Lyman-alpha Research Articles

Estimating the Effective Lifetime of the z ∼ 6 Quasar Population from the Composite Proximity Zone Profile

Abstract The lifetime of quasars can be estimated by means of their proximity zone sizes, which are regions of enhanced flux blueward of the Lyα emission line observed in the rest-frame UV spectra of high-redshift quasars because the intergalactic gas has a finite response time to the quasars’ radiation. We estimate the effective lifetime of the high-redshift quasar population from the composite transmitted flux profile within the proximity zone region of a sample of 15 quasars at 5.8 ≤ z ≤ 6.6 with precise systemic redshifts, and similar luminosities, i.e., −27.6 ≤ M 1450 ≤ −26.4, and thus a similar instantaneous ionizing power. We develop a Bayesian method to infer the effective lifetime from the composite spectrum, including robust estimates of various sources of uncertainty on the spectrum. We estimate an effective lifetime of the quasar population as a whole of log 10 ( t Q / yr ) = 5.7 − 0.3 ( − 0.5 ) + 0.5 ( + 0.8 ) given by the median and 68th (95th) percentile of the posterior probability distribution. While our result is consistent with previous quasar lifetime studies, it poses significant challenges on the current model for the growth of supermassive black holes located in the center of the quasars’ host galaxies, which requires that quasar lifetimes are more than an order of magnitude longer.

Lyα Line Properties at z = 3.78 and Their Environmental Dependence: A Case Study around a Massive Protocluster

Abstract Lyα-emitting galaxies (LAEs) are easily detectable in the high-redshift universe and are potentially efficient tracers of large-scale structure at early epochs, as long as their observed properties do not depend strongly on environment. We investigate the luminosity and equivalent width functions of LAEs in the overdense field of a protocluster at redshift z ≃ 3.78. Using a large sample of LAEs (many spectroscopically confirmed), we find that the Lyα luminosity distribution is well represented by a Schechter function with log ( L * / erg s − 1 ) = 43.26 − 0.22 + 0.20 and log ( ϕ * / Mpc − 3 ) = − 3.40 − 0.04 + 0.03 with α = −1.5. Fitting the equivalent width distribution as an exponential, we find a scale factor of ω = 79 − 15 + 15 Å. We also measured the Lyα luminosity and equivalent width functions using the subset of LAEs lying within the densest cores of the protocluster, finding similar values for L* and ω. Hence, despite having a mean overdensity more than 2× that of the general field, the shapes of the Lyα luminosity function and equivalent width distributions in the protocluster region are comparable to those measured in the field LAE population by other studies at similar redshift. While the observed Lyα luminosities and equivalent widths show correlations with the UV continuum luminosity in this LAE sample, we find that these are likely due to selection biases and are consistent with no intrinsic correlations within the sample. This protocluster sample supports the strong evolutionary trend observed in the Lyα escape fraction and suggests that LAEs at lower redshift can be on average significantly more dusty that their counterparts at higher redshift.

Constraints on the temperature-density relation of the intergalactic medium with non-negligible absorber spatial structure

We investigate evolution of physical parameters of the intergalactic medium using an analysis of Lya forest lines detected towards distant quasars. We used the enlarged sample of 98 quasars obtained with Keck/HIRES and VLT/UVES. We show that taking into account a finite spatial size of absorbers, regulated by pressure smoothing, significantly affects the inferred thermal parameters of the intergalactic gas, such as the hydrogen photoionization rate and parameters of the temperature-density relation. Using Bayesian framework we constrained for the first time the scale parameter between the Jeans length and characteristic size of the absorbers. We also discuss limitations of the method based on the analysis of the minimal broadending of Lya lines, which stem from the patchy nature of He II reionization.

Quasi-periodic pulsations with double periods observed in Lyα emission during solar flares

Quasi-periodic pulsations with double periods observed in Lyα emission during solar flares

The Role of Dust, UV Luminosity and Large-scale Environment on the Escape of Lyα Photons: A Case Study of a Protocluster Field at z = 3.1

Abstract We present a detailed characterization of the Lyα properties for 93 Lyα emitters (LAEs) at z ∼ 3.1 selected from the D1 field of the Canada–France–Hawaii Telescope Legacy Survey, including 24 members of a massive protocluster. The median-stacked Lyα image shows an extended Lyα halo (LAH) surrounding the galaxy with the exponential scale length 4.9 ± 0.7 kpc, which accounts for roughly half of the total line flux. Accounting for the LAH contribution, the total Lyα escape fraction, f esc, is 40% ± 26%. Combining the data set with existing measurements, we find a dependence of f esc on the galaxy’s UV slope (β) and UV luminosity (L UV). The simultaneous use of both parameters allows prediction of f esc within 0.18 dex, a substantial improvement over 0.23 dex when only β is used. The correlation between f esc and E(B − V) suggests that Lyα photons undergo interstellar dust attenuation in a similar manner to continuum photons. Yet, Lyα transmission is typically higher than that expected for continuum photons at a similar wavelength by a factor, which depends on UV luminosity, up to 2 in the samples we studied. These results hint at complex geometries and physical conditions of the interstellar medium, which affect the Lyα transmission or production. Alternatively, the dust law may change with luminosity leading to an over- or underestimation of f esc. Finally, we report that protocluster LAEs tend to be bluer and more UV luminous than their field cousins, resulting in systematically higher f esc values. We speculate that it may be due to the widespread formation of young low-mass galaxies in dense gas-rich environments.

Design of a Lyman-Alpha-Based BES for edge plasma density diagnosing on the HL-2A tokamak

A 20-channel edge Lyman-Alpha-Based Beam emission spectroscopy (LAB) system, which diagnoses edge density fluctuations by measuring the Doppler-shifted Lyman-alpha line (n= 2 → 1, 121.53 nm) emitting via the interaction of neutral beams and plasma particles, is under developing on the HL-2A tokamak. The radial observation range covers the main plasma from R= 1.98 m to 2.05 m with a spatial resolution of about 0.33 cm and a temporal resolution of 1 μs. The overall design for this system is completed, including the reflective collection optics, the spectrometer with a reflective toroidal grating, the detector array, and the vacuum system. Compared with the traditional beam emission spectroscopy (BES) which measures the Balmer-alpha line (n= 3 → 2, 656.10 nm), LAB promises to achieve higher signal-to-noise measurements of smaller-scale fluctuations and therefore detect previously unobserved low-amplitude pedestal turbulence.

Formation of the first galaxies in the aftermath of the first supernovae

ABSTRACT We perform high-resolution cosmological hydrodynamic simulations to study the formation of the first galaxies that reach the masses of 108 − 9 h−1 M⊙ at z = 9. The resolution of the simulations is high enough to resolve minihaloes and allow us to successfully pursue the formation of multiple Population (Pop) III stars, their supernova (SN) explosions, resultant metal-enrichment of the inter-galactic medium (IGM) in the course of the build-up of the system. Metals are ejected into the IGM by multiple Pop III SNe, but some of the metal-enriched gas falls back on to the halo after $\gtrsim 100~\rm Myr$. The star formation history of the first galaxy depends sensitively on the initial mass function (IMF) of Pop III stars. The dominant stellar population transits from Pop III to Pop II at z ∼ 12−15 in the case of power-law Pop III IMF, dn/dM ∝ M−2.35 with the mass range 10−500 M⊙. At z ≲ 12, stars are stably formed in the first galaxies with a star formation rate of ∼10−3−10−1 M⊙ yr −1. In contrast, for the case with a flat IMF, gas-deprived first galaxies form due to frequent Pop III pair-instability SNe, resulting in the suppression of subsequent Pop II star formation. In addition, we calculate UV continuum, Lyα- and Hα-line fluxes from the first galaxies. We show that the James Webb Space Telescope will be able to detect both UV continuum, Lyα and Hα line emission from first galaxies with halo mass ≳ 109 M⊙ at z ≳ 10.

Polarization of the Lyα Lines of H i and He ii as a Tool for Exploring the Solar Corona

Abstract The near-Earth space weather is driven by the quick release of magnetic free energy in the solar corona. Probing this extremely hot and rarified region of the extended solar atmosphere requires modeling the polarization of forbidden and permitted coronal lines. To this end, it is important to develop efficient codes to calculate the Stokes profiles that emerge from given three-dimensional (3D) coronal models and this should be done taking into account the symmetry breaking produced by the presence of magnetic fields and non-radial solar wind velocities. We have developed such a tool with the aim of theoretically predicting and interpreting spectropolarimetric observations of the solar corona in permitted and forbidden lines. In this paper, we show the results of a theoretical investigation of the linear polarization signals produced by scattering processes in the H i Lyα line at 1216 Å and in the He ii Lyα line at 304 Å using 3D coronal models by Predictive Science Inc. These spectral lines have very different critical magnetic fields for the onset of the Hanle effect (53 G and 850 G, respectively), as well as different sensitivities to the Doppler effect caused by the solar wind velocities. We study under which circumstances simultaneous observations of the scattering polarization in these Lyα lines can facilitate the determination of magnetic fields and macroscopic velocities in the solar corona.

The MOSDEF-LRIS Survey: Probing the ISM/CGM Structure of Star-forming Galaxies at z ∼ 2 Using Rest-UV Spectroscopy

Abstract The complex structure of gas, metals, and dust in the interstellar and circumgalactic medium (ISM and CGM, respectively) in star-forming galaxies can be probed by Lyα emission and absorption, low-ionization interstellar (LIS) metal absorption, and dust reddening E(B − V). We present a statistical analysis of the mutual correlations among Lyα equivalent width (EWLyα ), LIS equivalent width (EWLIS), and E(B − V) in a sample of 157 star-forming galaxies at z ∼ 2.3. With measurements obtained from individual deep rest-UV spectra and spectral energy distribution modeling, we find that the tightest correlation exists between EWLIS and E(B − V), although correlations among all three parameters are statistically significant. These results signal a direct connection between dust and metal-enriched H i gas and that they are likely cospatial. By comparing our results with the predictions of different ISM/CGM models, we favor a dusty ISM/CGM model where dust resides in H i gas clumps and Lyα photons escape through the low H i covering fraction/column density intraclump medium. Finally, we investigate the factors that potentially contribute to the intrinsic scatter in the correlations studied in this work, including metallicity, outflow kinematics, Lyα production efficiency, and slit loss. Specifically, we find evidence that scatter in the relationship between EWLyα and E(B − V) reflects the variation in the metal–to–H i covering fraction ratio as a function of metallicity and the effects of outflows on the porosity of the ISM/CGM. Future simulations incorporating star formation feedback and the radiative transfer of Lyα photons will provide key constraints on the spatial distributions of neutral hydrogen gas and dust in the ISM/CGM structure.

The Evolution of the Lyman-alpha Luminosity Function during Reionization

Abstract The time frame in which hydrogen reionization occurred is highly uncertain, but can be constrained by observations of Lyman-alpha (Lyα) emission from distant sources. Neutral hydrogen in the intergalactic medium (IGM) attenuates Lyα photons emitted by galaxies. As reionization progressed the IGM opacity decreased, increasing Lyα visibility. The galaxy Lyα luminosity function (LF) is thus a useful tool to constrain the timeline of reionization. In this work, we model the Lyα LF as a function of redshift, z = 5–10, and average IGM neutral hydrogen fraction, x ¯ Hɪ . We combine the Lyα luminosity probability distribution obtained from inhomogeneous reionization simulations with a model for the UV LF to model the Lyα LF. As the neutral fraction increases, the average number density of Lyα emitting galaxies decreases, and are less luminous, though for x ¯ Hɪ ≲ 0.4 there is only a small decrease in the Lyα LF. We use our model to infer the IGM neutral fraction at z = 6.6, 7.0, and 7.3 from observed Lyα LFs. We conclude that there is a significant increase in the neutral fraction with increasing redshift: x ¯ Hɪ ( z = 6.6 ) = 0.08 − 0.05 + 0.08 , x ¯ Hɪ ( z = 7.0 ) = 0.28 ± 0.05 and x ¯ Hɪ ( z = 7.3 ) = 0.83 − 0.07 + 0.06 . We predict trends in the Lyα luminosity density and Schechter parameters as a function of redshift and the neutral fraction. We find that the Lyα luminosity density decreases as the universe becomes more neutral. Furthermore, as the neutral fraction increases, the faint-end slope of the Lyα LF steepens, and the characteristic Lyα luminosity shifts to lower values; hence, we conclude that the evolving shape of the Lyα LF—not just its integral—is an important tool to study reionization.

CVD diamond detectors for fast VUV and SX-ray diagnostics on FTU

The diagnostic performances of photodetectors based on Chemical Vapor Deposition (CVD) single crystal diamonds that were installed on one of the equatorial ports of the FTU tokamak during the last six months of operation of the machine are reported. Examples of plasma fast events have been collected in several different plasma conditions, confirming the fast response capabilities of diamond detectors and the high S/N ratio. During the runaway control and mitigation experiments, for example, the so-called Anomalous DopplerInstabilities were observed as sharp peaks of Ly-α emission caused by fast electrons hitting the wall, as a result of RE beam instabilities, perfectly correlated in time with other magnetic diagnostics and fast EC polychromator signals. Fast oscillations in the plasma emission are also observed in the presence of tearing modes, while other interesting observations relate to pellet ablation processes. The CVD diamond detectors were installed on FTU in view of their possible use for replacement of the Si photodiodes currently adopted for Soft X-ray tomography on future devices with harsher radiation environments. In fact, it was realized that the relatively flat response of the UV diamond sensor opened the possibility of using these detectors as bolometers. The first encouraging results have prompted launching an R&D program for the development of full-fledged diamond bolometers, which will be especially well suited for the coverage of the divertor and edge regions in high performance devices, in the energy range from 10 eV to about 20 keV.

Revealing the formation histories of the first stars with the cosmic near-infrared background

ABSTRACT The cosmic near-infrared background (NIRB) offers a powerful integral probe of radiative processes at different cosmic epochs, including the pre-reionization era when metal-free, Population III (Pop III) stars first formed. While the radiation from metal-enriched, Population II (Pop II) stars likely dominates the contribution to the observed NIRB from the reionization era, Pop III stars – if formed efficiently – might leave characteristic imprints on the NIRB, thanks to their strong Lyα emission. Using a physically motivated model of first star formation, we provide an analysis of the NIRB mean spectrum and anisotropy contributed by stellar populations at z > 5. We find that in circumstances where massive Pop III stars persistently form in molecular cooling haloes at a rate of a few times $10^{-3}\, \mathrm{ M}_\odot \ \mathrm{yr}^{-1}$, before being suppressed towards the epoch of reionization (EoR) by the accumulated Lyman–Werner background, a unique spectral signature shows up redward of $1\, \mu$m in the observed NIRB spectrum sourced by galaxies at z > 5. While the detailed shape and amplitude of the spectral signature depend on various factors including the star formation histories, initial mass function, LyC escape fraction and so forth, the most interesting scenarios with efficient Pop III star formation are within the reach of forthcoming facilities, such as the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer. As a result, new constraints on the abundance and formation history of Pop III stars at high redshifts will be available through precise measurements of the NIRB in the next few years.

Lyman-alpha emitters and the 21 cm power spectrum as probes of density–ionization correlation in the epoch of reionization

ABSTRACT Due to the large cross-section of Ly α photons with hydrogen, Lyman-alpha emitters (LAEs) are sensitive to the presence of neutral hydrogen in the intergalactic medium (IGM) during the epoch of reionization (EoR): the period in the Universe’s history where neutral hydrogen in the IGM is ionized. The type of correlation between the ionized regions of the IGM with respect to the underlying intrinsic LAEs has a pronounced effect on the number of observed LAEs and their apparent clustering. As a result, observations of LAEs during the EoR can be used as a probe of the EoR morphology. Here, we build on previous works where we parametrize the density–ionization correlation during the EoR, and study how the observed number density and angular correlation function (ACF) of LAEs depend on this parametrization. Using Subaru measurements of the number density of LAEs and their ACF at z = 6.6, we place constraints on the EoR morphology. We find that measurements of LAEs at z = 6.6 alone cannot distinguish between different density–ionization models at $68{{\ \rm per\ cent}}$ credibility. However, adding information regarding the number density, and ACF, of LAEs at z = 6.6 to 21 cm power spectrum measurements using the hydrogen Epoch of Reionization Array at the mid-point of reionization can rule out uncorrelated and outside-in reionization at $99{{\ \rm per\ cent}}$ credibility.

Lunar Surface Composition Constraints from Maturity-corrected Far-ultraviolet Reflectance Maps

Abstract Far-ultraviolet (FUV) observations by the Lunar Reconnaissance Orbiter Lyman Alpha Mapping Project (LAMP) have shown that the lunar surface reflectance in the ultraviolet is sensitive to changes in both composition and maturity at wavelengths >170 nm. This can lead to uncertainties in the interpretation of features that appear in maps created using LAMP data from this wavelength range. Here we utilize a correction based on the optical maturity parameter to remove large-scale immaturity features from LAMP spectral slope and band ratio maps. After performing the correction, the LAMP maps more accurately represent the FUV lunar surface in the context of composition. Corrected LAMP maps show good correlation with lunar FeO, plagioclase, and bulk silicate abundance maps for moderate- to high-iron regions, indicating a sensitivity in the LAMP data to differences in mineral composition in those regions. These maps represent a unique view into a relatively unexplored region of the spectrum and showcase the ability to perform compositional mapping and mineral identification using FUV remote-sensing measurements.

Gamma-ray bursts as probes of high-redshift Lyman-αemitters and radiative transfer models

Aims.We present the updated census and statistics of Lyman-αemitting long gamma-ray burst host galaxies (LAE-LGRBs). We investigate the properties of a subsample of LAE-LGRBs and test the shell model that is commonly used to fit Lyman-α(Lyα) emission line spectra.Methods.We considered all LGRB host galaxies with relevant publicly available information. We defined a golden sample of four LAE-LGRBs (GRBs 011211, 021004, 060926, and 070110) with afterglow and host galaxy observations allowing us to constrain the shell modeling of the Lyαline.Results.The census results in 29 detected LAE-LGRBs. We present 5 new Lyαemission detections in host-galaxy spectra and the corresponding unpublished VLT/X-shooter data (GRBs 060926, 070110, 081121, 081222, and 100424A). From the comparison of the statistics and properties of LAE-LGRBs to those of LAE samples in the literature, we find evidence of Lyαsuppression in dusty systems. The fraction of LAE-LGRBs in the overall LGRB hosts is lower than that found for Lyman-break galaxy (LBG) samples at similar redshift range. This result can arise because the selection criteria of the parent samples are different and the spectral observations of LGRB samples are shallower than those of LBG. However, we find that LAE-LGRBs are representative of Lyαemission from the bulk of UV-selected galaxies atz ∼ 2. We find that the golden sample of LAE-LGRBs we studied consists of complex systems characterized by multiple emission blobs and by signs of possible galaxy interactions. The fitting procedure recovers the HIcolumn densities (NHI) measured from the afterglow spectra and the other properties described by the shell-model parameters in the two low-NHIcases, but it fails to do this in the other two cases with highNHI. The afterglows of most LGRBs and LAE-LGRBs show log(NHI/cm−2) > 20.3, implying that statistically, the bulk of Lyαphotons that is expected to be produced by massive stars in the star-forming region hosting the GRB will be surrounded by these opaque lines of sight. We therefore interpret our results in the context of more sophisticated models and of different dominant Lyα-emitting regions. We also compare LAE-LGRBs to LAE Lyman continuum (LyC) leakers in the literature in terms of the properties that are identified as possible indirect indicators of LyC leakage. We find that only one LGRB (GRB 021004) would likely be a strong LyC leaker and discuss the validity of these indicators at high redshift. While our work shows that LGRBs are useful tools for probing LAEs and radiative transfer models, larger statistics are required to strengthen our findings.

The MUSE-Wide survey: Three-dimensional clustering analysis of Lyman-α emitters at 3.3 < z < 6

We present an analysis of the spatial clustering of 695 Lyα-emitting galaxies (LAEs) in the MUSE-Wide survey. All objects have spectroscopically confirmed redshifts in the range 3.3 < z < 6. We employed the K-estimator, an alternative clustering statistic, adapted and optimized for our sample. We also explore the standard two-point correlation function approach, which is however less suited for a pencil-beam survey such as ours. The results from both approaches are consistent. We parametrize the clustering properties in two ways, (i) following the standard approach of modelling the clustering signal with a power law (PL), and (ii) adopting a halo occupation distribution (HOD) model of the two-halo term. Using the K-estimator and applying HOD modelling, we infer a large-scale bias of bHOD = 2.80−0.38+0.38 at a median redshift of the number of galaxy pairs ⟨zpair⟩ ≃ 3.82, while the best-fit power-law analysis gives bPL = 3.03−0.52+1.51 (r0 = 3.60−0.90+3.10 comoving h−1 Mpc and γ = 1.30−0.45+0.36). The implied typical dark matter halo (DMH) mass is log(MDMH/[h−1 M⊙]) = 11.34−0.27+0.23 (adopting b = bHOD and assuming σ8 = 0.8). We study possible dependencies of the clustering signal on object properties by bisecting the sample into disjoint subsets, considering Lyα luminosity, UV absolute magnitude, Lyα equivalent width, and redshift as variables. We find no evidence for a strong dependence on the latter three variables but detect a suggestive trend of more luminous Lyα emitters clustering more strongly (thus residing in more massive DMHs) than their lower Lyα luminosity counterparts. We also compare our results to mock LAE catalogs based on a semi-analytic model of galaxy formation and find a stronger clustering signal than in our observed sample, driven by spikes in the simulated z-distributions. By adopting a galaxy-conserving model we estimate that the Lyα-bright galaxies in the MUSE-Wide survey will typically evolve into galaxies hosted by halos of log(MDMH/[h−1 M⊙]) ≈ 13.5 at redshift zero, suggesting that we observe the ancestors of present-day galaxy groups.

Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). XIV. A Candidate Type II Quasar at z = 6.1292

Abstract We present deep Keck/MOSFIRE near-infrared spectroscopy of a strong Lyα emitting source at z = 6.1292, HSC J142331.71−001809.1, which was discovered by the SHELLQS program from imaging data of the Subaru Hyper Suprime-Cam (HSC) survey. This source is one of five objects that show narrow (FWHM < 500 km s−1) and prominent (L Lyα > 1044 erg s−1) Lyα emission lines at absolute 1450 Å continuum magnitudes of M 1450 ∼ −22 mag. Its rest-frame Lyα equivalent width (EW) is 370 ± 30 Å. In the 2 hr Keck/MOSFIRE spectrum in Y band, the high-ionization C iv λλ1548,1550 doublet emission line was clearly detected with FWHM = 120 − 20 + 20 km s−1 and a total rest-frame EW of 37 − 5 + 6 Å. We also report the detection of weak continuum emission, and the tentative detection of O iii] λλ1661,1666 in the 4 hr J-band spectrum. Judging from the UV magnitude, line widths, luminosities, and EWs of Lyα and C iv, we suggest that this source is a reionization-era analog of classical type-II AGNs, although there is a possibility that it represents a new population of AGN/galaxy composite objects in the early universe. We compare the properties of J1423−0018 to intermediate-redshift type-II AGNs and C iv emitters seen in z = 6–7 galaxy samples. Further observations of other metal emission lines in the rest-frame UV or optical, along with X-ray follow-up observations of the z = 6–7 narrow-line quasars, are needed for more robust diagnostics and to determine their nature.

ALMA Observations of Lyα Blob 1: Multiple Major Mergers and Widely Distributed Interstellar Media

Abstract We present observations of a giant Lyα blob (LAB) in the SSA22 protocluster at z = 3.1, SSA22-LAB1, taken with the Atacama Large Millimeter/submillimeter Array. Dust continuum, along with [C ii] 158 μm and CO(4–3) line emission have been detected in LAB1, showing complex morphology and kinematics across a ∼100 kpc central region. Seven galaxies at z = 3.0987–3.1016 in the surroundings are identified in [C ii] and dust continuum emission, with two of them potential companions or tidal structures associated with the most massive galaxies. Spatially resolved [C ii] and infrared luminosity ratios for the widely distributed media (L [Cɪɪ]/L IR ≈ 10−2−10−3) suggest that the observed extended interstellar media are likely to have originated from star formation activity and the contribution from shocked gas is probably not dominant. LAB1 is found to harbor a total molecular gas mass M mol = (8.7 ± 2.0) × 1010 M ⊙, concentrated in the core region of the Lyα-emitting area. While (primarily obscured) star formation activity in the LAB1 core is one of the most plausible power sources for the Lyα emission, multiple major mergers found in the core may also play a role in making LAB1 exceptionally bright and extended in Lyα as a result of cooling radiation induced by gravitational interactions.

Stellar feedback in a clumpy galaxy at z ∼ 3.4

ABSTRACT Giant star-forming regions (clumps) are widespread features of galaxies at z ≈ 1−4. Theory predicts that they can play a crucial role in galaxy evolution, if they survive to stellar feedback for >50 Myr. Numerical simulations show that clumps’ survival depends on the stellar feedback recipes that are adopted. Up to date, observational constraints on both clumps’ outflows strength and gas removal time-scale are still uncertain. In this context, we study a line-emitting galaxy at redshift z ≃ 3.4 lensed by the foreground galaxy cluster Abell 2895. Four compact clumps with sizes ≲280 pc and representative of the low-mass end of clumps’ mass distribution (stellar masses ≲2 × 108 M⊙) dominate the galaxy morphology. The clumps are likely forming stars in a starbursting mode and have a young stellar population (∼10 Myr). The properties of the Lyman-α (Lyα) emission and nebular far-ultraviolet absorption lines indicate the presence of ejected material with global outflowing velocities of ∼200–300 km s−1. Assuming that the detected outflows are the consequence of star formation feedback, we infer an average mass loading factor (η) for the clumps of ∼1.8–2.4 consistent with results obtained from hydrodynamical simulations of clumpy galaxies that assume relatively strong stellar feedback. Assuming no gas inflows (semiclosed box model), the estimates of η suggest that the time-scale over which the outflows expel the molecular gas reservoir (≃7 × 108 M⊙) of the four detected low-mass clumps is ≲50 Myr.

Effect of stellar flares and coronal mass ejections on the atmospheric escape from hot Jupiters

AbstractSpectral observations in the Ly-α line have shown that atmospheric escape is variable and for the exoplanet HD189733b, the atmospheric evaporation goes from undetected to enhanced evaporation in a 1.5 years interval. To understand the temporal variation in the atmospheric escape, we investigate the effect of flares, winds, and CMEs on the atmosphere of hot Jupiter HD189733b using 3D self-consistent radiation hydrodynamic simulations. We consider four cases: first, the quiescent phase including stellar wind; secondly, a flare; thirdly, a CME; and fourthly, a flare followed by a CME. We find that the flare alone increases the atmospheric escape rate by only 25%, while the CME leads to a factor of 4 increments, in comparison to the quiescent case. We also find that the flare alone cannot explain the observed high blue-shifted velocities seen in the Ly-α. The CME, however, leads to an increase in the velocity of escaping atmospheres, enhancing the blue-shifted transit depth.