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Venemans B.P.,Max Planck Institute for Astronomy | Venemans B.P.,European Southern Observatory | McMahon R.G.,University of Cambridge | Walter F.,Max Planck Institute for Astronomy | And 7 more authors.
Astrophysical Journal Letters | Year: 2012

Using the IRAM Plateau de Bure Interferometer, we report the detection of the 158 μm [C II] emission line and underlying dust continuum in the host galaxy of the quasar ULAS J112001.48+064124.3 (hereafter J1120+0641) at z = 7.0842 ± 0.0004. This is the highest redshift detection of the [C II] line to date, and allows us to put the first constraints on the physical properties of the host galaxy of J1120+0641. The [C II] line luminosity is 1.2 ± 0.2 × 109L , which is a factor 4 lower than observed in a luminous quasar at z = 6.42 (SDSS J1148+5251). The underlying far-infrared (FIR) continuum has a flux density of 0.61 ± 0.16 mJy, similar to the average flux density of z 6 quasars that were not individually detected in the rest-frame FIR. Assuming that the FIR luminosity of L FIR = 5.8 × 1011-1.8 × 1012L is mainly powered by star formation, we derive a star formation rate in the range 160-440M yr-1 and a total dust mass in the host galaxy of 6.7 × 107-5.7 × 108 M (both numbers have significant uncertainties given the unknown nature of dust at these redshifts). The [C II] line width of σV = 100 ± 15kms-1 is among the smallest observed when compared to the molecular line widths detected in z 6 quasars. Both the [C II] and dust continuum emission are spatially unresolved at the current angular resolution of 2.0 × 1.7arcsec2 (corresponding to 10 × 9kpc2 at the redshift of J1120+0641). © 2012. The American Astronomical Society. All rights reserved..

Maier D.,Institute Of Radioastronomie Millimetrique | Reverdy J.,Institute Of Radioastronomie Millimetrique | Billon-Pierron D.,Institute Of Radioastronomie Millimetrique | Barbier A.,Institute Of Radioastronomie Millimetrique
IEEE Transactions on Terahertz Science and Technology | Year: 2012

The Eight MIxer Receiver (EMIR) is a multi-band millimeter wave receiver installed since 2009 at the 30 m telescope of the Institut de Radio Astronomie Millimtrique (IRAM) at Pico Veleta in Spain. In autumn 2011, Band 3 and Band 4 will be equipped with state-of-the-art sideband-separating mixers with 8 GHz intermediate frequency (IF) bandwidth. For Band 3 a sideband-separating mixer has been developed within the European project AMSTAR${+}$ in order to replace the currently employed single-sideband mixer. The new mixer has an IF bandwidth twice as large as the current one, and two sidebands, thus doubling the continuum sensitivity of the receiver. The mixer currently installed in Band 4 will simply be upgraded to 8 GHz IF bandwidth by changing its IF components. © 2011 IEEE.

Liszt H.S.,U.S. National Radio Astronomy Observatory | Pety J.,Institute Of Radioastronomie Millimetrique | Pety J.,Paris Observatory
Astronomy and Astrophysics | Year: 2012

Aims.We wish to relate the degree scale structure of galactic diffuse clouds to sub-arcsecond atomic and molecular absorption spectra obtained against extragalactic continuum background sources. Methods. We used the ARO 12 m telescope to map J = 1-0 CO emission at 1′ resolution over 30′ fields around the positions of 11 background sources occulted by 20 molecular absorption line components, of which 11 had CO emission counterparts. We compared maps of CO emission to sub-arcsec atomic and molecular absorption spectra and to the large-scale distribution of interstellar reddening. Results. 1) The same clouds, identified by their velocity, were seen in absorption and emission and atomic and molecular phases, not necessarily in the same direction. Sub-arcsecond absorption spectra are a preview of what is seen in CO emission away from the continuum. 2) The CO emission structure was amorphous in 9 cases, quasi-periodic or wave-like around B0528+134 and tangled and filamentary around BL Lac. 3) Strong emission, typically 4-5 K at E B-V < 0.15 mag and up to 10-12 K at E B-V ≈ 0.3 mag was found, much brighter than toward the background targets. Typical covering factors of individual features at the 1 K km s -1 level were 20%. 4) CO-H 2 conversion factors as much as 4-5 times below the mean value N(H 2)/W CO = 2 × 10 20 H 2 cm -2 (K km s -1) -1 are required to explain the luminosity of CO emission at/above the level of 1 K km s -1. Small conversion factors and sharp variability of the conversion factor on arcminute scales are due primarily to CO chemistry and need not represent unresolved variations in reddening or total column density. Conclusions. Like Fermi and Planck we see some gas that is dark in CO and other gas in which CO is overluminous per H 2. A standard CO-H 2 conversion factor applies overall owing to balance between the luminosities per H 2 and surface covering factors of bright and dark CO, but with wide variations between sightlines and across the faces of individual clouds. © 2012 ESO.

Liszt H.S.,U.S. National Radio Astronomy Observatory | Pety J.,Institute Of Radioastronomie Millimetrique | Pety J.,Paris Observatory
Astrophysical Journal | Year: 2016

Elaborating on a formalism that was first expressed some 40 years ago, we consider the brightness of low-lying millimeter-wave rotational lines of strongly polar molecules at the threshold of detectability. We derive a simple expression relating the brightness to the line-of-sight integral of the product of the total gas and molecular number densities and a suitably defined temperature-dependent excitation rate into the upper level of the transition. Detectability of a line is contingent only on the ability of a molecule to channel enough of the ambient thermal energy into the line, and the excitation can be computed in bulk by summing over rates without solving the multilevel rate equations, or computing optical depths and excitation temperatures. Results for + HCO , HNC, and CS are compared with escape-probability solutions of the rate equations using closed-form expressions for the expected range of validity of our ansatz, with the result that gas number densities as high as - 104 cm3or optical depths as high as 100 can be accommodated in some cases. For densities below a well-defined upper bound, the range of validity of the discussion can be cast as an upper bound on the line brightness which is 0.3 K for the J = 1-0 lines and 0.8-1.7 K for the J = 2-1 lines of these species. The discussion casts new light on the interpretation of line brightnesses under conditions of weak excitation, simplifies derivation of physical parameters, and eliminates the need to construct grids of numerical solutions of the rate equations. © 2016. The American Astronomical Society. All rights reserved.

Bujarrabal V.,Observatorio Astronomico Nacional OAN IGN | Alcolea J.,Observatorio Astronomico Nacional OAN IGN | Van Winckel H.,Catholic University of Leuven | Santander-Garcia M.,Observatorio Astronomico Nacional OAN IGN | And 2 more authors.
Astronomy and Astrophysics | Year: 2013

Context. There is a group of binary post-AGB stars that show conspicuous near-infrared (NIR) excess, which is usually assumed to arise from hot dust in very compact possibly rotating disks. These stars are surrounded by significantly fainter nebulae than the standard, well studied protoplanetary and planetary nebulae (PPNe, PNe). Aims. We aim to identify and study extended rotating disks around these stars and shed light on the role of disks in the formation and shaping of planetary nebulae. Methods. We present high-sensitivity mm-wave observations of CO lines in 24 objects of this type. The resulting CO lines are compared with profiles expected to arise from rotating disks from both theoretical and observational grounds. We derive simple formulae that allow us to determine the mass of the CO-emitting gas and estimate its extent. The reliability and uncertainty of the methods are also widely discussed. Results. CO emission is detected in most observed sources, and the line profiles show that the emissions very probably come from disks in rotation. We derive typical values of the disk mass between 10-3 and 10-2 M ⊙ about two orders of magnitude lower than the (total) masses of standard PPNe. The high-detection rate (upper limits being not very significant) clearly confirm that the NIR excess of these stars arises from compact disks in rotation, which are likely the inner parts of those found here. Low-velocity outflows are also found in about eight objects with moderate expansion velocities of ~10 km s-1 to be compared with the velocities of about 100 km s-1 often found in standard PPNe. Except for two sources with complex profiles, the outflowing gas in our objects represents a minor nebular component. Our simple estimates of the typical disk sizes yields values ̃0.5-1 arcsec, which is between 5 × 1015 and 3 × 1016 cm. Estimates of the linear momenta carried by the outflows, which can only be performed in a few well studied objects, also yield moderate values when compared to the linear momenta that can be released by the stellar radiation pressure (contrary, again, to the case of the very massive and fast bipolar outflows in standard PPNe that are strongly overluminous). The mass and dynamics of nebulae around various classes of post-AGB stars differ very significantly, and we can expect the formation of PNe with very different properties. © 2013 ESO.

Agundez M.,CSIC - Institute of Materials Science | Cernicharo J.,CSIC - Institute of Materials Science | Guelin M.,Institute Of Radioastronomie Millimetrique
Astronomy and Astrophysics | Year: 2015

We conducted radioastronomical observations of 9 dark clouds with the IRAM 30 m telescope. We present the first identification in space of the ketenyl radical (HCCO) toward the starless core Lupus-1A and the molecular cloud L483 and the detection of the related molecules ketene (H2CCO) and acetaldehyde (CH3CHO) in these two sources and 3 additional dark clouds. We also report the detection of the formyl radical (HCO) in the 9 targeted sources and of propylene (CH2CHCH3) in 4 of the observed sources, which significantly extends the number of dark clouds where these molecules are known to be present. We have derived a beam-averaged column density of HCCO of ∼5 × 1011 cm-2 in both Lupus-1A and L483, which means that the ketenyl radical is just ∼10 times less abundant than ketene in these sources. The non-negligible abundance of HCCO found implies that there must be a powerful formation mechanism able to counterbalance the efficient destruction of this radical through reactions with neutral atoms. The column densities derived for HCO, (0.5-2.7) ×1012 cm-2, and CH2CHCH3, (1.9-4-2) ×1013 cm-2, are remarkably uniform across the sources where these species are detected, confirming their ubiquity in dark clouds. Gas phase chemical models of cold dark clouds can reproduce the observed abundances of HCO, but cannot explain the presence of HCCO in Lupus-1A and L483 and the high abundances derived for propylene. The chemistry of cold dark clouds needs to be revised in light of these new observational results. © 2015 ESO.

Agundez M.,University of Paris Descartes | Cernicharo J.,CSIC - National Institute of Aerospace Technology | Guelin M.,Institute Of Radioastronomie Millimetrique
Astrophysical Journal Letters | Year: 2010

Amechanism based on the penetration of interstellar ultraviolet photons into the inner layers of clumpy circumstellar envelopes (CSEs) around asymptotic giant branch stars is proposed to explain the non-equilibrium chemistry observed in such objects. We show through a simple modeling approach that in CSEs with a certain degree of clumpiness or with moderately low mass loss rates (a few 10-7M⊙ yr-1) a photochemistry can take place in the warm and dense inner layers, inducing important changes in the chemical composition. In carbon-rich objects water vapor and ammonia would be formed with abundances of 10-8-10-6 relative to H 2, while in oxygen-rich envelopes ammonia and carbon-bearing molecules such as HCN and CS would form with abundances of 10 -9-10-7 relative to H2. The proposed mechanism would explain the recent observation of warm water vapor in the carbon-rich envelope IRC+10216 with the Herschel Space Observatory and predict that H 2O should be detectable in other carbon-rich objects. © 2010 The American Astronomical Society. All rights reserved.

Pulliam R.L.,University of Arizona | Savage C.,Los Alamos National Laboratory | Agundez M.,University of Paris Descartes | Cernicharo J.,CSIC - National Institute of Aerospace Technology | And 2 more authors.
Astrophysical Journal Letters | Year: 2010

A new interstellar molecule, KCN, has been identified toward the circumstellar envelope of the carbon-rich asymptotic giant branch star, IRC+10216 - the fifthmetal cyanide species to be detected in space. Fourteen rotational transitions of this T-shaped, asymmetric top were searched for in the frequency range of 83-250 GHz using the Arizona Radio Observatory (ARO) 12 m Kitt Peak antenna, the IRAM 30 m telescope, and the ARO Submillimeter Telescope. Distinct lines were measured for 10 of these transitions, including the K a = 1 and 2 asymmetry components of the J = 11→10 and J = 10→9 transitions, i.e., the K-ladder structure distinct to an asymmetric top. These data are some of themost sensitive astronomical spectra at λ∼1 and 3mmobtained to date, with 3σ noise levels ∼0.3 mK, made possible by new ALMA technology. The line profiles from the ARO and IRAM telescopes are consistent with a shell-like distribution for KCN with r outer ∼ 15″, but with an inner shell radius that extends into warmer gas. The column density for KCN in IRC+10216 was found to be N tot ≈ 1.0×1012 cm-2 with a rotational temperature of Trot ∼ 53 K. The fractional abundance was calculated to be f(KCN/H2) ∼ 6×10-10, comparable to that of KCl. The presence of KCN in IRC+10216, along with MgNC, MgCN, NaCN, and AlNC, suggests that cyanide/isocyanide species are the most common metal-containing molecules in carbon-rich circumstellar gas. © 2010. The American Astronomical Society. All rights reserved.

Liszt H.S.,U.S. National Radio Astronomy Observatory | Pety J.,Institute Of Radioastronomie Millimetrique | Pety J.,Paris Observatory | Lucas R.,Al MA
Astronomy and Astrophysics | Year: 2010

Aims. We wish to separate and quantify the CO luminosity and CO-H 2 conversion factor applicable to diffuse but partially-molecular ISM when H2 and CO are present but C+ is the dominant form of gas-phase carbon. Methods. We discuss galactic lines of sight observed in Hi, HCO+ and CO where CO emission is present but the intervening clouds are diffuse (locally AV ≲ 1 mag) with relatively small CO column densities NCO ≲ 2 × 1016 cm-2. We separate the atomic and molecular fractions statistically using EB-V as a gauge of the total gas column density and compare NH2 to the observed CO brightness. Results. Although there are H 2-bearing regions where CO emission is too faint to be detected, the mean ratio of integrated CO brightness to NH2 for diffuse ISM does not differ from the usual value of 1K km s-1 of integrated CO brightness per 2 × 1020 H2 cm-2. Moreover, the luminosity of diffuse CO viewed perpendicular to the galactic plane is 2/3 that seen at the Solar galactic radius in surveys of CO emission near the galactic plane. Conclusions. Commonality of the CO-H2 conversion factors in diffuse and dark clouds can be understood from considerations of radiative transfer and CO chemistry. There is unavoidable confusion between CO emission from diffuse and dark gas and misattribution of CO emission from diffuse to dark or giant molecular clouds. The character of the ISM is different from what has been believed if CO and H2 that have been attributed to molecular clouds on the verge of star formation are actually in more tenuous, gravitationally-unbound diffuse gas. © ESO 2010.

Cernicharo J.,CSIC - Institute of Materials Science | Marcelino N.,U.S. National Radio Astronomy Observatory | Agundez M.,CSIC - Institute of Materials Science | Guelin M.,Institute Of Radioastronomie Millimetrique | Guelin M.,French National Center for Scientific Research
Astronomy and Astrophysics | Year: 2015

Thermally-pulsating AGB stars provide three-fourths of the matter returned to the interstellar medium. The mass and chemical composition of their ejecta largely control the chemical evolution of galaxies. Yet, both the mass loss process and the gas chemical composition remain poorly understood. We present maps of the extended 12CO and 13CO emissions in IRC+10216, the envelope of CW Leo, the high mass loss star the closest to the Sun. IRC+10216 is nearly spherical and expands radially with a velocity of 14.5 km s-1. The observations were made On-the-Fly with the IRAM 30 m telescope; their sensibility, calibration, and angular resolution are far higher than all previous studies. The telescope resolution at λ = 1.3 mm (11″ HPBW) corresponds to an expansion time of 500 yr. The CO emission consists of a centrally peaked pedestal and a series of bright, nearly spherical shells. It peaks on CW Leo and remains relatively strong up to rphot = 180″. Further out the emission becomes very weak and vanishes as CO gets photodissociated. As CO is the best tracer of the gas up to rphot, the maps show the mass loss history in the last 8000 yr. The bright CO shells denote over-dense regions. They show that the mass loss process is highly variable on timescales of hundreds of years. The new data, however, do not support previous claims of a strong decrease of the average mass loss in the last few thousand years. The over-dense shells are not perfectly concentric and extend farther to the N-NW. The typical shell separation is 800-1000 yr in the middle of the envelope, but seems to increase outwards. The shell-intershell brightness contrast is ≥3. All those key features can be accounted for if CW Leo has a companion star with a period ≃800 yr that increases the mass loss rate when it comes close to periastron. Higher angular resolution observations are needed to fully resolve the dense shells and measure the density contrast. The latter plays an essential role in our understanding of the envelope chemistry. © ESO 2015.

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