3P1 3P0 Research Articles

CI Traces the Disk Atmosphere in the IM Lup Protoplanetary Disk

The central star and its energetic radiation fields play a vital role in setting the vertical and radial chemical structure of planet-forming disks. We present observations that, for the first time, clearly reveal the UV-irradiated surface of a protoplanetary disk. Specifically, we spatially resolve the atomic-to-molecular (C i-to-CO) transition in the IM Lup disk with Atacama Large Millimeter/submillimeter Array archival observations of [C i] 3P1–3P0. We derive a C i emitting height of z/r ≳ 0.5 with emission detected out to a radius of ≈600 au. Compared to other systems with C i heights inferred from unresolved observations or models, the C i layer in the IM Lup disk is at scale heights almost double that of other disks, confirming its highly flared nature. C i arises from a narrow, optically thin layer that is substantially more elevated than that of 12CO (z/r ≈ 0.3–0.4), which allows us to directly constrain the physical gas conditions across the C i-to-CO transition zone. We also compute a radially resolved C i column density profile and find a disk-averaged C i column density of 2 × 1016 cm−2, which is ≈3–20× lower than that of other disks with spatially resolved C i detections. We do not find evidence for vertical substructures or spatially localized deviations in C i due, e.g., to either an embedded giant planet or a photoevaporative wind that have been proposed in the IM Lup disk, but emphasize that deeper observations are required for robust constraints.

Cosmic-ray-driven enhancement of the C0/CO abundance ratio in W 51 C

Abstract We examine spatial variations of the C0$/$CO abundance ratio (XC/CO) in the vicinity of the γ-ray supernova remnant W 51 C, based on [C i] (3P1–3P0), 12CO(1–0), and 13CO(1–0) observations with the ASTE and Nobeyama 45 m telescopes. We find that XC/CO varies in a range of 0.02–0.16 (0.05 in median) inside the molecular clouds of AV > 100 mag, where photodissociation of CO by the interstellar UV is negligible. Furthermore, XC/CO is locally enhanced by a factor of up to four near the W 51 C center, depending on the projected distance from the W 51 C center. In high-AV molecular clouds, XC/CO is determined by the ratio of the cosmic-ray (CR) ionization rate to the H2 density, and we find no clear spatial variation of the H2 density against the projected distance. Hence, the high CR ionization rate may locally enhance XC/CO near the W 51 C center. We also find that the observed spatial extent of the enhanced XC/CO (∼17 pc) is consistent with the diffusion distance of CRs with an energy of 100 MeV. This fact suggests that the low-energy CRs accelerated in W 51 C enhance XC/CO. The CR ionization rate in the XC/CO-enhanced cloud is estimated to be 3 × 10−16 s−1 on the basis of time-dependent photodissociation region simulations of XC/CO, the value of which is 30 times higher than that in the standard Galactic environment. These results demonstrate that [C i] is a powerful probe to investigate the interaction between CRs and the interstellar medium for a wide area in the vicinity of supernova remnants.

Dust, CO, and [C i]: cross-calibration of molecular gas mass tracers in metal-rich galaxies across cosmic time

ABSTRACT We present a self-consistent cross-calibration of the three main molecular gas mass tracers in galaxies, namely the 12CO(1–0), [C i](3P1–3P0) lines, and the submm dust continuum emission, using a sample of 407 galaxies, ranging from local discs to submillimetre-selected galaxies (SMGs) up to z ≈ 6. A Bayesian statistical method is used to produce galaxy-scale universal calibrations of these molecular gas indicators, that hold over 3–4 orders of magnitude in infrared luminosity, LIR. Regarding the dust continuum, we use a mass-weighted dust temperature, Tmw, determined using new empirical relations between temperature and luminosity. We find the average L/Mmol gas mass conversion factors (including He) to be ${\alpha _{850}}=6.9\times 10^{12}\, \rm W\, Hz^{-1}\, M_{\odot }^{-1}$, αCO = 4.0 M⊙ (κ km s−1 pc2)−1, and $\alpha _{\rm C\, I}$ = 17.0 M⊙ (κ km s−1 pc2)−1, based on the assumption that the mean dust properties of the sample (κH = gas-to-dust ratio/dust emissivity) will be similar to those of local metal rich galaxies and the Milky Way. The tracer with the least intrinsic scatter is [C i](1–0), while CO(1–0) has the highest. The conversion factors show a weak but significant correlation with LIR which is not apparent when Tmw is held constant. Assuming dust properties typical of metal-rich galaxies, we infer a neutral carbon abundance ${X_{\rm C\, I}}=\rm [C^0/\rm{H_2}]=1.6\times 10^{-5}$, similar to that in the Milky Way. We find no evidence for bi-modality of αCO between main-sequence (MS) galaxies and those with extreme star-formation intensity, i.e. ultraluminous infrared galaxies (ULIRGs) and SMGs. The means of the three conversion factors are found to be similar between MS galaxies and ULIRGs/SMGs, to within 10–20 per cent. The overarching conclusion of our work is that, for metal-rich galaxies, near-universal average values for αCO, $X_{\rm C\, I}$, and κH are adequate for global molecular gas estimates within the expected uncertainties. The 1σ scatter in our optimized values for αCO, $X_{\rm C\, I}$, and κH are 0.14, 0.11, and 0.15 dex, respectively.

ASTE Band 10 (787–950 GHz) heterodyne receiver: System description, commissioning, and science verification

Abstract We report the system description and results of the commissioning and science verification (CSV) of the Band 10 (787–950 GHz) heterodyne receiver for ASTE (Atacama Submillimeter Telescope Experiment), a 10 m submillimeter telescope at the ALMA (Atacama Large Millimeter/submillimeter Array) site in Chile. The new ASTE Band 10 receiver cartridge was refurbished from a prototype ALMA Band 10 receiver with SIS mixers employing high critical current density junctions. We installed the new receiver on ASTE and carried out its CSV. The best double-sideband (DSB) system noise temperature achieved on ASTE toward the zenith was ∼1500 K (PWV ∼ 0.5 mm). As a part of CSV activities, we performed science verification observations to demonstrate ASTE Band 10 capabilities to the community. Wide-field images were successfully obtained toward the well-studied OMC-1 region with both [C i](3P2–3P1) and 12CO(J = 7–6) lines. In addition, we partially carried out observations toward a super star cluster RCW 38, [C i](3P1–3P0), images of which were already obtained by ASTE. We demonstrated the capability of ASTE Band 10 observations toward bright and extended objects like giant molecular clouds.

The molecular gas resolved by ALMA in the low-metallicity merging dwarf galaxy Haro 11

Context.The physical mechanisms driving starbursts and quenching in less massive (M* ≤ 1010 M⊙) galaxies are unclear. The merger is one of the inescapable processes referred to as both starburst and quenching in massive galaxies. However, the effects of the merger on star formation in dwarf galaxies and their evolution are still uncertain.Aims.We aim to explore how star formation in dwarf galaxies is both triggered and quenched by studying metal-poor gas-rich dwarf mergers based on multi-band observations at a spatial resolution of ∼460 pc.Methods.We use archival data of Atacama Large Millimetre Array (Band 3 and 8) and Very Large Telescope/Multi Unit Spectroscopic Explorer to map CO(J = 1–0), [CI](3P1–3P0), and Hαemission in one of the most extreme merging starburst dwarf galaxies, Haro 11.Results.We find the molecular gas is assembled around the central two star-forming regions (knots B and C). The molecular and ionized gas and stellar components show complex kinematics, indicating that the gas is probably at a combined stage of collision of clouds and feedback from star formation. The peak location and distribution of [CI](1–0) closely coincide with the CO(1–0) emission, meaning that it might trace the same molecular gas as CO in such a dwarf merger starburst galaxy. The enhancement of line ratios (∼0.5) of [CI]/CO around knot C is probably generated by the dissociation of CO molecules by cosmic rays and far-ultraviolet photons. Globally, Haro 11 and its star-forming regions share similar star formation efficiency (SFE) to the high-zstarburst galaxies or the clumps in nearby ultraluminous infrared galaxies.Conclusions.Given the high SFE, the high specific star formation rate, small stellar mass, low metallicity, and deficient HI gas, Haro 11 could be an analog of a high-zdwarf starburst and the potential progenitor of the nearby less massive elliptical galaxies. The significantly smaller turbulent pressure and viral parameter is probably triggering the intense starbursts. We predict that Haro 11 will quench atM* ≤ 8.5 × 109 M⊙.

Spatially-resolved relation between [C i] 3P1–3P0 and 12CO (1–0) in Arp 220

Abstract We present $\sim {0.^{\prime \prime }3}$ (114 pc) resolution maps of [C i] 3P1–3P0 (hereafter [C i] (1–0)) and 12CO (1–0) obtained toward Arp 220 with the Atacama Large Millimeter/submillimeter Array. The overall distribution of the [C i] (1–0) emission is consistent with the CO (1–0). While the [C i] (1–0) and CO (1–0) luminosities of the system follow the empirical linear relation for the unresolved ULIRG sample, we find a sublinear relation between [C i] (1–0) and CO (1–0) using the spatially-resolved data. We measure the [C i] (1–0)$/$CO (1–0) luminosity ratio per pixel in star-forming environments of Arp 220 and investigate its dependence on the CO (3–2)$/$CO (1–0) ratio (RCO). On average, the [C i] (1–0)$/$CO (1–0) luminosity ratio is almost constant up to RCO ≃ 1 and then increases with RCO. According to the radiative transfer analysis, a high C i$/$CO abundance ratio is required in regions with high [C i] (1–0)$/$CO (1–0) luminosity ratios and RCO > 1, suggesting that the C i$/$CO abundance ratio varies at ∼100 pc scale in Arp 220. The [C i] (1–0)$/$CO (1–0) luminosity ratio depends on multiple factors and may not be straightforward to interpret. We also find the high-velocity components traced by [C i] (1–0) in the western nucleus, likely associated with the molecular outflow. The [C i] (1–0)$/$CO (1–0) luminosity ratio in the putative outflow is 0.87 ± 0.28, which is four times higher than the average ratio of Arp 220. While there is a possibility that the [C i] (1–0) and CO (1–0) emission traces different components, we suggest that the high line ratios are likely to be because of elevated C i$/$CO abundance ratios based on our radiative transfer analysis. A C i-rich and CO-poor gas phase in outflows could be caused by the irradiation of the cosmic rays, the shock heating, and the intense radiation field.

An ACA Survey of [C i] 3 P 1−3 P 0, CO J = 4 − 3, and Dust Continuum in Nearby U/LIRGs

Abstract We present the results of surveying [C i] 3 P 1–3 P 0, 12CO J = 4 − 3, and 630 μm dust continuum emission for 36 nearby ultra/luminous infrared galaxies (U/LIRGs) using the Band 8 receiver mounted on the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array. We describe the survey, observations, data reduction, and results; the main results are as follows. (i) We confirmed that [C i] 3 P 1–3 P 0 has a linear relationship with both the 12CO J = 4 − 3 and 630 μm continuum. (ii) In NGC 6052 and NGC 7679, 12CO J = 4 − 3 was detected but [C i] 3 P 1–3 P 0 was not detected with a [C i] 3 P 1–3 P 0/12CO J = 4 − 3 ratio of ≲0.08. Two possible scenarios of weak [C i] 3 P 1–3 P 0 emission are C0-poor/CO-rich environments and an environment with an extremely large [C i] 3 P 1–3 P 0 missing flux. (iii) There is no clear evidence showing that galaxy mergers, AGNs, and dust temperatures control the ratios of [C i] 3 P 1–3 P 0/12CO J = 4 − 3 and L [ C I ] ( 1 − 0 ) ′ / L 630 μ m . (iv) We compare our nearby U/LIRGs with high-z galaxies, such as galaxies on the star formation main sequence (MS) at z ∼ 1 and submillimeter galaxies (SMGs) at z = 2–4. We found that the mean value for the [C i] 3 P 1–3 P 0/12CO J = 4 − 3 ratio of U/LIRGs is similar to that of SMGs but smaller than that of galaxies on the MS.

ALMA View of the ρ Ophiuchi A PDR with a 360 au Beam: The [C i] Emission Originates from the Plane-parallel PDR and Extended Gas

Abstract We present the results of data analysis of the [C i] (3 P 1–3 P 0) emission from the ρ Ophiuchi A photon-dominated region (PDR) obtained in the ALMA ACA standalone mode with a spatial resolution of 2.″6 (360 au). The [C i] emission shows filamentary structures with a width of ∼1000 au, which are adjacent to the shell structure seen in the 4.5 μm map. We found that the 4.5 μm emission, C0, and CO are distributed in this order from the excitation star (S1) in a complementary pattern. These results indicate that [C i] is emitted from a thin layer in the PDR generated by the excitation star, as predicted in the plane-parallel PDR model. In addition, extended [C i] emission was also detected, which shows nearly uniform integrated intensity over the entire field of view (1.′6 × 1.′6). The line profile of the extended component is different from that of the above shell component. The column density ratio of C0 to CO in the extended component was ∼2, which is significantly higher than those of Galactic massive star-forming regions (0.1–0.2). These results suggest that [C i] is emitted also from the extended gas with a density of cm−3, which is not greatly affected by the excitation star.

Atomic carbon [C i](3P1–3P0) mapping of the nearby galaxy M 83

Abstract Atomic carbon (C i) has been proposed to be a global tracer of the molecular gas as a substitute for CO, however, its utility remains unproven. To evaluate the suitability of C i as the tracer, we performed [C i](3P1–3P0) [hereinafter [C i](1–0)] mapping observations of the northern part of the nearby spiral galaxy M 83 with the Atacama Submillimeter Telescope Experiment (ASTE) telescope and compared the distributions of [C i](1–0) with CO lines [CO(1–0), CO(3–2), and 13CO(1–0)], H i, and infrared (IR) emission (70, 160, and 250 μm). The [C i](1–0) distribution in the central region is similar to that of the CO lines, whereas [C i](1–0) in the arm region is distributed outside the CO. We examined the dust temperature, Tdust, and dust mass surface density, Σdust, by fitting the IR continuum-spectrum distribution with a single-temperature modified blackbody. The distribution of Σdust shows a much better consistency with the integrated intensity of CO(1–0) than with that of [C i](1–0), indicating that CO(1–0) is a good tracer of the cold molecular gas. The spatial distribution of the [C i] excitation temperature, Tex, was examined using the intensity ratio of the two [C i] transitions. An appropriate Tex at the central, bar, arm, and inter-arm regions yields a constant [C]$/$[H2] abundance ratio of ∼7 × 10−5 within a range of 0.1 dex in all regions. We successfully detected weak [C i](1–0) emission, even in the inter-arm region, in addition to the central, arm, and bar regions, using spectral stacking analysis. The stacked intensity of [C i](1–0) is found to be strongly correlated with Tdust. Our results indicate that the atomic carbon is a photodissociation product of CO, and consequently, compared to CO(1–0), [C i](1–0) is less reliable in tracing the bulk of “cold” molecular gas in the galactic disk.

Observations of the [C i] (3P1–3P0) emission toward the massive star-forming region RCW 38: Further evidence for highly-clumped density distribution of the molecular gas

Abstract We present observations of the 3P1–3P0 fine-structure line of atomic carbon using the ASTE 10m sub-mm telescope towards RCW 38, the youngest super star cluster in the Milky Way. The detected [C i] emission is compared with the CO J = 1–0 image cube presented in Fukui et al. (2016, ApJ, 820, 26) which has an angular resolution of 40″ (∼0.33 pc). The overall distribution of the [C i] emission in this cluster is similar to that of the 13CO emission. The optical depth of the [C i] emission was found to be τ = 0.1–0.6, suggesting mostly optically thin emission. An empirical conversion factor from the [C i] integrated intensity to the H2 column density was estimated as X[C i]$= 6.3 \times 10 ^{20}\:$cm−2 K−1 km−1 s (for visual extinction: AV ≤ 10 mag) and 1.4 × 1021 cm−2 K−1 km−1 s (for AV of 10–100 mag). The column density ratio of the [C i] to CO (N[C i]$/N_{\rm CO}$) was derived as ∼0.1 for AV of 10–100 mag, which is consistent with that of the Orion cloud presented in Ikeda et al. (2002, ApJ, 571, 560). However, our results cover an AV regime of up to 100 mag, which is wider than the coverage found in Orion, which reaches up to ∼60 mag. Such a high [C i]$/$CO ratio in a high-AV region is difficult to explain via the plane-parallel photodissociation region model, which predicts that this ratio is close to 0 due to the heavy shielding of the ultraviolet (UV) radiation. Our results suggest that the molecular gas in this cluster is highly clumpy, allowing deep penetration of UV radiation even at averaged AV values of 100 mag. Recent theoretical works have presented models consistent with such clumped gas distribution with a sub-pc clump size (e.g., Tachihara et al. 2018, arXiv:1811.02224).

Extremely Low Molecular Gas Content in the Vicinity of a Red Nugget Galaxy at z = 1.91

Abstract We present Atacama Large Millimeter/submillimeter Array Band 5 observations of a galaxy at z = 1.91, GDS24569, in search of molecular gas in its vicinity via the [C i] 3P1–3P0 line. GDS24569 is a massive ( ), passively evolving galaxy, characterized by compact morphology with an effective radius of ∼0.5 kpc. We apply two blind detection algorithms to the spectral data cubes and find no promising detection in or around GDS24569 out to a projected distance of ∼320 kpc, while a narrow tentative line (4.1σ) is identified at +1200 km s−1 by one of the algorithms. From the nondetection of [C i], we place a 3σ upper limit on molecular hydrogen mass, ∼ 7.1 × 109 M ⊙, which converts to an extremely low gas-to-stellar mass fraction of ≲ 5%. We conduct a spectral energy distribution modeling by including optical to far-infrared data and find a considerably high ( ∼ 0.1%) dust-to-stellar mass ratio, i.e., ∼10–100× higher than those of local early-type galaxies. In combination with a previous result of an insufficient number of surrounding satellite galaxies, it is suggested that GDS24569 is unlikely to experience significant size evolution via satellite mergers. We discuss possible physical mechanisms that quenched GDS24569.

The 300-pc scale ALMA view of [C i] 3P1–3P0, CO J = 1–0, and 609-μm dust continuum in a luminous infrared galaxy

ABSTRACT We present high-quality Atacama Large Millimeter/submillimeter Array (ALMA) Band 8 observations of the [C i] 3P1–3P0 line and 609-μm dust continuum emission towards the nearby luminous infrared galaxy (LIRG) IRAS F18293-3413, as well as matched resolution (300-pc scale) Band 3 CO J = 1–0 data, which allow us to assess the use of the [C i] 3P1–3P0 line as a total gas mass estimator. We find that the [C i] line basically traces structures detected in CO (and dust) and a mean (median) [C i]/CO luminosity ($L^{\prime }_{\rm [C\, {\small I}]}$/$L^{\prime }_{\rm CO}$) ratio of 0.17 (0.16) with a scatter of 0.04. However, a pixel-by-pixel comparison revealed that there is a radial $L^{\prime }_{\rm [C\, {\small I}]}$/$L^{\prime }_{\rm CO}$ gradient and a superlinear $L^{\prime }_{\rm CO}$ versus $L^{\prime }_{\rm [C\, {\small I}]}$ relation (slope = 1.54 ± 0.02) at this spatial scale, which can be explained by radial excitation and/or line opacity gradients. Based on the molecular gas masses converted from the dust continuum emission, we found that the CO-to-H2 and [C i]-to-H2 conversion factors are relatively flat across the molecular gas disc with a median value of 3.5$^{+1.9}_{-1.3}$ and 20.7$^{+9.2}_{-4.9}$ M⊙ (K km s−1 pc2)−1, respectively. A non-LTE calculation yields that typical molecular gas properties seen in nearby (U)LIRGs ($n_{\rm H_2}$ = 103−4 cm−3, Tkin ∼ 50 K, and $X_{\rm C\, {\small I}}$ = (0.8–2.3) × 10−5) can naturally reproduce the derived [C i]-to-H2 conversion factor. However, we caution that a careful treatment of the physical gas properties is required in order to measure H2 gas mass distributions in galaxies using a single [C i] line. Otherwise, a single [C i] line is not a good molecular gas estimator in a spatially resolved manner.

ALMA Observations of Multiple CO and C Lines toward the Active Galactic Nucleus of NGC 7469: An X-Ray-dominated Region Caught in the Act

Abstract We used the Atacama Large Millimeter/submillimeter Array to map 12CO(J = 1–0), 12CO(J = 2–1), 12CO(J = 3–2), 13CO(J = 2–1), and [C i](3 P 1–3 P 0) emission lines around the type 1 active galactic nucleus (AGN) of NGC 7469 (z = 0.0164) at ∼100 pc resolutions. The CO lines are bright in both the circumnuclear disk (central ∼300 pc) and the surrounding starburst (SB) ring (∼1 kpc diameter), with two bright peaks on either side of the AGN. By contrast, the [C i](3 P 1–3 P 0) line is strongly peaked on the AGN. Consequently, the brightness temperature ratio of [C i](3 P 1–3 P 0) to 13CO(2–1) is ∼20 at the AGN, as compared to ∼2 in the SB ring. Our local thermodynamic equilibrium (LTE) and non-LTE models indicate that the enhanced line ratios (or C i enhancement) are due to an elevated C0/CO abundance ratio (∼3–10) and temperature (∼100–500 K) around the AGN as compared to the SB ring (abundance ratio ∼1, temperature ≲100 K), which accords with the picture of the X-ray-dominated region. Based on dynamical modelings, we also provide CO(1–0)-to- and [C i](3 P 1–3 P 0)-to-molecular mass conversion factors at the central ∼100 pc of this AGN as α CO = 4.1 and α C i = 4.4 M ⊙ (K km s−1 pc2)−1, respectively. Our results suggest that the C i enhancement is potentially a good marker of AGNs that could be used in a new submillimeter diagnostic method toward dusty environments.

The Herschel SPIRE Fourier Transform Spectrometer Spectral Feature Finder – IV. Neutral carbon detection in the SPIRE FTS spectra

ABSTRACT The SPIRE Fourier Transform Spectrometer (FTS) Spectral Feature Finder (FF), developed within the Herschel Spectral and Photometric Imaging Receiver (SPIRE) FTS instrument team, is an automated spectral feature fitting routine that attempts to find significant features in SPIRE FTS spectra. The 3P1–3P0 and 3P2–3P1 neutral carbon fine structure lines are common features in carbon-rich far-infrared astrophysical sources. These features can be difficult to detect using an automated feature detection routine due to their typically low amplitude and line blending. In this paper, we describe and validate the FF subroutine designed to detect the neutral carbon emission observed in SPIRE spectral data.

Deceptively cold dust in the massive starburst galaxy GN20 at z ∼ 4

We present new observations, carried out with IRAM NOEMA, of the atomic neutral carbon transitions [C I](3P1–3P0) at 492 GHz and [C I](3P2–3P1) at 809 GHz of GN20, a well-studied star-bursting galaxy at z = 4.05. The high luminosity line ratio [C I](3P2–3P1) /[C I](3P1–3P0) implies an excitation temperature of 48+14−9 K, which is significantly higher than the apparent dust temperature of Td = 33 ± 2 K (β = 1.9) derived under the common assumption of an optically thin far-infrared dust emission, but fully consistent with Td = 52 ± 5 K of a general opacity model where the optical depth (τ) reaches unity at a wavelength of λ0 = 170 ± 23 μm. Moreover, the general opacity solution returns a factor of ∼2× lower dust mass and, hence, a lower molecular gas mass for a fixed gas-to-dust ratio, than with the optically thin dust model. The derived properties of GN20 thus provide an appealing solution to the puzzling discovery of starbursts appearing colder than main-sequence galaxies above z > 2.5, in addition to a lower dust-to-stellar mass ratio that approaches the physical value predicted for starburst galaxies.

First Detection of Submillimeter-wave [13C i] 3P1–3P0 Emission in a Gaseous Debris Disk of 49 Ceti with ALMA

Abstract We have detected the submillimeter-wave fine-structure transition (3 P 1–3 P 0) of 13C, [13C i], in the gaseous debris disk of 49 Ceti with the Atacama Large Millimeter/submillimeter Array (ALMA). Recently, the [C i] 3 P 1–3 P 0 emission has been spatially resolved in this source with ALMA. In this data set, the F = 3/2–1/2 hyperfine component of [13C i], which is blueshifted by 2.2 km s−1 from the normal species line, [C i], has been identified in the outer part of the 49 Ceti disk, thanks to the narrow velocity widths of the gas components. The [C i]/[13C i] line intensity ratio is found to be 12 ± 3, which is significantly lower than the 12C/13C abundance ratio of 77 in the interstellar medium. This result clearly reveals that the [C i] emission is optically thick in 49 Ceti at least partly, as speculated by the previous work. As far as we know, this is the first detection of [13C i] 3 P 1–3 P 0 emission at 492 GHz not only in debris disks but also in the interstellar medium.

First Subarcsecond Submillimeter-wave [C i] Image of 49 Ceti with ALMA

Abstract We present the first subarcsecond images of 49 Ceti in the [C i] 3 P 1–3 P 0 emission and the 614 μm dust continuum emission observed with Atacama Large Millimeter/submillimeter Array (ALMA), as well as that in the CO(J = 3–2) emission prepared by using the ALMA archival data. The spatial distribution of the 614 μm dust continuum emission is found to have a broad-ring structure with a radius of about 100 au around the central star. A substantial amount of gas is also associated with 49 Ceti. The [C i] emission map shows two peaks inside the dust ring, and its overall extent is comparable to that of the dust continuum emission and the CO emission. We find that the [C i]/CO(J = 3–2) intensity ratio significantly varies along the major axis. The ratio takes the minimum value of 1.8 around the dust peak position, and increases inward and outward. The enhanced ratio around the central star (∼3) likely originates from the stellar UV radiation, while that in the outer disk (∼10) is from the interstellar UV radiation. Such complex distributions of the [C i] and CO(J = 3–2) emission will be key to understanding the origin of the gas in 49 Ceti, and will also provide a stringent constraint on physical and chemical models of gaseous debris disks.

Planck’s Dusty GEMS

The bright 3P1–3P0 ([CI] 1–0) and 3P2–3P1 ([CI] 2–1) lines of atomic carbon are becoming more and more widely employed as tracers of the cold neutral gas in high-redshift galaxies. Here we present observations of these lines in the 11 galaxies of the set of Planck’s Dusty GEMS, the brightest gravitationally lensed galaxies on the extragalactic submillimeter sky probed by the Planck satellite. We have [CI] 1–0 and [CI] 2–1 measurements for seven and eight of these galaxies, respectively, including four galaxies where both lines have been measured. We use our observations to constrain the gas excitation mechanism, excitation temperatures, optical depths, atomic carbon and molecular gas masses, and carbon abundances. Ratios of LCI/LFIR are similar to those found in the local universe, and suggest that the total cooling budget through atomic carbon has not significantly changed in the last 12 Gyr. Both lines are optically thin and trace 1 − 6 × 107 M⊙ of atomic carbon. Carbon abundances, XCI, are between 2.5 and 4 × 10−5, for an ultra-luminous infrared galaxy (ULIRG) CO-to-H2 conversion factor of αCO = 0.8 M⊙ / [K km s−1 pc2]. Ratios of molecular gas masses derived from [CI] 1–0 and CO agree within the measurement uncertainties for five galaxies, and agree to better than a factor of two for another two with [CI] 1–0 measurements, after carefully taking CO excitation into account. This does not support the idea that intense, high-redshift starburst galaxies host large quantities of “CO-dark” gas. These results support the common assumptions underlying most molecular gas mass estimates made for massive, dusty, high-redshift starburst galaxies, although the good agreement between the masses obtained with both tracers cannot be taken as independent confirmation of either αCO or XCI.

Velocity profiles of [CII], [CI], CO, and [OI] and physical conditions in four star-forming regions in the Large Magellanic Cloud

Aims. The aim of our study is to investigate the physical properties of the star-forming interstellar medium (ISM) in the Large Magellanic Cloud (LMC) by separating the origin of the emission lines spatially and spectrally. The LMC provides a unique local template to bridge studies in the Galaxy and high redshift galaxies because of its low metallicity and proximity, enabling us to study the detailed physics of the ISM in spatially resolved individual star-forming regions. Following Okada et al. (Okada, Y., Requena-Torres, M. A., Güsten, R., et al. 2015, A&A, 580, A54), we investigate different phases of the ISM traced by carbon-bearing species in four star-forming regions in the LMC, and model the physical properties using the KOSMA-τ PDR model. Methods. We mapped 3–13 arcmin2 areas in 30 Dor, N158, N160, and N159 along the molecular ridge of the LMC in [C II] 158 μm with GREAT on board SOFIA. We also observed the same area with CO(2-1) to (6-5), 13CO(2-1) and (3-2), [C I] 3P1–3P0 and 3P2–3P1 with APEX. For selected positions in N159 and 30 Dor, we observed [O I] 145 μm and [O I] 63 μm with upGREAT. All spectra are velocity resolved. Results. In all four star-forming regions, the line profiles of CO, 13CO, and [C I] emission are similar, being reproduced by a combination of Gaussian profiles defined by CO(3-2), whereas [C II] typically shows wider line profiles or an additional velocity component. At several positions in N159 and 30 Dor, we observed the velocity-resolved [O I] 145 and 63 μm lines for the first time. At some positions, the [O I] line profiles match those of CO, at other positions they are more similar to the [C II] profiles. We interpret the different line profiles of CO, [C II] and [O I] as contributions from spatially separated clouds and/or clouds in different physical phases, which give different line ratios depending on their physical properties. We modeled the emission from the CO, [C I], [C II], and [O I] lines and the far-infrared continuum emission using the latest KOSMA-τ PDR model, which treats the dust-related physics consistently and computes the dust continuum SED together with the line emission of the chemical species. We find that the line and continuum emissions are not well-reproduced by a single clump ensemble. Toward the CO peak at N159 W, we propose a scenario that the CO, [C II], and [O I] 63 μm emission are weaker than expected because of mutual shielding among clumps.

Detection of CI line emission towards the oxygen-rich AGB star omi Ceti

We present the detection of neutral atomic carbon CI(3P1–3P0) line emission towards omi Cet. This is the first time that CI is detected in the envelope around an oxygen-rich M-type asymptotic giant branch (AGB) star. We also confirm the previously tentative CI detection around V Hya, a carbon-rich AGB star. As one of the main photodissociation products of parent species in the circumstellar envelope (CSE) around evolved stars, CI can be used to trace sources of ultraviolet (UV) radiation in CSEs. The observed flux density towards omi Cet can be reproduced by a shell with a peak atomic fractional abundance of 2.4 × 10−5 predicted based on a simple chemical model where CO is dissociated by the interstellar radiation field. However, the CI emission is shifted by ~4 km s−1 from the stellar velocity. Based on this velocity shift, we suggest that the detected CI emission towards omi Cet potentially arises from a compact region near its hot binary companion. The velocity shift could, therefore, be the result of the orbital velocity of the binary companion around omi Cet. In this case, the CI column density is estimated to be 1.1 × 1019 cm−2. This would imply that strong UV radiation from the companion and/or accretion of matter between two stars is most likely the origin of the CI enhancement. However, this hypothesis can be confirmed by high-angular resolution observations.