• The 12C/ 13C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

      Halfen, D. T.; Woolf, N. J.; Ziurys, L. M.; Univ Arizona, Dept Chem & Biochem; Univ Arizona, Dept Astron, Arizona Radio Observ (IOP PUBLISHING LTD, 2017-08-22)
      A study has been conducted of 12C/13C ratios in five complex molecules in the Galactic center. H2CS, CH3CCH, NH2CHO, CH2CHCN, and CH3CH2CN and their 13C-substituted species have been observed in numerous transitions at 1, 2, and 3 mm, acquired in a spectral-line survey of Sgr B2(N), conducted with the telescopes of the Arizona Radio Observatory (ARO). Between 22 and 54 individual, unblended lines for the 12C species and 2–54 for 13C-substituted analogs were modeled in a global radiative transfer analysis. All five molecules were found to consistently exhibit two velocity components near VLSR ∼ 64 and 73 km s−1, with column densities ranging from Ntot ∼ 3 × 1014 − 4 × 1017 cm−2 and ∼2 × 1013 − 1 × 1017 cm−2 for the 12C and 13C species, respectively. Based on 14 different isotopic combinations, ratios were obtained in the range 12C/13C = 15 ± 5 to 33 ± 13, with an average value of 24 ± 7, based on comparison of column densities. These measurements better anchor the 12C/13C ratio at the Galactic center, and suggest a slightly revised isotope gradient of 12C/13C = 5.21(0.52) DGC + 22.6(3.3). As indicated by the column densities, no preferential 13C enrichment was found on the differing carbon sites of CH3CCH, CH2CHCN, and CH3CH2CN. Because of the elevated temperatures in Sgr B2(N), 13C isotopic substitution is effectively “scrambled,” diminishing chemical fractionation effects. The resulting ratios thus reflect stellar nucleosynthesis and Galactic chemical evolution, as is likely the case for most warm clouds.
    • ALMA Observations of Fragmentation, Substructure, and Protostars in High-mass Starless Clump Candidates

      Svoboda, Brian E.; Shirley, Yancy L.; Traficante, Alessio; Battersby, Cara; Fuller, Gary A.; Zhang, Qizhou; Beuther, Henrik; Peretto, Nicolas; Brogan, Crystal; Hunter, Todd; et al. (IOP PUBLISHING LTD, 2019-11-15)
      The initial physical conditions of high-mass stars and protoclusters remain poorly characterized. To this end, we present the first targeted ALMA Band 6 1.3 mm continuum and spectral line survey toward high-mass starless clump candidates, selecting a sample of 12 of the most massive candidates (4 x 10(2) M-circle dot less than or similar to Mcl less than or similar to 4 x 10(3) M-circle dot) within d(circle dot) < 5 kpc. The joint 12 + 7 m array maps have a high spatial resolution of.3000 au (0.015 pc,.syn 0.8) and have high point-source mass-completeness down to M >> 0.3 M. at 6srms (or 1srms column density sensitivity of N = 1.1 x 10(22) cm(-2)). We discover previously undetected signposts of low-luminosity star formation from CO J = 2 -> 1 and SiO J = 5 -> 4 bipolar outflows and other signatures toward 11 out of 12 clumps, showing that current MIR/FIR Galactic plane surveys are incomplete to low-and intermediate-mass protostars (L-bol less than or similar to 50 L-circle dot), and emphasizing the necessity of high-resolution follow-up. We compare a subset of the observed cores with a suite of radiative transfer models of starless cores. We find a high-mass starless core candidate with a model-derived mass consistent with 29(15)(52)M(circle dot) when integrated over size scales of R < 2 x 10(4) au. Unresolved cores are poorly fit by radiative transfer models of externally heated Plummer density profiles, supporting the interpretation that they are protostellar even without detection of outflows. A high degree of fragmentation with rich substructure is observed toward 10 out of 12 clumps. We extract sources from the maps using a dendrogram to study the characteristic fragmentation length scale. Nearest neighbor separations, when corrected for projection with Monte Carlo random sampling, are consistent with being equal to the clump average thermal Jeans length (lambda(j,th); i.e., separations equal to 0.4-1.6 x lambda(j,th)). In the context of previous observations that, on larger scales, see separations consistent with the turbulent Jeans length or the cylindrical thermal Jeans scale (approximate to 3-4 x lambda(j, th)), our findings support a hierarchical fragmentation process, where the highest-density regions are not strongly supported against thermal gravitational fragmentation by turbulence or magnetic fields.
    • An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud. II. CCS and HC7N Chemistry and Three Modes of Star Formation in the Filaments

      Seo, Young Min; Majumdar, Liton; Goldsmith, Paul F.; Shirley, Yancy L.; Willacy, Karen; Ward-Thompson, Derek; Friesen, Rachel; Frayer, David; Church, Sarah E.; Chung, Dongwoo; et al. (IOP PUBLISHING LTD, 2019-02-01)
      We present deep CCS and HC7N observations of the L1495-B218 filaments in the Taurus molecular cloud obtained using the K-band focal plane array on the 100 m Green Bank Telescope. We observed the L1495-B218 filaments in CCS J(N) = 2(1)-1(0) and HC7N J = 21-20 with a spectral resolution of 0.038 km s(-1) and an angular resolution of 31" We observed strong CCS emission in both evolved and young regions and weak emission in two evolved regions. HC7N emission is observed only in L1495A-N and L1521D. We find that CCS and HC7N intensity peaks do not coincide with NH3 or dust continuum intensity peaks. We also find that the fractional abundance of CCS does not show a clear correlation with the dynamical evolutionary stage of dense cores. Our findings and chemical modeling indicate that the fractional abundances of CCS and HC7N are sensitive to the initial gas-phase C/O ratio, and they are good tracers of young condensed gas only when the initial C/O is close to solar value. Kinematic analysis using multiple lines, including NH3, HC7N, CCS, CO, HCN, and HCO+, suggests that there may be three different star formation modes in the L1495-B218 filaments. At the hub of the filaments, L1495A/B7N has formed a stellar cluster with large-scale inward flows (fast mode), whereas L1521D, a core embedded in a filament, is slowly contracting because of its self-gravity (slow mode). There is also one isolated core that appears to be marginally stable and may undergo quasi-static evolution (isolated mode).

      Bieging, John H.; Patel, Saahil; Peters, William L.; Toth, L. Viktor; Marton, Gábor; Zahorecz, Sarolta; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2016-09-26)
      We present the results of a program to map the Sh2-235 molecular cloud complex in the CO and (CO)-C-13 J = 2 - 1 transitions using the Heinrich Hertz Submillimeter Telescope. The map resolution is 38 '' (FWHM), with an rms noise of 0.12K brightness temperature, for a velocity resolution of 0.34 km s(-1). With the same telescope, we also mapped the CO J = 3 - 2 line at a frequency of 345 GHz, using a 64 beam focal plane array of heterodyne mixers, achieving a typical rms noise of 0.5 K brightness temperature with a velocity resolution of 0.23 km s(-1). The three spectral line data cubes are available for download. Much of the cloud appears to be slightly sub-thermally excited in the J = 3 level, except for in the vicinity of the warmest and highest column density areas, which are currently forming stars. Using the CO and (CO)-C-13. J = 2 - 1 lines, we employ an LTE model to derive the gas column density over the entire mapped region. Examining a 125 pc(2). region centered on the most active star formation in the vicinity of Sh2-235, we find that the young stellar object surface density scales as approximately the 1.6-power of the gas column density. The area distribution function of the gas is a steeply declining exponential function of gas column density. Comparison of the morphology of ionized and molecular gas suggests that the cloud is being substantially disrupted by expansion of the H II regions, which may be triggering current star formation.
    • The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds. VI. The Cep OB3 Cloud (Cepheus B and C) in CO J=2-1, (CO)-C-13 J=2-1, and CO J=3-2

      Bieging, John H.; Patel, Saahil; Hofmann, Ryan; Peters, William L.; Kainulainen, Jouni; Zhang, Miaomiao; Stutz, Amelia M.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10)
      We present (1) new fully sampled maps of CO and (CO)-C-13 J = 2-1 emission and CO J = 3-2 emission toward the molecular clouds Cep B and C, associated with the Cep OB3 association; (2) a map of extinction, A(V), derived from IR colors of background stars; and (3) the distribution of young stellar objects (YSOs) over the same field as the molecular maps. An LTE analysis of the CO and (CO)-C-13. maps yields the distribution of molecular column densities and temperatures. Substantial variations are evident across the clouds; smaller subregions show correlations between molecular properties and dust extinction, consistent with a picture of outer photodissociation regions with a layer of CO-dark molecular gas, a CO self-shielded interior, and an inner cold dense region where CO is largely depleted onto grains. Comparing the distribution of YSOs with molecular gas surface density shows a power-law relation very similar in slope to that for the giant molecular cloud associated with the H II region Sh2-235 from a previous paper in this series that employed the same methodology. We note the presence of several compact, isolated CO emission sources in the J = 3-2 maps. The gas temperature and (CO)-C-13. velocity dispersion yield a map of the sonic Mach number, which varies across the cloud but always exceeds unity, confirming the pervasiveness of supersonic turbulence over length scales greater than or similar to 0.1 pc (the map resolution). We also compute a J = 2-1 CO X-factor that varies with position but is, on average, within. 20% of the Galactic average derived from CO J = 1-0 observations.

      Svoboda, Brian E.; Shirley, Yancy L.; Battersby, Cara; Rosolowsky, Erik W.; Ginsburg, Adam G.; Ellsworth-Bowers, Timothy P.; Pestalozzi, Michele R.; Dunham, Miranda K.; Evans II, Neal J.; Bally, John; et al. (IOP PUBLISHING LTD, 2016-05-05)
      We sort 4683 molecular clouds between 10 degrees < l < 65 degrees from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 mu m sources, mid-IR color-selected YSOs, H2O and CH3OH masers, and UCH II. regions. We also present a combined NH3-derived gas kinetic temperature and H2O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial (alpha similar to 0.7) with >75% of clumps with known distance being gravitationally bound (alpha < 2). These samples show a statistically significant increase in the median clump mass of Delta M similar to 170-370 M-circle dot from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at (M) over dot similar to 200-440 M-circle dot Myr(-1) for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii). a variation in the ratio of starless to protostellar clump lifetime that scales as similar to M-0.4. By comparing to the observed number of CH3OH maser containing clumps, we estimate the phase. lifetime of massive (M > 10(3) M-circle dot) starless clumps to be 0.37 +/- 0.08 Myr (M/10(3) M-circle dot)(-1); the majority (M < 450 M-circle dot) have phase. lifetimes longer than their average freefall time.
    • CO (J = 1–0) Observations toward Filamentary Molecular Clouds in the Galactic Region with l = [169.°75, 174.°75], b = [−0.°75, 0.°5]

      Xiong, Fang; Chen, Xuepeng; Zhang, Qizhou; Yang, Ji; Fang, Min; Zhang, Miaomiao; Guo, Weihua; Sun, Li; Univ Arizona, Dept Astron (IOP PUBLISHING LTD, 2019-07-30)
      We present observations of the CO isotopologues (12CO, 13CO, and C18O) toward the Galactic region with 169fdg75 ≤ l ≤ 174fdg75 and −0fdg75 ≤ b ≤ 0fdg5 using the Purple Mountain Observatory 13.7 m millimeter-wavelength telescope. Based on the 13CO (J = 1 − 0) data, we find five molecular clouds within the velocity range between −25 and 8 km s−1 that are all characterized by conspicuous filamentary structures. We have identified eight filaments with a length of 6.38–28.45 pc, a mean H2 column density of 0.70 × 1021–6.53 × 1021 cm−2, and a line mass of 20.24–161.91 M ☉ pc−1, assuming a distance of ~1.7 kpc. Gaussian fittings to the inner parts of the radial density profiles lead to a mean FWHM width of 1.13 ± 0.01 pc. The velocity structures of most filaments present continuous distributions with slight velocity gradients. We find that turbulence is the dominant internal pressure to support the fragmentation of filaments instead of thermal pressure. Most filaments have virial parameters smaller than 2; thus, they are gravitationally bound. Four filaments have an LTE line mass close to the virial line mass. We further extract dense clumps using the 13CO data and find that 64% of the clumps are associated with the filaments. According to the complementary IR data, most filaments have associated Class II young stellar objects. Class I objects are mainly found to be located in the filaments with a virial parameter close to 1. Within two virialized filaments, 12CO outflows have been detected, indicating ongoing star-forming activity therein.

      Keating, Garrett K.; Marrone, Daniel P.; Bower, Geoffrey C.; Leitch, Erik; Carlstrom, John E.; DeBoer, David R.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2016-10-07)
      We present a measurement of the abundance of carbon monoxide in the early universe, utilizing the final results from the CO Power Spectrum Survey (COPSS). Between 2013 and 2015, we performed observations with the Sunyaev-Zel'dovich Array to measure aggregate CO emission from z similar to 3 galaxies with the intensity mapping technique. Data were collected on 19 fields, covering an area of 0.7 square degrees, over the frequency range 27-35 GHz. With these data, along with data analyzed in COPSS I, we are able to observe the CO(1-0) transition within the redshift range z = 2.3-3.3 for spatial frequencies between k = 0.5-10 h Mpc(-1), spanning a comoving volume of 4.9 x 10(6) h(-3) Mpc(3). We present estimates of contributions from continuum sources and ground illumination within our measurement. We constrain the amplitude of the CO power spectrum to P-CO = 3.0(-1.3)(+1.3) x 10(3) mu K-2(h(-1) Mpc)(3), or Delta(2)(CO)(k=1 h Mpc(-1)) = 1.5(-0.7)(+0.7) x 10(3) mu K-2, at 68% confidence, and PCO > 0 at 98.9% confidence. These results are a factor of 10 improvement in sensitivity compared to those of COPSS I. With this measurement, we constrain on the CO(1-0) galaxy luminosity function at z similar to 3. Assuming that CO emission is proportional to halo mass and using theoretical estimates of the scatter in this relationship, we constrain the ratio of CO(1-0) luminosity to halo mass to A(CO) = 6.3(-2.1)(+1.4) x 10 (7) L circle dot M circle dot-1. Assuming a Milky Way-like linear relationship between CO luminosity and molecular gas mass, we estimate a mass fraction of molecular gas of f(H2) = 5.5(-2.2)(+3.4) x 10(-2) for halos with masses of similar to 10(12)M(circle dot). Using theoretical estimates for the scaling of molecular gas mass fraction and halo mass, we estimate the cosmic molecular gas density to be rho(z similar to 3) (H-2) = 1.1(-0.4)(+0.7) x 10(8) M(circle dot)Mpc(-3).
    • Deep millimeter spectroscopy observations toward NGC 1068

      Qiu, Jianjie; Wang, Junzhi; Shi, Yong; Zhang, Jiangshui; Fang, Min; Li, Fei; Univ Arizona, Dept Astron (EDP SCIENCES S A, 2018-05-15)
      Aims. We aim for a better understanding of gas properties in the circum-nuclear disk (CND) region of the nearby gas-rich Seyfert 2 galaxy NGC 1068. We focus on line identification and the basic physical parameters estimation of molecular gas in the CND region. Methods. We used the IRAM 30 m telescope to conduct deep millimeter spectroscopy observations toward the center of NGC 1068. Results. Thirty-two lines were detected in this galaxy, 15 lines of wich were detected for the first time. With a sensitivity better by about a factor of 4 than observations in the literature for this source at 3 mm band, we detected several weak lines for the first time in this source, such as lines from CH3CCH, CH3OCH3, and (HCO+)-O-18. Column densities of these molecules were estimated based on line emissions. Some marginal detections in the literature, such as (HNC)-C-13 (1-0), were confirmed. CH3OCH3 was detected for the first time in external galaxies. Lines from several carbon chain molecules and shock-related molecules were also detected in this source.
    • Deuteration of ammonia in the starless core Ophiuchus/H-MM1

      Harju, J.; Daniel, F.; Sipilae, O.; Caselli, P.; Pineda, J. E.; Friesen, R. K.; Punanova, A.; Guesten, R.;; Wiesenfeld, L.; Myers, P. C.; et al. (EDP SCIENCES S A, 2017-03-30)
      Context. Ammonia and its deuterated isotopologues probe physical conditions in dense molecular cloud cores. The time-dependence of deuterium fractionation and the relative abundances of different nuclear spin modifications are supposed to provide a means of determining the evolutionary stages of these objects. Aims. We aim to test the current understanding of spin-state chemistry of deuterated species by determining the abundances and spin ratios of NH2D, NHD2 and ND3 in a quiescent, dense cloud. Methods. Spectral lines of NH3, NH2D, NHD2, ND3 and N2D+ were observed towards a dense, starless core in Ophiuchus with the APEX, GBT and IRAM 30-m telescopes. The observations were interpreted using a gas-grain chemistry model combined with radiative transfer calculations. The chemistry model distinguishes between the different nuclear spin states of light hydrogen molecules, ammonia and their deuterated forms. Different desorption schemes can be considered. Results. High deuterium fractionation ratios with NH2D = NH3 similar to 0 : 4, NHD2 = NH2D similar to 0 : 2 and ND3 = NHD2 similar to 0 : 06 are found in the core. The observed ortho/para ratios of NH2D and NHD2 are close to the corresponding nuclear spin statistical weights. The chemistry model can approximately reproduce the observed abundances, but consistently predicts too low ortho/para-NH2D, and too large ortho/para-NHD2 ratios. The longevity of N2H+ and NH3 in dense gas, which is prerequisite to their strong deuteration, can be attributed to the chemical inertia of N-2 on grain surfaces. Conclusions. The discrepancies between the chemistry model and the observations are likely to be caused by the fact that the model assumes complete scrambling in principal gas-phase deuteration reactions of ammonia, which means that all the nuclei are mixed in reactive collisions. If, instead, these reactions occur through proton hop/hydrogen abstraction processes, statistical spin ratios are to be expected. The present results suggest that while the deuteration of ammonia changes with physical conditions and time, the nuclear spin ratios of ammonia isotopologues do not probe the evolutionary stage of a cloud.
    • Exotic Carbon Chemistry in a Planetary Nebula: The Unusual Case of K4-47

      Schmidt, D. R.; Ziurys, L. M.; Univ Arizona, Dept Chem & Biochem; Univ Arizona, Dept Astron & Steward Observ (IOP PUBLISHING LTD, 2019-08-20)
      Millimeter molecular line observations have been conducted toward the young (similar to 900 yr) bipolar planetary nebula (PN) K4-47, using the 12 m antenna and the Submillimeter Telescope of the Arizona Radio Observatory, and the Institut de Radioastronomie Millimetrique 30 m Telescope. Measurements at 1, 2, and 3 mm of multiple transitions were carried out to ensure the accuracy of all molecular identifications. K4-47 was found to be unusually chemically rich, containing three complex species, CH3CN, H2CNH, and CH3CCH, which have never before been observed in a planetary nebula. In addition, HC3N, N2H+, H2CO, c-C3H2, and SiO have been identified in this object, as well as a variety of C-13-substituted isotopologues ((H2CO)-C-13, c-(CCCH2)-C-13, c-(CCCH2)-C-13, (CH3CN)-C-13, (CH3CN)-C-13, (CH3CCH)-C-13, and (CH3CCH)-C-13), including all three doubly C-13-substituted varieties of HC3N-the first known object in which all three species have been detected. After CO and H-2, the most abundant molecules in K4-47 are CCH and CN, which have abundances of f similar to 8 x 10(-7), relative to molecular hydrogen. Surprisingly, the next most abundant molecule is CH 3 CCH, which has f similar to 6 x 10(-7), followed by HCN with an abundance of similar to 5 x 10(-7). The results suggest that K4-47 is the most chemically complex planetary nebula currently known. The molecular content of K4-47 closely resembles that of the C-star IRC+10216, but with lower abundances, except for HCO+, H2CO, and CH3CCH. The PN also chemically and morphologically resembles the bipolar protoplanetary nebula CRL 618, with similar enrichments of C-13, N-15, and O-17, suggestive of an explosive process at the end of the asymptotic giant branch.
    • Formation of Interstellar C60 from Silicon Carbide Circumstellar Grains

      Bernal, J. J.; Haenecour, P.; Howe, J.; Zega, T. J.; Amari, S.; Ziurys, L. M.; Univ Arizona, Dept Chem & Biochem; Univ Arizona, Lunar & Planetary Lab; Univ Arizona, Dept Mat Sci & Engn; Univ Arizona, Steward Observ, Dept Astron; et al. (IOP PUBLISHING LTD, 2019-10-01)
      We have conducted laboratory experiments with analog crystalline silicon carbide (SiC) grains using transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). The 3C polytype of SiC was used—the type commonly produced in the envelopes of asymptotic giant branch (AGB) stars. We rapidly heated small (~50 nm) synthetic SiC crystals under vacuum to ~1300 K and bombarded them with 150 keV Xe ions. TEM imaging and EELS spectroscopic mapping show that such heating and bombardment leaches silicon from the SiC surface, creating layered graphitic sheets. Surface defects in the crystals were found to distort the six-membered rings characteristic of graphite, creating hemispherical structures with diameters matching that of C60. Such nonplanar features require the formation of five-membered rings. We also identified a circumstellar grain, preserved inside the Murchison meteorite, that contains the remnant of an SiC core almost fully encased by graphite, contradicting long-standing thermodynamic predictions of material condensation. Our combined laboratory data suggest that C60 can undergo facile formation from shock heating and ion bombardment of circumstellar SiC grains. Such heating/bombardment could occur in the protoplanetary nebula phase, accounting for the observation of C60 in these objects, in planetary nebulae (PNs) and other interstellar sources receiving PN ejecta. The synthesis of C60 in astronomical sources poses challenges, as the assembly of 60 pure carbon atoms in an H-rich environment is difficult. The formation of C60 from the surface decomposition of SiC grains is a viable mechanism that could readily occur in the heterogeneous, hydrogen-dominated gas of evolved circumstellar shells.

      Barnes, Peter J.; Hernandez, Audra K.; O’Dougherty, Stefan N.; Schap III, William J.; Muller, Erik; Univ Arizona, Coll Opt Sci (IOP PUBLISHING LTD, 2016-10-27)
      We report the second complete molecular line data release from the Census of High-and Medium-mass Protostars (CHaMP), a large-scale, unbiased, uniform mapping survey at sub-parsec resolution, of millimeter-wave line emission from 303 massive, dense molecular clumps in the Milky Way. This release is for all (CO)-C-12 J = 1 -> 0 emission associated with the dense gas, the first from Phase II of the survey, which includes (CO)-C-12, (CO)-C-13, and (CO)-O-18. The observed clump emission traced by both (CO)-C-12 and HCO+ (from Phase I) shows very similar morphology, indicating that, for dense molecular clouds and complexes of all sizes, parsec-scale clumps contain. similar to 75% of the mass, while only 25% of the mass lies in extended (>10 pc) or "low density" components in these same areas. The mass fraction of all gas above a density of 10(9) m(-3) is xi(9) greater than or similar to 50%. This suggests that parsec-scale clumps may be the basic building blocks of the molecular interstellar medium, rather than the standard GMC concept. Using (CO)-C-12 emission, we derive physical properties of these clumps in their entirety, and compare them to properties from HCO+, tracing their denser interiors. We compare the standard X-factor converting I (CO)-C-12 to N-H2 with alternative conversions, and show that only the latter give whole-clump properties that are physically consistent with those of their interiors. We infer that the clump population is systematically closer to virial equilibrium than when considering only their interiors, with perhaps half being long-lived (10s of Myr), pressure-confined entities that only terminally engage in vigorous massive star formation, supporting other evidence along these lines that was previously published.
    • High-resolution Near-IR Spectral Mapping with H-2 and [Fe II] Lines of Multiple Outflows around LkH alpha 234

      Oh, Heeyoung; Pyo, Tae-Soo; Koo, Bon-Chul; Yuk, In-Soo; Kaplan, Kyle F.; Lee, Yong-Hyun; Sokal, Kimberly R.; Mace, Gregory N.; Park, Chan; Lee, Jae-Joon; et al. (IOP PUBLISHING LTD, 2018-05)
      We present a high-resolution, near-IR spectroscopic study of multiple outflows in the LkH alpha 234 star formation region using the Immersion GRating INfrared Spectrometer (IGRINS). Spectral mapping over the blueshifted emission of HH 167 allowed us to distinguish at least three separate, spatially overlapped outflows in H-2 and [Fe II] emission. We show that the H-2 emission represents not a single jet but rather complex multiple outflows driven by three known embedded sources: MM1, VLA 2, and VLA 3. There is a redshifted H-2 outflow at a low velocity, V-LSR < +50 km s(-1), with respect to the systemic velocity of V-LSR = -11.5 km s(-1), that coincides with the H2O masers seen in earlier radio observations 2 '' southwest of VLA 2. We found that the previously detected [Fe II] jet with vertical bar V-LSR vertical bar > 100 km s(-1) driven by VLA 3B is also detected in H-2 emission and confirm that this jet has a position angle of about 240 degrees. Spectra of the redshifted knots at 14 ''-65 '' northeast of LkH alpha 234 are presented for the first time. These spectra also provide clues to the existence of multiple outflows. We detected high-velocity (50-120 km s(-1)) H-2 gas in the multiple outflows around LkH alpha 234. Since these gases move at speeds well over the dissociation velocity (> 40 km s(-1)), the emission must originate from the jet itself rather than H-2 gas in the ambient medium. Also, position-velocity and excitation diagrams indicate that emission from knot C in HH 167 comes from two different phenomena, shocks and photodissociation.
    • Imaging the molecular interstellar medium in a gravitationally lensed star-forming galaxy at z = 5.7

      Apostolovski, Yordanka; Aravena, Manuel; Anguita, Timo; Spilker, Justin; Weiß, Axel; Béthermin, Matthieu; Chapman, Scott C.; Chen, Chian-Chou; Cunningham, Daniel; De Breuck, Carlos; et al. (EDP SCIENCES S A, 2019-07-30)
      Aims. We present and study spatially resolved imaging obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of multiple (CO)-C-12(J = 6-5, 8-7, and 9-8) and two H2O(2(02)-1(11) and 2(11)-2(02)) emission lines and cold dust continuum toward the gravitationally lensed dusty star-forming galaxy SPT 0346-52 at z = 5.656. Methods. Using a visibility-domain source-plane reconstruction we probe the structure and dynamics of the different components of the interstellar medium (ISM) in this galaxy down to scales of 1 kpc in the source plane. Results. Measurements of the intrinsic sizes of the different CO emission lines indicate that the higher J transitions trace more compact regions in the galaxy. Similarly, we find smaller dust continuum intrinsic sizes with decreasing wavelength, based on observations at rest frame 130, 300, and 450 mu m. The source shows significant velocity structure, and clear asymmetry where an elongated structure is observed in the source plane with significant variations in their reconstructed sizes. This could be attributed to a compact merger or turbulent disk rotation. The differences in velocity structure through the different line tracers, however, hint at the former scenario in agreement with previous [CII] line imaging results. Measurements of the CO line ratios and magnifications yield significant variations as a function of velocity, suggesting that modeling of the ISM using integrated values could be misinterpreted. Modeling of the ISM in SPT 0346-52 based on delensed fluxes indicates a highly dense and warm medium, qualitatively similar to that observed in high-redshift quasar hosts.
    • Inflow Motions Associated with High-mass Protostellar Objects

      Yoo, Hyunju; Kim, Kee-Tae; Cho, Jungyeon; Choi, Minho; Wu, Jingwen; Evans, Neal J., II; Ziurys, L. M.; Univ Arizona, Dept Astron; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-04-02)
      We performed a molecular line survey of 82 high-mass protostellar objects in a search for inflow signatures associated with high-mass star formation. Using the (HCO+)-C-13 (1-0) line as an optically thin tracer, we detected a statistically significant excess of blue asymmetric line profiles in the HCO+ (1-0) transition, but nonsignificant excesses in the HCO+ (3-2) and H2CO (2(12)-1(11)) transitions. The negative blue excess for the HCN (3-2) transition suggests that the line profiles are affected by dynamics other than inflow motion. The HCO+ (1-0) transition thus seems to be the suitable tracer of inflow motions in high-mass star-forming regions, as previously suggested. We found 27 inflow candidates that have at least 1 blue asymmetric profile and no red asymmetric profile, and derived the inflow velocities to be 0.23-2.00 km s(-1) for 20 of them using a simple two-layer radiative transfer model. Our sample is divided into two groups in different evolutionary stages. The blue excess of the group in relatively earlier evolutionary stages was estimated to be slightly higher than that of the other in the HCO+ (1-0) transition.
    • Line Ratios Reveal N2H+ Emission Originates above the Midplane in TW Hydrae

      Schwarz, Kamber R.; Teague, Richard; Bergin, Edwin A.; Univ Arizona, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2019-05-03)
      Line ratios for different transitions of the same molecule have long been used as a probe of gas temperature. Here we use ALMA observations of the N2H+ J= 1-0 and J = 4-3 lines in the protoplanetary disk around TW Hya to derive the temperature at which these lines emit. We find an averaged temperature of 39 K with a 1 sigma uncertainty of 2 K for the radial range 0.'' 8-2 '', which is significantly warmer than the expected midplane temperature beyond 0 ''.5 in this disk. We conclude that the N2H+ emission in TW Hya is not emitting from near the midplane, but rather from higher in the disk, in a region likely bounded by processes such as photodissociation or chemical reprocessing of CO and N-2 rather than freeze-out.
    • Mapping observations of complex organic molecules around Sagittarius B2 with the ARO 12 m telescope

      Li, Juan; Wang, Junzhi; Qiao, Haihua; Quan, Donghui; Fang, Min; Du, Fujun; Li, Fei; Shen, Zhiqiang; Li, Shanghuo; Li, Di; et al. (OXFORD UNIV PRESS, 2020-01-04)
      We have performed high-sensitivity mapping observations of several complex organic molecules around Sagittarius B2 with the ARO 12 m telescope at 3 mm wavelength. Based on their spatial distribution, molecules can be classified as either 'extended', those detected not only in Sgr B2(N) and Sgr B2(M), or 'compact', those only detected toward or near Sgr B2(N) and Sgr B2(M). The 'extended' molecules include glycolaldehyde (CH2OHCHO), methyl formate (CH3OCHO), formic acid (t-HCOOH), ethanol (C2H5OH) and methyl amine (CH3NH2), while the 'compact' molecules include dimethyl ether (CH3OCH3), ethyl cyanide (C2H5CN), and amino acetonitrile (H2NCH2CN). These 'compact' molecules are likely produced under strong UV radiation, while the 'extended' molecules are likely formed at low temperatures, via gas-phase or grain-surface reactions. The spatial distribution of 'warm' CH2OHCHO at 89 GHz differs from the spatial distribution of 'cold' CH2OHCHO observed at 13 GHz. We found evidence for an overabundance of CH2OHCHO compared to that expected from the gas-phase model, which indicates that grain-surface reactions are necessary to explain the origin of CH2OHCHO in Sagittarius B2. Grain-surface reactions are also needed to explain the correlation between the abundances of 'cold' CH2OHCHO and C2H5OH. These results demonstrate the importance of grain-surface chemistry in the production of complex organic molecules.
    • Metals and dust content across the galaxies M 101 and NGC 628

      Vílchez, J M; Relaño, M; Kennicutt, R; De Looze, I; Mollá, M; Galametz, M; Univ Arizona, Steward Observ (OXFORD UNIV PRESS, 2019-03)
      We present a spatially resolved study of the relation between dust and metallicity in the nearby spiral galaxies M 101 (NGC 5457) and NGC 628 (M 74). We explore the relation between the chemical abundances of their gas and stars with their dust content and their chemical evolution. The empirical spatially resolved oxygen effective yield and the gas-to-dust mass ratio (GDR) across both disc galaxies are derived, sampling 1 dex in oxygen abundance. We find that the metal budget of the NGC 628 disc and most of the M 101 disc appears consistent with the predictions of the simple model of chemical evolution for an oxygen yield between half and one solar, whereas the outermost region (R >= 0.8 R-2(5)) of M 101 presents deviations suggesting the presence of gas flows. The GDR-metallicity relation shows a two slopes behaviour, with a break at 12 + log(O/H)P approximate to 8.4, a critical metallicity predicted by theoretical dust models when stardust production equals grain growth. A relation between GDR and the fraction of molecular to total gas, Sigma(H)(2)/Sigma(gas) is also found. We suggest an empirical relationship between GDR and the combination of 12 + log(O/H), for metallicity, and Sigma(H)(2)/Sigma(gas), a proxy for the molecular clouds fraction. The GDR is closely related with metallicity at low abundance and with Sigma(H)(2)/Sigma(gas) for higher metallicities suggesting interstellar medium dust growth. The ratio Sigma(star)/Sigma(dust) correlates well with 12 + log(O/H) and strongly with log(N/O) in both galaxies. For abundances below the critical one, the( )'stardust'( )production gives us a constant value suggesting a stellar dust yield similar to the oxygen yield.

      Lincowski, A. P.; Halfen, D. T.; Ziurys, L. M.; Univ Arizona, Dept Chem & Biochem; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2016-12-01)
      Pure rotational spectra of the rare isotopologues of titanium oxide, (TiO)-Ti-46, (TiO)-Ti-47, (TiO)-Ti-49, and (TiO)-Ti-50, have been recorded using a combination of Fourier transform millimeter-wave (FTmmW) and millimeter/submillimeter direct absorption techniques in the frequency range 62-538 GHz. This study is the first complete spectroscopic characterization of these species in their X-3 Delta(r) ground electronic states. The isotopologues were created by the reaction of N2O or O-2 and titanium vapor, produced either by laser ablation or in a Broida-type oven, and observed in the natural Ti isotopic abundances. Between 10 and 11 rotational transitions J + 1 <-> J were measured for each species, typically in all 3 spin-orbit ladders Omega-1,2, and 3. For (TiO)-Ti-47 and (TiO)-Ti-49, hyperfine structure was resolved, originating from the titanium-47 and titanium-49 nuclear spins of I = 5/2 and 7/2, respectively. For the Omega = 1 and 3 components, the hyperfine structure was found to follow a classic Lande pattern, while that for Omega = 2 appeared to be perturbed, likely a result of mixing with the nearby isoconfigurational a(1)Delta state. The spectra were analyzed with a case (a) Hamiltonian, and rotational, spin-orbit, and spin-spin parameters were determined for each species, as well as magnetic hyperfine and electric quadrupole constants for the two molecules with nuclear spins. The most abundant species, (TiO)-Ti-48, has been detected in circumstellar envelopes. These measurements will enable other titanium isotopologues to be studied at millimeter wavelengths, providing Ti isotope ratios that can test models of nucleosynthesis.