Radio studies of the Galactic center. I - The Sagittarius A complex

Pedlar, A.; Anantharamaiah, K. R.; Ekers, R. D.; Goss, W. M.; Gorkom, J. H. van; Schwarz, U. J.; Zhao, Jun‐Hui

doi:10.1086/167635

Cited by 132 publications

(187 citation statements)

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“…The nonthermal radio source Sgr A East is a young shelltype SNR with an angular size of 2 7×3 6 and a spectral index α = 0.76, where the flux density S ν ∝ν − α (Ekers et al 1983;Yusef-Zadeh & Morris 1987;Pedlar et al 1989). Thermal X-ray emission is concentrated in the interior of the remnant, suggesting that Sgr A East is a mixed morphology SNR interacting with the 50 km s −1 molecular cloud (Maeda et al 2002;Park et al 2005).…”

Section: Sgr a East Towermentioning

confidence: 99%

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SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

Yusef‐Zadeh

Wardle

Schödel

et al. 2016

ApJ

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We present high-resolution multiwavelength radio continuum images of the region within 150″ of SgrA * , revealing a number of new extended features and stellar sources in this region. First, we detect a continuous 2″ east-west ridge of radio emission, linking SgrA * and a cluster of stars associated with IRS 13 N and IRS 13E. The ridge suggests that an outflow of east-west blob-like structures is emerging from SgrA * . In particular, we find arc-like radio structures within the ridge with morphologies suggestive of photoevaporative protoplanetary disks. We use infrared K s and L′ fluxes to show that the emission has similar characteristics to those of a protoplanetary disk irradiated by the intense radiation field at the Galactic center. This suggests that star formation has taken place within the S-cluster 2″ from SgrA * . We suggest that the diffuse X-ray emission associated with Sgr A * is due to an expanding hot wind produced by the mass loss from B-type main sequence stars, and/or the disks of photoevaporation of low mass young stellar objects (YSOs) at a rate of ∼10 −6  M yr −1 . The proposed model naturally reduces the inferred accretion rate and is an alternative to the inflow-outflow style models to explain the underluminous nature of Sgr A * . Second, on a scale of 5″ from Sgr A * , we detect new cometary radio and infrared sources at a position angle PA∼50°which is similar to that of two other cometary sources X3 and X7, all of which face Sgr A * . In addition, we detect a striking tower of radio emission at a PA∼50°-60°along the major axis of the Sgr A East supernova remnant shell on a scale of 150″ from Sgr A * . We suggest that the cometary sources and the tower feature are tracing interaction sites of a mildly relativistic jet from Sgr A * with the atmosphere of stars and the nonthermal Sgr A East shell at a PA∼50°-60°with´-, and opening angle 10°. Lastly, we suggest that the east-west ridge of radio emission traces an outflow that is potentially associated with past flaring activity from Sgr A * . The position angle of the outflow driven by flaring activity is close to −90°.

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Section: Sgr a East Towermentioning

confidence: 99%

“…This picture implies that Sgr A East lies close to Sgr A * . The absorption of Sgr A West against Sgr A East (YusefZadeh & Morris 1987; Pedlar et al 1989) suggest that the NE jet must be moving away from us to be interacting with the shell of Sgr A East.…”

Section: The Sgr a East Towermentioning

confidence: 99%

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

Yusef‐Zadeh

Wardle

Schödel

et al. 2016

ApJ

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“…In the VLA 90 cm radio continuum image of Pedlar et al (1989), the Sgr A East shell has projected dimensions ≈3. 3 × 2.…”

Section: The Sgr a East Snrmentioning

confidence: 99%

Interstellar gas within ~10 pc of Sagittarius A^∗

Ferrière

2012

A&A

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Aims. We seek to obtain a coherent and realistic three-dimensional picture of the interstellar gas out to about 10 pc of the dynamical center of our Galaxy, which is supposed to be at Sgr A * . Methods. We review the existing observational studies on the different gaseous components that have been identified near Sgr A * , and retain all the information relating to their spatial configuration and/or physical state. Based on the collected information, we propose a three-dimensional representation of the interstellar gas, which describes each component in terms of both its precise location and morphology and its thermodynamic properties. Results. The interstellar gas near Sgr A * can be represented by five basic components, which are, by order of increasing size: (1) a central cavity with roughly equal amounts of warm ionized and atomic gases; (2) a ring of mainly molecular gas; (3) a supernova remnant filled with hot ionized gas; (4) a radio halo of warm ionized gas and relativistic particles; and (5) a belt of massive molecular clouds. While the halo gas fills ≈80% of the studied volume, the molecular components enclose ≈98% of the interstellar mass.

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“…The nonthermal radio emission from Sgr A East in the direction of Sgr A West is very faint, mainly because of the heavy absorption by the spiral-shaped group of thermal gas streams called the minispiral (Yusef-Zadeh & Morris 1987;Pedlar et al 1989;Anantharamaiah et al 1999). These authors also reported that a turnover (absorption) occurs at 90 cm from both Sgr A East and West, which suggests the presence of an ionized gas halo extending over the Sgr A complex.…”

Section: Dynamical Evolution I: Forward Shock and Ambient Environmentmentioning

confidence: 99%

“…The nondetection of X-rays from the radio shell and the steep synchrotron radio spectrum are both understood simply in terms of radiative energy loss (Pedlar et al 1989). Melia, Yusef-Zadeh, & Fatuzzo (1998) suggested the possibility that infrared light from Sgr A West might be Comptonized within the radio shell to the hard Xray band with a fairly high luminosity of L X ' 2 Â 10 35 ergs s À1 .…”

Section: X-ray Gasmentioning

confidence: 99%

AChandraStudy of Sagittarius A East: A Supernova Remnant Regulating the Activity of Our Galactic Center?

Maeda

Baganoff

Feigelson

et al. 2002

ApJ

191

222

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We report on the X-ray emission from the shell-like, nonthermal radio source Sgr A East (SNR 000.0+00.0), located in the inner few parsecs of the Galaxy based on observations made with the ACIS detector on board the Chandra X-Ray Observatory. This is the first time Sgr A East has been clearly resolved from other complex structures in the region. The X-ray-emitting region is concentrated within the central '2 pc of the larger radio shell. The spectrum shows strong K lines from highly ionized ions of S, Ar, Ca, and Fe. A simple isothermal plasma model gives electron temperature $2 keV, absorption column $1 Â 10 23 H cm À2 , luminosity $8 Â 10 34 ergs s À1 in the 2-10 keV band, and gas mass $2 1=2 M with a filling factor . The plasma appears to be rich in heavy elements, overabundant by roughly a factor of 4 with respect to solar abundances, and shows a spatial gradient of elemental abundance; the spatial distribution of iron is more compact than that of the lighter elements. The gas mass and elemental abundance of the X-ray emission support the long-standing hypothesis that Sgr A East is a supernova remnant (SNR), perhaps produced by the Type II supernova explosion of a massive star with a main-sequence mass of 13-20 M . The combination of the radio and X-ray morphologies classifies Sgr A East as a new metal-rich '' mixed morphology '' (MM) SNR. The size of the Sgr A East radio shell is the smallest of the known MM SNRs, which strongly suggests that the ejecta have expanded into a very dense interstellar medium. The ejecta-dominated chemical compositions of the plasma indicate that the ambient materials should be highly homogeneous. We thus evaluate a simplified dynamical evolution model where an SNR was formed about 10,000 yr ago and expanded into an ambient medium with a homogeneous density of 10 3 cm À3 . The model roughly reproduces most of the observed properties in the X-ray and radio wavelengths. A comparison with the radio observations requires the dense ambient medium to be ionized, but a luminous X-ray irradiator with an expected X-ray luminosity of $10 40 ergs s À1 is not currently present. The presence of the ionized gas may be explained if the massive black hole (MBH) associated with the compact, nonthermal radio source Sgr A* was bright in X-rays about 300 yr ago but is presently dim. It is possible that the dust/molecular ridge compressed by the forward shock of Sgr A East hit Sgr A* in the past, and the passage of the ridge may have supplied material to accrete onto the black hole in the past and may have removed material from the black hole vicinity, leading to its present quiescent state. This may be a specific example of the intimate relationship between an SNR and MBH accretion activity in galactic nuclei.

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Radio studies of the Galactic center. I - The Sagittarius A complex

Cited by 132 publications

References 0 publications

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

Interstellar gas within ~10 pc of Sagittarius A^∗

AChandraStudy of Sagittarius A East: A Supernova Remnant Regulating the Activity of Our Galactic Center?

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Radio studies of the Galactic center. I - The Sagittarius A complex

Cited by 132 publications

References 0 publications

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

Interstellar gas within ~10 pc of Sagittarius A∗

AChandraStudy of Sagittarius A East: A Supernova Remnant Regulating the Activity of Our Galactic Center?

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Interstellar gas within ~10 pc of Sagittarius A^∗