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Register a new userEnhanced UV radiation and dense clumps in Mrk231s molecular outflow
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We present interferometric observations of the CN(1-0) line emission in Mrk231 and combine them with previous observations of CO and other H$_2$ gas tracers to study the physical properties of the massive molecular outflow. We find a strong boost of the CN/CO(1-0) line luminosity ratio in the outflow, which is unprecedented compared to any other known Galactic or extragalactic source. For the dense gas phase in the outflow traced by the HCN and CN emissions, we infer $rm X_{rm CN}equiv [CN]/[H_2] > X_{rm HCN}$ by at least a factor of three, with H$_2$ gas densities of $n_{rm H_2}sim10^{5-6}$ cm$^{-3}$. In addition, for the first time, we resolve narrow spectral features in the HCN(1-0) and HCO$^+$(1-0) high-velocity line wings tracing the dense phase of the outflow. The velocity dispersions of these spectral features, $sigma_vsim7-20$ km s$^{-1}$, are consistent with those of massive extragalactic giant molecular clouds detected in nearby starburst nuclei. The H$_2$ gas masses inferred from the HCN data are quite high, $M_{mol}sim0.3-5times10^8$ $M_{odot}$. Our results suggest that massive, denser molecular gas complexes survive embedded into the more diffuse H$_2$ phase of the outflow, and that the chemistry of such outflowing dense clouds is affected by enhanced UV radiation.
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The article deals with observations of star-forming regions S231-S235 in quasi-thermal lines of ammonia (NH$_3$), cyanoacetylene (HC$_3$N) and maser lines of methanol (CH$_3$OH) and water vapor (H$_2$O). S231-S235 regions is situated in the giant molecular cloud G174+2.5. We selected all massive molecular clumps in G174+2.5 using archive CO data. For the each clump we determined mass, size and CO column density. After that we performed observations of these clumps. We report about first detections of NH$_3$ and HC$_3$N lines toward the molecular clumps WB89 673 and WB89 668. This means that high-density gas is present there. Physical parameters of molecular gas in the clumps were estimated using the data on ammonia emission. We found that the gas temperature and the hydrogen number density are in the ranges 16-30 K and 2.8-7.2$times10^3$ cm$^{-3}$, respectively. The shock-tracing line of CH$_3$OH molecule at 36.2 GHz is newly detected toward WB89 673.
We compare the directions of molecular outflows of 62 low-mass Class 0 and I protostars in nearby (<450 pc) star-forming regions with the mean orientations of the magnetic fields on 0.05-0.5 pc scales in the dense cores/clumps where they are embedded. The magnetic field orientations were measured using the JCMT POL-2 data taken by the BISTRO-1 survey and from the archive. The outflow directions were observed with interferometers in the literature. The observed distribution of the angles between the outflows and the magnetic fields peaks between 15 and 35 degrees. After considering projection effects, our results could suggest that the outflows tend to be misaligned with the magnetic fields by 50+/-15 degrees in three-dimensional space and are less likely (but not ruled out) randomly oriented with respect to the magnetic fields. There is no correlation between the misalignment and the bolometric temperatures in our sample. In several sources, the small-scale (1000-3000 au) magnetic fields is more misaligned with the outflows than their large-scale magnetic fields, suggesting that the small-scale magnetic field has been twisted by the dynamics. In comparison with turbulent MHD simulations of core formation, our observational results are more consistent with models in which the energy densities in the magnetic field and the turbulence of the gas are comparable. Our results also suggest that the misalignment alone cannot sufficiently reduce the efficiency of magnetic braking to enable formation of the observed number of large Keplerian disks with sizes larger than 30-50 au.
Recent surveys of the Galactic plane in the dust continuum and CO emission lines reveal that large ($gtrsim 50$~pc) and massive ($gtrsim 10^5$~$M_odot$) filaments, know as giant molecular filaments (GMFs), may be linked to galactic dynamics and trace the mid-plane of the gravitational potential in the Milky Way. We have imaged one entire GMF located at $lsim$52--54$^circ$ longitude, GMF54 ($sim$68~pc long), in the empirical dense gas tracers using the HCN(1--0), HNC(1--0), HCO$^+$(1--0) lines, and their $^{13}$C isotopologue transitions, as well as the N$_2$H$^+$(1--0) line. We study the dense gas distribution, the column density probability density functions (N-PDFs) and the line ratios within the GMF. The dense gas molecular transitions follow the extended structure of the filament with area filling factors between 0.06 and 0.28 with respect to $^{13}$CO(1--0). We constructed the N-PDFs of H$_2$ for each of the dense gas tracers based on their column densities and assumed uniform abundance. The N-PDFs of the dense gas tracers appear curved in log-log representation, and the HCO$^+$ N-PDF has the largest log-normal width and flattest power-law slope index. Studying the N-PDFs for sub-regions of GMF54, we found an evolutionary trend in the N-PDFs that high-mass star forming and Photon-Dominate Regions (PDRs) have flatter power-law indices. The integrated intensity ratios of the molecular lines in GMF54 are comparable to those in nearby galaxies. In particular, the N$_2$H$^+$/$^{13}$CO ratio, which traces the dense gas fraction, has similar values in GMF54 and all nearby galaxies except ULIRGs.
Using APEX-1 and APEX-2 observations, we have detected and studied the rotational lines of the HC$_3$N molecule (cyanoacetylene) in the powerful outflow/hot molecular core G331.512-0.103. We identified thirty-one rotational lines at $J$ levels between 24 and 39; seventeen of them in the ground vibrational state $v$=0 (9 lines corresponding to the main C isotopologue and 8 lines corresponding to the $^{13}$C isotopologues), and fourteen in the lowest vibrationally excited state $v_7$=1. Using LTE-based population diagrams for the beam-diluted $v$=0 transitions, we determined $T_{rm exc}$=85$pm$4 K and $N$(HC$_3$N)=(6.9$pm$0.8)$times$10$^{14}$ cm$^{-2}$, while for the beam-diluted $v_7$=1 transitions we obtained $T_{rm exc}$=89$pm$10 K and $N$(HC$_3$N)=2$pm$1$times$10$^{15}$ cm$^{-2}$. Non-LTE calculations using H$_2$ collision rates indicate that the HC$_3$N emission is in good agreement with LTE-based results. From the non-LTE method we estimated $T_{rm kin}$ $simeq$90~K, $n$(H$_2$)$simeq$2$times$10$^7$~cm$^{-3}$ for a central core of 6 arcsec in size. A vibrational temperature in the range from 130~K to 145~K was also determined, values which are very likely lower limits. Our results suggest that rotational transitions are thermalized, while IR radiative pumping processes are probably more efficient than collisions in exciting the molecule to the vibrationally excited state $v_7$=1. Abundance ratios derived under LTE conditions for the $^{13}$C isotopologues suggest that the main formation pathway of HC$_3$N is ${rm C}_2{rm H}_2 + {rm CN} rightarrow {rm HC}_3{rm N} + {rm H}$.
We present a spatio-kinematical analysis of the CO~($J$=2$rightarrow$1) line emission, observed with the Atacama Large Millimter/submillimter Array (ALMA), of the outflow associated with the most massive core, ALMA1, in the 70 $mu$m dark clump G010.991$-$00.082. The position-velocity (P-V) diagram of the molecular outflow exhibits a peculiar $mathsf{S}$-shaped morphology that has not been seen in any other star forming region. We propose a spatio-kinematical model for the bipolar molecular outflow that consists of a decelerating high-velocity component surrounded by a slower component whose velocity increases with distance from the central source. The physical interpretation of the model is in terms of a jet that decelerates as it entrains material from the ambient medium, which has been predicted by calculations and numerical simulations of molecular outflows in the past. One side of the outflow is shorter and shows a stronger deceleration, suggesting that the medium through which the jet moves is significantly inhomogeneous. The age of the outflow is estimated to be $tau$$approx$1300 years, after correction for a mean inclination of the system of $approx$57$^{circ}$.
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