Nonthermal filamentary radio features within 20 pc of the Galactic center

AbstractDeep imaging of the Sgr A complex at 6 cm wavelength with the B and C configurations of the Karl G. Jansky VLA† has revealed a new population of faint radio filaments. Like their brighter counterparts that have been observed throughout the Galactic center on larger scales, these filaments can extend up to ∼10 parsecs, and in most cases are strikingly uniform in brightness and curvature. Comparison with a survey of Paschen-α emission reveals that some of the filaments are emitting thermally, but most of these structures are nonthermal: local magnetic flux tubes illuminated by synchrotron emission. The new image reveals considerable filamentary substructure in previously known nonthermal filaments (NTFs). Unlike NTFs previously observed on larger scales, which tend to show a predominant orientation roughly perpendicular to the Galactic plane, the NTFs in the vicinity of the Sgr A complex are relatively randomly oriented. Two well-known radio sources to the south of Sgr A – sources E and F – consist of numerous quasi-parallel filaments that now appear to be particularly bright portions of a much larger, strongly curved, continuous, nonthermal radio structure that we refer to as the “Southern Curl”. It is therefore unlikely that sources E and F are Hii regions or pulsar wind nebulae. The Southern Curl has a smaller counterpart on the opposite side of the Galactic center – the Northern Curl – that, except for its smaller scale and smaller distance from the center, is roughly point-reflection symmetric with respect to the Southern Curl. The curl features indicate that some field lines are strongly distorted, presumably by mass flows. The point symmetry about the center then suggests that the flows originate near the center and are somewhat collimated.

Download Full-text

What are the Radio Filaments Near the Galactic Center?

Symposium - International Astronomical Union ◽

10.1017/s0074180900229756 ◽

1996 ◽

Vol 169 ◽

pp. 247-261 ◽

Cited By ~ 1

Author(s):

Mark Morris

Keyword(s):

Magnetic Field ◽

Galactic Center ◽

Galactic Plane ◽

Local Source ◽

Flux Tubes ◽

Flux Lines ◽

Magnetic Flux Tubes ◽

The Magnetic Field ◽

Relativistic Particles ◽

Projected Distance

A population of nonthermally-emitting radio filaments tens of parsecs in length has been observed within a projected distance of ∼130 pc of the Galactic center. More or less perpendicular to the Galactic plane, they appear to define the flux lines of a milligauss magnetic field. The characteristics of the known filaments are summarized. Three fundamental questions raised by these structures are discussed: 1) Do they represent magnetic flux tubes embedded within an ubiquitous, dipole magnetic field permeating the inner Galaxy, but which have been illuminated by some local source of relativistic particles, or are they instead isolated, self-sustaining current paths with an approximately force-free magnetic configuration in pressure equilibrium with the interstellar medium? 2) What is the source of either the magnetic field or the current? and 3) What is the source of the relativistic particles which provide the illuminating synchrotron radiation? We are nearer an answer to the the last of these questions than to the others, although several interesting models have been proposed.

Download Full-text

First results from the NuSTAR “mini-survey” of the Galactic center region

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314001094 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 439-443

Author(s):

Charles J. Hailey ◽

Keyword(s):

Galactic Center ◽

Galactic Plane ◽

Pulsar Wind Nebulae ◽

Telescope Array ◽

X Ray ◽

Center Region ◽

First Results ◽

Pulsar Wind ◽

Sgr A

AbstractOne of the major science objectives of the Nuclear Spectroscopic Telescope Array (NuSTAR) observatory is to perform the first sub-arcminute, hard X-ray survey of several square degrees of the Galactic plane, centered on a region near the Galactic center. As a prelude to the full survey, which began in July 2013, NuSTAR conducted a ∼500 ks, 0.3 × 0.4° “mini-survey” focused on Sgr A* and its environs. We present analysis of several candidate pulsar wind nebulae and filaments, which are revealed to be intense sources of X-ray emission at >10 keV.

Download Full-text

Ion velocity distributions within the LLBL and their possible implication to multiple reconnections

Annales Geophysicae ◽

10.5194/angeo-22-213-2004 ◽

2004 ◽

Vol 22 (1) ◽

pp. 213-236 ◽

Cited By ~ 4

Author(s):

O. L. Vaisberg ◽

L. A. Avanov ◽

T. E. Moore ◽

V. N. Smirnov

Keyword(s):

Magnetic Field ◽

Magnetic Flux ◽

Flux Tube ◽

Magnetic Flux Tube ◽

Flux Tubes ◽

Different Types ◽

Subsolar Point ◽

Magnetic Flux Tubes ◽

Ion Velocity ◽

Field Lines

Abstract. We analyze two LLBL crossings made by the Interball-Tail satellite under a southward or variable magnetosheath magnetic field: one crossing on the flank of the magnetosphere, and another one closer to the subsolar point. Three different types of ion velocity distributions within the LLBL are observed: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counter-streaming components of magnetosheath-type, and (c) distributions with three components, one of which has nearly zero parallel velocity and two counter-streaming components. Only the (a) type fits to the single magnetic flux tube formed by reconnection between the magnetospheric and magnetosheath magnetic fields. We argue that two counter-streaming magnetosheath-like ion components observed by Interball within the LLBL cannot be explained by the reflection of the ions from the magnetic mirror deeper within the magnetosphere. Types (b) and (c) ion velocity distributions would form within spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath and from magnetospheric plasma. The shapes of ion velocity distributions and their evolution with decreasing number density in the LLBL indicate that a significant part of the LLBL is located on magnetic field lines of long spiral flux tube islands at the magnetopause, as has been proposed and found to occur in magnetopause simulations. We consider these observations as evidence for multiple reconnection Χ-lines between magnetosheath and magnetospheric flux tubes. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; solar wind-magnetosphere interactions)

Download Full-text

7.13. The Sgr A East HII complex and associated features

Symposium - International Astronomical Union ◽

10.1017/s0074180900085090 ◽

1998 ◽

Vol 184 ◽

pp. 317-318 ◽

Cited By ~ 4

Author(s):

Keven I. Uchida ◽

Mark R. Morris ◽

Gene Serabyn ◽

David Fong ◽

Thomas Meseroll

Keyword(s):

Star Formation ◽

Massive Star ◽

Galactic Center ◽

Galactic Plane ◽

Alternative Hypothesis ◽

Rapid Expansion ◽

H Ii Regions ◽

Expansion Time ◽

Sgr A ◽

Relativistic Particles

The Sgr A East H ii complex consists of 4 compact H ii regions situated just east of and following, in an arc pattern, the edge of the Sgr A East nonthermal shell. Located between the arc of H ii regions and the nonthermal shell is a dense molecular ridge – presumably compressed – known as the “50 km/s cloud”. The hypothesis that these H ii regions delineate massive star formation provoked by the rapid expansion of Sgr A East into the molecular cloud is problematical because of the mismatch of the shell expansion and star formation time scales. We therefore examine the alternative hypothesis that Sgr A East is a quasi-static or slowly expanding structure fed from within by the release of relativistic particles from sources at or near the nucleus. The elongation of SgrA East along the Galactic plane is ascribed to the shear inherent in the velocity field this close to the Galactic center (GC). In this proceeding we discuss our ongoing efforts to model the effects of shear in detail, using the elongation of Sgr A East to constrain its expansion time scale.

Download Full-text

Detailed distributions of the CO J = (2 − 1)/J = (1 − 0) intensity ratios toward a large area of the central molecular zone

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000295 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 106-108

Author(s):

Kazufumi Torii ◽

Rei Enokiya ◽

Yasuo Fukui ◽

Hiroaki Yamamoto ◽

Akiko Kawamura ◽

...

Keyword(s):

Angular Resolution ◽

Galactic Center ◽

Galactic Plane ◽

Area Coverage ◽

High Angular Resolution ◽

Molecular Gas ◽

Large Area ◽

First Results ◽

Intensity Ratios ◽

Sgr A

AbstractWe present the first results of the new CO J = (2 − 1) observations toward the central molecular zone (CMZ) using the NANTEN2 telescope at an angular resolution of 100″. Large area coverage of 4° × 2° in l and b and a high angular resolution of 100″ enable us to investigate detailed structures of the molecular gas in the CMZ including peculiar molecular filaments perpendicularly to the Galactic plane to b > |0.5°|. The major components of the CMZ, e.g., Sgr A, Sgr B and Sgr C cloud complexes, show high CO J = (2 − 1)/J = (1 − 0) ratios around 0.9, indicating highly excited conditions of the molecular gas, while the local foreground components show less than 0.4. The molecular filaments show the typical ratios of 0.6–0.7 indicate that they are indeed located in the Galactic center.

Download Full-text

Nonlinear theory of non-axisymmetric resonant slow waves in straight magnetic flux tubes

Journal of Plasma Physics ◽

10.1017/s0022377800008965 ◽

2000 ◽

Vol 64 (5) ◽

pp. 579-599 ◽

Cited By ~ 2

Author(s):

I. BALLAI ◽

R. ERDÉLYI ◽

M. GOOSSENS

Keyword(s):

Solar Phys ◽

Normal Component ◽

Mhd Equations ◽

Mhd Waves ◽

Mean Flow ◽

Slab Geometry ◽

Flux Tubes ◽

Magnetic Flux Tubes ◽

Field Lines ◽

Connection Formulae

Nonlinear resonant slow magnetohydrodynamic (MHD) waves are studied in weakly dissipative isotropic plasmas for a cylindrical equilibrium model. The equilibrium magnetic field lines are unidirectional and parallel with the z axis. The nonlinear governing equations for resonant slow magnetoacoustic (SMA) waves are derived. Using the method of matched asymptotic expansions inside and outside the narrow dissipative layer, we generalize the connection formulae for the Eulerian perturbation of the total pressure and for the normal component of the velocity. These nonlinear connection formulae in dissipative cylindrical MHD are an important extention of the connection formulae obtained in linear ideal MHD [Sakurai et al., Solar Phys. 133, 227 (1991)], linear dissipative MHD [Goossens et al., Solar Phys. 175, 75 (1995); Erdélyi, Solar Phys. 171, 49 (1997)] and in nonlinear dissipative MHD derived in slab geometry [Ruderman et al., Phys. Plasmas4, 75 (1997)]. These generalized connection formulae enable us to connect the solutions at both sides of the dissipative layer without solving the MHD equations in the dissipative layer. We also show that the nonlinear interaction of harmonics in the dissipative layer is responsible for generating a parallel mean flow outside the dissipative layer.

Download Full-text

Tracing the Milky Way’s Vestigial Nuclear Jet

The Astrophysical Journal ◽

10.3847/1538-4357/ac224f ◽

2021 ◽

Vol 922 (2) ◽

pp. 254

Author(s):

Gerald Cecil ◽

Alexander Y. Wagner ◽

Joss Bland-Hawthorn ◽

Geoffrey V. Bicknell ◽

Dipanjan Mukherjee

Keyword(s):

Galactic Center ◽

Galactic Plane ◽

Hubble Space Telescope ◽

Seyfert Galaxy ◽

Radio Continuum ◽

X Ray ◽

Multiple Paths ◽

Ngc 1068 ◽

Sgr A ◽

Hydrodynamical Simulations

Abstract MeerKAT radio continuum and XMM-Newton X-ray images have recently revealed a spectacular bipolar channel at the Galactic Center that spans several degrees (∼0.5 kpc). An intermittent jet likely formed this channel and is consistent with earlier evidence of a sustained, Seyfert-level outburst fueled by black hole accretion onto Sgr A* several Myr ago. Therefore, to trace a now weak jet that perhaps penetrated, deflected, and percolated along multiple paths through the interstellar medium, relevant interactions are identified and quantified in archival X-ray images, Hubble Space Telescope Paschen α images and Atacama Large Millimeter/submillimeter Array millimeter-wave spectra, and new SOAR telescope IR spectra. Hydrodynamical simulations are used to show how a nuclear jet can explain these structures and inflate the ROSAT/eROSITA X-ray and Fermi γ-ray bubbles that extend ± 75° from the Galactic plane. Thus, our Galactic outflow has features in common with energetic, jet-driven structures in the prototypical Seyfert galaxy NGC 1068.

Download Full-text

Filamentary Structures Near the Galactic Center

Symposium - International Astronomical Union ◽

10.1017/s0074180900186590 ◽

1989 ◽

Vol 136 ◽

pp. 243-263 ◽

Cited By ~ 9

Author(s):

F. Yusef-Zadeh

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Galactic Center ◽

Galactic Plane ◽

Galactic Rotation ◽

Physical Interaction ◽

Magnetic Structures ◽

The Galaxy ◽

Field Lines ◽

The Magnetic Field

Recent studies of the Galactic center environment have revealed a wealth of new thermal and nonthermal features with unusual characteristics. A system of nonthermal filamentary structures tracing magnetic field lines are found to extend over 200pc in the direction perpendicular to the Galactic plane. Ionized structures, like nonthermal features, appear filamentary and show forbidden velocity fields in the sense of Galactic rotation and large line widths. Faraday rotation characteristics and the flat spectral index distributions of the nonthermal filaments suggest a mixture of thermal and nonthermal gas. Furthermore, the relative spatial distributions of the magnetic structures with respect to those of the ionized and molecular gas suggest a physical interaction between these two systems. In spite of numerous questions concerning the origin of the large-scale organized magnetic structures, the mechanism by which particles are accelerated to relativistic energies, and the source or sources of heating the dust and gas, recent studies have been able to distinguish the inner 200pc of the nucleus from the disk of the Galaxy in at least two more respects: (1) the recognition that the magnetic field has a large-scale structure and is strong, uniform and dynamically important; and (2) the physics of interstellar matter may be dominated by the poloidal component of the magnetic field.

Download Full-text

Micro-arcsecond astrometry with the VLBA

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308018929 ◽

2007 ◽

Vol 3 (S248) ◽

pp. 141-147 ◽

Cited By ~ 2

Author(s):

M. J. Reid

Keyword(s):

Galactic Center ◽

Galactic Plane ◽

Proper Motions ◽

Star Forming ◽

Star Forming Regions ◽

The Galaxy ◽

Trigonometric Parallaxes ◽

Sgr A ◽

Definition Of ◽

Almost All

AbstractThe VLBA is now achieving parallaxes and proper motions with accuracies approaching the micro-arcsecond domain. The apparent proper motion of Sgr A*, which reflects the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0/R0 and offers a dynamical definition of the Galactic plane with Sgr A*at its origin. The intrinsic motion of Sgr A*is very small and comparable to that expected for a supermassive black hole. Trigonometric parallaxes and proper motions for a number of massive star forming regions (MSFRs) have now been measured. For almost all cases, kinematic distances exceed the true distances, suggesting that the Galactic parameters, R0 and Θ0, are inaccurate. Solutions for the Solar Motion are in general agreement with those obtained from Hipparcos data, except that MSFRs appear to be rotating slower than the Galaxy. Finally, the VLBA has been used to measure extragalactic proper motions and to map masers in distant AGN accretion disks, which will yield direct estimates of H0.

Download Full-text

The Herschel view of the Galactic center

Proceedings of the International Astronomical Union ◽

10.1017/s174392131400009x ◽

2013 ◽

Vol 9 (S303) ◽

pp. 1-14

Author(s):

John Bally ◽

Keyword(s):

Star Formation ◽

Massive Star ◽

Galactic Center ◽

Galactic Plane ◽

Formation Rate ◽

Asymmetric Distribution ◽

The Galaxy ◽

Sgr A ◽

Almost All

AbstractThe 3.5 meter diameter Herschel Space Observatory conducted a ∼720 square-degree survey of the Galactic plane, the Herschel Galactic plane survey (Hi-GAL). These data provide the most sensitive and highest resolution observations of the far-IR to sub-mm continuum from the central molecular zone (CMZ) at λ = 70, 160, 250, 350, and 500 μm obtained to date. Hi-GAL can be used to map the distributions of temperature and column density of dust in CMZ clouds, warm dust in Hii regions, and identify highly embedded massive protostars and clusters and the dusty shells ejected by supergiant stars. These data enable classification of sources and re-evaluation of the current and recent star-formation rate in the CMZ. The outer CMZ beyond |l| = 0.9 degrees (Rgal > 130 pc) contains most of the dense (n > 104 cm−3 gas in the Galaxy but supports very little star formation. The Hi-GAL and Spitzer data show that almost all star formation occurs in clouds moving on x2 orbits at Rgal < 100 pc. While the 106 M⊙ Sgr B2 complex, the 50 km s−1 cloud near Sgr A, and the Sgr C region are forming clusters of massive stars, other clouds are relatively inactive star formers, despite their high densities, large masses, and compact sizes. The asymmetric distribution of dense gas about Sgr A* on degree scales (most dense CMZ gas and dust is at positive Galactic longitudes and positive VLSR) and compact 24 μm sources (most are at negative longitudes) may indicate that eposidic mini-starbursts occasionally ‘blow-out’ a portion of the gas on these x2 orbits. The resulting massive-star feedback may fuel the compact 30 pc scale Galactic center bubble associated with the Arches and Quintuplet clusters, the several hundred pc scale Sofue-Handa lobe, and the kpc-scale Fermi/LAT bubble, making it the largest ‘superbubble’ in the Galaxy. A consequence of this model is that in our Galaxy, instead of the supermassive black hole (SMBH) limiting star formation, star formation may limit the growth of the SMBH.

Download Full-text