Scientific Results in Press

An extended Sunyaev-Zel'dovich map of the most luminous X-ray cluster, RXJ1347-1145

E. Pointecouteau(¹), M. Giard(¹), A. Benoit(²), F.X. Désert(³), J.P. Bernard(⁴), N. Coron(⁴) and J.M. Lamarre(⁴),
(¹)Centre d'Etude Spatiale des Rayonnements, 9 av du colonel Roche, BP4346, 31028 Toulouse Cedex 4, France; (²)Centre de Recherche des Très Basses Températures 25 avenue des Martyrs, BP 166 , 38042 Grenoble Cedex 9, France; (³)Laboratoire d'Astrophysique de l'Observatoire de Grenoble, 414 rue de la Piscine, 38041 Grenoble Cedex 9, France; (⁴)Institut d'Astrophysique Spatiale, Bât 121, Université Paris-Sud, 91405 Orsay Cedex, France

Abstract:
The Sunyaev-Zel'dovich (SZ) effect is the Compton scattering of the 3K photons by the hot electrons in clusters of galaxies. It is now becoming a standard tool for the study of the baryonic diffuse matter in clusters (see e.g. the review by Birkinshaw (Phys. Rept. 310 (1999) 97-195).

  

Figure 7: SZ map of the z=0.51 cluster RXJ1347-145 in colours. X-ray contours from Rosat. The SZ effect shows up as a 3K background local brightness decrement at 2.1mm.

In a recent paper (ApJ (2001) 552, 42), we have presented a high resolution ( $22\hbox{$^{\prime\prime}$ }$ FWHM) extended map at 2.1mm of the SZ effect toward the most luminous X-ray cluster, RXJ1347-1145. These observations have been performed with the Diabolo photometer working at the focus of the 30m IRAM radiotelescope. We have derived a projected gas mass of $(1.1 \pm 0.1)\times 10^{14}\, h_{50}^{-5/2}$M$_\odot$ within an angular radius of $\theta=74''$(ie: projected radius of 0.6Mpc, H₀=50km/s/Mpc, $\Omega_m=0.3$, $\Omega_\Lambda=0.7$). This result matches very well the expected gas mass from the cluster models of X-ray data. With an unprecedented sensitivity level our measurement does not show significant departure from a spherical distribution.

The data analysis also allows us to characterize the 2.1mm flux of a well known radio source lying in the center of the cluster: $F_{RS}(2.1\textrm{mm})=5.7\pm 1.6$mJy. Hence we have demonstrated the usefulness of 2D information for SZ measurements, with respect to comparing to X-ray data and excluding point sources from the analysis. These data were obtained after 16 hours of integration time with a 3 beam dual channel photometer. Clearly the way forward is now to build 1 and 2mm fully sampled arrays of 100 to 1000 pixels in order to search for inhomogeneity in the SZ effect in clusters, peculiar velocities and complement Chandra and XMM-Newton data on clusters of galaxies. We are now actively working on such millimeter detectors that could be put on the 30m in the years to come.

Summary of an article published in ApJ 552, 42

An interferometric study of the HH288 molecular outflow

F. Gueth(¹),(²), P. Schilke(¹), and M.J. McCaughrean(³),
(¹)Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany; (²)Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France; (³)Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Abstract:
We present an interferometric study of the CO (j=1-0) line emission in the HH288 molecular outflow. The IRAM Plateau de Bure interferometer was used to obtain an 11-field mosaic covering the whole flow ($\sim$2 pc) with an angular resolution of about 3.5''(7000 AU at a distance of 2 kpc). The data were complemented with short-spacings derived from IRAM 30-m observations. The exciting source of HH288, IRAS00342+6347, is a young (dynamical age of the outflow $\simeq$ a few 10⁴ years) intermediate-mass (bolometric luminosity $\simeq 500\mbox{M$_\odot$ }$, envelope mass $\simeq 6$ to $30\mbox{M$_\odot$ }$) embedded protostar. This source is likely to be an intermediate-mass counterpart of a classical Class 0 low-mass protostar. HH288 is actually a quadrupolar outflow, and the angular resolution provided by the interferometric observations allows us to rule out models involving limb-brightened walls of a wide-angle single flow to explain such a morphology. The presence of two protostars in the central condensation is the most appealing explanation to account for the presence of the two flows. While the small East-West flow has a quite simple morphology and kinematics, the large North-South flow includes several overlapping structures, created by successive ejection events. Large collimated limb-brightened cavities are observed, with high-velocity material located along or near the flow axis. The internal structure of HH288, including morphological coincidence between the CO and H₂ emission, supports prompt entrainment at the head of large bow-shocks as the main formation process of molecular outflows from intermediate-mass protostars.

Accepted for publication in A&A

A 1.2mm MAMBO/IRAM-30m Survey of Dust Emission from the Highest Redshift PSS Quasars

A. Omont(¹), P. Cox(²), F. Bertoldi(³), R.G. McMahon (⁴), C. Carilli(⁵), K.G. Isaak(⁶),
(¹)Institut d'Astrophysique de Paris, CNRS, 98bis boulevard Arago, 75014 Paris, France; (²)Institut d'Astrophysique Spatiale, Université de Paris XI, 91405 Orsay, France; (³)Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany; (⁴)Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK; (⁵)National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801, USA; (⁶)Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, UK

Abstract:
We report 250 GHz (1.2mm) observations of redshift $\geq 3.8$ quasars from the Palomar Sky Survey (PSS) sample, using the Max-Planck Millimetre Bolometer (MAMBO) array at the IRAM 30-metre telescope. Eighteen sources were detected and upper limits were obtained for 44 with $3\sigma$ flux density limits in the range 1.5-4mJy. Adopting typical dust temperatures of 40-50K, we derive dust masses of $\approx 10^8-10^9 \mbox{M$_\odot$ }$ and far-infrared luminosities of order $10^{13} \mbox{M$_\odot$ }$. We suggest that a substantial fraction of this luminosity arises from young stars, implying star formation rates approaching $10^3 \mbox{M$_\odot$ }$/yr or more. The high millimetre detection rate supports current views on a connection between AGN and star forming activity, suggesting a parallel evolution of the central black hole and of the stellar core of a galaxy, although their growth-rate ratio seems higher than the mass ratio observed in nearby galaxies. The observed, exceptionally bright objects may trace the peaks of the primordial density field, the cores of future giant ellipticals.

Accepted for publication in A&A, preprints are available at astro-ph/0107005

Star formation in the bright rimmed globule IC1396N

C. Codella(¹), R. Bachiller(²), B. Nisini(³), P. Saraceno(¹) and L. Testi(⁴),
(¹)Istituto di Fisica dello Spazio Interplanetario, CNR, Area di Ricerca Tor Vergata, Via Fosso del Cavaliere 100, 00133 Roma, Italy; (²)Observatorio Astronómico Nacional (IGN), Apartado 1143, 28800 Alcalá de Henares (Madrid), Spain; (³)Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monteporzio, Italy; (⁴)Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

Abstract:
We report mm-wave multiline and continuum observations of IC1396N, a conspicuous bright rimmed globule excited by the O6.5 star HD206267 in the Cep OB2 association. Single-dish high resolution observations in CO and CS lines reveal the cometary structure of the globule with unprecedented detail. The globule head contains a dense core of 0.2 pc, whereas the tail, pointing away from the exciting star, has a total length of 0.8 pc. Two high velocity bipolar outflows have been identified in the CO maps: the first one is located around the position of a strong IRAS source in the head of the globule, and the second one, which was previously unknown, is located in the northern region. The outflows emerge from high density clumps which exhibit strong line emission of CS, HCO⁺, and DCO⁺. Within these clumps, the sources driving the outflows have been identified thanks to mm-wave continuum observations. The globule head harbors two YSOs separated by about 10⁴ AU.

SiO line observations of the central outflow unveals a highly collimated structure with four clumps of sizes $\leq 0.1$ pc, which are located along the outflow axis and suggest episodic events in the mass loss process from the central star. Kinetic temperatures of $\sim$ 50-100 K and hydrogen densities of fews 10⁶ cm^-3 have been estimated in the shocked regions traced by the strong SiO emission. The jet is also exposed to view by the means of interferometric HCO⁺ observations that confirms that it is very narrow ($\leq 0.02$ pc wide).

The detection of blue- and redshifted CO emission along the globule rim suggests that IC1396N is in a transient phase, undergoing one of the expansions or compressions predicted by theoretical models describing the evolution of cometary globules. Moreover, the CO data, together with near IR observations reported elsewhere, indicate that the star forming process is occurring also in the northern part of IC1396N, at 0.5 pc from the central CS peak. The present observations provide evidence that several star forming sites can develop even in a moderately massive globule like IC1396N.

Accepted for publication in A&A

The highly collimated bipolar outflow of OH231.8+4.2

Alcolea(¹), J.; Bujarrabal(²), V.; Sánchez Contreras(²),(³)), C.; Neri(⁴), R.; Zweigle, J.(⁴)
(¹)Observatorio Astronómico Nacional, Alfonso XII 3, 28014 Madrid, Spain, (²)Observatorio Astronómico Nacional, Ap. 1143, 28800 Alcalá de Henares, Spain, (³)Departamento de Astrofisica, Facultad C. Físicas, Universidad Complutense, 28040 Madrid, Spain, (⁴)IRAM, 300 rue de la Piscine, 38406 St. Martin-d'Hères, France

Abstract:
We present high spatial resolution observations of the CO molecular emission (J=1-0 and J=2-1 lines) in the post-AGB bipolar nebula OH231.8+4.2. High-quality NIR images (J, H, K' bands) of light scattered by grains were also obtained. Our observations probe the bulk of the nebular material, providing maps with a resolution $\sim 1\hbox{$^{\prime\prime}$ }$ of the mass distribution, both CO and NIR images being very closely coincident. The combination of the two ¹²CO lines has been used to measure the distribution of the kinetic temperature in the nebula, which is found to be very low, ranging between 8K, in the outer southern clumps, and 35K, in the central region. A relative temperature increase is found in the northernmost condensation, probably associated to a strong bow-like shock. Since velocities are also measured in CO, the dynamic parameters (kinetic momentum and energy) are also measured with high resolution. Most of the nebular mass ( $\sim 0.64\,M_\odot$) is located in the central condensation and flows at expansion velocities $\leq 40\,$kms^-1. The rest of the gas, $\sim 0.3\,M_\odot$ almost equally distributed in the two lobes, flows along the nebular axis at high velocities, that increase proportionally to the distance to the central star reaching values as large as 430kms^-1, as a result of a sudden acceleration happened about 770yr ago. The general mass distribution in OH231.8+4.2 is found to be clumpy and very elongated, with a length/width ratio reaching a factor 20 in the southern tail. In the center, however, we find a double hollow-lobe structure, similar to those found in other well studied protoplanetary nebulae. We stress the enormous kinetic linear momentum carried by the molecular nebula, about $27\,M_{\odot}$kms $^{-1}\,\,(5.5\,10^{39}$gcms^-1). The kinetic energy is also very high, $\sim 1700\,M_{\odot}$km²s $^{-4} \sim 3.4\,10^{46}\,$erg. Given the short time during which the acceleration of the molecular outflow took place, we conclude that the linear momentum carried by the stellar photons is about a factor 100 smaller than that carried by the outflow, even if the effects of multiple scattering are taken into account. We independently argue that radiation pressure directly acting onto grains (the mechanism thought to be responsible for the mass ejection in AGB envelopes) cannot explain the observed bipolar flow, since this would produce a significant shift between the dust and gas features that is not observed. Finally, we review the uncertain nature and evolutionary status of this unique object.

Appeared in A&A, 2001, 373, 932