J. B. Whiteoak

Max Planck Institute for Radio Astronomy, Bonn, North Rhine-Westphalia, Germany

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Publications (239)908.93 Total impact

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    ABSTRACT: We present molecular-line observations at millimetre, centimetre and infrared wavelengths of the region containing OH(1720 MHz) masers in the supernova remnant (SNR) G349.7+0.2, using the Australia Telescope (AT) Mopra antenna, the Swedish–ESO Submillimeter Telescope, the AT Compact Array and the UNSW Infrared Fabry–Perot narrow-band filter installed on the Anglo-Australian Telescope. Several molecular transitions were observed between 1.6 and 3 mm to constrain the physical parameters of the molecular cloud interacting with the SNR and to investigate the effects of the SNR shock on the gas chemistry. We detected shock-excited near-infrared H2 emission towards the centre of the SNR, revealing highly clumped molecular gas and a good correlation with published mid-infrared images from the Spitzer Space Telescope. An excellent correlation between the H2 clumps and OH(1720 MHz) maser positions supports the shock excitation of the OH(1720 MHz) maser emission. Furthermore, we detected OH absorption at 1665 and 1667 MHz which shows a good correlation with the shocked H2 emission and the masers. We found maser emission at 1665 MHz near the OH(1720 MHz) masers in this SNR, which is found to be associated with a GLIMPSE source SSTGLMC G349.7294+00.1747. We also detected 1665 and 1667 MHz OH masers, and weak 4.8 GHz H2CO absorption towards the ultracompact H ii region IRAS 17147–3725 located to the southeast of the SNR. We found no 4.7- or 6-GHz excited-state OH masers or 6-GHz CH3OH maser towards either the SNR or the H ii region.
    Monthly Notices of the Royal Astronomical Society 11/2010; 409(1):371 - 388. · 5.52 Impact Factor
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    ABSTRACT: With the goal of deriving the physical and chemical conditions of star-forming regions in the Large Magellanic Cloud (LMC), a spectral line survey of the prominent star-forming region N 113 is presented. The observations cover parts of the frequency range from 85 GHz to 357 GHz and include 63 molecular transitions from a total of 16 species, among them are the spectra of rare isotopologues. Maps of selected molecular lines as well as the 1.2 mm continuum distribution are also presented. Molecular abundances in the core of the complex are consistent with a photon-dominated region in a nitrogen deficient environment. While carbon monoxide (CO) shows optical depths of the order of tau ~ 10, 13CO is optically thin. The most prominent lines of carbon monosulfide (CS), HCN, and HCO+show signs of weak saturation (tau ~ 0.5). Densities range from 5 × 103 cm-3 for CO to almost 106 for CS, HCN, and a few other species, indicating that only the densest regions provide sufficient shielding, even for some of the most common species. An ortho- to para-formaldehyde (H2CO) ratio of ~ 3 hints at H2CO formation in a warm (gsim 40 K) environment. Isotope ratios are 12C/13C ~ 49 ± 5, 16O/18O ~2000 ± 250, 18O/17O ~ 1.7 ± 0.2, and 32S/34S ~ 15. Agreement with data from other star-forming clouds shows that the gas is well mixed in the LMC. The isotope ratios not only differ from those seen in the Galaxy, they also do not form a continuation of the trends observed with decreasing metallicity from the inner to the outer Galaxy. This implies that the outer Galaxy, even though showing an intermediate metallicity, is not providing a transition zone between the inner Galaxy and the metal-poor environment of the Magellanic Clouds. A part of this discrepancy is likely caused by differences in the age of the stellar populations in the outer Galaxy and the LMC. While, however, this scenario readily explains measured carbon and oxygen isotope ratios, nitrogen and sulfur still lack a self-consistent interpretation. Based on observations with the Swedish/ESO Submillimeter Telescope (SEST) at the European Southern Observatory (ESO; La Silla, Chile) and the Atacama Pathfinder EXperiment (APEX; Chajnantor, Chile) of the Max-Planck-Institut für Radioastronomie (MPIfR), ESO, and Onsala Space Observatory (OSO).
    The Astrophysical Journal 01/2009; 690(1):580-597. · 6.73 Impact Factor
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    ABSTRACT: The only unbiased molecular line survey of an extragalactic source published so far is the 2 mm survey toward NGC 253 (Martin et al. 2006). Here we propose to measure the nearby FR I radio galaxy Cen A with the MOPRA/MOPS system in the 3-4 mm wavelength range (79-115 GHz) and at K-band (20-28 GHz). This will elucidate chemistry, excitation and kinetic temperature of the nuclear gas seen in emission (broad line component) and will shed light onto the nature of the numerous narrow absorption lines that are detected along the line-of-sight toward the prominent nuclear radio continuum source.
    ATNF Proposal. 04/2007;
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    ABSTRACT: The recently published 2mm line survey of NGC253 has shown how spectral line surveys are powerful tools to get an understanding of the heating mechanisms and physical conditions of molecular material in the nuclei of galaxies. We propose to extend such studies not only to the brightest starbursts, but to different prototypical galaxies so we can really establish a chemical differentiation of the variety of environments we find in the extragalactic interestellar medium. This is a fundamental step to understand how the molecular material in the nuclei of galaxies is affected by the dominating heating mechanisms on the differents types of galaxies. Moreover, it opens up the possibility of classifying the galaxies according to this observed chemistry. This is specially important to characterized the dominant heating mechanism for the newly detected Submillimeter Galaxies which are heavily obscured even in the mid-IR. The currently available 8 GHz instantaneous bandwidth observable with MOPRA makes it an unique telescope to carry out these studies where large instantaneous bandwidths are required.
    ATNF Proposal. 04/2007;
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    ABSTRACT: The molecular void in NGC6334-FIRII, created by the ionization fronts and stellar winds of young massive stars, is a geometrically extremely simple target that is thus optimally suited for a study of a wide range of physical and chemical processes. Here we propose to use the MOPRA/MOPS broad band 8 GHz system to obtain spectral scans (20-28, 79-115 GHz) toward the void and its nearby environment. We intend (1) to reveal the dominant excitation mechanism at the inner edge of the cloud (PDR or shock?), (2) to study the physical and chemical parameters of the tenuous gas along the line-of-sight toward the void, (3) to search for the warm molecular component seen in H2 to study its kinematics and chemistry, and (4) to determine oxygen isotope ratios.
    ATNF Proposal. 04/2007;
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    ABSTRACT: The HCN (J=1-0) line is the primary indicator of dense (105 cm-3) molecular gas for extragalactic studies. However, the reliability of HCN as a tracer of dense gas mass has been questioned, given the possibility of abundance variations or mid-IR pumping. Alternatively, HCO+ has been proposed as a superior tracer of dense gas, although it may be enhanced along with ionized carbon in the presence of strong radiation fields. To investigate the variation in the HCN/HCO+ ratio across different environments, we have performed high-resolution simultaneous imaging in HCN and HCO+ of a circumnuclear starburst lacking nuclear activity (NGC 7552) and an HII region within the Large Magellanic Cloud (N113) using the upgraded Australia Telescope Compact Array. Variations in the HCN/HCO+ ratio as a function of spatial scale and IR emission brightness are discussed. This research was supported by an ARC/CSIRO Linkage Grant and the U. of Illinois.
    12/2006;
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    ABSTRACT: We request ATCA time to map the giant star forming region N159 in the Large Magellanic Cloud. The proposed 100 pointing mosaic in the dense molecular gas tracers HCO+ and HCN will be the highest resolution wide-field image of molecular gas in the LMC to date. The data will allow us, for the first time, to determine the clump mass function in a low-metallicity environment at the low-mass end and to study the spatial relationship of dense molecular cores and deeply embedded (proto)stellar objects. Moreover we will be able to investigate the thermal balance of the molecular gas by comparing CO, CI, C+, and high-resolution Spitzer data to the distribution of the very dense molecular gas.
    ATNF Proposal. 04/2006;
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    ABSTRACT: Cen A is the only radio galaxy whose nuclear environment can be studied by means of molecular spectroscopy on linear scales of 100 pc or less. Here we propose to map C3H2, SiO, CS and SO. This will allow us (1) to derive molecular masses and to compare them with the dynamic mass at the respective galactocentric radius, (2) to trace the distributions of the dense and the diffuse gas and (3) to elucidate the possible presence of shocks in this prototypical source.
    ATNF Proposal. 04/2006;
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    ABSTRACT: We have produced images of a number of galactic methanol sources in the 6.7 GHz (51–60A+) transition, and compared them with earlier maps of the 12.2-GHz (20 - 3-1 E) methanol masers. We find that, in several cases, the 6.7-GHz and 12.2-GHz maser positions are coincident to within 20 milliarcsec, placing a tight constraint on pumping mechanisms. We also confirm the 12.2-GHz result that the methanol masers tend to be located along lines, perhaps indicating jets, shock fronts, or edge-on protoplanetary discs.
    01/2006: pages 203-206;
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    ABSTRACT: We present aperture synthesis imaging of dense molecular gas in the Large Magellanic Cloud, taken with the prototype millimeter receivers of the Australia Telescope Compact Array (ATCA). Our observations of the N113 H II region reveal a condensation with a size of ~6" (1.5 pc) FWHM, detected strongly in the 1-0 lines of HCO+, HCN, and HNC, and weakly in C2H. Comparison of the ATCA observations with single-dish maps from the Mopra Telescope and sensitive spectra from the Swedish-ESO Submillimetre Telescope indicates that the condensation is a massive clump of ~104 Msolar within a larger ~105 Msolar molecular cloud. The clump is centered adjacent to a compact, obscured H II region that is part of a linear structure of radio continuum sources extending across the molecular cloud. We suggest that the clump represents a possible site for triggered star formation. Examining the integrated line intensities as a function of interferometer baseline length, we find evidence for decreasing HCO+/HCN and HCN/HNC ratios on longer baselines. These trends are consistent with a significant component of the HCO+ emission arising in an extended clump envelope and a lower HCN/HNC abundance ratio in dense cores.
    The Astrophysical Journal 01/2006; 649(1):224-234. · 6.73 Impact Factor
  • M. R. Cunningham, J. B. Whiteoak
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    ABSTRACT: The 3-mm transitions of HCN, HCO+ and HNC in the dense molecular clouds near the nucleus of the southern starburst galaxy NGC 4945 have been observed with three antennas of the Australia Telescope Compact Array (ATCA). Molecular-line emission was detected within the velocity range (300–800 km s−1) seen in single-dish spectra, although emission with extent greater than about 15 arcsec would not have been detected because of the lack of sufficiently small Compact Array (CA) baselines. Imaging the results at velocity intervals of 22.5 km s−1 and with a restoring beam of dimension 5.6 × 3.5 arcsec2 yielded images of typical deconvolved dimensions 7 × 3 arcsec2 (130 × 60 pc for an assumed galaxy distance of 4 Mpc). The positions of the images vary systematically with velocity, consistent with the result expected for a rotating molecular cloud ensemble viewed edge-on and inclined at a position angle (PA) of 45°. Although the brightest images occurred at velocities of the two major features (∼430 and ∼710 km s−1) in Swedish-ESO Submillimetre Telescope (SEST) spectra, the images at intervening velocities were unexpectedly faint or even in absorption. The results have been interpreted in terms of an extended cloud component not detected by the CA in conjunction with absorption against the nuclear continuum emission. Some of the HCO+ images are dominated by absorption and the overall results do not truly represent the cloud structure. The HNC results appear to contain little absorption, and the emission integrated over velocity yielded an elliptical image centred on an H2O ‘megamaser’ located at the galaxy's nucleus. The HNC position–velocity distribution along the major axis is consistent with an edge-on circumnuclear molecular ring with a rotational velocity of 135 km s−1. However, the ring radius of ∼60 km s−1 is significantly less than previously derived from carbon monoxide (CO) observations. It can be reconciled with the CO results if the HNC ring traces high-density gas concentrated around the inside of the molecular ring, whereas the CO traces low-density gas that extends to higher radii. The HNC feature appears to be associated with features revealed in published infrared (IR) studies of the distribution of dust and star formation regions in the nuclear region of NGC 4945. Limited results on the variation of HNC/HCN abundance ratios within the nuclear molecular clouds support previous conclusions that the clouds are at an advanced evolutionary stage within a starburst period.
    Monthly Notices of the Royal Astronomical Society 10/2005; 364(1):37 - 46. · 5.52 Impact Factor
  • Highlights of Astronomy. 01/2005;
  • Maria R. Hunt, John B. Whiteoak
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    ABSTRACT: Transitions of HCN, HCO+ and HNC have been observed in the nuclear region of the nearby edge-on spiral galaxy NGC 4945 with the Compact Array of the Australia Telescope during the commissioning phase of the new 3-mm system. The collection and reduction of the observations is described in this paper, and the distribution of the HNC and HCO+ emission is discussed. Comparison of the ATCA observations with single dish spectra from the SEST suggests that there is a compact component to the emission seen in both spectra, and a diffuse component seen only in the SEST spectra. Absorption against the nuclear continuum is seen in HCO+, suggesting the presence of dense gas in front of the nucleus.
    Astrophysics and Space Science 01/2005; 295:257-262. · 2.06 Impact Factor
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    ABSTRACT: We present near-infrared and millimetre-line observations of the Tornado nebula (G357.7-0.1). We detected 2.12 micron_m H2 1-0 S(1) line emission towards the suspected site of interaction with a molecular cloud revealed by the presence of an OH(1720 MHz) maser. The distribution of the H2 emission is well correlated with the nonthermal radio continuum emission from the Tornado, and the velocity of the H2 emission spans over 100 km/s, which both imply that the H2 emission is shock excited. We also detected millimetre-lines from 12CO and 13CO transitions at the velocity of the maser, and mapped the distribution of the molecular cloud in a 2 x 2 arcmin^2 region around the maser. The peak of the molecular cloud aligns well with an indentation in the nebula's radio continuum distribution, suggesting that the nebula's shock is being decelerated at this location, which is consistent with the presence of the OH(1720 MHz) maser and shocked H2 emission at that location. Comment: 10 pages, 8 figures, minor changes, accepted to MNRAS
    Monthly Notices of the Royal Astronomical Society 05/2004; · 5.52 Impact Factor
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    ABSTRACT: We have observed molecular-line transitions between 84 and 147 GHz in 24 dense southern molecular clouds with declinations south of -30 degrees using the Mopra and SEST radio telescopes. The results of observations of 2-mm and 3-mm transitions of the molecules CO, CS, C2H, CH3OH, HCN, HNC, HCO+, HC3N, OCS, HNCO and SO and several of their isotopomers are discussed in this paper, including ratios of the emission from the 12C, 13C and 18O isotopomers of CO, CS, HCO+, HCN and HNC. This paper lists the calibrated observational data for each molecular cloud and discusses some general properties of this sample. The calibration process for the Mopra antenna of the ATCA is described in an appendix.
    01/2004;
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    ABSTRACT: A multi-line millimeter-wave study of the nearby starburst galaxy NGC 4945 has been carried out using the Swedish-ESO Submillimeter Telescope (SEST). The study covers the frequency range from 82 GHz to 354 GHz and includes 80 transitions of 19 molecules. 1.3 mm continuum data of the nuclear source are also presented. An analysis of CO and 1.3 mm continuum fluxes indicates that the conversion factor between H2 column density and CO J=1-0 integrated intensity is smaller than in the galactic disk by factors of 5-10. A large number of molecular species indicate the presence of a prominent high density interstellar gas component characterized by nH_2˜ 105 cm-3. Some spectra show Gaussian profiles. Others exhibit two main velocity components, one at ˜450 km s-1, the other at ˜710 km s-1. While the gas in the former component has a higher linewidth, the latter component arises from gas that is more highly excited as is indicated by HCN, HCO+ and CN spectra. Abundances of molecular species are calculated and compared with abundances observed toward the starburst galaxies NGC 253 and M 82 and galactic sources. Apparent is an ``overabundance'' of HNC in the nuclear environment of NGC 4945. While the HNC/HCN J=1-0 line intensity ratio is ˜0.5, the HNC/HCN abundance ratio is ˜1. From a comparison of Ka=0 and 1 HNCO line intensities, an upper limit to the background radiation of 30 K is derived. While HCN is subthermally excited (Tex˜8 K), CN is even less excited (Tex˜3-4 K), indicating that it arises from a less dense gas component and that its N=2-1 line can be optically thin even though its N=1-0 emission is moderately optically thick. Overall, fractional abundances of NGC 4945 suggest that the starburst has reached a stage of evolution that is intermediate between those observed in NGC 253 and M 82. Carbon, nitrogen, oxygen and sulfur isotope ratios are also determined. Within the limits of uncertainty, carbon and oxygen isotope ratios appear to be the same in the nuclear regions of NGC 4945 and NGC 253. High 18O/17O, low 16O/18O and 14N/15N and perhaps also low 32S/34S ratios (6.4±0.3, 195±45, 105±25 and 13.5± 2.5 in NGC 4945, respectively) appear to be characteristic properties of a starburst environment in which massive stars have had sufficient time to affect the isotopic composition of the surrounding interstellar medium. Based on observations with the Swedish/ESO Submillimeter Telescope (SEST) at the European Southern Observatory (ESO), La Silla, Chile. Figures \ref{fig7} to \ref{fig15} are only available in electronic form at http://www.edpsciences.org
    Astronomy and Astrophysics 01/2004; 422(3):883-905. · 5.08 Impact Factor
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    F F Gardner, J B Whiteoak
    11/2003; 4:245-292.
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    Patrick Palmer, W. M. Goss, J. B. Whiteoak
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    ABSTRACT: The VLA was used to determine precise positions for 4765-MHz OH maser emission sources toward star-forming regions which had been observed about seven months earlier with the Effelsberg 100-meter telescope. The observations were successful for K3-50, DR21EX, W75N, and W49A. No line was detected toward S255: this line had decreased to less than 5 per cent of the flux density observed only seven months earlier. The time-variability of the observed features during the past 30 years is summarised. In addition, to compare with the Effelsberg observations, the 4750-MHz and 4660-MHz lines were observed in W49A. These lines were found to originate primarily from an extended region which is distinguished as an exceptional collection of compact continuum components as well as by being the dynamical centre of the very powerful H_2 O outflow. Comment: 11 pages, will require MN style file to process. MNRAS, accepted Oct 15, 2003
    Monthly Notices of the Royal Astronomical Society 10/2003; · 5.52 Impact Factor
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    ABSTRACT: We present millimetre and NIR molecular-line observations of the Tornado Nebula and its Eye. The observations were motivated by the presence of OH(1720 MHz) maser emission towards the nebula, believed to be an indicator of interaction between a supernova remnant and a molecular cloud. We found that the distribution of molecular gas around the Tornado complements its radio morphology, implying that the nebula's appearance has been influenced by the structure of the surrounding molecular gas. Our NIR H2 observations revealed the presence of shocked molecular gas at the location where the nebula is expanding into the surrounding molecular cloud.It has been suggested that the Eye of the Tornado is related to the nebula on the basis of their apparent proximity. Our NIR and millimetre-line observations show that the two objects are not spatially related. Brγ line emission, in conjunction with IR data at longer wavelengths and high-resolution radio continuum observations, suggests that the Eye is a massive protostellar source deeply embedded within a dense molecular core.
    Astronomische Nachrichten 08/2003; 324(S1):157 - 160. · 1.40 Impact Factor
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    ABSTRACT: The OH distribution in the Sgr A Complex has been observed in the 1612, 1665, 1667, and 1720 MHz OH transitions with the Very Large Array (VLA), in the BnA and DnC configurations. Spectral line maps have been produced with a channel velocity resolution of about 9 km s–1 and with angular resolutions of 4″ × 3″, and 24″ × 22″, respectively. Some clear results are highlighted here: i) the existence of an OH streamer inside the Circumnuclear Disk (CND) near Sgr A*, ii) absorption from the CND, iii) strong absorption towards the eastern and most of the western parts of the Sgr A East shell, iv) lack of absorption towards both Sgr A West and the compact H II-regions to the east of Sgr A East, v) a double-lobed structure of the High Negative Velocity Gas (HNVG) oriented to the northeast and southwest of Sgr A*, and vi) compact point-like maser emission in all four transitions. In particular, a 1720 MHz maser at –132 km s–1 in the CND as counterpart to a 1720 MHz maser at +132 km s–1 in the CND, was observed.
    Astronomische Nachrichten 08/2003; 324(S1):223 - 227. · 1.40 Impact Factor

Publication Stats

2k Citations
908.93 Total Impact Points

Institutions

  • 1994–2009
    • Max Planck Institute for Radio Astronomy
      Bonn, North Rhine-Westphalia, Germany
    • University of Western Sydney
      Penrith, New South Wales, Australia
  • 1993–2006
    • University of New South Wales
      • • School of Physics
      • • Department of Astrophysics and Optics
      Kensington, New South Wales, Australia
  • 1986–1987
    • NSF
      Ann Arbor, Michigan, United States
  • 1962–1984
    • The Commonwealth Scientific and Industrial Research Organisation
      Canberra, Australian Capital Territory, Australia
  • 1975
    • Monash University (Australia)
      Melbourne, Victoria, Australia