G. Busquet

SUBMILLIMETER LINE SPECTRUM OF THE SEYFERT GALAXY NGC 1068 FROM THE HERSCHEL-SPIRE FOURIER TRANSFORM SPECTROMETER*

The first complete submillimeter spectrum (190-670 mu m) of the Seyfert 2 galaxy NGC 1068 has been observed with the SPIRE Fourier transform spectrometer on board the Herschel Space Observatory. The sequence of CO lines (J(up) = 4-13), lines from H2O, the fundamental rotational transition of hydrogen fluoride, two o-H2O+ lines, and one line each from CH+ and OH+ have been detected, together with the two [C I] lines and the [N II] 205 mu m line. The observations in both single pointing mode with sparse image sampling and in mapping mode with full image sampling allow us to disentangle two molecular emission components, one due to the compact circumnuclear disk (CND) and one from the extended region encompassing the star-forming ring (SF-ring). Radiative transfer models show that the two CO components are characterized by densities of n(H-2) = 10(4.5) and 10(2.9) cm(-3) and temperatures of T-kin = 100 K and 127 K, respectively. A comparison of the CO line intensities with the photodissociation region (PDR) and X-ray-dominated region (XDR) models, together with the other observational constraints, such as the observed CO surface brightness and the radiation field, indicates that the best explanation for the CO excitation of the CND is an XDR with a density of n(H-2) similar to 10(4) cm(-3) and an X-ray flux of 9 erg s(-1) cm(-2), consistent with illumination by the active galactic nucleus, while the CO lines in the SF-ring are better modeled by a PDR. The detected water transitions, together with those observed with the Herschel PACS spectrometer, can be modeled by a large velocity gradient model with low temperature (T-kin similar to 40 K) and high density (n(H-2) in the range 10(6.7)-10(7.9) cm(-3)). The emission of H2O+ and OH+ are in agreement with PDR models with cosmic-ray ionization. The diffuse ionized atomic component observed through the [N II] 205 mu m line is consistent with previous photoionization models of the starburst.

Deuteration as an evolutionary tracer in massive-star formation

Context. Theory predicts, and observations confirm, that the column density ratio of a molecule containing D to its counterpart containing H can be used as an evolutionary tracer in the low-mass star formation process. Aims. Since it remains unclear if the high-mass star formation process is a scaled-up version of the low-mass one, we investigated whether the relation between deuteration and evolution can be applied to the high-mass regime. Methods. With the IRAM-30 m telescope, we observed rotational transitions of N 2 D + and N 2 H + and derived the deuterated fraction in 27 cores within massive star-forming regions understood to represent different evolutionary stages of the massive-star formation process. Results. The abundance of N 2 D + is higher at the pre-stellar/cluster stage, then drops during the formation of the protostellar object(s) as in the low-mass regime, remaining relatively constant during the ultra-compact HII region phase. The objects with the highest fractional abundance of N 2 D + are starless cores with properties very similar to typical pre-stellar cores of lower mass. The abundance of N 2 D + is lower in objects with higher gas temperatures as in the low-mass case but does not seem to depend on gas turbulence. Conclusions. Our results indicate that the N 2 D + -to-N 2 H + column density ratio can be used as an evolutionary indicator in both low-and high-mass star formation, and that the physical conditions influencing the abundance of deuterated species likely evolve similarly during the processes that lead to the formation of both low- and high-mass stars.

THE IDENTIFICATION OF FILAMENTS ON FAR-INFRARED AND SUBMILLIMITER IMAGES: MORPHOLOGY, PHYSICAL CONDITIONS AND RELATION WITH STAR FORMATION OF FILAMENTARY STRUCTURE

Observations of molecular clouds reveal a complex structure, with gas and dust often arranged in filamentary, rather than spherical geometries. The association of pre- and proto-stellar cores with the filaments suggests a direct link with the process of star formation. Any study of the properties of such filaments requires representative samples from different environments for an unbiased detection method. We developed such an approach using the Hessian matrix of a surface-brightness distribution to identify filaments and determine their physical and morphological properties. After testing the method on simulated, but realistic, filaments, we apply the algorithms to column-density maps computed from Herschel observations of the Galactic plane obtained by the Hi-GAL project. We identified ~500 filaments, in the longitude range of l = 216°.5 to l = 225°.5, with lengths from ~1 pc up to ~30 pc and widths between 0.1 pc and 2.5 pc. Average column densities are between 10^(20) cm^2 and 10^(22) cm^2. Filaments include the majority of dense material with N_H_2> 6 × 10^(21) cm^2. We find that the pre- and proto-stellar compact sources already identified in the same region are mostly associated with filaments. However, surface densities in excess of the expected critical values for high-mass star formation are only found on the filaments, indicating that these structures are necessary to channel material into the clumps. Furthermore, we analyze the gravitational stability of filaments and discuss their relationship with star formation.

The CHESS Survey of the L1157-B1 Shock Region: CO Spectral Signatures of Jet-driven Bow Shocks

The unprecedented sensitivity of Herschel coupled with the high resolution of the HIFI spectrometer permits studies of the intensity-velocity relationship I(v) in molecular outflows, over a higher excitation range than possible up to now. Over the course of the CHESS Key Program, we have observed toward the bright bow shock region L1157-B1, the CO rotational transitions between J = 5-4 and J = 16-15 with HIFI, and the J = 1-0, 2-1, and 3-2 with the IRAM 30 m and the Caltech Submillimeter Observatory telescopes. We find that all the line profiles I_(CO)(v) are well fit by a linear combination of three exponential laws ∝ exp (– |v/v_0|) with v_0 = 12.5, 4.4, and 2.5 km s^(–1). The first component dominates the CO emission at J ≥ 13, as well as the high-excitation lines of SiO and H_(2)O. The second component dominates for 3 ≤ J up ≤ 10 and the third one for J_up ≤ 2. We show that these exponentials are the signature of quasi-isothermal shocked gas components: the impact of the jet against the L1157-B1 bow shock (T_k ≃ 210 K), the walls of the outflow cavity associated with B1 (T_k ≃ 64 K), and the older cavity L1157-B2 (T_k ≃ 23 K), respectively. Analysis of the CO line flux in the large-velocity gradient approximation further shows that the emission arises from dense gas (n(H_2) ≥ 10^(5)-10^(6) cm^(–3)) close to LTE up to J = 20. We find that the CO J = 2-1 intensity-velocity relation observed in various other molecular outflows is satisfactorily fit by similar exponential laws, which may hold an important clue to their entrainment process.

Two Mass Distributions in the L 1641 Molecular Clouds: The Herschel connection of Dense Cores and Filaments in Orion A

We present the Herschel Gould Belt survey maps of the L\,1641 molecular clouds in Orion A. We extracted both the filaments and dense cores in the region. We identified which of dense sources are proto- or pre-stellar, and studied their association with the identified filaments. We find that although most (71%) of the pre-stellar sources are located on filaments there is still a significant fraction of sources not associated with such structures. We find that these two populations (on and off the identified filaments) have distinctly different mass distributions. The mass distribution of the sources on the filaments is found to peak at 4 Solar masses and drives the shape of the CMF at higher masses, which we fit with a power law of the form d

The CHESS survey of the L1157-B1 shock: the dissociative jet shock as revealed by Herschel–PACS

N

The CHESS survey of the L1157-B1 bow-shock: high and low excitation water vapor

/dlog

Herschel/SPIRE Submillimeter Spectra of Local Active Galaxies

M \propto M^{-1.4\pm0.4}

Properties of dense cores in clustered massive star-forming regions at high angular resolution

. The mass distribution of the sources off the filaments, on the other hand, peaks at 0.8 Solar masses and leads to a flattening of the CMF at masses lower than ~4 Solar masses. We postulate that this difference between the mass distributions is due to the higher proportion of gas that is available in the filaments, rather than in the diffuse cloud.

YOUNG STARLESS CORES EMBEDDED IN THE MAGNETICALLY DOMINATED PIPE NEBULA

Outflows generated by protostars heavily affect the kinematics and chemistry of the hosting molecular cloud through strong shocks that enhance the abundance of some molecules. L1157 is the prototype of chemically active outflows, and a strong shock, called B1, is taking place in its blue lobe between the precessing jet and the hosting cloud. We present the Herschel-PACS 55‐210 μm spectra of the L1157-B1 shock, showing emission lines from CO, H2O, OH, and [O i]. The spatial resolution of the PACS spectrometer allows us to map the warm gas traced by far-infrared (FIR) lines with unprecedented detail. The rotational diagram of the high-Jup CO lines indicates high-excitation conditions (Tex � 210 ± 10 K). We used a radiative transfer code to model the hot CO gas emission observed with PACS and in the CO(13‐12) and (10‐9) lines measured by Herschel-HIFI. We derive 200 < Tkin < 800 K and n ≥ 10 5 cm −3 .T he CO emission comes from a region of about 7 �� located at the rear of the bow shock where the [O i] and OH emission also originate. Comparison with shock models shows that the bright [O i] and OH emissions trace a dissociative J-type shock, which is also supported by a previous detection of [FeII] at the same position. The inferred mass-flux is consistent with the “reverse” shock where the jet is impacting on the L1157-B1 bow shock. The same shock may contribute significantly to the high-Jup CO emission.