Search

The kinematic information of the Radcliffe wave (RW) is essential for determining its existence and gaining insights into its origin and evolution. In this work, we present an accurate measurement of the vertical velocity ( V _Z ) of the RW by incorporating the radial velocity (RV) measures through two methods, which is crucial but was neglected previously. First, the velocities are measured toward young stars, using their RV measurements from APOGEE-2 and proper motion measurements from Gaia DR3. Second, we combine RV measurements toward clouds with proper motion measurements of associated young stellar objects to determine the vertical velocities of the clouds. The results reveal that the oscillations in V _Z are not synchronous with the vertical coordinate Z , which differs from the conclusions of previous studies. Instead, we find a 5 km s ^−1 kpc ^−1 gradient in V _Z along the RW, exhibiting a dipole-like pattern. Consequently, the kinematic arrangement does not show a corresponding coherence with the spatial arrangement, bringing the RW model into question.

C _4 H and c -C _3 H _2 , as unsaturated hydrocarbon molecules, are important for forming large organic molecules in the interstellar medium. We present mapping observations of C _4 H ( N = 9−8) lines, c -C _3 H _2 ( J _Ka _, _Kb = 2 _1,2 –1 _0,1 ), and H ^13 CO ^+ ( J = 1−0) toward 19 nearby cold molecular cores in the Milky Way with the IRAM 30 m telescope. C _4 H 9–8 was detected in 13 sources, while c -C _3 H _2 was detected in 18 sources. The widely existing C _4 H and c -C _3 H _2 molecules in cold cores provide material to form large organic molecules. Different spatial distributions between C _4 H 9–8 and c -C _3 H _2 2–1 were found. The relative abundances of these three molecules were obtained under the assumption of local thermodynamic equilibrium conditions with a fixed excitation temperature. The abundance ratio of C _4 H to c -C _3 H _2 ranged from 0.34 ± 0.09 in G032.93+02 to 4.65 ± 0.50 in G008.67+22. A weak correlation between C _4 H/H ^13 CO ^+ and c -C _3 H _2 /H ^13 CO ^+ abundance ratios was found, with a correlation coefficient of 0.46, which indicates that there is no tight astrochemical connection between C _4 H and c -C _3 H _2 molecules.

Dense outflowing gas, traced by transitions of molecules with large dipole moment, is important for understanding mass loss and feedback of massive star formation. HCN 3-2 and HCO ^+ 3-2 are good tracers of dense outflowing molecular gas, which are closely related to active star formation. In this study, we present on-the-fly mapping observations of HCN 3-2 and HCO ^+ 3-2 toward a sample of 33 massive star-forming regions using the 10-m Submillimeter Telescope. With the spatial distribution of line wings of HCO ^+ 3-2 and HCN 3-2, outflows are detected in 25 sources, resulting in a detection rate of 76%. The optically thin H ^13 CN and H ^13 CO ^+ 3-2 lines are used to identify line wings as outflows and estimate core mass. The mass M _out , momentum P _out , kinetic energy E _K , force F _out , and mass-loss rate ${\dot{M}}_{{\rm{out}}}$ of outflow and core mass, are obtained for each source. A sublinear tight correlation is found between the mass of dense molecular outflow and core mass, with an index of ∼0.8 and a correlation coefficient of 0.88.

Deuterated molecules are valuable probes for investigating the evolution and the kinematics in the earliest stages of star formation. In this study, we conduct a comprehensive investigation by performing a single-point survey of 101 starless clump candidates, and carrying out on-the-fly (OTF) observations of 11 selected sources, focusing on deuterated molecular lines using the IRAM 30 m telescope. In the single-point observation, we make 46 detections for DCO ^+ J = 1−0, 12 for DCN J = 1−0, 51 for DNC J = 1−0, 7 for N _2 D ^+ J = 1−0, 20 for DCO ^+ J = 2−1, and 10 for DCN J = 2−1. The starless clump candidates with deuterated molecule detections exhibit lower median kinetic temperatures and a narrower H _2 CO (1 _(0,1) −0 _(0,0) ) median full width at half maximum compared to those without such detections, while simultaneously displaying similar median values of 1.1 mm intensity, mass, and distance. Furthermore, our OTF observations reveal that deuterated molecules predominantly have peaks near the 1.1 mm continuum peaks, with the DCO ^+ J = 1−0 emission demonstrating higher intensity in the deuterated peak region compared to the DCN and DNC J = 1−0 emissions. Additionally, the majority of emissions from deuterated molecules and ^13 C isotopologues exhibit peak positions close to those of the 1.1 mm continuum peaks. By analyzing the 20″ × 20″ regions with strongest deuterated emissions in the OTF observations, we estimated deuterated abundances of 0.004−0.045, 0.011−0.040, and 0.004−0.038 for D _frac (HCN), D _frac (HCO ^+ ), and D _frac (HNC), respectively. The differential detection of deuterated molecular lines in our OTF observations could be attributed to variations in critical densities and formation pathways.

Peptide-like molecules, which have a close connection with the origin of life, have been detected in the Universe. Mapping observations of HCONH _2 and CH _3 CONH _2 , two of the simplest peptide-like molecules, are performed toward the Sagittarius B2 (Sgr B2) complex with the IRAM 30 m telescope. Seven transitions of HCONH _2 and five transitions of CH _3 CONH _2 are used in the analysis. The spatial distributions of the excitation temperature and column density of HCONH _2 in the molecular envelope of Sgr B2 are obtained by rotation diagrams. Assuming the same excitation temperature of HCONH _2 , the column densities of CH _3 CONH _2 are also calculated. The results show that the excitation temperature ranges from 6 to 46 K in the molecular envelope of Sgr B2. The abundance ratios between HCONH _2 and CH _3 CONH _2 are calculated to explore the relationship between them, as are those between HCONH _2 and HNCO. The abundance ratio of CH _3 CONH _2 /HCONH _2 varies from 10% to 20%, while that of HCONH _2 /HNCO ranges from 1.5% to 10%. CH _3 CONH _2 is enhanced with respect to HCONH _2 in the northwest region of Sgr B2. One transition of H ^13 CONH _2 is detected toward 12 positions of Sgr B2, from which a ^12 C/ ^13 C ratio of 28.7 is obtained. A time-dependent chemical model with a short-duration X-ray burst is used to explain the observed abundances of HCONH _2 and CH _3 CONH _2 , with the best-fitting result at T _dust = 53–56 K. More chemical reactions are required to be included in the model since the modeled abundance is lower than the observed one at the observed T _dust .

Protostellar outflows are considered a signpost of star formation. These outflows can cause shocks in the molecular gas and are typically traced by the line wings of certain molecules. HNCO (4–3) has been regarded as a shock tracer because of the high abundance in shocked regions. Here we present the first imaging results of HNCO (4–3) line wings toward nine sources in a sample of 23 massive star-forming regions using the Instituto de Radioastronomía Milimétrica 30 m Telescope. We adopt the velocity range of the full width of HC _3 N (10–9) and H ^13 CO ^+ (1–0) emissions as the central emission values, beyond which the emission from HNCO (4–3) is considered to be from line wings. The spatial distributions of the red and/or blue lobes of HNCO (4–3) emission nicely associate with those lobes of HCO ^+ (1–0) in most of the sources. High-intensity ratios of HNCO (4–3) to HCO ^+ (1–0) are obtained in the line wings. The derived column density ratios of HNCO to HCO ^+ are consistent with those previously observed toward massive star-forming regions. These results provide direct evidence that HNCO could trace outflow in massive star-forming regions. This work also implies that the formation of some HNCO molecules is related to shock, either on the grain surface or within the shocked gas.

Ions (e.g., ${{\rm{H}}}_{3}^{+}$ , H _2 O ^+ ) have been used extensively to quantify the cosmic-ray ionization rate (CRIR) in diffuse sightlines. However, measurements of the CRIR in low-to-intermediate density gas environments are rare, especially when background stars are absent. In this work, we combine molecular line observations of CO, OH, CH, and HCO ^+ in the star-forming cloud IC 348, and chemical models to constrain the value of the CRIR and study the response of the distribution of chemical abundances. The cloud boundary is found to have an A _V of approximately 4 mag. From the interior to the exterior of the cloud, the observed ^13 CO line intensities drop by an order of magnitude. The calculated average abundance of ^12 CO (assuming ^12 C/ ^13 C=65) is (1.2 ± 0.9) × 10 ^−4 , which decreases by a factor of 6 from the interior to the outside regions. The average abundance of CH (3.3 ± 0.7 × 10 ^−8 ) is in good agreement with previous findings in diffuse and translucent clouds ( A _V < 5 mag). However, we did not find a decline in CH abundance in regions of high extinction ( A _V ≃ 8 mag) as previously reported in Taurus. By comparing the observed molecular abundances and chemical models, we find a decreasing trend of the CRIR as A _V increases. The inferred CRIR of ζ _cr = (4.7 ± 1.5) × 10 ^−16 s ^−1 at low A _V is consistent with ${{\rm{H}}}_{3}^{+}$ measurements toward two nearby massive stars.

The cosmic-ray ionization rate (CRIR, ζ _2 ) is one of the key parameters controlling the formation and destruction of various molecules in molecular clouds. However, the current most commonly used CRIR tracers, such as ${{\rm{H}}}_{3}^{+}$ , OH ^+ , and H _2 O ^+ , are hard to detect and require the presence of background massive stars for absorption measurements. In this work, we propose an alternative method to infer the CRIR in diffuse clouds using the abundance ratios of OH/CO and HCO ^+ /CO. We have analyzed the response of chemical abundances of CO, OH, and HCO ^+ on various environmental parameters of the interstellar medium in diffuse clouds and found that their abundances are proportional to ζ _2 . Our analytic expressions give an excellent calculation of the abundance of OH for ζ _2 ≤ 10 ^−15 s ^−1 , which are potentially useful for modeling chemistry in hydrodynamical simulations. The abundances of OH and HCO ^+ were found to monotonically decrease with increasing density, while the CO abundance shows the opposite trend. With high-sensitivity absorption transitions of both CO (1–0) and (2–1) lines from Atacama Large Millimeter/submillimeter Array, we have derived the H _2 number densities ( ${n}_{{{\rm{H}}}_{2}}$ ) toward 4 lines of sight; assuming a kinetic temperature of T _k = 50 K, we find a range of (0.14 ± 0.03–1.2 ± 0.1) × 10 ^2 cm ^−3 . By comparing the observed and modeled HCO ^+ /CO ratios, we find that ζ _2 in our diffuse gas sample is in the range of ${1.0}_{-1.0}^{+14.8}$ × 10 ${}^{-16}\mbox{--}{2.5}_{-2.4}^{+1.4}$ × 10 ^−15 s ^−1 . This is ∼2 times higher than the average value measured at higher extinction, supporting an attenuation of CRs as suggested by theoretical models.

We have mapped 27 massive star-forming regions associated with water masers using three dense gas tracers: HC³N 10-9, HNC 1-0, and C²H 1-0. The FWHM sizes of HNC clumps and C²H clumps are about 1.5 and 1.6 times higher than those of HC³N, respectively, which can be explained by the fact that HC³N traces more dense gas than HNC and C²H. We found evidence for an increase in the optical depth of C²H with a "radius" from the center to the outer regions in some targets, supporting the chemical model of C²H. The C²H optical depth is found to decline as molecular clouds evolve to a later stage, suggesting that C²H might be used as a "chemical clock" for molecular clouds. The large-scale kinematic structure of clouds was investigated with three molecular lines. All of these sources show significant velocity gradients. The magnitudes of gradient are found to increase toward the inner region, indicating the differential rotation of clouds. Both the ratio of rotational to gravitational energy and the specific angular momentum seem to decrease toward the inner region, implying the obvious angular momentum transfer, which might be caused by magnetic braking. The average magnetic field strength and number density of molecular clouds is derived using the uniform magnetic sphere model. The derived magnetic field strengths range from 3 to 88 µG, with a median value of 13 µG. The mass-to-flux ratio of the molecular cloud is calculated to be much higher than the critical value with derived parameters, which agrees well with numerical simulations. [ABSTRACT FROM AUTHOR]

We present a ~1" (100 pc) resolution 12CO (3-2) map of the nearby intermediate-stage interacting galaxy pair NGC 4038/9 (the Antennae galaxies) obtained with the Submillimeter Array. We find that half the CO (3-2) emission originates in the overlap region where most of the tidally induced star formation had been previously found in shorter wavelength images, with the rest being centered on each of the nuclei. The gross distribution is consistent with lower resolution single-dish images, but we show for the first time the detailed distribution of the warm and dense molecular gas across this galaxy pair at resolutions comparable to the size of a typical giant molecular complex. While we find that 58% (33/57) of the spatially resolved Giant Molecular Associations (a few x 100 pc) are located in the overlap region, only ≤ 30% spatially coincides with the optically detected star clusters, suggesting that the bulk of the CO (3-2) emission traces the regions with very recent or near future star formation activity. The spatial distribution of the CO (3-2)/CO (1-0) integrated brightness temperature ratios mainly ranges between 0.3 and 0.6, which suggests that on average the CO (3-2) line in the Antennae is not completely thermalized and similar to the average values of nearby spirals. A higher ratio is seen in both nuclei and the southern complexes in the overlap region. A higher radiation field associated with intense star formation can account tbr the nucleus of NGC 4038 and the overlap region, but the nuclear region of NGC 4039 shows relatively little star formation or active galactic nucleus activity and cannot be easily explained. We show kinematical evidence that the high line ratio in NGC 4039 is possibly caused by gas inflow into the counter-rotating central disk. [ABSTRACT FROM AUTHOR]

Metals are thought to have profound effects on the internal structures of the molecular clouds in which stars are born. The absence of metals is expected to prevent gas from efficient cooling and fragmentation in theory. However, this effect has not yet been observed in low-metallicity environments, such as in the early universe and local dwarf galaxies, because of the lack of high-spatial-resolution maps of gas. We carried out Atacama Large Millimeter/submillimeter Array observations of the carbon monoxide (CO) J = 2–1 emission line at 1.4 parsec resolutions of a molecular cloud in DDO 70 at 7% solar metallicity, the most metal-poor galaxy currently known with a CO detection. In total, five clumps have been identified and they are found to more or less follow Larson’s law. Since the CO emission exists in regions with visual extinction AV around 1.0, we converted this AV to the gas-mass surface density using a gas-to-dust ratio of 4594 ± 2848 for DDO 70. We found that the CO clumps in DDO 70 exhibit significantly larger (on average four times) sizes than those at the same gas-mass surface densities in the massive star formation regions of the Milky Way. The existence of such large clumps appears to be consistent with theoretical expectations that gas fragmentation in low-metallicity clouds is suppressed. While our observation is only for one cloud in the galaxy, if it is representative, the above result implies suppressed gas fragmentation during the cloud collapse and star formation in the early universe. [ABSTRACT FROM AUTHOR]

We report the detection of an emission feature at the 12σ level with FWHM line width of about 450 km s−1 toward the nearest quasi-stellar object, QSO Mrk 231. Based on observations with the IRAM 30 m telescope and the Northern Extended Millimeter Array Interferometer, the 11–10 transition of molecular oxygen is the likely origin of the line with rest frequency close to 118.75 GHz. The velocity of the O2 emission in Mrk 231 coincides with the red wing seen in CO emission, suggesting that it is associated with the outflowing molecular gas, located mainly at about 10 kpc away from the central active galactic nucleus (AGN). This first detection of extragalactic molecular oxygen provides an ideal tool to study AGN-driven molecular outflows on dynamic timescales of tens of megayears. O2 may be a significant coolant for molecular gas in such regions affected by AGN-driven outflows. New astrochemical models are needed to explain the implied high molecular oxygen abundance in such regions several kiloparsecs away from the center of galaxies. [ABSTRACT FROM AUTHOR]

We present Submillimeter Array observations of seven massive molecular clumps that are dark in the far-infrared for wavelengths up to 70 μm. Our 1.3 mm continuum images reveal 44 dense cores, with gas masses ranging from 1.4 to 77.1 M⊙. Twenty-nine dense cores have masses greater than 8 M⊙ and the other 15 dense cores have masses between 1.4 and 7.5 M⊙. Assuming the core density follows a power law in radius ρ ∝ r−b, the index b is found to be between 0.6 and 2.1, with a mean value of 1.3. The virial analysis reveals that the dense cores are not in virial equilibrium. CO outflow emission was detected toward six out of seven molecular clumps and associated with 17 dense cores. For five of these cores, CO emissions appear to have line wings at velocities of greater than 30 km s−1 with respect to the source systemic velocity, which indicates that most of the clumps harbor protostars and thus are not quiescent in star formation. The estimated outflow timescale increases with core mass, which likely indicates that massive cores have longer accretion timescales than less massive ones. The fragmentation analysis shows that the masses of low-mass and massive cores are roughly consistent with thermal and turbulent Jeans masses, respectively. [ABSTRACT FROM AUTHOR]

We performed a survey in the SiO J = 5 → 4 line toward a sample of 199 Galactic massive star-forming regions at different evolutionary stages with the Submillimeter Telescope (SMT) 10 m and Caltech Submillimeter Observatory (CSO) 10.4 m telescopes. The sample consists of 44 infrared dark clouds (IRDCs), 86 protostellar candidates, and 69 young H ii regions. We detected SiO J = 5 → 4 line emission in 102 sources, with a detection rate of 57%, 37%, and 65% for IRDCs, protostellar candidates, and young H ii regions, respectively. We find both broad line emissions with full widths at zero power >20 km s−1 and narrow line emissions of SiO in objects at various evolutionary stages, likely associated with high-velocity shocks and low-velocity shocks, respectively. The SiO luminosities do not show apparent differences among various evolutionary stages in our sample. We find no correlation between the SiO abundance and the luminosity-to-mass ratio, indicating that the SiO abundance does not vary significantly in regions at different evolutionary stages of star formation. [ABSTRACT FROM AUTHOR]

We revisit the proposed extended Schmidt law, which posits that the star formation efficiency in galaxies depends on the stellar mass surface density, by investigating spatially resolved star formation rates (SFRs), gas masses, and stellar masses of star formation regions in a vast range of galactic environments, from the outer disks of dwarf galaxies, to spiral disks and to merging galaxies, as well as individual molecular clouds in M33. We find that these regions are distributed in a tight power law as ∝ , which is also valid for the integrated measurements of disk and merging galaxies at high-z. Interestingly, we show that star formation regions in the outer disks of dwarf galaxies with down to 10−5 yr−1 kpc−2, which are outliers of both the Kennicutt–Schmidt and Silk–Elmegreen laws, also follow the extended Schmidt law. Other outliers in the Kennicutt–Schmidt law, such as extremely metal-poor star formation regions, also show significantly reduced deviation from the extended Schmidt law. These results suggest an important role for existing stars in helping to regulate star formation through the effect of their gravity on the midplane pressure in a wide range of galactic environments. [ABSTRACT FROM AUTHOR]

We report the detection of widespread CH2OHCHO and HOCH2CH2OH emission in Galactic center giant molecular cloud Sagittarius B2 using the Shanghai Tianma 65 m Radio Telescope. Our observations show for the first time that the spatial distribution of these two important prebiotic molecules extends over 15 arcmin, corresponding to a linear size of approximately 36 pc. These two molecules are not just distributed in or near the hot cores. The abundance of these two molecules seems to decrease from the cold outer region to the central region associated with star formation activity. Results presented here suggest that these two molecules are likely to form through a low temperature process. Recent theoretical and experimental studies demonstrated that prebiotic molecules can be efficiently formed in icy grain mantles through several pathways. However, these complex ice features cannot be directly observed, and most constraints on the ice compositions come from millimeter observations of desorbed ice chemistry products. These results, combined with laboratory studies, strongly support the existence of abundant prebiotic molecules in ices. [ABSTRACT FROM AUTHOR]

We have compiled a sample of 26 metal-poor galaxies with 12 + log(O/H) < 8.1 with both infrared continuum and 1.4 GHz radio continuum data. By comparing to galaxies at higher metallicity, we have investigated the IR–radio relationship’s dependence on metallicity at the 24, 70, 100, and 160 μm bands, as well as the integrated FIR luminosity. It is found that metal-poor galaxies have on average lower than metal-rich ones, with larger offsets at longer IR wavelengths, from −0.06 dex in to −0.6 dex in . The of all galaxies as a whole at 160 μm show positive trends with the metallicity and IR-to-FUV ratio and negative trends with the IR color, while those at lower IR wavelengths show weaker correlations. We propose a mechanism that invokes the combined effects of low obscured-SFR-to-total-SFR fraction and warm dust temperature at low metallicity to interpret the above behavior of , with the former reducing the IR radiation and the latter further reducing the IR emission at longer IR wavelengths. Other mechanisms that are related to the radio emission, including the enhanced magnetic field strength and increased thermal radio contribution, are unable to reconcile the IR-wavelength-dependent differences of between metal-poor and metal-rich galaxies. In contrast to , the mean total-SFR-to-radio ratio of metal-poor galaxies is the same as that for metal-rich galaxies, indicating the 1.4 GHz radio emission is still an effective tracer of SFRs at low metallicity. [ABSTRACT FROM AUTHOR]

We present 2.5-square-degree C2H N = 1–0 and N2H+J = 1–0 maps of the ρ Ophiuchi molecular cloud complex. These are the first large-scale maps of the ρ Ophiuchi molecular cloud complex with these two tracers. The C2H emission is spatially more extended than the N2H+ emission. One faint N2H+ clump, Oph-M, and one C2H ring, Oph-RingSW, are identified for the first time. The observed C2H-to-N2H+ abundance ratio ([C2H]/[N2H+]) varies between 5 and 110. We modeled the C2H and N2H+ abundances with 1D chemical models, which show a clear decline of [C2H]/[N2H+] with chemical age. Such an evolutionary trend is little affected by temperatures when they are below 40 K. At high density (nH > 105 cm−3), however, the time it takes for the abundance ratio to drop at least one order of magnitude becomes less than the dynamical time (e.g., turbulence crossing time of ∼105 yr). The observed [C2H]/[N2H+] difference between L1688 and L1689 can be explained by L1688 having chemically younger gas in relatively less dense regions. The observed [C2H]/[N2H+] values are the results of time evolution, accelerated at higher densities. For the relatively low density regions in L1688 where only C2H emission was detected, the gas should be chemically younger. [ABSTRACT FROM AUTHOR]

We report Shanghai Tian Ma Radio Telescope (TMRT) detections of several long carbon-chain molecules in the C and Ku bands, including HC3N, HC5N, HC7N, HC9N, C3S, C6H, and C8H toward the starless cloud Serpens South 1a. We detected some transitions (HC9N J = 13–12, F = 12–11, and F = 14–13; H13CCCN J = 2–1, F = 1–0, and F = 1–1; HC13CCN J = 2–1, F = 2–2, F = 1–0, and F = 1–1; HCC13CN J = 2–1, F = 1–0, and F = 1–1) and resolved some hyperfine components (HC5N J = 6–5, F = 5–4; H13CCCN J = 2–1, F = 2–1) for the first time in the interstellar medium. The column densities of these carbon-chain molecules in the range 1012–1013 cm−2 are comparable to two carbon-chain molecule rich sources, TMC-1 and Lupus-1A. The abundance ratios are 1.00:(1.11 ± 0.15):(1.47 ± 0.18) for [H13CCCN]:[HC13CCN]:[HCC13CN]. This result implies that the 13C isotope is also concentrated in the carbon atom adjacent to the nitrogen atom in HC3N in Serpens South 1a, which is similar to TMC-1. The [HC3N]/[H13CCCN] ratio of 78 ± 9, the [HC3N]/[HC13CCN] ratio of 70 ± 8, and the [HC3N]/[HCC13CN] ratio of 53 ± 4 are also comparable to those in TMC-1. Serpens South 1a proves to be a suitable testing ground for understanding carbon-chain chemistry. [ABSTRACT FROM AUTHOR]

We studied the sulfur chemistry of massive star-forming regions through single-dish submillimeter spectroscopy. OCS, O13CS, 13CS, H2S, and SO transitions were observed toward a sample of massive star-forming regions with embedded UCH ii or CH ii regions. These sources could be divided into H ii-hot core and H ii-only sources based on their CH3CN emission. Our results show that the OCS line of thirteen sources is optically thick, with optical depth ranging from 5 to 16. Column densities of these molecules were computed under LTE conditions. CS column densities were also derived using its optically thin isotopologue 13CS. H2S is likely to be the most abundant gas-phase sulfuretted molecule in hot massive cores. Both the column density and abundance of sulfur-bearing molecules decrease significantly from H ii-hot core to H ii-only sources. Ages derived from hot core models appear to be consistent with star formation theories, suggesting that abundance ratios of [CS]/[SO], [SO]/[OCS], and [OCS]/[CS] could be used as chemical clocks in massive star-forming regions. [ABSTRACT FROM AUTHOR]