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Register a new userCarbon in different phases ([CII], [CI], and CO) in infrared dark clouds: Cloud formation signatures and carbon gas fractions
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Context: How do molecular clouds form out of the atomic phase? And what are the relative fractions of carbon in the ionized, atomic and molecular phase? These are questions at the heart of cloud and star formation. Methods: Using multiple observatories from Herschel and SOFIA to APEX and the IRAM 30m telescope, we mapped the ionized, atomic and molecular carbon ([CII]@1900GHz, [CI]@492GHz and C18O(2-1)@220GHz) at high spatial resolution (12-25) in four young massive infrared dark clouds (IRDCs). Results: The three carbon phases were successfully mapped in all four regions, only in one source the [CII] line remained a non-detection. Both the molecular and atomic phases trace the dense structures well, with [CI] also tracing material at lower column densities. [CII] exhibits diverse morphologies in our sample, from compact to diffuse structures probing the cloud environment. In at least two out of the four regions, we find kinematic signatures strongly indicating that the dense gas filaments have formed out of a dynamically active and turbulent atomic/molecular cloud, potentially from converging gas flows. The atomic-to-molecular carbon gas mass ratios are low between 7% and 12% with the lowest values found toward the most quiescent region. In the three regions where [CII] is detected, its mass is always higher by a factor of a few than that of the atomic carbon. The ionized carbon emission depends as well on the radiation field, however, we also find strong [CII] emission in a region without significant external sources, indicating that other processes, e.g., energetic gas flows can contribute to the [CII] excitation as well.
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The gas-solid budget of carbon in protoplanetary disks is related to the composition of the cores and atmospheres of the planets forming in them. The key gas-phase carbon carriers CO, C$^{0}$ and C$^{+}$ can now be observed in disks. The gas-phase carbon abundance in disks has not yet been well characterized, we aim to obtain new constraints on the [C]/[H] ratio in a sample of disks, and to get an overview of the strength of [CI] and warm CO emission. We carried out a survey of the CO$,6$--$5$ and [CI]$,1$--$0$ and $2$--$1$ lines towards $37$ disks with APEX, and supplemented it with [CII] data from the literature. The data are interpreted using a grid of models produced with the DALI code. We also investigate how well the gas-phase carbon abundance can be determined in light of parameter uncertainties. The CO$,6$--$5$ line is detected in $13$ out of $33$ sources, the [CI]$,1$--$0$ in $6$ out of $12$, and the [CI]$,2$--$1$ in $1$ out of $33$. With deep integrations, the first unambiguous detections of [CI]~$1$--$0$ in disks are obtained, in TW~Hya and HD~100546. Gas-phase carbon abundance reductions of a factor $5$--$10$ or more can be identified robustly based on CO and [CI] detections. The atomic carbon detection in TW~Hya confirms a factor $100$ reduction of [C]/[H]$_{rm gas}$ in that disk, while the data are consistent with an ISM-like carbon abundance for HD~100546. In addition, BP~Tau, T~Cha, HD~139614, HD~141569, and HD~100453 are either carbon-depleted or gas-poor disks. The low [CI]~$2$--$1$ detection rates in the survey mostly reflect insufficient sensitivity to detect T~Tauri disks. The Herbig~Ae/Be disks with CO and [CII] upper limits below the models are debris disk like systems. A roughly order of magnitude increase in sensitivity compared to our survey is required to obtain useful constraints on the gas-phase [C]/[H] ratio in most of the targeted systems.
We used the KOSMA 3m telescope to map the core 7x5 of the Galactic massive star forming region W3Main in the two fine structure lines of atomic carbon and four mid-J transitions of CO and 13CO. The maps are centered on the luminous infrared source IRS5 for which we obtained ISO/LWS data comprising four high-J CO transitions, CII, and OI at 63 and 145 micron. In combination with a KAO map of integrated line intensities of CII (Howe et al. 1991), this data set allows to study the physical structure of the molecular cloud interface regions where the occurence of carbon is believed to change from C+ to C0, and to CO. The molecular gas in W3Main is warmed by the far ultraviolet (FUV) field created by more than a dozen OB stars. Detailed modelling shows that most of the observed line intensity ratios and absolute intensities are consistent with a clumpy photon dominated region (PDR) of a few hundred unresolved clumps per 0.84pc beam, filling between 3 and 9% of the volume, with a typical clump radius of 0.025pc (2.2), and typical mass of 0.44Msun. The high-excitation lines of CO stem from a 100-200K layer, as also the CI lines. The bulk of the gas mass is however at lower temperatures.
We present first results of neutral carbon ([CI], 3P1 - 3P0 at 492 GHz) and carbon monoxide (13CO, J = 1 - 0) mapping in the Vela Molecular Ridge cloud C (VMR-C) and G333 giant molecular cloud complexes with the NANTEN2 and Mopra telescopes. For the four regions mapped in this work, we find that [CI] has very similar spectral emission profiles to 13CO, with comparable line widths. We find that [CI] has opacity of 0.1 - 1.3 across the mapped region while the [CI]/13CO peak brightness temperature ratio is between 0.2 to 0.8. The [CI] column density is an order of magnitude lower than that of 13CO. The H2 column density derived from [CI] is comparable to values obtained from 12CO. Our maps show CI is preferentially detected in gas with low temperatures (below 20 K), which possibly explains the comparable H2 column density calculated from both tracers (both CI and 12CO underestimate column density), as a significant amount of the CI in the warmer gas is likely in the higher energy state transition ([CI], 3P2 - 3P1 at 810 GHz), and thus it is likely that observations of both the above [CI] transitions are needed in order to recover the total H2 column density.
We present a statistical study on the [C I]($^{3} rm P_{1} rightarrow {rm ^3 P}_{0}$), [C I] ($^{3} rm P_{2} rightarrow {rm ^3 P}_{1}$) lines (hereafter [C I] (1$-$0) and [C I] (2$-$1), respectively) and the CO (1$-$0) line for a sample of (ultra)luminous infrared galaxies [(U)LIRGs]. We explore the correlations between the luminosities of CO (1$-$0) and [C I] lines, and find that $L_mathrm{CO(1-0)}$ correlates almost linearly with both $L_ mathrm{[CI](1-0)}$ and $L_mathrm{[CI](2-1)}$, suggesting that [C I] lines can trace total molecular gas mass at least for (U)LIRGs. We also investigate the dependence of $L_mathrm{[CI](1-0)}$/$L_mathrm{CO(1-0)}$, $L_mathrm{[CI](2-1)}$/$L_mathrm{CO(1-0)}$ and $L_mathrm{[CI](2-1)}$/$L_mathrm{[CI](1-0)}$ on the far-infrared color of 60-to-100 $mu$m, and find non-correlation, a weak correlation and a modest correlation, respectively. Under the assumption that these two carbon transitions are optically thin, we further calculate the [C I] line excitation temperatures, atomic carbon masses, and the mean [C I] line flux-to-H$_2$ mass conversion factors for our sample. The resulting $mathrm{H_2}$ masses using these [C I]-based conversion factors roughly agree with those derived from $L_mathrm{CO(1-0)}$ and CO-to-H$_2$ conversion factor.
The early evolutionary stage of brown dwarfs are not very well characterized, specially during the embedded phase. To gain insight into the dominant formation mechanism of very low-mass objects and brown dwarfs, we conducted deep observations at 870$mu$m with the LABOCA bolometer at the APEX telescope. Our goal was to identify young sub-mm sources in the Barnard 30 dark cloud. We complemented these data with multi-wavelength observations from the optical to the far-IR and. As a result, we have identified 34 submm sources and a substantial number of possible and probable Barnard 30 members within each individual APEX/LABOCA beam. They can be classified in three distinct groups. First, 15 out of these 34 have a clear optical or IR counterpart to the submm peak and nine of them are potential proto-BDs candidates. Moreover, a substantial number of them could be multiple systems. A second group of 13 sources comprises candidate members with significant infrared excesses located away from the central submm emission. All of them include brown dwarf candidates, some displaying IR excess, but their association with submm emission is unclear. In addition, we have found six starless cores and, based on the total dust mass estimate, three might be pre-substellar (or pre-BDs) cores. Finally, the complete characterization of our APEX/LABOCA sources, focusing on those detected at 24 and/or 70 $mu$m, indicates that in our sample of 34 submm sources there are, at least: two WTTs, four CTTs, five young stellar objects (YSOs), eight proto-BD candidates (with another three dubious cases), and one Very Low Luminosity object (VeLLO).
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