Far-ultraviolet Radiation Research Articles

Far-UVC light (222 nm) efficiently inactivates clinically significant antibiotic-resistant bacteria on diverse material surfaces.

This study is crucial, providing compelling evidence on Far-ultraviolet radiation C (Far-UVC) light's efficacy against clinically significant antibiotic-resistant bacteria-a pressing issue in microbiology and infection control. Our research employs antibiotic-resistant strains from clinically isolated bacteria, emphasizing real-world relevance. Simultaneously, we assess Far-UVC light (222 nm) across diverse material surfaces commonly found in clinical settings. This dual approach ensures practical applicability and broad relevance. Our comprehensive setup and rigorous methodologies unequivocally demonstrate Far-UVC light's potency in combating antibiotic-resistant bacteria. Since 222 nm far-UVC has a disinfection capability and is harmless to mammalian cells, this dual effectiveness positions Far-UVC as a secure tool for infection control, with potential applications in healthcare settings, mitigating antibiotic-resistant bacteria spread, and reducing healthcare-associated infections.

Chemistry in Externally FUV-irradiated Disks in the Outskirts of the Orion Nebula Cluster

Most stars are born in stellar clusters, and their protoplanetary disks, which are the birthplaces of planets, can, therefore, be affected by the radiation of nearby massive stars. However, little is known about the chemistry of externally irradiated disks, including whether or not their properties are similar to the so-far better-studied isolated disks. Motivated by this question, we present ALMA Band 6 observations of two irradiated Class II protoplanetary disks in the outskirts of the Orion Nebula Cluster to explore the chemical composition of disks exposed to (external) far-ultraviolet (FUV) radiation fields: the 216-0939 disk and the binary system 253-1536A/B, which are exposed to radiation fields of 102–103 times the average interstellar radiation field. We detect lines from CO isotopologues, HCN, H2CO, and C2H toward both protoplanetary disks. Based on the observed disk-integrated line fluxes and flux ratios, we do not find significant differences between isolated and irradiated disks. The observed differences seem to be more closely related to the different stellar masses than to the external radiation field. This suggests that these disks are far enough away from the massive Trapezium stars, that their chemistry is no longer affected by external FUV radiation. Additional observations toward lower-mass disks and disks closer to the massive Trapezium stars are required to elucidate the level of external radiation required to make an impact on the chemistry of planet formation in different kinds of disks.

Violent Starbursts and Quiescence Induced by Far-ultraviolet Radiation Feedback in Metal-poor Galaxies at High Redshift

JWST observations of galaxies at z ≳ 8 suggest that they are more luminous and clumpier than predicted by most models, prompting several proposals on the physics of star formation and feedback in the first galaxies. In this paper, we focus on the role of ultraviolet (UV) radiation in regulating star formation by performing a set of cosmological radiation hydrodynamics simulations of one galaxy at subparsec resolution with different radiative feedback models. We find that the suppression of cooling by far-UV (FUV) radiation (i.e., H2 dissociating radiation) from Population II stars is the main physical process triggering the formation of compact and massive star clusters and is responsible for the bursty star formation observed in metal-poor galaxies at z ≳ 10. Indeed, artificially suppressing FUV radiation leads to a less intense continuous mode of star formation distributed into numerous but low-mass open star clusters. Due to the intense FUV field, low-metallicity clouds remain warm (∼104 K) until they reach a relatively high density (≳103 cm−3), before becoming self-shielded and transitioning to a colder (∼100 K), partially molecular phase. As a result, star formation is delayed until the clouds accumulate enough mass to become gravitationally unstable. At this point, the clouds undergo rapid star formation, converting gas into stars with high efficiency. We therefore observe exceptionally bright galaxies (10 times brighter than for continuous star formation) and subsequent quenched “dead” galaxies that did not form stars for tens of Myr.

JWST observations of the Horsehead photon-dominated region

Context. The James Webb Space Telescope (JWST) has captured the sharpest infrared images ever taken of the Horsehead nebula, a prototypical moderately irradiated photon-dominated region (PDR) that is fully representative of most of the UV-illuminated molecular gas in the Milky Way and star-forming galaxies. Aims. We investigate the impact of far-ultraviolet (FUV) radiation emitted by a massive star on the edge of a molecular cloud in terms of photoevaporation, ionization, dissociation, H2 excitation, and dust heating. We also aim to constrain the structure of the edge of the PDR and its illumination conditions. Methods. We used NIRCam and MIRI to obtain 17 broadband and 6 narrowband maps of the illuminated edge of the Horsehead across a wide spectral range from 0.7 to 28 µm. We mapped the dust emission, including the aromatic and aliphatic infrared (IR) bands, scattered light, and several gas phase lines (e.g., Paa, Brα, H2 1-0 S(1) at 2.12 µm). For our analysis, we also associated two HST-WFC3 maps at 1.1 and 1.6 µm, along with HST-STIS spectroscopic observations of the Ha line. Results. We probed the structure of the edge of the Horsehead and resolved its spatial complexity with an angular resolution of 0.1 to 1″ (equivalent to 2 × 10−4 to 2 × 10−3 pc or 40 to 400 au at the distance of 400 pc). We detected a network of faint striated features extending perpendicularly to the PDR front into the HII region in NIRCam and MIRI filters sensitive to nano-grain emission, as well as in the HST filter at 1.1 µm, which traces light scattered by larger grains. This may indeed figure as the first detection of the entrainment of dust particles in the evaporative flow. The filamentary structure of the 1-0 S(1) line of H2 at the illuminated edge of the PDR presents numerous sharp sub-structures on scales as small as 1.5″. An excess of H2 emission compared to dust emission is found all along the edge, in a narrow layer (width around 1″, corresponding to 2 × 10−3 pc or 400 au) directly illuminated by σ-Orionis. The ionization front and the dissociation front appear at distances 1–2″ behind the external edge of the PDR and seem to spatially coincide, indicating a very small thickness of the neutral atomic layer (below 100 au). All broadband maps present strong color variations between the illuminated edge and the internal regions. This can be explained by dust attenuation in a scenario where the illuminating star σ-Orionis is slightly inclined compared to the plane of the sky, so that the Horsehead is illuminated from behind at an oblique angle. The deviations from predictions of the measured emissions in the Hα, Paα, and Brα lines also indicate dust attenuation. With a very simple model, we used the data to derive the main spectral features of the extinction curve. A small excess of extinction at 3 µm may be attributed to icy H2O mantles onto grains formed in dense regions. We also derived attenuation profiles from 0.7 to 25 µm across the PDR. In all lines of sight crossing the inner regions of the Horsehead, especially around the IR peak position, it appears that dust attenuation is non-negligible over the entire spectral range of the JWST.

From Stellar Nurseries to Old Stellar Populations: A Multi-wavelength Case of NGC 1055

Abstract Given the complex nature of galaxies’ interstellar medium (ISM), multi-wavelength data are required to probe the interplay among gas, dust, and stellar populations. Spiral galaxies are ideal laboratories for such a goal as they are rich in gas and dust. Using carbon monoxide (CO) along with GALEX far-ultraviolet (FUV) and Spitzer near-infrared (NIR) data we probe the correlations amongst the properties of stellar populations, gas, and dust over the disc of the spiral galaxy NGC 1055 at multiple angular resolutions, i.e. 2, 4, and 17 arcsec corresponding to a linear size of 144 pc, 288 pc, and 1.2 kpc, respectively. Our results indicate an asymmetry in the physical conditions along the galaxy’s disc, i.e. the gas is slightly more extended and brighter, and molecular gas mass is higher on the disc’s eastern side than the western side. All physical properties (i.e. molecular gas mass, CO line ratios, stellar mass, NIR emission) decrease from the centre going outwards in the disc with some exceptions (i.e. the extinction, FUV radiation, and the [3.6]−[4.5] colour). Our analysis indicates that the colour gets bluer (metallicity increases) halfway through the disc, then redder (metallicity decreases) going outwards further in the disc.

PDRs4All

Context. The James Webb Space Telescope (JWST) has captured the most detailed and sharpest infrared (IR) images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR). Aims. We investigate the fundamental interaction of far-ultraviolet (FUV) photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments. Methods. We utilized NIRCam and MIRI to obtain sub-arcsecond images over ~150″ and 42″ in key gas phase lines (e.g., Pa α, Br α, [FeII] 1.64 µm, H2 1−0 S(1) 2.12 µm, 0–0 S(9) 4.69 µm), aromatic and aliphatic infrared bands (aromatic infrared bands at 3.3–3.4 µm, 7.7, and 11.3 µm), dust emission, and scattered light. Their emission are powerful tracers of the IF and DF, FUV radiation field and density distribution. Using NIRSpec observations the fractional contributions of lines, AIBs, and continuum emission to our NIRCam images were estimated. A very good agreement is found for the distribution and intensity of lines and AIBs between the NIRCam and NIRSpec observations. Results. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of ~0.1–1″ (~0.0002–0.002 pc or ~40–400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. The spatial distribution of the AIBs reveals that the PDR edge is steep and is followed by an extensive warm atomic layer up to the DF with multiple ridges. A complex, structured, and folded H0/H2 DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar as our observations show that a 3D “terraced” geometry is required to explain the JWST observations. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate. Conclusions. This study offers an unprecedented dataset to benchmark and transform PDR physico-chemical and dynamical models for the JWST era. A fundamental step forward in our understanding of the interaction of FUV photons with molecular clouds and the role of FUV irradiation along the star formation sequence is provided.

A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk.

Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photodissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, which affects planet formation within the disks. We report James Webb Space Telescope and Atacama Large Millimeter Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modeling their kinematics and excitation allowed us to constrain the physical conditions within the gas. We quantified the mass-loss rate induced by the FUV irradiation and found that it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk.

High resolution modelling of [CII], [CI], [OIII], and CO line emission from the interstellar medium and circumgalactic medium of a star-forming galaxy at z ∼ 6.5

The circumgalactic medium (CGM) is a crucial component of galaxy evolution, but thus far its physical properties are highly unconstrained. As of yet, no cosmological simulation has reached convergence when it comes to constraining the cold and dense gas fraction of the CGM. Such components are also challenging to observe directly, as they require sub-millimetre (sub-mm) instruments with a high sensitivity to extended and mostly diffuse emission. We present a state-of-the-art theoretical effort at modelling the [CII] 158 μm, [CI](1−0) 609 μm, [CI](2−1) 370 μm, CO(3−2) 867 μm, and [OIII] 88 μm line emissions that arise from the interstellar medium (ISM) and CGM of galaxies, with the goal of studying the contribution from different cold (T < 104 K) components of galaxy halos. We used the high-resolution cosmological zoom-in simulation PONOS (mgas = 883.4 M⊙), which represents a typical star-forming galaxy system at z = 6.5, composed of a main disc with stellar mass M* = 2 × 109 M⊙ that is undergoing a major merger. We adopted different modelling approaches based on the photoionisation code CLOUDY. Our fiducial model uses radiative transfer post-processing with RAMSES-RT and KROME (KRAMSES-RT) to create more realistic far-ultraviolet (FUV) radiation fields, which we then compared to other sub-grid modelling approaches adopted in the literature. We find significant differences in the luminosity and in the contribution of different gas phases and galaxy components between the different modelling approaches. [CII] is the least model-dependant gas tracer, while [CI](1−0) and CO(3−2) are very model-sensitive. In all models, we find a significant contribution to the emission of [CII] (up to ∼10%) and [OIII] (up to ∼21%) from the CGM. Our fiducial global radiative transfer (RT) model produces a lower density, T ∼ 104 K tail of [CII] emission that is not seen in the other more simplistic models and that resides entirely in the CGM, ionised by the FUV background and producing the extended halos observed in [CII] at high-z. Notably, [CII] and [OIII] trace different regions of the CGM: [CII] arises from an accreting filament and from the tidal tails connecting the main disc and its merging satellites, while [OIII] traces a puffy halo surrounding the main disc, probably linked to supernova feedback. We discuss our results in the context of sub-mm observations. Using simulated spectra and mock maps, we show that, despite the rather compact angular extent of PONOS’s CGM, deep ALMA observations would not detect this component, even in [CII] which is the brightest available tracer. Instead, a next generation single-dish observatory such as the Atacama Large Aperture Submillimeter Telescope (AtLAST) could detect PONOS’ CGM in [CII] at a high signal-to-noise ratio, and possibly even in [OIII].

SUNRISE: The rich molecular inventory of high-redshift dusty galaxies revealed by broadband spectral line surveys

Understanding the nature of high-redshift dusty galaxies requires a comprehensive view of their interstellar medium (ISM) and molecular complexity. However, the molecular ISM at high redshifts is commonly studied using only a few species beyond 12C16O, limiting our understanding. In this paper, we present the results of deep 3 mm spectral line surveys using the NOrthern Extended Millimeter Array (NOEMA) targeting two strongly lensed dusty galaxies observed when the Universe was less than 1.8 Gyr old: APM 08279+5255, a quasar at redshift z = 3.911, and NCv1.143 (H-ATLAS J125632.7+233625), a z = 3.565 starburst galaxy. The spectral line surveys cover rest-frame frequencies from about 330 to 550 GHz for both galaxies. We report the detection of 38 and 25 emission lines in APM 08279+5255 and NCv1.143, respectively. These lines originate from 17 species, namely CO, 13CO, C18O, CN, CCH, HCN, HCO+, HNC, CS, C34S, H2O, H3O+, NO, N2H+, CH, c-C3H2, and the vibrationally excited HCN and neutral carbon. The spectra reveal the chemical richness and the complexity of the physical properties of the ISM. By comparing the spectra of the two sources and combining the analysis of the molecular gas excitation, we find that the physical properties and the chemical imprints of the ISM are different: the molecular gas is more excited in APM 08279+5255, which exhibits higher molecular gas temperatures and densities compared to NCv1.143; the molecular abundances in APM 08279+5255 are akin to the values of local active galactic nuclei (AGN), showing boosted relative abundances of the dense gas tracers that might be related to high-temperature chemistry and/or the X-ray-dominated regions, while NCv1.143 more closely resembles local starburst galaxies. The most significant differences between the two sources are found in H2O: the 448 GHz ortho-H2O(423 − 330) line is significantly brighter in APM 08279+5255, which is likely linked to the intense far-infrared radiation from the dust powered by AGN. Our astrochemical model suggests that, at such high column densities, far-ultraviolet radiation is less important in regulating the ISM, while cosmic rays (and/or X-rays and shocks) are the key players in shaping the molecular abundances and the initial conditions of star formation. Both our observed CO isotopologs line ratios and the derived extreme ISM conditions (high gas temperatures, densities, and cosmic-ray ionization rates) suggest the presence of a top-heavy stellar initial mass function. From the ∼330–550 GHz continuum, we also find evidence of nonthermal millimeter flux excess in APM 08279+5255 that might be related to the central supermassive black hole. Such deep spectral line surveys open a new window into the physics and chemistry of the ISM and the radiation field of galaxies in the early Universe.

C ii] Spectral Mapping of the Galactic Wind and Starbursting Disk of M82 with SOFIA

M82 is an archetypal starburst galaxy in the local Universe. The central burst of star formation, thought to be triggered by M82's interaction with other members in the M81 group, is driving a multiphase galaxy-scale wind away from the plane of the disk that has been studied across the electromagnetic spectrum. Here, we present new velocity-resolved observations of the [C ii] 158 μm line in the central disk and the southern outflow of M82 using the upGREAT instrument on board SOFIA. We also report the first detections of velocity-resolved (ΔV = 10 km s−1) [C ii] emission in the outflow of M82 at projected distances of ≈1–2 kpc south of the galaxy center. We compare the [C ii] line profiles to observations of CO and H i and find that likely the majority (>55%) of the [C ii] emission in the outflow is associated with the neutral atomic medium. We find that the fraction of [C ii] actually outflowing from M82 is small compared to the bulk gas outside the midplane (which may be in a halo or tidal streamers), which has important implications for observations of [C ii] outflows at higher redshift. Finally, by comparing the observed ratio of the [C ii] and CO intensities to models of photodissociation regions, we estimate that the far-ultraviolet (FUV) radiation field in the disk is ∼103.5 G 0, in agreement with previous estimates. In the outflow, however, the FUV radiation field is 2–3 orders of magnitudes lower, which may explain the high fraction of [C ii] arising from the neutral medium in the wind.

HCN emission from translucent gas and UV-illuminated cloud edges revealed by wide-field IRAM 30 m maps of the Orion B GMC

Context. Massive stars form within dense clumps inside giant molecular clouds (GMCs). Finding appropriate chemical tracers of the dense gas (n(H2) > several 104 cm−3 or AV > 8 mag) and linking their line luminosity with the star formation rate is of critical importance. Aims. Our aim is to determine the origin and physical conditions of the HCN-emitting gas and study their relation to those of other molecules. Methods. In the context of the IRAM 30m ORION-B large program, we present 5 deg2 (~250 pc2) HCN, HNC, HCO+, and CO J =1–0 maps of the Orion B GMC, complemented with existing wide-field [C I] 492 GHz maps, as well as new pointed observations of rotationally excited HCN, HNC, H13CN, and HN13C lines. We compare the observed HCN line intensities with radiative transfer models including line overlap effects and electron excitation. Furthermore, we study the HCN/HNC isomeric abundance ratio with updated photochemical models. Results. We spectroscopically resolve the HCN J = 1–0 hyperfine structure (HFS) components (and partially resolved J = 2−1 and 3−2 components). We detect anomalous HFS line intensity (and line width) ratios almost everywhere in the cloud. About 70% of the total HCN J = 1−0 luminosity, L′(HCN J = 1−0) = 110 K km s−1 pc−2, arises from AV < 8 mag. The HCN/CO J = 1−0 line intensity ratio, widely used as a tracer of the dense gas fraction, shows a bimodal behavior with an inflection point at AV < 3 mag typical of translucent gas and illuminated cloud edges. We find that most of the HCN J = 1−0 emission arises from extended gas with n(H2) < 104 cm−3, and even lower density gas if the ionization fraction is χe ≥ 10−5 and electron excitation dominates. This result contrasts with the prevailing view of HCN J = 1−0 emission as a tracer of dense gas and explains the low-AV branch of the HCN/CO J = 1−0 intensity ratio distribution. Indeed, the highest HCN/CO ratios (~ 0.1) at AV < 3 mag correspond to regions of high [C I] 492 GHz/CO J = 1−0 intensity ratios (>1) characteristic of low-density photodissociation regions. The low surface brightness (≲ 1 K km s−1) and extended HCN and HCO+ J = 1−0 emission scale with IFIR – a proxy of the stellar far-ultraviolet (FUV) radiation field – in a similar way. Together with CO J = 1−0, these lines respond to increasing IFIR up to G0 ≃ 20. On the other hand, the bright HCN J = 1−0 emission (> 6 K km s−1) from dense gas in star-forming clumps weakly responds to IFIR once the FUV field becomes too intense (G0 > 1500). In contrast, HNC J = 1−0 and [C I] 492 GHz lines weakly respond to IFIR for all G0. The different power law scalings (produced by different chemistries, densities, and line excitation regimes) in a single but spatially resolved GMC resemble the variety of Kennicutt-Schmidt law indexes found in galaxy averages. Conclusions. Given the widespread and extended nature of the [C I] 492 GHz emission, as well as its spatial correlation with that of HCO+, HCN, and 13CO J = 1−0 lines (in this order), we argue that the edges of GMCs are porous to FUV radiation from nearby massive stars. Enhanced FUV radiation favors the formation and excitation of HCN on large scales, not only in dense star-forming clumps, and it leads to a relatively low value of the dense gas mass to total luminosity ratio, α (HCN) = 29 M⊙/(K km s−1pc2) in Orion B. As a corollary for extragalactic studies, we conclude that high HCN/CO J = 1−0 line intensity ratios do not always imply the presence of dense gas, which may be better traced by HNC than by HCN.

Photoevaporation and Close Encounters: How the Environment around Cygnus OB2 Affects the Evolution of Protoplanetary Disks

In our Galaxy, star formation occurs in a variety of environments, with a large fraction of stars formed in clusters hosting massive stars. OB stars have an important feedback on the evolution of protoplanetary disks orbiting around nearby young stars and likely on the process of planet formation occurring in them. The nearby massive association Cyg OB2 is an outstanding laboratory to study this feedback. It is the closest massive association to our Sun and hosts hundreds of massive stars and thousands of low-mass members, both with and without disks. In this paper, we analyze the spatial variation of the disk fraction (i.e., the fraction of cluster members bearing a disk) in Cyg OB2 and study its correlation with the local values of far-ultraviolet (FUV) and extreme-ultraviolet (EUV) radiation fields and the local stellar surface density. We present definitive evidence that disks are more rapidly dissipated in the regions of the association characterized by intense local UV fields and large stellar density. In particular, the FUV radiation dominates disk dissipation timescales in the proximity (i.e., within 0.5 pc) of the O stars. In the rest of the association, EUV photons potentially induce a significant mass loss from the irradiated disks across the entire association, but the efficiency of this process is reduced at increasing distances from the massive stars owing to absorption by the intervening intracluster material. We find that disk dissipation due to close stellar encounters is negligible in Cyg OB2 and likely to have affected 1% or fewer of the stellar population. Disk dissipation is instead dominated by photoevaporation. We also compare our results to what has been found in other young clusters with different massive populations, concluding that massive associations like Cyg OB2 are potentially hostile to protoplanetary disks but that the environments where disks can safely evolve in planetary systems are likely quite common in our Galaxy.

Eta Carinae: The Dissipating Occulter Is an Extended Structure

Previous Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) longslit observations of Eta Carinae (η Car) identified numerous absorption features in both the stellar spectrum, and in the adjacent nebular spectra, along our line of sight (LOS). The absorption features became temporarily stronger when the ionizing far-ultraviolet radiation field was reduced by the periastron passage of the secondary star. Subsequently, dissipation of a dusty structure in our LOS has led to a long-term increase in the apparent brightness of η Car, an increase in the ionizing ultraviolet (UV) radiation, and the disappearance of absorption from multiple velocity-separated shells extending across the foreground Homunculus lobe. We use HST/STIS spectro-images, coupled with published infrared and radio observations, to locate this intervening dusty structure. The velocity and spatial information indicate the occulter is ≈1000 au in front of η Car. The Homunculus is a transient structure composed of dusty, partially ionized ejecta that eventually will disappear due to the relentless rain of ionizing radiation and wind from the current binary system along with dissipation and mixing with the interstellar medium. This evolving complex continues to provide an astrophysical laboratory that changes on human timescales.

Population study on MHD wind-driven disc evolution

Context. Current research has established magnetised disc winds as a promising way of driving accretion in protoplanetary discs. Aims. We investigate the evolution of large protoplanetary disc populations under the influence of magnetically driven disc winds as well as internal and external photoevaporation. We aim to constrain magnetic disc wind models through comparisons with observations. Methods. We ran 1D vertically integrated evolutionary simulations for low-viscosity discs, including magnetic braking and various outflows. The initial conditions were varied and chosen to produce populations that are representative of actual disc populations inferred from observations. We then compared the observables from the simulations (e.g. stellar accretion rate, disc mass evolution, disc lifetime, etc.) with observational data. Results. Our simulations show that to reach stellar accretion rates comparable to those found by observations (~10−8 M⊙ yr−1), it is necessary to have access not only to strong magnetic torques, but weak magnetic winds as well. The presence of a strong magnetic disc wind, in combination with internal photoevaporation, leads to the rapid opening of an inner cavity early on, allowing the stellar accretion rate to drop while the disc is still massive. Furthermore, our model supports the notion that external photoevaporation via the ambient far-ultraviolet radiation of surrounding stars is a driving force in disc evolution and could potentially exert a strong influence on planetary formation. Conclusions. Our disc population syntheses show that for a subset of magnetohydrodynamic wind models (weak disc wind, strong torque), it is possible to reproduce important statistical observational constraints. The magnetic disc wind paradigm thus represents a novel and appealing alternative to the classical α-viscosity scenario.

Physics and Chemistry of Radiation Driven Cloud Evolution. [C ii] Kinematics of IC 59, and IC 63

We used high-resolution [C ii] 158 μm mapping of two nebulae IC 59 and IC 63 from SOFIA/upGREAT in conjunction with ancillary data of the gas, dust, and polarization to probe the kinematics, structure, and magnetic properties of their photodissociation regions (PDRs). The nebulae are part of the Sh 2-185 H ii region that is illuminated by the B0 IVe star γ Cas. The velocity structure of each PDR changes with distance from γ Cas, which is consistent with driving by the radiation. Based on previous far-ultraviolet (FUV) flux measurements of, and the known distance to, γ Cas, along with the predictions of 3D distances to the clouds, we estimated the FUV radiation field strength (G 0) at the clouds. Assuming negligible extinction between the star and clouds, we find their 3D distances from γ Cas. For IC 63, our results are consistent with earlier estimates of distance from Andersson et al., locating the cloud at ∼2 pc from γ Cas at an angle of 58° to the plane of the sky behind the star. For IC 59, we derive a distance of 4.5 pc at an angle of 70° in front of the star. We do not detect any significant correlation between the orientation of the magnetic field and the velocity gradients of [C ii] gas, which indicates a moderate magnetic field strength. The kinetic energy in IC 63 is estimated to be an order of 10 higher than the magnetic energies. This suggests that kinetic pressure in this nebula is dominant.

High-angular-resolution NIR view of the Orion Bar revealed by Keck/NIRC2

Context. Nearby photo-dissociation regions (PDRs), where the gas and dust are heated by the far-ultraviolet (FUV) irradiation emitted from stars, are ideal templates with which to study the main stellar feedback processes. Aims. With this study, we aim to probe the detailed structures at the interfaces between ionized, atomic, and molecular gas in the Orion Bar. This nearby prototypical strongly irradiated PDR are among the first targets of the James Webb Space Telescope (JWST) within the framework of the PDRs4All Early Release Science program. Methods. We employed the subarcsecond resolution accessible with Keck-II NIRC2 and its adaptive optics system to obtain images of the vibrationally excited line H2 1−0 S(1) at 2.12 µm that are more detailed and complete than ever before. H2 1−0 S(1) traces the dissociation front (DF), and the [FeII] and Brγ lines, at 1.64 and 2.16 µm, respectively, trace the ionization front (IF). The former is a powerful tracer of the FUV radiation field strength and gas density distribution at the PDR edge, while the last two trace the temperature and density distribution from the ionized gas to the PDR. We obtained narrow-band filter images in these key gas line diagnostics over ~40″ at spatial scales of ~0.1″ (~0.0002 pc or ~40 AU at 414 pc). Results. The Keck/Near Infrared Camera 2 (NIRC2) observations spatially resolve a plethora of irradiated substructures such as ridges, filaments, globules, and proplyds. This portends what JWST should accomplish and how it will complement the highest resolution Atacama Large Millimeter/submillimeter Array (ALMA) maps of the molecular cloud. We observe a remarkable spatial coincidence between the H2 1−0 S(1) vibrational and HCO+ J = 4−3 rotational emission previously obtained with ALMA. This likely indicates the intimate link between these two molecular species and highlights that in high-pressure PDRs, the H/H2 and C+/C/CO transitions zones come closer than in a typical layered structure of a constant density PDR. The H/H2 dissociation front appears as a highly structured region containing substructures with a typical thickness of a few ~10−3 pc.

Survey of Orion Disks with ALMA (SODA)

Context. External far-ultraviolet (FUV) irradiation of protoplanetary disks has an important impact on their evolution and ability to form planets. However, nearby (< 300 pc) star-forming regions lack sufficiently massive young stars, while the Trapezium cluster and NGC 2024 have complicated star-formation histories and their O-type stars’ intense radiation fields (> 104 G0) destroy disks too quickly to study this process in detail. Aims. We study disk mass loss driven by intermediate (10 − 1000 G0) FUV radiation fields in L1641 and L1647, where it is driven by more common A0- and B-type stars. Methods. Using the large (N = 873) sample size offered by the Survey of Orion Disks with ALMA (SODA), we searched for trends in the median disk dust mass with FUV field strength across the region as a whole and in two separate regions containing a large number of irradiated disks. Results. For radiation fields between 1 − 100 G0, the median disk mass in the most irradiated disks drops by a factor ∼2 over the lifetime of the region, while the 95th percentile of disk masses drops by a factor 4 over this range. This effect is present in multiple populations of stars, and localized in space, to within 2 pc of ionizing stars. We fitted an empirical irradiation – disk mass relation for the first time: Mdust,median = −1.3−0.13+0.14 log10(FFUV/G0) + 5.2−0.19+0.18. Conclusions. This work demonstrates that even intermediate FUV radiation fields have a significant impact on the evolution of protoplanetary disks.

Bright extragalactic ALMA redshift survey (BEARS) III: detailed study of emission lines from 71Herscheltargets

ABSTRACTWe analyse the molecular and atomic emission lines of 71 bright Herschel-selected galaxies between redshifts 1.4 and 4.6 detected by the Atacama Large Millimeter/submillimeter Array. These lines include a total of 156 CO, [C i], and H2O emission lines. For 46 galaxies, we detect two transitions of CO lines, and for these galaxies we find gas properties similar to those of other dusty star-forming galaxy (DSFG) samples. A comparison to photodissociation models suggests that most of Herschel-selected galaxies have similar interstellar medium conditions as local infrared-luminous galaxies and high-redshift DSFGs, although with denser gas and more intense far-ultraviolet radiation fields than normal star-forming galaxies. The line luminosities agree with the luminosity scaling relations across five orders of magnitude, although the star formation and gas surface density distributions (i.e. Schmidt–Kennicutt relation) suggest a different star formation phase in our galaxies (and other DSFGs) compared to local and low-redshift gas-rich, normal star-forming systems. The gas-to-dust ratios of these galaxies are similar to Milky Way values, with no apparent redshift evolution. Four of 46 sources appear to have CO line ratios in excess of the expected maximum (thermalized) profile, suggesting a rare phase in the evolution of DSFGs. Finally, we create a deep stacked spectrum over a wide rest-frame frequency (220–890 GHz) that reveals faint transitions from HCN and CH, in line with previous stacking experiments.

222 nm far-UVC efficiently introduces nerve damage in Caenorhabditis elegans.

Far-ultraviolet radiation C light (far-UVC; 222 nm wavelength) has received attention as a safer light for killing pathogenic bacteria and viruses, as no or little DNA damage is observed after irradiation in mammalian skin models. Far-UVC does not penetrate deeply into tissues; therefore, it cannot reach the underlying critical basal cells. However, it was unclear whether far-UVC (222-UVC) irradiation could cause more biological damage at shallower depths than the 254 nm UVC irradiation (254-UVC), which penetrates more deeply. This study investigated the biological effects of 222- and 254-UVC on the small and transparent model organism Caenorhabditis elegans. At the same energy level of irradiation, 222-UVC introduced slightly less cyclobutane pyrimidine dimer damage to naked DNA in solution than 254-UVC. The survival of eggs laid during 0-4 h after irradiation showed a marked decrease with 254-UVC but not 222-UVC. In addition, defect of chromosomal condensation was observed in a full-grown oocyte by 254-UVC irradiation. In contrast, 222-UVC had a significant effect on the loss of motility of C. elegans. The sensory nervous system, which includes dopamine CEP and PVD neurons on the body surface, was severely damaged by 222-UVC, but not by the same dose of 254-UVC. Interestingly, increasing 254-UVC irradiation by about 10-fold causes similar damage to CEP neurons. These results suggest that 222-UVC is less penetrating, so energy transfer occurs more effectively in tissues near the surface, causing more severe damage than 254-UVC.

Reconstructing solar magnetic fields from historical observations

Context. The bright regions in the solar chromosphere and temperature minimum have a good spatial correspondence with regions of intense photospheric magnetic field. Bright regions are visible in different emission lines and parts of the continuum. Their observation started more than a hundred years ago with the invention of the spectroheliograph. While the historical spectroheliograms are essential for studying the long-term variability of the Sun, the modern satellite-borne observations can help us reveal the nature of chromospheric brightenings in previously unattainable detail. Aims. Our aim is to improve the understanding of the relation between magnetic fields and radiative structures byf studying modern seeing-free observations of far-ultraviolet (FUV) radiation around 1600 Å and photospheric magnetic fields. Methods. We used Helioseismic and Magnetic Imager (HMI) observations of photospheric magnetic fields and Atmospheric Imaging Assembly (AIA) observations of FUV contrast around 1600 Å. We developed a robust method to find contrast thresholds defining bright and dark AIA 1600 Å pixels, and we combine them to bright and dark clusters. We investigate the relation of magnetic fields and AIA 1600 Å radiation in bright and dark clusters. Results. We find that the percentage of bright pixels (ranging from 2% to 10%) almost entirely explains the observed variability of 1600 Å emission. We developed a multilinear regression model based on the percentages of bright and dark pixels, which can reliably predict the magnitude of the disk-averaged unsigned magnetic field. We find that bright and dark clusters closely correspond respectively to the populations of moderate (B > 55 G) and strong (B > 1365 G) magnetic field HMI clusters. The largest bright clusters have a constant mean unsigned magnetic field, as found previously for Ca II K plages. However, the magnetic field strength of bright clusters is 254.7 ± 0.1 G, which is roughly 100 G larger than found earlier for Ca II K plages.