scholarly journals Mid-Infrared Observations of the Galactic Center Arc and the Sgr A East HII Region

1989 ◽  
Vol 136 ◽  
pp. 287-292 ◽  
Author(s):  
F. Yusef-Zadeh ◽  
C. M. Telesco ◽  
R. Decher
Keyword(s):  
Galactic Center ◽  
Hii Regions ◽  
Radio Continuum ◽  
Radio Flux ◽  
Ir Camera ◽  
Hii Region ◽  
Sgr A ◽  
5 Ghz ◽  
Almost All ◽  
Ir Emission

We have used the 20-pixel IR camera to observe thermal IR emission from dust associated with the radio continuum Arc near the Galactic center and the cluster of HII regions in the immediate vicinity of Sgr A East. We detected strong 10μm emission from the eastern and western arched filaments (G0.1+0.08), from an unusual pistol-shaped structure known as G0.15–0.05 and from the brightest member of the Sgr A East HII region. Spatial maps of these features at 10μm with a resolution of 4.1″ × 4.2″ are presented and are compared with 5-GHz radio images. We find a general spatial correlation between the ionized gas and the dust distributions. The ratio of IR to radio flux densities is significantly different in the eastern and western arched filaments, which suggests that the source of heating has a softer spectrum along the eastern arched filaments. In addition, the ratio of IR to radio flux densities, which is typically ~10 in normal Galactic HII regions excited by O stars, is at least a factor of two higher than this value in almost all the sources we have observed. This suggests that additional mechanisms other than trapped Lymanαradiation should be present in heating the dust, e.g. stochastic heating of small dust grains by energetic particles associated with the nonthermal filaments.

scholarly journals 158μm [CII] Mapping of the Galactic Center Molecular Clouds

1989 ◽  
Vol 136 ◽  
pp. 151-155
Author(s):  
R. Genzel ◽  
G. J. Stacey ◽  
C. H. Townes ◽  
A. Poglitsch ◽  
N. Geis
Keyword(s):  
Emission Line ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Hii Regions ◽  
Radio Continuum ◽  
Large Intensity ◽  
Sgr A

We have made 55″ resolution maps of the 158 μm [CII] emission line in the region of the curved, thermal filaments and the +20 / +50 kms−1 molecular clouds in Sgr A. The [CII] emission is spatially well correlated with the radio continuum in the filaments. The large intensity of the [CII] radiation excludes shocks as the origin of the ionization and we conclude that the curved filaments are most likely photo-ionized HII regions at the surface of dense molecular clouds. Our [CII] maps of the +20 / +50 kms−1 clouds indicate that the +50 kms−1 cloud is close to (<10pc) Sgr A west while the more massive +20 kms−1 cloud is at a greater distance from the center (>30pc).

scholarly journals Long-Term Variations of the Compact Radio Source Sgr A∗ at the Galactic Center

1989 ◽  
Vol 136 ◽  
pp. 535-541 ◽  
Author(s):  
Jun-Hui Zhao ◽  
R. D. Ekers ◽  
W. M. Goss ◽  
K. Y. Lo ◽  
Ramesh Narayan
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
High Velocity ◽  
Galactic Center ◽  
Light Curves ◽  
Radio Flux ◽  
Compact Radio Source ◽  
Sgr A ◽  
Long Term Variations

We investigate the long-term flux density variations of the compact radio source Sgr A∗ at the galactic center by combining recent VLA observations with previous Green Bank interferometer data. We present radio flux density light-curves for Sgr A∗ at 20, 11, 6 and 3.7 cm from 1974 to 1987. Long-term variability with a timescale of at least 5 years is seen at 20 cm and there is evidence for more rapid variations at the shorter wavelengths. The variability timescales at 20, 11 and 6 cm fit the λ2 scaling predicted by the theory of refractive scintillation suggesting that the variability could be due to this cause. However, the timescales are relatively short, implying an unusually high velocity in the scattering screen. The modulation index of the variability is large and relatively independent of wavelength.

scholarly journals Radio Continuum Emission from the Nuclei of Normal Galaxies

1980 ◽  
Vol 5 ◽  
pp. 177-184 ◽  
Author(s):  
J. M. van der Hulst
Keyword(s):  
Radio Emission ◽  
Galactic Center ◽  
Galactic Nuclei ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Thermal Source ◽  
Very Large Array ◽  
Normal Galaxies ◽  
The Galaxy ◽  
Sgr A

During the last few years detailed and sensitive observations of the radio emission from the nuclei of many normal spiral galaxies has become available. Observations from the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO1), in particular, enable us to distinguish details on a scale of ≤100 pc for galaxies at distances less than 21 Mpc. The best studied nucleus, however, still is the center of our own Galaxy (see Oort 1977 and references therein). Its radio structure is complex. It consists of an extended non-thermal component 200 × 70 pc in size, with embedded therein several giant HII regions and the central source Sgr A (˜9 pc in size). Sgr A itself consists of a thermal source, Sgr A West, located at the center of the Galaxy, and a weaker, non-thermal source, Sgr A East. Sgr A West moreover contains a weak, extremely compact (≤10 AU) source. The radio morphology of several other galactic nuclei is quite similar to that of the Galactic Center, as will be discussed in section 2. Recent reviews of the radio properties of the nuclei of normal galaxies have been given by Ekers (1978a,b) and De Bruyn (1978). The latter author, however, concentrates on galaxies with either active nuclei or an unusual radio morphology. In this paper I will describe recent results from the Westerbork Synthesis Radio Telescope (WSRT, Hummel 1979), the NRAO 3-element interferometer (Carlson, 1977; Condon and Dressel 1978), and the VLA (Heckman et al., 1979; Van der Hulst et al., 1979). I will discuss the nuclear radio morphology in section 2, the luminosities in section 3, and the spectra in section 4. In section 5 I will briefly comment upon the possible implications for the physical processes in the nuclei that are responsible for the radio emission.

scholarly journals RADIO CONTINUUM OBSERVATIONS OF THE GALACTIC CENTER: PHOTOEVAPORATIVE PROPLYD-LIKE OBJECTS NEAR SGR A*

2015 ◽  
Vol 801 (2) ◽  
pp. L26 ◽  
Author(s):  
F. Yusef-Zadeh ◽  
D. A. Roberts ◽  
M. Wardle ◽  
W. Cotton ◽  
R. Schödel ◽  
...  
Keyword(s):  
Galactic Center ◽  
Radio Continuum ◽  
Sgr A

scholarly journals A Survey of Radio Recombination Line Emission From the Galactic Center Region

1989 ◽  
Vol 136 ◽  
pp. 159-166 ◽  
Author(s):  
K. R. Anantharamaiah ◽  
Farhad Yusef-Zadeh
Keyword(s):  
Galactic Center ◽  
Line Emission ◽  
Radio Continuum ◽  
Strong Line ◽  
Line Profiles ◽  
Ionized Gas ◽  
Center Region ◽  
Radio Recombination Line ◽  
Nonthermal Emission ◽  
Sgr A

Preliminary results of a systematic survey of H78α, H91α and H98β emission from the inner 40′ of the Galactic center region are presented. This region consists of two prominent continuum features, the Sgr A complex and the radio continuum Arc. In spite of much nonthermal emission arising from these two features, we detected strong line emission with large line widths in more than half of the observed 130 positions. Many of the detections are new, in particular −50 km s−1 ionized gas linking the Sgr A complex and the Arc, β line emission from GO.1+0.08 (the arched filaments), and α line emission from the loop-like structures which surround the non-thermal filaments near G0.2−0.05. We find that much of the detected lines are probably associated with the −50 km s−1 and the 20 km s−1 molecular clouds, known to lie near the Galactic center. We present line profiles of a number of Galactic center sources including Sgr B1, Sgr C and Sgr D.

scholarly journals Giant H II Regions in M81

1986 ◽  
Vol 116 ◽  
pp. 503-504 ◽  
Author(s):  
Michele Kaufman ◽  
R. C. Kennicutt ◽  
F. N. Bash
Keyword(s):  
Star Formation ◽  
Hii Regions ◽  
Radio Continuum ◽  
H Ii Regions ◽  
Hii Region ◽  
Distant Galaxies ◽  
Flux Measurements ◽  
Selection Of

Giant HII regions are important tracers of recent star formation in distant galaxies. For a selection of HII regions in our galaxy where the exciting stars can be identified, Rumstay (1985) finds that the measured Hα and radio continuum luminosities of an HII region correlate with the stellar ionizing flux derived from model atmospheres and the known exciting stars. Therefore, we use flux measurements of giant HII regions as an index of the distribution of O stars in M81.

scholarly journals Tracing the Milky Way’s Vestigial Nuclear Jet

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.

scholarly journals Micro-arcsecond astrometry with the VLBA

2007 ◽  
Vol 3 (S248) ◽  
pp. 141-147 ◽  
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.

scholarly journals SiO and H2O Masers in the Central Parsec of the Galaxy

1998 ◽  
Vol 164 ◽  
pp. 229-230 ◽  
Author(s):  
Karl M. Menten ◽  
Mark J. Reid
Keyword(s):  
Galactic Center ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Proper Motions ◽  
Infrared Images ◽  
Evolved Stars ◽  
The Galaxy ◽  
Sgr A ◽  
Central Parsec ◽  
Infrared Sources

AbstractWe have discovered maser emission from SiO and H2O molecules toward a number of evolved stars within the central parsec of our Galaxy. The maser positions can be registered with milliarcsecond precision relative to the radio continuum emission of the nonthermal Galactic center source Sgr A*. Since the masing stars are prominent infrared sources, our data can be used to locate the position of Sgr A* on infrared images of the Galactic center region. Using VLBA observations it will be possible to measure proper motions of the maser stars, which can be used to put constraints on the mass distribution in the central parsec.

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