ngvla The Next Generation Very Large Array

Transcription

1 NATIONAL RADIO ASTRONOMY OBSERVATORY Fine-Scale Non-Thermal Radio Filaments Throughout the Sagittarius A Complex Fertile grounds for the ngvla M.R. Morris (UCLA), J.-H. Zhao (CfA), W.M. Goss (NRAO) ngvla The Next Generation Very Large Array

2 Fine-Scale Non-Thermal Radio Filaments Throughout the Sagittarius A Complex M.R. Morris (UCLA), J.-H. Zhao (CfA), W.M. Goss (NRAO) Using a deep, broadband 6cm observation of the Sgr A complex obtained with the A configuration of the JVLA, we have produced a very high dynamic range, wide-field image that reveals a large population of nonthermal radio filaments (NTFs). The RMS noise level throughout most of the image is 5.5 µjy/beam over a 20 x 20 pc region, low enough to expose a number of relatively faint NTFs that had not previously been noted. Near the bright central point source, Sgr A*, the RMS noise level is 21 µjy/beam, which provides the best available view of a recently reported NTF that might be physically linked to Sgr A*. With a spatial resolution of 0.44 x 0.20, the image also reveals that many of the filaments consist of at least two and sometimes a greater number of fine-scale sub-filaments. The NTFs are known to be magnetic flux tubes that are illuminated by synchrotron radiation. Several of them display a strong curvature, which we interpret as distortions of the large-scale magnetic field by collimated, high-velocity gas flows. Study of the detailed internal structure of the NTFs with the ngvla would provide valuable and needed information on how and where the synchrotron-emitting electrons are produced.

3 Outline 1. Background 2. Our focus on Sgr A region 3. Gallery 4. A remarkable filament: linked to Sgr A*? 5. Role of ngvla

4 Some background Discovered with the VLA, nonthermal radio filaments at the Galactic center have been known since the early 80 s (Yusef-Zadeh, Morris & Chance 1984) NTFs à synchrotron emitters that delineate the local magnetic field Prominent example: the Radio Arc

5 C. Lang, MRM et al. 2014

6 Some background Discovered with the VLA, nonthermal radio filaments at the Galactic center have been known since the early 80 s (Yusef-Zadeh, Morris & Chance 1984) NTFs à synchrotron emitters that delineate the local magnetic field Prominent example: the Radio Arc Many NTFs are isolated

7 Lang, MRM, Echevarria 1999

8 Some background Discovered with the VLA, nonthermal radio filaments at the Galactic center have been known since the early 80 s (Yusef-Zadeh, Morris & Chance 1984) NTFs à synchrotron emitters that delineate the local magnetic field Prominent example: the Radio Arc Many NTFs are isolated NTFs are present throughout the Central Molecular Zone

9 Non-thermal Radio Filaments at 20cm Yusef-Zadeh, Hewitt, and Cotton 1984 à Indication of a predominantly vertical, or dipolar field

10 JVLA study of Sgr A: C band A, B, and C configurations Merging in progress B + C published -- Zhao, Morris, Goss 2016

11

12

13 JVLA study of Sgr A: C band A, B, and C configurations Merging in progress B + C published -- Zhao, Morris, Goss 2016 A-array image: rms = 4.5 µjy/bm, beam = 0.44 x 0.2, dynamic range: 160,000

14 Data analysis procedure (see J.-H. Zhao+ poster) Antenna-based delays Sgr A* variability

15 A array data only

16 Sgr A East features

17 NTFs in Sgr A East 40 ~ 1.7 pc

18 The nonthermal zoo

19 The Northern Curl a strongly distorted magnetic field structure Magnetic field lines bent by collimated outflows? Note the multiplicity of the filaments To Sgr A*

20

21 The Southern Curl a larger-scale magnetic distortion Multiplicity of filamentation not a pulsar wind nebula or a supernova remnant A + B array detail

22 Note the rough point reflection symmetry of the strongly curved magnetic features, except for the scale. This suggests a directed mass outflow into an ordered field. If v Alfvén ~ several 100 km/s, The flow speed must be very high.

23 Sgr A West Sgr A West Filament Or Bent Filament as reported originally by Yusef-Zadeh et al Sgr A* VLA 6cm A-array

24 The Sgr A West Filament is non-thermal! 5.5 GHz continuum Paschen-alpha

25 Spectral index, a = 0.7 S n ~ n -a So again, nonthermal Sgr A* Sgr A* C-band A array 0.44 x 0.20 X-band A-array 0.34 x 0.17

26 Is this filament linked to Sgr A*? Sgr A*

27 Range of possibilities: The Sgr A West filament is a normal NTF that is accidentally projected near Sgr A*, AND oriented in such a way that it suggests a connection Sgr A* is feeding relativistic particles into an organized local field, and those particles are constrained to diffuse along the local flux tube Sgr A* is driving a collimated outflow that feeds into the local field Something more exotic: a captured cosmic string? à In any case, why is it one-sided?

28 Role of ngvla Spatial resolution à subfilamentation: source and evolution of the relativistic particle population Proper motions: moving field lines Resolve Alfvén waves? Time domain à brightenings due to inhomogeneities in the collimated flows Sensitivity à Deeper probe of the haystack of filaments improved characterization of the magnetic field

29 Questions?