Discovery of a synchrotron-emitting halo around NGC 253

Carilli, C. L.; Holdaway, M. A.; Ho, P. T. P.; Pree, C. G. De

doi:10.1086/186606

Cited by 83 publications

(107 citation statements)

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“…to all but the largest angular scales. The rms noise level is, with 400 μJy beam −1 , slightly higher than in the map presented by Carilli et al (1992), which has a noise level of 350 μJy beam −1 at 30 resolution (Paper I).…”

Section: Vla Archive Datamentioning

confidence: 59%

“…In the outer ring (2.2−4.0 kpc), shown in Fig. 14, the evenparity axisymmetric disc magnetic field gives a reasonable fit to the data, except around 60 • −80 • . This deviation can be attributed to the "radio spur" that has already been identified by Carilli et al (1992) in total power radio continuum and which has a strong vertical field component. This finding agrees with our previous observations (Paper II), where we detected an even-parity axisymmetric disc field at lower resolution.…”

Section: Disc Magnetic Fieldmentioning

confidence: 75%

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Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253 III. Helical magnetic fields in the nuclear outflow

Heesen

Beck

Krause

et al. 2011

A&A

107

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Context. Magnetic fields are good tracers of gas compression by shock waves in the interstellar medium. These can be caused by the interaction of star-formation driven outflows from individual star formation sites as described in the chimney model. Integration along the line-of-sight and cosmic-ray diffusion may hamper detection of compressed magnetic fields in many cases. Aims. We study the magnetic field structure in the central part of the nuclear starburst galaxy NGC 253 with spatial resolutions between 40 and 150 pc to detect any filamentary emission associated with the nuclear outflow. As the nuclear region is much brighter than the rest of the disc we can distinguish this emission from that of the disc. Methods. We used radio polarimetric observations with the VLA. New observations at λ3 cm with 7. 5 resolution were combined with archive data at λλ 20 and 6 cm. We created a map of the rotation measure distribution between λλ 6 and 3 cm and compared it with a synthetic polarization map. Results. We find filamentary radio continuum emission in a geometrical distribution, which we interpret as the boundary of the NW nuclear outflow cone seen in projection. The scaleheight of the continuum emission is 150 ± 20 pc, regardless of the observing frequency. The equipartition magnetic field strength is 46 ± 10 μG for the total field and 21 ± 5 μG for the regular field in the filaments. We find that the ordered magnetic field is aligned along the filaments, in agreement with amplification due to compression. The perpendicular diffusion coefficient across the filaments is κ ⊥ = 1.5 × 10 28 cm 2 s −1 · E(GeV) 0.5±0.7 . In the SE part of the nuclear outflow cone the magnetic field is pointing away from the disc in form of a helix, with an azimuthal component increasing up to at least 1200 pc height, where it is about equal to the total component. The ordered magnetic field in the disc is anisotropic within a radius of 2.2 kpc. At larger radii, the large-scale field is regular and of even parity. Conclusions. The magnetic filaments indicate an interaction of the nuclear outflow with the interstellar medium. The magnetic field is able to collimate the outflow, which can explain the observed small opening angle of ≈26 • . Owing to the conservation of angular momentum by the plasma in the nuclear outflow, the field lines are frozen into the plasma, and they wind up into a helix. Strong adiabatic losses of the cosmic-ray electrons in the accelerated outflow can partly explain why the radio luminosity of the nucleus lies below the radio-FIR correlation.

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Section: Vla Archive Datamentioning

confidence: 59%

Section: Disc Magnetic Fieldmentioning

confidence: 75%

Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253 III. Helical magnetic fields in the nuclear outflow

Heesen

Beck

Krause

et al. 2011

A&A

107

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“…An associated extended CR halo was found by Carilli et al (1992), and investigated in more detail by Beck et al (1994). NGC 253 also has an extended halo of hot X-ray emitting ionized gas (Pietsch 1996;Fig.…”

Section: Other Edge-on Starburst Galaxiesmentioning

confidence: 79%

Gaseous Halos of Late-Type Spiral Galaxies

Dahlem¹

1997

PASP

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ABSTRACT. This article reviews the most recent observational results on disk-halo interactions in nearby galaxies. The implications of these results on our understanding of the structure of the interstellar medium (ISM) in our Galaxy and external spiral galaxies, with particular emphasis on the halo ISM, are discussed. Disk-halo interactions occur only above the brightest HII regions, which are found almost exclusively in late-type spirals and dwarf and irregular galaxies. Circumnuclear starbursts are the most energetic flavor of this phenomenon. The existence, the shapes, and the properties of gaseous halos depend on the level of energy input into the disk ISM per unit surface area, i.e., on the feedback of mass, momentum, and energy produced by vigorous star formation. Thus, current theoretical models of the ISM take into account that gaseous halos are natural extensions of disk ISMs and are heated by the winds and ionizing radiation of massive stars, and by the shock waves of Supernovae and their remnants. Observationally, this is reflected by the fact that all phases of the ISM known to exist in galaxy disks have also been detected in halos. Disk-halo interactions are a very effective way of redistributing energy, metals, and magnetic fields in galaxies and of expelling them into intergalactic space when outflows reach escape velocity. MOTIVATION AND OUTLINESpiral galaxies consist of three spatially and dynamically dinstinct components, namely bulge, disk, and halo. Of these, the central bulge consists primarily of old stars and has a low gas fraction. The disk and halo consist of stars plus gas, dust, and in many cases "dark matter." Here I want to concentrate on the interstellar medium (ISM) in the disks and halos of galaxies, with emphasis on late-type spirals. Massive dark halos will not be described (see, e.g., Ashman 1992; Holt and Bennett 1995). In the current context "latetype" stands for disk-dominated spirals with rather inconspicuous bulges (Hubble types Sb -Sdm). The ISM of elliptical galaxies and early-type spirals (S0-Sab) will also not be presented here (cf. Walsh et al. 1989;and Fabbiano 1989).Studies of the ISM contribute significantly to our understanding of the structure, kinematics, and evolution of galaxies. The level of star formation (SF), its spatial distribution, and its temporal changes depend strongly on the properties of the interstellar gas from which stars can form. Stars feed energy and metal-enriched matter back into the ambient medium via stellar winds and supernovae (SNe), thereby distributing processed material throughout the ISM. Hence, through this gas-star-gas cycle, the ISM becomes a mediator of SF.In Sec. 2, the different phases of the ISM in galaxies will be introduced, and Sec. 3 presents observations of the ISM in the Milky Way. Section 4 will show that the Galactic ISM is l A\\ correspondence should be directed to this address. not confined to the thin disk, but extends to high distances (z) above the plane, forming a gaseous halo. However, being located within the...

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“…The stronger magnetic field in the central regions leads to larger synchrotron loss, leading to the squeezed shape of many halos, e.g. NGC 253 (Carilli et al 1992;Beck et al 1994a;Heesen et al 2005) (Fig. 6), which is in contrast to its almost spherical X-ray halo (Pietsch et al 2000).…”

Section: Radio Halos Of Edge-on Galaxiesmentioning

confidence: 99%

Galactic dynamos and galactic winds

Beck

2008

Astrophys Space Sci

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Spiral galaxies host dynamically important magnetic fields which can affect gas flows in the disks and halos. Total magnetic fields in spiral galaxies are strongest (up to 30 µG) in the spiral arms where they are mostly turbulent or tangled. Polarized synchrotron emission shows that the resolved regular fields are generally strongest in the interarm regions (up to 15 µG). Faraday rotation measures of radio polarization vectors in the disks of several spiral galaxies reveal large-scale patterns which are signatures of coherent fields generated by a mean-field dynamo. Magnetic fields are also observed in radio halos around edge-on galaxies at heights of a few kpc above the disk. Cosmic-ray driven galactic winds transport gas and magnetic fields from the disk into the halo. The halo scale height and the electron lifetime allow to estimate the wind speed. The magnetic energy density is larger than the thermal energy density, but smaller than the kinetic energy density of the outflow. There is no observation yet of a halo with a large-scale coherent dynamo pattern. A global wind outflow may prevent the operation of a dynamo in the halo. Halo regions with high degrees of radio polarization at very large distances from the disk are excellent tracers of interaction between galaxies or ram pressure of the intergalactic medium. The observed extent of radio halos is limited by energy losses of the cosmic-ray electrons. Future low-frequency radio telescopes like LO-FAR and the SKA will allow to trace halo outflows and their interaction with the intergalactic medium to much larger distances.

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Discovery of a synchrotron-emitting halo around NGC 253

Cited by 83 publications

References 0 publications

Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253 III. Helical magnetic fields in the nuclear outflow

Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253 III. Helical magnetic fields in the nuclear outflow

Gaseous Halos of Late-Type Spiral Galaxies

Galactic dynamos and galactic winds

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