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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.

 

We report on the discovery of linear filaments observed in the CO(1-0) emission for a ∼2′ field of view toward the Sgr E star-forming region, centered at (l,b) = (358.°720, 0.°011). The Sgr E region is thought to be at the turbulent intersection of the “far dust lane” associated with the Galactic bar and the Central Molecular Zone (CMZ). This region is subject to strong accelerations, which are generally thought to inhibit star formation, yet Sgr E contains a large number of Hiiregions. We present¹²CO(1-0),¹³CO(1-0), and C¹⁸O(1-0) spectral line observations from the Atacama Large Millimeter/submillimeter Array and provide measurements of the physical and kinematic properties for two of the brightest filaments. These filaments have widths (FWHMs) of ∼0.1 pc and are oriented nearly parallel to the Galactic plane, with angles from the Galactic plane of ∼2°. The filaments are elongated, with lower-limit aspect ratios of ∼5:1. For both filaments, we detect two distinct velocity components that are separated by about 15 km s⁻¹. In the C¹⁸O spectral line data, with ∼0.09 pc spatial resolution, we find that these velocity components have relatively narrow (∼1–2 km s⁻¹) FWHM line widths when compared to other sources toward the Galactic center. The properties of these filaments suggest that the gas in the Sgr E complex is being “stretched,” as it is rapidly accelerated by the gravitational field of the Galactic bar while falling toward the CMZ, a result that could provide insights into the extreme environment surrounding this region and the large-scale processes that fuel this environment.

 

CMZoom survey observations with the Submillimeter Array are analyzed to describe the virial equilibrium (VE) and star-forming potential of 755 clumps in 22 clouds in the Central Molecular Zone (CMZ) of the Milky Way. In each cloud, nearly all clumps follow the column density–mass trendN∝M^s, wheres= 0.38 ± 0.03 is near the pressure-bounded limits_p= 1/3. This trend is expected when gravitationally unbound clumps in VE have similar velocity dispersion and external pressure. Nine of these clouds also harbor one or two distinctly more massive clumps. These properties allow a VE model of bound and unbound clumps in each cloud, where the most massive clump has the VE critical mass. These models indicate that 213 clumps have velocity dispersion 1–2 km s⁻¹, mean external pressure (0.5–4) × 10⁸cm⁻³K, bound clump fraction 0.06, and typical virial parameterα= 4–15. These mostly unbound clumps may be in VE with their turbulent cloud pressure, possibly driven by inflow from the Galactic bar. In contrast, most Sgr B2 clumps are bound according to their associated sources andN–Mtrends. When the CMZ clumps are combined into mass distributions, their typical power-law slope is analyzed with a model of stopped accretion. It also indicates that most clumps are unbound and cannot grow significantly, due to their similar timescales of accretion and dispersal, ∼0.2 Myr. Thus, virial and dynamical analyses of the most extensive clump census available indicate that star formation in the CMZ may be suppressed by a significant deficit of gravitationally bound clumps.

 

Young massive clusters (YMCs) are compact (≲1 pc), high-mass (>104 M⊙) stellar systems of significant scientific interest. Due to their rarity and rapid formation, we have very few examples of YMC progenitor gas clouds before star formation has begun. As a result, the initial conditions required for YMC formation are uncertain. We present high resolution (0.13 arcsec, ∼1000 au) ALMA observations and Mopra single-dish data, showing that Galactic Centre dust ridge ‘Cloud d’ (G0.412 + 0.052, mass = 7.6 × 104 M⊙, radius = 3.2 pc) has the potential to become an Arches-like YMC (104 M⊙, r ∼ 1 pc), but is not yet forming stars. This would mean it is the youngest known pre-star-forming massive cluster and therefore could be an ideal laboratory for studying the initial conditions of YMC formation. We find 96 sources in the dust continuum, with masses ≲3 M⊙ and radii of ∼103 au. The source masses and separations are more consistent with thermal rather than turbulent fragmentation. It is not possible to unambiguously determine the dynamical state of most of the sources, as the uncertainty on virial parameter estimates is large. We find evidence for large-scale (∼1 pc) converging gas flows, which could cause the cloud to grow rapidly, gaining 104 M⊙ within 105 yr. The highest density gas is found at the convergent point of the large-scale flows. We expect this cloud to form many high-mass stars, but find no high-mass starless cores. If the sources represent the initial conditions for star formation, the resulting initial mass function will be bottom heavy.

 

Abstract Star formation primarily occurs in filaments where magnetic fields are expected to be dynamically important. The largest and densest filaments trace the spiral structure within galaxies. Over a dozen of these dense (∼10 4 cm −3 ) and long (>10 pc) filaments have been found within the Milky Way, and they are often referred to as “bones.” Until now, none of these bones has had its magnetic field resolved and mapped in its entirety. We introduce the SOFIA legacy project FIELDMAPS which has begun mapping ∼10 of these Milky Way bones using the HAWC+ instrument at 214 μ m and 18.″2 resolution. Here we present a first result from this survey on the ∼60 pc long bone G47. Contrary to some studies of dense filaments in the Galactic plane, we find that the magnetic field is often not perpendicular to the spine (i.e., the center line of the bone). Fields tend to be perpendicular in the densest areas of active star formation and more parallel or random in other areas. The average field is neither parallel nor perpendicular to the Galactic plane or the bone. The magnetic field strengths along the spine typically vary from ∼20 to ∼100 μ G. Magnetic fields tend to be strong enough to suppress collapse along much of the bone, but for areas that are most active in star formation, the fields are notably less able to resist gravitational collapse.