scholarly journals The Galactic Center

1984 ◽  
Vol 110 ◽  
pp. 265-273
Author(s):  
K. Y. Lo
Keyword(s):  
High Resolution ◽  
Radio Source ◽  
Galactic Center ◽  
Minor Axis ◽  
Ionized Gas ◽  
Nonthermal Radio ◽  
The Galaxy ◽  
First Time ◽  
Source Structure

The center of our Galaxy contains an extremely compact nonthermal radio source. For the first time, elongation in the source structure has been detected. The long axis is nearly aligned with the minor axis of the Galaxy. Recent high resolution observations of the ionized gas within the central 3 parsecs suggest that matter may be falling in towards the center. This has interesting implications on the processes within our Galactic nucleus.

scholarly journals The Compact Nonthermal Radio Source at the Galactic Center: an Update

1989 ◽  
Vol 136 ◽  
pp. 527-534
Author(s):  
K. Y. Lo
Keyword(s):  
Radio Source ◽  
Galactic Center ◽  
Central Star ◽  
Radio Sources ◽  
Stellar Objects ◽  
Nonthermal Radio ◽  
Compact Radio Source ◽  
The Galaxy ◽  
Observational Status ◽  
Sgr A

We review the current observational status of Sgr A∗, the compact nonthermal radio source at the galactic center. Sgr A∗ is a unique radio source at a unique location of the Galaxy. It is unlike any compact radio source associated with known stellar objects, but it is similar to extragalactic nuclear compact radio sources. The positional offset between Sgr A∗ and IRS16 places little constraint on the nature of the underlying energy source, since IRS16 need not be the core of the central star cluster. Sgr A∗ is still the best candidate for marking the location of a massive collapsed object.

scholarly journals 10.4. Multi-wavelength VLBA mapping of Sgr A∗

1998 ◽  
Vol 184 ◽  
pp. 437-438
Author(s):  
Zhi-Qiang Shen ◽  
K. Y. Lo ◽  
Jun-Hui Zhao ◽  
Paul Ho
Keyword(s):  
Energy Source ◽  
Black Hole ◽  
Radio Source ◽  
Radio Sources ◽  
Massive Black Hole ◽  
Nonthermal Radio ◽  
The Galaxy ◽  
Multi Wavelength ◽  
Sgr A ◽  
Source Structure

Sgr A∗, the enigmatic compact nonthermal radio source located at the center of the Galaxy for many years has been considered as the signpost of a massive black hole (Rees 1982; Lo 1986; Falcke et al. 1997). Its properties are unique in the Galaxy, but it resembles other nuclear radio sources (Lo 1993). Efforts to delineate the source structure of Sgr A∗, in order to constraint the nature of the underlying energy source, have been ongoing since 1975 (Lo et al. 1975).

scholarly journals 7.15. The Fourier analysis of the observed velocity field of gas in the inner 1.5 pc of the Galaxy

1998 ◽  
Vol 184 ◽  
pp. 321-324
Author(s):  
A.M. Fridman ◽  
V.V. Lyakhovich ◽  
O.V. Khoruzhii ◽  
O.K. Silchenko
Keyword(s):  
Velocity Field ◽  
Fourier Analysis ◽  
Galactic Center ◽  
Second Harmonic ◽  
Density Wave ◽  
Ionized Gas ◽  
Density Maximum ◽  
Fourier Harmonic ◽  
Wave Nature ◽  
The Galaxy

The Fourier analysis of the observed velocity field of ionized gas in the inner 1.5 pc of the Galactic Center (obtained by Roberts and Goss, 1993) is made. As follows from the analysis, the observed field of residual velocities is dominated by the second Fourier harmonic. This fact can be treated as a consequence of the presence of an one-armed density wave with the density maximum along the Northern Arm plus the Western Arc structure. The wave nature of this structure is proved on the base of the behaviour of the phase of the second harmonic of line-of-sight velocity field in the whole region. The Fourier analysis shows also the presence of systematic radial velocity. We consider this flow as a quasi-stationary radial drift caused by one-armed nonlinear density wave (‘mini-spiral’).

The galactic center compact nonthermal radio source

1987 ◽  
Author(s):  
K. Y. Lo
Keyword(s):  
Radio Source ◽  
Galactic Center ◽  
Nonthermal Radio

scholarly journals Radio Emission from the Seyfert Galaxy NGC 5548

1982 ◽  
Vol 97 ◽  
pp. 191-192
Author(s):  
J. S. Ulvestad ◽  
A. S. Wilson ◽  
D. G. Wentzel
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Radio Source ◽  
Seyfert Galaxy ◽  
Central Component ◽  
The Galaxy ◽  
Ngc 5548

Weak radio emission from the type 1.5 Seyfert galaxy NGC 5548 has been mapped with high resolution at the VLA at both 1465 and 4885 MHz. The galaxy contains the largest (5.9 kpc) triple radio source known in a Seyfert galaxy. The central component of that triple is unresolved (<0.39×0.15 kpc) and has a flatter spectrum than the well-resolved outer lobes. In addition, the field surrounding NGC 5548 and two of the sources in that field have been mapped at 1465 MHz; the field sources are unlikely to be physically associated with NGC 5548.

scholarly journals Extreme Emission Line Outflows in the GPS Source 4C 12.50 (PKS 1345+12)

2003 ◽  
Vol 20 (1) ◽  
pp. 25-27 ◽  
Author(s):  
J. Holt ◽  
C. N. Tadhunter ◽  
R. Morganti
Keyword(s):  
High Resolution ◽  
Emission Line ◽  
Radio Source ◽  
Spectral Coverage ◽  
La Palma ◽  
Upper Limit ◽  
Line Region ◽  
The Galaxy ◽  
William Herschel

AbstractWe present high resolution spectra (0.7 Å/pix) of the GPS source 4C 12.50 with large spectral coverage (˜4500 Å) taken with the 4.2 m William Herschel Telescope, La Palma. The slit was aligned along PA 160° to include the nucleus and emission line region to the NW. An asymmetric halo extending 20 kpc NW and 12 kpc SE from the nucleus is clearly seen. At the position of the nucleus we observe unusually broad forbidden emission line components (broadest component: FWHM ˜ 2000 km s−1), blue shifted by up to 2000 km s−1 with respect to the halo of the galaxy and HI absorption. We interpret this as material in outflow. We measure E(B–V) = 1.44 for the broadest, most kinematically disturbed component, corresponding to an actual Hβ flux 130 times brighter than that measured. We calculate an upper limit for the mass of the line emitting gas of order 106 M⊙ for both the intermediate and broad components. Our results are consistent with 4C 12.50 being a young radio source.

The Population I Core of the Galaxy

1994 ◽  
Vol 11 (2) ◽  
pp. 191-193 ◽  
Author(s):  
David Allen ◽  
Michael Burton
Keyword(s):  
Mass Loss ◽  
Radio Source ◽  
Galactic Centre ◽  
Overtone Band ◽  
Nonthermal Radio ◽  
The Galaxy ◽  
Sgr A

Abstract We demonstrate the presence of a cluster of hot, population I stars at the very centre of the Galaxy, using the depth of the first overtone band of CO and the presence of emission in He I 2 ·058 μm and [Fell] 1·644μm to identify stars. The cluster is very compact and comprises at least several hundred stars. They lie close to the nonthermal radio source Sgr A* and dominate the luminosity and mass loss of the Galactic core. Their presence suggests that a starburst occurred at the Galactic centre.

scholarly journals G359.3–0.82: An Unusual Radio Source

1989 ◽  
Vol 136 ◽  
pp. 197-204
Author(s):  
F. Yusef-Zadeh ◽  
F. Yusef-Zadeh
Keyword(s):  
Radio Emission ◽  
Interstellar Medium ◽  
Radio Source ◽  
Relative Velocity ◽  
Galactic Center ◽  
Extragalactic Radio Source ◽  
Compact Source ◽  
Nonthermal Radio ◽  
Galactic Object

An unusual radio source exhibiting an axisymmetric, cometary morphology was recently reported by Yusef-Zadeh and Bally (1987) near the Galactic center. This source, G359.3–0.82, consists of a bright head containing a compact source followed by a tail exhibiting sinuous structure. Radio emission is highly polarized and has a nearly flat spectrum between λ6cm and λ20cm. Its location in the sky, spectrum, and lack of resemblance to any other extragalactic radio source suggested to us that this radio source is a Galactic object possibly lying near the Galactic center. New high-reslolution radio images obtained using the VLA confirm the remarkable morphology and strengthen the distinction between G359.3–0.82 and any known extragalactic radio source. The characteristics of G359.3–0.82 suggest that it may be a nonthermal radio wake produced by an object moving through the interstellar medium at a high relative velocity.

scholarly journals A Possible Nova from the IRAS Point Source Catalogue

1990 ◽  
Vol 122 ◽  
pp. 55-56
Author(s):  
P. Garcia-Lario ◽  
A. Manchado ◽  
K.C. Sahu ◽  
S.R. Pottasch
Keyword(s):  
High Resolution ◽  
Galactic Center ◽  
High Resolution Spectrum ◽  
Mean Velocity ◽  
Infrared Excess ◽  
The Galaxy ◽  
Balmer Lines ◽  
The Common ◽  
Rich Material ◽  
Infrared Data

AbstractDuring a spectroscopic survey of IRAS sources with infrared colours similar to those in planetary nebulae, IRAS 06518-1041 revealed itself as a possible nova-like object. The spectrum of IRAS 06518 – 1041, which is shown in Figure 1, presents strong and broad hydrogen Balmer lines together with broad permitted lines of He and C. This spectrum also shows a much weaker narrow nebular component, with forbidden lines of [OIII] and narrow Hα. The mean velocity associated to the observed line widths is about 800 km s−1. The observed emission lines correspond well to typical post-novae objects in the quiescent phase (Warner, 1989). Another argument which supports the idea of this object being a nova-like star is that there are some indications of the binarity of the source if we attend to the asymmetries observed both in the Hβ and Hα profiles. The high resolution spectrum at Hα shows the presence of a sharp double-peaked central emission from a low expanding envelope at a velocity of 35±5 km s−1, together with a much broader emission with velocities of several hundred kilometers. The displacement between both components is about 130 km s−1. This broad component could be due to the presence of an accretion disk around the system with hydrogen-rich material falling onto the compact companion. This is supported by the fact that the broad emission looks like the combination of different velocity components giving rise to a complex and asymmetric line profile. From this high resolution spectrum we derive a VLSR = 57 km s−1, which points to a distance of 5.5 kpc if we adopt the model rotation curve of the Galaxy given by Pottasch (1984) and a distance of 9 kpc from the Sun to the galactic center. The large infrared excess detected by the IRAS satellite is probably the result of the formation of dust grains in the outer parts of the common envelope at a temperature of about 160 K, as can be derived from the infrared data. This infrared excess is also present in other nova-like objects and is specially important in old and slow novae (Callus et al, 1987) where the continuous ejection of mass produces dust shells which are strong emitters in the infrared.

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