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Register a new userThe shocked gas of the BHR71 outflow observed by Herschel: indirect evidence for an atomic jet
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In the BHR71 region, two low-mass protostars drive two distinguishable outflows. They constitute an ideal laboratory to investigate the effects of shock chemistry and the mechanisms that led to their formation. We aim to define the morphology of the warm gas component of the BHR 71 outflow and at modelling its shocked component. We present the first far infrared Herschel images of the BHR71 outflow in the CO(14-13), H$_2$O (2$_{21}$-1$_{10}$), H$_2$O (2$_{12}$-1$_{01}$) and [OI] 145 $mu$m, lines, revealing the presence of several knots of warm, shocked gas associated with fast outflowing gas. In two of these knots we performed a detailed study of the physical conditions by comparing a large set of transitions from several molecules to a grid of shock models. Herschel lines ratios in the outflow knots are quite similar, showing that the excitation conditions of the fast moving gas do not change significantly within the first $sim$ 0.068 pc of the outflow, apart at the extremity of the southern blue-shifted lobe that is expanding outside the molecular cloud. Rotational diagram, spectral line profile and LVG analysis of the CO lines in knot A show the presence of two gas components: one extended, cold ($Tsim$80 K) and dense ($n$(H$_2$) = 3$times$10$^5$-4$times$10$^6$ cm$^{-3}$) and another compact (18 arcsec), warm ($T$ = 1700-2200 K) with slightly lower density ($n$(H$_2$) = (2-6)$times$10$^4$ cm$^{-3}$). In the two brightest knots (where we performed shock modelling) we found that H$_2$ and CO are well fitted with non-stationary (young) shocks. These models, however, significantly underestimate the observed fluxes of [OI] and OH lines, but are not too far off those of H$_2$O, calling for an additional, possibly dissociative, J-type shock component. Our modelling indirectly suggests that an additional shock component exists, possibly a remnant of the primary jet
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During the formation of a star, material is ejected along powerful jets that impact the ambient material. This outflow regulates star formation by e.g. inducing turbulence and heating the surrounding gas. Understanding the associated shocks is therefore essential to the study of star formation. We present comparisons of shock models with CO, H2, and SiO observations in a pure shock position in the BHR71 bipolar outflow. These comparisons provide an insight into the shock and pre-shock characteristics, and allow us to understand the energetic and chemical feedback of star formation on Galactic scales. New CO (Jup = 16, 11, 7, 6, 4, 3) observations from the shocked regions with the SOFIA and APEX telescopes are presented and combined with earlier H2 and SiO data (from the Spitzer and APEX telescopes). The integrated intensities are compared to a grid of models that were obtained from a magneto-hydrodynamical shock code which calculates the dynamical and chemical structure of these regions combined with a radiative transfer module based on the large velocity gradient approximation. The CO emission leads us to update the conclusions of our previous shock analysis: pre-shock densities of 1e4 cm-3 and shock velocities around 20-25 km s-1 are still constrained, but older ages are inferred ( 4000 years). We evaluate the contribution of shocks to the excitation of CO around forming stars. The SiO observations are compatible with a scenario where less than 4% of the pre-shock SiO belongs to the grain mantles. We infer outflow parameters: a mass of 1.8x1e-2 Msun was measured in our beam, in which a momentum of 0.4 Msun km s-1 is dissipated, for an energy of 4.2x1e43erg. We analyse the energetics of the outflow species by species. Comparing our results with previous studies highlights their dependence on the method: H2 observations only are not sufficient to evaluate the mass of outflows.
The physical state of the gas in the central 500 pc of NGC~5128 (the radio galaxy Centaurus A - Cen A), was investigated using the far-infrared fine-structure lines of carbon, oxygen, and nitrogen, as well as the CO(4-3) molecular line. The circumnuclear disk (CND) is traced by emission from dust and the neutral gas ([CI] and CO). A gas outflow with a line-of-sight velocity of 60 km/s is evident in both species. The center of the CND is bright in [OI], [OIII], and [CII]; [OI]63mu emission dominates that of [CII] even though it is absorbed with optical depths of 1.0-1.5. The outflow is well-traced by the [NII] and [NIII] lines and also seen in the [CII] and [OIII] lines that peak in the center. Ionized gas densities are moderate in the CND and low everywhere else. Neutral gas densities range from 4000 per cm3 (outflow, extended thin disk ETD) to 20 000 per cm3 (CND). The CND radiation field is weak compared to the ETD starburst field. The outflow has a much stronger radiation field. The total mass of all the CND gas is 9 x 10^(7) M(o) and the mass of the outflowing gas is only 15%-30% of that. The outflow most likely originates from the shock-dominated CND cavity surrounding the central black hole. With a factor of three uncertainty, the mass outflow rate is about 2 M(o)/yr, a thousand times higher than the accretion rate of the black hole. Without replenishment, the CND will be depleted in 15-120 million years. However, the outflow velocity is well below the escape velocity.
We present 70 and 160 micron Herschel science demonstration images of a field in the Orion A molecular cloud that contains the prototypical Herbig-Haro objects HH 1 and 2, obtained with the Photodetector Array Camera and Spectrometer (PACS). These observations demonstrate Herschels unprecedented ability to study the rich population of protostars in the Orion molecular clouds at the wavelengths where they emit most of their luminosity. The four protostars previously identified by Spitzer 3.6-40 micron imaging and spectroscopy are detected in the 70 micron band, and three are clearly detected at 160 microns. We measure photometry of the protostars in the PACS bands and assemble their spectral energy distributions (SEDs) from 1 to 870 microns with these data, Spitzer spectra and photometry, 2MASS data, and APEX sub-mm data. The SEDs are fit to models generated with radiative transfer codes. From these fits we can constrain the fundamental properties of the protostars. We find luminosities in the range 12-84 L_sun and envelope densities spanning over two orders of magnitude. This implies that the four protostars have a wide range of envelope infall rates and evolutionary states: two have dense, infalling envelopes, while the other two have only residual envelopes. We also show the highly irregular and filamentary structure of the cold dust and gas surrounding the protostars as traced at 160 microns.
In the framework of the WISH key program, several H2O (E_u>190 K), high-J CO, [OI], and OH transitions are mapped with PACS in two shock positions along the two prototypical low-luminosity outflows L1448 and L1157. Previous HIFI H2O observations (E_u=53-249 K) and complementary Spitzer mid-IR H2 data are also used, with the aim of deriving a complete picture of the excitation conditions. At all selected spots a close spatial association between H2O, mid-IR H2, and high-J CO emission is found, whereas the low-J CO emission traces either entrained ambient gas or a remnant of an older shock. The excitation analysis at L1448-B2 suggests that a two-component model is needed to reproduce the H2O, CO, and mid-IR H2 lines: an extended warm component (T~450 K) is traced by the H2O emission with E_u =53-137 K and by the CO lines up to J=22-21, and a compact hot component (T=1100 K) is traced by the H2O emission with E_u>190 K and by the higher-J CO lines. At L1448-B2 we obtain an H2O abundance (3-4)x10^{-6} for the warm component and (0.3-1.3)x10^{-5} for the hot component; we also detect OH and blue-shifted [OI] emission, spatially coincident with the other molecular lines and with [FeII] emission. This suggests a dissociative shock for these species, related to the embedded atomic jet. On the other hand, a non-dissociative shock at the point of impact of the jet on the cloud is responsible for the H2O and CO emission. The other examined shock positions show an H2O excitation similar to L1448-B2, but a slightly higher H2O abundance (a factor of 4). The two gas components may represent a gas stratification in the post-shock region. The extended and low-abundance warm component traces the post-shocked gas that has already cooled down to a few hundred Kelvin, whereas the compact and possibly higher-abundance hot component is associated with the gas that is currently undergoing a shock episode.
Previous far-infrared observations at low-angular resolution have reported the presence of water associated with low-velocity outflow shocks and protostellar envelopes. The outflow driven by the intermediate-mass class 0 protostar Cep E is among the most luminous outflows detected so far. Using the IRAM 30m telescope, we searched for and detected the para-water line emission at 183 GHz in the Cep E star-forming core. The emission arises from high-velocity gas close to the protostar, which is unresolved in the main beam of the telescope. Complementary observations at 2 resolution with the Plateau de Bure interferometer helped establish the origin of the emission detected and the physical conditions in the emitting gas. The water line profile and its spatial distribution are very similar to those of SiO. We find that the water emission arises from warm ($sim 200K$), dense ($(1-2)times 10^6cmmt$) gas, and its abundance is enhanced by one to two orders of magnitude with respect to the protostellar envelope. We detect water emission in strong shocks from the high-velocity jet at 1000 AU from the protostar. Despite the large beam size of the telescope, such emission should be detectable with Herschel.
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