We report the results of high-resolution molecular line observations of the high-velocity compact cloud HCN-0.085-0.094 with the Atacama Large Millimeter/submillimeter Array. The HCN J = 4-3, HCO+ J ...= 4-3, and CS J = 7-6 line images reveal that HCN-0.085-0.094 consists mainly of three small clumps with extremely broad velocity widths. Each of the three clumps has a 5.5 GHz radio continuum counterpart in its periphery toward Sgr A*. The positional relationship indicates that their surfaces have been ionized by ultraviolet photons from young stars in the central cluster, suggesting the clumps are in close proximity to the Galactic nucleus. One of the three clumps has a ring-like structure with a very steep velocity gradient. This kinematical structure suggests an orbit around a point-like object with a mass of ∼104 M . The absence of stellar counterparts indicates that the point-like object may be a quiescent black hole. This discovery adds another intermediate-mass black hole candidate in the central region of our Galaxy.
We report the discovery of molecular gas streams orbiting around an invisible massive object in the central region of our Galaxy, based on the high-resolution molecular line observations with the ...Atacama Large Millimeter/submillimeter Array. The morphology and kinematics of these streams can be reproduced well through two Keplerian orbits around a single point mass of (3.2 0.6) × 104 M . We also found ionized gas toward the inner part of the orbiting gas, indicating dissociative shock and/or photoionization. Our results provide new circumstantial evidences for a wandering intermediate-mass black hole in the Galactic center, suggesting also that high-velocity compact clouds can be probes of quiescent black holes that abound in our Galaxy.
Abstract
We report the results of observations toward the center of the molecular cloud CO 0.02–0.02 made using the Atacama Large Millimeter/Submillimeter Array. The successfully obtained 1″ ...resolution images of CO
J
= 3–2, H
13
CN
J
= 4–3, H
13
CO
+
J
= 4–3, SiO
J
= 8–7, CH
3
OH
J
K
a
,
K
c
= 7
1,7
–6
1,6
A
+
lines, and 900
μ
m continuum show several new features, which have not been identified in previous observations. The dense gas probe (H
13
CN, SiO, CH
3
OH) images are dominated by a pair of northeast-southwest elongated filaments, which may be the main body of CO 0.02–0.02. Two striped patterns perpendicular to each other (F1 and F2) and a high-velocity feature (HV), which appear in different velocity ranges, were prominent in the CO image. An emission hole that may represent an expanding feature was found in the F1 velocity range. F2 appeared to align along the western edge of a 20 pc × 13 pc ellipse (the Large Shell) identified in the single-dish CO map. The HV contains eight compact clumps at the positive high-velocity end of the CO emissions. Based on these results, we propose a formation scenario for CO 0.02–0.02; internal explosions of supernovae, external perturbations by the Large Shell, and gravitational acceleration by a less-luminous star cluster have formed CO 0.02–0.02 in its current state.
Abstract
In this paper, we report the discovery of an isolated, peculiar compact cloud with a steep velocity gradient at 2.′6 northwest of Sgr A*. This “Tadpole” molecular cloud is unique owing to ...its characteristic head-tail structure in the position–velocity space. By tracing the CO
J
= 3–2 intensity peak in each velocity channel, we noticed that the kinematics of the Tadpole can be well reproduced by a Keplerian motion around a point-like object with a mass of 1 × 10
5
M
⊙
. Changes in line intensity ratios along the orbit are consistent with the Keplerian orbit model. The spatial compactness of the Tadpole and absence of bright counterparts in other wavelengths indicate that the object could be an intermediate-mass black hole.
Abstract
We performed a systematic search for broad-velocity-width molecular features (BVFs) in the disk part of our Galaxy by using the CO
J
= 1–0 survey data obtained with the Nobeyama Radio ...Observatory 45 m telescope. From this search, 58 BVFs were identified. In comparisons with the infrared and radio continuum images, 36 BVFs appeared to have both infrared and radio continuum counterparts, and 15 of them are described as molecular outflows from young stellar objects in the literature. In addition, 21 BVFs have infrared counterparts only, and eight of them are described as molecular outflows in the literature. One BVF (CO 16.134–0.553) does not have any luminous counterpart in the other wavelengths, which suggests that it may be an analog of high-velocity compact clouds in the Galactic center.
We discovered two small high-velocity compact clouds (HVCCs) in the HCN J = 4-3 and J = 3-2 maps of the central 20 pc of our Galaxy. Both HVCCs have broad velocity widths ( km s−1) and compact sizes ...( ), and originate from the dense molecular clouds in the position-velocity space. One of them has a faint counterpart in a Paschen- image. Their spatial structure, kinematics, and absence of luminous stellar object are compatible with the notion that each of the small HVCCs is driven by the plunge of an invisible compact object into a molecular cloud. Such objects are most likely inactive, isolated black holes.
Abstract
We performed Nyquist-sampled mapping observations of the central molecular zone of our Galaxy in the J = 1–0 lines of CO, 13CO, and C18O using the 45 m telescope at the Nobeyama Radio ...Observatory. The newly obtained data sets were an improvement by a factor of four in spatial resolution of the CO data previously obtained with the same telescope 22 years ago, providing the highest angular resolution CO atlas of this special area of the Galaxy. The data cover the area: −0${^{\circ}_{.}}$8 ≤ l ≤ +1${^{\circ}_{.}}$4 and −0${^{\circ}_{.}}$35 ≤ b ≤ +0${^{\circ}_{.}}$35 with a 15″ beamwidth. Total intensity ratios for CO J = 3–2/J = 1–0, 13CO/CO J = 1–0 and C18O/13CO J = 1–0, are 0.70 ± 0.06, 0.12 ± 0.01, and 0.14 ± 0.01, respectively. The high-resolution CO images show the fine structure of the molecular gas and enable us to identify a number of compact clouds with broad velocity widths, i.e., high-velocity compact clouds. We conducted a detailed comparison of our CO J = 1–0 data with the CO J = 3–2 data obtained with the James Clerk Maxwell Telescope to derive the distribution and kinematics of the highly excited gas. Three, out of four, of the previously identified high CO J = 3–2/J = 1–0 ratio areas at l = +1${^{\circ}_{.}}$3, 0${^{\circ}_{.}}$0, and −0${^{\circ}_{.}}$4 were confirmed with a higher spatial resolution. In addition to these, we identified several very compact, high CO J = 3–2/J = 1–0 spots with broad velocity widths for the first time. These are candidates for accelerated gas in the vicinity of invisible, point-like massive objects.
Abstract
This study developed an automated identification procedure for compact clouds with broad velocity widths in the spectral-line data cubes of highly crowded regions. The procedure was applied ...to the CO
J
= 3 − 2 line data, obtained using the James Clerk Maxwell Telescope, to identify 184 high-velocity dispersion compact clouds (HVDCCs), which are a category of peculiar molecular clouds found in the central molecular zone of our Galaxy. A list of HVDCCs in the area −1.°4 ≤
l
≤ +2.°0, −0.°25 ≤
b
≤ +0.°25 was presented with their physical parameters, CO
J
= 3 − 2/
J
= 1 − 0 intensity ratios, and morphological classifications. Consequently, the list provides several intriguing sources that may have been driven by encounters with pointlike massive objects, local energetic events, or cloud-to-cloud collisions.
CO-0.40-0.22 is a peculiar molecular cloud that is compact and has an extraordinary broad velocity width. It is found in the central molecular zone (CMZ) of our Galaxy. In this direction, there is ...another cloud with an H2O maser spot at a lower velocity. A collision with this low-velocity cloud could be responsible for the broad velocity width of CO-0.40-0.22. We performed phase-referencing very long baseline interferometry (VLBI) astrometry with VERA and detected the annual parallax of the H2O maser spot in the low-velocity cloud to be 0.33 0.14 mas, which corresponds to a distance of from the Sun. This implies that the low-velocity cloud is located in the Galactic disk on the near side of the CMZ.
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