Damas Segovia, Ancor: Magnetic Outflows in the Virgo Galaxy NGC 4388. - Bonn, 2017. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-47938
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-47938,
author = {{Ancor Damas Segovia}},
title = {Magnetic Outflows in the Virgo Galaxy NGC 4388},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2017,
month = jul,

note = {We investigate the effects of ram pressure on the ordered magnetic field of the edge-on Virgo galaxy NGC 4388 hosting a radio halo and strong nuclear outflows. New radio images in total and polarized intensity were obtained within the CHANG-ES EVLA project. The unprecedented noise level reached allows us to detect striking new features of the ordered magnetic field. The nuclear outflow driven by an AGN extends far into the halo to about 5,kpc from the center and is spatially correlated with $Ha$ and X-ray emission. For the first time, a southern outflow is detected. Above and below both spiral arms we find extended blobs of polarized emission with an ordered field oriented perpendicular to the disk, probably generated by a galactic wind driven by star formation in the underlying spiral arms. The synchrotron lifetime of the cosmic-ray electrons (CREs) in these regions yields a mean outflow velocity of $(270pm70)kms$, in agreement with a galactic wind scenario. The observed symmetry of the polarized halo features in NGC 4388 excludes a compression of the halo gas by the ram pressure of the intracluster medium (ICM). The assumption of equilibrium between the halo pressure and the ICM ram pressure allows an estimate of the ICM density that is consistent with both the ICM density derived from X-ray observations and recent textit{Planck} Sunyaev--Zel'dovich measurements. The detection of a faint radio halo around cluster galaxies can thus be used for an estimate of ICM ram pressure.
We find an asymmetry in the Faraday rotation measure $RM$ pattern of the southern part of the northern hotspot at the end of the northern nuclear outflow. The profile of this hotspot can be interpreted as the magnetic field changing its direction along the line of sight. We suspect that this $RM$ asymmetry could be due to the action of a precessing nuclear outflow of the northern and southern filaments with respect to the center of the galaxy. Another indication of the precession is the wiggling structure seen in the magnetic field vectors along the southern nuclear outflow.
We show that a precession model of the nuclear outflow gives similar structures in the morphology of the radio polarization filaments in the halo of NGC 4388. The precession model allows us to estimate a velocity of $1300-2300,rm{km,s^{-1}}$ and $500-1000,rm{km,s^{-1}}$ for the northern and southern parts of the nuclear outflow, respectively. We find a similar structure between the direction of the modeled precessing outflow and the observed sign of $RM$s. We interpret this similarity as the result of the magnetic field following the helical direction of a precessing nuclear outflow, which is an independent proof of precession as a plausible scenario in the nuclear outflow of this galaxy.
Complementary observations at S-band and X-band (VLA) and at $610,rm{MHz}$ (GMRT) in order to confirm and further study the new features found in the radio halo of this galaxy. A spectral index distribution analysis of the nuclear outflow in NGC,4388 suggests diffusive shock acceleration of CREs produced by the interaction with the ICM environment. Our estimates give velocities and inclination for the northern and the southern nuclear outflows that agree with the ones estimated by the precession model. The action of ram pressure probably pushes the ISM material towards the north giving rise to different velocities and hence Mach numbers in both halves of the outflow.},

url = {https://hdl.handle.net/20.500.11811/7211}

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