ترغب بنشر مسار تعليمي؟ اضغط هنا

Revealing Cosmic Magnetism with Radio Polarimetry

87   0   0.0 ( 0 )
 نشر من قبل Bryan Gaensler
 تاريخ النشر 2007
  مجال البحث فيزياء
والبحث باللغة English
 تأليف Bryan M. Gaensler




اسأل ChatGPT حول البحث

While gravitation sustains the on-going evolution of the cosmos, it is magnetism that breaks gravitys symmetry and that provides the pathway to the non-thermal Universe. By enabling processes such as anisotropic pressure support, particle acceleration, and jet collimation, magnetism has for billions of years regulated the feedback vital for returning matter to the interstellar and intergalactic medium. After reviewing recent results that demonstrate the unique view of magnetic fields provided by radio astronomy, I explain how the Square Kilometre Array will provide data that will reveal what cosmic magnets look like, how they formed, and what role they have played in the evolving Universe.

قيم البحث

اقرأ أيضاً

Polarimetric study in the UV and optical has been one of the keys to reveal the structure and nature of active galactic nuclei (AGN). Combined with the HSTs high spatial resolution, it has directly confirmed the predicted scattering geometry of ~100 pc scale and accurately located the hidden nuclear position in some nearby active galaxies. Recently, we are using optical spectropolarimetry to reveal the nature of the accretion flow in the central engine of quasars. This is to use polarized light to de-contaminate the spectrum and investigate the Balmer edge spectral feature, which is otherwise buried under the strong emission from the outer region surrounding the central engine.
Magnetic field is ubiquitous in the Universe and it plays essential roles in various astrophysical phenomena, yet its real origin and evolution are poorly known. This article reviews current understanding of magnetic fields in the interstellar medium , the Milky Way Galaxy, external galaxies, active galactic nuclei, clusters of galaxies, and the cosmic web. Particularly, the review concentrates on the achievements that have been provided by centimeter and meter wavelength radio observations. The article also introduces various methods to analyze linear polarization data, including synchrotron radiation, Faraday rotation, depolarization, and Faraday tomography.
135 - Jennifer West 2019
Magnetic fields are involved in every astrophysical process on every scale: from planetary and stellar interiors to neutron stars, stellar wind bubbles and supernova remnants; from the interstellar medium in galactic disks, nuclei, spiral arms and ha los to the intracluster and intergalactic media. They are involved in essentially every particle acceleration process and are thus fundamental to non-thermal physics in the Universe. Key questions include the origin of magnetic fields, their evolution over cosmic time, the amplification and decay processes that modify their strength, and their impact on other processes such as star formation and galaxy evolution. Astrophysical plasmas provide a unique laboratory for testing magnetic dynamo theory. The study of magnetic fields requires observations that span the wavelength range from radio through infrared, optical, UV, X-ray, and gamma-ray. Canada has an extremely strong record of research in cosmic magnetism, and has a significant leadership role in several ongoing and upcoming global programs. This white paper will review the science questions to be addressed in the study of cosmic magnetic fields and will describe the observational and theoretical opportunities and challenges afforded by the telescopes and modelling capabilities of today and tomorrow.
Revealing the cosmic reionisation history is at the frontier of extragalactic astronomy. The power spectrum of the cosmic microwave background (CMB) polarisation can be used to constrain the reionisation history. Here we propose a CMB-independent met hod using fast radio bursts (FRBs) to directly measure the ionisation fraction of the intergalactic medium (IGM) as a function of redshift. FRBs are new astronomical transients with millisecond timescales. Their dispersion measure (DM$_{rm IGM}$) is an indicator of the amount of ionised material in the IGM. Since the differential of DM$_{rm IGM}$ against redshift is proportional to the ionisation fraction, our method allows us to directly measure the reionisation history without any assumption on its functional shape. As a proof of concept, we constructed mock non-repeating FRB sources to be detected with the Square Kilometre Array, assuming three different reionisation histories with the same optical depth of Thomson scattering. We considered three cases of redshift measurements: (A) spectroscopic redshift for all mock data, (B) spectroscopic redshift for 10% of mock data, and (C) redshift estimated from an empirical relation of FRBs between their time-integrated luminosity and rest-frame intrinsic duration. In all cases, the reionisation histories are consistently reconstructed from the mock FRB data using our method. Our results demonstrate the capability of future FRBs in constraining the reionisation history.
A novel diagnostic of cosmic-ray modified shocks by polarimetry of H $alpha$ emissions is suggested. In a cosmic-ray modified shock, the pressure of cosmic rays is sufficiently high compared to the upstream ram pressure to force the background plasma to decelerate (measured in the shock rest frame). Simultaneously, a fraction of the hydrogen atoms co-existing in the upstream plasma collide with the decelerated protons and undergo charge-exchange reactions. As a result, hydrogen atoms with the same bulk velocity of the decelerated protons are generated. We show that when the shock is observed from edge-on, the H $alpha$ radiated by these upstream hydrogen atoms is linearly polarized with a sizable degree of a few per cent as a result of resonant scattering of Ly $beta$. The polarization direction depends strongly on the velocity modification; the direction is parallel to the shock surface for the case of no modification, while the direction is parallel to the shock velocity for the case of a modified shock.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا