Multi-Array λ2 and 6cm Radio Continuum Observations of Sgr A West

Sub-arcsecond (down to 0.1″ × 0.2″) radio continuum observations using the VLA2 in a number of configurations have been carried out in order to investigate the fine-scale morphological details of the ionized gas and the distribution of spectral index along the triskelian-shaped figure of Sgr A West. In addition to finding a number of isolated patches of thermally-emitting gas and an absorbing feature at λ6cm within three arcminutes of the Galactic center, we have observed:1) radio continuum emission from IRS-7, implying that the stellar wind from this supergiant is externally ionized. An improved position for this object was obtained.2) the circular mini-cavity located along the east-west bar of Sgr A West. This feature has a diameter of 2-arcseconds and may have been created by a spherical wind, the source of which is yet to be identified; the seemingly most plausible candidate, IRS-16, is offset by 3″ from the center of the cavity.Spectral index maps having a resolution of 0.7″ × 0.3″ were made from scaled array observations at λ2cm and 6cm. They show that the eastern arm has a spectral index near −0.1, while the northern arm and the bar have positive spectral indices, indicating perhaps a partial opacity effect. The spectral index of IRS-7 is +0.6, consistent with that expected from a completely ionized stellar wind.

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Radio observations of evaporating objects in the Cygnus OB2 region

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935179 ◽

2019 ◽

Vol 627 ◽

pp. A58 ◽

Cited By ~ 1

Author(s):

N. L. Isequilla ◽

M. Fernández-López ◽

P. Benaglia ◽

C. H. Ishwara-Chandra ◽

S. del Palacio

Keyword(s):

Thermal Emission ◽

Radio Continuum ◽

Continuum Emission ◽

Spectral Indices ◽

Ionized Gas ◽

Low Frequencies ◽

Thermal Origin ◽

Index Maps ◽

Photoionization Rate ◽

Gas Component

We present observations of the Cygnus OB2 region obtained with the Giant Metrewave Radio Telescope (GMRT) at frequencies of 325 and 610 MHz. In this contribution we focus on the study of proplyd-like objects (also known as free-floating evaporating gas globules or frEGGs) that typically show an extended cometary morphology. We identify eight objects previously studied at other wavelengths and derive their physical properties by obtaining their optical depth at radio-wavelengths. Using their geometry and the photoionization rate needed to produce their radio-continuum emission, we find that these sources are possibly ionized by a contribution of the stars Cyg OB2 #9 and Cyg OB2 #22. Spectral index maps of the eight frEGGs were constructed, showing a flat spectrum in radio frequencies in general. We interpret these as produced by optically thin ionized gas, although it is possible that a combination of thermal emission, not necessarily optically thin, produced by a diffuse gas component and the instrument response (which detects more diffuse emission at low frequencies) can artificially generate negative spectral indices. In particular, for the case of the Tadpole we suggest that the observed emission is not of non-thermal origin despite the presence of regions with negative spectral indices in our maps.

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Radio Continuum Emission from the Nuclei of Normal Galaxies

Highlights of Astronomy ◽

10.1017/s1539299600003877 ◽

1980 ◽

Vol 5 ◽

pp. 177-184 ◽

Cited By ~ 2

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.

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Rotating ionized gas ring around the Galactic center IRS13E3

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psz089 ◽

2019 ◽

Vol 71 (5) ◽

Cited By ~ 6

Author(s):

Masato Tsuboi ◽

Yoshimi Kitamura ◽

Takahiro Tsutsumi ◽

Ryosuke Miyawaki ◽

Makoto Miyoshi ◽

...

Keyword(s):

Galactic Center ◽

Mass Density ◽

Angular Size ◽

High Mass ◽

Continuum Emission ◽

Supporting Evidence ◽

Recombination Line ◽

Ionized Gas ◽

Sgr A ◽

The Continuum

Abstract We detected a compact ionized gas associated physically with IRS13E3, an intermediate mass black hole (IMBH) candidate in the Galactic center, in the continuum emission at 232 GHz and H30α recombination line using ALMA Cy.5 observation (2017.1.00503.S, P.I. M.Tsuboi). The continuum emission image shows that IRS13E3 is surrounded by an oval-like structure. The angular size is 0${^{\prime\prime}_{.}}$093 ± 0${^{\prime\prime}_{.}}$006 × 0${^{\prime\prime}_{.}}$061 ± 0${^{\prime\prime}_{.}}$004 (1.14 × 1016 cm × 0.74 × 1016 cm). The structure is also identified in the H30α recombination line. This is seen as an inclined linear feature in the position–velocity diagram, which is usually a defining characteristic of a rotating gas ring around a large mass. The gas ring has a rotating velocity of Vrot ≃ 230 km s−1 and an orbit radius of r ≃ 6 × 1015 cm. From these orbit parameters, the enclosed mass is estimated to be $M_{\mathrm{IMBH}}\simeq 2.4\times 10^{4}\, M_{\odot }$. The mass is within the astrometric upper limit mass of the object adjacent to Sgr A*. Considering IRS13E3 has an X-ray counterpart, the large enclosed mass would be supporting evidence that IRS13E3 is an IMBH. Even if a dense cluster corresponds to IRS13E3, the cluster would collapse into an IMBH within τ < 107 yr due to the very high mass density of $\rho \gtrsim 8\times 10^{11}\, M_{\odot }\:$pc−3. Because the orbital period is estimated to be as short as T = 2πr/Vrot ∼ 50–100 yr, the morphology of the observed ionized gas ring is expected to be changed in the next several decades. The mean electron temperature and density of the ionized gas are $\bar{T}_{\mathrm{e}}=6800\pm 700\:$K and $\bar{n}_{\mathrm{e}}=6\times 10^{5}\:$cm−3, respectively. Then the mass of the ionized gas is estimated to be $M_{\mathrm{gas}}=4\times 10^{-4}\, M_{\odot }$.

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900186474 ◽

1989 ◽

Vol 136 ◽

pp. 159-166 ◽

Cited By ~ 6

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.

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SiO and H2O Masers in the Central Parsec of the Galaxy

International Astronomical Union Colloquium ◽

10.1017/s0252921100045334 ◽

1998 ◽

Vol 164 ◽

pp. 229-230 ◽

Cited By ~ 1

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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Radio continuum and radio recombination line observations of the Galactic center lobe

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000374 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 129-131

Author(s):

Halca Nagoshi ◽

Kenta Fujisawa ◽

Yuzo Kubose

Keyword(s):

Electron Temperature ◽

Galactic Center ◽

Thermal Emission ◽

Radio Continuum ◽

Continuum Emission ◽

Recombination Line ◽

Ionized Gas ◽

Radio Recombination Line ◽

Spatial Coverage ◽

The Continuum

AbstractRadio continuum (cont) and radio recombination line (RRL) observations with the Yamaguchi 32-m radio telescope toward the lower part of the Galactic center lobe (GCL) in the Galactic center region are presented. While two ridges of the GCL were seen in both continuum and RRL images, the spatial coverage of the ridges of the continuum and RRL is not coincident. We distinguish the continuum emission of the GCL into thermal and non-thermal emission by assuming an electron temperature of the ionized gas of 4370 K, estimated based on the line width (14.1 km s−1). The thermal emission was found to be located inside and surrounded by the non-thermal emission.

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NIKA2 observations around LBV stars Emission from stars and circumstellar material

EPJ Web of Conferences ◽

10.1051/epjconf/202022800023 ◽

2020 ◽

Vol 228 ◽

pp. 00023

Author(s):

J. Ricardo Rizzo ◽

Alessia Ritacco ◽

Cristobal Bordiu

Keyword(s):

Thermal Emission ◽

Continuum Emission ◽

Core Collapse ◽

Spectral Indices ◽

Ionized Gas ◽

Dark Cloud ◽

High Frequencies ◽

Circumstellar Material ◽

Dark Clouds ◽

Luminous Blue Variable

Luminous Blue Variable (LBV) stars are evolved massive objects, previous to core-collapse supernova. LBVs are characterized by photometric and spectroscopic variability, produced by strong and dense winds, mass-loss events and very intense UV radiation. LBVs strongly disturb their surroundings by heating and shocking, and produce important amounts of dust. The study of the circumstellar material is therefore crucial to understand how these massive stars evolve, and also to characterize their effects onto the interstellar medium. The versatility of NIKA2 is a key in providing simultaneous observations of both the stellar continuum and the extended, circumstellar contribution. The NIKA2 frequencies (150 and 260 GHz) are in the range where thermal dust and free-free emission compete, and hence NIKA2 has the capacity to provide key information about the spatial distribution of circumstellar ionized gas, warm dust and nearby dark clouds; non-thermal emission is also possible even at these high frequencies. We show the results of the first NIKA2 survey towards five LBVs. We detected emission from four stars, three of them immersed in tenuous circumstellar material. The spectral indices show a complex distribution and allowed us to separate and characterize different components. We also found nearby dark clouds, with spectral indices typical of thermal emission from dust. Spectral indices of the detected stars are negative and hard to be explained only by free-free processes. In one of the sources, G79.29+0.46, we also found a strong correlation of the 1mm and 2mm continuum emission with respect to nested molecular shells at ≈1 pc from the LBV. The spectral index in this region clearly separates four components: the LBV star, a bubble characterized by free-free emission, and a shell interacting with a nearby infrared dark cloud.

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How far actually is the Galactic Center IRS 13E3 from Sagittarius A*?

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa016 ◽

2020 ◽

Vol 72 (3) ◽

Author(s):

Masato Tsuboi ◽

Yoshimi Kitamura ◽

Takahiro Tsutsumi ◽

Ryosuke Miyawaki ◽

Makoto Miyoshi ◽

...

Keyword(s):

Galactic Center ◽

Three Dimensional ◽

Line Of Sight ◽

Recombination Line ◽

Intermediate Mass ◽

Ionized Gas ◽

Sagittarius A ◽

Projection Distance ◽

Spectroscopic Information ◽

Sgr A

Abstract The Galactic Center IRS 13E cluster is a very intriguing infrared object located at ${\sim } 0.13$ pc from Sagittarius A$^\ast$ (Sgr A$^\ast$) in projection distance. There are arguments both for and against the hypothesis that a dark mass like an intermediate mass black hole (IMBH) exists in the cluster. We recently detected the rotating ionized gas ring around IRS 13E3, which belongs to the cluster, in the H30$\alpha$ recombination line using ALMA. The enclosed mass is derived to be $M_{\mathrm{encl.}}\simeq 2\times 10^{4}\, M_\odot$, which agrees with an IMBH and is barely less than the astrometric upper limit mass of an IMBH around Sgr A$^\ast$. Because the limit mass depends on the true three-dimensional (3D) distance from Sgr A$^\ast$, it is very important to determine it observationally. However, the 3D distance is indefinite because it is hard to determine the line-of-sight (LOS) distance by usual methods. We attempt here to estimate the LOS distance from spectroscopic information. The CH$_3$OH molecule is easily destroyed by the cosmic rays around Sgr A$^{\ast }$. However, we detected a highly excited CH$_3$OH emission line in the ionized gas stream associated with IRS 13E3. This indicates that IRS 13E3 is located at $r\gtrsim 0.4$ pc from Sgr A$^{\ast }$.

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