Publications (12)19.78 Total impact
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Article: Coordinated multi-wavelength observations of Sgr A*
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ABSTRACT: We report on recent near-infrared (NIR) and X-ray observations of Sagittarius A* (Sgr A*), the electromagnetic manifestation of the ~4x10^6 solar masses super-massive black hole (SMBH) at the Galactic Center. The goal of these coordinated multi-wavelength observations is to investigate the variable emission from Sgr A* in order to obtain a better understanding of the underlying physical processes in the accretion flow/outflow. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope (July 2005, May 2007) and the ACIS-I instrument aboard the Chandra X-ray Observatory (July 2005). We report on a polarized NIR flare synchronous to a 8x1033 erg/s X-ray flare in July 2005, and a further flare in May 2007 that shows the highest sub-flare to flare contrast observed until now. The observations can be interpreted in the framework of a model involving a temporary disk with a short jet. In the disk component flux density variations can be explained due to hot spots on relativistic orbits around the central SMBH. The variations of the sub-structures of the May 2007 flare are interpreted as a variation of the hot spot structure due to differential rotation within the disk. Comment: 15 pages, 7 figures, contribution for the conference "The Universe under the Microscope" (AHAR 2008), to be published in Journal of Physics: Conference Series by Institute of Physics Publishing10/2008; -
Article: Coordinated mm/sub-mm observations of Sagittarius A* in May 2007
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ABSTRACT: At the center of the Milky Way, with a distance of ~8 kpc, the compact source Sagittarius A* (SgrA*) can be associated with a super massive black hole of ~4x10^6 solar masses. SgrA* shows strong variability from the radio to the X-ray wavelength domains. Here we report on simultaneous NIR/sub-millimeter/X-ray observations from May 2007 that involved the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope, the Australian Telescope Compact Array (ATCA), the US mm-array CARMA, the IRAM 30m mm-telescope, and other telescopes. We concentrate on the time series of mm/sub-mm data from CARMA, ATCA, and the MAMBO bolometer at the IRAM 30m telescope. Comment: 7 pages, 3 figures, contribution for the conference "The Universe under the Microscope" (AHAR 2008), to be published in Journal of Physics: Conference Series by Institute of Physics Publishing10/2008; -
Article: Continuum emission in NGC1068 and NGC3147: Indications for a turnover in the core spectra
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ABSTRACT: We present new interferometric observations of the continuum emission at mm wavelengths in the Seyfert galaxies NGC1068 and NGC3147. Three mm continuum peaks are detected in NGC1068, one centered on the core, one associated with the jet and the third one with the counter-jet. This is the first significant detection of the radio jet and counter-jet at mm wavelengths in NGC1068. While the fluxes of the jet components agree with a steep spectral index extrapolated from cm-wavelengths, the core fluxes indicate a turnover of the inverted cm- into a steep mm-spectrum at roughly 50GHz which is most likely caused by electron-scattered synchrotron emission. As in NGC 1068, the spectrum of the pointlike continuum source in NGC3147 also shows a turnover between cm and mm-wavelengths at 25GHz resulting from synchrotron self-absorption different to NGC1068. This strongly resembles the spectrum of SgrA*, the weakly active nucleus of our own galaxy, and M81*, a link between SgrA* and Seyfert galaxies in terms of activity sequence, which may display a similar turnover. Comment: 8 pages, 5 figures, accepted for publication in A&A09/2005; -
Article: Molecular gas and continuum emission in 3C48: Evidence for two merger nuclei?
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ABSTRACT: We present new interferometer observations of the CO(1-0) line and mm continuum emission from 3C48 - one of the nearest examples of a merger activating a quasar. Our new CO data show that most of the CO is not in a disk around the quasar 3C48, but rather in a second nucleus associated with the source 3C48A ~1" to the north-east, recently studied in the near-IR by Zuther et al. (2004). This main CO source has a strong velocity gradient (140km/s over about 1"). Our new data also show a second, weaker CO source at the QSO itself. At 1.2mm, the continuum emission is elongated in the direction of the radio jet and towards 3C48A. We model the 1.2mm continuum with three different sources in 3C48 - the 3C48 QSO, the 3C48 jet, and the second nucleus 3C48A. We suggest that the unusually bright and extended nature of the jet may be due to its interaction with the second merger nucleus 3C48A. Comment: 11 pages, 11 figures, accepted for publication in A&A05/2005; -
Article: Q0957+561 revised: CO emission from a disk at z=1.4
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ABSTRACT: Based on additional interferometric observations, we reanalysed the CO(2-1) and 3mm continuum emission of Q0957+561, a lensed QSO at a redshift of z=1.4141. The emission in the CO(2-1) lines reveals a gas-rich host galaxy with a peculiar double-peaked profile at one of the two lensed images. Our new interferometric CO maps of the host galaxy agree well with HST images obtained by Keeton et al. (2000) and we thus argue that the two velocity components arise from molecular gas in the disk of the host galaxy. We also present new model calculations, all in excellent agreement with recent time delay measurements and simulations. Comment: 8 pages, 5 figures, accepted for publication in A&A, Table1 corrected11/2004; -
Article: Submillimeter spectrum and dust mass of the primeval galaxy IRAS 10214 + 4724
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ABSTRACT: We measured with the IRAM 30 m telescope the continuum flux of the extremely luminous primeval galaxy IRAS 10214 +4724 at a wavelength of 1.2 mm. This is the longest wavelength at which this galaxy's thermal continuum radiation has been detected; at z = 2.286, it corresponds to a rest wavelength of 370 microns. From the entire continuum spectrum we estimate a dust temperature of 80 K, and from the optically thin radiation at 370 microns (rest frame) we find a dust mass of 2.5 x 10 exp 8/sq h solar masses. For the H2 mass of 1 x 10 exp 11/sq h solar masses implied by the CO line luminosity, this yields a ratio of the mass of gas (H2 + He) to warm dust of 500, which is surprisingly normal for a galaxy at z = 2.3. It is the same value as observed in the central regions of nearby luminous galaxies that have solar metallicity. The ratio of observed CO and 370 microns (rest-frame) luminosities in 10214 + 4724, essentially the gas-to-dust mass ratio, is the same as in nearby galaxies. Hence, in this galaxy, most of the heavy elements have already been produced, at nearly present-day abundances.The Astrophysical Journal 09/1992; 398:L25-L27. · 6.02 Impact Factor -
Article: Strong H2O maser emission from the peculiar galaxy NGC 3079
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ABSTRACT: H2O maser emission with an (isotropic) total luminosity of ˜500 Lsun has been detected in the peculiar galaxy NGC 3079, within 5" of the nucleus; this is the most powerful maser yet detected. The peak flux density is 11 Jy. The H2O features, centered on vLSR= 960 km s-1, cover a velocity range of at least 140 km s-1. A possible detection of a ˜200 Lsun H2O maser is also reported. Less luminous maser emission, detected by Claussen et al. (1984) towards NGC 1068, NGC 3034, and NGC 4258, is confirmed. We failed, however, to obtain a clear detection toward NGC 6946. H2O pump mechanisms are discussed in view of their ability to produce the luminosities observed.Astronomy and Astrophysics 11/1984; 141:L1-L3. · 4.59 Impact Factor -
Article: A Search for H2O Emission from Orion Population Stars
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ABSTRACT: Eighty-one stars of the "Orion population" were searched for H2O maser emission at 22 GHz. The search was made over a radial velocity interval ranging from 130 km s-1 for the majority of the stars to ˜800 km s-1 for a few selected stars. Water maser emission was detected at the positions of only two stars. One of them, AS 501, is probably a long-period variable, and should therefore be removed from the list of the Orion population. The only other star detected, T Tauri, was already known to be associated with an H2O source. However, differing positions had been reported in the literature. We confirm that the H2O emission comes from T Tauri itself, to an accuracy of ±5". New H2O features at radial velocities of 9.6 and 11.8 km s-1 are reported. Upper limits are given for all the other stars investigated. Implications of the lack of H2O maser emission from most of the Orion population stars are briefly discussed.Astronomy and Astrophysics 12/1980; 94:80. · 4.59 Impact Factor -
Article: Observations of the oxygen-18 isotope of formaldehyde
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ABSTRACT: Observations have been made with the Effelsberg 100-m telescope of the 4.389-GHz absorption line of H2(C-12)(O-18) toward Sgr A, Sgr B2, W33, and W51. Comparison with earlier H2(C-13)(O-16) data shows that the H2(C-13)(O-16)/H2(C-12)(O-18) ratio is 5 + or - 1; that is, close to the terrestrial (C-13)(O-16)/(C-12)(O-18) value of 5.5, in all sources. The results are in agreement with those of Tucker et al. (1979) for formaldehyde, but differ significantly from the ratios obtained from carbon monoxide.Astronomy and Astrophysics 02/1979; 73:L13-L15. · 4.59 Impact Factor -
Article: A Search for H2O Emission from Young Stars
Mitteilungen der Astronomischen Gesellschaft Hamburg. 52:29. -
Article: Spectroscopic studies of the disk and halo of M82.
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Article: Continuum emission in NGC 1068 and NGC 3147: indications for a turnover in the core spectra
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ABSTRACT: We present new interferometric observations of the continuum emission at mm wavelengths in the Seyfert galaxies NGC 1068 and NGC 3147. Three mm continuum peaks are detected in NGC 1068, one centered on the core, one associated with the jet and the third one with the counter-jet. This is the first significant detection of the radio jet and counter-jet at mm wavelengths in NGC 1068. While the fluxes of the jet components agree with a steep spectral index extrapolated from cm-wavelengths, the core fluxes indicate a turnover of the inverted cm- into a steep mm-spectrum at roughly ~50 GHz which is most likely caused by electron-scattered synchrotron emission. As in NGC 1068, the spectrum of the pointlike continuum source in NGC 3147 also shows a turnover between cm and mm-wavelengths at ~25 GHz resulting from synchrotron self-absorption different to NGC 1068. This strongly resembles the spectrum of Sgr A$^\star$, the weakly active nucleus of our own galaxy, and M 81$^\star$, a link between Sgr A$^\star$ and Seyfert galaxies in terms of activity sequence, which may display a similar turnover.http://dx.doi.org/10.1051/0004-6361:20053729.
Top co-authors
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Institutions
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1992
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CSU Mentor
Long Beach, CA, USA
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1979
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Max Planck Institute for Radio Astronomy
Bonn, North Rhine-Westphalia, Germany
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