[en] New observations of Sgr A have been carried out with the Jansky VLA in the B and C arrays using the broadband (2 GHz) continuum mode at 5.5 GHz. The field of view covers the central 13′ (30 pc) region of the radio-bright zone at the Galactic center. Using the multi-scale and multi-frequency-synthesis (MS-MFS) algorithms in CASA, we have imaged Sgr A with a resolution of 1″, achieving an rms noise of 8 μJy beam"−"1, and a dynamic range of 100,000:1. Both previously known and newly identified radio features in this region are revealed, including numerous filamentary sources. The radio continuum image is compared with Chandra X-ray images, with a CN emission-line image obtained with the Submillimeter Array and with detailed Paschen-α images obtained with Hubble Space Telescope/NICMOS. We discuss several prominent features in the radio image. The “Sgr A west Wings” extend 2′ (5 pc) from the NW and SE tips of the Sgr A west H ii region (the “Mini-spiral”) to positions located 2.9 and 2.4 arcmin to the northwest and southeast of Sgr A*, respectively. The NW wing, along with several other prominent features, including the previously identified “NW Streamers,” form an elongated radio lobe (NW lobe), oriented nearly perpendicular to the Galactic plane. This radio lobe, with a size of 6.′3 × 3.′2 (14.4 pc × 7.3 pc), has a known X-ray counterpart. In the outer region of the NW lobe, a row of three thermally emitting rings is observed. A field containing numerous amorphous radio blobs extends for a distance of ∼2 arcmin beyond the tip of the SE wing; these newly recognized features coincide with the SE X-ray lobe. Most of the amorphous radio blobs in the NW and SE lobes have Paschen-α counterparts. We propose that they have been produced by shock interaction of ambient gas concentrations with a collimated nuclear wind or an outflow that originated from within the circumnuclear disk (CND). We also discuss the possibility that the ionized wind or outflow has been launched by radiation force produced by the central star cluster. Finally, we remark on the detailed structure of a prominent radio emission feature located within the shell of the Sgr A east supernova remnant. Because this feature—the “Sigma Front”—correlates well in shape and orientation with the nearby edge of the CND, we propose that it is a reflected shock wave resulting from the impact of the Sgr A east blast wave on the CND

[en] Using Jansky Very Large Array data obtained from high-resolution observations at 5.5 GHz at multiple epochs in 2014 and 2019, we have detected a population of radio variables and transients in the radio-bright zone at the Galactic center. With observations covering a sky area of 180 arcmin² at an angular resolution of 0.″4, we report new detections of 110 Galactic center compact radio (GCCR) sources with a size of <1″. The flux densities of GCCR sources exceed 70 μJy, with at least 10σ significance. Among these sources, 82 are variable or transient and 28 are nonvariable. About 10% of them are expected to be extragalactic background sources. We discuss the possible astrophysical nature of the detected sources. As compared to the Galactic disk (GD) population of normal pulsars (NPs) and millisecond pulsars (MSPs), a majority (80%) of the GCCR sources appear to fall within the high flux density tail of the pulsar distribution, as extrapolated from a sample of NPs in the GD. However, MSPs extrapolated from the GD population are too weak to have contributed significantly to the GCCR population that has been detected. We also cross-correlated the GCCR sources with X-ray sources in Chandra X-ray catalogs and found that 42 GCCR sources have candidate X-ray counterparts. Most of the GCCR sources having X-ray counterparts are likely to be associated with unresolved or slightly resolved radio jets launched from X-ray binaries with a compact object, either a black hole or a neutron star.

[en] We report the Very Large Array (VLA) detection of the radio counterpart of the X-ray object referred to as the 'Cannonball', which has been proposed to be the remnant neutron star resulting from the creation of the Galactic center supernova remnant, Sagittarius A East. The radio object was detected both in our new VLA image from observations in 2012 at 5.5 GHz and in archival VLA images from observations in 1987 at 4.75 GHz and in the period from 1990 to 2002 at 8.31 GHz. The radio morphology of this object is characterized as a compact, partially resolved point source located at the northern tip of a radio 'tongue' similar to the X-ray structure observed by Chandra. Behind the Cannonball, a radio counterpart to the X-ray plume is observed. This object consists of a broad radio plume with a size of 30''×15'', followed by a linear tail having a length of 30''. The compact head and broad plume sources appear to have relatively flat spectra (∝ν^α) with mean values of α = –0.44 ± 0.08 and –0.10 ± 0.02, respectively, and the linear tail shows a steep spectrum with the mean value of –1.94 ± 0.05. The total radio luminosity integrated from these components is ∼8 × 10³³ erg s^–1, while the emission from the head and tongue amounts for only ∼1.5 × 10³¹ erg s^–1. Based on the images obtained from the two epochs' observations at 5 GHz, we infer the proper motion of the object: μ_α = 0.001 ± 0.003 arcsec yr^–1 and μ_δ = 0.013 ± 0.003 arcsec yr^–1. With an implied velocity of 500 km s^–1, a plausible model can be constructed in which a runaway neutron star surrounded by a pulsar wind nebula was created in the event that produced Sgr A East. The inferred age of this object, assuming that its origin coincides with the center of Sgr A East, is approximately 9000 yr

[en] We report on the submillimeter properties of Sgr A* derived from observations with the Submillimeter Array and its polarimeter. We ftid that the spectrum of Sgr A* between 230 and 690 GHz is slightly decreasing when measured simultaneously, indicating a transition to optically thin emission around 300-400 GHz. We also present very sensitive and well calibrated measurements of the polarization of Sgr A* at 230 and 345 GHz. With these data we are able to show for the frst time that the polarization of Sgr A* varies on hour timescales, as has been observed for the total intensity. On one night we fhd variability that may arise from a polarized 'blob' orbiting the black hole. Finally, we use the ensemble of observations to determine the rotation measure. This represents the frst statistically significant rotation measure determination and the only one made without resorting to comparing position angles measured at separate epochs. We frid a rotation measure of (-5.6 ± 0.7) x 10⁵ rad m², with no evidence for variability on inter-day timescales at the level of the measurement error. The stability constrains interday flictuations in the accretion rate to 8%. The mean intrinsic polarization position angle is 167⁰±7⁰ and we detect variations of 31⁺¹⁸_-9 degrees. This separation of intrinsic polarization changes and possible rotation measure flictuations is now possible because of the frequency coverage and sensitivity of our data. The observable rotation measure restricts the accretion rate to the range 2 x 10^-7 M o-dot yr^-1 to 2 x 10^-9 M o-dot yr^-1, if the magnetic field is near equipartition and ordered

[en] We present dust polarization and CO molecular line images of NGC 7538 IRS 1. We combined data from the Submillimeter Array, the Combined Array for Research in Millimeter-wave Astronomy, and the James Clerk Maxwell Telescope to make images with ∼2.''5 resolution at 230 and 345 GHz. The images show a remarkable spiral pattern in both the dust polarization and molecular outflow. These data dramatically illustrate the interplay between a high infall rate onto IRS 1 and a powerful outflow disrupting the dense, clumpy medium surrounding the star. The images of the dust polarization and the CO outflow presented here provide observational evidence for the exchange of energy and angular momentum between the infall and the outflow. The spiral dust pattern, which rotates through over 180° from IRS 1, may be a clumpy filament wound up by conservation of angular momentum in the infalling material. The redshifted CO emission ridge traces the dust spiral closely through the MM dust cores, several of which may contain protostars. We propose that the CO maps the boundary layer where the outflow is ablating gas from the dense gas in the spiral.

[en] We present observations of the ¹²CO(J = 6–5) line and 686 GHz continuum emission in NGC 253 with the Submillimeter Array at an angular resolution of ∼4″. The ¹²CO(J = 6–5) emission is clearly detected along the disk and follows the distribution of the lower ¹²CO line transitions with little variation of the line ratios. A large velocity gradient analysis suggests a two-temperature model of the molecular gas in the disk, likely dominated by a combination of low-velocity shocks and the disk-wide photodissociation regions. Only marginal ¹²CO(J = 6–5) emission is detected in the vicinity of the expanding shells at the eastern and western edges of the disk. While the eastern shell contains gas even warmer (T_kin > 300 K) than the hot gas component (T_kin = 300 K) of the disk, the western shell is surrounded by gas much cooler (T_kin = 60 K) than the eastern shell but somewhat hotter than the cold gas component of the disk (for similar H₂ and CO column densities), indicative of different (or differently efficient) heating mechansisms. The continuum emission at 686 GHz in the disk agrees well in shape and size with that at lower (sub)millimeter frequencies, exhibiting a spectral index consistent with thermal dust emission. We find dust temperatures of ∼10–30 K and largely optically thin emission. However, our fits suggest a second (more optically thick) dust component at higher temperatures ($T_{\mathrm{d}}><!--\; >\; -->60$ K), similar to the molecular gas. We estimate a global dust mass of ∼10⁶ $M_{\odot <!--\; ???\; -->}$ for the disk, translating into a gas-to-dust mass ratio of a few hundred, consistent with other nearby active galaxies.

[en] We present observations of CO(3–2) and ¹³CO(3–2) emission near the supernebula in the dwarf galaxy NGC 5253, which contains one of the best examples of a potential globular cluster in formation. The 0.″3 resolution images reveal an unusual molecular cloud, “Cloud D1,” that is coincident with the radio-infrared supernebula. The ∼6 pc diameter cloud has a linewidth, Δ v = 21.7 $\mathrm{k}\mathrm{m}{\mathrm{s}}^{-<!--\; ???\; -->1}$, that reflects only the gravitational potential of the star cluster residing within it. The corresponding virial mass is 2.5 × 10⁵ $M_{\odot <!--\; ???\; -->}$. The cluster appears to have a top-heavy initial mass function, with M _* ≳ 1–2 $M_{\odot <!--\; ???\; -->}$. Cloud D1 is optically thin in CO(3–2), probably because the gas is hot. Molecular gas mass is very uncertain but constitutes <35% of the dynamical mass within the cloud boundaries. In spite of the presence of an estimated ∼1500–2000 O stars within the small cloud, the CO appears relatively undisturbed. We propose that Cloud D1 consists of molecular clumps or cores, possibly star-forming, orbiting with more evolved stars in the core of the giant cluster.

[en] We report new results based on the analysis of the Submillimeter Array (SMA) and Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations of NGC 7538 IRS 1 at 1.3 and 3.4 mm with subarcsecond resolutions. With angular resolutions ∼0.''7, the SMA and CARMA observations show that the continuum emission at 1.3 and 3.4 mm from the hyper-compact H II region IRS 1 is dominated by a compact source with a tail-like extended structure to the southwest of IRS 1. With a CARMA B-array image at 1.3 mm convolved to 0.''1, we resolve the hyper-compact H II region into two components: an unresolved hyper-compact core, and a north-south extension with linear sizes of <270 AU and ∼2000 AU, respectively. The fine structure observed with CARMA is in good agreement with the previous Very Large Array results at centimeter wavelengths, suggesting that the hyper-compact H II region at the center of IRS 1 is associated with an ionized bipolar outflow. We image the molecular lines OCS(19-18) and CH₃CN(12-11) as well as ¹³CO(2-1) surrounding IRS 1, showing a velocity gradient along the southwest-northeast direction. The spectral line profiles in ¹³CO(2-1), CO(2-1), and HCN(1-0) observed toward IRS 1 show broad redshifted absorption, providing evidence for gas infall with rates in the range of 3-10 × 10^–3 M _☉ yr^–1 inferred from our observations.

[en] We present the first high-energy X-ray (>10 keV) observations of the non-thermal filament G359.97-0.038 using the Nuclear Spectroscopic Telescope Array (NuSTAR). This filament is one of approximately 20 X-ray filaments of unknown origin located in the central 20 pc region in the Galactic Center near Sgr A*. Its NuSTAR and Chandra broadband spectrum is characterized by a single power law with Γ = 1.3 ± 0.3 that extends from 2 to 50 keV, with an unabsorbed luminosity of 1.3 × 10"3"3 erg s"–"1 (d/8 kpc)"2 in the 2-8 keV band. Despite possessing a cometary X-ray morphology that is typical of a pulsar wind nebula (PWN) in high-resolution Chandra imaging, our spatially resolved Chandra spectral analysis found no significant spectral softening along the filament as would be expected from particle synchrotron cooling. Coincident radio emission is detected using the Very Large Array at 5.5 and 8.3 GHz. We examine and subsequently discard a PWN or magnetic flux tube as the origin of G359.97-0.038. We use broadband spectral characteristics and a morphological analysis to show that G359.97-0.038 is likely an interaction site between the shell of Sgr A East and an adjacent molecular cloud. This is supported by CS molecular line spectroscopy and the presence of an OH maser