R. -J. Dettmar

Publications (13)22.93 Total impact

• Source

  Available from: ArXiv

  Article: Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253 I. The distribution and transport of cosmic rays

  V. Heesen, R. Beck, M Krause, R. -J. Dettmar
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  ABSTRACT: The diffusive and convective CR transport in NGC 253 from the disk into the halo is investigated using the local CR bulk speed. The connection between the CR transport and the galactic wind is outlined. We observed NGC 253 with the VLA at lambda 6.2 cm in a mosaic with 15 pointings. The missing zero-spacing flux density of the VLA mosaic was filled in using observations with the 100-m Effelsberg telescope. We also obtained a new lambda 3.6 cm map from Effelsberg observations and reproduced VLA maps at lambda 20 cm and lambda 90 cm. We find a thin and a thick radio disk with exponential scaleheights of 0.3 kpc and 1.7 kpc at lambda 6.2 cm. The equipartition total magnetic field strength between 7 micro G and 18 micro G in the disk is remarkably high. We use the spectral aging of the cosmic ray electrons (CREs) seen in the vertical profiles of the spectral index to determine a lower limit for the global CR bulk speed as (170+/-70) km/s. The linear correlation between the scaleheights and the CRE lifetimes, as evident from the dumbbell shaped halo, requires a vertical CR transport with a bulk speed of (300+/-30) km/s in the northeastern halo, similar to the escape velocity of 280 km/s. This shows the presence of a "disk wind" in NGC253. In the southwestern halo, the transport is mainly diffusive with a diffusion coefficient of (2.0+/-0.2) 10E29 cm^2 s^-1. In the northeastern halo, the CR transport is convective and more efficient than in the southwestern halo. The luminous material is transported by the disk wind, which can explain the different amounts of extra-planar HI, Halpha, and soft X-ray emission in the two halo parts. Future low-frequency radio observations will provide the data to analyze the vertical velocity profile of galactic winds.
  01/2009;
• Source

  Available from: ArXiv

  Article: The magnetic field structure in NGC 253 in presence of a galactic wind

  V. Heesen, M Krause, R. Beck, R. -J. Dettmar
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  ABSTRACT: We present radio continuum polarimetry observations of the nearby edge-on galaxy NGC 253 which possesses a very bright radio halo. Using the vertical synchrotron emission profiles and the lifetimes of cosmic-ray electrons, we determined the cosmic-ray bulk speed as (300+/-30) km/s, indicating the presence of a galactic wind in this galaxy. The large-scale magnetic field was decomposed into a toroidal axisymmetric component in the disk and a poloidal component in the halo. The poloidal component shows a prominent X-shaped magnetic field structure centered on the nucleus, similar to the magnetic field observed in other edge-on galaxies. Faraday rotation measures indicate that the poloidal field has an odd parity (antisymmetric). NGC 253 offers the possibility to compare the magnetic field structure with models of galactic dynamos and/or galactic wind flows. Comment: 6 pages, 5 figures, in the proceedings of the IAU Symposium 259: "Cosmic magnetic fields: from planets, to stars and galaxies", Teneriffe, November 2008, in press
  12/2008;
• Source

  Available from: ArXiv

  Article: Cosmic rays and the magnetic field of the nearby starburst galaxy NGC 253

  V. Heesen, R. -J. Dettmar, M Krause, R. Beck
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  ABSTRACT: Using radio polarimetry we study the connection between the transport of cosmic rays (CR's), the three-dimensional magnetic field structure, and features of other ISM phases in the halo of NGC 253. We present a new sensitive radio continuum map of NGC 253 obtained from combined VLA and Effelsberg observations at lambda 6.2 cm. We find a prominent radio halo with a scaleheight of the thick radio disk of 1.7 kpc. The linear dependence between the local scaleheight of the vertical continuum emission and the cosmic ray electron (CRE) lifetime requires a vertical CR bulk speed of 270 km s^-1. The magnetic field structure of NGC 253 resembles an ``X''-shaped configuration where the orientation of the large-scale magnetic field is plane-parallel only in the inner regions of the disk and at small distances from the galactic midplane. At larger galactocentric radii and further away from the midplane the vertical component becomes important. This is most clearly visible at the location of the ``radio spur'' southeast of the nucleus, where the magnetic field orientation is almost vertical. We made a simple model for the dominant toroidal (r,phi) magnetic field component using a spiral magnetic field with prescribed inclination and pitch angle. The residual poloidal (r,phi,z) magnetic field component which was revealed by subtracting the model from the observations shows a distinct ``X''-shaped magnetic field orientation centered on the nucleus. The orientation angle of the poloidal magnetic field is consistent with a magnetic field transport described by the superposition of the vertical CR bulk speed and the rotation velocity. Hence, we propose a disk wind which transports cosmic rays, magnetic field, and (partially) ionized gas from the disk into the halo. Comment: 3 pages, 2 figures, in the proceedings of the conference: "From planets to dark energy: the modern radio universe", Manchester, October 2007
  01/2008;
• Chapter: Photometry and radio continuum observations of galaxies

  R. -J. Dettmar, R. Beck, R. Wielebinski
  10/2006: pages 79-84;
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  Available from: articles.adsabs.harvard.edu

  Article: The Radio Halo of the Starburst Galaxy NGC 253

  V. Heesen, M. Krause, R. Beck, R.-J. Dettmar
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  ABSTRACT: We have conducted 3.6 cm radio continuum observations of the nearby starburst galaxy NGC 253 with the Effelsberg 100-m telescope. The polarized emission reveals a prominent radio halo with the magnetic field mainly aligned parallel to the galactic disk. We detected several radio spurs emerging from the disk into the halo. These radio spurs have no preferred alignment with respect to the nuclear starbust. Actually, they may be connected to the underlying starforming disk by a convective comic ray driven galactic wind. With recently obtained VLA-D observations at 6 cm, to be combined with Effelsberg data, we will be able to examine this connection in more detail.
  05/2005; -1:156-161.
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  Available from: adsabs.harvard.edu

  Article: An Effelsberg/VLA radio continuum survey of an optically selected sample of edge-on spiral galaxies

  E. Hummel, R. Beck, R.-J. Dettmar
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  ABSTRACT: The results of an extensive radio continuum survey at 5 GHz with the 100 m Effelsberg telescope and the Very Large Array of a large sample of edge-on spiral galaxies (181 galaxies) are presented. The aim of this survey was to find candidates for more extensive studies on radio halos and on outflow phenomena from the nuclei of these galaxies.
  Astronomy and Astrophysics Supplement Series 01/1991; 87:309-317.
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  Available from: articles.adsabs.harvard.edu

  Article: The detection of CO in NGC 4594

  E. Bajaja, M. Krause, R. Wielebinski, R.-J. Dettmar
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  ABSTRACT: The early-type spiral galaxy NGC 4594 (M 104, the 'Sombrero' galaxy) has been observed in the (1-0) and (2-1) line transitions of (C-12)O with the 30-m mm-radio telescope of IRAM at Pico Veleta. Here, the detections of molecular material at + or - 140 arcsec from the nucleus of M 104 along the major axis are presented. The location of the detected CO coincides with the inner H I annulus, the dust ring, and the peaks of radio continuum emission. No CO was detected in the nuclear area of NGC 4594. The detection is discussed in an evolutionary scenario for the interstellar medium in early-type disk galaxies.
  Astronomy and Astrophysics 12/1990; 241:411-415. · 4.59 Impact Factor
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  Available from: adsabs.harvard.edu

  Article: The large-scale radio continuum structure of the Sombrero galaxy (NGC 4594)

  E. Bajaja, R.-J. Dettmar, E. Hummel, R. Wielebinski
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  ABSTRACT: The authors observed the nearly edge-on early-type spiral galaxy NGC 4594 (M104, the "Sombrero" galaxy) with the Very Large Array and have detected extended emission at 1.49 GHz with a total flux of about 13 mJy. This emission originates in two components, a ring associated with the H I and dust rings, and a spheroidal component with a large z extent. The contribution of the latter to the total flux is twice as much as that of the ring. Comparison with Hα measurements indicates that less than 10% of the disk emission is thermal. The star formation rate derived from Hα and from the radio continuum is rather low (0.8 M_sun;yr-1) which is consistent with the low radio surface brightness and FIR emission. The authors detected linearly polarized emission in a spur that emerges from the active nucleus.
  Astronomy and Astrophysics 07/1988; 202:35-40. · 4.59 Impact Factor
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  Available from: articles.adsabs.harvard.edu

  Article: The minor axis profiles of galaxies with box- and peanut-shaped bulges

  R.-J. Dettmar, R. Wielebinski
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  ABSTRACT: CCD surface photometry of the minor axis brightness profiles of five edge-on galaxies with box- or peanut-shaped bulges is presented. The profile of NGC 5746 consists of two separate components and looks very much similar to the unusual and until now unique profile of NGC 4565. The distinct difference between the minor axis profiles of NGC 4565 and NGC 5746 and the other 4 profiles presented here shows that galaxies with such bulges are not a homogeneous group.
  Astronomy and Astrophysics 09/1986; 167:L21-L23. · 4.59 Impact Factor
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  Available from: adsabs.harvard.edu

  Article: Neutral hydrogen and radio continuum observations of NGC 55

  E. Hummel, R.-J. Dettmar, R. Wielebinski
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  ABSTRACT: The neutral hydrogen emission and radio continuum emission of the Magellanic-type galaxy NGC 55 were observed with the Very Large Array at a resolution of about 40 arcsec. An integrated H I flux of 1600 Jy km/s, corresponding to a total H I mass of 1.5 x 10 to the 9th solar masses is found. The total H I distribution, which is not centered on the bar, shows a warp and looks disturbed on the most western side. The extent of the H I emission is comparable to the optical dimensions. The velocity field shows a large-scale asymmetry with respect to the center of the bar, confirming the mass asymmetry indicated by the optical light distribution. About 80 percent of the total mass resides in the disk while the remaining 20 percent of the mass is in the off-centered component. The centers of the two components are 2.1 kpc apart.
  Astronomy and Astrophysics 08/1986; 166:97-106. · 4.59 Impact Factor
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  Available from: articles.adsabs.harvard.edu

  Article: An optical shell associated with the clumpy irregular galaxy Markarian 325

  R. J. Dettmar, U. Klein, R. Wielebinski, J. Heidmann
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  ABSTRACT: Deep plates of the clumpy irregular galaxy Mkn 325 have been taken which exhibit a shell-like structure of about 22 kpc galactocentric distance. This is reminiscent of the ripples frequently found around merger galaxies, but it could also be a shock produced by a star formation burst and ploughing through the interstellar medium.
  Astronomy and Astrophysics 12/1983; 130:424. · 4.59 Impact Factor
• Article: Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253

  V. Heesen, M Krause, R. Beck, R. -J. Dettmar
  [show abstract] [hide abstract]
  ABSTRACT: Context. There are several edge-on galaxies with a known magnetic field structure in their halo. A vertical magnetic field significantly enhances the cosmic-ray transport from the disk into the halo. This could explain the existence of the observed radio halos.Aims. We observed NGC 253 that possesses one of the brightest radio halos discovered so far. Since this galaxy is not exactly edge-on ($i=78^\circ$) the disk magnetic field has to be modeled and subtracted from the observations in order to study the magnetic field in the halo.Methods. We used radio continuum polarimetry with the VLA in D-configuration and the Effelsberg 100-m telescope. NGC 253 has a very bright nuclear point-like source, so that we had to correct for instrumental polarization. We used appropriate Effelsberg beam patterns and developed a tailored polarization calibration to cope with the off-axis location of the nucleus in the VLA primary beams. Observations at $\lambda\lambda$6.2 cm and 3.6 cm were combined to calculate the RM distribution and to correct for Faraday rotation.Results. The large-scale magnetic field consists of a disk $(r,\phi)$ and a halo $(r,z)$ component. The disk component can be described as an axisymmetric spiral field pointing inwards with a pitch angle of $25^\circ \pm 5^\circ$ which is symmetric with respect to the plane (even parity). This field dominates in the disk, so that the observed magnetic field orientation is disk parallel at small distances from the midplane. The halo field shows a prominent X-shape centered on the nucleus similar to that of other edge-on galaxies. We propose a model where the halo field lines are along a cone with an opening angle of $90\degr \pm 30\degr$ and are pointing away from the disk in both the northern and southern halo (even parity). We can not exclude that the field points inwards in the northern halo (odd parity). The X-shaped halo field follows the lobes seen in H$\alpha$ and soft X-ray emission.Conclusions. Dynamo action and a disk wind can explain the X-shaped halo field. The nuclear starburst-driven superwind may further amplify and align the halo field by compression of the lobes of the expanding superbubbles. The disk wind is a promising candidate for the origin of the gas in the halo and for the expulsion of small-scale helical fields as requested for efficient dynamo action.
  http://dx.doi.org/10.1051/0004-6361/200911698.
• Article: Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253

  V. Heesen, R. Beck, M Krause, R. -J. Dettmar
  [show abstract] [hide abstract]
  ABSTRACT: Context. Nearby edge-on galaxies showing a synchrotron halo are nearly ideal objects for studying the transport of cosmic rays (CRs) in galaxies. Among them, the nearby starburst galaxy NGC 253 hosts a galactic wind indicated by various ISM phases in its halo.Aims. The diffusive and convective CR transport from the disk into the halo is investigated using the local CR bulk speed. The connection between the CR transport and the galactic wind is outlined.Methods. We observed NGC 253 with the VLA at $\lambda$6.2 cm in a mosaic with 15 pointings. The missing zero-spacing flux density of the VLA mosaic was filled in using observations with the 100-m Effelsberg telescope. We also obtained a new $\lambda$3.6 cm map from Effelsberg observations and reproduced VLA maps at $\lambda$20 cm and $\lambda$90 cm. The high dynamic range needed due to the strong nuclear point-like source was addressed with a special data calibration scheme for both the single-dish and the interferometric observations.Results. We find a thin and a thick radio disk with exponential scaleheights of 0.3 kpc and 1.7 kpc at $\lambda$6.2 cm. The equipartition total magnetic field strength between 7 $\mu$G and 18 $\mu$G in the disk is remarkably high. We use the spectral aging of the cosmic ray electrons (CREs) seen in the vertical profiles of the spectral index to determine a lower limit for the global CR bulk speed as 170 $\pm$ 70 km s$^{-1}$. The linear correlation between the scaleheights and the CRE lifetimes, as evident from the dumbbell shaped halo, requires a vertical CR transport with a bulk speed of 300 $\pm$ 30 km s$^{-1}$ in the northeastern halo, similar to the escape velocity of 280 km s$^{-1}$. This shows the presence of a “disk wind” in NGC 253. In the southwestern halo, the transport is mainly diffusive with a diffusion coefficient of 2.0 $\pm$ 0.2 $\times$ 10$^{29}$ cm$^2$ s$^{-1}$.Conclusions. Measuring the radio synchrotron scaleheight and estimating the CRE lifetime allow us to determine the bulk speed of the CR transport into the halo. The transport is convective and more efficient in the northeastern halo, while it is diffusive in the southwestern halo. The luminous material is transported by the disk wind, which can explain the different amounts of extra-planar H I, H$\alpha$, and soft X-ray emission in the two halo parts. Future low-frequency radio observations will provide the data to analyze the vertical velocity profile of galactic winds.
  http://dx.doi.org/10.1051/0004-6361:200810543.