High Column Density Research Articles

Intense Star Cluster Formation: Stellar Masses, the Mass Function, and the Fundamental Mass Scale

Within the birth environment of a massive globular cluster, the combination of a luminous young stellar population and a high column density induces a state in which the thermal optical depth and radiation pressure are both appreciable. In this state, the sonic mass scale, which influences the peak of the stellar mass function, is tied to a fundamental scale composed of the Planck mass and the mass per particle. Thermal feedback also affects the opacity-limited minimum mass and how protostellar outflows and binary fragmentation modify stellar masses. Considering the regions that collapse to form massive stars, we argue that thermal stabilization is likely to flatten the high-mass slope of the initial mass function. Among regions that are optically thick to thermal radiation, we expect the stellar population to become increasingly top-heavy at higher column densities, although this effect can be offset by lowering the metallicity. A toy model is presented that demonstrates these effects and in which radiation pressure leads to gas dispersal before all of the mass is converted into stars.

Can Supernovae from Runaway Stars Mimic the Signs of Absorbing “Supervirial” Gas?

The recent detection of large column density absorption lines from highly ionized gas in a few directions through the circumgalactic medium (CGM) of the Milky Way (MW) has been puzzling. The inferred temperature from these absorption lines far exceeds the virial temperature of the MW, and the column densities are also too large to be easily explained. In this paper, we propose a novel idea to explain these observations and claim that they may not have originated from the CGM, but from a totally different type of source, namely, stellar ejecta from supernovae (SNe) above the Galactic disk that happen to lie in the line of sight to the background quasars. About ∼20% of massive OB stars (progenitors of core-collapse supernovae) are known to be runaway stars that have high ejection velocities near the Galactic plane and can end up exploding as SNe above the Galactic disk. We show that the associated reverse shock in the supernova remnant in the early nonradiative phase can heat the ejecta to temperatures of ≳107 K and can naturally explain the observed high column density of ions in the observed “supervirial” phase along with α-enriched supersolar abundance that is typical of core-collapse supernovae. However, SNe from runaway stars has a covering fraction of ≲0.7% and thus can only explain the observations along limited sightlines.

The JWST-PRIMAL archival survey. A JWST/NIRSpec reference sample for the physical properties and Lyman-alpha absorption and emission of ~ 600 galaxies at z = 5:0 - 13:4

One of the surprising early findings with has been the discovery of a strong ``roll-over'' or a softening of the absorption edge of in a large number of galaxies at \(z 6\), in addition to systematic offsets from photometric redshift estimates and fundamental galaxy scaling relations. This has been interpreted as strong cumulative damped absorption (DLA) wings from high column densities of neutral atomic hydrogen ( signifying major gas accretion events in the formation of these galaxies. To explore this new phenomenon systematically, we assembled the PRImordial gas Mass AssembLy (PRIMAL) legacy survey of 584 galaxies at $z=5.0-13.4$, designed to study the physical properties and gas in and around galaxies during the reionization epoch. We characterized this benchmark sample in full and spectroscopically derived the galaxy redshifts, metallicities, star formation rates, and ultraviolet (UV) slopes. We defined a new diagnostic, the damping parameter to measure and quantify the net effect of emission strength, the fraction in the intergalactic medium, or the local column density for each source. The survey is based on the spectroscopic DAWN Archive (DJA-Spec). We describe DJA-Spec in this paper, detailing the reduction methods, the post-processing steps, and basic analysis tools. All the software, reduced spectra, and spectroscopically derived quantities and catalogs are made publicly available in dedicated repositories. We find that the fraction of galaxies showing strong integrated DLAs with $N_ HI $ only increases slightly from $ 60<!PCT!>$ at $z 6$ up to $ 65-90<!PCT!>$ at $z>8$. Similarly, the prevalence and prominence of emission is found to increase with decreasing redshift, in qualitative agreement with previous observational results. Strong emitters (LAEs) are predominantly found to be associated with low-metallicity and UV faint galaxies. By contrast, strong DLAs are observed in galaxies with a variety of intrinsic physical properties, but predominantly at high redshifts and low metallicities. Our results indicate that strong DLAs likely reflect a particular early assembly phase of reionization-era galaxies, at which point they are largely dominated by pristine gas accretion. At $z=8-10$, this gas gradually cools and forms into stars that ionize their local surroundings, forming large ionized bubbles and producing strong observed emission at $z<8$.

A SPectroscopic Survey of Biased Halos In the Reionization Era (ASPIRE): Broad-line AGN at z = 4−5 Revealed by JWST/NIRCam WFSS

Low-luminosity active galactic nuclei (AGNs) with low-mass black holes (BHs) in the early universe are fundamental to understanding the BH growth and their coevolution with the host galaxies. Utilizing JWST NIRCam Wide Field Slitless Spectroscopy, we perform a systematic search for broad-line Hα emitters (BHAEs) at z ≈ 4–5 in 25 fields of the A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) project, covering a total area of 275 arcmin2. We identify 16 BHAEs with FWHM of the broad components spanning from ∼1000 to 3000 km s−1. Assuming that the broad line widths arise as a result of Doppler broadening around BHs, the implied BH masses range from 107 to 108 M ⊙, with broad Hα-converted bolometric luminosities of 1044.5–1045.5 erg s−1 and Eddington ratios of 0.07–0.47. The spatially extended structure of the F200W stacked image may trace the stellar light from the host galaxies. The Hα luminosity function indicates an increasing AGN fraction toward the higher Hα luminosities. We find possible evidence for clustering of BHAEs: two sources are at the same redshift with a projected separation of 519 kpc; one BHAE appears as a composite system residing in an overdense region with three close companion Hα emitters. Three BHAEs exhibit blueshifted absorption troughs indicative of the presence of high column density gas. We find that the broad-line-selected and photometrically selected BHAE samples exhibit different distributions in the optical continuum slopes, which can be attributed to their different selection methods. The ASPIRE broad-line Hα sample provides a good database for future studies of faint AGN populations at high redshift.

Post-outburst chemistry in a Very Low-Luminosity Object. Peculiar high abundance of nitric oxide

Very Low Luminosity Objects (VeLLOs) are deeply embedded, and extremely faint objects (L$_ int $ $<$ 0.1 L$_ odot $), and are thought to be in the quiescent phase of the episodic accretion process. They fill an important gap in our understanding of star formation. The VeLLO in the isolated DC3272+18 cloud has undergone an outburst in the past sim 10$^4$ yr, and is thus an ideal target for investigating the chemical inventory in the gas phase of an object of its type. The aim of this study is to investigate the direct impact of the outburst on the chemical processes in the object and identify molecules that can act as tracers of past heating events. Observations with the Atacama Pathfinder EXperiment (APEX) in four spectral windows in the frequency range of 213.6--272.4 GHz have been carried out to identify molecules that can be directly linked to the past outburst; to utilize the line fluxes, column densities, and the abundance ratios of the detected species to characterize the different physical components of the VeLLO; and to probe for the presence of complex organic molecules. Nitric oxide (NO) is detected for the first time in a source of this type, and its formation could be induced by the sublimation of grain-surface species during the outburst. In addition, the observations securely detect CH$_3$OH, H$_2$CO, D$_2$CO, SO, SO$_2$, CO, 13CO, C18O, N$_2$D$^+$, HCO$^+$, DCO$^+$, HCN, DCN, HNC, c-C$_3$H$_2$, and C$_2$D. The upper state energies of the securely detected lines and their derived line intensity ratios indicate that most of the probed material stems from regions of cold gas in the envelope enshrouding the VeLLO in the DC3272+18 cloud with a temperature of sim 10 K. In addition, c-C$_3$H$_2$ traces a second, warmer gas reservoir with a temperature of sim 35 K. The high D/H ratio derived from D$_2$CO points toward its origin from the prestellar stage, while deuteration of the gas-phase species DCO$^+$, DCN, and C$_2$D could still be ongoing in the gas in the envelope. The gas probed by the observations already cooled down after the past heating event caused by the outburst, but it still has lasting effects on the chemistry in the envelope of the VeLLO. CH$_3$OH, H$_2$CO, SO, SO$_2$, and CO sublimated from grains during the outburst and have not fully frozen out yet, which indicates that the outburst took place $<$ 10$^4$ yr ago. A pathway to form NO directly in the gas phase is from the photodissociation products created after the sublimation of H$_2$O and NH$_3$ from the ices. While the present time water snowline has likely retreated to a pre-outburst small radius, the volatile NO species is still extensively present in the gas phase, as is evident by its high column density relative to methanol in the observations. This suggests that NO could be potentially used to trace the water snowline in outbursting sources. In order to rule out nonthermal desorption processes that could also have led to the formation of NO, this proposition has to be verified with future observations at a higher spatial resolution, and by searching for NO in additional targets.

Extended CO(1–0) survey and ammonia measurements towards two bubble regions in W5

The feedback effect of massive stars can either accelerate or inhibit star formation activity within molecular clouds. Studying the morphology of molecular clouds near W5 offers an excellent opportunity to examine this feedback effect. We conducted a comprehensive survey of the W5 complex using the Purple Mountain Observatory 13.7 m millimeter telescope. This survey includes 12CO, 13CO, and C18O (J = 1 − 0), with a sky coverage of 6.6 deg2 (136.0° < l < 138.75°, 0° < b < 2.4°). Furthermore, we performed simultaneous observations of the NH3 (1,1) and NH3 (2,2) lines in the four densest star-forming regions of W5, using the 26 m radio telescope of the Xinjiang Astronomy Observatory (XAO). Our analysis of the morphological distribution of the molecular clouds, distribution of high-mass young stellar objects (HMYSOs), 13CO/C18O abundance ratio, and the stacked average spectral line distribution at different 8 μm thresholds provide compelling evidence of triggering. Within the mapped region, we identified a total of 212 molecular clumps in the 13CO cube data using the astrodendro algorithm. Remarkably, approximately 26.4% (56) of these clumps demonstrate the potential to form massive stars and 42.9% (91) of them are gravitationally bound. Within clumps that are capable of forming high-mass stars, there is a distribution of class I YSOs, all located in dense regions near the boundaries of the HII regions. The detection of NH3 near the most prominent cores reveals moderate kinetic temperatures and densities (as CO). Comparing the Tkin and Tex values reveals a reversal in trends for AFGL 4029 (higher Tex and lower Tkin) and W5-W1, indicating the inadequacy of optically thick CO for dense region parameter calculations. Moreover, a comparison of the intensity distributions between NH3 (1,1) and C18O (1–0) in the four densest region reveals a notable depletion effect in AFGL 4029, characterised by a low Tkin (9 K) value and a relatively high NH3 column density, 2.5 × 1014 cm−2. By classifying the 13CO clumps as: “feedback,” “non-feedback,” “outflow,” or “non-outflow” clumps, we observe that the parameters of the “feedback” and “outflow” clumps exhibit variations based on the intensity of the internal 8 μm flux and the outflow energy, respectively. These changes demonstrate a clear linear correlation, which distinctly separate them from the parameter distributions of the “non-feedback” and “non-outflow” clumps, thus providing robust evidence to support a triggering scenario.

Turbulent circumnuclear disc and cold gas outflow in the newborn radio source 4C 31.04

We present deep kiloparsec- and parsec-scale neutral atomic hydrogen (H I) absorption observations of a very young radio source (≤5000 years), 4C 31.04, using the Westerbork Synthesis Radio Telescope (WSRT) and the Global Very Long Baseline Interferometry (VLBI) array. Using z = 0.0598, derived from molecular gas observations, we detect, at both kpc and pc scales, a broad absorption feature (FWZI = 360 km s−1) centred at the systemic velocity, and narrow absorption (FWZI = 6.6 km s−1) redshifted by 220 km s−1, both previously observed. Additionally, we detect a new blueshifted, broad, shallow absorption wing. At pc scales, the broad absorption at the systemic velocity is detected across the entire radio source while the shallow wing is only seen against part of the eastern lobe. The gas has higher H I column density along the eastern lobe than along the western one. The velocity dispersion of the gas is high (≥40 km s−1) along the entire radio continuum, and is highest (≥60 km s−1) in the region including the outflow and the radio hot spot. While we detect a velocity gradient along the western lobe and parts of the eastern lobe at PA ∼ 5° −10°, most of the gas along the rest of the eastern lobe exhibits no signs of rotation. Earlier optical spectroscopy suggests that the optical AGN is very weak. We therefore conclude that the radio lobes of 4C 31.04 are expanding into a circumnuclear disc, partially disrupting it and making the gas highly turbulent. The distribution of gas is predominantly smooth at the spatial resolution of ∼4 pc studied here. However, clumps of gas are also present, particularly along the eastern lobe. This lobe appears to be strongly interacting with the clouds and driving an outflow ∼35 pc from the radio core, with a mass-outflow rate of 0.3 ≤ Ṁ ≤ 1.4 M⊙ year−1. It is likely that this interaction has caused the eastern lobe to be rebrightened, giving the source an asymmetric morphology. We compare our observations with the predictions of a recent analytical model regarding the survival of atomic gas clouds in radio-jet-driven outflows and find that the existence of a subkpc-scale outflow in this case could imply inefficient mixing of the cold gas with the hot medium and high gas density, leading to very short cooling times. Overall, our study provides further evidence of the strong impact of radio jets on the cold interstellar medium (ISM) in the early stages of their evolution and supports the predictions of numerical simulations regarding jet–ISM interactions and the nature of the circumnuclear gas into which the jets expand.

MUSE Analysis of Gas around Galaxies (MAGG) - VI. The cool and enriched gas environment of z≳3 Lyα emitters

We present a novel dataset that extends our view of the cosmic gas around $z 3-4$ Lyalpha emitters (LAEs) in the Muse Analysis of Gas around Galaxies (MAGG) survey by tracing a cool and enriched gas phase through 47 absorbers identified in newly obtained VLT/X-shooter near-infrared quasar spectra. Jointly with the more ionized gas traced by systems and the neutral from previous work, we find that LAEs are distributed inside cosmic structures that contain multiphase gas in composition and temperature. All gas phases are a strong function of the large-scale galaxy environment: the and the strength and kinematics positively correlate with the number of associated galaxies, and it is $ times more likely to detect metal absorbers around groups of LAEs than isolated ones. Exploring the redshift evolution, the covering factor of around groups of LAEs and isolated ones remains approximately constant from $z to $z but the one of around group galaxies drops by $z Adding the cool enriched gas traced by the absorbers to the results that we obtained for the and gas, we put forward a picture in which LAEs lie along gas filaments that contain high column-density systems and are enriched by strong and absorbers. While the gas appears to be more centrally concentrated near LAEs, weaker systems instead trace a more diffuse gas phase extended up to larger distances around the galaxies.

ALMA-IMF

Context. The star formation process leads to an increased chemical complexity in the interstellar medium. Sites associated with high-mass star and cluster formation exhibit a so-called hot core phase, characterized by high temperatures and column densities of complex organic molecules. Aims. We aim to systematically search for and identify a sample of hot cores toward the 15 Galactic protoclusters of the ALMA-IMF Large Program and investigate their statistical properties. Methods. We built a comprehensive census of hot core candidates toward the ALMA-IMF protoclusters based on the detection of two CH3OCHO emission lines at 216.1 GHz. We used the source extraction algorithm GExt2D to identify peaks of methyl formate (CH3OCHO) emission, a complex species commonly observed toward sites of star formation. We performed a cross-matching with the catalog of thermal dust continuum sources from the ALMA-IMF 1.3 mm continuum data to infer their physical properties. Results. We built a catalog of 76 hot core candidates with masses ranging from ~0.2 M⊙ to ~80 M⊙, of which 56 are new detections. A large majority of these objects, identified from methyl formate emission, are compact and rather circular, with deconvolved full width at half maximum (FWHM) sizes of ~2300 au on average. The central sources of two target fields show more extended, but still rather circular, methyl formate emission with deconvolved FWHM sizes of ~6700 au and 13 400 au. About 30% of our sample of methyl formate sources have core masses above 8 M⊙ and range in size from ~1000 au to 13 400 au, which is in line with measurements of archetypical hot cores. The origin of the CH3OCHO emission toward the lower-mass cores may be explained as a mixture of contributions from shocks or may correspond to objects in a more evolved state (i.e., beyond the hot core stage). We find that the fraction of hot core candidates increases with the core mass, suggesting that the brightest dust cores are all in the hot core phase. Conclusions. Our results suggest that most of these compact methyl formate sources are readily explained by simple symmetric models, while collective effects from radiative heating and shocks from compact protoclusters are needed to explain the observed extended CH3OCHO emission. The large fraction of hot core candidates toward the most massive cores suggests that they rapidly enter the hot core phase and that feedback effects from the forming protostar(s) impact their environment on short timescales.

Abundant hydrocarbons in the disk around a very-low-mass star

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.

Low CI/CO abundance ratio revealed by HST UV spectroscopy of CO-rich debris discs

ABSTRACT The origin and evolution of CO gas in debris discs has been debated since its initial detection. The gas could have a primordial origin, as a remnant of the protoplanetary disc or a secondary exocometary origin. This paper investigates the origin of gas in two debris discs, HD110058 and HD131488, using Hubble Space Telescope (HST) observations of CI and CO, which play critical roles in the gas evolution. We fitted several electronic transitions of CI and CO rovibronic bands to derive column densities and temperatures for each system, revealing high CO column densities (∼3–4 orders of magnitude higher than β Pictoris), and low CI/CO ratios in both. Using the exogas model, we simulated the radial evolution of the gas in the debris disc assuming a secondary gas origin. We explored a wide range of CO exocometary release rates and α viscosities, which are the key parameters of the model. Additionally, we incorporated photodissociation due to stellar ultraviolet (UV) to the exogas model and found that it is negligible for typical CO-rich discs and host stars, even at a few au due to the high radial optical depths in the Extreme ultraviolet radiation (EUV). We find that the current steady-state secondary release model cannot simultaneously reproduce the CO and CI HST-derived column densities, as it predicts larger CI/CO ratios than observed. Our direct UV measurement of low CI/CO ratios agrees with results derived from recent Atacama Large Millimetre/submillimetre Array findings and may point to vertical layering of CI, additional CI removal, CO shielding processes, or different gas origin scenarios.

Likely detection of magnetic field related LFQPO in the soft X-ray rebrightening of GRS 1915+105

Utilizing NICER observations, we present an analysis of the soft X-ray rebrightening event of GRS 1915+105 observed in 2021. During this event, we observed the emergence of a stable long-lasting low-frequency quasi-periodic oscillation (LFQPO) with frequencies ranging from 0.17 to 0.21 Hz. Through a careful spectral analysis, we demonstrate that a low-temperature Compton-thick gas model characterizes the emitted radiation well. By examining the spectrum and identifying numerous absorption lines, we discerned a transition in the wind properties. This transition was marked by a shift from a state characterized by low speed, high column density, and high ionization degree to one featuring still low speed, but low column density and ionization degree. Intriguingly, the presence or absence of the QPO signal is perfectly correlated with these distinct wind characteristics. The low-speed wind observed could be indicative of a “failed wind”, while the observed shift implies a transition from a magnetically to a thermally driven wind. Notably, this QPO signal exclusively manifested itself during the magnetically driven phase, suggesting the possibility of a novel perturbation associated with magnetic effects.

The outflowing ionised gas of I Zw 1 observed by HST COS

Aims. We present an analysis of the Hubble Space Telescope Cosmic Origins Spectrograph spectrum of I Zw 1 aiming to probe the absorbing medium associated with the active galactic nucleus (AGN). Methods. We fitted the emission spectrum and performed spectral analysis of the identified absorption features to derive the corresponding ionic column densities and covering fractions of the associated outflows. We employed photoionisation modelling to constrain the total column density and the ionisation parameter of four detected kinematic components. By investigating the implications of the results together with the observed kinematic properties of both emission and absorption features, we derived constraints on the structure and geometry of the absorbing medium in the AGN environment. Results. We find and characterise absorption line systems from outflowing ionised gas in four distinct kinematic components, located at −60, −280, −1950, and −2900 km s−1 with respect to the source rest frame. While the two slower outflows are consistent with a full covering of the underlying radiation source, the well-constrained doublet line ratios of the faster two, higher column density, outflows suggest partial covering, with a covering fraction of Cf ∼ 0.4. The faster outflows show also line-locking in the N V doublet, a signature of acceleration via line absorption. This makes I Zw 1 possibly the closest object that shows evidence for hosting line-driven winds. The observed −1950 km s−1 absorption is likely due to the same gas as an X-ray warm absorber. Furthermore, the behaviour in UV and X-ray bands implies that this outflow has a clumpy structure. We find that the highly asymmetric broad emission lines in I Zw 1, indicative of a collimated, outflowing broad line region, are covered by the absorbing gas. Finally, the strongest UV–X-ray absorber may be connected to some of the blueshifted line emission, indicative of a more spatially extended structure of this ionised medium.

The transient event in NGC 1566 from 2017 to 2019

Context. NGC 1566 is a local face-on Seyfert galaxy and is known for exhibiting recurrent outbursts that are accompanied by changes in spectral type. The most recent transient event occurred from 2017 to 2019 and was reported to be accompanied by a change in Seyfert classification from Seyfert 1.8 to Seyfert 1.2. Aims. We aim to study the transient event in detail by analyzing the variations in the optical broad-line profiles. In particular, we intend to determine the structure and kinematics of the broad-line region. Methods. We analyzed data from an optical spectroscopic variability campaign of NGC 1566 taken with the 9.2 m Southern African Large Telescope (SALT) between July 2018 and October 2019 triggered by the detection of hard X-ray emission in June 2018. We supplemented this data set with optical to near-infrared (NIR) spectroscopic archival data taken by VLT/MUSE in September 2015 and October 2017, and investigated the emission from different line species during the event. Results. NGC 1566 exhibits pronounced spectral changes during the transient event. We observe the emergence and fading of a strong power-law-like blue continuum as well as strong variations in the Balmer, He I, and He II lines and the coronal lines [Fe VII], [Fe X], and [Fe XI]. Moreover, we detect broad double-peaked emission line profiles of O Iλ8446 and the Ca IIλλ8498, 8542, 8662 triplet. This is the first time that genuine double-peaked O Iλ8446 and Ca IIλλ8498, 8542, 8662 emission in AGN is reported in the literature. All broad lines show a clear redward asymmetry with respect to their central wavelength and we find indications for a significant blueward drift of the total line profiles during the transient event. The profiles and the FWHM of the Balmer lines remain largely constant during all observations. We show that the double-peaked emission line profiles are well approximated by emission from a low-inclination, relativistic eccentric accretion disk, and that single-peaked profiles can be obtained by broadening due to scale-height-dependent turbulence. Small-scale features in the O I and Ca II lines suggest the presence of inhomogeneities in the broad-line region. Conclusions. We conclude that the broad-line region in NGC 1566 is dominated by the kinematics of a relativistic eccentric accretion disk. The broad-line region can be modeled to be vertically stratified with respect to scale-height turbulence with O I and Ca II being emitted close to the disk in a region with high (column) density, while the Balmer and helium lines are emitted at greater scale height above the disk. The observed blueward drift might be attributed to a low-optical-depth wind launched during the transient event. Except for this wind, the observed kinematics of the broad-line region remain largely unchanged during the transient event.

Distribution and Properties of Molecular Gas toward the Monoceros OB1 Region

We perform a comprehensive CO study toward the Monoceros OB1 (Mon OB1) region based on the Milky Way Imaging Scroll Painting survey at an angular resolution of about 50″. The high-sensitivity data, together with the high dynamic range, show that molecular gas in the 8° × 4° region displays complicated hierarchical structures and various morphology (e.g., filamentary, cavity-like, shell-like, and other irregular structures). Based on Gaussian decomposition and clustering for 13CO data, a total of 263 13CO structures are identified in the whole region, and 88% of raw data flux is recovered. The dense gas with relatively high column density from the integrated CO emission is mainly concentrated in the region where multiple 13CO structures are overlapped. Combining the results of 32 large 13CO structures with distances from Gaia DR3, we estimate an average distance of 729−45+45pc for the giant molecular cloud (GMC) complex. The total mass of the GMC complex traced by 12CO, 13CO, and C18O is 1.1 × 105 M ⊙, 4.3 × 104 M ⊙, and 8.4 × 103 M ⊙, respectively. The dense gas fraction shows a clear difference between Mon OB1 GMC East (12.4%) and Mon OB1 GMC West (3.3%). Our results show that the dense gas environment is closely linked to the nearby star-forming regions. On the other hand, star-forming activities have a great influence on the physical properties of the surrounding molecular gas (larger velocity dispersion, higher temperatures, more complex velocity structures, etc.). We also discuss the distribution/kinematics of molecular gas associated with nearby star-forming activities.

Identifying H i Emission and UV Absorber Associations near the Magellanic Stream

We present a new technique to identify associations of H i emission in the Magellanic Stream (MS) and ultraviolet (UV) absorbers from 92 QSO sight lines near the MS. We quantify the level of associations of individual H i elements to the main H i body of the Stream using Wasserstein distance-based models, and derive characteristic spatial and kinematic distances of the H i emission in the MS. With the emission-based model, we further develop a comparison metric, which identifies the dominant associations of individual UV absorbers with respect to the MS and nearby galaxies. For ionized gas associated with the MS probed by C ii, C iv, Si ii, Si iii, Si iv, we find that the ion column densities are generally ∼0.5 dex higher than those that are not associated, and that the gas is more ionized toward the tail of the MS as indicated by the spatial trend of the C ii/C iv ratios. For nearby galaxies, we identify potential new absorbers associated with the circumgalactic medium of M33 and NGC 300, and affirm the associations of absorbers with IC 1613 and the Wolf–Lundmark–Mellote galaxy. For M31, we find the previously identified gradient in column densities as a function of the impact parameter, and that absorbers with higher column densities beyond M31's virial radius are more likely to be associated with the MS. Our analysis of absorbers associated with the Magellanic Clouds reveals the presence of continuous and blended diffuse ionized gas between the Stream and the Clouds. Our technique can be applied to future applications of identifying associations within physically complex gaseous structures.

Impacts of energetic particles from T Tauri flares on inner protoplanetary discs

ABSTRACT T Tauri stars are known to be magnetically active stars subject to strong flares observed in X-rays. These flares are likely due to intense magnetic reconnection events during which a part of the stored magnetic energy is converted into kinetic energy of supra-thermal particles. Since T Tauri stars are surrounded by an accretion disc, these particles may influence the disc dynamics and chemistry. This work continues on a previous stationary model, which showed that energetic particles accelerated during flares can produce a strong ionization rate at high column densities in the inner accretion disc. The present model includes non-stationary sequences of flaring events sampled by a Chandra X-ray survey of nearby young stellar objects. We calculate the averaged ionization rate expected in a radius range 0.08–0.6 au from the central star. We confirm that energetic particles produced by the flares dominate the ionization of the disc up to column densities of $10^{25}~\rm {cm^{-2}}$. We further study the main consequences of this additional source of ionization on the viscosity, the accretion rate, the volumetric heating rate, and the chemical complexity of inner protoplanetary discs.

GA-NIFS: Early-stage feedback in a heavily obscured active galactic nucleus at z = 4.76

Dust-obscured galaxies are thought to represent an early evolutionary phase of massive galaxies in which the active galactic nucleus (AGN) is still deeply buried in significant amounts of dusty material and its emission is strongly suppressed. The unprecedented sensitivity of the James Webb Space Telescope (JWST) enabled us for the first time to detect the rest-frame optical emission of heavily obscured AGNs and unveil the properties of the hidden accreting super-massive black holes (BHs). In this work, we present the JWST/NIRSpec integral field spectroscopy (IFS) data of ALESS073.1, a massive (log(M⋆/M⊙) = 10.98) dusty, star-forming galaxy at z = 4.755 hosting an AGN at its center. The detection of a very broad (> 9000 km s−1) Hα emission associated with the broad line region (BLR) confirms the presence of a BH (log(MBH/M⊙) > 8.7) accreting at less than 18% of its Eddington limit. The identification of the BLR classifies the target as a type 1 AGN despite the observed high column density of NH ∼ 1024 cm−2. The rest-frame optical emission lines also reveal a fast (∼1700 km s−1) ionized gas outflow marginally resolved in the galaxy center. The high sensitivity of NIRSpec allowed us to perform the kinematic analysis of the narrow Hα component, which indicates that the warm ionized gas velocity field is consistent with disk rotation. Interestingly, we find that in the innermost nuclear regions (< 1.5 kpc), the intrinsic velocity dispersion of the disk reaches ∼150 km s−1, which is ∼2 − 3 times higher than the velocity dispersion inferred from the [C II] 158 μm line tracing mostly cold gas. Since at large radii the velocity dispersion of the warm and cold gas are comparable, we conclude that the outflows are injecting turbulence in the warm ionized gas in the central region, but they are not sufficiently powerful to disrupt the dense gas and quench star formation. These findings support the scenario that dust-obscured galaxies represent the evolutionary stage preceding the unobscured quasar when all gas and dust are removed from the host.

Resolved ALMA observations of water in the inner astronomical units of the HL Tau disk

The water molecule is a key ingredient in the formation of planetary systems, with the water snowline being a favourable location for the growth of massive planetary cores. Here we present Atacama Large Millimeter/submillimeter Array data of the ringed protoplanetary disk orbiting the young star HL Tauri that show centrally peaked, bright emission arising from three distinct transitions of the main water isotopologue (H216O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathrm{H}}_{2}^{16}{\\mathrm{O}}$$\\end{document}). The spatially and spectrally resolved water content probes gas in a thermal range down to the water sublimation temperature. Our analysis implies a stringent lower limit of 3.7 Earth oceans of water vapour available within the inner 17 astronomical units of the system. We show that our observations are limited to probing the water content in the atmosphere of the disk, due to the high dust column density and absorption, and indicate that the main water isotopologue is the best tracer to spatially resolve water vapour in protoplanetary disks.

Cosmic Reionization on Computers: Statistics, Physical Properties, and Environments of Lyman Limit Systems at z ∼ 6

Lyman limit systems (LLSs) are dense hydrogen clouds with high enough H i column densities to absorb Lyman continuum photons emitted from distant quasars. Their high column densities imply an origin in dense environments; however, the statistics and distribution of LLSs at high redshifts still remain uncertain. In this paper, we use self-consistent radiative transfer cosmological simulations from the Cosmic Reionization on Computers (CROC) project to study the physical properties of LLSs at the tail end of cosmic reionization at z ∼ 6. We generate 3000 synthetic quasar sight lines to obtain a large number of LLS samples in the simulations. In addition, with the high physical fidelity and resolution of CROC, we are able to quantify the association between these LLS samples and nearby galaxies. Our results show that the fraction of LLSs spatially associated with nearby galaxies increases with H i column density. Moreover, we find that LLSs that are not near any galaxy typically reside in filamentary structures connecting neighboring galaxies in the intergalactic medium (IGM). This quantification of the distribution and association of LLSs to large-scale structure informs our understanding of the IGM–galaxy connection during the “Epoch of Reionization,” and provides a theoretical basis for interpreting future observations.