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Aims. We study the effects of an inhomogeneous interstellar medium (ISM) on the strength and the shape of the Lyman alpha (Lyα) line in starburst galaxies. Methods. Using our 3D Monte Carlo Lyα radiation transfer code, we have studied the radiative transfer of Lyα, UV, and optical continuum photons in homogeneous and clumpy shells of neutral hydrogen and dust surrounding a central source. Our simulations predict the Lyα and continuum escape fraction, the Lyα equivalent width EW(Lyα), the Lyα line profile, and their dependence on the geometry of the gas distribution and the main input physical parameters. Results. The ISM clumpiness is found to have a strong impact on the Lyα line radiative transfer, leading to a strong dependence of the emergent features of the Lyα line (escape fraction, EW(Lyα)) on the ISM morphology. Although a clumpy and dusty ISM appears more transparent to radiation (both line and continuum) compared to an equivalent homogeneous ISM of equal dust optical depth, we find that the Lyα photons are, in general, still more attenuated than UV continuum radiation. As a consequence, the observed equivalent width of the Lyα line (EWobs(Lyα)) is lower than the intrinsic one (EWint(Lyα)) for nearly all clumpy ISM configurations being considered. There are, however, special conditions under which Lyα photons escape more easily than the continuum, resulting in an enhanced EWobs(Lyα). The requirement for this to happen is that the ISM is almost static (galactic outflows ⩽200 km s-1), extremely clumpy (with density contrasts >107 in HI between clumps and the interclump medium), and very dusty (E(B-V) > 0:30). When these conditions are fulfilled, the emergent Lyα line profile generally shows no velocity shift and little asymmetry. Otherwise, the Lyα line profile is very similar to the one expected for homogeneous media. Conclusions. Given the asymmetry and velocity shifts generally observed in star-forming galaxies with Lyα emission, we therefore conclude that clumping is unlikely to significantly enhance their relative Lyα/UV transmission. [ABSTRACT FROM AUTHOR]

Context. The Lyman alpha emission line of neutral hydrogen is an important tool for finding galaxies at high redshift, thus for probing the structure of the early universe. However, the resonance nature of the line and its sensitivity to dust and neutral gas is still not fully understood. Aims. We present measurements of the velocity, covering fraction and optical depth of neutral gas in front of two well-known, local blue compact galaxies that show Lyman alpha in emission: ESO 338-IG 04 and Haro 11. We thus observationally test the hypothesis that Lyman alpha can escape through neutral gas by being Doppler shifted out of resonance. Methods. We present integral field spectroscopy, obtained with the GIRAFFE/Argus spectrograph at VLT/FLAMES in Paranal, Chile. The excellent wavelength resolution allowed us to accurately measure the velocity of the ionized and neutral gas through the Ha emission and Na D absorption, which trace the ionized medium and cold interstellar gas, respectively. We also present independent measurements from the VLT/X-shooter spectrograph that confirm our results. Results. For ESO 338-1004 we measure no significant shift of neutral gas: the best fit velocity offset is -15 ± 1 6km s-1. For Haro 11, we see an outflow from knot B at 44 ± 13 km s-1, and infalling gas towards knot C with 32 ± 12 km s-1. Based on the relative strength of the Na D absorption lines, we estimate low covering fractions of neutral gas (down to 10%) in all three cases. Conclusions. The Na D absorption most likely occurs in dense clumps with higher column densities than the medium in which the bulk of the Ly α scattering takes place. Still, we find no strong correlation between outfiowing neutral gas and strong Ly α emission. The Ly α photons from these two galaxies are therefore likely to be escaping due to a low column density and/or covering fraction. [ABSTRACT FROM AUTHOR]

We analyze the clump population of the spiral galaxy Sp 1149 at redshift 1.5. Located behind the galaxy cluster MACS J1149.5+2223, Sp 1149 has been significantly magnified allowing us to study the galaxy on physical scales down to ∼100 pc. The galaxy cluster frame is among the targets of the Cluster Lensing And Supernova survey with Hubble (CLASH), an ongoing Hubble Space Telescope (HST) Multi-Cycle Treasury program. We have used the publicly available multi-band imaging data set to reconstruct the spectral energy distributions of the clumps in Sp 1149, and derive, by means of stellar evolutionary models, their physical properties. We found that 40% of the clumps observed in Sp 1149 are older than 30 Myr and can be as old as 300 Myr. These are also the more massive (luminous) clumps in the galaxy. Among the complexes in the local reference sample, the star-forming knots in luminous blue compact galaxies could be considered progenitor analogs of these long-lived clumps. The remaining 60% of clumps have colors comparable to local cluster complexes, suggesting a similar young age. We observe that the Sp 1149 clumps follow the M α R2 relation similar to local cluster complexes, suggesting similar formation mechanisms although they may have different initial conditions (e.g., higher gas surface densities). We suggest that the galaxy is experiencing a slow decline in star formation rate and a likely transitional phase toward a more quiescent star formation mode. The older clumps have survived between 6 and 20 dynamical times and are all located at projected distances smaller than 4 kpc from the center. Their current location suggests migration toward the center and the possibility of being the building blocks of the bulge. On the other hand, the dynamical timescale of the younger clumps is significantly shorter, meaning that they are quite close to their birthplace. We show that the clumps of Sp 1149 may account for the expected metal-rich globular cluster population usually associated with the bulge and thick disk components of local spirals. [ABSTRACT FROM AUTHOR]

Aims. To investigate the ingredients, which allow star-forming galaxies to present Ly line in emission, we studied the kinematics and gas phase metallicity of the interstellar medium. Methods. We used multi-object near-infrared spectroscopy with Magellan/MMIRS to study nebular emission from z~2-3 starforming galaxies discovered in three MUSYC fields. Results. We detected emission lines from four active galactic nuclei and 13 high-redshift star-forming galaxies, including H lines down to a flux of (4 ± 1)E-17 erg s-1 cm-2. This yielded seven new redshifts. The most common emission line detected is [OIII]5007, which is sensitive to metallicity. We were able to measure metallicity (Z) for two galaxies and to set upper (lower) limits for another two (two). The metallicity values are consistent with 0:3 < Z=Z < 1.2, 12 + log (O/H) ~ 8.2-8.8. Comparing the Lya central wavelength with the systemic redshift, we find ▵ vLyα -[OIII]5007 = 70-270 km s-1. Conclusions. High-redshift star-forming galaxies, Lya emitting (LAE) galaxies, and Ha emitters appear to be located in the low mass, high star-formation rate (SFR) region of the SFR versus stellar mass diagram, confirming that they are experiencing burst episodes of star formation, which are building up their stellar mass. Their metallicities are consistent with the relation found for z ~ 2.2 galaxies in the Z versus stellar mass plane. The measured ▵ vLyα -[OIII]5007 values imply that outflows of material, driven by star formation, could be present in the z ~ 2-3 LAEs of our sample. Comparing with the literature, we note that galaxies with lower metallicity than ours are also characterized by similar ▵ vLyα -[OIII]5007 velocity o sets. Strong F([OIII]5007) is detected in many Lyα emitters. Therefore, we propose the F(Lya)/F([OIII]5007) flux ratio as a tool for the study of high-redshift galaxies; while influenced by metallicity, ionization, and Lya radiative transfer in the ISM, it may be possible to calibrate this ratio to primarily trace one of these effects. [ABSTRACT FROM AUTHOR]

Context. Lyman-α emission is commonly used as star formation tracer in cosmological studies. Nevertheless, resonant scattering strongly affects the resulting luminosity, leading to variable and unpredictable escape fractions in different objects. Aims. To understand how the Lyα escape fraction depends on the properties of the star-forming regions, we need high spatial resolution multiwavelength studies of nearby Lyα emitters, like Haro 2. Methods. We study the Lyα emission of Haro 2 in connection with the properties of the young stellar population, the characteristics of the interstellar medium, the distribution and intensity of the Balmer emission lines and the properties of the X-ray emission. We have used HST-STIS spectral images along the major and minor axes of Haro 2 to characterize the Lyα emission, as well as FOC UV, WFPC-2 optical and NICMOS near infrared broadband-filter images to analyze the properties of the stellar population. WFPC-2 Hα image and ground-based spectroscopy allow us to study the Balmer emission lines. Finally, Chandra/ACIS X-ray images provide resolved distribution of the X-ray emission at various energy bands. The observational data are analyzed by comparison with the predictions from evolutionary synthesis models to constrain the properties of the star formation episode. Results. The UV, Hα and far infrared luminosities of the Haro 2 nuclear starburst are well reproduced assuming a young stellar population with ages ∼3.5–5.0 Myr, affected by differential intestellar extinctions. A significant fraction of the stars are completely obscured in the UV, being identifiable only indirectly by their contribution to the ionization of the gas and to the far infrared emission. The diffuse soft X-ray emission extending over the whole source is attributed to gas heated by the mechanical energy released by the starburst. A compact hard X-ray emission (likely an UltraLuminous X-ray source) has been identified in a star-forming condensation to the southeast. Both compact and diffuse Lyα emission components are observed along the major and minor axes in STIS spectral images. Lyα is spatially decoupled from Balmer lines emission, Balmer decrement and UV continuum. However, the diffuse Lyα component is spatially correlated with the diffuse soft X-ray emission. Moreover, unlike the compact Lyα emission, diffuse Lyα shows luminosities larger than predicted from Hα, assuming case B recombination and considering the dust extinction as derived from Hα/Hβ. Conclusions. The Lyα emission closely associated to the massive stellar clusters is strongly affected by the properties of the surrounding neutral gas (presence of outflows, dust abundance), leading to even a range of escape fractions at different locations within the same starburst. On the other hand, we propose that the diffuse Lyα emission originates in gas ionized by the hot plasma responsible for the soft X-ray radiation, as suggested by their spatial correlation and by the measured L(Hα)/L0.4−2.4 keV ratios. Calibration of Lyα as star formation rate tracer should therefore include both effects (destruction vs. enhancement) to avoid biases in the study of galaxies at cosmological distances. [ABSTRACT FROM AUTHOR]

The Ly α line is an important diagnostic of star formation and activity in galaxies. The analysis of Ly α is complicated due to the resonant nature of the line and radiative transfer effects. High spectral resolution studies of local starburst galaxies with the unprecedented UV capabilities of the HST have shown that this line is either seen in absorption or in emission and in the latter case with a P Cygni profile indicative of a large scale outflow of neutral gas. Moreover, HST imaging obtained with HST-ACS of a sample of 6 star-forming galaxies has revealed that a substantial fraction of the Ly α photons are diffused far away from the emissive knots. Since the importance of Ly α for tracing large scale structure, correlation functions, and galaxy formation is recognized, Ly α will remain a very important probe of the distant universe for the foreseeable future, and it is therefore imperative to acquire a better understanding of what mechanisms regulate our ability to detect this line. [ABSTRACT FROM AUTHOR]

We present JWST/MIRI MRS spatially resolved ∼5 − 28 μm observations of the central ∼4 − 8 kpc of the ultraluminous infrared galaxy and broad absorption line quasar Mrk 231. These are part of the Mid-Infrared Characterization of Nearby Iconic galaxy Centers (MICONIC) program of the MIRI European Consortium guaranteed time observations. No high excitation lines (i.e., [Mg V] at 5.61 μm or [Ne V] at 14.32 μm) typically associated with the presence of an active galactic nucleus (AGN) are detected in the nuclear region of Mrk 231. This is likely due to the intrinsically X-ray weak nature of its quasar. Some intermediate ionization potential lines, for instance, [Ar III] at 8.99 μm and [S IV] at 10.51 μm, are not detected either, even though they are clearly observed in a star-forming region ∼920 pc south-east of the AGN. Thus, the strong nuclear mid-infrared (mid-IR) continuum is also in part hampering the detection of faint lines in the nuclear region. The nuclear [Ne III]/[Ne II] line ratio is consistent with values observed in star-forming galaxies. Moreover, we resolve for the first time the nuclear starburst in the mid-IR low-excitation line emission (size of ∼400 pc, FWHM). Several pieces of evidence also indicate that it is partly obscured even at these wavelengths. At the AGN position, the ionized and warm molecular gas emission lines have modest widths (W80 ∼ 300 km s−1). There are, however, weak blueshifted wings reaching velocities v02 ≃ − 400 km s−1 in [Ne II]. The nuclear starburst is at the center of a large (∼8 kpc), massive rotating disk with widely-spread, low velocity outflows. Given the high star formation rate of Mrk 231, we speculate that part of the nuclear outflows and the large-scale non-circular motions observed in the mid-IR are driven by its powerful nuclear starburst. [ABSTRACT FROM AUTHOR]

By using an ultradeep JWST/MIRI image at 5.6 μ m in the Hubble eXtreme Deep Field, we constrain the role of strong H α emitters (HAEs) during "cosmic reionization" at z ≃ 7–8. Our sample of HAEs is comprised of young (<35 Myr) galaxies, except for one single galaxy (≈300 Myr), with low stellar masses (≲109 M ⊙). These HAEs show a wide range of rest-frame UV continuum slopes (β), with a median value of β = −2.15 ± 0.21, which broadly correlates with stellar mass. We estimate the ionizing photon production efficiency (ξ ion,0) of these sources (assuming f esc,LyC = 0%), which yields a median value log 10 (ξ ion , 0 / (Hz erg − 1)) = 25.50 − 0.12 + 0.10 . We show that ξ ion,0 positively correlates with H α equivalent width and specific star formation rate. Instead ξ ion,0 weakly anticorrelates with stellar mass and β. Based on the β values, we predict f esc , LyC = 4 % − 2 + 3 , which results in log 10 (ξ ion / (Hz erg − 1)) = 25.55 − 0.13 + 0.11 . Considering this and related findings from the literature, we find a mild evolution of ξ ion with redshift. Additionally, our results suggest that these HAEs require only modest escape fractions (f esc,rel) of 6%–15% to reionize their surrounding intergalactic medium. By only considering the contribution of these HAEs, we estimated their total ionizing emissivity ( N ̇ ion ) as N ̇ ion = 10 50.53 ± 0.45 s − 1 Mpc − 3 . When comparing their N ̇ ion with non-HAE galaxies across the same redshift range, we find that that strong, young, and low-mass emitters may have played an important role during cosmic reionization. [ABSTRACT FROM AUTHOR]

Dusty star-forming galaxies emit most of their light at far-infrared to millimeter wavelengths as their star formation is highly obscured. Far-infrared and millimeter observations have revealed their dust, neutral and molecular gas properties. The sensitivity of JWST at rest-frame optical and near-infrared wavelengths now allows the study of the stellar and ionized gas content. We investigate the spatially resolved distribution and kinematics of the ionized gas in GN20, a dusty star-forming galaxy at z = 4.0548. We present deep MIRI/MRS integral field spectroscopy of the near-infrared rest-frame emission of GN20. We detect spatially resolved Paα, out to a radius of 6 kpc, distributed in a clumpy morphology. The star formation rate derived from Paα (144 ± 9 M⊙ yr−1) is only 7.7 ± 0.5% of the infrared star formation rate (1860 ± 90 M⊙ yr−1). We attribute this to very high extinction (AV = 17.2 ± 0.4 mag, or AV, mixed = 44 ± 3 mag), especially in the nucleus of GN20, where only faint Paα is detected, suggesting a deeply buried starburst. We identify four, spatially unresolved, clumps in the Paα emission. Based on the double peaked Paα profile, we find that each clump consists of at least two sub-clumps. We find mass upper limits consistent with them being formed in a gravitationally unstable gaseous disk. The ultraviolet bright region of GN20 does not have any detected Paα emission, suggesting an age of more than 10 Myr for this region of the galaxy. From the rotation profile of Paα, we conclude that the gas kinematics are rotationally dominated and the vrot/σm = 3.8 ± 1.4 is similar to low-redshift luminous infrared galaxies. From the Paα kinematics, we cannot distinguish between a rotational profile of a large disk and a late stage merger mimicking a disk. We speculate that GN20 is in the late stage of a major merger, where the clumps in a large gas-rich disk are created by the major merger, while the central starburst is driven by the merger event. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "JOYS: Disentangling the warm and cold material in the high-mass IRAS 23385+6053 cluster." The article focuses on topics such as star formation, individual objects in the ISM (Interstellar Medium), stars with jets, and massive stars. The authors of the article are listed as C. Gieser, H. Beuther, E. F. van Dishoeck, L. Francis, M. L. van Gelder, L. Tychoniec, P. J. Kavanagh, G. Perotti, A. Caratti o Garatti, T. P. Ray, P. Klaassen, K. Justtanont, H. Linnartz, W. R. M. Rocha, K. Slavicinska, L. Colina, M. Güdel, Th. Henning, P.-O. Lagage, G. Östlin, B. Vandenbussche, C. Waelkens, and G. Wright. [Extracted from the article]

Context. Space-based mid-infrared (IR) spectroscopy is a powerful tool for the characterization of important star formation tracers of warm gas which are unobservable from the ground. The previous mid-IR spectra of bright high-mass protostars with the Infrared Space Observatory (ISO) in the hot-core phase typically show strong absorption features from molecules such as CO2, C2H2, and HCN. However, little is known about their fainter counterparts at earlier stages. Aims. We aim to characterize the gas-phase molecular features in James Webb Space Telescope Mid-Infrared Instrument Medium Resolution Spectrometer (MIRI/MRS) spectra of the young and clustered high-mass star-forming region IRAS 23385+6053. Methods. Spectra were extracted from several locations in the MIRI/MRS field of view, targeting two mid-IR sources tracing embedded massive protostars as well as three H2 bright outflow knots at distances of >8000 au from the multiple. Molecular features in the spectra were fit with local thermodynamic equilibrium (LTE) slab models, with their caveats discussed in detail. Results. Rich molecular spectra with emission from CO, H2, HD, H2O, C2H2, HCN, CO2, and OH are detected towards the two mid-IR sources. However, only CO and OH are seen towards the brightest H2 knot positions, suggesting that the majority of the observed species are associated with disks or hot core regions rather than outflows or shocks. The LTE model fits to 12CO2, C2H2, HCN emission suggest warm 120–200 K emission arising from a disk surface around one or both protostars. The abundances of CO2 and C2H2 of ~10−7 are consistent with previous observations of high-mass protostars. Weak ~500 K H2O emission at ~6–7 µm is detected towards one mid-IR source, whereas 250–1050 K H2O absorption is found in the other. The H2O absorption may occur in the disk atmosphere due to strong accretion-heating of the midplane, or in a disk wind viewed at an ideal angle for absorption. CO emission may originate in the hot inner disk or outflow shocks, but NIRSpec data covering the 4.6 µm band head are required to determine the physical conditions of the CO gas, as the high temperatures seen in the MIRI data may be due to optical depth. OH emission is detected towards both mid-IR source positions and one of the shocks, and is likely excited by water photodissociation or chemical formation pumping in a highly non-LTE manner. Conclusions. The observed molecular spectra are consistent with disks having already formed around two protostars in the young IRAS 23385+6054 system. Molecular features mostly appear in emission from a variety of species, in contrast to the more evolved hot core phase protostars which typically show only absorption; however, further observations of young high-mass protostars are needed to disentangle geometry and viewing angle effects from evolution. [ABSTRACT FROM AUTHOR]

We study the resolved stellar populations and derive the star formation history of NGC 5474, a peculiar star-forming dwarf galaxy at a distance of ∼7 Mpc, using Hubble Space Telescope Advanced Camera for Surveys data from the Legacy Extragalactic UV Survey (LEGUS) programme. We apply an improved colour–magnitude diagram fitting technique based on the code sfera and use the latest PARSEC–COLIBRI stellar models. Our results are the following. The off-centre bulge-like structure, suggested to constitute the bulge of the galaxy, is dominated by star formation (SF) activity initiated 14 Gyr ago and lasted at least up to 1 Gyr ago. Nevertheless, this component shows clear evidence of prolonged SF activity (lasting until ∼10 Myr ago). We estimate the total stellar mass of the bulge-like structure to be (5.0 ± 0.3) × 108 M⊙. Such a mass is consistent with published suggestions that this structure is in fact an independent system orbiting around and not within NGC 5474's disc. The stellar overdensity located to the South–West of the bulge-like structure shows a significant SF event older than 1 Gyr, while it is characterized by two recent peaks of SF, around ∼10 and ∼100 Myr ago. In the last Gyr, the behaviour of the stellar disc is consistent with what is known in the literature as 'gasping'. The synchronized burst at 10–35 Myr in all components might hint to the recent gravitational interaction between the stellar bulge-like structure and the disc of NGC 5474. [ABSTRACT FROM AUTHOR]

Very-low-mass stars (those less than 0.3 solar masses) host orbiting terrestrial planets more frequently than other types of stars. The compositions of those planets are largely unknown but are expected to relate to the protoplanetary disk in which they form. We used James Webb Space Telescope mid-infrared spectroscopy to investigate the chemical composition of the planet-forming disk around ISO-ChaI 147, a 0.11-solar-mass star. The inner disk has a carbon-rich chemistry; we identified emission from 13 carbon-bearing molecules, including ethane and benzene. The high column densities of hydrocarbons indicate that the observations probe deep into the disk. The high carbon-to-oxygen ratio indicates radial transport of material within the disk, which we predict would affect the bulk composition of any planets forming in the disk.

The nearby Supernova 1987A was accompanied by a burst of neutrino emission, which indicates that a compact object (a neutron star or black hole) was formed in the explosion. There has been no direct observation of this compact object. In this work, we observe the supernova remnant with JWST spectroscopy, finding narrow infrared emission lines of argon and sulfur. The line emission is spatially unresolved and blueshifted in velocity relative to the supernova rest frame. We interpret the lines as gas illuminated by a source of ionizing photons located close to the center of the expanding ejecta. Photoionization models show that the line ratios are consistent with ionization by a cooling neutron star or a pulsar wind nebula. The velocity shift could be evidence for a neutron star natal kick.