Special A&A Letters edition for recent high-resolution PdBI results

Editorial A&A Letters 468 (2007):
The IRAM interferometer, located on the Plateau de Bure at 2500 meters altitude in the French Alps, has entered a new era since the beginning of 2006. The tracks, on which the six 15-meter diameter antennas move, have been extended, nearly doubling the east-west and north-south baselines. The largest separation of the antennas is now 760 meters, enabling sub-arcsecond angular resolution at millimeter wavelengths.

This special issue of Astronomy & Astrophysics Letters presents first results with the extended baselines of the Plateau de Bure interferometer. Eleven Letters report observations done at sub-arcsecond resolution of objects ranging from nearby star-forming regions and evolved stars to starburst galaxies.

M. Walmsley and C. Bertout

PdBI sub-arcsecond study of the SiO microjet in HH212 Origin and collimation of class 0 jets

S. Cabrit$(^{1})$, C. Codella$(^{2})$, F. Gueth$(^{3})$, B. Nisini$(^{4})$, A. Gusdorf$(^{5})$, C. Dougados$(^{6})$, and F. Bacciotti$(^{7})$
$(^{1})$LERMA, UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France, $(^{2})$INAF, Istituto di Radioastronomia, Sezione di Firenze, Largo E. Fermi 5, 50125 Firenze, Italy, $(^{3})$IRAM, 300 rue de la Piscine, 38406 Grenoble Cedex, France, $(^{4})$INAF-Osservatorio Astrofisico di Roma, via di Frascati 33, 00040 Monte Catone, Italy, $(^{5})$Physics Department, The University, Durham DH1 3LE, UK, $(^{6})$Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex, France, $(^{7})$INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

Abstract:
Context. The bipolar HH 212 outflow has been mapped in SiO using the extended configuration of the Plateau de Bure Interferometer (PdBI), revealing a highly collimated SiO jet closely associated with the H2 jet component. Aims. We study at unprecedented resolution ($0\farcs34$ across the jet axis) the properties of the innermost SiO "microjet" within 1000 AU of this young Class 0 source, to compare it with atomic microjets from more evolved sources and to constrain its origin. Methods. The SiO channel maps are used to investigate the microjet collimation and velocity structure. A large velocity gradient analysis is applied to SiO $(2-1)$, $(5-4)$ and $(8-7)$ data from the PdBI and the Submillimeter Array to constrain the SiO opacity and abundance. Results. The HH212 Class 0 microjet shows striking similarities in collimation and energetic budget with atomic microjets from T Tauri sources. Furthermore, the SiO lines appear optically thick, unlike what is generally assumed. We infer $T_{\rm k}$ $\simeq$ 50-500 K and an SiO/H$_2$ abundance $\ge 4 \times 10^{-8} - 6 \times 10^5$ for $n({\rm H_2}) = 10^7 - 10^5$ cm$^{-3}$, i.e. $0.05-90$% of the elemental silicon. Conclusions. This similar jet width, regardless of the presence of a dense envelope, definitely rules out jet collimation by external pressure, and favors a common MHD self-collimation (and possibly acceleration) process at all stages of star formation. We propose that the more abundant SiO in Class 0 jets could mainly result from rapid ($\leq 25$ yrs) molecular synthesis at high jet densities.

Appeared in: A&A 468, L29

The IC 1396 N proto-cluster at a scale of $\sim 250$ AU

R. Neri$(^{1})$, A. Fuente$(^{2})$, C. Ceccarelli$(^{3})$, P. Caselli$(^{4,5})$, D. Johnstone$(^{6, 7})$, E. F. van Dishoeck$(^{8})$, F. Wyrowski$(^{9})$, M. Tafalla$(^{2})$, B. Lefloch$(^{3})$, and R. Plume$(^{10})$
$(^{1})$Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St Martin d'Hères Cedex, France $(^{2})$Observatorio Astronómico Nacional (OAN), Apdo. 112, 28803 Alcalá de Henares (Madrid), Spain, $(^{3})$Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France, $(^{4})$Osservatorio Astrofisico di Arcetri (INAF), Largo E. Fermi 5, 50125 Firenze, Italy, $(^{5})$Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 0213, USA, $(^{6})$Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada, $(^{7})$National Research Council of Canada, Herzberg Institute, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada, $(^{8})$Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands, $(^{9})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany, $(^{10})$University of Calgary, 2500 University Drive NW, Alberta T2N 1N4, Canada

Abstract:
Aims. We investigate the mm-morphology of IC 1396 N with unprecedented spatial resolution to analyze its dust and molecular gas properties, and draw comparisons with objects of similar mass. Methods. We have carried out sensitive observations in the most extended configurations of the IRAM Plateau de Bure interferometer, to map the thermal dust emission at 3.3 and 1.3 mm, and the emission from the $J=13_k\rightarrow 12_k$ hyperfine transitions of methyl cyanide (CH$_3$CN). Results. We unveil the existence of a sub-cluster of hot cores in IC 1396 N, distributed in a direction perpendicular to the emanating outflow. The cores are embedded in a common envelope of extended and diffuse dust emission. We find striking differences in the dust properties of the cores ( $\beta\simeq 0$) and the surrounding envelope ( $\beta\simeq 1$), very likely testifying to differences in the formation and processing of dust material. The CH$_3$CN emission peaks towards the most massive hot core and is marginally extended in the outflow direction.

Appeared in: A&A 468, L33

Protostellar clusters in intermediate mass (IM) star forming regions

A. Fuente$(^{1})$, C. Ceccarelli$(^{2})$, R. Neri$(^{3})$, T. Alonso-Albi$(^{1})$, P. Caselli$(^{4,5})$, D. Johnstone$(^{6, 7})$, E. F. van Dishoeck$(^{8})$, and F. Wyrowski$(^{9})$
$(^{1})$Observatorio Astronómico Nacional (OAN), Apdo. 112, 28803 Alcalá de Henares (Madrid), Spain, $(^{2})$Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France, $(^{3})$Institute de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St Martin d'Hères Cedex, France, $(^{4})$INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy, $(^{5})$Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 0213, $(^{6})$Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada, $(^{7})$National Research Council of Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada, $(^{8})$Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands, $(^{9})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Abstract:
Context. The transition between the low density groups of T Tauri stars and the high density clusters around massive stars occurs in the intermediate-mass (IM) range ( $M_*\sim 2 - 8 \mbox{M$_\odot$}$ ). High spatial resolution studies of IM young stellar objects (YSO) can provide important clues to understand the clustering in massive star forming regions. Aims. Our aim is to search for clustering in IM Class 0 protostars. The high spatial resolution and sensitivity provided by the new A configuration of the Plateau de Bure Interferometer (PdBI) allow us to study the clustering in these nearby objects. Methods. We have imaged three IM Class 0 protostars (Serpens-FIRS 1, IC1396 N, CB 3) in the continuum at 3.3 and 1.3 mm using the PdBI. The sources have been selected with different luminosity to investigate the dependence of the clustering process on the luminosity of the source. Results. Only one millimeter (mm) source is detected towards the low luminosity source Serpens-FIRS 1. Towards CB 3 and IC1396 N, we detect two compact sources separated by $\sim 0.05$ pc. The 1.3 mm image of IC1396 N, which provides the highest spatial resolution, reveal that one of these cores is splitted in, at least, three individual sources.

Appeared in: A&A 468, L37

Minkowski's footprint revisited Planetary nebula formation from a single sudden event?

J. Alcolea$(^{1})$, R. Neri$(^{2})$, and V. Bujarrabal$(^{3})$
$(^{1})$Observatorio Astronómico Nacional (OAN-IGN), Calle Alfonso XII 3, 28014 Madrid, Spain, $(^{2})$Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 St. Martin d'Hères, France, $(^{3})$Observatorio Astronómico Nacional (OAN-IGN), Apartado 112, 28803 Alcalá de Henares, Spain

Abstract:
Context. M 1-92 can be considered an archetype of bipolar pre-planetary nebulae. It shows a clear axial symmetry, along with the kinematics and momentum excess characteristic of this class of envelopes around post-AGB stars. Aims. By taking advantage of the new extended configuration of the IRAM Plateau de Bure interferometer, we wanted to study the morphology and velocity field of the molecular gas better in this nebula, particularly in its central part. Methods. We performed sub-arcsecond resolution interferometric observations of the $J=2-1$ rotational line of $^{13}$CO in M 1-92. Results. We found that the equatorial component is a thin flat disk, which expands radially with a velocity proportional to the distance to the center. The kinetic age of this equatorial flow is very similar to that of the two lobes. The small widths and velocity dispersion in the gas forming the lobe walls confirm that the acceleration responsible for the nebular shape could not last more than 100-120 yr. Conclusions. The present kinematics of the molecular gas can be explained as the result of a single brief acceleration event, after which the nebula reached an expansion velocity field with axial symmetry. In view of the similarity to other objects, we speculate on the possibility that the whole nebula was formed as a result of a magneto-rotational explosion in a common-envelope system.

Appeared in: A&A 468, L41

The nebula around the post-AGB star 89 Herculis

V. Bujarrabal$(^{1})$, H. Van Winckel$(^{2})$, R. Neri$(^{3})$, J. Alcolea$(^{4})$, A. Castro-Carrizo$(^{3})$, and P. Deroo$(^{2})$
$(^{1})$Observatorio Astronómico Nacional (OAN-IGN), Apartado 112, 28803 Alcalá de Henares, Spain, $(^{2})$Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium, $(^{3})$Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 St. Martin d'Hères, France, $(^{4})$Observatorio Astronómico Nacional (OAN-IGN), C/ Alfonso XII 3, 28014 Madrid, Spain

Abstract:
Aims. We aim to study the structure of the nebula around the post-AGB, binary star 89 Her. The presence of a rotating disk around this star had been proposed but not been yet confirmed by observations. Methods. We present high-resolution PdBI maps of CO $J=2-1$ and $1-0$. Properties of the nebula are directly derived from the data and model fitting. We also present N-band interferometric data on the extent of the hot dust emission, obtained with the VLTI. Results. Two nebular components are found: (a) an extended hour-glass-like structure, with expansion velocities of $\sim 7$ km s$^{-1}$ and a total mass $\sim 3\times 10^{-3}$ M$_\odot$, and (b) an unresolved very compact component, smaller than $\sim 0{\farcs}4$ and with a low total velocity dispersion of $\sim 5$ km s$^{-1}$. We cannot determine the velocity field in the compact component, but we argue that it can hardly be in expansion, since this would require too recent and too sudden an ejection of mass. On the other hand, assuming that this component is a Keplerian disk, we derive disk properties that are compatible with expectations for such a structure; in particular, the size of the rotating gas disk should be very similar to the extent of the hot dust component from our VLTI data. Assuming that the equator of the extended nebula coincides with the binary orbital plane, we provide new results on the companion star mass and orbit.

Appeared in: A&A 468, L45

Jet-disturbed molecular gas near the Seyfert 2 nucleus in M 51

S. Matsushita$(^{1})$, S. Muller$(^{1})$, and J. Lim$(^{1})$
$(^{1})$Academia Sinica, Institute of Astronomy and Astrophysics, PO Box 23-141, Taipei 106, Taiwan, R.O.C.

Abstract:
Context. Previous molecular gas observations at arcsecond-scale resolution of the Seyfert 2 galaxy M 51 suggest the presence of a dense circumnuclear rotating disk, which may be the reservoir for fueling the active nucleus and obscures it from direct view in the optical. However, our recent interferometric CO$(3-2)$ observations show a hint of a velocity gradient perpendicular to the rotating disk, which suggests a more complex structure than previously thought. Aims. To image the putative circumnuclear molecular gas disk at sub-arcsecond resolution to better understand both the spatial distribution and kinematics of the molecular gas. Methods. We carried out CO$(2-1)$ and CO$(1-0)$ line observations of the nuclear region of M 51 with the new A configuration of the IRAM Plateau de Bure Interferometer, yielding a spatial resolution lower than 15 pc. Results. The high resolution images show no clear evidence of a disk, aligned nearly east-west and perpendicular to the radio jet axis, as suggested by previous observations, but show two separate features located on the eastern and western sides of the nucleus. The western feature shows an elongated structure along the jet and a good velocity correspondence with optical emission lines associated with the jet, suggesting that this feature is a jet-entrained gas. The eastern feature is elongated nearly east-west ending around the nucleus. A velocity gradient appears in the same direction with increasingly blueshifted velocities near the nucleus. This velocity gradient is in the opposite sense of that previously inferred for the putative circumnuclear disk. Possible explanations for the observed molecular gas distribution and kinematics are that a rotating gas disk disturbed by the jet, gas streaming toward the nucleus, or a ring with another smaller counter- or Keplarian-rotating gas disk inside.

Appeared in: A&A 468, L49

Distribution of the molecular absorption in front of the quasar B0218+357

S. Muller$(^{1})$, M. Guélin$(^{2})$, F. Combes$(^{3})$, and T. Wiklind$(^{4})$
$(^{1})$Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), PO Box 23-141, Taipei, 106 Taiwan, $(^{2})$Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la piscine, 38406 St Martin d'Hères, France, $(^{3})$Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France, $(^{4})$ESA Space Telescope Division, STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA

Abstract:
The line of sight to the quasar B0218+357, one of the most studied lensed systems, intercepts a z = 0.68 spiral galaxy, which splits its image into two main components A and B, separated by ca. $0{\farcs}3$, and gives rise to molecular absorption. Although the main absorption component has been shown to arise in front of image A, it is not established whether some absorption from other velocity components is also occuring in front of image B. To tackle this question, we have observed the HCO$^+(2-1)$ absorption line during the commissioning phase of the new very extended configuration of the Plateau de Bure Interferometer, in order to trace the position of the absorption as a function of frequency. Visibility fitting of the self-calibrated data allowed us to achieve position accuracy between 12 and 80 mas per velocity component. Our results clearly demonstrate that all the different velocity components of the HCO$^+(2-1)$ absorption arise in front of the south-west image A of the quasar. We estimate a flux ratio $f_{\rm A}/f_{\rm B} = 4.2_{-1.0}^{+1.8}$ at 106 GHz.

Appeared in: A&A 468, L53

Black hole in the West nucleus of Arp 220

D. Downes$(^{1})$ and A. Eckart$(^{2, 3})$
$(^{1})$Institut de Radio Astronomie Millimétrique, Domaine Universitaire, 38406 St. Martin d'Hères, France, $(^{2})$I.Physikalisches Institut, Universität zu Köln, Zulpicherstrasse 77, 50937 Köln, Germany, $(^{3})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Abstract:
We present new observations with the IRAM Interferometer, in its longest-baseline configuration, of the CO$(2-1)$ line and the 1.3 mm dust radiation from the Arp 220 nuclear region. The dust source in the West nucleus has a size of $0{\farcs}19 \times 0{\farcs}13$ and a 1.3 mm brightness temperature of 90 K. This implies that the dust ring in the West nucleus has a high opacity, with $\tau = 1$ at 1.1 mm. Not only is the dust ring itself optically thick in the submm and far-IR, but it is surrounded by the previously-known, rapidly rotating molecular disk of size $0{\farcs}5$ that is also optically thick in the mid-IR. The molecular ring is cooler than the hot dust disk because the CO$(2-1)$ line is seen in absorption against the dust disk. The dust ring is massive ($10^9$M$_\odot$), compact (radius 35 pc), and hot (true dust temperature 170 K). It resembles rather strikingly the dust ring detected around the quasar APM 08279+52, and is most unlike the warm, extended dust sources in starburst galaxies. Because there is a strong temperature gradient from the hot dust ring to the cooler molecular disk, the heating must come from a concentrated source, an AGN accretion disk that is completely invisible at optical wavelengths, and heavily obscured in hard X-rays.

Appeared in: A&A 468, L57

Molecular gas in NUclei of GAlaxies (NUGA): VI. Detection of a molecular gas disk/torus via HCN in the Seyfert 2 galaxy NGC 6951?

M. Krips$(^{1})$, R. Neri$(^{2})$, S. García-Burillo$(^{3})$, F. Combes$(^{4})$, E. Schinnerer$(^{5})$, A. J. Baker$(^{6})$, A. Eckart$(^{7})$, F. Boone$(^{5})$, L. Hunt$(^{8})$, S. Leon$(^{9})$, and L. J. Tacconi$(^{10})$
$(^{1})$Harvard-Smithsonian Center for Astrophysics, SMA project, 645 N A`ohoku Pl., Hilo, HI,96720, USA, $(^{2})$Institut de Radio Astronomie Millimétrique (IRAM), 38406, Saint Martin d'Hères, France, $(^{3})$Observatorio Astronómico Nacional (OAN)- Observatorio de Madrid, C/ Alfonso XII 3, 28014 Madrid, Spain, $(^{4})$Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France, $(^{5})$Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany, $(^{6})$Department of Physics and Astronomy, Rutgers, State University of NJ, 136 Frelinghuysen Rd., Piscataway, NJ 08854-8019, USA, $(^{7})$Universität zu Köln, I.Physikalisches Institut, Zülpicher Str. 77, 50937 Köln, Germany, $(^{8})$INAF-Istituto di Radioastronomia/Sezione Firenze Largo E. Fermi 5, 50125 Firenze, Italy, $(^{9})$IRAM, Avenida Divina Pastora, 7, Núcleo Central, 18012 Granada, Spain, $(^{10})$Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany

Abstract:
Context. Several studies of nearby active galaxies indicate significantly higher HCN-to-CO intensity ratios in AGN (e.g., NGC 1068) than in starburst (e.g., M 82) environments. HCN enhancement can be caused by many different effects, such as higher gas densities and/or temperatures, UV/X-ray radiation, and non-collisional excitation. As active galaxies often exhibit intense circumnuclear star formation, high angular resolution/high sensitivity observations are of paramount importance to disentangling the influence of star formation from that of nuclear activity on the chemistry of the surrounding molecular gas. The tight relation of HCN enhancement and nuclear activity may qualify HCN as an ideal tracer of molecular gas close to the AGN, providing complementary and additional information to that gained via CO. Aims. NGC 6951 houses nuclear and starburst activity, making it an ideal testbed in which to study the effects of different excitation conditions on the molecular gas. Previous lower angular resolution/sensitivity observations of HCN$(1-0)$ carried out with the Nobeyama Millimeter array by Kohno et al. (1999a, ApJ, 511, 157) led to the detection of the starburst ring, but no central emission has been found. Our aim was to search for nuclear HCN emission and, if successful, for differences of the gas properties of the starburst ring and the nucleus. Methods. We used the new A, B, C and D configurations of the IRAM PdBI array to observe HCN$(1-0)$ in NGC 6951 at high angular resolution ( $1\hbox{$^{\prime\prime}$}\equiv96$ pc) and sensitivity. Results. We detect very compact ($\leq$50 pc) HCN emission in the nucleus of NGC 6951, supporting previous hints of nuclear gas structure. Our observations also reveal HCN emission in the starburst ring and resolve it into several peaks, leading to a higher coincidence between the HCN and CO distributions than previously reported by Kohno et al. (1999a). Conclusions. We find a significantly higher HCN-to-CO intensity ratio ($\geq 0.4$) in the nucleus than in the starburst ring ($0.02-0.05$). As for NGC 1068, this might result from a higher HCN abundance in the centre due to an X-ray dominated gas chemistry, but a higher gas density/temperature or additional non-collisional excitation of HCN cannot be entirely ruled out, based on these observations. The compact HCN emission is associated with rotating gas in a circumnuclear disk/torus.

Appeared in: A&A 468, L63

Sub-arcsecond CO(1-0) and CO(2-1) observations of the ultraluminous infrared galaxy IRAS 10190+1322

J. Graciá-Carpio$(^{1})$, P. Planesas$(^{1})$, and L. Colina$(^{2})$
$(^{1})$Observatorio Astronómico Nacional (OAN), Observatorio de Madrid, Alfonso XII 3, 28014 Madrid, Spain, $(^{2})$Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Estructura de la Materia, Serrano 121, 28006 Madrid, Spain

Abstract:
We present the results of high resolution mapping of the CO$(1-0)$ and CO$(2-1)$ emission of the ultraluminous infrared galaxy (ULIRG) IRAS 10190+1322, with the IRAM interferometer, down to an angular resolution of $\sim 0.3\hbox{$^{\prime\prime}$}$. This object is composed of two interacting galaxies with a projected nuclear separation of 6 kpc, and was selected to analyze the physical and dynamical properties of the molecular gas in each galaxy in order to study the conditions that lead a galaxy pair to become ultraluminous in the infrared. With the exception of Arp 220, the closest ULIRG, this is the first time that the CO emission is morphologically and kinematically resolved in the two interacting galaxies of a ULIRG system. In one of the galaxies the molecular gas is highly concentrated, distributed in a circumnuclear disk of 1.7 kpc in size. The molecular gas in the presumably less infrared luminous galaxy is distributed in a more extended disk of 7.4 kpc. The molecular gas mass accounts for $\sim 10$% of the dynamical mass in each galaxy. Both objects are rich enough in molecular gas, $M_{\rm gas} \sim 4\times 10^{9}$M$_\odot$, as to experience an infrared ultraluminous phase.

Appeared in: A&A 468, L67

Fueling the central engine of radio galaxies I. The molecular/dusty disk of 4C 31.04

S. García-Burillo$(^{1})$, F. Combes$(^{2})$, R. Neri$(^{3})$, A. Fuente$(^{1})$, A. Usero$(^{1,4})$, S. Leon$(^{5})$, and J. Lim$(^{6})$
$(^{1})$ Observatorio Astronómico Nacional, Alfonso XII, 3, 28014 Madrid, Spain, $(^{2})$ Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France, $(^{3})$ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, $(^{4})$ Centre for Astrophysics Research, University of Hertfordshire, College Lane, AL10 9AB, UK, $(^{5})$ Instituto de Astrofísica de Andalucía, C Bajo de Huétor, 50, 18008 Granada, Spain, $(^{6})$ Inst. of Astron. and Astrophysics, Academia Sinica, PO Box 23-141, Taipei 106, Taiwan

Abstract:
We report the detection of a massive ( $M_{\rm gas} > 5\times 10^{9}$ M$_\odot$) molecular/dusty disk of 1.4 kpc-size fueling the central engine of the compact symmetric object (CSO) 4C 31.04, based on high-resolution ( $0{\farcs}5 - 1{\farcs}2$) observations done with the IRAM Plateau de Bure interferometer (PdBI). These observations allow us for the first time to detect and map the continuum emission from dust at 218 GHz in the disk of a CSO. The case for a massive disk is confirmed by detection of strong HCO$^+(1-0)$ line emission and absorption. The molecular gas mass of 4C 31.04 is in the range $0.5\times 10^{10} - 5\times 10^{10}$ M$_\odot$. While the distribution and kinematics of the gas roughly correspond to those of a rotating disk, we find evidence of distortions and non-circular motions that suggest the disk is not in a dynamically relaxed state. We discuss the implications of these results for the understanding of the evolution of radio galaxies.

Appeared in: A&A 468, L71