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1. The SEDIGISM survey: First Data Release and overview of the Galactic structure

   https://doi.org/10.1093/mnras/staa2369  

   Schuller, F ; Urquhart, J S ; Csengeri, T ; Colombo, D ; Duarte-Cabral, A ; Mattern, M ; Ginsburg, A ; Pettitt, A R ; Wyrowski, F ; Anderson, L ; et al ( December 2020 , Monthly Notices of the Royal Astronomical Society)

   The SEDIGISM (Structure, Excitation and Dynamics of the Inner Galactic Interstellar Medium) survey used the APEX telescope to map 84 deg2 of the Galactic plane between ℓ = −60° and +31° in several molecular transitions, including 13CO (2 – 1) and C18O (2 – 1), thus probing the moderately dense (∼103 cm−3) component of the interstellar medium. With an angular resolution of 30 arcsec and a typical 1σ sensitivity of 0.8–1.0 K at 0.25 km s−1 velocity resolution, it gives access to a wide range of structures, from individual star-forming clumps to giant molecular clouds and complexes. The coverage includes a good fraction of the first and fourth Galactic quadrants, allowing us to constrain the large-scale distribution of cold molecular gas in the inner Galaxy. In this paper, we provide an updated overview of the full survey and the data reduction procedures used. We also assess the quality of these data and describe the data products that are being made publicly available as part of this First Data Release (DR1). We present integrated maps and position–velocity maps of the molecular gas and use these to investigate the correlation between the molecular gas and the large-scale structural features of the Milky Way such as the spiral arms, Galactic bar and Galactic Centre. We find that approximately 60 per cent of the molecular gas is associated with the spiral arms and these appear as strong intensity peaks in the derived Galactocentric distribution. We also find strong peaks in intensity at specific longitudes that correspond to the Galactic Centre and well-known star-forming complexes, revealing that the 13CO emission is concentrated in a small number of complexes rather than evenly distributed along spiral arms.

    

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2. WISDOM project – V. Resolving molecular gas in Keplerian rotation around the supermassive black hole in NGC 0383

   https://doi.org/10.1093/mnras/stz2598  

   North, Eve V. ; Davis, Timothy A. ; Bureau, Martin ; Cappellari, Michele ; Iguchi, Satoru ; Liu, Lijie ; Onishi, Kyoko ; Sarzi, Marc ; Smith, Mark D. ; Williams, Thomas G. ( September 2019 , Monthly Notices of the Royal Astronomical Society)

   As part of the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM), we present a measurement of the mass of the supermassive black hole (SMBH) in the nearby early-type galaxy NGC 0383 (radio source 3C 031). This measurement is based on Atacama Large Millimeter/sub-millimeter Array (ALMA) cycle 4 and 5 observations of the 12CO(2–1) emission line with a spatial resolution of 58 × 32 pc2 (0.18 arcsec × 0.1 arcsec). This resolution, combined with a channel width of 10 km s−1, allows us to well resolve the radius of the black hole sphere of influence (measured as RSOI = 316 pc  =  0.98 arcsec), where we detect a clear Keplerian increase of the rotation velocities. NGC 0383 has a kinematically relaxed, smooth nuclear molecular gas disc with weak ring/spiral features. We forward model the ALMA data cube with the Kinematic Molecular Simulation (KinMS) tool and a Bayesian Markov Chain Monte Carlo method to measure an SMBH mass of (4.2 ± 0.7) × 109 M⊙, a F160W-band stellar mass-to-light ratio that varies from 2.8 ± 0.6 M⊙/L$_{\odot ,\, \mathrm{F160W}}$ in the centre to 2.4 ± 0.3 M⊙$/\rm L_{\odot ,\, \mathrm{F160W}}$ at the outer edge of the disc and a molecular gas velocity dispersion of 8.3 ± 2.1 km s−1(all 3σ uncertainties). We also detect unresolved continuum emission across the full bandwidth, consistent with synchrotron emission from an active galactic nucleus. This work demonstrates that low-J CO emission can resolve gas very close to the SMBH ($\approx 140\, 000$ Schwarzschild radii) and hence that the molecular gas method is highly complimentary to megamaser observations, as it can probe the same emitting material.

    

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3. The SEDIGISM survey: The influence of spiral arms on the molecular gas distribution of the inner Milky Way

   https://doi.org/10.1051/0004-6361/202141287  

   Colombo, D. ; Duarte-Cabral, A. ; Pettitt, A. R. ; Urquhart, J. S. ; Wyrowski, F. ; Csengeri, T. ; Neralwar, K. R. ; Schuller, F. ; Menten, K. M. ; Anderson, L. ; et al ( February 2022 , Astronomy & Astrophysics)

   The morphology of the Milky Way is still a matter of debate. In order to shed light on uncertainties surrounding the structure of the Galaxy, in this paper, we study the imprint of spiral arms on the distribution and properties of its molecular gas. To do so, we take full advantage of the SEDIGISM (Structure, Excitation, and Dynamics of the Inner Galactic Interstellar Medium) survey that observed a large area of the inner Galaxy in the 13 CO (2–1) line at an angular resolution of 28′′. We analyse the influences of the spiral arms by considering the features of the molecular gas emission as a whole across the longitude–velocity map built from the full survey. Additionally, we examine the properties of the molecular clouds in the spiral arms compared to the properties of their counterparts in the inter-arm regions. Through flux and luminosity probability distribution functions, we find that the molecular gas emission associated with the spiral arms does not differ significantly from the emission between the arms. On average, spiral arms show masses per unit length of ~10 5 –10 6 M ⊙ kpc −1 . This is similar to values inferred from data sets in which emission distributions were segmented into molecular clouds. By examining the cloud distribution across the Galactic plane, we infer that the molecular mass in the spiral arms is a factor of 1.5 higher than that of the inter-arm medium, similar to what is found for other spiral galaxies in the local Universe. We observe that only the distributions of cloud mass surface densities and aspect ratio in the spiral arms show significant differences compared to those of the inter-arm medium; other observed differences appear instead to be driven by a distance bias. By comparing our results with simulations and observations of nearby galaxies, we conclude that the measured quantities would classify the Milky Way as a flocculent spiral galaxy, rather than as a grand-design one. 

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4. CMZoom III: Spectral line data release

   https://doi.org/10.1093/mnras/stad388  

   Callanan, Daniel ; Longmore, Steven N. ; Battersby, Cara ; Hatchfield, H. Perry ; Walker, Daniel L. ; Henshaw, Jonathan ; Keto, Eric ; Barnes, Ashley ; Ginsburg, Adam ; Kauffmann, Jens ; et al ( February 2023 , Monthly Notices of the Royal Astronomical Society)

   We present an overview and data release of the spectral line component of the SMA Large Program, CMZoom. CMZoom observed 12CO (2–1), 13CO (2–1), and C18O (2–1), three transitions of H2CO, several transitions of CH3OH, two transitions of OCS, and single transitions of SiO and SO within gas above a column density of N(H2) ≥ 1023 cm−2 in the Central Molecular Zone (CMZ; inner few hundred pc of the Galaxy). We extract spectra from all compact 1.3 mm CMZoom continuum sources and fit line profiles to the spectra. We use the fit results from the H2CO 3(0, 3)–2(0, 2) transition to determine the source kinematic properties. We find ∼90 per cent of the total mass of CMZoom sources have reliable kinematics. Only four compact continuum sources are formally self-gravitating. The remainder are consistent with being in hydrostatic equilibrium assuming that they are confined by the high external pressure in the CMZ. We find only two convincing proto-stellar outflows, ruling out a previously undetected population of very massive, actively accreting YSOs with strong outflows. Finally, despite having sufficient sensitivity and resolution to detect high-velocity compact clouds (HVCCs), which have been claimed as evidence for intermediate mass black holes interacting with molecular gas clouds, we find no such objects across the large survey area.

    

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5. Evidence of a Cloud–Cloud Collision from Overshooting Gas in the Galactic Center

   https://doi.org/10.3847/1538-4357/ad01be  

   Gramze, Savannah R. ; Ginsburg, Adam ; Meier, David S. ; Ott, Juergen ; Shirley, Yancy ; Sormani, Mattia C. ; Svoboda, Brian E. ( December 2023 , The Astrophysical Journal)

   The Milky Way is a barred spiral galaxy withbar lanesthat bring gas toward the Galactic center. Gas flowing along these bar lanes often overshoots, and instead of accreting onto the Central Molecular Zone (CMZ), it collides with the bar lane on the opposite side of the Galaxy. We observed G5, a cloud that we believe is the site of one such collision, near the Galactic center at (ℓ,b) = ( +5.4, −0.4) with the Atacama Large Millimeter/submillimeter Array/Atacama Compact Array. We took measurements of the spectral lines¹²COJ= 2 → 1,¹³COJ= 2 → 1, C¹⁸OJ= 2 → 1, H₂COJ= 3₀₃→ 2₀₂, H₂COJ= 3₂₂→ 2₂₁, CH₃OHJ= 4₂₂→ 3₁₂, OCSJ= 18 → 17, and SiOJ= 5 → 4. We observed a velocity bridge between two clouds at ∼50 and ∼150 km s⁻¹in our position–velocity diagram, which is direct evidence of a cloud–cloud collision. We measured an average gas temperature of ∼60 K in G5 using H₂CO integrated-intensity line ratios. We observed that the¹²C/¹³C ratio in G5 is consistent with optically thin, or at most marginally optically thick¹²CO. We measured$1.5\times {10}^{19}{\mathrm{cm}}^{-2}{(\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1})}^{-1}$for the local X_CO, 10–20× less than the average Galactic value. G5 is strong direct observational evidence of gas overshooting the CMZ and colliding with a bar lane on the opposite side of the Galactic center.

    

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