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Sökning: WFRF:(Farnes J. S.) > (2018) > LOFAR MSSS: Flatten...

  • Chyz̊y, K.T.Jagiellonian University in Kraków, Poland (författare)

LOFAR MSSS: Flattening low-frequency radio continuum spectra of nearby galaxies

  • Artikel/kapitelEngelska2018

Förlag, utgivningsår, omfång ...

  • 2018-11-07
  • EDP Sciences,2018
  • electronicrdacarrier

Nummerbeteckningar

  • LIBRIS-ID:oai:research.chalmers.se:9a94d8a7-be7f-486f-a53a-b02df45acbd9
  • https://doi.org/10.1051/0004-6361/201833133DOI
  • https://research.chalmers.se/publication/506144URI

Kompletterande språkuppgifter

  • Språk:engelska
  • Sammanfattning på:engelska

Ingår i deldatabas

Klassifikation

  • Ämneskategori:art swepub-publicationtype
  • Ämneskategori:ref swepub-contenttype

Anmärkningar

  • Aims. The shape of low-frequency radio continuum spectra of normal galaxies is not well understood, the key question being the role of physical processes such as thermal absorption in shaping them. In this work we take advantage of the LOFAR Multifrequency Snapshot Sky Survey (MSSS) to investigate such spectra for a large sample of nearby star-forming galaxies. Methods. Using the measured 150 MHz flux densities from the LOFAR MSSS survey and literature flux densities at various frequencies we have obtained integrated radio spectra for 106 galaxies characterised by different morphology and star formation rate. The spectra are explained through the use of a three-dimensional model of galaxy radio emission, and radiation transfer dependent on the galaxy viewing angle and absorption processes. Results. Our galaxies' spectra are generally flatter at lower compared to higher frequencies: the median spectral index αlow measured between ≈ 50 MHz and 1.5 GHz is -0.57 ± 0.01 while the high-frequency one αhigh, calculated between 1.3 GHz and 5 GHz, is -0.77 ± 0.03. As there is no tendency for the highly inclined galaxies to have more flattened low-frequency spectra, we argue that the observed flattening is not due to thermal absorption, contradicting the suggestion of Israel & Mahoney (1990, ApJ, 352, 30). According to our modelled radio maps for M 51-like galaxies, the free-free absorption effects can be seen only below 30 MHz and in the global spectra just below 20 MHz, while in the spectra of starburst galaxies, like M 82, the flattening due to absorption is instead visible up to higher frequencies of about 150 MHz. Starbursts are however scarce in the local Universe, in accordance with the weak spectral curvature seen in the galaxies of our sample. Locally, within galactic disks, the absorption effects are distinctly visible in M 51-like galaxies as spectral flattening around 100-200 MHz in the face-on objects, and as turnovers in the edge-on ones, while in M 82-like galaxies there are strong turnovers at frequencies above 700 MHz, regardless of viewing angle. Conclusions. Our modelling of galaxy spectra suggests that the weak spectral flattening observed in the nearby galaxies studied here results principally from synchrotron spectral curvature due to cosmic ray energy losses and propagation effects. We predict much stronger effects of thermal absorption in more distant galaxies with high star formation rates. Some influence exerted by the Milky Way's foreground on the spectra of all external galaxies is also expected at very low frequencies.

Ämnesord och genrebeteckningar

Biuppslag (personer, institutioner, konferenser, titlar ...)

  • Jurusik, W.Jagiellonian University in Kraków, Poland (författare)
  • Piotrowska, J.Jagiellonian University in Kraków, Poland (författare)
  • Nikiel-Wroczyński, B.Jagiellonian University in Kraków, Poland (författare)
  • Heesen, V.Universität Hamburg,University of Hamburg,University of Southampton (författare)
  • Vacca, V.Istituto nazionale di astrofisica (INAF) (författare)
  • Nowak, N.Jagiellonian University in Kraków, Poland (författare)
  • Paladino, R.Istituto nazionale di astrofisica (INAF) (författare)
  • Surma, P.Jagiellonian University in Kraków, Poland (författare)
  • Sridhar, S. S.Netherlands Institute for Radio Astronomy (ASTRON),Rijksuniversiteit Groningen,University of Groningen (författare)
  • Heald, G.Commonwealth Scientific and Industrial Research Organisation (CSIRO) (författare)
  • Beck, R.Max Planck Gesellschaft zur Förderung der Wissenschaften e.V. (MPG),Max Planck Society for the Advancement of Science (MPG) (författare)
  • Conway, John,1963Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)jconway (författare)
  • Sendlinger, K.Ruhr-Universität Bochum (författare)
  • Curyło, M.Jagiellonian University in Kraków, Poland (författare)
  • Mulcahy, D. D.University of Manchester,Max Planck Gesellschaft zur Förderung der Wissenschaften e.V. (MPG),Max Planck Society for the Advancement of Science (MPG) (författare)
  • Broderick, J.W.Netherlands Institute for Radio Astronomy (ASTRON) (författare)
  • Hardcastle, M. J.University of Hertfordshire (författare)
  • Callingham, J. R.Netherlands Institute for Radio Astronomy (ASTRON) (författare)
  • Gurkan, G.Commonwealth Scientific and Industrial Research Organisation (CSIRO) (författare)
  • Iacobelli, M.Netherlands Institute for Radio Astronomy (ASTRON) (författare)
  • Rottgering, H.Universiteit Leiden (UL),Leiden University (UL) (författare)
  • Adebahr, B.Ruhr-Universität Bochum (författare)
  • Shulevski, A.Universiteit Van Amsterdam,University of Amsterdam (författare)
  • Dettmar, R. -J.Ruhr-Universität Bochum (författare)
  • Breton, R. P.University of Manchester (författare)
  • Clarke, A. O.University of Manchester (författare)
  • Farnes, J.S.University Of Oxford (författare)
  • Orru, E.Netherlands Institute for Radio Astronomy (ASTRON) (författare)
  • Pandey, V. N.Netherlands Institute for Radio Astronomy (ASTRON) (författare)
  • Pandey-Pommier, M.CRAL Le Centre de Recherche Astronomique de Lyon (författare)
  • Pizzo, R.Netherlands Institute for Radio Astronomy (ASTRON) (författare)
  • Riseley, C. J.Commonwealth Scientific and Industrial Research Organisation (CSIRO) (författare)
  • Rowlinson, A.Netherlands Institute for Radio Astronomy (ASTRON) (författare)
  • Scaife, A. M. M.University of Manchester (författare)
  • Stewart, A.The University of Sydney (författare)
  • van der Horst, A. J.George Washington University (författare)
  • van Weeren, R.Universiteit Leiden (UL),Leiden University (UL) (författare)
  • Jagiellonian University in Kraków, PolandUniversität Hamburg (creator_code:org_t)

Sammanhörande titlar

  • Ingår i:Astronomy and Astrophysics: EDP Sciences6190004-63611432-0746

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