Aims: Most studies of high-mass star formation focus on massive and/or luminous clumps, but the physical properties of their larger scale environment are poorly known. In this work, we aim at... Show moreAims: Most studies of high-mass star formation focus on massive and/or luminous clumps, but the physical properties of their larger scale environment are poorly known. In this work, we aim at characterising the effects of clustered star formation and feedback of massive stars on the surrounding medium by studying the distribution of warm gas through mid-J$^{12}$CO and $^{13}$CO observations. Methods: We present APEX $^{12}$CO(6-5), (7-6), $^{13}$CO(6-5), (8-7) and HIFI $^{13}$CO(10-9) maps of the star forming region G327.36-0.6 with a linear size of ~{}3 pc { imes} 4 pc. We infer the physical properties of the emitting gas on large scales through a local thermodynamic equilibrium analysis, while we apply a more sophisticated large velocity gradient approach on selected positions. Results: Maps of all lines are dominated in intensity by the photon dominated region around the Hii region G327.3-0.5. Mid-J$^{12}$CO emission is detected over the whole extent of the maps with excitation temperatures ranging from 20 K up to 80 K in the gas around the Hii region, and H$_{2}$ column densities from few 10$^{21}$ cm$^{-2}$ in the inter-clump gas to 3 { imes} 10$^{22}$ cm$^{-2}$ towards the hot core G327.3-0.6. The warm gas (traced by $^{12}$ and $^{13}$CO(6-5) emission) is only a small percentage (~{}10%) of the total gas in the infrared dark cloud, while it reaches values up to ~{}35% of the total gas in the ring surrounding the Hii region. The $^{12}$CO ladders are qualitatively compatible with photon dominated region models for high density gas, but the much weaker than predicted $^{13}$CO emission suggests that it comes from a large number of clumps along the line of sight. All lines are detected in the inter-clump gas when averaged over a large region with an equivalent radius of 50''(~{}0.8 pc), implying that the mid-J$^{12}$CO and $^{13}$CO inter-clump emission is due to high density components with low filling factor. Finally, the detection of the $^{13}$CO(10-9) line allows to disentangle the effects of gas temperature and gas density on the CO emission, which are degenerate in the APEX observations alone. Show 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. 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
Context. Understanding the physical phenomena involved in the earlierst stages of protostellar evolution requires knowledge of the heating and cooling processes that occur in the surroundings of a... Show moreContext. Understanding the physical phenomena involved in the earlierst stages of protostellar evolution requires knowledge of the heating and cooling processes that occur in the surroundings of a young stellar object. Spatially resolved information from its constituent gas and dust provides the necessary constraints to distinguish between different theories of accretion energy dissipation into the envelope. Aims. Our aims are to quantify the far-infrared line emission from low-mass protostars and the contribution of different atomic and molecular species to the gas cooling budget, to determine the spatial extent of the emission, and to investigate the underlying excitation conditions. Analysis of the line cooling will help us characterize the evolution of the relevant physical processes as the protostar ages. Methods. Far-infrared Herschel-PACS spectra of 18 low-mass protostars of various luminosities and evolutionary stages are studied in the context of the WISH key program. For most targets, the spectra include many wavelength intervals selected to cover specific CO, H$_{2}$O, OH, and atomic lines. For four targets the spectra span the entire 55-200 {$μ$}m region. The PACS field-of-view covers ~{}47'' with the resolution of 9.4''. Results. Most of the protostars in our sample show strong atomic and molecular far-infrared emission. Water is detected in 17 out of 18 objects (except TMC1A), including 5 Class I sources. The high-excitation H$_{2}$O 8$_{18}$-7$_{07}$ 63.3 {$μ$}m line (E$_u$/k$_B$ = 1071 K) is detected in 7 sources. CO transitions from J = 14-13 up to J = 49 - 48 are found and show two distinct temperature components on Boltzmann diagrams with rotational temperatures of ~{}350 K and ~{}700 K. H$_{2}$O has typical excitation temperatures of ~{}150 K. Emission from both Class 0 and I sources is usually spatially extended along the outflow direction but with a pattern that depends on the species and the transition. In the extended sources, emission is stronger off source and extended on {amp}{ge}10,000 AU scales; in the compact sample, more than half of the flux originates within 1000 AU of the protostar. The H$_{2}$O line fluxes correlate strongly with those of the high-J CO lines, both for the full array and for the central position, as well as with the bolometric luminosity and envelope mass. They correlate less strongly with OH fluxes and not with [O I] fluxes. In contrast, [O I] and OH often peak together at the central position. Conclusions. The PACS data probe at least two physical components. The H$_{2}$O and CO emission very likely arises in non-dissociative (irradiated) shocks along the outflow walls with a range of pre-shock densities. Some OH is also associated with this component, most likely resulting from H$_{2}$O photodissociation. UV-heated gas contributes only a minor fraction to the CO emission observed by PACS, based on the strong correlation between the shock-dominated CO 24-23 line and the CO 14-13 line. [O I] and some of the OH emission probe dissociative shocks in the inner envelope. The total far-infrared cooling is dominated by H$_{2}$O and CO, with the fraction contributed by [O I] increasing for Class I sources. Consistent with previous studies, the ratio of total far-infrared line emission over bolometric luminosity decreases with the evolutionary state. Appendices A-J are available in electronic form at http://www.aanda.orgShow less
Tak, F.; Chavarría, L.; Herpin, F.; Wyrowski, F.; Walmsley, C.; Dishoeck, E.F. van; ... ; Tafalla, M. 2013
Context. Water is a key constituent of star-forming matter, but the origin of its line emission and absorption during high-mass star formation is not well understood. Aims: We study the velocity... Show moreContext. Water is a key constituent of star-forming matter, but the origin of its line emission and absorption during high-mass star formation is not well understood. Aims: We study the velocity profiles of low-excitation H$_{2}$O lines toward 19 high-mass star-forming regions and search for trends with luminosity, mass, and evolutionary stage. Methods: We decompose high-resolution Herschel-HIFI line spectra near 990, 1110 and 1670 GHz into three distinct physical components. Dense cores (protostellar envelopes) are usually seen as narrow absorptions in the H$_{2}$O 1113 and 1669 GHz ground-state lines, the H$_{2}$O 987 GHz excited-state line, and the H$_{2}$$^{18}$O 1102 GHz ground-state line. In a few sources, the envelopes appear in emission in some or all studied lines, indicating higher temperatures or densities. Broader features due to outflows are usually seen in absorption in the H$_{2}$O 1113 and 1669 GHz lines, in 987 GHz emission, and not seen in H$_{2}$$^{18}$O, indicating a lower column density and a higher excitation temperature than the envelope component. A few outflows are detected in H$_{2}$$^{18}$O, indicating higher column densities of shocked gas. In addition, the H$_{2}$O 1113 and 1669 GHz spectra show narrow absorptions by foreground clouds along the line of sight. The lack of corresponding features in the 987 GHz and H$_{2}$$^{18}$O lines indicates a low column density and a low excitation temperature for these clouds, although their derived H$_{2}$O ortho/para ratios are close to 3. Results: The intensity of the ground state lines of H$_{2}$O at 1113 and 1669 GHz does not show significant trends with source luminosity, envelope mass, or evolutionary state. In contrast, the flux in the excited-state 987 GHz line appears correlated with luminosity and the H$_{2}$$^{18}$O line flux appears correlated with the envelope mass. Furthermore, appearance of the envelope in absorption in the 987 GHz and H$_{2}$$^{18}$O lines seems to be a sign of an early evolutionary stage, as probed by the mid-infrared brightness and the L$_{bol}$/M$_{env}$ ratio of the source. Conclusions: The ground state transitions of H$_{2}$O trace the outer parts of the envelopes, so that the effects of star formation are mostly noticeable in the outflow wings. These lines are heavily affected by absorption, so that line ratios of H$_{2}$O involving the ground states must be treated with caution, especially if multiple clouds are superposed as in the extragalactic case. The isotopic H$_{2}$$^{18}$O line appears to trace the mass of the protostellar envelope, indicating that the average H$_{2}$O abundance in high-mass protostellar envelopes does not change much with time. The excited state line at 987 GHz increases in flux with luminosity and appears to be a good tracer of the mean weighted dust temperature of the source, which may explain why it is readily seen in distant galaxies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.orgShow less
Leurini, S.; Wyrowski, F.; Herpin, F.; Tak, F.; Güsten, R.; Dishoeck, E.F. van 2013
Aims: Most studies of high-mass star formation focus on massive and/or luminous clumps, but the physical properties of their larger scale environment are poorly known. In this work, we aim at... Show moreAims: Most studies of high-mass star formation focus on massive and/or luminous clumps, but the physical properties of their larger scale environment are poorly known. In this work, we aim at characterising the effects of clustered star formation and feedback of massive stars on the surrounding medium by studying the distribution of warm gas through mid-J$^{12}$CO and $^{13}$CO observations. Methods: We present APEX $^{12}$CO(6-5), (7-6), $^{13}$CO(6-5), (8-7) and HIFI $^{13}$CO(10-9) maps of the star forming region G327.36-0.6 with a linear size of ~{}3 pc { imes} 4 pc. We infer the physical properties of the emitting gas on large scales through a local thermodynamic equilibrium analysis, while we apply a more sophisticated large velocity gradient approach on selected positions. Results: Maps of all lines are dominated in intensity by the photon dominated region around the Hii region G327.3-0.5. Mid-J$^{12}$CO emission is detected over the whole extent of the maps with excitation temperatures ranging from 20 K up to 80 K in the gas around the Hii region, and H$_{2}$ column densities from few 10$^{21}$ cm$^{-2}$ in the inter-clump gas to 3 { imes} 10$^{22}$ cm$^{-2}$ towards the hot core G327.3-0.6. The warm gas (traced by $^{12}$ and $^{13}$CO(6-5) emission) is only a small percentage (~{}10%) of the total gas in the infrared dark cloud, while it reaches values up to ~{}35% of the total gas in the ring surrounding the Hii region. The $^{12}$CO ladders are qualitatively compatible with photon dominated region models for high density gas, but the much weaker than predicted $^{13}$CO emission suggests that it comes from a large number of clumps along the line of sight. All lines are detected in the inter-clump gas when averaged over a large region with an equivalent radius of 50''(~{}0.8 pc), implying that the mid-J$^{12}$CO and $^{13}$CO inter-clump emission is due to high density components with low filling factor. Finally, the detection of the $^{13}$CO(10-9) line allows to disentangle the effects of gas temperature and gas density on the CO emission, which are degenerate in the APEX observations alone. Show less
