M. Fich

University of Waterloo, Waterloo, Ontario, Canada

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Publications (116)262.87 Total impact

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    ABSTRACT: Context: The physical origin behind organic emission in embedded low-mass star formation has been fiercely debated in the last two decades. A multitude of scenarios have been proposed, from a hot corino to PDRs on cavity walls to shock excitation. Aims: The aim of this paper is to determine the location and the corresponding physical conditions of the gas responsible for organics emission lines. The outflows around the small protocluster NGC 2071 are an ideal testbed to differentiate between various scenarios. Methods: Using Herschel-HIFI and the SMA, observations of CH3OH, H2CO and CH3CN emission lines over a wide range of excitation energies were obtained. Comparisons to a grid of radiative transfer models provide constraints on the physical conditions. Comparison to H2O line shape is able to trace gas-phase synthesis versus a sputtered origin. Results: Emission of organics originates in three spots: the continuum sources IRS 1 ('B') and IRS 3 ('A') as well as a outflow position ('F'). Densities are above 10$^7$ cm$^{-3}$ and temperatures between 100 to 200 K. CH3OH emission observed with HIFI originates in all three regions and cannot be associated with a single region. Very little organic emission originates outside of these regions. Conclusions: Although the three regions are small (<1,500 AU), gas-phase organics likely originate from sputtering of ices due to outflow activity. The derived high densities (>10$^7$ cm$^{-3}$) are likely a requirement for organic molecules to survive from being destroyed by shock products. The lack of spatially extended emission confirms that organic molecules cannot (re)form through gas-phase synthesis, as opposed to H2O, which shows strong line wing emission. The lack of CH3CN emission at 'F' is evidence for a different history of ice processing due to the absence of a protostar at that location and recent ice mantle evaporation.
    07/2014;
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    ABSTRACT: NGC 7129 FIRS 2 (hereafter FIRS 2) is an intermediate-mass (2 to 8 Msun) protostar located at a distance of 1250 pc. High spatial resolution observations are required to resolve the hot core at its center. We present a molecular survey from 218200 MHz to 221800 MHz carried out with the IRAM Plateau de Bure Interferometer. These observations were complemented with a long integration single-dish spectrum taken with the IRAM 30m telescope. We used a Local Thermodynamic Equilibrium (LTE) single temperature code to model the whole dataset. The interferometric spectrum is crowded with a total of ~300 lines from which a few dozens remain unidentified yet. The spectrum has been modeled with a total of 20 species and their isomers, isotopologues and deuterated compounds. Complex molecules like methyl formate (CH3OCHO), ethanol (CH3CH2OH), glycolaldehyde (CH2OHCHO), acetone (CH3COCH3), dimethyl ether (CH3OCH3), ethyl cyanide (CH3CH2CN) and the aGg' conformer of ethylene glycol (aGg'-(CH2OH)_2) are among the detected species. The detection of vibrationally excited lines of CH3CN, CH3OCHO, CH3OH, OCS, HC3N and CH3CHO proves the existence of gas and dust at high temperatures. In fact, the gas kinetic temperature estimated from the vibrational lines of CH3CN, ~405 K, is similar to that measured in massive hot cores. Our data allow an extensive comparison of the chemistry in FIRS~2 and the Orion hot core. We find a quite similar chemistry in FIRS 2 and Orion. Most of the studied fractional molecular abundances agree within a factor of 5. Larger differences are only found for the deuterated compounds D2CO and CH2DOH and a few molecules (CH3CH2CN, SO2, HNCO and CH3CHO). Since the physical conditions are similar in both hot cores, only different initial conditions (warmer pre-collapse phase in the case of Orion) and/or different crossing time of the gas in the hot core can explain this behavior.
    05/2014;
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    ABSTRACT: We describe a search for submillimeter emission in the vicinity of one of the most distant, luminous galaxies known, HerMES FLS3 at z=6.34, exploiting it as a signpost to a potentially biased region of the early Universe, as might be expected in hierarchical structure formation models. Imaging to the confusion limit with the innovative, wide-field submillimeter bolometer camera, SCUBA-2, we are sensitive to colder and/or less luminous galaxies in the surroundings of HFLS3. We use the Millennium Simulation to illustrate that HFLS3 may be expected to have companions if it is as massive as claimed, but find no significant evidence from the surface density of SCUBA-2 galaxies in its vicinity, or their colors, that HFLS3 marks an over-density of dusty, star-forming galaxies. We cannot rule out the presence of dusty neighbours with confidence, but deeper 450-um imaging has the potential to more tightly constrain the redshifts of nearby galaxies, at least one of which likely lies at z>~5. If associations with HFLS3 can be ruled out, this could be taken as evidence that HFLS3 is less biased than a simple extrapolation of the Millennium Simulation may imply. This could suggest either that it represents a rare short-lived, but highly luminous, phase in the evolution of an otherwise typical galaxy, or that this system has suffered amplification due to a foreground gravitational lens and so is not as intrinsically luminous as claimed.
    The Astrophysical Journal 03/2014; 793(1). · 6.73 Impact Factor
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    ABSTRACT: We mapped five massive star forming regions with the SCUBA-2 camera on the James Clerk Maxwell Telescope (JCMT). Temperature and column density maps are obtained from the SCUBA-2 450 and 850 $\mu$m images. Most of the dense clumps we find have central temperatures below 20 K with some as cold as 8 K, suggesting that they have no internal heating due to the presence of embedded protostars. This is surprising, because at the high densities inferred from these images and at these low temperatures such clumps should be unstable, collapsing to form stars and generating internal heating. The column densities at the clump centres exceed 10$^{23}$ cm$^{-2}$, and the derived peak visual extinction values are from 25-500 mag for $\beta$ = 1.5-2.5, indicating highly opaque centres. The observed cloud gas masses range from $\sim$ 10 to 10$^{3}$ M$_{\odot}$. The outer regions of the clumps follow an $r^{-2.36\pm0.35}$ density distribution and this power-law structure is observed outside of typically 10$^{4}$ AU. All these findings suggest that these clumps are high-mass starless clumps and most likely contain high-mass starless cores.
    12/2013; 147(3).
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    ABSTRACT: MS$\,$0451.6$-$0305 is a rich galaxy cluster whose strong lensing is particularly prominent at submm wavelengths. We combine new SCUBA-2 data with imaging from Herschel SPIRE and PACS and HST in order to try to understand the nature of the sources being lensed. In the region of the "giant submm arc," we uncover seven multiply imaged galaxies (up from the previously known three), of which six are found to be at a redshift of $z\sim2.9$, and possibly constitute an interacting system. Using a novel forward-modelling approach, we are able to simultaneously deblend and fit SEDs to the individual galaxies that contribute to the giant submm arc, constraining their dust temperatures, far infrared luminosities and star formation rates. The submm arc first identified by SCUBA can now be seen to be composed of at least five distinct sources, four of these within the galaxy group at $z\sim2.9$. The total unlensed luminosity for this galaxy group is $(3.1\pm0.3) \times 10^{12}\,\mathrm{L}_\odot$, which gives an unlensed star formation rate of $(450\pm50)$ M$_\odot$ yr$^{-1}$. From the properties of this system, we see no evidence of evolution towards lower temperatures in the dust temperature versus far-infrared luminosity relation for high redshift galaxies.
    12/2013;
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    ABSTRACT: SCUBA-2 is an innovative 10000 pixel bolometer camera operating at submillimetre wavelengths on the James Clerk Maxwell Telescope (JCMT). The camera has the capability to carry out wide-field surveys to unprecedented depths, addressing key questions relating to the origins of galaxies, stars and planets. With two imaging arrays working simultaneously in the atmospheric windows at 450 and 850 microns, the vast increase in pixel count means that SCUBA-2 maps the sky 100-150 times faster than the previous SCUBA instrument. In this paper we present an overview of the instrument, discuss the physical characteristics of the superconducting detector arrays, outline the observing modes and data acquisition, and present the early performance figures on the telescope. We also showcase the capabilities of the instrument via some early examples of the science SCUBA-2 has already undertaken. In February 2012, SCUBA-2 began a series of unique legacy surveys for the JCMT community. These surveys will take 2.5 years and the results are already providing complementary data to the shorter wavelength, shallower, larger-area surveys from Herschel. The SCUBA-2 surveys will also provide a wealth of information for further study with new facilities such as ALMA, and future telescopes such as CCAT and SPICA.
    01/2013;
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    ABSTRACT: The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an HI-selected sample of 155 galaxies spanning all morphological types with distances less than 25 Mpc. We describe the scientific goals of the survey, the sample selection, and the observing strategy. We also present an atlas and analysis of the CO J=3-2 maps for the 47 galaxies in the NGLS which are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide range of molecular gas mass fractions in the galaxies in this sample and explore the correlation of the far-infrared luminosity, which traces star formation, with the CO luminosity, which traces the molecular gas mass. By comparing the NGLS data with merging galaxies at low and high redshift which have also been observed in the CO J=3-2 line, we show that the correlation of far-infrared and CO luminosity shows a significant trend with luminosity. This trend is consistent with a molecular gas depletion time which is more than an order of magnitude faster in the merger galaxies than in nearby normal galaxies. We also find a strong correlation of the L(FIR)/L(CO3-2) ratio with the atomic to molecular gas mass ratio. This correlation suggests that some of the far-infrared emission originates from dust associated with atomic gas and that its contribution is particularly important in galaxies where most of the gas is in the atomic phase.
    06/2012;
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    ABSTRACT: NGC 7129 FIRS 2 is a young intermediate-mass (IM) protostar, which is associated with two energetic bipolar outflows and displays clear signs of the presence of a hot core. It has been extensively observed with ground based telescopes and within the WISH Guaranteed Time Herschel Key Program. We present new observations of the C18O 3-2 and the HDO 3_{12}-2_{21} lines towards NGC 7129 FIRS 2. Combining these observations with Herschel data and modeling their emissions, we constrain the C18O and HDO abundance profiles across the protostellar envelope. In particular, we derive the abundance of C18O and HDO in the hot core. The intensities of the C18O lines are well reproduced assuming that the C18O abundance decreases through the protostellar envelope from the outer edge towards the centre until the point where the gas and dust reach the CO evaporation temperature (~20-25 K) where the C18O is released back to the gas phase. Once the C18O is released to the gas phase, the modelled C18O abundance is found to be ~1.6x10^{-8}, which is a factor of 10 lower than the reference abundance. This result is supported by the non-detection of C18O 9-8, which proves that even in the hot core (T_k>100 K) the CO abundance must be 10 times lower than the reference value. Several scenarios are discussed to explain this C18O deficiency. One possible explanation is that during the pre-stellar and protostellar phase, the CO is removed from the grain mantles by reactions to form more complex molecules. Our HDO modeling shows that the emission of HDO 3_{12}-2_{21} line is maser and comes from the hot core (T_k>100 K). Assuming the physical structure derived by Crimier et al. (2010), we determine a HDO abundance of ~0.4 - 1x10^{-7} in the hot core of this IM protostar, similar to that found in the hot corinos NGC 1333 IRAS 2A and IRAS 16293-2422.
    Astronomy and Astrophysics 02/2012; · 5.08 Impact Factor
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    ABSTRACT: The Gould Belt Legacy Survey will map star-forming regions within 500 pc, using HARP (Heterodyne Array Receiver Programme), SCUBA-2 (Submillimetre Common-User Bolometer Array 2) and POL-2 (Polarimeter 2) on the James Clerk Maxwell Telescope (JCMT). This paper describes HARP observations of the J = 3-2 transitions of 13CO and C18O towards Orion A. The 1500-resolution observations cover 5 pc of the Orion filament, including OMC1 (inc. BN-KL and Orion Bar), OMC 2/3 and OMC 4, and allow a comparative study of the molecular gas properties throughout the star-forming cloud. The filament shows a velocity gradient of ~1 km/s /pc between OMC 1, 2 and 3, and high velocity emission is detected in both isotopologues. The Orion Nebula and Bar have the largest masses and line widths, and dominate the mass and energetics of the high velocity material. Compact, spatially resolved emission from CH3CN, 13CH3OH, SO, HCOOCH3, C2H5OH, CH3CHO and CH3OCHO is detected towards the Orion Hot Core. The cloud is warm, with a median excitation temperature of ~24 K; the Orion Bar has the highest excitation temperature gas, at >80 K. The C18O excitation temperature correlates well with the dust temperature (to within 40%). The C18O emission is optically thin, and the 13CO emission is marginally optically thick; despite its high mass, OMC 1 shows the lowest opacities. A virial analysis indicates that Orion A is too massive for thermal or turbulent support, but is consistent with a model of a filamentary cloud that is threaded by helical magnetic fields. The variation of physical conditions across the cloud is reflected in the physical characteristics of the dust cores....continued
    01/2012;
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    åp. 01/2012; 537:A17.
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    Gopika Sreenilayam, Michel Fich
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    ABSTRACT: We estimate the mass, temperature, and luminosity of the hot (≥100 K), cool (20-40 K), and cold (≤20 K) dust in the environs of Galactic H II regions using Infrared Astronomical Satellite (IRAS) and Submillimeter Common User Bolometric Array (SCUBA) data. A total of 83 clouds have been examined using IRAS data. A two-component model spectral energy distribution (SED) of hot and cool dust is used to fit the IRAS data. All of the SEDs use a graphite/silicate mix of grains in an MRN distribution. A three-component model SED is fitted to combined SCUBA and IRAS data for 15 clouds near H II regions to measure the cold dust component. Surprisingly, the ratio of the bolometric luminosity of the cool dust to the hot dust appears to be the same (2.8) in virtually all objects. The cool dust has typically four-five orders of magnitude greater mass than the hot dust. However, the mass in cold dust is much greater than the mass in cool and hot dust. We also find some evidence for a relationship between the cool and cold dust masses. These results may prove useful for using IR observations for estimating gas masses in extragalactic systems with active high-mass star formation.
    The Astronomical Journal 05/2011; 142(1):4. · 4.97 Impact Factor
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    ABSTRACT: In the wake of the Decadal Survey and a January 2011 meeting of NASA's Exoplanet Exploration Program Analysis Group (ExoPAG), one might be tempted to conclude that space interferometry is dead. We explain why this slogan is hyperbole, summarize the steps currently being taken to prepare for a space-based far-IR interferometer, and reiterate the science case for an imaging and spectroscopic interferometer - SPIRIT - that would operate in space at long infrared wavelengths. Space-based interferometry is alive and well, but the center of activity has shifted to a spectral region (25 to 400 microns) in which no alternative measurement technique can provide information essential to answering several scientific questions deemed compelling by the Decadal Survey. Astrophysicists will use SPIRIT to: discover how the conditions for habitability arise during planetary system formation; find and characterize exoplanets by measuring their sculpting effects on protoplanetary and debris disks; and study the formation, merger history, and star formation history of galaxies.
    05/2011;
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    Mohaddesseh Azimlu, Michel Fich
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    ABSTRACT: The properties of molecular clouds associated with 10 HII regions were studied using CO observations. We identified 142 dense clumps within our sample and found that our sources are divided into two categories: those with clumps that show a power law size-line width relation (Type I) and those which do not show any relation (Type II). The clumps in the Type I sources have larger power law indices than found in previous studies. The clumps in the Type II sources have larger line widths and show evidence (such as outflows) of current active star formation within the clump. We suggest that the lack of a size-line width relation is a sign of current active star formation. Massive clumps seem to have similar masses calculated by different methods but lower mass clumps have larger virial masses compared to velocity integrated and LTE mass. We found no relation between mass distribution of the clumps and distance from the H~II region ionization front, but a weak decrease of the excitation temperature with increasing distance from the ionized gas. The clumps in collected shells around the H~II regions have slightly larger line widths but no relation was found between line width and distance from the H~II region, which probably indicates that the internal dynamics of the clumps are not affected by the ionized gas. Internal sources of turbulence, such as outflows and stellar winds from young proto-stars may have a more important role on the molecular gas dynamics. We suggest that large line width and larger size-line width power law indices are therefore the initial characteristics of clumps in massive star forming clouds and that some may evolve into objects similar to our Type II sources, where local "second generation" stars are forming and eliminating the size-line-width relation.
    02/2011;
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    Mohaddesseh Azimlu, Michel Fich
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    ABSTRACT: The properties of molecular clouds associated with 10 H II regions were studied using CO observations. We identified 142 dense clumps within our sample and found that our sources are divided into two categories: those with clumps that show a power-law size-line-width relation (Type I) and those that do not show any relation (Type II). The clumps in the Type I sources have larger power-law indices than found in previous studies. The clumps in the Type II sources have larger line widths than do the clumps in the Type I sources. The mass M LTE increases with DeltaV for both 12CO and 13CO lines in Type I sources. No relation was found for Type II sources. Type II sources show evidence (such as outflows) of current active star formation within the clump and we suggest that the lack of a size-line-width relation is a sign of current active star formation. For both types of sources, no relation was found between volume density and size, but overall larger clumps have smaller volume density, indicating that smaller clumps are more evolved and have contracted to smaller sizes and higher densities. Massive clumps seem to have similar masses calculated by different methods but lower mass clumps have larger virial masses compared to velocity integrated (X-factor) and local thermodynamic equilibrium mass. We found no relation between mass distribution of the clumps and distance from the H II region ionization front, but a weak decrease of the excitation temperature with increasing distance from the ionized gas. The clumps in collected shells around the H II regions have slightly larger line widths but no relation was found between line width and distance from the H II region, which probably indicates that the internal dynamics of the clumps are not affected by the ionized gas. Internal sources of turbulence, such as outflows and stellar winds from young proto-stars, may have a more important role on the molecular gas dynamics. We suggest that large line width and larger size-line-width power-law indices are therefore the initial characteristics of clumps in massive star-forming clouds (e.g., our Type I sources) and that some may evolve into objects similar to our Type II sources, where local "second generation" stars are forming and eliminating the size-line-width relation.
    The Astronomical Journal 01/2011; 141(4). · 4.97 Impact Factor
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    ABSTRACT: We present H_2O and H_218O profiles observed toward Intermediate Mass YSOs with HIFI onboard Herschel. The data presented has unprecedented resolution at these wavelengths and constitute a part of the legacy of the Water in Star Forming Regions with Herschel (WISH) Key Program. Intermediate Mass YSOs exhibit properties common to both low- and high-mass stars and can, in some cases, act as a nearby, more easily observable proxy to high-mass star formation but can also elucidate the differences between low- and high-mass star formation, and under what conditions these differences occur. Our sources have been chosen to encompass a range of properties in order to investigate what water can tell us about these important objects and include; Class 0 and Class 1 objects; those forming in isolation and in clustered environments; and, sources with or without known outflow. In this presentation we compare and contrast water profiles among our sources. The observations were made toward the YSO but the H_2O profiles are dominated by the outflow rather than the central envelope and can be modelled as consisting of a broad component due to the outflow, a medium component due to the envelope and, in the case of the ground state lines a narrow component in absorption resulting from self-absorption by the cold outer envelope. Despite this commonality, the observed profiles are distinct from source to source, see the figure comparing the H_2O 110--101 among a sample of our sources.
    Proceedings of the International Astronomical Union 01/2011; 280.
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    ABSTRACT: HERSCHEL-HIFI observations of water from the intermediate mass protostar NGC7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this star formation environment. Six spectral settings, covering four H216O and two H218O lines, were observed and all but one H218O line were detected. The four H2 16 O lines discussed here share a similar morphology: a narrower, \approx 6 km/s, component centered slightly redward of the systemic velocity of NGC7129 FIRS 2 and a much broader, \approx 25 km/s component centered blueward and likely associated with powerful outflows. The narrower components are consistent with emission from water arising in the envelope around the intermediate mass protostar, and the abundance of H2O is constrained to \approx 10-7 for the outer envelope. Additionally, the presence of a narrow self-absorption component for the lowest energy lines is likely due to self-absorption from colder water in the outer envelope. The broader component, where the H2O/CO relative abundance is found to be \approx 0.2, appears to be tracing the same energetic region that produces strong CO emission at high J.
    Astronomy and Astrophysics 11/2010; 521(41). · 5.08 Impact Factor
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    ABSTRACT: 'Water In Star-forming regions with Herschel' (WISH) is a key programme dedicated to studying the role of water and related species during the star-formation process and constraining the physical and chemical properties of young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIFI) on the Herschel Space Observatory observed three deeply embedded protostars in the low-mass star-forming region NGC1333 in several H2-16O, H2-18O, and CO transitions. Line profiles are resolved for five H16O transitions in each source, revealing them to be surprisingly complex. The line profiles are decomposed into broad (>20 km/s), medium-broad (~5-10 km/s), and narrow (<5 km/s) components. The H2-18O emission is only detected in broad 1_10-1_01 lines (>20 km/s), indicating that its physical origin is the same as for the broad H2-16O component. In one of the sources, IRAS4A, an inverse P Cygni profile is observed, a clear sign of infall in the envelope. From the line profiles alone, it is clear that the bulk of emission arises from shocks, both on small (<1000 AU) and large scales along the outflow cavity walls (~10 000 AU). The H2O line profiles are compared to CO line profiles to constrain the H2O abundance as a function of velocity within these shocked regions. The H2O/CO abundance ratios are measured to be in the range of ~0.1-1, corresponding to H2O abundances of ~10-5-10-4 with respect to H2. Approximately 5-10% of the gas is hot enough for all oxygen to be driven into water in warm post-shock gas, mostly at high velocities.
    Astronomy and Astrophysics 11/2010; 521(30). · 5.08 Impact Factor
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    ABSTRACT: SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H2O) < 7x10^-9). We investigate the chemistry of water vapor in starless cores beyond the previous upper limits using the highly improved angular resolution and sensitivity of Herschel and measure the abundance of water vapor during evolutionary stages just preceding star formation. High spectral resolution observations of the fundamental ortho water (o-H2O) transition (557 GHz) were carried out with Herschel HIFI toward two starless cores: B68, a Bok globule, and L1544, a prestellar core embedded in the Taurus molecular cloud complex. The rms in the brightness temperature measured for the B68 and L1544 spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km s^-1. The continuum level is 3.5+/-0.2 mK in B68 and 11.4+/-0.4 mK in L1544. No significant feature is detected in B68 and the 3 sigma upper limit is consistent with a column density of o-H2O N(o-H2O) < 2.5x10^13 cm^-2, or a fractional abundance x(o-H2O) < 1.3x10^-9, more than an order of magnitude lower than the SWAS upper limit on this source. The L1544 spectrum shows an absorption feature at a 5 sigma level from which we obtain the first value of the o-H2O column density ever measured in dark clouds: N(o-H2O) = (8+/-4)x10^12 cm^-2. The corresponding fractional abundance is x(o-H2O) ~ 5x10^-9 at radii > 7000 AU and ~2x10^-10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H2O) profile peaking at ~10^-8, 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible. Herschel has provided the first measurement of water vapor in dark regions. Prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) are very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds.
    Astronomy and Astrophysics 11/2010; 521. · 5.08 Impact Factor
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    ABSTRACT: Context. Water is a key molecule in the star formation process, but its spatial distribution in star-forming regions is not well known. Aims: We study the distribution of dust continuum and H2O and 13CO line emission in DR21, a luminous star-forming region with a powerful outflow and a compact H ii region. Methods: Herschel-HIFI spectra near 1100 GHz show narrow 13CO 10-9 emission and H2O 111-000 absorption from the dense core and broad emission from the outflow in both lines. The H2O line also shows absorption by a foreground cloud known from ground-based observations of low-J CO lines. Results: The dust continuum emission is extended over 36” FWHM, while the 13CO and H2O lines are confined to ≈24” or less. The foreground absorption appears to peak further North than the other components. Radiative transfer models indicate very low abundances of ~2×10-10 for H2O and ~8×10-7 for 13CO in the dense core, and higher H2O abundances of ~4×10-9 in the foreground cloud and ~7×10-7 in the outflow. Conclusions: The high H2O abundance in the warm outflow is probably due to the evaporation of water-rich icy grain mantles, while the H2O abundance is kept down by freeze-out in the dense core and by photodissociation in the foreground cloud.
    Astronomy and Astrophysics 11/2010; 518(107). · 5.08 Impact Factor
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    ABSTRACT: The Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory allows the first observations of light diatomic molecules at high spectral resolution and in multiple transitions. Here, we report deep integrations using HIFI in different lines of hydrides towards the high-mass star forming region AFGL 2591. Detected are CH, CH+, NH, OH+, H2O+, while NH+ and SH+ have not been detected. All molecules except for CH and CH+ are seen in absorption with low excitation temperatures and at velocities different from the systemic velocity of the protostellar envelope. Surprisingly, the CH(JF,P = 3/2_2,- - 1/2_1,+) and CH+(J = 1 - 0, J = 2 - 1) lines are detected in emission at the systemic velocity. We can assign the absorption features to a foreground cloud and an outflow lobe, while the CH and CH+ emission stems from the envelope. The observed abundance and excitation of CH and CH+ can be explained in the scenario of FUV irradiated outflow walls, where a cavity etched out by the outflow allows protostellar FUV photons to irradiate and heat the envelope at larger distances driving the chemical reactions that produce these molecules.
    Astronomy and Astrophysics 11/2010; 521(44). · 5.08 Impact Factor

Publication Stats

447 Citations
262.87 Total Impact Points

Institutions

  • 2003–2013
    • University of Waterloo
      • Department of Physics and Astronomy
      Waterloo, Ontario, Canada
  • 1984
    • University of Maryland, College Park
      • Department of Astronomy
      Maryland, United States
  • 1983
    • University of California, Berkeley
      Berkeley, California, United States