Magnetic fields in the absence of spiral density waves – NGC 4414

Soida, M.; Beck, Rainer; Urbanik, M.; Braine, J.

doi:10.1051/0004-6361:20021100

Cited by 34 publications

(31 citation statements)

References 29 publications

(50 reference statements)

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“…The observed asymmetry of the outer H  distribution suggests this, but it is also supported by asymmetries in the magnetic field (Soida et al 2002).…”

Section: Ngc 4414mentioning

confidence: 70%

HALOGAS observations of NGC 4414: fountains, interaction, and ram pressure

Blok

Józsa

Patterson

et al. 2014

A&A

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We present deep H  imaging of the nearby spiral galaxy NGC 4414, taken as part of the Westerbork HALOGAS (Hydrogen Accretion in LOcal GAlaxieS) survey. The observations show that NGC 4414 can be characterized by a regularly rotating inner H  disk, and a more disturbed outer disk. Modeling of the kinematics shows that the outer disk is best described by a U-shaped warp. Deep optical imaging also reveals the presence of a low surface brightness stellar shell, indicating a minor interaction with a dwarf galaxy at some stage in the past. Modeling of the inner disk suggests that about 4 percent of the inner H  is in the form of extra-planar gas. Because of the disturbed nature of the outer disk, this number is difficult to constrain for the galaxy as a whole. These new, deep observations of NGC 4414 presented here show that even apparently undisturbed galaxies are interacting with their environment.

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“…The observed asymmetry of the outer H  distribution suggests this, but it is also supported by asymmetries in the magnetic field (Soida et al 2002).…”

Section: Ngc 4414mentioning

confidence: 70%

HALOGAS observations of NGC 4414: fountains, interaction, and ram pressure

Blok

Józsa

Patterson

et al. 2014

A&A

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“…Taken together, all of the observations indicate a tendency for magnetic fields to be oriented in spiral patterns in disk galaxies, even in galaxies with no spiral structure visible in the gaseous or stellar morphology (e.g. NGC 4414; Soida et al 2002). Where spiral arms are visible, the fields tend to be more ordered in the interarm regions.…”

Section: Introductionmentioning

confidence: 74%

The Westerbork SINGS survey

Heald¹,

Braun

Edmonds

2009

A&A

210

292

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A sample of large northern Spitzer Infrared Nearby Galaxies Survey (SINGS) galaxies has recently been observed with the Westerbork Synthesis Radio Telescope (WSRT). We present observations of the linearly polarized radio continuum emission in this WSRT-SINGS galaxy sample. Of the 28 galaxies treated in this paper, 21 are detected in polarized radio continuum at 18-and 22-cm wavelengths. We utilize the rotation measure synthesis (RM-Synthesis) method, as implemented by Brentjens & de Bruyn (2005, A&A, 441, 1217, to coherently detect polarized emission from a large fractional bandwidth, while simultaneously assessing the degree of Faraday rotation experienced by the radiation along each line-of-sight. This represents the first time that the polarized emission and its Faraday rotation have been systematically probed down to ∼10 μJy beam −1 RMs for a large sample of galaxies. Non-zero Faraday rotation is found to be ubiquitous in all of the target fields, from both the Galactic foreground and the target galaxies themselves. In this paper, we present an overview of the polarized emission detected in each of the WSRT-SINGS galaxies. The most prominent trend is a systematic modulation of the polarized intensity with galactic azimuth, such that a global minimum in the polarized intensity is seen toward the kinematically receding major axis. The implied large-scale magnetic field geometry is discussed in a companion paper. A second novel result is the detection of multiple nuclear Faraday depth components that are offset to both positive and negative RM by 100−200 rad m −2 in all targets that host polarized (circum-)nuclear emission.

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“…Ordered (regular and/or anisotropic) field traced by the polarized synchrotron emission form spiral patterns in almost every galaxy, even in ring galaxies (Chyży & Buta 2008), in flocculent galaxies without massive spiral arms (Soida et al 2002), and in the central regions of galaxies and circum-nuclear gas rings (Fig. 4).…”

Section: Structure Of Ordered Galactic Magnetic Fieldsmentioning

confidence: 99%

Magnetism in galaxies – Observational overview and next generation radio telescopes

Beck

2010

Proc. IAU

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Abstract. The strength and structure of cosmic magnetic fields is best studied by observations of radio continuum emission, its polarization and its Faraday rotation. Fields with a well-ordered spiral structure exist in many types of galaxies. Total field strengths in spiral arms and bars are 20-30 µG and dynamically important. Strong fields in central regions can drive gas inflows towards an active nucleus. The strongest regular fields (10-15 µG) are found in interarm regions, sometimes forming "magnetic spiral arms" between the optical arms. The typical degree of polarization is a few % in spiral arms, but high (up to 50%) in interarm regions. The detailed field structures suggest interaction with gas flows. Faraday rotation measures of the polarization vectors reveals large-scale patterns in several spiral galaxies which are regarded as signatures of large-scale (coherent) fields generated by dynamos. -Polarization observations with the forthcoming large radio telescopes will open a new era in the observation of magnetic fields and should help to understand their origin. Low-frequency radio synchrotron emission traces low-energy cosmic ray electrons which can propagate further away from their origin. LOFAR (30-240 MHz) will allow us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in galaxy clusters and in the Milky Way. Polarization at higher frequencies (1-10 GHz), to be observed with the EVLA, MeerKAT, APERTIF and the SKA, will trace magnetic fields in the disks and central regions of galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources with ASKAP and the SKA are dedicated to measure magnetic fields in distant intervening galaxies and clusters, and will be used to model the overall structure and strength of the magnetic field in the Milky Way.

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Magnetic fields in the absence of spiral density waves – NGC 4414

Cited by 34 publications

References 29 publications

HALOGAS observations of NGC 4414: fountains, interaction, and ram pressure

HALOGAS observations of NGC 4414: fountains, interaction, and ram pressure

The Westerbork SINGS survey

Magnetism in galaxies – Observational overview and next generation radio telescopes

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