Abstract The Radio Arc is a system of organized nonthermal filaments (NTFs) located within the Galactic center (GC) region of the Milky Way. Recent observations of the Radio Arc NTFs revealed a magnetic field that alternates between being parallel and rotated with respect to the orientation of the filaments. This pattern is in stark contrast to the predominantly parallel magnetic field orientations observed in other GC NTFs. To help elucidate the origin of this pattern, we analyze spectro-polarimetric data of the Radio Arc NTFs using an Australian Telescope Compact Array data set covering the continuous frequency range from ∼4 to 11 GHz at a spectral resolution of 2 MHz. We fit depolarization models to the spectral polarization data to characterize Faraday effects along the line of sight. We assess whether structures local to the Radio Arc NTFs may contribute to the unusual magnetic field orientation. External Faraday effects are identified as the most likely origin of the rotation observed for the Radio Arc NTFs; however, internal Faraday effects are also found to be likely in regions of parallel magnetic field. The increased likelihood of internal Faraday effects in parallel magnetic field regions may be attributed to the effects of structures local to the GC. One such structure could be the Radio Shell local to the Radio Arc NTFs. Future studies are needed to determine whether this alternating magnetic field pattern is present in other multi-stranded NTFs, or is a unique property resulting from the complex interstellar region local to the Radio Arc NTFs.
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A Very Large Array Study of Newly Discovered Southern Latitude Nonthermal Filaments in the Galactic Center: Radio Continuum Total-intensity and Spectral Index Properties
The nonthermal filament (NTF) radio structures clustered within a few hundred parsecs of the Galactic center (GC) are apparently unique to this region of the Galaxy. Recent radio images of the GC using MeerKAT at 1 GHz have revealed a multitude of faint, previously unknown NTF bundles (NTFBs), some of which are comprised of as many as 10 or more individual filaments. In this work we present Very Large Array observations at the
- NSF-PAR ID:
- 10385668
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 941
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 123
- Size(s):
- ["Article No. 123"]
- Sponsoring Org:
- National Science Foundation
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ABSTRACT We present a study of molecular gas, traced via CO (3–2) from Atacama Large Millimeter/submillimeter Array data, of four z < 0.2, ‘radio quiet’, type 2 quasars (Lbol ∼ 1045.3–1046.2 erg s−1; L$_{\mathrm{1.4\, GHz}}\sim 10^{23.7}\!-\!10^{24.3}$ W Hz−1). Targets were selected to have extended radio lobes (≥ 10 kpc), and compact, moderate-power jets (1–10 kpc; Pjet ∼ 1043.2–1043.7 erg s−1). All targets show evidence of central molecular outflows, or injected turbulence, within the gas discs (traced via high-velocity wing components in CO emission-line profiles). The inferred velocities (Vout = 250–440 km s−1) and spatial scales (0.6–1.6 kpc), are consistent with those of other samples of luminous low-redshift active galactic nuclei. In two targets, we observe extended molecular gas structures beyond the central discs, containing 9–53 per cent of the total molecular gas mass. These structures tend to be elongated, extending from the core, and wrap-around (or along) the radio lobes. Their properties are similar to the molecular gas filaments observed around radio lobes of, mostly ‘radio loud’, brightest cluster galaxies. They have the following: projected distances of 5–13 kpc; bulk velocities of 100–340 km s−1; velocity dispersion of 30–130 km s−1; inferred mass outflow rates of 4–20 M⊙ yr−1; and estimated kinetic powers of 1040.3–1041.7 erg s−1. Our observations are consistent with simulations that suggest moderate-power jets can have a direct (but modest) impact on molecular gas on small scales, through direct jet–cloud interactions. Then, on larger scales, jet-cocoons can push gas aside. Both processes could contribute to the long-term regulation of star formation.
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Abstract Supermassive black holes in active galactic nuclei are known to launch relativistic jets, which are observed across the entire electromagnetic spectrum and thought to be efficient particle accelerators. Their primary radiation mechanism for radio emission is polarized synchrotron emission produced by a population of nonthermal electrons. In this Letter, we present a global general relativistic magnetohydrodynamical (GRMHD) simulation of a magnetically arrested disk (MAD). After the simulation reaches the MAD state, we show that waves are continuously launched from the vicinity of the black hole and propagate along the interface between the jet and the wind. At this interface, a steep gradient in velocity is present between the mildly relativistic wind and the highly relativistic jet. The interface is, therefore, a shear layer, and due to the shear, the waves generate roll-ups that alter the magnetic field configuration and the shear layer geometry. We then perform polarized radiation transfer calculations of our GRMHD simulation and find signatures of the waves in both total intensity and linear polarization, effectively lowering the fully resolved polarization fraction. The telltale polarization signatures of the waves could be observable by future very long baseline interferometric observations, e.g., the next-generation Event Horizon Telescope.
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null (Ed.)ABSTRACT Synchrotron-emitting, non-thermal filaments (NTFs) have been observed near the Galactic centre for nearly four decades, yet their physical origin remains unclear. Here we investigate the possibility that NTFs are produced by the destruction of molecular clouds by the gravitational potential of the Galactic centre. We show that this model predicts the formation of a filamentary structure with length on the order of tens to hundreds of pc, a highly ordered magnetic field along the axis of the filament, and conditions conducive to magnetic reconnection that result in particle acceleration. This model therefore yields the observed magnetic properties of NTFs and a population of relativistic electrons, without the need to appeal to a dipolar, ∼mG, Galactic magnetic field. As the clouds can be both completely or partially disrupted, this model provides a means of establishing the connection between filamentary structures and molecular clouds that is observed in some, but not all, cases.more » « less
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