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L1157-mm powers a molecular outflow that is well-known for its shock-induced chemical activity in several hot-spots. We have studied the molecular emission toward L1157-mm searching for a jet component responsible for these spots. We used the IRAM 30m telescope to observe the vicinity of L1157-mm in several lines of SiO. The SiO(5-4) and SiO(6-5) spectra toward L1157-mm present blue and red detached components about 45 km/s away from the ambient cloud. These extremely high-velocity (EHV) components are similar to those found in the L1448 and IRAS 04166+2706 outflows, and probably arise from a molecular jet driven by L1157-mm. Observations of off-center positions indicate that the jet is unresolved in SiO(5-4) (<11). The EHV jet seen in SiO probably excites L1157-B1 and the other chemically active spots of the L1157 outflow.
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We present a multiline CS survey towards the brightest bow-shock B1 in the prototypical chemically active protostellar outflow L1157. We made use of (sub-)mm data obtained in the framework of the Chemical HErschel Surveys of Star forming regions (CHESS) and Astrochemical Surveys at IRAM (ASAI) key science programs. We detected $^{12}$C$^{32}$S, $^{12}$C$^{34}$S, $^{13}$C$^{32}$S, and $^{12}$C$^{33}$S emissions, for a total of 18 transitions, with $E_{rm u}$ up to $sim$ 180 K. The unprecedented sensitivity of the survey allows us to carefully analyse the line profiles, revealing high-velocity emission, up to 20 km s$^{-1}$ with respect to the systemic. The profiles can be well fitted by a combination of two exponential laws that are remarkably similar to what previously found using CO. These components have been related to the cavity walls produced by the $sim$ 2000 yr B1 shock and the older ($sim$ 4000 yr) B2 shock, respectively. The combination of low- and high-excitation CS emission was used to properly sample the different physical components expected in a shocked region. Our CS observations show that this molecule is highlighting the dense, $n_{rm H_2}$ = 1--5 $times$ 10$^{5}$ cm$^{-3}$, cavity walls produced by the episodic outflow in L1157. In addition, the highest excitation (E$_u$ $geq$ 130 K) CS lines provide us with the signature of denser (1--5 $times$ 10$^{6}$ cm$^{-3}$) gas, associated with a molecular reformation zone of a dissociative J-type shock, which is expected to arise where the precessing jet impacting the molecular cavities. The CS fractional abundance increases up to $sim$ 10$^{-7}$ in all the kinematical components. This value is consistent with what previously found for prototypical protostars and it is in agreement with the prediction of the abundances obtained via the chemical code Astrochem.
The isocyanic acid (HNCO) presents an extended distribution in the centers of the Milky Way and the spiral galaxy IC342. Based on the morphology of the emission and the HNCO abundance with respect to H2, several authors made the hypothesis that HNCO could be a good tracer of interstellar shocks. Here we test this hypothesis by observing a well-known Galactic source where the chemistry is dominated by shocks. We have observed several transitions of HNCO towards L1157-mm and two positions (B1 and B2) in the blue lobe of the molecular outflow. The HNCO line profiles exhibit the same characteristics of other well-known shock tracers like CH3OH, H2CO, SO or SO2. HNCO, together with SO2 and OCS, are the only three molecules detected so far whose emission is much more intense in B2 than in B1, making these species valuable probes of chemical differences along the outflow. The HNCO abundance with respect to H2 is 0.4-1.8 10^-8 in B1 and 0.3-1 10^-7 in B2. These abundances are the highest ever measured, and imply an increment with respect to L1157-mm of a factor up to 83, demonstrating that this molecule is actually a good shock tracer. Our results probe that shocks can actually produce the HNCO abundance measured in galactic nuclei and even higher ones. We propose that the gas phase abundance of HNCO is due both to grain mantles erosion by the shock waves and by neutral-neutral reactions in gas phase involving CN and O2. The observed anticorrelation of CN and HNCO fluxes supports this scenario. The observed similarities of the HNCO emission and the sulfured molecules may arise due to formation pathways involving also O2.
UltraFast Outflows (UFOs), seen as X-ray blueshifted absorption lines in active galactic nuclei (AGNs), are considered to be a key mechanism for AGN feedback. In this scenario, UFO kinetic energy is transferred into the cold and extended molecular outflow observed at the mm/sub-mm wavelength, which blows away the gas and suppresses star formation and accretion onto the central black hole (BH). However, the energy transfer between the inner UFO and the outer molecular outflow has not yet fully studied mainly due to the limited sample. In this paper, we performed comparison of their kinetic energy using the mm/sub-mm published data and the X-ray archival data. Among fourteen Seyfert galaxies whose molecular outflows are detected in the IRAM/PdBI data, eight targets are bright enough to perform spectral fitting in X-ray, and we have detected UFO absorption lines in six targets with 90% significance level, using XMM-Newton and Suzaku satellites. The time-averaged UFO kinetic energy was derived from the spectral fitting. As a result, we have found that the energy-transfer rate (kinetic energy ratio of the molecular outflow to the UFO) ranges from $sim7times10^{-3}$ to $sim$1, and has a negative correlation with the BH mass, which shows that the AGN feedback is more efficient in the lower mass BHs. This tendency is consistent with the theoretical prediction that the cooling time scale of the outflowing gas becomes longer than the flow time scale when the BH mass is smaller.
We present the first detection of polarization around the Class 0 low-mass protostar L1157-mm at two different wavelengths. We show polarimetric maps at large scales (10 resolution at 350 um) from the SHARC-II Polarimeter and at smaller scales (1.2-4.5 at 1.3 mm) from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The observations are consistent with each other and show inferred magnetic field lines aligned with the outflow. The CARMA observations suggest a full hourglass magnetic field morphology centered about the core; this is only the second well-defined hourglass detected around a low-mass protostar to date. We apply two different methods to CARMA polarimetric observations to estimate the plane-of-sky magnetic field magnitude, finding values of 1.4 and 3.4 mG.
We have imaged 24 spectral lines in the Central Molecular Zone (CMZ) around the Galactic Centre, in the range 42 to 50 GHz. The lines include emission from the CS, CH3OH, HC3N, SiO, HNCO, HOCO+, NH2CHO, OCS, HCS+, CCS, C34S, 13CS, 29SiO, H13CCCN, HCC13CN and HC5}N molecules, and three hydrogen recombination lines. The area covered is Galactic longitude -0.7 to 1.8 deg. and latitude -0.3 to 0.2 deg., including the bright cores around Sgr A, SgrB2, SgrC and G1.6-0.025. This work used the 22-m Mopra radio telescope in Australia, obtaining ~ 1.8 km/s spectral and ~ 65 arcsec spatial resolution. We present peak images from this study and conduct a principal component analysis on the integrated emission from the brightest 10 lines, to study similarities and differences in the line distribution. We examine the integrated line intensities and line ratios in selected apertures around the bright cores, as well as for the complete mapped region of the CMZ. We compare these 7-mm lines to the corresponding lines in the 3-mm band, for five molecules, to study the excitation. There is a variation in 3-mm to 7-mm line ratio across the CMZ, with relatively higher ratio in the centre around Sgr B2 and Sgr A. We find that the lines are sub-thermally excited, and from modelling with RADEX find that non-LTE conditions apply, with densities of order 10^4 cm^{-3}.
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