CO Observations Research Articles

Gas and Dust Shadows in the TW Hydrae Disk

We present new observations of CO J = 2 − 1 emission from the protoplanetary disk around TW Hya. Emission is detected out to 240 au (4″) and found to exhibit azimuthal variations up to 20% beyond 180 au (3″), with the west side of the disk brighter than the east. This asymmetry is interpreted as tracing the shadow previously seen in scattered light. A re-analysis of the multi-epoch observations of the dust shadow in scattered light from Debes et al. suggests that an oscillatory motion would provide a better model of the temporal evolution of the dust shadow rather than orbital motion. Both models predict an angular offset between the dust shadow and the gas shadow of up to ∼100°. We attribute this offset to the finite rate at which dust grains and gas molecules can exchange heat, dominated by the collisional rate between gas molecules and dust grains, t coll. The angular offsets derived are equivalent to collisional timescales that range from the near-instantaneous up to t coll ∼ 10 yr, depending on whether a straight or curved dust shadow, as suggested by Hubble Space Telescope observations reported by Debes et al., is adopted. The inferred range of t coll are consistent with those predictions based on representative gas densities, temperatures, gas-to-dust ratios and grain sizes. These results represent the first time empirical constraints can be placed on t coll.

NOEMA observations support a recoiling black hole in 3C 186

3C 186 is a powerful radio-loud quasar (a quasi-stellar object) at the center of a cool-core cluster at z = 1.06. Previous studies have reported evidence for a projected spatial offset of ∼1″ between the isophotal center of the galaxy and the point-source quasi-stellar object (QSO) as well as a spectral shift of ∼2000 km s−1 between the narrow and broad line region of the system. In this work we report high-resolution molecular gas CO(4→3) observations of the system taken with the NOEMA interferometer. We clearly detect a large reservoir of molecular gas, MH2 ∼ 8 × 1010 M⊙, that is co-spatial with the host galaxy and likely associated with a rotating disk-like structure. We firmly confirm both the spatial offset of the galaxy’s gas reservoir with respect to the continuum emission of the QSO and the spectral offset with respect to the redshift of the broad line region. Our morphological and kinematical analysis confirms that the most likely scenario to explain the 3C 186 system is that the QSO is a kicked super-massive black hole (SMBH), which we believe may have resulted from a strong gravitational wave recoil as two SMBHs coalesced after the merger of their host galaxies.

Extreme Variation in Star Formation Efficiency across a Compact, Starburst Disk Galaxy

Abstract We report on the internal distribution of star formation efficiency in IRAS 08339+6517 (hereafter IRAS08), using ∼200 pc resolution CO(2 − 1) observations from NOEMA. The molecular gas depletion time changes by 2 orders-of-magnitude from disk-like values in the outer parts to less than 108 yr inside the half-light radius. This translates to a star formation efficiency per freefall time that also changes by 2 orders-of-magnitude, reaching 50%–100%, different than local spiral galaxies and the typical assumption of constant, low star formation efficiencies. Our target is a compact, massive disk galaxy that has a star formation rate 10× above the z = 0 main sequence; Toomre Q ≈ 0.5−0.7 and high gas velocity dispersion (σ mol ≈ 25 km s−1). We find that IRAS08 is similar to other rotating, starburst galaxies from the literature in the resolved Σ SFR ∝ Σ mol N relation. By combining resolved literature studies we find that the distance from the main sequence is a strong indicator of the Kennicutt-Schmidt power-law slope, with slopes of N ≈ 1.6 for starbursts from 100 to 104 M ⊙ pc−2. Our target is consistent with a scenario in which violent disk instabilities drive rapid inflows of gas. It has low values of Toomre-Q, and also at all radii, the inflow timescale of the gas is less than the depletion time, which is consistent with the flat metallicity gradients in IRAS08. We consider these results in light of popular star formation theories; in general observations of IRAS08 find the most tension with theories in which star formation efficiency is a constant. Our results argue for the need of high-spatial-resolution CO observations for a larger number of similar targets.

Breaking Orion's Veil with fossil outflows

Context. The role of feedback in the self-regulation of star formation is a fundamental question in astrophysics. The Orion Nebula is the nearest site of ongoing and recent massive star formation. It is a unique laboratory for the study of stellar feedback. Recent SOFIA [C II] 158 μm observations have revealed an expanding bubble, the Veil shell, that is powered by stellar winds and ionization feedback. Aims. We have identified a protrusion-like substructure in the northwestern portion of the Orion Veil shell that may indicate additional, highly directional feedback mechanisms. Our goal is to investigate the origin of the protrusion by quantifying its possible driving mechanisms. Methods. We use the [C II] 158 μm map of the Orion Nebula obtained with the upGREAT instrument on board SOFIA. The spectral and spatial resolution of the observations are 0.3 km s−1 and 16", respectively. The velocity-resolved [C II] observations allow us to construct position-velocity (pv) diagrams to measure the morphology and the expansion velocity of the protrusion. For the morphology, we also use new observations of 12CO and 13CO J = 2-1 (to trace molecular gas), Spitzer 8 μm observations (to trace the far-ultraviolet-illuminated surfaces of photodissociation regions), and Hα observations (to trace ionized gas). For the kinematics, we perform a line-profile analysis of [C II], 13CO, and 12CO at 12 positions, covering the entire protrusion. To quantify the stellar feedback, we estimate the mass of the protrusion by fitting the dust thermal emission. We compare the kinetic energy with the stellar wind of θ1 Ori C and the momentum of the outflows of massive protostars to investigate the driving mechanism of the protrusion. Results. The pv diagrams reveal two half-shells expanding at velocities of +6 km s−1 and +12 km s−1. We find that the protrusion has a diameter of ~1.3 pc with a ~45 M⊙ shell expanding at +12 km s−1 at the northwestern rim of the Veil. The thickness of the expanding shell is ~0.1 pc. Using the mass in the limb-brightened shell and the maximum expansion velocity, we calculate the kinetic energy and the momentum of the protrusion to be ~7 × 1046 erg and 540 M⊙ km s−1, respectively. We consider three possible origins for this protrusion: fossil outflow cavities created by jets and outflows during the protostellar accretion phase, preexisting "clumpiness" in the OMC-1 core, and the stellar wind during the main-sequence phase. Based on the energetics and the morphology, we conclude that the northwestern part of the preexisting cloud was locally perturbed by outflows ejected from massive protostars in the Trapezium cluster. This suggests that the protrusion of the Veil is the result of mechanical rather than radiative feedback. Furthermore, we argue that the location of the protrusion is a suitable place to break Orion's Veil owing to the photo-ablation from the walls of the protrusion. Conclusions. We conclude that the outflows of massive protostars can influence the morphology of the future H II region and even cause breakages in the ionization front. Specifically, the interaction of stellar winds of main-sequence stars with the molecular core preprocessed by the protostellar jet is important.

Velocity Anisotropy in Self-gravitating Molecular Clouds. II. Observation

Abstract The view on velocity structures in molecular clouds and their relationship with magnetic fields (B field) has evolved during the past decade from almost no correlation to highly parallel. Our numerical simulations suggest a more nuanced picture: Depending on whether the self-gravity is dynamically dominant, the velocity field can be governed by either contraction (at high densities) or turbulence (at low densities), and their anisotropies will tend to be either perpendicular or parallel, respectively, to the B fields. High-density regions are always embedded in the low-density fore/background, so the velocity behaviors from lines of sight (LOSs) with high column densities will be a mixture of orthogonal anisotropies, which can be hard to interpret and necessitates zooming in onto certain LOS scales to better characterize localized behaviors. We tested and confirmed the above prediction with CO observations of the Taurus molecular cloud.

A SUBLIME 3D Model for Cometary Coma Emission: The Hypervolatile-rich Comet C/2016 R2 (PanSTARRS)

Abstract The coma of comet C/2016 R2 (PanSTARRS) is one of the most chemically peculiar ever observed, in particular due to its extremely high CO/H2O and N 2 + /H2O ratios, and unusual trace volatile abundances. However, the complex shape of its CO emission lines, as well as uncertainties in the coma structure and excitation, has lead to ambiguities in the total CO production rate. We performed high-resolution, spatially, spectrally, and temporally resolved CO observations using the James Clerk Maxwell Telescope and Submillimeter Array to elucidate the outgassing behavior of C/2016 R2. Results are analyzed using a new, time-dependent, three-dimensional radiative transfer code (SUBlimating gases in LIME; SUBLIME, based on the open-source version of the LIne Modeling Engine), incorporating for the first time, accurate state-to-state collisional rate coefficients for the CO–CO system. The total CO production rate was found to be in the range of (3.8 − 7.6) × 1028 s−1 between 2018 January 13 and February 1 (at r H = 2.8–2.9 au), with a mean value of (5.3 ± 0.6) × 1028 s−1. The emission is concentrated in a near-sunward jet, with a half-opening angle of ∼62° and an outflow velocity of 0.51 ± 0.01 km s−1, compared to 0.25 ± 0.01 km s−1 in the ambient (and nightside) coma. Evidence was also found for an extended source of CO emission, possibly due to icy grain sublimation around 1.2 × 105 km from the nucleus. Based on the coma molecular abundances, we propose that the nucleus ices of C/2016 R2 can be divided into a rapidly sublimating apolar phase, rich in CO, CO2, N2, and CH3OH, and a predominantly frozen (or less abundant), polar phase containing more H2O, CH4, H2CO, and HCN.

Multiwavelength and Multi-CO View of the Minor Merger Driven Star Formation in the Nearby LIRG NGC 3110

We present Atacama Large Millimeter/submillimeter Array observations of multiple 12CO, 13CO, and C18O lines and 2.9 mm and 1.3 mm continuum emission toward the nearby interacting luminous infrared galaxy NGC 3110, supplemented with similar spatial resolution Hα, 1.4 GHz continuum, and K-band data. We estimate the typical CO-to-H2 conversion factor of 1.7 M ⊙ (K km s−1 pc2)−1 within the disk using local thermal equilibrium-based and dust-based H2 column densities, and measure the 1 kpc scale surface densities of the star formation rate (ΣSFR), super star clusters (ΣSSC), molecular gas mass, and star formation efficiency (SFE) toward the entire gas disk. These parameters show a peak in the southern part of the southern spiral arm (SFE ∼ 10−8.2 yr−1, ΣSFR ∼ 10−0.6 M ⊙ kpc−2 yr−1, ΣSSC ∼ 6.0 kpc−2), which is likely attributable to the ongoing tidal interaction with the companion galaxy MCG-01-26-013, as well as toward the circumnuclear region. We also find that thermal free–free emission contributes to a significant fraction of the millimeter continuum emission at the position of the southern peak. These measurements imply that the peak of the southern arm is an active and young star-forming region, whereas the central part of NGC 3110 is a site of long-continued star formation. We suggest that during the early stage of the galaxy–galaxy interaction in which the mass ratio was high in NGC 3110, fragmentation along the main galaxy arms is an important driver of merger-induced star formation, and that massive gas inflow results in dusty nuclear starbursts.

VLA detects CO(1–0) emission in the z = 3.65 quasar SDSS J160705+533558

We present CO(1–0) observations of the high-redshift quasar SDSS J160705+533558 (z = 3.653) using the Karl G. Jansky Very Large Array (VLA). We detect CO emission associated with the quasar and at ∼16.8 kpc projected distance from it, separated by ∼800 km s−1 in velocity. The total molecular gas mass of this system is ∼5 × 1010 M⊙. By comparing our CO detections with previous submillimetre (submm) observations of the source, an offset between the different emission components is revealed: the peak of the submm emission is offset from the quasar and from the CO companion detected in our VLA data. To explain our findings, we propose a scenario similar to that for the Antennae galaxies: SDSS J160705+533558 might be a merger system in which the quasar and the CO companion are the merging galaxies, whose interaction resulted in the formation of a dusty, star-forming overlap region between the galaxies that is dominant at the submm wavelengths.

After The Fall: Resolving the Molecular Gas in Post-starburst Galaxies

Post-starburst (PSB), or “E + A,” galaxies represent a rapid transitional phase between major, gas-rich mergers and gas-poor, quiescent, early-type galaxies. Surprisingly, many PSBs have been shown to host a significant interstellar medium (ISM), despite theoretical predictions that the majority of the star-forming gas should be expelled in active galactic nuclei– or starburst-driven outflows. To date, the resolved properties of this surviving ISM have remained unknown. We present high-resolution ALMA continuum and CO(2–1) observations in six gas- and dust-rich PSBs, revealing for the first time the spatial and kinematic structure of their ISM on sub-kpc scales. We find extremely compact molecular reservoirs, with dust and gas surface densities rivaling those found in (ultra)luminous infrared galaxies. We observe spatial and kinematic disturbances in all sources, with some also displaying disk-like kinematics. Estimates of the internal turbulent pressure in the gas exceed those of normal star-forming disks by at least 2 orders of magnitude, and rival the turbulent gas found in local interacting galaxies, such as the Antennae. Though the source of this high turbulent pressure remains uncertain, we suggest that the high incidence of tidal disruption events in PSBs could play a role. The star formation in these PSBs’ turbulent central molecular reservoirs is suppressed, forming stars only 10% as efficiently as starburst galaxies with similar gas surface densities. “The fall” of star formation in these galaxies was not precipitated by complete gas expulsion or redistribution. Rather, this high-resolution view of PSBs’ ISM indicates that star formation in their remaining compact gas reservoirs is suppressed by significant turbulent heating.

Investigation of the Characteristics of CO (1-0) Line Integrated Emission Intensity in Extragalactic Spirals

This paper aims to deal with the understanding of the properties of the molecular gas hydrogen in the extragalactic spirals sample. It is critical to make observations of CO (J = 1-0) line emission for spiral galaxies, particularly those with an energetic nucleus. In the sample of spiral galaxies compiled, a carbon monoxide CO (1-0) emission line can be observed. This sample of galaxies' gas kinematics and star-forming should be analyzed statistically utilizing appropriate atomic gas HI, molecular gas H2, infrared (1μm-1000μm), visual (at λblue-optical=4400A0), and radio spectrum (at νradio=1.4 GHz and 5GHz) databases. STATISTICA is software that allows us to perform this statistical analysis. The presence of a high scale of star formation activity in these galaxies is dependent linearly on the correlations between galactic luminosities. Our findings show that thermal radio luminosity and LFIR are closely related to CO line luminosity. Further, LCO and MH2 have a steep linear relationship, where the slope of the regression log LCO - LogMH2 equals 1. The LCO-SFR and LFIR-SFR relationship slopes are nearly linear (slope ~1), with a strong partial correlation RCO-SFR of 0.73 between LCO-SFR and a significant correlation RFIR-SFR of 0.5 between LFIR-SFR, according to the statistical analysis. The correlation between the rate of star formation (SFR) and hydrogen gas in spirals is significant in several fields of astrophysics. Hence, it is asserted that the important point of the current study is that there is a significant link between SFR and the actual amount of cold hydrogen gas (Mgas) for the simple reason that in our spiral analysis, the mean atomic cold gas amount quantity is almost 6 times greater than the molecular gaseous amount.

Detection of the S(1) Rotational Line of H2 toward IRC+10216: A Simultaneous Measurement of the Mass-loss Rate and CO Abundance

Abstract We report the first detection of the S(1) pure rotational line of ortho-H2 at 17.04 μm in an asymptotic giant branch star, using observations of IRC+10216 with the Echelon-cross-echelle Spectrograph (EXES) mounted on the Stratospheric Observatory for Infrared Astronomy. This line, which was observed in a very high-sensitivity spectrum (rms noise ≃0.04% of the continuum), was detected in the wing of a strong telluric line and displayed a P Cygni profile. The spectral ranges around the frequencies of the S(5) and S(7) ortho-H2 transitions were observed as well but no feature was detected in spectra with sensitivities of 0.12% and 0.09% regarding the continuum emission, respectively. We used a radiation transfer code to model these three lines and derived a mass-loss rate of (2.43 ± 0.21) × 10−5 M ⊙ yr−1 without using the CO abundance. The comparison of this rate with previous estimates derived from CO observations suggests that the CO abundance relative to H2 is (6.7 ± 1.4) × 10−4. From this quantity and previously reported molecular abundances, we estimate the O/H and C/H ratios to be (3.3 ± 0.7) × 10−4 and >(5.2 ± 0.9) × 10−4, respectively. The C/O ratio is >1.5 ± 0.4. The absence of the S(5) and S(7) lines of ortho-H2 in our observations can be explained by the opacity of hot dust within 5 R ⋆ from the center of the star. We estimate the intensity of the S(0) and S(2) lines of para-H2 to be ≃0.1% and 0.2% of the continuum, respectively, which are below the detection limit of EXES.

A 2–3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946

The complex physical, kinematic, and chemical properties of galaxy centres make them interesting environments to examine with molecular line emission. We present new 2 − 4″ (∼75 − 150 pc at 7.7 Mpc) observations at 2 and 3 mm covering the central 50″ (∼1.9 kpc) of the nearby double-barred spiral galaxy NGC 6946 obtained with the IRAM Plateau de Bure Interferometer. We detect spectral lines from ten molecules: CO, HCN, HCO+, HNC, CS, HC3N, N2H+, C2H, CH3OH, and H2CO. We complemented these with published 1 mm CO observations and 33 GHz continuum observations to explore the star formation rate surface density ΣSFRon 150 pc scales. In this paper, we analyse regions associated with the inner bar of NGC 6946 – the nuclear region (NUC), the northern (NBE), and southern inner bar end (SBE) and we focus on short-spacing corrected bulk (CO) and dense gas tracers (HCN, HCO+, and HNC). We find that HCO+correlates best with ΣSFR, but the dense gas fraction (fdense) and star formation efficiency of the dense gas (SFEdense) fits show different behaviours than expected from large-scale disc observations. The SBE has a higher ΣSFR,fdense, and shocked gas fraction than the NBE. We examine line ratio diagnostics and find a higher CO(2−1)/CO(1−0) ratio towards NBE than for the NUC. Moreover, comparison with existing extragalactic datasets suggests that using the HCN/HNC ratio to probe kinetic temperatures is not suitable on kiloparsec and sub-kiloparsec scales in extragalactic regions. Lastly, our study shows that the HCO+/HCN ratio might not be a unique indicator to diagnose AGN activity in galaxies.

The PHANGS-MUSE survey

We present the PHANGS-MUSE survey, a programme that uses the MUSE integral field spectrograph at the ESO VLT to map 19 massive (9.4 < log(M⋆/M⊙)< 11.0) nearby (D ≲ 20 Mpc) star-forming disc galaxies. The survey consists of 168 MUSE pointings (1′ by 1′ each) and a total of nearly 15 × 106spectra, covering ∼1.5 × 106independent spectra. PHANGS-MUSE provides the first integral field spectrograph view of star formation across different local environments (including galaxy centres, bars, and spiral arms) in external galaxies at a median resolution of 50 pc, better than the mean inter-cloud distance in the ionised interstellar medium. This ‘cloud-scale’ resolution allows detailed demographics and characterisations of H IIregions and other ionised nebulae. PHANGS-MUSE further delivers a unique view on the associated gas and stellar kinematics and provides constraints on the star-formation history. The PHANGS-MUSE survey is complemented by dedicated ALMA CO(2–1) and multi-band HST observations, therefore allowing us to probe the key stages of the star-formation process from molecular clouds to H IIregions and star clusters. This paper describes the scientific motivation, sample selection, observational strategy, data reduction, and analysis process of the PHANGS-MUSE survey. We present our bespoke automated data-reduction framework, which is built on the reduction recipes provided by ESO but additionally allows for mosaicking and homogenisation of the point spread function. We further present a detailed quality assessment and a brief illustration of the potential scientific applications of the large set of PHANGS-MUSE data products generated by our data analysis framework. The data cubes and analysis data products described in this paper represent the basis for the first PHANGS-MUSE public data release and are available in the ESO archive and via the Canadian Astronomy Data Centre.

The Kiloparsec-scale Neutral Atomic Carbon Outflow in the Nearby Type 2 Seyfert Galaxy NGC 1068: Evidence for Negative AGN Feedback

Abstract Active galactic nucleus (AGN) feedback is postulated as a key mechanism for regulating star formation within galaxies. Studying the physical properties of the outflowing gas from AGNs is thus crucial for understanding the coevolution of galaxies and supermassive black holes. Here we report 55 pc resolution ALMA neutral atomic carbon [C i] 3 P 1−3 P 0 observations toward the central 1 kpc of the nearby Type 2 Seyfert galaxy NGC 1068, supplemented by 55 pc resolution CO(J = 1−0) observations. We find that [C i] emission within the central kiloparsec is strongly enhanced by a factor of >5 compared to the typical [C i]/CO intensity ratio of ∼0.2 for nearby starburst galaxies (in units of brightness temperature). The most [C i]-enhanced gas (ratio > 1) exhibits a kiloparsec-scale elongated structure centered at the AGN that matches the known biconical ionized gas outflow entraining molecular gas in the disk. A truncated, decelerating bicone model explains well the kinematics of the elongated structure, indicating that the [C i] enhancement is predominantly driven by the interaction between the ISM in the disk and the highly inclined ionized gas outflow (which is likely driven by the radio jet). Our results strongly favor the “CO dissociation scenario” rather than the “in situ C formation” one, which prefers a perfect bicone geometry. We suggest that the high-[C i]/CO intensity ratio gas in NGC 1068 directly traces ISM in the disk that is currently dissociated and entrained by the jet and the outflow, i.e., the “negative” effect of the AGN feedback.

Fabrication and preliminary evaluation of alginate hydrogel-based magnetic springs with actively targeted heating and drug release mechanisms for cancer therapy

In this study, we developed calcium alginate hydrogel-based magnetic springs containing magnetically aligned Fe 2 O 3 magnetic nanoparticles (MNPs) to render them responsive toward magnetic fields. Under a low-frequency magnetic field, a torque was exerted on the springs propelling them along their long axis. In contrast, under a high-frequency alternating magnetic field (AMF) of 200 kHz, the temperature of the spring increased up to 45 °C, making them suitable for magnetic hyperthermia. Moreover, the heat caused thermal stresses, resulting in the spring's mechanical deformation (shrinkage) that accelerated the drug release. Based on the observation of CO 2 using mass spectra, we verified the boundary conditions prevailing during thermal deformation and thermal cracking. In the AMF condition, a spring temperature of 43 °C was attained, and the drug release was about 35% higher than that of physiological temperature (37 °C). In addition, the mechanical and thermal properties of the magnetic hydrogel were investigated based on the concentration and alignment of MNP, because these properties affect the locomotion the drug release mechanism of the hydrogel. Ultimately, the viability of the spring for active targeted heating and drug release was verified via various in-vitro tests.

Now You See It, Now You Don’t: Star Formation Truncation Precedes the Loss of Molecular Gas by ∼100 Myr in Massive Poststarburst Galaxies at z ∼ 0.6

Abstract We use ALMA observations of CO(2–1) in 13 massive (M * ≳ 1011 M ⊙) poststarburst galaxies at z ∼ 0.6 to constrain the molecular gas content in galaxies shortly after they quench their major star-forming episode. The poststarburst galaxies in this study are selected from the Sloan Digital Sky Survey spectroscopic samples (Data Release 14) based on their spectral shapes, as part of the Studying QUenching at Intermediate-z Galaxies: Gas, angu L → ar momentum, and Evolution ( SQuIGG L ⃗ E ) program. Early results showed that two poststarburst galaxies host large H2 reservoirs despite their low inferred star formation rates (SFRs). Here we expand this analysis to a larger statistical sample of 13 galaxies. Six of the primary targets (45%) are detected, with M H 2 ≳ 10 9 M ⊙. Given their high stellar masses, this mass limit corresponds to an average gas fraction of 〈 f H 2 ≡ M H 2 / M * 〉 ∼ 7 % or ∼14% using lower stellar masses estimates derived from analytic, exponentially declining star formation histories. The gas fraction correlates with the D n 4000 spectral index, suggesting that the cold gas reservoirs decrease with time since burst, as found in local K+A galaxies. Star formation histories derived from flexible stellar population synthesis modeling support this empirical finding: galaxies that quenched ≲150 Myr prior to observation host detectable CO(2–1) emission, while older poststarburst galaxies are undetected. The large H2 reservoirs and low SFRs in the sample imply that the quenching of star formation precedes the disappearance of the cold gas reservoirs. However, within the following 100–200 Myr, the SQuIGG L ⃗ E galaxies require the additional and efficient heating or removal of cold gas to bring their low SFRs in line with standard H2 scaling relations.

CO(2–1)/CO(1–0) Line Ratio on a ∼100 Parsec Scale in the Nearby Barred Galaxy NGC 1300

Abstract CO(2–1) emission is often used as a tracer of giant molecular clouds (GMCs) as an alternative to CO(1–0) emission in recent years. Therefore, understanding the environmental dependence of the line ratio of CO(2–1)/CO(1–0), R 21, on the GMC scale is important to accurately estimate the mass of GMCs. We thus measured R 21 in the strongly barred galaxy NGC 1300, where star formation activity strongly depends on galactic structure, on a ∼100 pc scale. CO images were obtained from the Atacama Large Millimeter/submillimeter Array and the Nobeyama 45 m telescope. The resultant typical R 21 in NGC 1300 is 0.57 ± 0.06. We find environmental variations in R 21: it is the highest in the bar-end region (0.72 ± 0.08), followed by arm (0.60 ± 0.07) and bar regions (0.50 ± 0.06). GMCs with Hα emission show a systematically higher ratio (0.67 ± 0.07) than those without Hα (0.47 ± 0.05). In the bar region, where massive star formation is suppressed, Hα emission is not associated with most GMCs, resulting in the lowest R 21. These results raise a possibility that properties of GMCs derived from CO(2–1) observations with the assumption of a constant R 21 are different from those derived from CO(1–0) observations. Furthermore, we find the R 21 measured on the kiloparsec scale tends to be lower than that of the GMCs, probably due to the presence of an extended diffuse molecular gas in NGC 1300.

IRAM 30 m CO-line Observation toward the PeVatron Candidate G106.3+2.7: Direct Interaction between the Shock and the Molecular Cloud Remains Uncertain

Abstract The supernova remnant (SNR) G106.3+2.7 was recently found to be one of the few potential Galactic hadronic PeVatrons. Aiming to test the solidity of the SNR’s association with the molecular clouds (MCs) that are thought to be responsible for hadronic interaction, we performed a new CO observation with the IRAM 30 m telescope toward its “belly” region, which is coincident with the centroid of the γ-ray emission. There is a filament structure in the local standard of rest velocity interval −8 to −5 km s−1 that nicely follows the northern radio boundary of the SNR. We have seen asymmetric broad profiles of 12CO lines, with widths of a few km s−1, along the northern boundary and in the “belly” region of G106.3+2.7, but similar 12CO-line profiles are also found outside the SNR boundary. Further, the low 12CO J = 2–1/J = 1–0 line ratios suggest the MCs are cool. Therefore, it is still uncertain whether the MCs are directly disturbed by the SNR shocks, but we do find some clues that the MCs are nearby and thus can still be illuminated by the protons that escaped from the SNR. Notably, we find an expanding molecular structure with a velocity of ∼3.5 km s−1 and a velocity gradient of the MCs across the SNR from ∼−3 to −7 km s−1, which could be explained as the effect of the wind blown by the SNR’s progenitor star.

China's Terrestrial Carbon Sink Over 2010–2015 Constrained by Satellite Observations of Atmospheric CO2 and Land Surface Variables

AbstractThe magnitude and distribution of China's terrestrial carbon sink remain uncertain due to insufficient constraints at large scales, whereby satellite data offer great potential for reducing the uncertainty. Here, we present two carbon sink estimates for China constrained either by satellite CO2 column concentrations (XCO2) within the Global Carbon Assimilation System or by remotely sensed soil moisture and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) in addition to in situ CO2 observations within the Carbon Cycle Data Assimilation System. They point to a moderate size of carbon sinks of 0.34 ± 0.14 (mean ± unc.) and 0.43 ± 0.09 PgC/yr during 2010–2015, which are supported by an inventory‐based estimate for forest and soil carbon sink (0.26 PgC/yr) and fall in the range of contemporary ensemble atmospheric inversions (0.25–0.48 PgC/yr). They also agree reasonably well on interannual variations, which reflect the carbon sink anomalies induced by regional droughts in southwest China. Furthermore, their spatial distributions are broadly consistent that of the forest inventory‐based estimate, indicating that the largest carbon sinks locate in central and eastern China. Their estimates for forest carbon sink coincide fairly well with the inventory‐based estimate across different regions, especially when aggregated to the north and south of China. Although enhanced recently by afforestation, China's carbon sink was also significantly weakened by regional droughts, which were often not fully represented in previous in situ CO2‐based inversions due to insufficient observations. Our results suggest that satellite‐based atmospheric CO2 and land surface observations are vital in characterizing terrestrial net carbon fluxes at regional scales.

A Census of Protostellar Outflows in Nearby Molecular Clouds

Abstract We adopt the deep learning method casi-3d (Convolutional Approach to Structure Identification-3D) to systemically identify protostellar outflows in 12CO and 13CO observations of the nearby molecular clouds, Ophiuchus, Taurus, Perseus, and Orion. The total outflow masses are 267 M ⊙, 795 M ⊙, 1305 M ⊙, and 6332 M ⊙ for Ophiuchus, Taurus, Perseus, and Orion, respectively. We show the outflow mass in each cloud is linearly proportional to the total number of young stellar objects. The estimated total 3D deprojected outflow energies are 9 × 1045 erg, 6 × 1046 erg, 1.2 × 1047 erg, and 6 × 1047 erg for Ophiuchus, Taurus, Perseus, and Orion, respectively. The energy associated with outflows is sufficient to offset turbulent dissipation at the current epoch for all four clouds. All clouds also exhibit a break point in the spatial power spectrum of the outflow prediction map, which likely corresponds to the typical outflow mass and energy injection scale.