arXiv subjects

V. Pietu

Publications and source records attributed to V. Pietu.

At least 19 recordsLinked to original sources

arXiv2025

Edge-On Disk Study (EODS) III: Molecular Stratification in the Flying Saucer Disk

Context: Investigating the vertical distribution of molecular content in protoplanetary disks remains difficult in most disks mildly inclined along the line of sight. In contrast, edge-on disks provide a direct (tomographic) view of the 2D molecular brightness. Aims: We study the radial and vertical molecular distribution as well as the gas temperature and density by observing the Keplerian edge-on disk surrounding the Flying Saucer, a Class II object located in Ophiuchus. Methods: We use new and archival ALMA data to perform a tomography of $^{12}$CO, $^{13}$CO, C$^{18}$O, CN, HCN, CS, H$_2$CO, c-C$_3$H$_2$, N$_2$D$^+$, DCN and $^{13}$CS. We analyze molecular tomographies and model data using the radiative transfer code DiskFit. Results: We directly measure the altitude above the mid-plane for each observed species. For the first time, we unambiguously demonstrate the presence of a common molecular layer and measure its thickness: most molecules are located at the same altitude versus radius. Beyond CO, as predicted by chemical models, the CN emission traces the upper boundary of the molecular layer, whereas the deuterated species (DCN and N2D+) resides below one scale-height. Our best fits from DiskFit show that most observed transitions in the molecular layer are thermalized because their excitation temperature is the same, around 17-20 K. Conclusions: These long-integration observations clearly reveal a molecular layer predominantly located around 1-2 scale height, at a temperature above the CO freeze-out temperature. The deuterated molecules are closer to the mid-plane and N2D+ may be a good proxy for the CO snowline. Some molecules, such as CN and H2CO, are likely influenced by the disk environment, at least beyond the mm dust disk radius. The direct observation of the molecular stratification opens the door to detailed chemical modeling in this disk which appears representative of T Tauri disks.

astro-ph.EP↗

arXiv2024

PRODIGE -- Envelope to Disk with NOEMA III. The origin of complex organic molecule emission in SVS13A

Complex Organic Molecules (COMs) have been found toward low-mass protostars but the origins of the COM emission are still unclear. It can be associated with, for example, hot corinos, outflows, and/or accretion shock/disk atmosphere. We have conducted NOEMA observations toward SVS13A from the PROtostars & DIsks: Global Evolution (PRODIGE) program. Our previous \ce{DCN} observations reveal a possible infalling streamer, which may affect the chemistry of the central protobinary by inducing accretion outbursts and/or shocked gas. Here, we further analyze six O-bearing COMs: CH3OH, aGg'-(CH2OH)2, C2H5OH, CH2(OH)CHO, CH3CHO, and CH3OCHO. Although the COM emission is not spatially resolved, we constrain the source sizes to $\lesssim0.3-0.4$ arcsec (90$-$120 au) by conducting uv-domain Gaussian fitting. Interestingly, the high-spectral resolution data reveal complex line profiles with multiple peaks showing differences between these six O-bearing COMs. The LTE fitting unveils differences in excitation temperatures and emitting areas among these COMs. We further conduct multiple-velocity-component LTE fitting to decompose the line emission into different kinematic components. Up to 6 velocity components are found from the LTE modeling. The temperature, column density, and source size of these components from each COM are obtained. We find a variety in excitation temperatures ($100-500$ K) and source sizes (D$\sim10-70$ au) from these kinematic components from different COMs. The emission of each COM can trace several components and different COMs most likely trace different regions. Given this complex structure, we suggest that the central region is inhomogeneous and unlikely to be heated by only protostellar radiation. We conclude that accretion shocks induced by the large-scale infalling streamer likely exist and contribute to the complexity of the COM emission.

astro-ph.GA↗

arXiv2024

PRODIGE -- Planet-forming disks in Taurus with NOEMA. I. Overview and first results for 12CO, 13CO, and C18O

We are performing a line survey of 8 planet-forming Class II disks in Taurus with the IRAM NOrthern Extended Millimeter Array (NOEMA), as a part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution; PIs: P. Caselli and Th. Henning). Compact and extended disks around T Tauri stars CI, CY, DG, DL, DM, DN, IQ Tau, and UZ Tau E are observed in ~80 lines from >20 C-, O,- N-, and S-bearing species. The observations in four spectral settings at 210-280 GHz with $1σ$ rms sensitivity of ~ 8-12 mJy/beam at 0.9" and 0.3 km/s resolution will be completed in 2024. The uv-visibilities are fitted with the DiskFit model to obtain key stellar and disk properties. In this paper, the combined $^{12}$CO, $^{13}$CO and C$^{18}$O $J = 2-1$ data are presented. We find that the CO fluxes and disk masses inferred from dust continuum tentatively correlate with the CO emission sizes. We constrain dynamical stellar masses, geometries, temperatures, the CO column densities and gas masses for each disk. The best-fit temperatures at 100 au are ~ 17-37 K, and decrease radially with the power-law exponent q ~ 0.05-0.76. The inferred CO column densities decrease radially with the power-law exponent p ~ 0.2-3.1. The gas masses estimated from $^{13}$CO (2-1) are ~ $0.001-0.2 M_\textrm{Sun}$. The best-fit CO column densities point to severe CO freeze-out in the disks. The DL Tau disk is an outlier, and has either stronger CO depletion or lower gas mass than the rest of the sample. The CO isotopologue ratios are roughly consistent with the observed values in disks and the low-mass star-forming regions.

astro-ph.GA↗

arXiv2023

A resolved rotating disk wind from a young T Tauri star in the Bok globule CB26

The disk-outflow connection plays a key role in extracting excess angular momentum from a forming protostar. We have previously reported the discovery of a small molecular outflow from the edge-on T Tauri star in the Bok globule CB26 that shows a peculiar velocity pattern, reminiscent of an outflow that corotates with the disk. We report new, high-resolution mm-interferometric observations of CB26 with the aim of revealing the morphology and kinematics of the outflow at the disk-outflow interface. The IRAM PdBI was used to observe CO(2-1) at 1.3mm with a resolution of 0.5". Using a physical model of the disk, which was derived from the dust emission, we employed chemo-dynamical modeling combined with line radiative transfer to constrain kinematic parameters and to construct a model of the CO emission from the disk that allowed us to separate the emission of the disk from that of the outflow. Our observations confirm the disk-wind nature of the rotating molecular outflow from CB26. The new high-resolution data reveal an X-shaped morphology of the CO emission close to the disk, and vertical streaks extending from the disk surface with a small half-opening angle of ~7deg, which can be traced out to vertical heights of ~500au. We interpret this emission as the combination of the disk atmosphere and a well-collimated disk wind, which we trace down to vertical heights of 40au, where it is launched from the surface of the flared disk at radii of 20-45au. The observed CO outflow has a total momentum flux of 1e-5 Msun km/s/yr, which is nearly three orders of magnitude larger than the maximum thrust that can be provided by the luminosity of the central star. We conclude that photoevaporation cannot be the main driving mechanism for this outflow, but it must be predominantly an MHD disk wind. It is thus far the best-resolved rotating disk wind observed to be launched from a circumstellar disk.

astro-ph.SR↗

arXiv2021

An unbiased NOEMA 2.6 to 4 mm survey of the GG Tau ring: First detection of CCS in a protoplanetary disk

Molecular line surveys are among the main tools to probe the structure and physical conditions in protoplanetary disks (PPDs), the birthplace of planets. The large radial and vertical temperature as well as density gradients in these PPDs lead to a complex chemical composition, making chemistry an important step to understand the variety of planetary systems. We aimed to study the chemical content of the protoplanetary disk surrounding GG Tau A, a well-known triple T Tauri system. We used NOEMA with the new correlator PolyFix to observe rotational lines at 2.6 to 4 mm from a few dozen molecules. We analysed the data with a radiative transfer code to derive molecular densities and the abundance relative to $^{13}$CO, which we compare to those of the TMC1 cloud and LkCa15 disk. We report the first detection of CCS in PPDs. We also marginally detect OCS and find 16 other molecules in the GG Tauri outer disk. Ten of them had been found previously, while seven others ($^{13}$CN, N$_2$H$^+$, HNC, DNC, HC$_3$N, CCS, and C$^{34}$S) are new detections in this disk. The analysis confirms that sulphur chemistry is not yet properly understood. The D/H ratio, derived from DCO$^{+}$/HCO$^{+}$, DCN/HCN, and DNC/HNC ratios, points towards a low temperature chemistry. The detection of the rare species CCS confirms that GG Tau is a good laboratory to study the protoplanetary disk chemistry, thanks to its large disk size and mass.

astro-ph.SR↗

arXiv2020

GG Tau A: gas properties and dynamics from the cavity to the outer disk

We used new ALMA $^{13}$CO and C$^{18}$O(3-2) observations obtained at high angular resolution ($\sim$0.2") together with previous CO(3-2) and (6-5) ALMA data and continuum maps at 1.3 and 0.8 mm in order to determine the gas properties (temperature, density, and kinematics) in the cavity and to a lesser extent in the outer disk of GG Tau A, the prototype of a young triple T Tauri star that is surrounded by a massive and extended Keplerian outer disk. By deprojecting, we studied the radial and azimuthal gas distribution and its kinematics. We also applied a new method to improve the deconvolution of the CO data and in particular better quantify the emission from gas inside the cavity. We perform local and nonlocal thermodynamic equilibrium studies in order to determine the excitation conditions and relevant physical parameters inside the ring and in the central cavity. Residual emission after removing a smooth-disk model indicates unresolved structures at our angular resolution, probably in the form of irregular rings or spirals. The outer disk is cold, with a temperature $<20$ K beyond 250 au that drops quickly (r$^{-1}$). The kinematics of the gas inside the cavity reveals infall motions at about 10% of the Keplerian speed. We derive the amount of gas in the cavity, and find that the brightest clumps, which contain about 10% of this mass, have kinetic temperatures 40$-$80 K, CO column densities of a few 10$^{17}$ cm$^{-2}$, and H$_2$ densities around 10$^7$ cm$^{-3}$. Although the gas in the cavity is only a small fraction of the disk mass, the mass accretion rate throughout the cavity is comparable to or higher than the stellar accretion rate. It is accordingly sufficient to sustain the circumstellar disks on a long timescale.

astro-ph.SR↗

arXiv2016

The hybrid disks: a search and study to better understand evolution of disks

The increased sensitivity of millimeter-wave facilities now makes possible the detection of low amounts of gas in debris disks. Some of the gas-rich debris disks harbor peculiar properties, with possible pristine gas and secondary generated dust. The origin of the gas in these hybrid disks is strongly debated and the current sample is too sparse to understand this phenomenon. More detections are necessary to increase the statistics on this population. Lying at the final stages of evolution of proto-planetary disks and at the beginning of the debris disk phase, these objects could provide new insight into the processes involved in the making of planetary systems. We carried out a deep survey of the 12CO(2-1) and 12CO(3-2) lines with the APEX and IRAM radiotelescopes in young debris disks selected according to hybrid disk properties. The survey is complemented with a bibliographic study of the ratio between the emission of the gas and the continuum (S_CO/F_cont) in CTTS, Herbig Ae, WTTS, hybrid, and debris disks. Our sub-mm survey comprises 25 stars, including 17 new targets, and we increase the sensitivity limit by a factor 2 on eight sources compared to similar published studies. We report a 4sigma tentative detection of a double-peaked 12CO(2-1) line around HD23642; an eclipsing binary located in the Pleiades. We also reveal a correlation between the emission of the CO gas and the dust continuum from CTTS, Herbig Ae and few debris disks. The observed trend of the gas to dust flux ratio suggests a concurrent dissipation of the dust and gas components. Hybrid disks systematically lie above this trend, suggesting that these systems may witness a transient phase, when the dust has evolved more rapidly than the gas, with a flux ratio S_CO/F_cont enhanced by a factor of between 10 and 100 compared to standard (proto-)planetary disks.

astro-ph.SR↗

arXiv2015

An Overview of the 2014 ALMA Long Baseline Campaign

A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ~15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from September to late November 2014, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ~350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

astro-ph.IM↗

arXiv2015

First Results from High Angular Resolution ALMA Observations Toward the HL Tau Region

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0.075 arcseconds (10 AU) to 0.025 arcseconds (3.5 AU), revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72pm0.05 degrees) and position angle (+138.02pm0.07 degrees). We obtain a high-fidelity image of the 1.0 mm spectral index ($α$), which ranges from $α\sim2.0$ in the optically-thick central peak and two brightest rings, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation include an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO+ (1-0) which exhibits a pattern over LSR velocities from 2-12 km/s consistent with Keplerian motion around a ~1.3 solar mass star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protostars XZ Tau (A/B) and LkHa358 at 2.9 mm.

astro-ph.SR↗

arXiv2012

CID: Chemistry In Disks VII. First detection of HC3N in protoplanetary disks

Molecular line emission from protoplanetary disks is a powerful tool to constrain their physical and chemical structure. Nevertheless, only a few molecules have been detected in disks so far. We take advantage of the enhanced capabilities of the IRAM 30m telescope by using the new broad band correlator (FTS) to search for so far undetected molecules in the protoplanetary disks surrounding the TTauri stars DM Tau, GO Tau, LkCa 15 and the Herbig Ae star MWC 480. We report the first detection of HC3N at 5 sigma in the GO Tau and MWC 480 disks with the IRAM 30-m, and in the LkCa 15 disk (5 sigma), using the IRAM array, with derived column densities of the order of 10^{12}cm^{-2}. We also obtain stringent upper limits on CCS (N < 1.5 x 10^{12} cm^{-3}). We discuss the observational results by comparing them to column densities derived from existing chemical disk models (computed using the chemical code Nautilus) and based on previous nitrogen and sulfur-bearing molecule observations. The observed column densities of HC3N are typically two orders of magnitude lower than the existing predictions and appear to be lower in the presence of strong UV flux, suggesting that the molecular chemistry is sensitive to the UV penetration through the disk. The CCS upper limits reinforce our model with low elemental abundance of sulfur derived from other sulfur-bearing molecules (CS, H2S and SO).

astro-ph.SR↗

arXiv2012

A search for linear polarization in the active galactic nucleus 3C 84 at 239 and 348 GHz

We report a search for linear polarization in the active galactic nucleus (AGN) 3C 84 (NGC 1275) at observed frequencies of 239 GHz and 348 GHz, corresponding to rest-frame frequencies of 243 GHz and 354 GHz. We collected polarization data with the IRAM Plateau de Bure Interferometer via Earth rotation polarimetry. We do not detect linear polarization. Our analysis finds 3-sigma upper limits on the degree of polarization of 0.5% and 1.9% at 239 GHz and 348 GHz, respectively. We regard the influence of Faraday conversion as marginal, leading to expected circular polarizations <0.3%. Assuming depolarization by a local Faraday screen, we constrain the rotation measure, as well as the fluctuations therein, to be 10^6 rad/m^2. From this we estimate line-of-sight magnetic field strengths of >100 microG. Given the physical dimensions of 3C 84 and its observed structure, the Faraday screen appears to show prominent small-scale structure, with \DeltaRM > 10^6 rad/m^2 on projected spatial scales <1 pc.

astro-ph.GA↗

arXiv2012

The first IRAM/PdBI polarimetric millimeter survey of active galactic nuclei. II. Activity and properties of individual sources

We present an analysis of the linear polarization of six active galactic nuclei - 0415+379 (3C~111), 0507+179, 0528+134 (OG+134), 0954+658, 1418+546 (OQ+530), and 1637+574 (OS+562). Our targets were monitored from 2007 to 2011 in the observatory-frame frequency range 80-253 GHz, corresponding to a rest-frame frequency range 88-705 GHz. We find average degrees of polarization m_L ~ 2-7%; this indicates that the polarization signals are effectively averaged out by the emitter geometries. We see indication for fairly strong shocks and/or complex, variable emission region geometries in our sources, with compression factors <0.9 and/or changes in viewing angles by >10 deg. An analysis of correlations between source fluxes and polarization parameter points out special cases: the presence of (at least) two distinct emission regions with different levels of polarization (for 0415+379) as well as emission from a single, predominant component (for 0507+179 and 1418+546). Regarding the evolution of flux and polarization, we find good agreement between observations and the signal predicted by "oblique shock in jet" scenarios in one source (1418+546). We attempt to derive rotation measures for all sources, leading to actual measurements for two AGN and upper limits for three sources. We derive values of RM = -39,000 +/- 1,000 (stat) +/- 13,000 (sys) rad/m^2 and RM = 420,000 +/- 10,000 (stat) +/- 110,000 (sys) rad/m^2 for 1418+546 and 1637+574, respectively; these are the highest values reported to date for AGN. These values indicate magnetic field strengths of the order ~0.0001 G. For 0415+379, 0507+179, and 0954+658 we derive upper limits |RM| < 17,000 rad/m^2. From the relation |RM| ~ nu^a we find a = 1.9 +/- 0.3 for 1418+546, in good agreement with a = 2 as expected for a spherical or conical outflow.

astro-ph.CO↗

arXiv2011

The long-term millimeter activity of active galactic nuclei

We analyze the long-term evolution of the fluxes of six active galactic nuclei (AGN) - 0923+392, 3C 111, 3C 273, 3C 345, 3C 454.3, and 3C 84 - in the frequency range 80-267 GHz using archival calibration data of the IRAM Plateau de Bure Interferometer. Our dataset spans a long timeline of ~14 years with 974-3027 flux measurements per source. We find strong (factors ~2-8) flux variability on timescales of years for all sources. The flux density distributions of five out of six sources show clear signatures of bi- or even multimodality. Our sources show mostly steep (alpha~0.5-1), variable spectral indices that indicate outflow dominated emission; the variability is most probably due to optical depth variations. The power spectra globally correspond to red-noise spectra with five sources being located between the cases of white and flicker noise and one source (3C 111) being closer to the case of random walk noise. For three sources the low-frequency ends of their power spectra appear to be upscaled in spectral power by factors ~2-3 with respect to the overall powerlaws. In two sources, 3C 454.3 and 3C 84, the 1.3-mm emission preceeds the 3-mm emission by ~55 and ~300 days, respectively, probably due to (combinations of) optical depth and emission region geometry effects. We conclude that the source emission cannot be described by uniform stochastic emission processes; instead, a distinction of "quiescent" and (maybe multiple) "flare" states of the source emission appears to be necessary.

astro-ph.CO↗

arXiv2010

Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions

Abridged: We detail and benchmark two sophisticated chemical models developed by the Heidelberg and Bordeaux astrochemistry groups. The main goal of this study is to elaborate on a few well-described tests for state-of-the-art astrochemical codes covering a range of physical conditions and chemical processes, in particular those aimed at constraining current and future interferometric observations of protoplanetary disks. We consider three physical models: a cold molecular cloud core, a hot core, and an outer region of a T Tauri disk. Our chemical network (for both models) is based on the original gas-phase osu_03_2008 ratefile and includes gas-grain interactions and a set of surface reactions for the H-, O-, C-, S-, and N-bearing molecules. The benchmarking is performed with the increasing complexity of the considered processes: (1) the pure gas-phase chemistry, (2) the gas-phase chemistry with accretion and desorption, and (3) the full gas-grain model with surface reactions. Using atomic initial abundances with heavily depleted metals and hydrogen in its molecular form, the chemical evolution is modeled within 10^9 years. The time-dependent abundances calculated with the two chemical models are essentially the same for all considered physical cases and for all species, including the most complex polyatomic ions and organic molecules. This result however required a lot of efforts to make all necessary details consistent through the model runs, e.g. definition of the gas particle density, density of grain surface sites, the strength and shape of the UV radiation field, etc. The reference models and the benchmark setup, along with the two chemical codes and resulting time-dependent abundances are made publicly available in the Internet: http://www.mpia.de/homes/semenov/Chemistry_benchmark/home.html

astro-ph.GA↗

arXiv2010

Searching for sub-stellar companion into the LkCa15 proto-planetary disk

Recent sub-millimetric observations at the Plateau de Bure interferometer evidenced a cavity at ~ 46 AU in radius into the proto-planetary disk around the T Tauri star LkCa15 (V1079 Tau), located in the Taurus molecular cloud. Additional Spitzer observations have corroborated this result possibly explained by the presence of a massive (>= 5 MJup) planetary mass, a brown dwarf or a low mass star companion at about 30 AU from the star. We used the most recent developments of high angular resolution and high contrast imaging to search directly for the existence of this putative companion, and to bring new constraints on its physical and orbital properties. The NACO adaptive optics instrument at VLT was used to observe LkCa15 using a four quadrant phase mask coronagraph to access small angular separations at relatively high contrast. A reference star at the same parallactic angle was carefully observed to optimize the quasi-static speckles subtraction (limiting our sensitivity at less than 1.0). Although we do not report any positive detection of a faint companion that would be responsible for the observed gap in LkCa15's disk (25-30 AU), our detection limits start constraining its probable mass, semi-major axis and eccentricity. Using evolutionary model predictions, Monte Carlo simulations exclude the presence of low eccentric companions with masses M >= 6 M Jup and orbiting at a >= 100 AU with significant level of confidence. For closer orbits, brown dwarf companions can be rejected with a detection probability of 90% down to 80 AU (at 80% down to 60 AU). Our detection limits do not access the star environment close enough to fully exclude the presence of a brown dwarf or a massive planet within the disk inner activity (i.e at less than 30 AU). Only, further and higher contrast observations should unveil the existence of this putative companion inside the LkCa15 disk.

astro-ph.EP↗

arXiv2010

Chemistry in Disks. III. -- Photochemistry and X-ray driven chemistry probed by the ethynyl radical (CCH) in DM Tau, LkCa 15, and MWC 480

We studied several representative circumstellar disks surrounding the Herbig Ae star MWC 480 and the T Tauri stars LkCa 15 and DM Tau at (sub-)millimeter wavelengths in lines of CCH. Our aim is to characterize photochemistry in the heavily UV-irradiated MWC 480 disk and compare the results to the disks around cooler T Tauri stars. We detected and mapped CCH in these disks with the IRAM Plateau de Bure Interferome- ter in the C- and D-configurations in the (1-0) and (2-1) transitions. Using an iterative minimization technique, the CCH column densities and excitation conditions are con- strained. Very low excitation temperatures are derived for the T Tauri stars. These values are compared with the results of advanced chemical modeling, which is based on a steady-state flared disk structure with a vertical temperature gradient, and a gas- grain chemical network with surface reactions. Both model and observations suggest that CCH is a sensitive tracer of the X-ray and UV irradiation. The predicted radial dependency and source to source variations of CCH column densities qualitatively agree with the observed values, but the predicted column densities are too low by a factor of several. The chemical model fails to reproduce high concentrations of CCH in very cold disk midplane as derived from the observed low excitation condition for both the (1-0) and (2-1) transitions.

astro-ph.GA↗

arXiv2010

The First IRAM/PdBI Polarimetric Millimeter Survey of Active Galactic Nuclei. I. Global Properties of the Sample

We have studied the linear polarization of 86 active galactic nuclei (AGN) in the observed frequency range 80-267 GHz (3.7-1.1mm in wavelength), corresponding to rest-frame frequencies 82-738 GHz, with the IRAM Plateau de Bure Interferometer (PdBI). The large number of measurements, 441, makes our analysis the largest polarimetric AGN survey in this frequency range to date. We extracted polarization parameters via earth rotation polarimetry with unprecedented median precisions of ~0.1% in polarization fractions and ~1.2 degrees in polarization angles. For 73 of 86 sources we detect polarization at least once. The degrees of polarization are as high as ~19%, with the median over all sources being ~4%. Source fluxes and polarizations are typically highly variable, with fractional variabilities up to ~60%. We find that BLLac sources have on average the highest level of polarization. There appears to be no correlation between degree of polarization and redshift, indicating that there has been no substantial change of polarization properties since z~2.4. Our polarization and spectral index distributions are in good agreement with results found from various samples observed at cm/radio wavelengths; thus our frequency range is likely tracing the signature of synchrotron radiation without noticeable contributions from other emission mechanisms. The "millimeter-break" located at frequencies >1 THz appears to be not detectable in the frequency range covered by our survey.

astro-ph.CO↗

arXiv2008

Rotating molecular outflows: the young T Tauri star in CB26

The disk-outflow connection is thought to play a key role in extracting excess angular momentum from a forming proto-star. Though jet rotation has been observed in a few objects, no rotation of molecular outflows has been unambiguously reported so far. We report new millimeter-interferometric observations of the edge-on T Tauri star - disk system in the isolated Bok globule CB26. The aim of these observations was to study the disk-outflow relation in this 1Myr old low-mass young stellar object. The IRAM PdBI array was used to observe 12CO(2-1) at 1.3mm in two configurations, resulting in spectral line maps with 1.5 arcsec resolution. We use an empirical parameterized steady-state outflow model combined with 2-D line radiative transfer calculations and chi^2-minimization in parameter space to derive a best-fit model and constrain parameters of the outflow. The data reveal a previously undiscovered collimated bipolar molecular outflow of total length ~2000 AU, escaping perpendicular to the plane of the disk. We find peculiar kinematic signatures that suggest the outflow is rotating with the same orientation as the disk. However, we could not ultimately exclude jet precession or two misaligned flows as possible origin of the observed peculiar velocity field. There is indirect indication that the embedded driving source is a binary system, which, together with the youth of the source, could provide the clue to the observed kinematic features of the outflow. CB26 is so far the most promising source to study the rotation of a molecular outflow. Assuming that the outflow is rotating, we compute and compare masses, mass flux, angular momenta, and angular momentum flux of disk and outflow and derive disk dispersal timescales of 0.5...1 Myr, comparable to the age of the system.

astro-ph↗