼10% AGN fraction. Moreover, we reveal that a new correlation may exist between Lyα equivalent width and the offset between Lyα and UV emission (Δd Lyα ), with a median Δd Lyα ∼ 1 kpc. This could be explained by the Lyα radiative transfer process in both the interstellar medium and circumgalactic medium. The results usher in a new era of detailed analysis on high-z LAEs with the JWST capability.

MIDIS: JWST NIRCam and MIRI Unveil the Stellar Population Properties of Lyα Emitters and Lyman-break Galaxies at z ≃ 3–7

We study the stellar population properties of 182 spectroscopically confirmed (MUSE/VLT) Lyα emitters (LAEs) and 450 photometrically selected Lyman-break galaxies (LBGs) at z = 2.8–6.7 in the Hubble Extreme Deep Field. Leveraging the combined power of Hubble Space Telescope and JWST NIRCam and MIRI observations, we analyze their rest-frame UV-through-near-IR spectral energy distributions, with MIRI playing a crucial role in robustly assessing the LAEs’ stellar masses and ages. Our LAEs are low-mass objects (log10(M⋆/M⊙)≃7.5) with little or no dust extinction (E(B − V) ≃ 0.1) and a blue UV continuum slope (β ≃ −2.2). While 75% of our LAEs are young (<100 Myr), the remaining 25% have significantly older stellar populations (≥100 Myr). These old LAEs are statistically more massive, less extinct, and have lower specific star formation rate than young LAEs. Besides, they populate the plane of M ⋆ versus star formation rate along the main sequence of star-forming galaxies, while young LAEs populate the starburst region. The comparison between the LAEs’ properties and those of a stellar-mass-matched sample of LBGs shows no statistical difference between these objects, except for the LBGs’ redder UV continuum slope and marginally larger E(B − V) values. Interestingly, 48% of the LBGs have ages <10 Myr and are classified as starbursts, but lack detectable Lyα emission. This is likely due to H i resonant scattering and/or dust-selective extinction. Overall, we find that JWST observations are crucial in determining the properties of LAEs and shedding light on their comparison with LBGs.

Multiple Emission Lines of Hα Emitters at z ∼ 2.3 from the Broad- and Medium-band Photometry in the ZFOURGE Survey

We present a multiple emission line study of ∼1300 Hα emitters (HAEs) at z ∼ 2.3 in the ZFOURGE survey. In contrast to the traditional spectroscopic method, our sample is selected based on the flux excess in the ZFOURGE K s broadband data relative to the best-fit stellar continuum. Using the same method, we also extract the strong diagnostic emission lines for these individual HAEs: [O iii] λ λ4959, 5007 and [O ii] λ λ3726, 3729. Our measurements demonstrate good consistency with those obtained from spectroscopic surveys. We investigate the relationship between the equivalent widths (EWs) of these emission lines and various galaxy properties, including stellar mass, stellar age, star formation rate, specific star formation rate, and ionization state (O32). We have identified a discrepancy between HAEs at z ∼ 2.3 and typical local star-forming galaxies observed in the Sloan Digital Sky Survey, suggesting the evolution of lower gas-phase metallicity (Z) and higher ionization parameters (U) with redshift. Notably, we have observed a significant number of low-mass HAEs exhibiting exceptionally high EW[O iii]. Their galaxy properties are comparable to those of extreme objects, such as extreme O3 emitters and Lyα emitters at z ≃ 2–3. Considering that these characteristics may indicate potential strong Lyman continuum leakage, higher-redshift analogs of the low-mass HAEs could be significant contributors to the cosmic reionization. Further investigations of this particular population are required to gain a clearer understanding of galaxy evolution and cosmic reionization.

JADES: The emergence and evolution of Lyα emission and constraints on the intergalactic medium neutral fraction

The rest-frame UV recombination emission line Lyα can be powered by ionising photons from young massive stars in star-forming galaxies, but the fact that it can be resonantly scattered by neutral gas complicates its interpretation. For reionisation-era galaxies, a neutral intergalactic medium will scatter Lyα from the line of sight, making Lyα a useful probe of the neutral fraction evolution. Here, we explore Lyα in JWST/NIRSpec spectra from the ongoing JADES programme, which targets hundreds of galaxies in the well-studied GOODS-S and GOODS-N fields. These sources are UV-faint (−20.4 &lt; MUV &lt; −16.4) and thus represent a poorly explored class of galaxy. We fitted the low spectral resolution spectra (R ∼ 100) of a subset of 84 galaxies in GOODS-S with zspec &gt; 5.6 (as derived with optical lines) with line and continuum models to search for significant line emission. Through exploration of the R100 data, we find evidence for Lyα in 17 sources. This sample allowed us to place observational constraints on the fraction of galaxies with Lyα emission in the redshift range 5.6 &lt; z &lt; 7.5, with a decrease from z = 6 to z = 7. We also find a positive correlation between the Lyα equivalent width and MUV, as seen in other samples. We used these results to estimate the neutral gas fraction at z ∼ 7, and our estimates are in agreement with previous results (XHI ∼ 0.5 − 0.9).

Exploring the Gas-phase Metallicity Gradients of Star-forming Galaxies at Cosmic Noon

We explore the relationships between the [O/H] gas-phase metallicity radial gradients and multiple galaxy properties for 238 star-forming galaxies at 0.6 < z < 2.6 selected from the CANDELS Lyα Emission at Reionization survey with stellar mass 8.5<logM*/M⊙<10.5 . The gradients cover the range from −0.11 to 0.22 dex kpc−1, with the median value close to 0. We reconstruct the nonparametric star formation histories (SFHs) of the galaxies with spectral energy distribution modeling using Prospector with more than 40 photometric bands from the Hubble Space Telescope, Spitzer, and ground-based facilities. In general, we find weak or no correlations between the metallicity gradients and most galaxy properties, including the mass-weighted age, recent star formation rate, dust attenuation, and morphology as quantified by both parametric and nonparametric diagnostics. We find a significant but moderate correlation between the gradients and the “evolutionary time,” a temporal metric that characterizes the evolutionary status of a galaxy, with flatter gradients observed in more evolved galaxies. Also, there is evidence that galaxies with multiple star formation episodes in their SFHs tend to develop more negative gas-phase metallicity gradients (higher [O/H] at the center). We conclude that gas kinematics, e.g., radial inflows and outflows, is likely an important process in setting the gas-phase metallicity gradients, in addition to the evolution of the SFH radial profile. Since the gradients are largely independent of the galaxies’ physical properties and only weakly dependent on their SFH, it would appear that the timescale of the gas kinematics is significantly shorter than the evolution of star formation.

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During recombination, the cosmic background radiation is disturbed, in particular, by Lyman-alpha emissions from neutral hydrogen. It is proposed to account for the subsequent time-dependent partial thermalization of the Lyα\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document} energy content in an analytically solvable nonlinear diffusion model. The amplitude of the partially thermalized and redshifted Lyα\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document} line is found to be too low to be visible in the cosmic microwave spectrum, in accordance with previous numerical models and Planck observations.

The Magellan M2FS Spectroscopic Survey of High-redshift Galaxies: The Brightest Lyman-break Galaxies at z ∼ 6

We present a study of a sample of 45 spectroscopically confirmed, UV luminous galaxies at z ∼ 6. They were selected as bright Lyman-break galaxies (LBGs) using deep multiband optical images in more than 2 deg2 of the sky, and subsequently identified via their strong Lyα emission. The majority of these LBGs span an absolute UV magnitude range from −22.0 to −20.5 mag with Lyα equivalent width (EW) between ∼10 and ∼200 Å, representing the most luminous galaxies at z ∼ 6 in terms of both UV continuum emission and Lyα line emission. We model the spectral energy distributions of 10 LBGs that have deep infrared observations from Hubble Space Telescope, JWST, and/or Spitzer, and find that they have a wide range of stellar masses and ages. They also have high star formation rates ranging from a few tens to a few hundreds of solar mass per year. Five of the LBGs have JWST or HST images, and four of them show compact morphology in these images, including one that is roughly consistent with a point source, suggesting that UV luminous galaxies at this redshift are generally compact. The fraction of our photometrically selected LBGs with strong Lyα emission (EW > 25 Å) is about 0.2, which is consistent with previous results and supports a moderate evolution of the intergalactic medium opacity at the end of cosmic reionization. Using deep X-ray images, we do not find evidence of strong active galactic nucleus (AGN) activity in these galaxies, but our constraint is loose, and we are not able to rule out the possibility of any weak AGN activity.

Photoionization of Nitrile-substituted Naphthalene and Benzene: Cation Spectroscopy, Photostability, and Implications for Photoelectric Gas Heating

We investigate the vacuum ultraviolet (VUV) photodynamics of gas phase 1- and 2-cyanonaphthalene and cyanobenzene, recently detected in the Taurus molecular cloud, by combining synchrotron radiation and a double imaging electron/ion coincidence setup. The high-resolution threshold photoelectron spectra (TPES) of all three molecules are obtained experimentally from which the adiabatic ionization energies are reported with very high accuracy, particularly for 2-cyanonaphthalene, for which no data exist at this level of precision. Theoretical calculations are performed to compare with the TPES for the ground electronic state of the cations. Furthermore, the different features observed in the extended TPES have been assigned to the different molecular orbitals with the help of the outer valence Green's function calculations. The present experiments also shed light on the kinetic energy distribution of the photoelectrons as a function of the incident photon energy, to describe their contribution to the photoelectric heating effect in the interstellar medium. In this context, we show how kinetic energy distributions can be obtained from our data for any given photon energy, such as the omnipresent Lyα line, or any given interstellar radiation field (ISRF). In addition, from the total ion yields, we estimate the photorates for a few ISRFs. Finally, we discuss the photodissociation of the two cyanonaphthalenes, quoting the activation energies of the dissociation channels with the help of Rice–Ramsperger–Kassel–Marcus modeling. It is observed that CN substitution does not cause any appreciable change to the VUV dissociative photoionization relaxation channel.

Insight from JWST/Near Infrared Camera into galaxy overdensities around bright Lyman-alpha emitters during reionization: implications for ionized bubbles at z ∼ 9

ABSTRACT Several studies have detected Lyman-alpha (Ly α) from bright ($M_{\small UV}\lesssim -21.5$) galaxies during the early stages of reionization despite the significantly neutral intergalactic medium. To explain these detections, it has been suggested that z &amp;gt; 7 Ly α emitters (LAEs) inhabit physical Mpc (pMpc)-scale ionized regions powered by overdensities of faint galaxies; however, systematic searches for these overdensities near LAEs have been challenging. Here, we use Cosmic Evolution Early Release Science JWST/Near Infrared Camera imaging to search for large-scale galaxy overdensities near two very ultraviolet (UV)-bright, z = 8.7 LAEs in the Extended Groth Strip (EGS) field. We colour select 27 z = 8.4–9.1 candidates, including the one LAE in the footprint (EGSY8p7). From spectral energy distribution models, we infer moderately faint UV luminosities ($-21.2\lesssim {M_{\small UV}}\lesssim -19.1$) and stellar masses of M* ≈ 107.5–8.8 M⊙. All are efficient ionizing agents ($\xi _{\text{ion}}^{*}\approx 10^{25.5-26.0}$ Hz erg−1) and are generally morphologically simple with only one compact (re ≲ 140 to ∼650 pc) star-forming component. 13 candidates lie within 5 arcmin of EGSY8p7, leading to a factor-of-four galaxy overdensity at ≲5 arcmin (∼1.4 projected pMpc at z ∼ 8.7) separations from EGSY8p7. Separations of 10–15 arcmin (∼2.7–4.1 projected pMpc) are consistent with an average field. The spatial distribution of our sample may qualitatively suggest an R ≥ 2 pMpc ionized bubble encompassing both LAEs in EGS, which is theoretically unexpected but may be possible for a galaxy population four times more numerous than the average to create with moderate escape fractions (fesc ≳ 0.15) over long times (≳ 200 Myr). Upcoming spectroscopic follow-up will characterize the size of any ionized bubble that may exist and the properties of the galaxies powering such a bubble.