Μm Emission Line Research Articles

The radio-infrared nebula in II Zw 40: clusters forming in colliding elongated clouds

ABSTRACT II Zw 40 is a starburst dwarf and merger product, and holds a radio-infrared supernebula excited by thousands of embedded OB stars. We present here observations of three aspects of the supernebula: maps of the K and KU radio continuum that trace dense ionized gas with spatial resolution ${\sim} 0.1^{\prime \prime }$, a spectral data cube of the [S iv]$10.5\,\mu$m emission line that measures the kinematics of the ionized gas with velocity resolution 4.5 km s$^{-1}$, and an ALMA (Atacama Large Millimeter Array) spectral cube of the CO(3-2) line that probes the dense warm molecular gas with spatial and velocity resolution comparable to the ionized gas. The observations suggest that the supernebula is the overlap, collision or merger of two star clusters, each associated with an elongated molecular cloud. We accordingly modelled the supernebula with simulations of colliding clusters. The model that best agrees with the data is a grazing collision that has distorted the gas and stars to create the distinctive structures observed. These models may have wide applicability in the cluster-rich regions of young starbursts.

Bright-rimmed clouds in IC 1396

Aims. We investigate the dynamical and physical structures of bright-rimmed clouds (BRCs) in a nearby H II region. We focused on carbon- and oxygen-bearing species that trace photon-dominated regions (PDRs) and warm molecular cloud surfaces in order to understand the effect of UV radiation from the exciting stars on the cloud structure. Methods. We mapped four regions around the most prominent BRCs at scales of 4–10 arcmin in the H II region IC 1396 (IC 1396A, B, D, and E) in [C II] 158 µm with (up)GREAT on board SOFIA. IC 1396 is predominantly excited by an O6.5V star. Toward IC 1396A, we also observed [O I] 63 µm and 145 µm. We combined these observations with JCMT archive data, which provide the low-J transitions of CO, 13CO, and C18O. All spectra are velocity-resolved. Results. The line profiles in the four mapped regions show a variety of velocity structures, which we investigated in detail for all observed emission lines. IC 1396B and D show clearly distinct velocity components that overlap along the line of sight. We find no clear sign of photoevaporating flows in the [C II] spectra, although the uncertainty in the location of the BRCs along the line of sight makes this interpretation inconclusive. Our analysis of the [13C II] emission in IC1396 A, which has the best signal-to-noise ratio, suggests that the [C II] is likely mostly optically thin. The heating efficiency, measured by the ([C II]+[O I] 63 µm)/far-infrared intensity ratio, is higher in the northern part of IC 1396A than in the southern part, which may indicate a difference in the dust properties of the two areas. Conclusions. The complex velocity structures identified in the BRCs of IC 1396, which is apparently a relatively simple H II region, highlight the importance of velocity-resolved data for disentangling different components along the line of sight and thus facilitating a detailed study of the dynamics of the cloud. We also demonstrate that the optically thin [13C II] and [O I] 145 µm emission lines are essential for a conclusive interpretation of the [C II] 158 µm and [O I] 63 µm line profiles.

Fe II] 1.644 µm imaging survey of planetary nebulae with low-ionisation structures

Low-ionisation structures (LISs) are commonly found in planetary nebulae (PNe), but they are still poorly understood. The recent discovery of unforeseen molecular hydrogen gas (H2) has impacted what we think we know about these microstructures and PNe. To obtain an overall understanding of LISs, we carried out an [Fe II] 1.644 µm imagery survey in PNe with LISs, with the aim to detect the [Fe II] 1.644µm emission line, a common tracer of shocks. We present the first detection of [Fe II] 1.644 µmline directly associated with the LISs in four out of five PNe. The theoretical H I 12-4 recombination line was also computed either from the Brγ or the Hβ line and subtracted from the observed narrow-band line fluxes. The [Fe II] 1.644 µm flux ranges from 1 to 40 ×10−15 ergs cm−2 s−1 and the intensity from 2 to 90 ×10−5 erg s−1 cm−2 sr−1. The R(Fe)=[Fe II] 1.644 µm/Brγ line ratio was also computed and found to range between 0.5 and 7. In particular, the [Fe II] 1.644 µm line was detected in NGC 6543 (R(Fe)<0.15), along with the outer pairs of LISs in NGC 7009 (R(Fe)<0.25) and the jet-like LISs in IC 4634 (R(Fe)~1), and in several LISs in NGC 6571 (2<R(Fe)<7). The low R(Fe) result for NGC 6543 is attributed to the UV radiation from the central star. In contrast, the higher values in NGC 6571 and IC 4634 are indicative of shocks. The moderate R(Fe) in NGC 7009 likely indicates the contribution of both mechanisms.

The Coronal Lines of the High-excitation, Fe ii-type Nova V2467 Cygni

Optical and infrared spectra are presented for the nova V2467 Cygni from the period of its maximum excitation. The spectra indicate exceptionally high excitation for a Fe ii-type nova, exhibiting [Si x] 1.4305 μm and several emission lines that we associate with C vi. Along with numerous coronal features, V2467 Cygni also displayed low-excitation nebular lines. A CLOUDY analysis indicates a temperature of 5.5 × 105 for its exciting source, a very heterogeneous emission line region, and an ejected mass ≥1.5 × 10−4 L ☉.

A phenomenological study of the evolution of shock-induced O i emission lines in the spectrum of nova V2891 Cygni

ABSTRACT The eruption of Nova V2891 Cygni in 2019 offers a rare opportunity to explore the shock-induced processes in novae ejecta. The spectral evolution shows noticeable differences in the evolution of various oxygen emission lines such as O i 7773 Å, O i 8446 Å, O i 1.1286 μm, O i 1.3164 μm, etc. Here, we use spectral synthesis code cloudy to study the temporal evolution of these oxygen emission lines. Our photoionization model requires the introduction of a component with a very high density ($n \sim 10^{11}$ cm$^{-3}$) and an enhanced oxygen abundance (O/H $\sim$ 28) to produce the O i 7773 Å emission line, suggesting a stratification of material with high oxygen abundance within the ejecta. An important outcome is the behaviour of the O i 1.3164 μm line, which could only be generated by invoking the collisional ionization models in cloudy. Our phenomenological analysis suggests that O i 1.3164 μm emission originates from a thin, dense shell characterized by a high density of about $10^{12.5}\!-\!10^{12.8}$ cm$^{-3}$, which is most likely formed due to the strong internal collisions. If such is the case, the O i 1.3164 μm emission presents itself as a tracer of shock-induced dust formation in V2891 Cyg. The collisional ionization models have also been successful in creating the high-temperature conditions ($\sim 7.07\!-\!7.49 \times 10^5$ K) required to reproduce the observed high ionization potential coronal lines, which coincide with the epoch of dust formation and evolution of the O i 1.3164 μm emission line.

A Spatially Resolved [C ii] Survey of 31 z ∼ 7 Massive Galaxies Hosting Luminous Quasars

The [C ii] 158 μm emission line and the underlying far-infrared (FIR) dust continuum are important tracers for studying star formation and kinematic properties of early galaxies. We present a survey of the [C ii] emission lines and FIR continua of 31 luminous quasars at z > 6.5 using the Atacama Large Millimeter Array (ALMA) and the NOrthern Extended Millimeter Array at sub-arcsec resolution. This survey more than doubles the number of quasars with [C ii] and FIR observations at these redshifts and enables statistical studies of quasar host galaxies deep into the epoch of reionization. We detect [C ii] emission in 27 quasar hosts with a luminosity range of L [C II] = (0.3–5.5) × 109 L ⊙ and detect the FIR continuum of 28 quasar hosts with a luminosity range of L FIR = (0.5–13.0) × 1012 L ⊙. Both L [C II] and L FIR are correlated (ρ ≃ 0.4) with the quasar bolometric luminosity, albeit with substantial scatter. The quasar hosts detected by ALMA are clearly resolved with a median diameter of ∼5 kpc. About 40% of the quasar host galaxies show a velocity gradient in [C ii] emission, while the rest show either dispersion-dominated or disturbed kinematics. Basic estimates of the dynamical masses of the rotation-dominated host galaxies yield M dyn = (0.1–7.5) × 1011 M ⊙. Considering our findings alongside those of literature studies, we found that the ratio between M BH and M dyn is about 10 times higher than that of local M BH–M dyn relation on average but with substantial scatter (the ratio difference ranging from ∼0.6 to 60) and large uncertainties.

A high-redshift calibration of the [O I]-to-H I conversion factor in star-forming galaxies

The assembly and build-up of neutral atomic hydrogen (H I) in galaxies is one of the most fundamental processes in galaxy formation and evolution. Studying this process directly in the early universe is hindered by the weakness of the hyperfine 21-cm H Iline transition, impeding direct detections and measurements of the H Igas masses (MHI). Here we present a new method to inferMHIof high-redshift galaxies using neutral, atomic oxygen as a proxy. Specifically, we derive metallicity-dependent conversion factors relating the far-infrared [O I]-63 μm and [O I]-145 μm emission line luminosities andMHIin star-forming galaxies atz ≈ 2 − 6 using gamma-ray bursts (GRBs) as probes. We calibrate the [O I]-to-H Iconversion factor relying on a sample of local galaxies with direct measurements ofMHIand [O I]-63 μm and [O I]-145 μm line luminosities in addition to the SIGAMEhydrodynamical simulation framework at similar epochs (z ≈ 0). We find that the [O I]63 μm-to-H Iand [O I]145 μm-to-H Iconversion factors, here denotedβ[OI]−63 μmandβ[OI]−145 μm, respectively, universally appear to be anti-correlated with the gas-phase metallicity. The GRB measurements further predict a mean ratio ofL[OI]−63 μm/L[OI]−145 μm = 1.55 ± 0.12 and reveal generally less excited [C II] over [O I] compared to the local galaxy sample. Thez ≈ 0 galaxy sample also shows systematically higherβ[OI]−63 μmandβ[OI]−145 μmconversion factors than the GRB sample, indicating either suppressed [O I] emission in local galaxies likely due to their lower hydrogen densities or more extended, diffuse H Igas reservoirs traced by the H I21-cm. Finally, we apply these empirical calibrations to the few detections of [O I]-63 μm and [O I]-145 μm line transitions atz ≈ 2 from the literature and further discuss the applicability of these conversion factors to probe the H Igas content in the dense, star-forming interstellar medium (ISM) of galaxies well into the epoch of reionization.

Absorption and Self-absorption of [C ii] and [O i] Far Infrared Lines toward a Bright Bubble in the Nessie Infrared Dark Cloud

Using the upGREAT instrument on board the Stratospheric Observatory for Infrared Astronomy, we imaged [C ii] 157.74 and [O i] 63.18 μm line emission from a bright photodissociation region (PDR) associated with an ionized bubble located in the Nessie Nebula, a filamentary infrared dark cloud. A comparison with Australia Telescope Compact Array data reveals a classic photodissociation region (PDR) structure, with a uniform progression from ionized gas, to photodissociated gas, and to molecular gas from the bubble’s interior to its exterior. [O i] line emission from the bubble’s PDR reveals self-absorption features. Toward a far-IR bright protostar, both [O i] and [C ii] show an absorption feature at a velocity of −18 km s−1, the same velocity as an unrelated foreground molecular cloud. Since the gas density in typical molecular clouds is well below the [O i] and [C ii] critical densities, the excitation temperatures for both lines are low (∼20 K). The Meudon models demonstrate that the surface of a molecular cloud, externally illuminated by a standard G 0 = 1 interstellar radiation field, can produce absorption features in both transitions. Thus, the commonly observed [O i] and [C ii] self-absorption and absorption features plausibly arise from the subthermally excited, externally illuminated photodissociated envelopes of molecular clouds. The luminous young stellar object AGAL337.916-00.477, located precisely where the expanding bubble strikes the Nessie filament, is associated with two shock tracers: NH3 (3,3) maser emission and SiO 2−1 emission, indicating an interaction between the bubble and the filament. The interaction of the expanding bubble with its parental dense filament has triggered star formation.

The Extended [C ii] under Construction? Observation of the Brightest High-z Lensed Star-forming Galaxy at z = 6.2

We present results of [C ii] 158 μm emission line observations, and report the spectroscopic redshift confirmation of a strongly lensed (μ ∼ 20) star-forming galaxy, MACS0308-zD1 at z = 6.2078 ± 0.0002. The [C ii] emission line is detected with a signal-to-noise ratio >6 within the rest-frame UV-bright clump of the lensed galaxy (zD1.1) and exhibits multiple velocity components; the narrow [C ii] has a velocity full width half maximum (FWHM) of 110 ± 20 km s−1, while broader [C ii] is seen with an FWHM of 230 ± 50 km s−1. The broader [C ii] component is blueshifted (−80 ± 20 km s−1) with respect to the narrow [C ii] component, and has a morphology that extends beyond the UV-bright clump. We find that, while the narrow [C ii] emission is most likely associated with zD1.1, the broader component is possibly associated with a physically distinct gas component from zD1.1 (e.g., outflowing or inflowing gas). Based on the nondetection of λ 158μm dust continuum, we find that MACS0308-zD1's star formation activity occurs in a dust-free environment indicated by a strong upper limit of infrared luminosity ≲9 × 108 L ⊙. Targeting this strongly lensed faint galaxy for follow-up Atacama Large Millimeter/submillimeter Array and JWST observations will be crucial to characterize the details of typical galaxy growth in the early Universe.

The [CII] 158 μm emission line as a gas mass tracer in high redshift quiescent galaxies

A great deal of effort has been made in recent years to probe the gas fraction evolution of massive quiescent galaxies (QGs); however, a clear picture has not yet been established. Recent spectroscopic confirmations at z > 3 offer the chance to measure the residual gas reservoirs of massive galaxies a few hundred Myr after their death and to study how fast quenching proceeds in a highly star-forming Universe. Even so, stringent constraints at z > 2 remain hardly accessible with the Atacama Large Millimeter/submillimeter Array (ALMA) when adopting molecular gas tracers commonly used for the quenched population. In this Letter we propose overcoming this impasse by using the carbon [CII] 158 μm emission line to systematically probe the gaseous budget of unlensed QGs at z > 2.8, when these galaxies could still host non-negligible star formation on an absolute scale and when the line becomes best observable with ALMA (Bands 8 and 7). Predominantly used for star-forming galaxies to date, this emission line is the best choice to probe the gas budget of spectroscopically confirmed QGs at z > 3, reaching 2–4 and 13–30 times deeper than dust continuum emission (ALMA band 7) and CO(2–1)/(1–0) (Very Large Array, VLA, K − Kα bands), respectively, at fixed integration time. Exploiting archival ALMA observations, we place conservative 3σ upper limits on the molecular gas fraction (fmol = MH2/M⋆) of ADF22-QG1 (fmol < 21%) and ZF-COS-20115 (fmol < 3.2%), two of the best-studied high-z QGs in the literature, and GS-9209 (fmol < 72%), the most distant massive QG discovered to date. The deep upper limit found for ZF-COS-20115 is three times lower than previously anticipated for high-z QGs suggesting, at best, the existence of a large scatter in the fmol distribution of the first QGs. Lastly, we discuss the current limitations of the method and propose ways to mitigate some of them by exploiting ALMA bands 9 and 10.

Gauging the mass of metals in the gas phase of galaxies from the Local Universe to the Epoch of Reionization

The chemical enrichment of dust and metals are vital processes in constraining the star formation history of the universe. These are important ingredients in the formation and evolution of galaxies overall. Previously, the dust masses of high-redshift star-forming galaxies have been determined through their far-infrared continuum, however, equivalent, and potentially simpler, approaches to determining the metal masses have yet to be explored at z ≳ 2. Here, we present a new method of inferring the metal mass in the interstellar medium (ISM) of galaxies out to z ≈ 8, using the far-infrared [C II]−158 μm emission line as a proxy. We calibrated the [C II]-to-MZ, ISM conversion factor based on a benchmark observational sample at z ≈ 0, in addition to gamma-ray burst sightlines at z > 2 and cosmological hydrodynamical simulations of galaxies at z ≈ 0 and z ≈ 6. We found a universal scaling across redshifts of log(MZ, ISM/M⊙) = log(L[CII]/L⊙)−0.45, with a 0.4 dex scatter, which is constant over more than two orders of magnitude in metallicity. We applied this scaling to recent surveys for [C II] in galaxies at z ≳ 2 and compared their inferred MZ, ISM to their stellar mass (M⋆). In particular, we determined the fraction of metals retained in the gas-phase ISM, MZ, ISM/M⋆, as a function of redshift and we showed that an increasing fraction of metals reside in the ISM of galaxies at higher redshifts. We place further constraints on the cosmic metal mass density in the ISM (ΩZ, ISM) at z ≈ 5 and ≈7 based on recent estimates of the [C II]−158 μm luminosity functions at these epochs, yielding ΩZ,ISM = 6.6−4.3+13 × 10−7 M⊙ Mpc−3 (z ≈ 5) and ΩZ,ISM = 2.0−1.3+3.5 × 10−7 M⊙ Mpc−3 (z ≈ 7), respectively. These results are consistent with the expected metal yields from the integrated star formation history at the respective redshifts. This suggests that the majority of metals produced at z ≳ 5 are confined to the ISM, with strong implications that disfavor efficient outflow processes at these redshifts. Instead, these results suggest that the extended [C II] halos predominantly trace the extended neutral gas reservoirs of high-z galaxies.

Bright Beacons? ALMA Non-detection of a Supposedly Bright [O i] 63 μm Line in a Redshift-6 Dusty Galaxy

Abstract We report a non-detection of the [O i] 63 μm emission line from the z = 6.03 galaxy G09.83808 using ALMA Band 9 observations, refuting the previously claimed detection with APEX by Rybak et al.; the new upper limit on the [O i] 63 μm flux is almost 20-times lower. [O i] 63 μm line could be a powerful tracer of neutral gas in the Epoch of Reionization: yet our null result shows that detecting [O i] 63 μm from z ≥ 6 galaxies is more challenging than previously hypothesized.

The Gas and Stellar Content of a Metal-poor Galaxy at z = 8.496 as Revealed by JWST and ALMA

We present a joint analysis of the galaxy S04590 at z = 8.496 based on NIRSpec, NIRCam, and NIRISS observations obtained as part of the Early Release Observations program of the James Webb Space Telescope (JWST) and the far-infrared [C ii] 158 μm emission line detected by dedicated Atacama Large Millimeter/submillimeter Array (ALMA) observations. We determine the physical properties of S04590 from modeling of the spectral energy distribution (SED) and through the redshifted optical nebular emission lines detected with JWST/NIRSpec. The best-fit SED model reveals a low-mass (M ⋆ = 107.2–108 M ⊙) galaxy with a low oxygen abundance of derived from the strong nebular and auroral emission lines. Assuming that [C ii] effectively traces the interstellar medium, we estimate the total gas mass of the galaxy to be M gas = (8.0 ± 4.0) × 108 M ⊙ based on the luminosity and spatial extent of [C ii]. This yields an exceptionally high gas fraction, f gas = M gas/(M gas + M ⋆) ≳ 90%, though one still consistent with the range expected for low metallicity. We further derive the metal mass of the galaxy based on the gas mass and gas-phase metallicity, which we find to be consistent with the expected metal production from Type II supernovae. Finally, we make the first constraints on the dust-to-gas (DTG) and dust-to-metal (DTM) ratios of galaxies in the epoch of reionization at z ≳ 6, showing overall low mass ratios of logDTG < −3.8 and logDTM < −0.5, though they are consistent with established scaling relations and in particular with those of the local metal-poor galaxy I Zwicky 18. Our analysis highlights the synergy between ALMA and JWST in characterizing the gas, metal, and stellar content of the first generation of galaxies.

Structure and kinematics of a massive galaxy at z ∼ 7

Context. Observations of the rest-frame UV emission of high-redshift galaxies suggest that the early stages of galaxy formation involve disturbed structures. Imaging the cold interstellar medium (ISM) can provide a unique view of the kinematics associated with the assembly of galaxies. Aims. In this paper, we analyze the spatial distribution and kinematics of the cold ionized gas of the normal star-forming galaxy COS-2987030247 at z = 6.8076, based on new high-resolution observations of the [C II] 158 μm line emission obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. The analysis of these observations allowed us to: compare the spatial distribution and extension of the [C II] and rest-frame UV emission, model the [C II] line data-cube using the 3DBAROLO code, and measure the [C II] luminosity and star formation rate (SFR) surface densities in the galaxy subregions. Results. The system is found to be composed of a main central source, a fainter north extension, and candidate [C II] companions located 10-kpc away. We find similar rest-frame UV and [C II] spatial distributions, suggesting that the [C II] emission emerges from the star-forming regions. The agreement between the UV and [C II] surface brightness radial profiles rules out diffuse, extended [C II] emission (often called a [C II] halo) in the main galaxy component. The [C II] velocity map reveals a velocity gradient in the north-south direction, suggesting ordered motion, as commonly found in rotating-disk galaxies. However, higher resolution observations would be needed to rule out a compact merger scenario. Our model indicates an almost face-on galaxy (i ∼ 20°), with a average rotational velocity of 86 ± 16 km s−1 and a low average velocity dispersion, σ &lt; 30 km s−1. This result implies a dispersion lower than the expected value from observations and semi-analytic models of high redshift galaxies. Furthermore, our measurements indicate that COS-2987030247 and its individual regions systematically lie within the local L[CII]-SFR relationship, yet slightly below the local Σ[CII]-ΣUV relation. Conclusions. We argue that COS-2987030247 is a candidate rotating disk experiencing a short period of stability which will possibly become perturbed at later times by accreting sources.

An upper limit on [O III] 88 μm and 1.2 mm continuum emission from a JWSTz ≈ 12–13 galaxy candidate with ALMA

A number of newz &gt; 11 galaxy candidates have recently been identified based on publicJames WebbSpace Telescope (JWST) NIRCam observations. Spectroscopic confirmation of these candidates is necessary to robustly measure their redshift and put them in the context of our understanding of the buildup of galaxies in the early Universe. GLASS-z13 is one of these candidates, with a reported photometric redshiftz &gt; 11.9. I present publicly available Atacama Large Millimeter/submillimeter Array (ALMA) band 6 Director’s Discretionary Time observations (project 2021.A.00020.S; PI T. Bakx), taken to acquire a spectroscopic redshift for GLASS-z13 by searching for [O III] 88 μm line emission in the redshift rangez = 11.9 − 13.5. No [O III] 88 μm emission is detected in integrated spectra extracted within an aperture around GLASS-z13, nor when using an automated line finding algorithm (applying different uv-weighting strategies for the imaging). In addition, 1.2 mm continuum emission associated with GLASS-z13 is not detected either. If GLASS-z13 is atz ≈ 12 − 13, this implies a 3-σupper limit on the [O III] 88 μm and rest-frame ∼90 μm continuum emission of ∼1 × 108 L⊙and 10.8 μJy, respectively. The non-detection of [O III] 88 μm and continuum emission does not necessarily imply that GLASS-z13 is not atz ≈ 12 − 13. It can also be explained by a low metallicity (∼0.2 Z⊙or lower) and/or high-density (at least 100 cm−3) interstellar medium. This work demonstrates the synergy between ALMA and JWST to study the properties of the first galaxies; although, JWST/NIRSpec spectroscopy will be necessary to confirm or reject the high photometric redshift of GLASS-z13.

Comparison of [CII] 158µm line widths to luminosities

Acomparison of [CII] 158µm emission line widths to different luminosities is presented to decide if any luminosity relates to velocity dispersion. [CII] 158 µm emission lines are observed with Herschel PACS for 379 galaxies and the archival data for [CII] line widths are taken from http://cassis.sirtf.com/ herschel/. Emission line widths are compared to [CII] luminosities, to near-infrared 1.6µm luminosities and to infrared 22µm luminosities. H magnitudes are taken from 2MASS catalogue, and 22µm fluxes from the WISE catalogue.

HI-H2 transition: Exploring the role of the magnetic field

Context. Atomic gas in the diffuse interstellar medium (ISM) is organized in filamentary structures. These structures usually host cold and dense molecular clumps. The Galactic magnetic field is considered to play an important role in the formation of these clumps. Aims. Our goal is to explore the role of the magnetic field in the HI-H2 transition process. Methods. We targeted a diffuse ISM filamentary cloud toward the Ursa Major cirrus where gas transitions from atomic to molecular. We probed the magnetic field properties of the cloud with optical polarization observations. We performed multiwavelength spectroscopic observations of different species in order to probe the gas phase properties of the cloud. We observed the CO (J = 1−0) and (J = 2−1) lines in order to probe the molecular content of the cloud. We also obtained observations of the [C ii] 157.6µm emission line in order to trace the CO-dark H2 gas and estimate the mean volume density of the cloud. Results. We identified two distinct subregions within the cloud. One of the regions is mostly atomic, while the other is dominated by molecular gas, although most of it is CO-dark. The estimated plane-of-the-sky magnetic field strength between the two regions remains constant within uncertainties and lies in the range 13–30 µG. The total magnetic field strength does not scale with density. This implies that gas is compressed along the field lines. We also found that turbulence is trans-Alfvénic, with MA ≈ 1. In the molecular region, we detected an asymmetric CO clump whose minor axis is closer, with a 24° deviation, to the mean magnetic field orientation than the angle of its major axis. The H i velocity gradients are in general perpendicular to the mean magnetic field orientation except for the region close to the CO clump, where they tend to become parallel. This phenomenon is likely related to gas undergoing gravitational infall. The magnetic field morphology of the target cloud is parallel to the H i column density structure of the cloud in the atomic region, while it tends to become perpendicular to the H i structure in the molecular region. On the other hand, the magnetic field morphology seems to form a smaller offset angle with the total column density shape (including both atomic and molecular gas) of this transition cloud. Conclusions. In the target cloud where the H i–H2 transition takes place, turbulence is trans-Alfvénic, and hence the magnetic field plays an important role in the cloud dynamics. Atomic gas probably accumulates preferentially along the magnetic field lines and creates overdensities where molecular gas can form. The magnetic field morphology is probed better by the total column density shape of the cloud, and not its H i column density shape.

Analysis of emission line widhts of [CII]158μm

A study of [CII] 158 μm emission line profiles observed with Herschel PACS for 379 galaxies is presented. Emission line widths are compared to [CII] luminosities, to near-infrared 1.6 μm luminosities and to infrared 22 μm luminosities to decide if any luminosity relates to velocity dispersion. Archival data for [CII] fluxes and line profiles are taken from http://cassis.sirtf.com/ herschel/. Line profiles are classified as Gaussian, flattened and asymmetric. H magnitudes are taken from 2MASS catalogues, and 22 μm fluxes from the WISE catalogue. These luminosities are compared to [CII] line Full Width Half Maximum. Asymmetric profiles are not primarily AGN, which indicates that asymmetries are not produced primarily by outflows from the nuclear region. [CII] line widths do not show a significant correlation with any measure of galaxy luminosity. The correlation having smallest dispersion is with the H band luminosity for which L(H) ~ FWHM0.73, which is a much flatter correlation than the L ~ FWHM4 previously found for optical.

The ALMA REBELS Survey: Average [C ii] 158 μm Sizes of Star-forming Galaxies from z ∼ 7 to z ∼ 4

We present the average [C ii] 158 μm emission line sizes of UV-bright star-forming galaxies at z ∼ 7. Our results are derived from a stacking analysis of [C ii] 158 μm emission lines and dust continua observed by the Atacama Large Millimeter/submillimeter Array (ALMA), taking advantage of the large program Reionization Era Bright Emission Line Survey. We find that the average [C ii] emission at z ∼ 7 has an effective radius r e of 2.2 ± 0.2 kpc. It is ≳2× larger than the dust continuum and the rest-frame UV emission, in agreement with recently reported measurements for z ≲ 6 galaxies. Additionally, we compared the average [C ii] size with 4 < z < 6 galaxies observed by the ALMA Large Program to INvestigate [C ii] at Early times (ALPINE). By analyzing [C ii] sizes of 4 < z < 6 galaxies in two redshift bins, we find an average [C ii] size of r e = 2.2 ± 0.2 kpc and r e = 2.5 ± 0.2 kpc for z ∼ 5.5 and z ∼ 4.5 galaxies, respectively. These measurements show that star-forming galaxies, on average, show no evolution in the size of the [C ii] 158 μm emitting regions at redshift between z ∼ 7 and z ∼ 4. This finding suggests that the star-forming galaxies could be morphologically dominated by gas over a wide redshift range.

Monitoring Inner Regions in the RY Tau Jet

We present multiepoch observations of the RY Tau jet for Hα and [Fe ii] 1.644 μm emission lines obtained with the Subaru Coronagraphic Extreme-AO and Visible Aperture Masking Polarimetric Imager for Resolved Exoplanetary Structures (VAMPIRES), Gemini Near-infrared Integral Field Spectrograph, and Keck/OSIRIS in 2019–2021. These data show a series of four knots within 1″ consistent with the proper motion of ∼0.″3 yr−1, analogous to the jets associated with another few active T Tauri stars. However, the spatial intervals between the knots suggest the time intervals of the ejections of about 1.2, 0.7, and 0.7 yr, significantly shorter than those estimated for the other stars. These Hα images contrast with the archival Very Large Telescope Spectro-Polarimetric High-contrast Exoplanet Research and Zurich IMaging POLarimeter (ZIMPOL) observations from 2015, which showed only a single knot-like feature at ∼0.″25. The difference between the 2015 and 2019–2021 epochs suggests an irregular ejection interval within the six-year range. Such variations of the jet ejection may be related to a short-term (<1 yr) variability of the mass accretion rate. We compared the peaks of the Hα emissions with the ZIMPOL data taken in 2015, showing the brighter profile at the base (<0.″3) than the 2020–2021 VAMPIRES profiles due to time-variable mass ejection rates or the heating–cooling balance in the jet. The observed jet knot structures may be alternatively attributed to stationary shocks, but a higher angular resolution is required to confirm its detailed origin.