PR 0402/09

Infant Galaxies: Small and Hyperactive   
Fabian Walter, Max-Planck-Institut für Astronomie Heidelberg (Germany) ; Dominik Riechers du Max-Planck-Institut für Astronomie Heidelberg (Germany) and California Institute of Technology Pasadena (USA) ; Pierre Cox and Roberto Neri, Institut de Radioastronomie Millimétrique Grenoble (France) ; Chris Carilli, National Radio Astronomy Observatory Socorro (USA) ; Frank Bertoldi, Argelander Institut für Astronomie Bonn (Germany) ; Axel Weiss, Max-Planck-Institut für Radioastronomie Bonn (Germany) ; Roberto Maiolino, Istituto Nazionale di Astrofisica, Osservatorio Rome (Italy)

When galaxies are born, do their stars form everywhere at once, or only within a small core region? Recent measurements provide the first concrete evidence that star-forming regions in infant galaxies are indeed small - but also hyperactive, producing stars at astonishingly high rates.

This is the conclusion drawn from recent observations of one of the most distant known galaxies: a so-called quasar with the designation J1148+5251. Light from this galaxy takes 12.8 billion years to reach Earth; in turn, astronomical observations show the galaxy as it appeared 12.8 billion years ago, providing a glimpse of the very early stages of galactic evolution, less than a billion years after the Big Bang.

The observers, an international team of researchers led by scientists from the Max Planck Institute for Astronomy, made use of the IRAM Interferometer, a German-French-Spanish radio telescope, to obtain images of a very special kind: They recorded the infrared radiation emitted by J1148+5251 at a specific frequency associated with ionized carbon atoms, which is a reliable indicator of ongoing star formation. The resulting images show sufficient detail to allow, for the first time, the measurement of the size of a very early star-forming region. With this information, the researchers were able to conclude that, at the time, stars were forming in the core region of J1148+5251 at record rates - any faster, and star formation would have been in conflict with the laws of physics.

The results will be published in the February 5 issue (Volume 457, No. 7230) of the journal Nature.

For more details see the full press releases on English, French and German.

PR 1216/08

HCO mapping of the Horsehead : Tracing the illuminated dense molecular cloud surfaces   
M. Gerin, J.R. Goicoechea, J. Pety, P. Hily-Blant Laboratoire de Radioastronomie ENS, Paris, France

Stellar UV radiation is one important feedback mechanism for regulating star formation. It dissociates molecules and ionizes and heats the gas and the dust in photon dominated regions (PDRs). Star formation is revealed by this interaction, as it produces strong emission lines from the UV-excited gas. The investigation of a variety of tracers of the physics and chemistry of PDRs is a prerequisite for understanding the large scale roles of these feedback mechanisms. PDR models are used to understand the evolution of the UV irradiated matter both in our Galaxy and in external galaxies.

The illuminated edge of the Horsehead nebular, at only 450 pc distance, is one of the best studied PDRs. High sensitivity and spatial resolution maps of the horsehead nebula have been obtained with the IRAM 30m and PdBI (Gerin et al. 2008). These maps show that the formyl radical HCO is confined in a thin filament which delineates the UV illuminated edge of the nebula. The formyl radical HCO therefore appears to be a tracer of PDR at millimeter wavelengths, which could be used to trace UV dominated environments in the local and distant universe, whatever the visual extinction. Although state of the art chemical models fail to reproduce the observed abundance, two promising paths have been proposed by Gerin et al. 2008, which should be further investigated.

The inset shows high angular resolution maps of the integrated intensity of H¹³CO⁺, HCO, CCH and vibrationally excited H₂ emission. The PDR edge, delineated by the red vertical line, is illuminated by σ Ori lying to the right.

For more details see arXiv:0811.1470

PR 1212/08

Photoevaporating circumstellar disks around Herbig Be stars   
T. Alonso-Albi, A. Fuente, R. Bachiller, R. Neri, P. Planesas, L.Testi, O. Berné C. Joblin Observatorio Astronomico National, Madrid, Spain

A search for circumstellar disks around Herbig Be stars has been carried out using the NRAO Very Large Array (VLA) and the IRAM Plateau de Bure (PdB) interferometers. Thus far, we have observed 6 objects (R Mon, MWC 1080, MWC 137, MWC 297, Z CMa and LKHα215) with 4 successful detections (R Mon, MWC 1080, MWC 297, Z CMa).

The disk mass is usually only a small percentage (less than 10%) of the mass of the whole envelope in HBe stars, in contrast to what is usually found in the lower mass T Tauri and Herbig Ae stars. In addition, although massive disks (~0.1 M_sun) are found in very young objects (~10⁴ yr), the masses of the disks around Herbig Be stars are usually 5-10 times lower than those around lower mass stars (<0.01 M_sun). High angular resolution and very sensitive interferometric observations are required to detect their emission at millimeter wavelengths. We propose that disk photo-evaporation is responsible for this behavior. In Herbig Be stars the UV radiation disperses the gas of the outer disk on a time-scale of a few 10⁵ yr. Once the outer part of the disk is gone, the entire gaseous disk is photo-evaporated in a very short time-scale (~10⁵ yr) and only a small dusty disk composed of large grains remains. The whole process completes before the envelope is blown away.

The observed SED and model predictions for R Mon: the different emission components that contribute to the SED as predicted by our model are drawn in different colours. The emission of the star itself is drawn in green. The disk emission is separated in three components: inner rim emission (magenta), surface layer emission (red) and the midplane emission (blue). Note that the disk around R~Mon is fitted without the presence of an inner rim. The emission from the envelope is drawn in yellow. The free-free emission is shown in magenta. The disk emission and the disk+envelope emission appear as a two continuous black lines.

For more details see arXiv:0812.1636

PR 1125/08

First detection of glycolaldehyde outside the Galactic Center   
M.T. Beltran, C. Codella, S. Viti, R. Neri, R. Cesaroni Universitat de Barcelona-CSIC, Barcelona, Spain

For more details see ApJ, 690, L93

PR 0403/08

Global multi-wavelength campaign on M81* confirms accretion mass scaling from stellar to galactic black holes   
S. Markoff, M. Novak, A. Young, H.L. Marshall, C.R. Canizares, A. Peck, M. Krips, G. Petitpas, R. Schödel, G.C. Bower, P. Chandra, A. Ray, M. Muno, S. Gallagher, S. Hornstein, C.C. Cheung Sterrenkundig Instituut "Anton Pannekoek", Amsterdam, The Netherlands

Evidence has been steadily accumulating in the last years that accretion and emission processes related massive black holes are fundamentally similar to the physics in stellar mass black holes. However, in order to compare the low/hard state of X-ray binaries to galactic black holes, it is necessary to observe sources that accrete at highly sub-Eddington rates. Those sources are rare targets because of their intrinsic faintness. An additional challenge is that - because of the strong variability of the targets - multi-wavelength observations of these objects must be performed (quasi-) simultaneously. Sagittarius A*, the black hole at the center of the Milky Way used to be the only such object with reliable observations from radio to X-ray wavelengths.

An unprecedented coordinated multi-wavelength campaign focused on the low-luminosity active galactic nucleus in M81* from February to Augst 2005. Centered around five epochs of Chandra X-ray observations, this global campaign included the Giant Meterwave Radio Telescope, the Very Large Array and Very Large Baseline Array, the Plateau de Bure Interferometer at IRAM, the Submillimeter Array and Lick Observatory.

We compare the obtained spectrum of M81* to our Galactic center weakly active nucleus Sgr A*, which has undergone similar campaigns, as well as to weakly accreting X-ray binaries in the context of outflow-dominated models. We find that the physics of weakly-accreting black holes scales predictably with mass, and that the exact same model which successfully describes hard state X-ray binaries applies to M81*, with very similar physical parameters.

For more details see astro-ph/0804.0344

PR 0326/08

Detection of amino acetonitrile in Sgr B2(N)    A. Belloche, K.M. Menten, C. Comito, H.S.P. Müller, P. Schilke, J. Ott, S. Thorwirth, C. Hieret Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany

PR 0130/08

Interferometric Detections of GOODS 850-5 at 1 mm and 1.4 GHz    H. Dannerbauer, F. Walter, G. Morrison Max-Planck-Institut für Astronomie (MPIA), Heidelberg, Germany

Using the Plateau de Bure Interferometer at 1.25 mm we obtained (at subarcsecond accuracy) the position of the submillimeter bright source GOODS 850-5 (also known as GN 10) in the GOODS-North field (MM J123633+6214.1, flux density: S_{1.25 mm} = 5.0 ± 1.0 mJy). At the time of proposing the PdBI observations (September 2005) this source was undetected at 1.4 GHz down to 40 µJy, thus being a good candidate for lying at very high redshift (z~4).

Interestingly, this submillimeter bright galaxy (SMG) is undetected in deep ACS imaging (limit: i₇₇₅=28.4mag), faint in Spitzer IRAC and MIPS 24 µm; and its position is coincident with the position found in recent submillimeter mapping obtained at the SMA by Wang and coworkers. In the meantime deeper VLA observations were obtained from us as well, resulting in a solid detection (S_20cm=34.4 ± 4.2 µJy; in agreement with a 3 sigma detection previously reported by Pope and coworkers) and consistent with the PdBI position.

We apply different photometric redshift estimators using measurements of the dusty, mid/far-infrared part of the SED and derive a redshift z~4. GOODS 850-5 represents one of the few solid candidates of a high-z (z > 3) SMG that contribute to the cosmic star formation rate density at early cosmic times.

In the figure we show 20'' x 20'' ACS z₈₅₀, IRAC 8.0 µm, MIPS 24 µm, and radio images of the field of MM J123633+6214.1. PdBI contours of 1.25 continuum emission of MM J123633+6214.1 are overlaid on the ACS z₈₅₀ image and start at 3 mJy with steps of 1 mJy; 3.0'' circles are drawn on the PdBI position in the IRAC 8.0 µm, MIPS 24 µm, and radio images.

For more details see ApJ, Vol 673, 2008, L127-L130

PR 1206/07

Vigorous star formation with low efficiency in massive disk galaxies at z=1.5    E. Daddi, H. Dannerbauer, D. Elbaz, M. Dickinson, G. Morrison, D. Stern, S. Ravindranath Service d'Astrophysique (CEA Saclay), France

Plateau de Bureau Interferometric observations have revealed for the first time a new galaxy formation mode in the distant Universe. Two z=1.5 galaxies were observed in their gas cooling CO emission lines, selected to lie in the mass-star formation rate correlation at their redshift, thus being representative of massive high-z galaxies. Both sources were detected with high confidence, despite possible expectations based on existing correlations between CO and FIR luminosities of galaxies. These disk-like galaxies are borderline ULIRGs but with star formation efficiency similar to that of local spirals, and an order of magnitude lower than that in submm galaxies.

This suggests a CO to total gas conversion factor similar to local spirals, gas consumption timescales approaching 1 Gyr or longer and molecular gas masses reaching ~10¹¹M_sun, comparable to or larger than the estimated stellar masses. These results support a major role of in situ gas consumption over cosmological timescales and with relatively low star formation efficiency, analogous to that of local spiral disks, for the formation of today's most massive galaxies and their central black holes.

Given the high space density of similar galaxies, ~10^-4 Mpc^-3, this implies a widespread presence of gas rich galaxies in the early Universe, many of which might be within reach of detailed investigations of current and planned facilities.

The figure on the left shows the relation between FIR and CO luminosities of local and distant galaxies, compared to the data for the 2 newly observed BzK galaxies at z=1.5. The maps and spectra of the 2 newly observed BzK galaxies can be viewed as well.

For more details see astro-ph/0711.4995 (ApJL, in press)

PR 0531/07

The nebula around the post-AGB star 89 Herculis    V. Bujarrabal, H. Van Winckel, R. Neri, J. Alcolea, A. Castro-Carrizo, P. Deroo Observatorio Astronomico Nacional, Spain

We have performed high-resolution PdBI maps of CO J=2-1 and 1-0 of 89 Her, using in particular the newly extended A configuration. We also present N-band interferometric data on the extent of the hot dust emission, obtained with the VLTI. 89 Her is a well know post-AGB star, surrounded by a (protoplanetary) nebula that has been proposed to harbor an inner rotating disk. The presence of keplerian disks in protoplanetary nebulae is important, since they could explain the ejection of collimated, energetic jets, characteristic of post-AGB stars. However, the study of the dynamics of such structures needs CO mapping with very high resolution, and they had been only confirmed in one post-AGB object (the Red Rectangle).

Our CO maps show two nebular components: (a) an extended hour-glass-like structure, with expansion velocities of ~7 km/s, and (b) an unresolved very compact component, smaller than ~0.4'' and with a low total velocity dispersion of ~5 km/s. 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. We therefore conclude that it is probably a keplerian disk with a very small extent (diameter ≤ 10¹⁵ cm).

In the figure we show the J=2-1 maps, together with a description of our nebula model and its predictions; the compact unresolved component is represented in the model by the black circle.

For more details see astro-ph/0703718 (A&A, in press)

PR 0402/07

A highly-collimated SiO jet in the HH212 protostellar outflow    C. Codella, S. Cabrit, F. Gueth, R.Cesaroni, F. Bacciotti, Lefloch, B., McCaughrean, M.J. INAF - Istituto di Radioastronomia, Italy

We mapped the inner 40'' of the HH212 Class 0 outflow in the SiO(2-1), (5-4) lines in the mm and continuum using the PdB interferometer in its extended configurations. The unprecedented angular resolution (down to 0.34'') allows accurate comparison with a new, deep H₂ image obtained at the VLT.

The SiO emission is confined to a highly-collimated bipolar jet along the outflow main axis. It can be traced down to 500 AU of the driving source, in a region that is heavily obscured in the H₂ images. Where both species are detected, SiO shows the same overall kinematics and structure as H₂, indicating that both molecules are tracing the same material. Transverse cuts reveal no velocity gradient compatible with jet rotation above 1 km s^-1 on a scale ~0.3'', in contrast to previous claims in H₂. We find evidence that the high-velocity SiO gas is not tracing a wide-angle wind but is already confined inside a narrow cone of semi-opening angle <6^o at ≤500AU from the protostar.

For more details see Astronomy and Astrophysics, Volume 462, 2007, L53 - L57

PR 0330/07

¹³CO observations of the pre-Planetary Nebula M1-92 in the newly extended configurations    J. Alcolea, R. Neri, V. Bujarrabal Observatorio Astronomico Nacional, Spain

When solar-mass type of stars run out of nuclear fuel at their cores, the grow enormously becoming red giants. In this phase of their lives, stars pulsate and loss a good deal of their mass trough a steady spherical wind of dust and gas, which forms a circumstellar envelope (CSE). As the stars evolve, the mass loss becomes higher and the circumstellar envelope thicker. At some point, the mass loss is so large that the whole stellar mantle is lost and the hot tiny stellar core becomes exposed. The star floods the envelope with ultraviolet photons, that destroy molecules and ionize atoms forming a planetary nebulae (PN). However CSEs are roughly spherically symmetric whereas PNe are not. How this fantastic metamorphosis may happen is one of the mysteries in stellar evolution. This transformation occurs in less than 1000 yr, during the so called pre-Planetary Nebula (pPN) phase. Because these phase is brief, pPNe are rare and located rather far away from us, and so to study these transforming envelopes sub-arcsecond resolution is mandatory.

M1-92 is one of these rare objects that have been observed and studied in detail. Taking advance of the new extended configurations of the IRAM Plateau de Bure interferometer, we have conducted observations of ¹³CO J=2-1 in this source, which have been merged with previously published data, yielding the most sensitive maps ever obtained in this transition and a spatial resolution of about 0.3''. On the top we show the map of the total integrated emission. The inset shows the continuum HST image at 547 nm. Tick marks are the same in the two plots. On the bottom we show the position vs. velocity diagram for a cut along the symmetry axis of the nebula. In the central part we have used data from the new-A configuration only. This plot also represents the structure of the nebula, for which the linear scale is given by the vertical bar. From these results we conclude that this 1 solar mass nebula was formed 1000 yr ago as the result of a magneto-rotational driven explosion, probably induced by the presence of a low-mass stellar companion.

For more details see astro-ph/0701455 (A&A in press)

PR 0228/07

Interferometric multi-wavelength (sub)millimeter continuum study of the young high-mass protocluster IRAS 05358+3543    H. Beuther, S. Leurini, P. Schilke, F. Wyrowski, K.M. Menten, Q. Zhang, Max-Planck-Institut für Astronomie, Heidelberg, Germany

Aims: We study the small-scale structure of massive star-forming regions through interferometric observations in several (sub)mm wavelength bands. These observations resolve multiple sources, yield mass and column density estimates, and give information about the density profiles as well as the dust and temperature properties.
Methods: We observed the young massive star-forming region IRAS05358+3543 at high-spatial resolution in the continuum emission at 3.1 and 1.2mm with the Plateau de Bure Interferometer, and at 875 and 438µm with the Submillimeter Array. The observations are accompanied by VLA 3.6cm archival continuum data.
Results: We resolve at least four continuum sub-sources that are likely of protostellar nature. Two of them are potentially part of a proto-binary system with a projected separation of 1700AU. Additional (sub)mm continuum peaks are not necessarily harboring protostars but maybe caused by the multiple molecular outflows. The spectral energy distributions (SEDs) of the sub-sources show several features. The main power house mm1, which is associated with CH₃OH maser emission, a hypercompact HII region and a mid-infrared source, exhibits a typical SED with a free-free emission component at cm and long mm wavelengths and a cold dust component in the (sub)mm part of the spectrum (spectral index between 1.2mm and 438µm α ~3.6). The free-free emission corresponds to a Lyman continuum flux of an embedded 13M_sun B1 star. The coldest source of the region, mm3, has α~3.7 between 1.2mm and 875µm, but has lower than expected fluxes in the shorter wavelength 438µm band. This turnover of the Planck-function sets an upper limit on the dust temperature of mm3 of approximately 20K. The uv-data analysis of the density structure of individual sub-cores reveals distributions with power-law indices between 1.5 and 2. This resembles the density distributions of the larger-scale cluster-forming clump as well as those from typical low-mass cores.

For more details see Astronomy and Astrophysics, Volume 466, Issue 3, May II 2007, pp. 1065-1076

PR 0216/07

Multi-epoch dual frequency mm-observations of the nucleus of M81    R. Schödel, M. Krips, S. Markoff, R. Neri, A. Eckart, I. Physikalisches Institut Universität zu Köln, Köln, Germany

While there is a fairly good understanding of the physical mechanisms at work in bright AGN, where accretion is thought to be related to thin, fairly cool radiatively efficient disks, there are still many open questions concerning the physical mechanisms at work in Low Luminosity AGN that accrete in the extreme sub-Eddington regime. The primary testbed for these theories is Sagittarius A*, the supermassive black hole at the center of the Milky Way that radiates at only about 10^-9 times its Eddington luminosity. In order to base existing theories on a broader observational basis, it is important to extend our insights from this system to other objects and build a bridge toward higher luminosity galactic nuclei. M81*, the nucleus of the nearby spiral galaxy M81, is in its emission properties very similar to Sagittarius A*. It appears to be a by a factor of 10⁴ upscaled version of Sagittarius A* and is thus an ideal target. We present observations at 3 and 1 mm that were obtained within the framework of a coordinated, multi-wavelength campaign on M81*. We find that M81* is a continuously variable source with the higher variability observed at the shorter wavelength. Like Sgr A*, M81* appears to display the strongest flux density and variability in the mm-to-submm regime. There remains still some ambiguity concerning the exact location of the turnover frequency from optically thick to optically thin emission. The observed variability time scales point to an upper size limit of the emitting region of the order of merely 25 Schwarzschild radii.

In the figures on the left the flux densities of M81* as measured on 24 February, 14/15 July, and 20 July 2005 are shown. The black boxes mark the flux density at 3 mm and the green crosses mark the flux density at 1 mm. The exact frequencies are indicated in the titles of the individual panels. The error bars indicate relative, not absolute, uncertainties.

For more details see Astronomy and Astrophysics, Volume 463, Issue 2, February IV 2007, pp. 551-557

PR 0628/06

A new probe of dense gas at high redshift: detection of HCO⁺(5-4) line emission in APM 08729+5255    S. García-Burillo, J. Graciá-Carpio, M. Guélin, R. Neri, P. Cox, P. Planesas, P. M. Solomon, L. J. Tacconi, P. A. Vanden Bout, Observatorio Astronómico Nacional, (IGN, MFom), Madrid, Spain

The quasar APM 08279+5255 at redshift z=3.91 is one of the most luminous sources in the universe and, therefore, is the right object to study the role of the molecular gas in the processes of star formation and nuclear activity at high redshift. The detection of HCO+ J=5-4 emission based on observations conducted at the IRAM Plateau de Bure interferometer is a step forward in the knowledge of the role of dense molecular gas in star formation. In fact, multi-species observations of molecular lines are an essential tool to study the processes that produce the high luminosity of ultraluminous infrared galaxies in the local universe and of sub-millimeter galaxies at high redshift that are currently being probed by molecular lines using the IRAM telescopes.

This is the first detection of HCO+ at such a high redshift. Its intensity is only 4 times weaker than that of the CO J=4-3 line measured towards this object (Downes et al 1999), therefore it is several times stronger than what is found in nearby starburst galaxies. The HCO+ line characteristics are consistent with those derived from the HCN J=5-4 line emission in this quasar recently measured also at Bure (Wagg et al 2005), what suggests that both emissions come roughly from the same region surrounding the active galactic nucleus (AGN). However the similar intensity measured for both lines was unexpected as it was not predicted by simple radiative transfer models under the hypothesis of collisional excitation and similar chemical abundance. Infrared pumping of both lines around the AGN is one of the possible explanations, but observations of additional transitions of these and other dense molecular gas tracers will be needed to explain the characteristics of the gas and of the excitation of the lines that leads to their high intensities.

For more details see astro-ph/0605656 (ApJL in press)

PR 0413/06

The Plateau de Bure Interferometer Gets a Sharper View!   

The beginning of the year 2006 was highlighted on Plateau de Bure by moving the array for the first time into the new extended A-configuration. The change of configuration was accomplished on Friday, 13th January 2006 in less than one day, thanks to excellent weather conditions and a perfect preparation of the tracks. A few hours later fringes were obtained on the new baselines and shortly after a baseline solution with excellent precision. The first scientific project was successfully observed in the new A configuration the following morning, again under excellent atmospheric conditions and on January 24th already 14 tracks have been completed. More ...

To visit the page of less recent results, please go to the archive.