R. Gusten

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

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Publications (19)23.17 Total impact

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    ABSTRACT: We report on the design and on-site performance of the recently upgraded FLASH$^{+}$ instrument operated at the APEX telescope in the Chilean Atacama desert in 5100 m altitude. The dual-channel receiver allows parallel observations in the atmospheric submillimeter windows between 268 and 516 GHz. A signal of in total 16 GHz is processed simultaneously. Equipped with state-of-the-art sideband separating mixers (spin-off developments from the ALMA bands 7 and 8), its outstanding on-sky performance makes FLASH$^{+}$ a most efficient spectral line mapping machine. Operation is fully automated and allows flexible remote observations from the APEX base in San Pedro de Atacama.
    Terahertz Science and Technology, IEEE Transactions on. 01/2014; 4(5):588-596.
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    ABSTRACT: We report ground-based follow-up observations of the exceptional source, ID141, one the brightest sources detected so far in the H-ATLAS cosmological survey. ID141 was observed using the IRAM 30-meter telescope and Plateau de Bure interferometer (PdBI), the Submillimeter Array (SMA) and the Atacama Pathfinder Experiment (APEX) submillimeter telescope to measure the dust continuum and emission lines of the main isotope of carbon monoxide and carbon ([C I] and [C II]). The detection of strong CO emission lines with the PdBI confirms that ID141 is at high redshift (z=4.243 +/- 0.001). The strength of the continuum and emission lines suggests that ID141 is gravitationally lensed. The width (Delta V (FWHM) ~ 800 km/s}) and asymmetric profiles of the CO and carbon lines indicate orbital motion in a disc or a merger. The properties derived for ID141 are compatible with a ultraluminous (L_FIR ~ 8.5 +/- 0.3 x 10^13/mu_L Lsun, where mu_L is the amplification factor, dense (n ~ 10^4 cm^-3) and warm (T_kin ~ 40K) starburst galaxy, with an estimated star-formation rate of (0.7 to 1.7) x 10^4/mu_L Msun/yr. The carbon emission lines indicate a dense (n ~ 10^4 cm^-3) Photo-Dominated Region, illuminated by a far-UV radiation field a few thousand times more intense than that in our Galaxy. In conclusion, the physical properties of the high-z galaxy, ID141, are remarkably similar to those of local ultraluminous infrared galaxies.
    The Astrophysical Journal 07/2011; 740(2). · 6.73 Impact Factor
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    ABSTRACT: Spectral surveys provide the only way to determine the full molecular inventory of an object and hence build a comprehensive view of the state of the molecular gas and its role in star formation and the structure and evolution of the ISM. Of course spectral surveys also provide the most efficient method of identifying new and unexpected species that have to be include in the chemical networks. The most extensive and complete survey of an extragalactic system has been the continuous spectral survey from 129 GHz to 175 GHz carried out by Martín et al. (2006) toward NGC253. This first spectral line surveys at 2 mm towards the prototypical starbursts galaxies NGC253 have shown an unexpected chemical richness. Due to the limitations of observing at a single atmospheric window, missing maybe part of the material that will affect the chemistry, our next step has been to extend the extragalactic spectral line survey of NGC253. Using the APEX telescope we have extend the survey to higher frequencies and carried out the first spectral line survey of an AGN nucleus like NGC4945, and a close ULIRG, ARP220. Those Surveys allow as to get better estimates on the physical and chemical characteristics of the three galaxies, as well to search for better tracers to study the star-formation in those distant objects, with different physical characteristics. We present here the three spectral surveys together with some new observations of several anions and dense tracers observed in a larger sample of galaxies, covering more types of galaxies, i.e. seyfert.
    Proceedings of the International Astronomical Union 05/2011;
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    ABSTRACT: Hydrides are key ingredients of interstellar chemistry since they are the initial products of chemical networks that lead to the formation of more complex molecules. The fundamental rotational transitions of light hydrides fall into the submillimeter wavelength range. Using the APEX telescope, we observed the long sought hydrides SH+ and OH+ in absorption against the strong continuum source Sagittarius B2(M). Both, absorption from Galactic center gas as well as absorption from diffuse clouds in intervening spiral arms in a large velocity range are observed. The detected absorption of a continuous velocity range on the line-of-sight shows these hydrides to be an abundant component of diffuse clouds. In addition, we used the strongest submillimeter dust continuum sources in the inner Galaxy to serve as background candles for a systematic census of these hydrides in diffuse clouds and massive star forming regions of our Galaxy and initial results of this survey are presented. For this survey, the CHAMP+ array receiver as well as the MPIfR THz receiver was used. We will discuss the scientific potential of the first THz atmospheric window from 1.0 to 1.1 THz for observations from the Chajnantor high site.
    Proceedings of the International Astronomical Union 01/2011; 280.
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    ABSTRACT: We discuss the detection of absorption by interstellar hydrogen fluoride (HF) along the sight line to the submillimeter continuum sources W49N and W51. We have used Herschel's HIFI instrument in dual beam switch mode to observe the 1232.4762 GHz J = 1 - 0 HF transition in the upper sideband of the band 5a receiver. We detected foreground absorption by HF toward both sources over a wide range of velocities. Optically thin absorption components were detected on both sight lines, allowing us to measure - as opposed to obtain a lower limit on - the column density of HF for the first time. As in previous observations of HF toward the source G10.6-0.4, the derived HF column density is typically comparable to that of water vapor, even though the elemental abundance of oxygen is greater than that of fluorine by four orders of magnitude. We used the rather uncertain N(CH)-N(H2) relationship derived previously toward diffuse molecular clouds to infer the molecular hydrogen column density in the clouds exhibiting HF absorption. Within the uncertainties, we find that the abundance of HF with respect to H2 is consistent with the theoretical prediction that HF is the main reservoir of gas-phase fluorine for these clouds. Thus, hydrogen fluoride has the potential to become an excellent tracer of molecular hydrogen, and provides a sensitive probe of clouds of small H2 column density. Indeed, the observations of hydrogen fluoride reported here reveal the presence of a low column density diffuse molecular cloud along the W51 sight line, at an LSR velocity of ~ 24kms-1, that had not been identified in molecular absorption line studies prior to the launch of Herschel. Comment: 4 pages, 3 figures, A&A Letter special issue, accepted on 07/13/2010
    07/2010;
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    ABSTRACT: We report a detection of the fundamental rotational transition of hydrogen fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal of contaminating features associated with common molecules ("weeds"), the HF spectrum shows a P-Cygni profile, with weak redshifted emission and strong blue-shifted absorption, associated with the low-velocity molecular outflow. We derive an estimate of 2.9 x 10^13 cm^-2 for the HF column density responsible for the broad absorption component. Using our best estimate of the H2 column density within the low-velocity molecular outflow, we obtain a lower limit of ~1.6 x 10^-10 for the HF abundance relative to hydrogen nuclei, corresponding to 0.6% of the solar abundance of fluorine. This value is close to that inferred from previous ISO observations of HF J=2--1 absorption towards Sgr B2, but is in sharp contrast to the lower limit of 6 x 10^-9 derived by Neufeld et al. (2010) for cold, foreground clouds on the line of sight towards G10.6-0.4. Comment: 5 pages, 3 figures, paper to be published in the Herschel special issue of A&A letters
    07/2010;
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    ABSTRACT: Mon R2, at a distance of 830 pc, is the only ultracompact HII region (UC HII) where the photon-dominated region (PDR) between the ionized gas and the molecular cloud can be resolved with Herschel. HIFI observations of the abundant compounds 13CO, C18O, o-H2-18O, HCO+, CS, CH, and NH have been used to derive the physical and chemical conditions in the PDR, in particular the water abundance. The 13CO, C18O, o-H2-18O, HCO+ and CS observations are well described assuming that the emission is coming from a dense (n=5E6 cm-3, N(H2)>1E22 cm-2) layer of molecular gas around the UC HII. Based on our o-H2-18O observations, we estimate an o-H2O abundance of ~2E-8. This is the average ortho-water abundance in the PDR. Additional H2-18O and/or water lines are required to derive the water abundance profile. A lower density envelope (n~1E5 cm-3, N(H2)=2-5E22 cm-2) is responsible for the absorption in the NH 1_1-0_2 line. The emission of the CH ground state triplet is coming from both regions with a complex and self-absorbed profile in the main component. The radiative transfer modeling shows that the 13CO and HCO+ line profiles are consistent with an expansion of the molecular gas with a velocity law, v_e =0.5 x (r/Rout)^{-1} km/s, although the expansion velocity is poorly constrained by the observations presented here. Comment: 4 pages, 5 figures
    Astronomy and Astrophysics 07/2010; 521:L23. · 5.08 Impact Factor
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    ABSTRACT: We discuss the first astronomical detection of the CF+ (fluoromethylidynium) ion, obtained by observations of the J=1-0 (102.6 GHz), J=2-1 (205.2 GHz) and J=3-2 (307.7 GHz) rotational transitions toward the Orion Bar region. Our search for CF+, carried out using the IRAM 30m and APEX 12m telescopes, was motivated by recent theoretical models that predict CF+ abundances of a few times 1.E-10 in UV-irradiated molecular regions where C+ is present. The CF+ ion is produced by exothermic reactions of C+ with HF. Because fluorine atoms can react exothermically with H2, HF is predicted to be the dominant reservoir of fluorine, not only in well-shielded regions but also in the surface layers of molecular clouds where the C+ abundance is large. The observed CF+ line intensities imply the presence of CF+ column densities of at least 1.E+12 cm-2 over a region of size at least ~ 1 arcmin, in good agreement with theoretical predictions. They provide support for our current theories of interstellar fluorine chemistry, which suggest that hydrogen fluoride should be ubiquitous in interstellar gas clouds and widely detectable in absorption by future satellite and airborne observatories. Comment: 4 pages, including 4 figures. To appear in a special A&A issue on "First Science with APEX"
    03/2006;
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    ABSTRACT: The CO N+ Deuterium Observations Receiver (CONDOR) is an astronomical heterodyne receiver that successfully operates between 1.25-1.53 THz. The instrument follows the standard heterodyne design, using a solid state local oscillator and a superconducting NbTiN hot electron bolometer (HEB) as a mixer. For easy maintenance at the telescope CONDOR is the first receiver that cools the HEB with a closed-cycle system using a pulse tube cooler. The system has receiver noise temperatures around 1500 K and spectral Allan variance times of about 30 s. In November 2005, CONDOR was successfully commissioned on the 12-m Atacama Pathfinder Experiment.
    01/2006;
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    ABSTRACT: We report the first astronomical detection of the CF+ (fluoromethylidynium) ion obtained by recent observations of its J = 1 - 0 (102.6 GHz), J = 2 - 1 (205.2 GHz), and J = 3 - 2 (307.7 GHz) pure rotational emissions toward the Orion Bar. Our search for CF+, carried out using the IRAM 30m and APEX 12m telescopes, was motivated by recent theoretical models that predict CF+ abundances of a few x E-10 in UV-irradiated molecular regions where C+ is present. The measurements confirm the predictions. They provide support for our current theories of interstellar fluorine chemistry, which suggest that hydrogen fluoride should be ubiquitous in interstellar gas clouds. Comment: 2 pages, 1 figure (uses iaus.sty), to appear in IAU Symposium No. 231, Astrochemistry - Recent Successes and Current Challenges, eds. D. C. Lis, G. A. Blake & E. Herbst (Cambridge Univ. Press)
    Proceedings of the International Astronomical Union 09/2005;
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    ABSTRACT: The Heterodyne Instrument for the Far-Infrared (HIFI) is a single sky-pixel, high-resolution (>300.000), spectrometer for ESA's Herschel Space Observatory. The instrument is designed to provide a wide and continuous frequency coverage with a velocity resolved resolution and a high sensitivity. This allows detailed investigations of a wide variety of astronomical sources, ranging from solar system objects, star formation regions to nuclei of galaxies. The frequency bands cover many emission and absorption lines of molecules, like H<sub>2</sub>O, and atomic and ionic lines, like CII, NII. The instrument comprises of 5 frequency bands covering 480-150 GHz with SIS mixers and a sixth dual band for the 1410-1910 GHz range with Hot Electron Bolometer Mixers. The Local Oscillator (LO) subsystem consists of a Ka-band synthesiser followed by 14 chains of frequency multipliers, 2 for each frequency band. Each frequency band has two mixers operating on orthogonal polarisations. All mixers are designed to have a noise performance close to the quantum noise limit. One frequency band is operated at a time. Modular design of the Focal Plane Unit, with a common optical path for all the mixer bands, and of the Local Oscillator Unit with a common LO Source Unit for all the LO chains, make the instrument very compact. A pair of Auto-Correlators and a pair of Acousto-Optic spectrometers process the two IF signals from the dual-polarisation front-ends and provide instantaneous frequency coverage of 4 GHz, resulting in a set of resolutions (140 KHz to 1 MHz), better than <0.1 Km/s. The instrument development is in an advanced state with mixers and LO chains approaching aimed performance.
    Infrared and Millimeter Waves, 2004 and 12th International Conference on Terahertz Electronics, 2004. Conference Digest of the 2004 Joint 29th International Conference on; 11/2004
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    8th International Symposium on Space Terahertz Technology, Harvard University, MA; 03/1997
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    01/1995; 75:222.
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    ABSTRACT: We report the first measurements of the high-gas density tracing J=10-9 CS and C34S transitions towards 8 galactic star forming cores. With the J=10 level 160 K above ground, and critical densities for excitation of ˜107.8 cm-3, these lines provide unique information about the ultra-dense cloud cores next to the star forming regions which cannot be deduced from less excited levels. Comparison with lower rotational transitions reveals strong excitation gradients across the cores. The high intensity of the submm transitions requires densities ≥ 107 cm-3 if excited by collisions. However, because by selection our sources are closely associated with luminous embedded objects, we also investigate in detail the effect of IR pumping into the v=1 vibrational level on the v=0 rotational population.
    Astronomy and Astrophysics 05/1993; 273:L23. · 5.08 Impact Factor
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    ABSTRACT: The Galactic Center is the nearest example of a galactic nucleus. Recent observations of the molecular gas in the vicinity of the Galactic Center suggest possible infall motions. In this paper, we review the observed morphology, kinematics, and the outstanding questions. The importance of these types of studies is obvious. As the nearest example, the details which we can study in the Galactic Center may have implications on understanding the processes which take place in more distant system.
    03/1990; 16:143.
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    ABSTRACT: Using the 100-m antenna of the Max-Planck-Institut for Radioastronomie in Effelsberg, FRG, the authors have observed with 40arcsec resolution the region around the Herbig-Haro 1 and 2 objects in the (1,1) and (2,2) inversion lines of NH3. The integrated intensity peaks at a position equidistant from the objects HH 1 and 2 that coincides exactly with the central exciting source found by Pravdo et al. (1985). The emission region is elongated with its major axis roughly perpendicular to the line joining the HH 1 and 2 objects. By analyzing the kinematics, it is concluded that the structure is a relatively smooth, slowly rotating, and expanding (or infalling) disk seen nearly edge-on. The disk radial motion is resolved and occurs at a radius of ≡ 0.15 pc, and the center of the disk appears to be evacuated. This situation is consistent with the absence of centralized heating.
    Astronomy and Astrophysics 04/1988; 197:235-241. · 5.08 Impact Factor
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    ABSTRACT: We will report on the APEX-SZ bolometer camera which houses a 320 element Transition-Edge Sensor (TES) bolometer array designed to survey for galaxy clusters using the 12-meter diameter APEX telescope sited in Chile. Design and fabrication of the TES bolometer array will be discussed, as well as its integration with a frequency-domain SQUID multiplexed readout system. The full configuration of the APEX-SZ camera was deployed in April 2007. A preliminary galaxy cluster map from this deployment will be presented.
    Journal of Low Temperature Physics 151(3):697-702. · 1.18 Impact Factor
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    ABSTRACT: The APEX-SZ instrument is a millimeter-wave cryogenic receiver designed to observe galaxy clusters via the Sunyaev-Zel'dovich effect from the 12 m APEX telescope on the Atacama plateau in Chile. The receiver contains a focal plane of 280 superconducting transition-edge sensor (TES) bolometers instrumented with a frequency-domain multiplexed readout system. The bolometers are cooled to 280 mK via a three-stage helium sorption refrigerator and a mechanical pulse-tube cooler. Three warm mirrors, two 4 K lenses, and a horn array couple the TES bolometers to the telescope. APEX-SZ observes in a single frequency band at 150 GHz with 1' angular resolution and a 22' field-of-view, all well suited for cluster mapping. The APEX-SZ receiver has played a key role in the introduction of several new technologies including TES bolometers, the frequency-domain multiplexed readout, and the use of a pulse-tube cooler with bolometers. As a result of these new technologies, the instrument has a higher instantaneous sensitivity and covers a larger field-of-view than earlier generations of Sunyaev-Zel'dovich instruments. Since its commissioning in April 2007, APEX-SZ has been used to map tens of clusters. We describe the design of the receiver and its performance when installed on the APEX telescope.