scholarly journals IRTF/TEXES observations of the H ii regions H1 and H2 in the Galactic Centre

2017 ◽  
Vol 470 (1) ◽  
pp. 561-575 ◽  
Author(s):  
Hui Dong ◽  
John H. Lacy ◽  
Rainer Schödel ◽  
Francisco Nogueras-Lara ◽  
Teresa Gallego-Calvente ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Galactic Center ◽  
Galactic Centre ◽  
H Ii Regions ◽  
Stellar Cluster ◽  
The Galaxy ◽  
H Ii Region ◽  
Sgr A ◽  
Projected Distance

Abstract We present new [Ne ii] (12.8 μm) IRTF/TEXES observations of the Galactic Center H ii regions H1 and H2, which are at a projected distance of ∼11 pc from the centre of the Galaxy. The new observations allow us to map the radial velocity distributions of ionized gas. The high spectroscopic resolution (∼4 km s−1) helps us to disentangle different velocity components and enables us to resolve previous ambiguity regarding the nature of these sources. The spatial distributions of the intensity and radial velocity of the [Ne ii] line are mapped. In H1, the intensity distributions of the Paschen-α (1.87 μm) and [Ne ii] lines are significantly different, which suggests a strong variation of extinction across the H ii region of AK ∼ 0.56. The radial velocity distributions across these H ii regions are consistent with the predictions of a bow-shock model for H1 and the pressure-driven model for H2. Furthermore, we find a concentration of bright stars in H2. These stars have similar H − Ks colours and can be explained as part of a 2-Myr-old stellar cluster. H2 also falls on the orbit of the molecular clouds, suggested to be around Sgr A*. Our new results confirm what we had previously suggested: The O supergiant P114 in H1 is a runaway star, moving towards us through the −30 to 0 km s−1 molecular cloud, whereas the O If star P35 in H2 formed in situ, and may mark the position of a so-far unknown small star cluster formed within the central 30 pc of the Galaxy.

scholarly journals G−0.02−0.07, the compact H ii region complex nearest to the galactic center with ALMA

2019 ◽  
Vol 71 (6) ◽  
Author(s):  
Masato Tsuboi ◽  
Yoshimi Kitamura ◽  
Kenta Uehara ◽  
Atsushi Miyazaki ◽  
Ryosuke Miyawaki ◽  
...  
Keyword(s):  
Shock Wave ◽  
Galactic Center ◽  
Emission Lines ◽  
Continuum Emission ◽  
Molecular Gas ◽  
H Ii Regions ◽  
Recombination Line ◽  
The Galaxy ◽  
H Ii Region ◽  
Absorption Features

Abstract We have observed the compact H ii region complex nearest to the dynamical center of the Galaxy, G−0.02−0.07, using ALMA in the H42α recombination line, CS J = 2–1, H13CO+J = 1–0, and SiO v = 0, J = 2–1 emission lines, and the 86 GHz continuum emission. The H ii regions HII-A to HII-C in the cluster are clearly resolved into a shell-like feature with a bright half and a dark half in the recombination line and continuum emission. The analysis of the absorption features in the molecular emission lines show that H ii-A, B, and C are located on the near side of the “Galactic center 50 km s−1 molecular cloud” (50MC), but HII-D is located on the far side of it. The electron temperatures and densities ranges are Te = 5150–5920 K and ne = 950–2340 cm−3, respectively. The electron temperatures in the bright half are slightly lower than those in the dark half, while the electron densities in the bright half are slightly higher than those in the dark half. The H ii regions are embedded in the ambient molecular gas. There are some molecular gas components compressed by a C-type shock wave around the H ii regions. From the line width of the H42α recombination line, the expansion velocities of HII-A, HII-B, HII-C, and HII-D are estimated to be Vexp = 16.7, 11.6, 11.1, and 12.1 km s−1, respectively. The expansion timescales of HII-A, HII-B, HII-C, and HII-D are estimated to be tage ≃ 1.4 × 104, 1.7 × 104, 2.0 × 104, and 0.7 × 104 yr, respectively. The spectral types of the central stars from HII-A to HII-D are estimated to be O8V, O9.5V, O9V, and B0V, respectively. These derived spectral types are roughly consistent with the previous radio estimation. The positional relation among the H ii regions, the SiO molecule enhancement area, and Class-I maser spots suggest that a shock wave caused by a cloud–cloud collision propagated along the line from HII-C to HII-A in the 50MC. The shock wave would have triggered the massive star formation.

scholarly journals Mini-Spiral at the Galactic Center: A Link between its Structure and the Value of a Central Point Mass

1996 ◽  
Vol 169 ◽  
pp. 241-246
Author(s):  
A.M. Fridman ◽  
O.V. Khoruzhii ◽  
V.V. Lyakhovich ◽  
L. Ozernoy ◽  
L. Blitz
Keyword(s):  
Galactic Center ◽  
Density Wave ◽  
Neutral Hydrogen ◽  
Wave Model ◽  
Molecular Gas ◽  
Stellar Cluster ◽  
Nonthermal Radio ◽  
H Ii Region ◽  
Circumnuclear Disk ◽  
Sgr A

The innermost 2 pc contain a rotating ring (“circumnuclear disk”) of molecular gas, neutral hydrogen, and dust with an embedded H II region called Sgr A West; a dense stellar cluster; and a compact nonthermal radio source Sgr A∗ (for a recent review, see Blitz et al. 1993). The clumped, spiral-shaped morphology of Sgr A West, sometimes called lthe mini-spiral”, has been a subject of numerous speculations concerning its origin (for a review, see Genzel & Townes 1987). Lacy et al. (1991) demonstrated that both the kinematics and shape of a part of Sgr A West can be fairly well approximated using an one-armed density-wave model.

scholarly journals FIR Spectroscopy of the Galactic Center: Hot and Warm Molecular Gas

2016 ◽  
Vol 11 (S322) ◽  
pp. 168-169
Author(s):  
Javier R. Goicoechea ◽  
Mireya Etxaluze ◽  
José Cernicharo ◽  
Maryvonne Gerin ◽  
Jerome Pety ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Galactic Center ◽  
Rotational Line ◽  
Molecular Gas ◽  
Central Cavity ◽  
Stellar Cluster ◽  
Line Intensities ◽  
The Galaxy ◽  
Circumnuclear Disk ◽  
Sgr A

AbstractThe angular resolution (~10″) achieved by the Herschel Space Observatory ~3.5 m telescope at FIR wavelengths allowed us to roughly separate the emission toward the inner parsec of the galaxy (the central cavity) from that of the surrounding circumnuclear disk (the CND). The FIR spectrum toward Sgr A* is dominated by intense [O iii], [O i], [C ii], [N iii], [N ii], and [C i] fine-structure lines (in decreasing order of luminosity) arising in gas irradiated by the strong UV field from the central stellar cluster. The high-J CO rotational line intensities observed at the interface between the inner CND and the central cavity are consistent with a hot isothermal component at Tk ≈ 103.1 K and n(H2)≈ 104 cm−3. They are also consistent with a distribution of lower temperatures at higher gas density, with most CO at Tk≈300 K. The hot CO component (either the bulk of the CO column density or just a small fraction depending on the above scenario) likely results from a combination of UV and shock-driven heating. If UV-irradiated and heated dense clumps do not exist, shocks likely dominate the heating of the hot molecular gas component. Although this component is beam diluted in our FIR observations, it may be resolved at much higher angular resolution. An ALMA project using different molecular tracers to characterize UV-irradiated shocks in the innermost layers of the CND is ongoing.

scholarly journals 7.13. The Sgr A East HII complex and associated features

1998 ◽  
Vol 184 ◽  
pp. 317-318 ◽  
Author(s):  
Keven I. Uchida ◽  
Mark R. Morris ◽  
Gene Serabyn ◽  
David Fong ◽  
Thomas Meseroll
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Galactic Center ◽  
Galactic Plane ◽  
Alternative Hypothesis ◽  
Rapid Expansion ◽  
H Ii Regions ◽  
Expansion Time ◽  
Sgr A ◽  
Relativistic Particles

The Sgr A East H ii complex consists of 4 compact H ii regions situated just east of and following, in an arc pattern, the edge of the Sgr A East nonthermal shell. Located between the arc of H ii regions and the nonthermal shell is a dense molecular ridge – presumably compressed – known as the “50 km/s cloud”. The hypothesis that these H ii regions delineate massive star formation provoked by the rapid expansion of Sgr A East into the molecular cloud is problematical because of the mismatch of the shell expansion and star formation time scales. We therefore examine the alternative hypothesis that Sgr A East is a quasi-static or slowly expanding structure fed from within by the release of relativistic particles from sources at or near the nucleus. The elongation of SgrA East along the Galactic plane is ascribed to the shear inherent in the velocity field this close to the Galactic center (GC). In this proceeding we discuss our ongoing efforts to model the effects of shear in detail, using the elongation of Sgr A East to constrain its expansion time scale.

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 10.2. High proper motions in the vicinity of Sgr A∗: unambiguous evidence for a massive central black hole

1998 ◽  
Vol 184 ◽  
pp. 433-434
Author(s):  
A. M. Ghez ◽  
B. L. Klein ◽  
C. McCabe ◽  
M. Morris ◽  
E. E. Becklin
Keyword(s):  
Black Hole ◽  
Milky Way ◽  
Galactic Center ◽  
Robust Method ◽  
Proper Motions ◽  
Central Black Hole ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
Sgr A

Although the notion that the Milky Way galaxy contains a supermassive central black hole has been around for more than two decades, it has been difficult to prove that one exists. The challenge is to assess the distribution of matter in the few central parsecs of the Galaxy. Assuming that gravity is the dominant force, the motion of the stars and gas in the vicinity of the putative black hole offers a robust method for accomplishing this task, by revealing the mass interior to the radius of the objects studied. Thus objects located closest to the Galactic Center provide the strongest constraints on the black hole hypothesis.

scholarly journals Colliding winds in and around the stellar group IRS 13E at the galactic centre

2019 ◽  
Vol 492 (2) ◽  
pp. 2481-2496 ◽  
Author(s):  
Q Daniel Wang ◽  
Jun Li ◽  
Christopher M P Russell ◽  
Jorge Cuadra
Keyword(s):  
Thermal Emission ◽  
Ambient Medium ◽  
Velocity Spread ◽  
Galactic Centre ◽  
X Ray ◽  
Stellar Group ◽  
Cool Gas ◽  
Sgr A ◽  
Colliding Winds ◽  
Projected Distance

ABSTRACT IRS 13E is an enigmatic compact group of massive stars located in projection only 3.6 arcsec away from Sgr A*. This group has been suggested to be bounded by an intermediate-mass black hole (IMBH). We present a multiwavelength study of the group and its interplay with the environment. Based on Chandra observations, we find the X-ray spectrum of IRS 13E can be well characterized by an optically thin thermal plasma. The emission peaks between two strongly mass-losing Wolf–Rayet stars of the group. These properties can be reasonably well reproduced by simulated colliding winds of these two stars. However, this scenario underpredicts the X-ray intensity in outer regions. The residual emission likely results from the ram-pressure confinement of the IRS 13E group wind by the ambient medium and is apparently associated with a shell-like warm gas structure seen in Pa α and in ALMA observations. These latter observations also show strongly peaked thermal emission with unusually large velocity spread between the two stars. These results indicate that the group is colliding with the bar of the dense cool gas mini-spiral around Sgr A*. The extended X-ray morphology of IRS 13E and its association with the bar further suggest that the group is physically much farther away than the projected distance from Sgr A*. The presence of an IMBH, while favourable to keep the stars bound together, is not necessary to explain the observed stellar and gas properties of IRS 13E.

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 The LAMOST spectroscopic survey of planetary nebulae in M31 and M33

2016 ◽  
Vol 12 (S323) ◽  
pp. 388-389
Author(s):  
Maosheng Xiang ◽  
Xiaowei Liu ◽  
Meng Zhang ◽  
Haibo Yuan ◽  
Zhiying Huo
Keyword(s):  
Radial Velocity ◽  
Planetary Nebulae ◽  
Radial Velocities ◽  
Velocity Measurements ◽  
The Galaxy ◽  
Galaxy Center ◽  
Projected Distance

AbstractWe present LAMOST observations and radial velocity measurements of about 1500 planetary nebulae (PNe) in M31 and M33. Most of the PNe are previously known, but 36 of them are newly discovered in the outskirts of M31, and the furthest one has a projected distance larger than 50 kpc away from the galaxy center. Eighteen objects in the area of M33 are probably newly discovered PNe, and quite a few of them are associated with previously known clusters. For all the 1500 PNe, homogeneous radial velocities are measured from the LAMOST spectra, with a typical uncertainty of a few km s−1.

scholarly journals A new MIR bow shock source in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 150-152 ◽  
Author(s):  
N. Sabha ◽  
M. Zamaninasab ◽  
A. Eckart ◽  
L. Moser
Keyword(s):  
Black Hole ◽  
Symmetry Axis ◽  
Galactic Center ◽  
Bow Shock ◽  
Shock Source ◽  
Stellar Cluster ◽  
Supermassive Black Hole ◽  
Sgr A ◽  
Central Parsec

AbstractWe find a convex-like feature at a distance of 0.68 pc (17″) from the position of the supermassive black hole, Sgr A*, at the center of the nuclear stellar cluster. This feature resembles a stellar bow shock with a symmetry axis pointing to the center. We discuss the possible nature of the feature and the implications of its alignment with other dusty comet-like objects inside the central parsec.

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