We present VIsible Multi-Object Spectrograph (VIMOS) observations of a galaxy quintuply imaged by the Frontier Fields galaxy cluster RXC J2248.7-4431 . This sub-, high- galaxy has been recently... Show moreWe present VIsible Multi-Object Spectrograph (VIMOS) observations of a galaxy quintuply imaged by the Frontier Fields galaxy cluster RXC J2248.7-4431 . This sub-, high- galaxy has been recently discovered by Monna et al. (2013) using dropout techniques with the 16-band HST photometry acquired as part of the Cluster Lensing And Supernova survey with Hubble (CLASH). Obtained as part of the CLASH-VLT survey, the VIMOS medium-resolution spectra of this source show a very faint continuum between 8700 å and 9300 å and a prominent emission line at 8643 , which can be readily identified with Lyman- at . The emission line exhibits an asymmetric profile, with a more pronounced red wing. The rest-frame equivalent width of the line is , relatively well constrained thanks to the detection of the UV continuum, which is rarely achieved for a sub- galaxy at this redshift. After correcting formagnification, the star formation rate (SFR) estimated from the Ly line is SFRLyyr and that estimated from the UV data is SFRUVyr. We estimate that the effective radius of the source is kpc, which implies a star formation surface mass density yrkpc and, using the Kennicutt-Schmidt relation, a gas surface mass density pc. Our results support the idea that this magnified, distant galaxy is a young and compact object with luminosity at , when the Universe was just 1 Gyr old, with a similar amount of mass in gas and stars. In the spirit of the Frontier Fields initiative, we also publish the redshifts of several multiply imaged sources and other background objects, which will help improving the strong-lensing model of this galaxy cluster. This work is based on data collected at ESO VLT (prog.ID 186.A-0798) and at NASA HST. Show less
We present wide area, deep, high-resolution 153 MHz GMRT observations of the NOAO Boötes field, adding to the extensive, multi-wavelength data of this region. The observations, data reduction, and... Show moreWe present wide area, deep, high-resolution 153 MHz GMRT observations of the NOAO Boötes field, adding to the extensive, multi-wavelength data of this region. The observations, data reduction, and catalogue construction and description are described here. The seven pointings produced a final mosaic covering 30 square degrees with a resolution of 25{Prime}. The rms noise is 2 mJy beam$^{-1}$ in the centre of the image, rising to 4-5 mJy beam$^{-1}$ on the edges, with an average of 3 mJy beam$^{-1}$. Seventy-five per cent of the area has an rms {lt}4 mJy beam$^{-1}$. The extracted source catalogue contains 1289 sources detected at 5{$σ$}, of which 453 are resolved. We estimate the catalogue to be 92 per cent reliable and 95 per cent complete at an integrated flux density limit of 14 mJy. The flux densities and astrometry have been corrected for systematic errors. We calculate the differential source counts, which are in good agreement with those in the literature and provide an important step forward in quantifying the source counts at these low frequencies and low flux densities. The GMRT 153 MHz sources have been matched to the 1.4 GHz NVSS and 327 MHz WENSS catalogues and spectral indices were derived. Table A.1 (Catalogue) is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A55Show less
Context. The Gaia mission will produce a stereoscopic map of the Milky Way by collecting highly accurate positions, parallaxes and proper motions for about 1 billion stars. These astrometric... Show moreContext. The Gaia mission will produce a stereoscopic map of the Milky Way by collecting highly accurate positions, parallaxes and proper motions for about 1 billion stars. These astrometric parameters will be determined through the astrometric core solution of the Gaia mission which will employ about 10$^{8}$ primary sources (a subset of the observed sources with the best astrometric properties). The attitude of the spacecraft is reconstructed as part of the astrometric solution and provides the reference frame relative to which the astrometric measurements are obtained. This implies extreme demands on the accuracy of the attitude reconstruction. Aims: This paper presents an analysis of the capabilities and limitations of the Gaia attitude reconstruction, focusing on the effects on the astrometry of bright (V {lsim} 11) stars and the implications of employing cubic B-splines in the modelling of the attitude measurements. Methods: We simulate the attitude of the spacecraft using a realistic and very detailed model that considers not only physical effects but also technical aspects like the control system and thruster noise. We include the effect of shorter integration times for the bright stars on the effective attitude and we estimate the residual modelling noise in the reconstruction of the attitude. Results: We provide an analysis of the dependency of the residual modelling noise in the reconstructed attitude with respect to the following parameters: integration time, B-spline knot interval, micro-propulsion system noise, and number of observations per second. Conclusions: The final noise in the attitude reconstruction for Gaia is estimated to be {ap}20 {$μ$}as, and the main source will be the micro-propulsion system. However its effect on the astrometric performance will be limited, adding up to 7 {$μ$}as rms to the parallax uncertainties. This is larger than the 4 {$μ$}as from previous estimations and would affect the performance for the brightest (V {lsim} 11) stars. Show less
Guenther, E.; Fridlund, M.; Alonso, R.; Carpano, S.; Deeg, H.; Deleuil, M.; ... ; Tingley, B. 2013
Context. Studies of transiting extrasolar planets are of key importance for understanding the nature of planets outside our solar system because their masses, diameters, and bulk densities can be... Show moreContext. Studies of transiting extrasolar planets are of key importance for understanding the nature of planets outside our solar system because their masses, diameters, and bulk densities can be measured. An important part of transit-search programmes is the removal of false-positives. In the case of the CoRoT space mission, the majority of the false-positives are removed by a detailed analysis of the light curves and by seeing-limited imaging in- and out-of-transit. However, the critical question is how many of the candidates that passed all these tests are false-positives. Such false-positives can be caused by eclipsing binaries, which are either related or unrelated to the targets. Aims: For our study we selected 25 CoRoT candidates that have already been screened against false-positives using detailed analysis of the light curves and seeing-limited imaging, which has transits that are between 0.7 and 0.05% deep. Our aim is to search for companion candidates that had not been recognized in previous observations. Methods: We observed 20 candidates with the adaptive optics imager NaCo and 18 with the high-resolution infrared spectrograph CRIRES. Results: We found previously unknown stars within 2'' of the targets in seven of the candidates. All of these are too faint and too close to the targets to have been previously detected with seeing-limited telescopes in the optical. Our study thus leads to the surprising results that if we remove all candidates excluded by the sophisticated analysis of the light-curve, as well as carrying out deep imaging with seeing-limited telescopes, still 28-35% of the remaining candidates are found to possess companions that are bright enough to be false-positives. Conclusions: Given that the companion candidates cluster around the targets and that the J - K colours are consistent with physical companions, we conclude that the companion candidates are more likely to be physical companions rather than unrelated field stars. Based on observations obtained at the European Southern Observatory at Paranal, Chile in programmes 282.C-5015A, 282.C-5015B, 282.C-5015C, 285.C-5045A, and 285.C-5045B, 086.C-0235A, 086.C-0235B, 088.C-0707A, 088.C-0707B, 090.C-0251A, 090.C-0251B, and 091.C-203(A).Appendices A and B are available in electronic form at http://www.aanda.orgShow less
Context. Whether high mass stars continue to accrete material beyond the formation of an HII region is still an open question. Ionized infall and outflow have been seen in some sources, but their... Show moreContext. Whether high mass stars continue to accrete material beyond the formation of an HII region is still an open question. Ionized infall and outflow have been seen in some sources, but their ties to the surrounding molecular gas are not well constrained. Aims: We aim to quantify the ionized and molecular gas dynamics in a high mass star forming region (K3-50A) and their interaction. Methods: We present CARMA observations of the 3mm continuum, HCO$^{+}$ and H41{$α$} emission, and VLA continuum observations at 23 GHz and 14.7 GHz to quantify the gas and its dynamics in K3-50A. Results: We find large scale dynamics consistent with previous observations. On small scales, we find evidence for interaction between the ionized and molecular gas that suggests the ionized outflow is entraining the molecular one. This is the first time such an outflow entrained by photo ionized gas has been observed. Conclusions: Accretion may be ongoing in K3-50A because an ionized bipolar outflow is still being powered, which is in turn entraining part of the surrounding molecular gas. This outflow scenario is similar to that predicted by ionization feedback models. Show less
Del Moro, A.; Alexander, D.; Mullaney, J.; Daddi, E.; Pannella, M.; Bauer, F.; ... ; Xue, Y. 2013
Context. A tight correlation exists between far-infrared and radio emission for star-forming galaxies (SFGs), which seems to hold out to high redshifts (z {ap} 2). Any excess of radio emission... Show moreContext. A tight correlation exists between far-infrared and radio emission for star-forming galaxies (SFGs), which seems to hold out to high redshifts (z {ap} 2). Any excess of radio emission over that expected from star formation processes is most likely produced by an active galactic nucleus (AGN), often hidden by large amounts of dust and gas. Identifying these radio-excess sources will allow us to study a population of AGN unbiased by obscuration and thus find some of the most obscured, Compton-thick AGN, which are in large part unidentified even in the deepest X-ray and infrared (IR) surveys. Aims: We present here a new spectral energy distribution (SED) fitting approach that we adopt to select radio-excess sources amongst distant star-forming galaxies in the GOODS-Herschel (North) field and to reveal the presence of hidden, highly obscured AGN. Methods: Through extensive SED analysis of 458 galaxies with radio 1.4 GHz and mid-IR 24 {$μ$}m detections using some of the deepest Chandra X-ray, Spitzer and Herschel infrared, and VLA radio data available to date, we have robustly identified a sample of 51 radio-excess AGN (~{}1300 deg$^{-2}$) out to redshift z {ap} 3. These radio-excess AGN have a significantly lower far-IR/radio ratio (q {lt} 1.68, 3{$σ$}) than the typical relation observed for star-forming galaxies (q {ap} 2.2). Results: We find that {ap}45% of these radio-excess sources have a dominant AGN component in the mid-IR band, while for the remainders the excess radio emission is the only indicator of AGN activity. The presence of an AGN is also confirmed by the detection of a compact radio core in deep VLBI 1.4 GHz observations for eight of our radio-excess sources ({ap}16%; {ap}66% of the VLBI detected sources in this field), with the excess radio flux measured from our SED analysis agreeing, to within a factor of two, with the radio core emission measured by VLBI. We find that the fraction of radio-excess AGN increases with X-ray luminosity reaching ~{}60% at L$_X$ {ap} 10$^{44}$ - 10$^{45}$ erg s$^{-1}$, making these sources an important part of the total AGN population. However, almost half (24/51) of these radio-excess AGN are not detected in the deep Chandra X-ray data, suggesting that some of these sources might be heavily obscured. Amongst the radio-excess AGN we can distinguish three groups of objects: i) AGN clearly identified in infrared (and often in X-rays), a fraction of which are likely to be distant Compton-thick AGN; ii) moderate luminosity AGN (L$_X$ {lsim} 10$^{43}$ erg s$^{-1}$) hosted in strong star-forming galaxies; and iii) a small fraction of low accretion-rate AGN hosted in passive (i.e. weak or no star-forming) galaxies. We also find that the specific star formation rates (sSFRs) of the radio-excess AGN are on average lower that those observed for X-ray selected AGN hosts, indicating that our sources are forming stars more slowly than typical AGN hosts, and possibly their star formation is progressively quenching. Tables 1, 3 and Appendices are available in electronic form at http://www.aanda.orgShow less
Uitert, E. van.; Hoekstra, H.; Franx, M.; Gilbank, D.; Gladders, M.; Yee, H. 2013
We present the results of a weak gravitational lensing analysis to determine whether the stellar mass or else the velocity dispersion is more closely related to the amplitude of the lensing signal... Show moreWe present the results of a weak gravitational lensing analysis to determine whether the stellar mass or else the velocity dispersion is more closely related to the amplitude of the lensing signal around galaxies, hence to the projected distribution of dark matter. The lensing signal on smaller scales than the virial radius corresponds most closely to the lensing velocity dispersion in the case of a singular isothermal profile, but is also sensitive on larger scales to the clustering of the haloes. We have selected over 4000 lens galaxies at a redshift z {lt} 0.2 with concentrated (or bulge-dominated) surface brightness profiles from the ~{}300 square degree overlap between the Red-sequence Cluster Survey 2 (RCS2) and the data release 7 (DR7) of the Sloan Digital Sky Survey (SDSS). We consider both the spectroscopic velocity dispersion and a model velocity dispersion (a combination of the stellar mass, the size, and the Sérsic index of a galaxy). Comparing the model and spectroscopic velocity dispersion we find that they correlate well for galaxies with concentrated brightness profiles. We find that the stellar mass and the spectroscopic velocity dispersion trace the amplitude of the lensing signal on small scales equally well. The model velocity dispersion, however, does significantly worse. A possible explanation is that the halo properties that determine the small-scale lensing signal - mainly the total mass - also depend on the structural parameters of galaxies, such as the effective radius and Sérsic index, but we lack data for a definitive conclusion. Show less
Iacobelli, M.; Haverkorn Van Rijsewijk, M.; Katgert, P. 2013
Context. Rotation measure synthesis of the Westerbork Synthesis Radio Telescope (WSRT) observations at {$λ$} ~{} 2 m of the FAN region at l = 137{deg}, b = +7{deg} shows the morphology of... Show moreContext. Rotation measure synthesis of the Westerbork Synthesis Radio Telescope (WSRT) observations at {$λ$} ~{} 2 m of the FAN region at l = 137{deg}, b = +7{deg} shows the morphology of structures in the ionized interstellar medium. Aims: We interpret the diffuse polarized synchrotron emission in terms of coherent structures in the interstellar medium and the properties of the interstellar magnetic field. Methods: We performed statistical analysis of the polarization data cube obtained through rotation measure synthesis. For the first time, cross-correlation is applied to identify and characterize polarized structures in Faraday depth space. Complementary information about the medium are derived from H{$α$} emission, properties of nearby pulsars, and optical polarized starlight measurements. Results: We find an overall asymmetric Faraday dispersion function in a Faraday depth range of [-13, +5] rad m$^{-2}$, which is peaked around -1 rad m$^{-2}$. Three morphological patterns are recognized, showing structures on scales from degrees down to the beam size. The first structure is a nearby synchrotron emission component with low Faraday depth, filling the entire field of view. The second pattern is a circular polarization structure with enhanced (negative) Faraday depth, which has the same morphology as a low-emission region within the third component. This third component is interpreted as the background in which the circular structure is embedded. At low Faraday depth values, a low gradient across the imaged field is detected, almost aligned with the Galactic plane. Power spectra of polarized structures in Faraday depth space provide evidence of turbulence. Conclusions: A sign reversal in Faraday depth from the nearby component to the circular component indicates a reversal of the magnetic field component along the line of sight, from towards the observer and nearby to away from the observer at large distances. The distance to the nearby, extended component is estimated as {lsim}100 pc, which suggests that this structure corresponds to the Local Bubble wall. For the circular component, various physical interpretations are discussed. The most likely explanation is that the circular component seems to be the presence of a nearby (~{}200 pc away) relic Strömgren sphere, associated with an old unidentified white dwarf star and expanding in a low-density environment. Faraday rotation datacubes are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A56Show less
Nisini, B.; Santangelo, G.; Antoniucci, S.; Benedettini, M.; Codella, C.; Giannini, T.; ... ; Dishoeck, E.F. van 2013
Context. Water is a key probe of shocks and outflows from young stars because it is extremely sensitive to both the physical conditions associated with the interaction of supersonic outflows with... Show moreContext. Water is a key probe of shocks and outflows from young stars because it is extremely sensitive to both the physical conditions associated with the interaction of supersonic outflows with the ambient medium and the chemical processes at play. Aims: Our goal is to investigate the spatial and velocity distribution of H$_{2}$O along outflows, its relationship with other tracers, and its abundance variations. In particular, this study focuses on the outflow driven by the low-mass protostar L1448-C, which previous observations have shown to be one of the brightest H$_{2}$O emitters among the class 0 outflows. Methods: To this end, maps of the o-H$_{2}$O 1$_{10}$-1$_{01}$ and 2$_{12}$-1$_{01}$ transitions taken with the Herschel-HIFI and PACS instruments, respectively, are presented. For comparison, complementary maps of the CO(3-2) and SiO(8-7) transitions, obtained at the JCMT, and the H$_{2}$ S(0) and S(1) transitions, taken from the literature, were used as well. Physical conditions and H$_{2}$O column densities were inferred using large velocity gradient radiative transfer calculations. Results: The water distribution appears to be clumpy, with individual peaks corresponding to shock spots along the outflow. The bulk of the 557 GHz line is confined to radial velocities in the range {plusmn}10-50 km s$^{-1}$, but extended emission at extreme velocities (up to v$_r$ ~{} 80 km s$^{-1}$) is detected and is associated with the L1448-C extreme high-velocity (EHV) jet. The H$_{2}$O 1$_{10}$-1$_{01}$/CO(3-2) ratio shows strong variations as a function of velocity that likely reflect different and changing physical conditions in the gas that is responsible for the emissions from the two species. In the EHV jet, a low H$_{2}$O/SiO abundance ratio is inferred, which could indicate molecular formation from dust-free gas directly ejected from the proto-stellar wind. The ratio between the two observed H$_{2}$O lines and the comparison with H$_{2}$ indicate averaged T$_{kin}$ and n(H$_{2}$) values of ~{}300-500 K and 5 { imes} 10$^{6}$ cm$^{-3}$, respectively, while a water abundance with respect to H$_{2}$ of about 0.5-1 { imes} 10$^{-6}$ along the outflow is estimated, in agreement with results found by previous studies. The fairly constant conditions found all along the outflow imply that evolutionary effects on the timescales of outflow propagation do not play a major role in the H$_{2}$O chemistry. Conclusions: The results of our analysis show that the bulk of the observed H$_{2}$O lines comes from post-shocked regions where the gas, after being heated to high temperatures, has already been cooled down to a few hundred K. The relatively low derived abundances, however, call for some mechanism that diminishes the H$_{2}$O gas in the post-shock region. Among the possible scenarios, we favor H$_{2}$O photodissociation, which requires the superposition of a low-velocity nondissociative shock with a fast dissociative shock able to produce a far-ultraviolet field of sufficient strength. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Appendices are available in electronic form at http://www.aanda.orgShow less
Context. According to traditional gas-phase chemical models, O$_{2}$ should be abundant in molecular clouds, but until recently, attempts to detect interstellar O$_{2}$ line emission with ground-... Show moreContext. According to traditional gas-phase chemical models, O$_{2}$ should be abundant in molecular clouds, but until recently, attempts to detect interstellar O$_{2}$ line emission with ground- and space-based observatories have failed. Aims: Following the multi-line detections of O$_{2}$ with low abundances in the Orion and {$ρ$} Oph A molecular clouds with Herschel, it is important to investigate other environments, and we here quantify the O$_{2}$ abundance near a solar-mass protostar. Methods: Observations of molecular oxygen, O$_{2}$, at 487 GHz toward a deeply embedded low-mass Class 0 protostar, NGC 1333-IRAS 4A, are presented, using the Heterodyne Instrument for the Far Infrared (HIFI) on the Herschel Space Observatory. Complementary data of the chemically related NO and CO molecules are obtained as well. The high spectral resolution data are analysed using radiative transfer models to infer column densities and abundances, and are tested directly against full gas-grain chemical models. Results: The deep HIFI spectrum fails to show O$_{2}$ at the velocity of the dense protostellar envelope, implying one of the lowest abundance upper limits of O$_{2}$/H$_{2}$ at {le}6 { imes} 10$^{-9}$ (3{$σ$}). The O$_{2}$/CO abundance ratio is less than 0.005. However, a tentative (4.5{$σ$}) detection of O$_{2}$ is seen at the velocity of the surrounding NGC 1333 molecular cloud, shifted by 1 km s$^{-1}$ relative to the protostar. For the protostellar envelope, pure gas-phase models and gas-grain chemical models require a long pre-collapse phase (~{}0.7-1 { imes} 10$^{6}$ years), during which atomic and molecular oxygen are frozen out onto dust grains and fully converted to H$_{2}$O, to avoid overproduction of O$_{2}$ in the dense envelope. The same model also reproduces the limits on the chemically related NO molecule if hydrogenation of NO on the grains to more complex molecules such as NH$_{2}$OH, found in recent laboratory experiments, is included. The tentative detection of O$_{2}$ in the surrounding cloud is consistent with a low-density PDR model with small changes in reaction rates. Conclusions: The low O$_{2}$ abundance in the collapsing envelope around a low-mass protostar suggests that the gas and ice entering protoplanetary disks is very poor in O$_{2}$. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.orgReduced spectra (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/558/A58Show less
Aims: In the framework of the Water In Star-forming regions with Herschel (WISH) key program, several H$_{2}$O (E$_u$ {gt} 190 K), high-J CO, [Oi], and OH transitions are mapped with Herschel... Show moreAims: In the framework of the Water In Star-forming regions with Herschel (WISH) key program, several H$_{2}$O (E$_u$ {gt} 190 K), high-J CO, [Oi], and OH transitions are mapped with Herschel-PACS in two shock positions along two prototypical outflows around the low-luminosity sources L1448 and L1157. Previous Herschel-HIFI H$_{2}$O observations (E$_u$ = 53-249 K) are also used. The aim is to derive a complete picture of the excitation conditions at the selected shock positions. Methods: We adopted a large velocity gradient analysis (LVG) to derive the physical parameters of the H$_{2}$O and CO emitting gas. Complementary Spitzer mid-IR H$_{2}$ data were used to derive the H$_{2}$O abundance. Results: Consistent with other studies, at all selected shock spots a close spatial association between H$_{2}$O, mid-IR H$_{2}$, 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, conducted in detail at the L1448-B2 position, suggests that a two-component model is needed to reproduce the H$_{2}$O, CO, and mid-IR H$_{2}$ lines: an extended warm component (T ~{} 450 K) is traced by the H$_{2}$O 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 H$_{2}$O emission with E$_u$ {gt} 190 K and by the higher-J CO transitions. At L1448-B2 we obtain an H$_{2}$O abundance (3-4) { imes} 10$^{-6}$ for the warm component and (0.3-1.3) { imes} 10$^{-5}$ for the hot component and a CO abundance of a few 10$^{-5}$ in both components. In L1448-B2 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 H$_{2}$O and CO emission. The other examined shock positions show an H$_{2}$O excitation similar to L1448-B2, but a slightly higher H$_{2}$O abundance (a factor of ~{}4). Conclusions: 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. This hot gas component is more affected by evolutionary effects on the timescales of the outflow propagation, which explains the observed H$_{2}$O abundance variations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix A is available in electronic form at http://www.aanda.orgShow less
San Jose Garcia, I.; Mottram, J.C.; Kristensen, L.; Dishoeck, E.F. van; Yıldız, U.; Tak, F.; ... ; Johnstone, D. 2013
Context. Our understanding of the star formation process has traditionally been confined to certain mass or luminosity boundaries because most studies focus only on low-, intermediate-, or high... Show moreContext. Our understanding of the star formation process has traditionally been confined to certain mass or luminosity boundaries because most studies focus only on low-, intermediate-, or high-mass star-forming regions. Therefore, the processes that regulate the formation of these different objects have not been effectively linked. As part of the ''Water In Star-forming regions with Herschel'' (WISH) key programme, water and other important molecules, such as CO and OH, have been observed in 51 embedded young stellar objects (YSOs). The studied sample covers a range of luminosities from {lt}1 to {gt}10$^{5}$L$_{⊙}$. Aims: We analyse the CO line emission towards a large sample of embedded protostars in terms of both line intensities and profiles. This analysis covers a wide luminosity range in order to achieve better understanding of star formation without imposing luminosity boundaries. In particular, this paper aims to constrain the dynamics of the environment in which YSOs form. Methods: Herschel-HIFI spectra of the $^{12}$CO J = 10-9, $^{13}$CO J = 10-9 and C$^{18}$O J = 5-4, J = 9-8 and J = 10-9 lines were analysed for a sample of 51 embedded protostars. In addition, JCMT spectra of $^{12}$CO J = 3-2 and C$^{18}$O J = 3-2 extend this analysis to cooler gas components. We focussed on characterising the shape and intensity of the CO emission line profiles by fitting the lines with one or two Gaussian profiles. We compared the values and results of these fits across the entire luminosity range covered by WISH observations. The effects of different physical parameters as a function of luminosity and the dynamics of the envelope-outflow system were investigated. Results: All observed CO and isotopologue spectra show a strong linear correlation between the logarithms of the line and bolometric luminosities across six orders of magnitude on both axes. This suggests that the high-J CO lines primarily trace the amount of dense gas associated with YSOs and that this relation can be extended to larger (extragalactic) scales. The majority of the detected $^{12}$CO line profiles can be decomposed into a broad and a narrow Gaussian component, while the C$^{18}$O spectra are mainly fitted with a single Gaussian. For low- and intermediate-mass protostars, the width of the C$^{18}$O J = 9-8 line is roughly twice that of the C$^{18}$O J = 3-2 line, suggesting increased turbulence/infall in the warmer inner envelope. For high-mass protostars, the line widths are comparable for lower- and higher-J lines. A broadening of the line profile is also observed from pre-stellar cores to embedded protostars, which is due mostly to non-thermal motions (turbulence/infall). The widths of the broad $^{12}$CO J = 3-2 and J = 10-9 velocity components correlate with those of the narrow C$^{18}$O J = 9-8 profiles, suggesting that the entrained outflowing gas and envelope motions are related but independent of the mass of the protostar. These results indicate that physical processes in protostellar envelopes have similar characteristics across the studied luminosity range. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.orgShow less
Context. Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks, but its photodissociation under interstellar conditions has never been... Show moreContext. Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks, but its photodissociation under interstellar conditions has never been properly studied. The partitioning of nitrogen between N and N$_{2}$ controls the formation of more complex prebiotic nitrogen-containing species. Aims: The aim of this work is to gain a better understanding of the interstellar N$_{2}$ photodissociation processes based on recent detailed theoretical and experimental work and to provide accurate rates for use in chemical models. Methods: We used an approach similar to that adopted for CO in which we simulated the full high-resolution line-by-line absorption + dissociation spectrum of N$_{2}$ over the relevant 912-1000 å wavelength range, by using a quantum-mechanical model which solves the coupled-channels Schrödinger equation. The simulated N$_{2}$ spectra were compared with the absorption spectra of H$_{2}$, H, CO, and dust to compute photodissociation rates in various radiation fields and shielding functions. The effects of the new rates in interstellar cloud models were illustrated for diffuse and translucent clouds, a dense photon dominated region and a protoplanetary disk. Results: The unattenuated photodissociation rate in the Draine (1978, ApJS, 36, 595) radiation field assuming an N$_{2}$ excitation temperature of 50 K is 1.65 { imes} 10$^{-10}$ s$^{-1}$, with an uncertainty of only 10%. Most of the photodissociation occurs through bands in the 957-980 å range. The N$_{2}$ rate depends slightly on the temperature through the variation of predissociation probabilities with rotational quantum number for some bands. Shielding functions are provided for a range of H$_{2}$ and H column densities, with H$_{2}$ being much more effective than H in reducing the N$_{2}$ rate inside a cloud. Shielding by CO is not effective. The new rates are 28% lower than the previously recommended values. Nevertheless, diffuse cloud models still fail to reproduce the possible detection of interstellar N$_{2}$ except for unusually high densities and/or low incident UV radiation fields. The transition of N { arr} N$_{2}$ occurs at nearly the same depth into a cloud as that of C$^{+}$ { arr} C { arr} CO. The orders-of-magnitude lower N$_{2}$ photodissociation rates in clouds exposed to black-body radiation fields of only 4000 K can qualitatively explain the lack of active nitrogen chemistry observed in the inner disks around cool stars. Conclusions: Accurate photodissociation rates for N$_{2}$ as a function of depth into a cloud are now available that can be applied to a wide variety of astrophysical environments. Appendices are available in electronic form at http://www.aanda.orgShow less
Klaassen, P.D.; Juhasz, A.; Mathews, G.S.; Mottram, J.C.; De Gregorio-Monsalvo, I.; Dishoeck, E.F. van; ... ; Testi, L. 2013
Disk winds have been postulated as a mechanism for angular momentum release in protostellar systems for decades. HD 163296 is a Herbig Ae star surrounded by a disk and has been shown to host a... Show moreDisk winds have been postulated as a mechanism for angular momentum release in protostellar systems for decades. HD 163296 is a Herbig Ae star surrounded by a disk and has been shown to host a series of HH knots (HH 409) with bow shocks associated with the farthest knots. Here we present ALMA science verification data of CO J = 2-1 and J = 3-2 emission, which are spatially coincident with the blue shifted jet of HH knots, and offset from the disk by -18.6 km s$^{-1}$. The emission has a double corkscrew morphology and extends more than 10'' from the disk with embedded emission clumps coincident with jet knots. We interpret this double corkscrew as emission from material in a molecular disk wind, and that the compact emission near the jet knots is being heated by the jet that is moving at much higher velocities. We show that the J = 3-2 emission is likely heavily filtered by the interferometer, but the J = 2-1 emission suffers less due to the larger beam and sensitivity to larger scale structures. Excitation analysis suggests temperatures exceeding 900 K in these compact features, with the wind mass, momentum and energy being of order 10$^{-5}$ M$_{⊙}$, 10$^{-4}$ M$_{⊙}$ km s$^{-1}$ and 10$^{40}$ erg, respectively. The high mass loss rate suggests that this star is dispersing the disk faster than it is funneling mass onto the star. Show less
Context. We have analysed far-infrared spectra of 32 circumstellar disks around Herbig Ae/Be and T Tauri stars obtained within the Herschel key programme Dust, Ice and Gas in Time (DIGIT). The... Show moreContext. We have analysed far-infrared spectra of 32 circumstellar disks around Herbig Ae/Be and T Tauri stars obtained within the Herschel key programme Dust, Ice and Gas in Time (DIGIT). The spectra were taken with the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel Space Observatory. In this paper we focus on the detection and analysis of the 69 {$μ$}m emission band of the crystalline silicate forsterite. Aims: This work aims at providing an overview of the 69 {$μ$}m forsterite bands present in the DIGIT sample. We use characteristics of the emission band (peak position and FWHM) to derive the dust temperature and to constrain the iron content of the crystalline silicates. With this information, constraints can be placed on the spatial distribution of the forsterite in the disk and the formation history of the crystalline grains. Methods: The 69 {$μ$}m forsterite emission feature is analysed in terms of position and shape to derive the temperature and composition of the dust by comparison to laboratory spectra of that band. The PACS spectra are combined with existing Spitzer IRS spectra and we compare the presence and strength of the 69 {$μ$}m band to the forsterite bands at shorter wavelengths. Results: A total of 32 disk sources have been observed. Out of these 32, 8 sources show a 69 {$μ$}m emission feature that can be attributed to forsterite. With the exception of the T Tauri star AS 205, all of the detections are for disks associated with Herbig Ae/Be stars. Most of the forsterite grains that give rise to the 69 {$μ$}m bands are found to be warm (~{}100-200 K) and iron-poor (less than ~{}2% iron). AB Aur is the only source where the emission cannot be fitted with iron-free forsterite requiring approximately 3-4% of iron. Conclusions: Our findings support the hypothesis that the forsterite grains form through an equilibrium condensation process at high temperatures. The large width of the emission band in some sources may indicate the presence of forsterite reservoirs at different temperatures. The connection between the strength of the 69 and 33 {$μ$}m bands shows that at least part of the emission in these two bands originates fom the same dust grains. We further find that any model that can explain the PACS and the Spitzer IRS observations must take the effects of a wavelength dependent optical depth into account. We find weak indications of a correlation of the detection rate of the 69 {$μ$}m band with the spectral type of the host stars in our sample. However, the sample size is too small to obtain a definitive result. Appendix A is available in electronic form at http://www.aanda.orgShow less
Context. Over the last few years, the chemistry of molecules other than CO in the planet-forming zones of disks is starting to be explored with Spitzer and high-resolution ground-based data.... Show moreContext. Over the last few years, the chemistry of molecules other than CO in the planet-forming zones of disks is starting to be explored with Spitzer and high-resolution ground-based data. However, these studies have focused only on a few simple molecules. Aims: The aim of this study is to put observational constraints on the presence of more complex organic and sulfur-bearing molecules predicted to be abundant in chemical models of disks and to simulate high resolution spectra in view of future missions. Methods: High signal-to-noise ratio (S/N) Spitzer spectra of the near edge-on disks IRS 46 and GV Tau are used to search for mid-infrared absorption bands of various molecules. These disks are good laboratories because absorption studies do not suffer from low line/continuum ratios that plague emission data. Simple local thermodynamic equilibrium (LTE) slab models are used to infer column densities (or upper limits) and excitation temperatures. Results: Mid-infrared bands of HCN, C$_{2}$H$_{2}$ and CO$_{2}$ are clearly detected toward both sources. The HCN and C$_{2}$H$_{2}$ absorption arises in warm gas with excitation temperatures of 400-700 K, whereas the CO$_{2}$ absorption originates in cooler gas of ~{}250 K. Column densities and their ratios are comparable for the two sources. No other absorption features are detected at the 3{$σ$} level. Column density limits of the majority of molecules predicted to be abundant in the inner disk - C$_{2}$H$_{4}$, C$_{2}$H$_{6}$, C$_{6}$H$_{6}$, C$_{3}$H$_{4}$, C$_{4}$H$_{2}$, CH$_{3}$, HNC, HC$_{3}$N, CH$_{3}$CN, NH$_{3}$ and SO$_{2}$ - are determined and compared with disk models. Conclusions: The inferred abundance ratios and limits with respect to C$_{2}$H$_{2}$ and HCN are roughly consistent with models of the chemistry in high temperature gas. Models of UV irradiated disk surfaces generally agree better with the data than pure X-ray models. The limit on NH$_{3}$/HCN implies that evaporation of NH$_{3}$-containing ices is only a minor contributor. The inferred abundances and their limits also compare well with those found in comets, suggesting that part of the cometary material may derive from warm inner disk gas. The high resolution simulations show that future instruments on the James Webb Space Telescope (JWST), the Extremely Large Telescopes (ELTs), the Stratospheric Observatory for Infrared Astronomy (SOFIA) and the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) can probe up to an order of magnitude lower abundance ratios and put important new constraints on the models, especially if pushed to high S/Ns. Appendices are available in electronic form at http://www.aanda.orgShow less
Mottram, J.C.; Dishoeck, E.F. van; Schmalzl, M.; Kristensen, L.; Visser, R.; Hogerheijde, M.R.; Bruderer, S. 2013
Context. For stars to form, material must fall inwards from core scales through the envelope towards the central protostar. While theories of how this takes place have been around for some time,... Show moreContext. For stars to form, material must fall inwards from core scales through the envelope towards the central protostar. While theories of how this takes place have been around for some time, the velocity profile around protostars is poorly constrained. The combination of observations in multiple transitions of a tracer which is sensitive to kinematics and radiative transfer modelling of those lines has the potential to break this deadlock. Aims: Seven protostars observed with the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory as part of the ''Water in star-forming regions with Herschel'' (WISH) survey show infall signatures in water line observations. We aim to constrain the infall velocity and the radii over which infall is taking place within the protostellar envelopes of these sources. We will also use these data to constrain the chemistry of cold water. Methods: We use 1-D non-LTE ratran radiative transfer models of the observed water lines to constrain the infall velocity and chemistry in the protostellar envelopes of six Class 0 protostars and one Class I source. We assume a free-fall velocity profile and, having found the best fit, vary the radii over which infall takes place. Results: In the well-studied Class 0 protostar NGC 1333-IRAS4A we find that our observations probe infall over the whole envelope to which our observations are sensitive (r {gsim} 1000 AU). For L1527, L1157, BHR71 and IRAS 15398 infall takes place on core to envelope scales (i.e. ~{}10 000-3000 AU). In Serpens-SMM4 and GSS30 the inverse P-Cygni profiles seen in the ground-state lines are more likely due to larger-scale motions or foreground clouds. Models including a simple consideration of the chemistry are consistent with the observations, while using step abundance profiles are not. The non-detection of excited water in the inner envelope in six out of seven protostars is further evidence that water must be heavily depleted from the gas-phase at these radii. Conclusions: Infall in four of the sources is supersonic and in all sources must take place at the outer edge of the envelope, which may be evidence that collapse is global or outside-in rather than inside-out. The mass infall rate in NGC 1333-IRAS4A is large ({gsim}10$^{-4}$M$_{⊙}$ yr$^{-1}$), higher than the mass outflow rate and expected mass accretion rates onto the star. This suggests that any flattened disk-like structure on small scales will be gravitationally unstable, potentially leading to rotational fragmentation and/or episodic accretion. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix A is available in electronic form at http://www.aanda.orgShow less
Aims: Herschel-HIFI spectra of H$_{2}$O towards low-mass protostars show a distinct velocity component not seen in observations from the ground of CO or other species. The aim is to characterise... Show moreAims: Herschel-HIFI spectra of H$_{2}$O towards low-mass protostars show a distinct velocity component not seen in observations from the ground of CO or other species. The aim is to characterise this component in terms of excitation conditions and physical origin. Methods: A velocity component with an offset of ~{}10 km s$^{-1}$ detected in spectra of the H$_{2}$O 1$_{10}$-1$_{01}$ 557 GHz transition towards six low-mass protostars in the ''Water in star-forming regions with Herschel'' (WISH) programme is also seen in higher-excited H$_{2}$O lines. The emission from this component is quantified and local excitation conditions are inferred using 1D slab models. Data are compared to observations of hydrides (high-J CO, OH$^{+}$, CH$^{+}$, C$^{+}$, OH) where the same component is uniquely detected. Results: The velocity component is detected in all six targeted H$_{2}$O transitions (E$_{up}$ ~{} 50-250 K), as well as in CO 16-15 towards one source, Ser SMM1. Inferred excitation conditions imply that the emission arises in dense (n ~{} 5 { imes} 10$^{6}$-10$^{8}$ cm$^{-3}$) and hot (T ~{} 750 K) gas. The H$_{2}$O and CO column densities are {gsim}10$^{16}$ and 10$^{18}$ cm$^{-2}$, respectively, implying a low H$_{2}$O abundance of ~{}10$^{-2}$ with respect to CO. The high column densities of ions such as OH$^{+}$ and CH$^{+}$ (both {gsim}10$^{13}$ cm$^{-2}$) indicate an origin close to the protostar where the UV field is strong enough that these species are abundant. The estimated radius of the emitting region is 100 AU. This component likely arises in dissociative shocks close to the protostar, an interpretation corroborated by a comparison with models of such shocks. Furthermore, one of the sources, IRAS 4A, shows temporal variability in the offset component over a period of two years which is expected from shocks in dense media. High-J CO gas detected with Herschel-PACS with T$_{rot}$ ~{} 700 K is identified as arising in the same component and traces the part of the shock where H$_{2}$ reforms. Thus, H$_{2}$O reveals new dynamical components, even on small spatial scales in low-mass protostars. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Show less
Context. The measure of the water deuterium fractionation is a relevant tool for understanding mechanisms of water formation and evolution from the prestellar phase to the formation of planets and... Show moreContext. The measure of the water deuterium fractionation is a relevant tool for understanding mechanisms of water formation and evolution from the prestellar phase to the formation of planets and comets. Aims: The aim of this paper is to study deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B, to compare their HDO abundance distributions with other star-forming regions, and to constrain their HDO/H$_{2}$O abundance ratios. Methods: Using the Herschel/HIFI instrument as well as ground-based telescopes, we observed several HDO lines covering a large excitation range (E$_{up}$/k = 22-168 K) towards these protostars and an outflow position. Non-local thermal equilibrium radiative transfer codes were then used to determine the HDO abundance profiles in these sources. Results: The HDO fundamental line profiles show a very broad component, tracing the molecular outflows, in addition to a narrower emission component and a narrow absorbing component. In the protostellar envelope of NGC 1333 IRAS 4A, the HDO inner (T {ge} 100 K) and outer (T {lt} 100 K) abundances with respect to H$_{2}$ are estimated with a 3{$σ$} uncertainty at 7.5$_{-3.0}$$^{+3.5}$ { imes} 10$^{-9}$ and 1.2$_{-0.4}$$^{+0.4}$ { imes} 10$^{-11}$, respectively, whereas in NGC 1333 IRAS 4B they are 1$_{-0.9}$$^{+1.8}$ { imes} 10$^{-8}$ and 1.2$_{-0.4}$$^{+0.6}$ { imes} 10$^{-10}$, respectively. Similarly to the low-mass protostar IRAS 16293-2422, an absorbing outer layer with an enhanced abundance of deuterated water is required to reproduce the absorbing components seen in the fundamental lines at 465 and 894 GHz in both sources. This water-rich layer is probably extended enough to encompass the two sources, as well as parts of the outflows. In the outflows emanating from NGC 1333 IRAS 4A, the HDO column density is estimated at about (2-4) { imes} 10$^{13}$ cm$^{-2}$, leading to an abundance of about (0.7-1.9) { imes} 10$^{-9}$. An HDO/H$_{2}$O ratio between 7 { imes} 10$^{-4}$ and 9 { imes} 10$^{-2}$ is also derived in the outflows. In the warm inner regions of these two sources, we estimate the HDO/H$_{2}$O ratios at about 1 { imes} 10$^{-4}$-4 { imes} 10$^{-3}$. This ratio seems higher (a few %) in the cold envelope of IRAS 4A, whose possible origin is discussed in relation to formation processes of HDO and H$_{2}$O. Conclusions: In low-mass protostars, the HDO outer abundances range in a small interval, between ~{}10$^{-11}$ and a few 10$^{-10}$. No clear trends are found between the HDO abundance and various source parameters (L$_{bol}$, L$_{smm}$, L$_{smm}$/L$_{bol}$, T$_{bol}$, L$_{bol}$$^{0.6}$/M$_{env}$). A tentative correlation is observed, however, between the ratio of the inner and outer abundances with the submillimeter luminosity. Based on observations carried out with the Herschel/HIFI instrument, the Institut de Radioastronomie Millimétrique (IRAM) 30 m Telescope, the James Clerk Maxwell Telescope (JCMT), and one of the ESO telescopes at the La Silla Paranal, the Atacama Pathfinder Experiment (APEX, programme ID 090.C-0239). Herschel is an ESA space observatory with science instruments provided by European-led principal Investigator consortia and with important participation from NASA. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). The JCMT is operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the United Kingdom, the Netherlands Organization for Scientific Research, and the National Research Council of Canada. APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the ESO, and the Onsala Space Observatory.Appendices are available in electronic form at http://www.aanda.orgShow less
Tafalla, M.; Liseau, R.; Nisini, B.; Bachiller, R.; Santiago-García, J.; Dishoeck, E.F. van; ... ; Yıldız, U. 2013
Context. Water is a potential tracer of outflow activity because it is heavily depleted in cold ambient gas and is copiously produced in shocks. Aims: We present a survey of the water emission in... Show moreContext. Water is a potential tracer of outflow activity because it is heavily depleted in cold ambient gas and is copiously produced in shocks. Aims: We present a survey of the water emission in a sample of more than 20 outflows from low-mass young stellar objects with the goal of characterizing the physical and chemical conditions of the emitting gas. Methods: We used the HIFI and PACS instruments on board the Herschel Space Observatory to observe the two fundamental lines of ortho-water at 557 and 1670 GHz. These observations were part of the ''Water In Star-forming regions with Herschel'' (WISH) key program, and have been complemented with CO and H$_{2}$ data. Results: The emission of water has a different spatial and velocity distribution from that of the J = 1-0 and 2-1 transitions of CO. On the other hand, it has a similar spatial distribution to H$_{2}$, and its intensity follows the H$_{2}$ intensity derived from IRAC images. This suggests that water traces the outflow gas at hundreds of kelvins that is responsible for the H$_{2}$ emission, and not the component at tens of kelvins typical of low-J CO emission. A warm origin of the water emission is confirmed by a remarkable correlation between the intensities of the 557 and 1670 GHz lines, which also indicates that the emitting gas has a narrow range of excitations. A radiative transfer analysis shows that while there is some ambiguity in the exact combination of density and temperature values, the gas thermal pressure nT is constrained within less than a factor of 2. The typical nT over the sample is 4 { imes} 10$^{9}$ cm$^{-3}$K, which represents an increase of 10$^{4}$ with respect to the ambient value. The data also constrain the water column density within a factor of 2 and indicate values in the sample between 2 { imes} 10$^{12}$ and 10$^{14}$ cm$^{-2}$. When these values are combined with estimates of the H$_{2}$ column density, the typical water abundance is only 3 { imes} 10$^{-7}$, with an uncertainty of a factor of 3. Conclusions: Our data challenge current C-shock models of water production through the combination of wing-line profiles, high gas compressions, and low abundances. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Show less
