C. Lefèvre

Lambda = 3 mm line survey of nearby active galaxies

We used the IRAM 30m telescope to observe the frequency range [86-116]GHz towards the central regions of the starburst galaxies M83, M82, and NGC253, the AGNs M51, NGC1068, and NGC7469, and the ULIRGs Arp220 and Mrk231. Assuming LTE conditions, we calculated the column densities of 27 molecules and 10 isotopologues. Among others, we report the first tentative detections of CH3CHO, HNCO, and NS in M82 and, for the first time in the extragalactic medium, HC5N in NGC253. Halpha recombination lines were only found in M82 and NGC253. Vibrationally excited lines of HC3N were only detected in Arp220. CH3CCH emission is only seen in the starburst-dominated galaxies. By comparison of the fractional abundances among the galaxies, we looked for the molecules that are best suited to characterise the chemistry of starbursts, AGNs and ULIRGs, as well as the differences among galaxies within the same group.

Galactic cold cores

Context. The Galactic Cold Cores project has carried out Herschel photometric observations of 116 fields where the Planck survey has found signs of cold dust emission. The fields contain sources in different environments and different phases of star formation. Previous studies have revealed variations in their dust submillimetre opacity. Aims. The aim is to measure the value of dust opacity spectral index and to understand its variations spatially and with respect to other parameters, such as temperature, column density, and Galactic location. Methods. The dust opacity spectral index β and the dust colour temperature T are derived using Herschel and Planck data. The relation between β and T is examined for the whole sample and inside individual fields. Results. Based on IRAS and Planck data, the fields are characterised by a median colour temperature of 16.1 K and a median opacity spectral index of β = 1.84. The values are not correlated with Galactic longitude. We observe a clear T–β anti-correlation. In Herschel observations, constrained at lower resolution by Planck data, the variations follow the column density structure and β_(FIR) can rise to ~2.2 in individual clumps. The highest values are found in starless clumps. The Planck 217 GHz band shows a systematic excess that is not restricted to cold clumps and is thus consistent with a general flattening of the dust emission spectrum at millimetre wavelengths. When fitted separately below and above 700 μm, the median spectral index values are β_(FIR) ~ 1.91 and β(mm) ~ 1.66. Conclusions. The spectral index changes as a function of column density and wavelength. The comparison of different data sets and the examination of possible error sources show that our results are robust. However, β variations are partly masked by temperature gradients and the changes in the intrinsic grain properties may be even greater.

Dust properties inside molecular clouds from coreshine modeling and observations

Context. Using observations to deduce dust properties, grain-size distribution, and physical conditions in molecular clouds is a highly degenerate problem.Aims. The coreshine phenomenon, a scattering process at 3.6 and 4.5 μm that dominates absorption, has revealed its ability to explore the densest parts of clouds. We use this effect to constrain the dust parameters. The goal is to investigate to what extent grain growth (at constant dust mass) inside molecular clouds is able to explain the coreshine observations. We aim to find dust models that can explain a sample of Spitzer coreshine data. We also examine the consistency with near-infrared data we obtained for a few clouds.Methods. We selected four regions with a very high occurrence of coreshine cases: Taurus-Perseus, Cepheus, Chameleon, and L183/L134. We built a grid of dust models and investigated the key parameters to reproduce the general trend of surface brightnesses and intensity ratios of both coreshine and near-infrared observations with the help of a 3D Monte Carlo radiative transfer code. The grid parameters allowed us to investigate the effect of coagulation upon spherical grains up to 5 μm in size derived from the DustEm diffuse interstellar medium grains. Fluffiness (porosity or fractal degree), ices, and a handful of classical grain-size distributions were also tested. We used the near- and mostly mid-infrared intensity ratios as strong discriminants between dust models.Results. The determination of the background-field intensity at each wavelength is a key issue. In particular, an especially strong background field explains why we do not see coreshine in the Galactic plane at 3.6 and 4.5 μm. For starless cores, where detected, the observed 4.5 μm/3.6 μm coreshine intensity ratio is always lower than ~0.5, which is also what we find in the models for the Taurus-Perseus and L183 directions. Embedded sources can lead to higher fluxes (up to four times higher than the strongest starless core fluxes) and higher coreshine ratios (from 0.5 to 1.1 in our selected sample). Normal interstellar radiation-field conditions are sufficient to find suitable grain models at all wavelengths for starless cores. The standard interstellar grains are not able to reproduce observations and, because of the multiwavelength approach, only a few grain types meet the criteria set by the data. Porosity does not affect the flux ratios, while the fractal dimension helps to explain coreshine ratios, but does not seem able to reproduce near-infrared observations without a mix of other grain types.Conclusions. Combined near- and mid-infrared wavelengths confirm the potential of revealing the nature and size distribution of dust grains. Careful assessment of the environmental parameters (interstellar and background fields, embedded or nearby reddened sources) is required to validate this new diagnostic.

Galactic cold cores - V. Dust opacity

Context. The project Galactic Cold Cores has carried out Herschel photometric observations of interstellar clouds where the Planck satellite survey has located cold and compact clumps. The sources represent different stages of cloud evolution from starless clumps to protostellar cores and are located in different Galactic environments. Aims. We examine this sample of 116 Herschel fields to estimate the submillimetre dust opacity and to search for variations that might be attributed to the evolutionary stage of the sources or to environmental factors, including the location within the Galaxy. Methods. The submillimetre dust opacity was derived from Herschel data, and near-infrared observations of the reddening of background stars are converted into near-infrared optical depth. We investigated the systematic errors affecting these parameters and used modelling to correct for the expected biases. The ratio of 250 μm and J band opacities is correlated with the Galactic location and the star formation activity. We searched for local variations in the ratio τ(250 μm)/τ(J) using the correlation plots and opacity ratio maps. Results. We find a median ratio of τ(250 μm) /τ(J) = (1.6 ± 0.2) × 10^(-3), which is more than three times the mean value reported for the diffuse medium. Assuming an opacity spectral index β = 1.8 instead of β = 2.0, the value would be lower by ~ 30%. No significant systematic variation is detected with Galactocentric distance or with Galactic height. Examination of the τ(250 μm) /τ(J) maps reveals six fields with clear indications of a local increase of submillimetre opacity of up to τ(250 μm) /τ(J) ~ 4 × 10^(-3) towards the densest clumps. These are all nearby fields with spatially resolved clumps of high column density. Conclusions. We interpret the increase in the far-infrared opacity as a sign of grain growth in the densest and coldest regions of interstellar clouds.

Can we trace very cold dust from its emission alone

Context. Dust is a good tracer of cold dark clouds but its column density is di cult to quantify. Aims. We want to check whether the far-infrared and submillimeter high‐resolution data from Herschel SPIRE and PACS cameras combined with ground-based telescope bolometers allow us to retrieve the whole dust content of cold dark clouds. Methods. We compare far-infrared and submillimeter emission across L183 to the 8 m absorption map from Spitzer data and fit modified blackbody functions towards three di erent positions. Results. We find that none of the Herschel SPIRE channels follow the cold dust profile seen in absorption. Even the ground-based submillimeter telescope observations, although more closely following the absorption profile, cannot help to characterize the cold dust without external information such as the dust column density itself. The di erence in dust opacity can reach up to a factor of 3 in prestellar cores of high extinction. Conclusions. In dark clouds, the amount of very cold dust cannot be measured from its emission alone. In particular, studies of dark clouds based only on Herschel data can miss a large fraction of the dust content. This has an impact on core and filament density profiles, masse and stability estimates.

First image of the L1157 molecular jet by the CALYPSO IRAM-PdBI survey

Context. Fast jets are thought to be a crucial ingredient of star formation because they might extract angular momentum from the disk and thus allow mass accretion onto the star. However, it is unclear whether jets are ubiquitous, and likewise, their contribution to mass and angular momentum extraction during protostar formation remains an open question. Aims. Our aim is to investigate the ejection process in the low-mass Class 0 protostar L1157. This source is associated with a spectacular bipolar outflow, and the recent detection of high-velocity SiO suggests the occurrence of a jet. Methods. Observations of CO 2 −1 and SiO 5 − 4 at ~ \hbox{

Absence of coreshine in the Gum/Vela region

0\farcs8

On the importance of scattering at 8 μm: Brighter than you think

} resolution were obtained with the IRAM Plateau de Bure Interferometer (PdBI) as part of the CALYPSO large program. The jet and outflow structure were fit with a precession model. We derived the column density of CO and SiO, as well as the jet mass-loss rate and mechanical luminosity. Results. High-velocity CO and SiO emission resolve for the first time the first 200 au of the outflow-driving molecular jet. The jet is strongly asymmetric, with the blue lobe ~0.65 times slower than the red lobe. This suggests that the large-scale asymmetry of the outflow is directly linked to the jet velocity and that the asymmetry in the launching mechanism has been at work for the past 1800 yr. Velocity asymmetries are common in T Tauri stars, which suggests that the jet formation mechanism from Class 0 to Class II stages might be similar. Our model simultaneously fits the properties of the inner jet and of the clumpy 0.2 pc scale outflow by assuming that the jet precesses counter-clockwise on a cone inclined by 73° to the line of sight with an opening angle of 8° on a period of ~1640 yr. The estimated jet mass flux and mechanical luminosity are Ṁ jet ~ 7.7 × 10 -7 M ⊙ yr -1 and L jet ~ 0.9 L ⊙ , indicating that the jet could extract at least 25% of the gravitational energy released by the forming star.

Grain size limits derived from 3.6 μm and 4.5 μm coreshine

Context. We recently discovered mid-infrared light scattering by mi cron-size grains deeply buried in dark clouds. We have named this coreshine. We also showed that this e ffect is widespread across the Galaxy except in the Gum /Vela region, the only region among those we explored without any trace of coreshine. Aims. We aim to check whether the Gum /Vela situation is a chance e ff ct or if coreshine is really absent from the region. Methods. We explored the entire available Spitzer /Infrared Red Array Camera (IRAC) archive centered on the Gum /Vela region in search of the coreshine e ff ct. Results. Out of 24 validated objects (of a total of 32), we found three c ases of coreshine and three possible other cases, while we detect nine cases of non-coreshine emission (bright rimmed clouds – BRC – or polycyclic aromatic hydrocarbon – PAH – emis sion). This is markedly di fferent from our previous galactic-wide survey with a ratio of 7–8 coreshine cases per PAH case. In Gum /Vela, a majority of the clouds with protostars or young stellar obje cts do not show a coreshine e ffect, while in the galactic-wide survey, 75% of the protostellar clouds do. Conclusions. The rare occurence of coreshine, outnumbered by PAH and BRC c ases, together with a large number of protostars, let us conclude that the Gum Nebula is a supernova remnant (SN R), and that the blast wave has both reset the grain size distr ibution and induced the formation of several protostars. The absenc e of oreshine in the vicinity of several of the Class I object s also implies that the growth time for grains to e fficiently scatter mid-infrared radiation exceeds the Class I life duration, which is typically 2× 105 years, and it also implies that the blast wave has reached the se clouds only recently despite the age of the Gum region (ove r 1.5 My). This is consistent with their large distance from the center of the SNR.

CALYPSO view of SVS 13A with PdBI: Multiple jet sources

Context. Extinction and emission of dust models need for observational constraints to be validated. The coreshine phenomenon has already shown the importance of scattering in the 3 to 5 micron range and its ability to validate dust properties for dense cores. Aims. We want to investigate whether scattering can also play a role at longer wavelengths and to place even tighter constraints on the dust properties. Methods. We analyze the inversion of the Spitzer 8 micron map of the dense molecular cloud L183, to examine the importance of scattering as a potential contributor to the line-of-sight extinction. Results. The column density deduced from the inversion of the 8 micron map, when we neglect scattering, disagrees with all the other column density measurements of the same region. Modeling confirms that scattering at 8 microns is not negligible with an intensity of several hundred kJy per sr. This demonstrates the need of efficiently scattering dust grains at MIR wavelengths up to 8 microns. Coagulated aggregates are good candidates and might also explain the discrepancy at high extinction between E(J-K) et tau(9.7) toward dense molecular clouds. Further investigation requires considering efficiently scattering dust grains including ices as realistic dust models.