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    Wyświetlanie 1-8 z 8
    Tytuł:
    CHANG-ES : XXXIII : a 20 kpc radio bubble in the halo of the star-forming galaxy NGC 4217
    Autorzy:
    Dettmar, R.-J.
    Heesen, V.
    Wang, Q. D.
    Yang, Y.
    Crocker, R.
    Li, J.-T.
    Gajović, L.
    Kiehn, A.
    Irwin, J.
    Stein, M.
    Soida, Marian
    Brüggen, M.
    Wiegert, T.
    Henriksen, R.
    Opis:
    Context. Cosmic rays may be dynamically very important in driving large-scale galactic winds. Edge-on galaxies give us an outsider’s view of radio haloes, and of their extra-planar cosmic-ray electrons and magnetic fields. Aims. We present a new radio continuum imaging study of the nearby edge-on galaxy NGC 4217. We examine the distribution of extra-planar cosmic rays and magnetic fields. We observed it with both the Jansky Very Large Array (JVLA) in the S band (2–4 GHz) and the LOw Frequency ARray (LOFAR) at 144 MHz. Methods. We measured vertical intensity profiles and exponential scale heights. We re-imaged both the JVLA and LOFAR data at matched angular resolution in order to measure radio spectral indices between 144 MHz and 3 GHz. Confusing point-like sources were subtracted prior to imaging. We then fitted intensity profiles with cosmic-ray electron advection models, using an isothermal wind model that is driven by a combination of Results. We discover a large-scale radio halo on the north-western side of the galactic disc. The morphology is reminiscent of a bubble extending up to 20 kpc from the disc. We find spectral ageing in the bubble, which allowed us to measure the advection speeds of the cosmic-raypressure from the hot gas and cosmic rays. electrons, which accelerate from 300 to 600 km s$^{−1}$. Assuming energy equipartition between the cosmic rays and the magnetic field, we estimate the bubble may have been inflated by a modest 10% of the kinetic energy injected by supernovae over its dynamical timescale of 35 Myr. While no active galactic nucleus (AGN) has been detected, such activity in the recent past cannot be ruled out. Conclusions. Non-thermal bubbles with sizes of tens of kiloparsecs may be a ubiquitous feature of star-forming galaxies, and if so this would demonstrate the influence of feedback. Determining possible contributions by AGN feedback will require deeper observations.
    Dostawca treści:
    Repozytorium Uniwersytetu Jagiellońskiego
    Artykuł
    Tytuł:
    CHANG-ES : XXVI. Insights into cosmic-ray transport from radio halos in edge-on galaxies
    Autorzy:
    Bomans, D. J.
    Heesen, V.
    Stein, Y.
    Paladino, R.
    Strong, A.
    Adebahr, B.
    Dettmar, R. -J.
    English, J.
    Vargas, C. J.
    Tabatabaei, F. S.
    Li, J.
    Beck, R.
    Stein, M.
    Chyży, Krzysztof
    Brüggen, M.
    Wiegert, T.
    Opis:
    Context. Galactic winds play a key role in regulating the evolution of galaxies over cosmic time. In recent years, the role of cosmic rays (CRs) in the formation of the galactic wind has increasingly gained attention. Therefore, we use radio continuum data to analyse the CR transport in edge-on galaxies. Aims. With newly reduced radio continuum data of five edge-on galaxies (NGC 891, NGC 3432, NGC 4013, NGC 4157, and NGC 4631), we plan to set new constraints on the morphology of radio halos and the physical properties of galactic winds driven by stellar feedback. By distinguishing between the central and outer regions of the galaxies, our study setup allows us to search for variations in the radio halo profile or CR transport along the galactic disk. Methods. Data from the LOFAR Two-metre Sky Survey (LoTSS) Data Release 2 at 144 MHz (HBA) and reprocessed data from the Very Large Array (VLA) at 1.5 GHz (L band) from the Continuum Halos in Nearby Galaxies – an EVLA Survey (CHANG-ES) enable us to increase the extent of the analysed radio continuum profile significantly (up to a factor of 2) compared to previous studies. We computed thermal emission maps using a mixture approach with Hα and near-infrared data, which were then subtracted to yield radio synchrotron emission maps. Then we compiled non-thermal spectral index maps and computed intensity profiles using a box integration approach. Lastly, we performed 1D CR transport modelling. Results. The non-thermal spectral index maps show evidence that the LoTSS maps are affected by thermal absorption in star-forming regions. The scale height analysis reveals that most of the galaxies are equally well fitted with a one-component instead of a two-component exponential profile. We find a bi-modality within our sample. While NGC 3432 and NGC 4013 have similar scale heights in the L band and HBA, the low-frequency scale heights of NGC 891, NGC 4157, and NGC 4631 exceed their high-frequency counterpart significantly. The 1D CR transport modelling shows agreement between the predicted magnetic field strength and the magnetic field strength estimates of equipartition measurements. Additionally, we find an increasing difference in wind velocities (with increasing height over the galactic disk) between the central and outer regions of the analysed galaxies.
    Dostawca treści:
    Repozytorium Uniwersytetu Jagiellońskiego
    Artykuł
      Wyświetlanie 1-8 z 8

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