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Register a new userRotating Ionized Gas Ring around the Galactic Center IRS13E3
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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 H30$alpha$ 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 $0.093pm0.006times 0.061pm0.004$ ( $1.14times10^{16}$ cm $times 0.74times10^{16}$ cm). The structure is also identified in the H30$alpha$ 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 $V_mathrm{rot}simeq230$ km s$^{-1}$ and an orbit radius of $rsimeq6times10^{15}$ cm. From these orbit parameters, the enclosed mass is estimated to be $M_{mathrm{IMBH}}simeq2.4times10^4$ $M_odot$. The mass is within the astrometric upper limit mass of the object adjacent to Sgr A$^{ast}$. 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 $tau<10^7$ years due to the very high mass density of $rho gtrsim8times10^{11} M_odot pc^{-3}$. Because the orbital period is estimated to be as short as $T=2pi r/V_mathrm{rot}sim 50-100$ 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 $bar{T}_{mathrm e}=6800pm700$ K and $bar{n}_{mathrm e}=6times10^5$ cm$^{-3}$, respectively. Then the mass of the ionized gas is estimated to be $M_{mathrm{gas}}=4times10^{-4} M_odot$.
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We have observed the Galactic Center (GC) region at 0.154 and 0.255 GHz with the GMRT. A total of 62 compact likely extragalactic sources are detected. Their scattering sizes go down linearly with increasing angular distance from the GC up to about 1 deg. The apparent scattering sizes of sources are more than an order of magnitude down than predicted earlier by the NE2001 model of Galactic electron distribution within 359.5 deg < l < 0.5 deg and -0.5 deg <b <0.5 deg (Hyperstrong scattering region) of the Galaxy. High free-free optical depths are observed towards most of the extended nonthermal sources within 0.6 deg from the GC. Significant variation of optical depth indicate the absorbing medium is patchy at an angular scale of 10 and electron density is ~10 per cc that matches with the NE2001 model. This model predicts the extragalactic (EG) sources to be resolved out from 1.4 GHz interferometric surveys. However, 8 likely EG sources out of 10 expected in the region are present in 1.4 GHz catalog. Ionized interfaces of dense molecular clouds to the ambient medium are most likely responsible for strong scattering and low radio frequency absorption. However, dense GC clouds traced by CS $J=1-0$ emission are found to have a narrow distribution of ~0.2 deg across the Galactic plane. Angular distribution of most of the EG sources seen through the so called Hyperstrong scattering region are random in $b$, and typically ~7 out of 10 sources will not be seen through to the dense molecular clouds, and it explains why most of them are not scatter broadened at 1.4 GHz.
We address the spatial scale, ionization structure, mass and metal content of gas at the Milky Way disk-halo interface detected as absorption in the foreground of seven closely-spaced, high-latitude halo blue horizontal branch stars (BHBs) with heights z = 3 - 14 kpc. We detect transitions that trace multiple ionization states (e.g. CaII, FeII, SiIV, CIV) with column densities that remain constant with height from the disk, indicating that the gas most likely lies within z < 3.4 kpc. The intermediate ionization state gas traced by CIV and SiIV is strongly correlated over the full range of transverse separations probed by our sightlines, indicating large, coherent structures greater than 1 kpc in size. The low ionization state material traced by CaII and FeII does not exhibit a correlation with either N$_{rm HI}$ or transverse separation, implying cloudlets or clumpiness on scales less than 10 pc. We find that the observed ratio log(N_SiIV/ N_CIV), with a median value of -0.69+/-0.04, is sensitive to the total carbon content of the ionized gas under the assumption of either photoionization or collisional ionization. The only self-consistent solution for photoionized gas requires that Si be depleted onto dust by 0.35 dex relative to the solar Si/C ratio, similar to the level of Si depletion in DLAs and in the Milky Way ISM. The allowed range of values for the areal mass infall rate of warm, ionized gas at the disk-halo interface is 0.0003 < dM_gas / dtdA [M_sun kpc^-2 yr^-] < 0.006. Our data support a physical scenario in which the Milky Way is fed by complex, multiphase processes at its disk-halo interface that involve kpc-scale ionized envelopes or streams containing pc-scale, cool clumps.
We present high-resolution archival Atacama Large Millimeter/submillimeter Array (ALMA) CO J=3-2 and J=6-5 and HCO+ J=4-3 observations and new CARMA CO and 13CO J=1-0 observations of the luminous infrared galaxy NGC 1614. The high-resolution maps show the previously identified ring-like structure while the CO J=3-2 map shows extended emission that traces the extended dusty features. We combined these new observations with previously published Submillimeter Array CO and 13CO J=2-1 observations to constrain the physical conditions of the molecular gas at a resolution of 230 pc using a radiative transfer code and a Bayesian likelihood analysis. At several positions around the central ring-like structure, the molecular gas is cold (20-40 K) and dense (> 10^{3.0} cm^{-3}) . The only region that shows evidence of a second molecular gas component is the hole in the ring. The CO-to-13CO abundance ratio is found to be greater than 130, more than twice the local interstellar medium value. We also measure the CO-to-H_{2} conversion factor, alpha_{CO}, to range from 0.9 to 1.5 M_sol (K km/s pc^{2})^{-1}.
Thermal images of cold dust in the Central Molecular Zone of the Milky Way, obtained with the far-infrared cameras on-board the Herschel satellite, reveal a 3x10^7 solar masses ring of dense and cold clouds orbiting the Galactic Center. Using a simple toy-model, an elliptical shape having semi-major axes of 100 and 60 parsecs is deduced. The major axis of this 100-pc ring is inclined by about 40 degrees with respect to the plane-of-the-sky and is oriented perpendicular to the major axes of the Galactic Bar. The 100-pc ring appears to trace the system of stable x_2 orbits predicted for the barred Galactic potential. Sgr A* is displaced with respect to the geometrical center of symmetry of the ring. The ring is twisted and its morphology suggests a flattening-ratio of 2 for the Galactic potential, which is in good agreement with the bulge flattening ratio derived from the 2MASS data.
In 2011, we discovered a compact gas cloud (G2) with roughly three Earth masses that is falling on a near-radial orbit toward the massive black hole in the Galactic Center. The orbit is well constrained and pericenter passage is predicted for early 2014. Our data beautifully show that G2 gets tidally sheared apart due to the massive black holes force. During the next months, we expect that in addition to the tidal effects, hydrodynamics get important, when G2 collides with the hot ambient gas around Sgr A*. Simulations show that ultimately, the clouds material might fall into the massive black hole. Predictions for the accretion rate and luminosity evolution, however, are very difficult due to the many unknowns. Nevertheless, this might be a unique opportunity in the next years to observe how gas feeds a massive black hole in a galactic nucleus.
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