M87 at metre wavelengths: the LOFAR picture
Abstract
M87 is a giant elliptical galaxy located in the centre of the Virgo cluster, which harbours a supermassive black hole of mass 6.4x10^9 M_sun, whose activity is responsible for the extended (80 kpc) radio lobes that surround the galaxy. The energy generated by matter falling onto the central black hole is ejected and transferred to the intra-cluster medium via a relativistic jet and morphologically complex systems of buoyant bubbles, which rise towards the edges of the extended halo. Here we present the first observations made with the new Low-Frequency Array (LOFAR) of M87 at frequencies down to 20 MHz. Images of M87 were produced at low radio frequencies never explored before at these high spatial resolution and dynamic range. To disentangle different synchrotron models and place constraints on source magnetic field, age and energetics, we also performed a detailed spectral analysis of M87 extended radio-halo using these observations together with archival data. We do not find any sign of new extended emissions; on the contrary the source appears well confined by the high pressure of the intra-cluster medium. A continuous injection of relativistic electrons is the model that best fits our data, and provides a scenario in which the lobes are still supplied by fresh relativistic particles from the active galactic nuclei. We suggest that the discrepancy between the low-frequency radio-spectral slope in the core and in the halo implies a strong adiabatic expansion of the plasma as soon as it leaves the core area. The extended halo has an equipartition magnetic field strength of ~10 uG, which increases to ~13 uG in the zones where the particle flows are more active. The continuous injection model for synchrotron ageing provides an age for the halo of ~40 Myr, which in turn provides a jet kinetic power of 6-10x10^44 erg/s.
Keywords
Cite
@article{arxiv.1210.1346,
title = {M87 at metre wavelengths: the LOFAR picture},
author = {F. de Gasperin and E. Orru' and M. Murgia and A. Merloni and H. Falcke and R. Beck and R. Beswick and L. Birzan and A. Bonafede and M. Bruggen and G. Brunetti and K. Chyzy and J. Conway and J. H. Croston and T. Ensslin and C. Ferrari and G. Heald and S. Heidenreich and N. Jackson and G. Macario and J. McKean and G. Miley and R. Morganti and A. Offringa and R. Pizzo and D. Rafferty and H. Roettgering and A. Shulevski and M. Steinmetz and C. Tasse and S. van der Tol and W. van Driel and R. J. van Weeren and J. E. van Zwieten and A. Alexov and J. Anderson and A. Asgekar and M. Avruch and M. Bell and M. R. Bell and M. Bentum and G. Bernardi and P. Best and F. Breitling and J. W. Broderick and A. Butcher and B. Ciardi and R. J. Dettmar and J. Eisloeffel and W. Frieswijk and H. Gankema and M. Garrett and M. Gerbers and J. M. Griessmeier and A. W. Gunst and T. E. Hassall and J. Hessels and M. Hoeft and A. Horneffer and A. Karastergiou and J. Koehler and Y. Koopman and G. Kuper and P. Maat and G. Mann and M. Mevius and D. D. Mulcahy and H. Munk and R. Nijboer and M. Kuniyoshi and J. Noordam and H. Paas and M. Pandey and V. N. Pandey and A. Polatidis and W. Reich and A. . P. Schoenmakers and J. Sluman and O. Smirnov and C. Sobey and B. Stappers and J. Swinbank and M. Tagger and Y. Tang and I. van Bemmel and W. van Cappellen and A. P. van Duin and M. van Haarlem and J. van Leeuwen and R. Vermeulen and C. Vocks and S. White and M. Wise and O. Wucknitz and P. Zarka},
journal= {arXiv preprint arXiv:1210.1346},
year = {2015}
}
Comments
22 pages, 16 figures - Accepted in A&A