ALMA Uncovers Highly Filamentary Structure toward the Sgr E Region

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 H ii regions. We present 12CO(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

A smoother end to the dark ages

Independent lines of evidence suggest that the first stars, which ended the cosmic dark ages, came in pairs, rather than singly. This could change the prevailing view that the early Universe had a Swiss-cheese-like appearance.Comment: Nature News and Views, April 7, 201

The filamentary structures in the CO emission toward the Milky Way disk

We present a statistical study of the filamentary structure orientation in the CO emission observations obtained in the Milky Way Imaging Scroll Painting survey in the range 25 (.)degrees . degrees 8 < l < 49 (.)degrees . degrees 7, |b| <= 1 (.)degrees degrees 25, and -100 < v(LSR) < 135 km s(-1). We found that most of the filamentary structures in the (CO)-C-12 and (CO)-C-13 emission do not show a global preferential orientation either parallel or perpendicular to the Galactic plane. However, we found ranges in Galactic longitude and radial velocity where the (CO)-C-12 and (CO)-C-13 filamentary structures are parallel to the Galactic plane. These preferential orientations are different from those found for the HI emission. We consider this an indication that the molecular structures do not simply inherit these properties from parental atomic clouds. Instead, they are shaped by local physical conditions, such as stellar feedback, magnetic fields, and Galactic spiral shocks

Warpfield population synthesis: The physics of (extra-)Galactic star formation and feedback-driven cloud structure and emission from sub-to-kpc scales

We present a novel method to model galactic-scale star formation and emission of star clusters and a multiphase interstellar medium (ISM). We combine global parameters, including star formation rate and metallicity, with the 1D cloud evolution code warpfield to model the sources of feedback within a star-forming galaxy. Within individual star-forming regions, we include stellar evolution, stellar winds, radiation pressure, and supernovae, all coupled to the dynamical evolution of the 1D parental cloud in a highly non-linear fashion. Heating of the diffuse galactic gas and dust is calculated self-consistently with the age-, mass-, and density-dependent escape fractions of photons from these fully resolved local star-forming regions. We construct the interstellar radiation field, and we employ the multifrequency radiative transfer code polaris to produce synthetic emission maps for a one-to-one comparison with observations. We apply this to a cosmological simulation of a Milky-Way-like galaxy built-up in a high-resolution MHD simulation of cosmic structure formation. From this, we produce the multiscale/phase distribution of ISM density and temperature and present a synthesized all-sky H α map. We use a multipole expansion to show that the resulting maps reproduce all observed statistical emission characteristics. Next, we predict [S iii] 9530 Å, a key emission line that will be observed in several large forthcoming surveys. It suffers less extinction than other lines and provides information about star formation in very dense environments that are otherwise observationally inaccessible optically. Finally, we explore the effects of differential extinction, and discuss the consequences for the interpretation of H α emission at different viewing angles by an extragalactic observer

Star Formation in the Milky Way and Nearby Galaxies

We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star formation rates are discussed, and updated prescriptions for calculating star formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.Comment: 55 pages, 15 figures, in press for Annual Reviews of Astronomy and Astrophysics; Updated with corrected equation 5, improved references, and other minor change

The complex multiscale structure in simulated and observed emission maps of the proto-cluster cloud G0.253+0.016 ('the Brick')

The Central Molecular Zone (the central ∼500 pc of the Milky Way) hosts molecular clouds in an extreme environment of strong shear, high gas pressure and density, and complex chemistry. G0.253+0.016, also known as 'the Brick', is the densest, most compact, and quiescent of these clouds. High-resolution observations with the Atacama Large Millimetre/submillimetre Array (ALMA) have revealed its complex, hierarchical structure. In this paper we compare the properties of recent hydrodynamical simulations of the Brick to those of the ALMA observations. To facilitate the comparison, we post-process the simulations and create synthetic ALMA maps of molecular line emission from eight molecules. We correlate the line emission maps to each other and to the mass column density and find that HNCO is the best mass tracer of the eight emission lines within the simulations. Additionally, we characterize the spatial structure of the observed and simulated cloud using the density probability distribution function (PDF), spatial power spectrum, fractal dimension, and moments of inertia. While we find good agreement between the observed and simulated data in terms of power spectra and fractal dimensions, there are key differences in the density PDFs and moments of inertia, which we attribute to the omission of magnetic fields in the simulations. This demonstrates that the presence of the Galactic potential can reproduce many cloud properties, but additional physical processes are needed to fully explain the gas structure

The Galactic dynamics revealed by the filamentary structure in atomic hydrogen emission

We present a study of the filamentary structure in the neutral atomic hydrogen (H ̄I) emission at the 21 cm wavelength toward the Galactic plane using the 16 2.2-resolution observations in the H ̄I 4(HI4PI) survey. Using the Hessian matrix method across radial velocity channels, we identified the filamentary structures and quantified their orientations using circular statistics. We found that the regions of the Milky Waya's disk beyond 10 kpc and up to roughly 18 kpc from the Galactic center display H ̄I filamentary structures predominantly parallel to the Galactic plane. For regions at lower Galactocentric radii, we found that the H ̄I filaments are mostly perpendicular or do not have a preferred orientation with respect to the Galactic plane. We interpret these results as the imprint of supernova feedback in the inner Galaxy and Galactic rotation and shear in the outer Milky Way. We found that the H ̄I filamentary structures follow the Galactic warp and flaring and that they highlight some of the variations interpreted as the effect of the gravitational interaction with satellite galaxies. In addition, the mean scale height of the filamentary structures is lower than that sampled by the bulk of the H ̄I emission, thus indicating that the cold and warm atomic hydrogen phases have different scale heights in the outer galaxy. Finally, we found that the fraction of the column density in H ̄I filaments is almost constant up to approximately 18 kpc from the Galactic center. This is possibly a result of the roughly constant ratio between the cold and warm atomic hydrogen phases inferred from the H ̄I absorption studies. Our results indicate that the H ̄I filamentary structures provide insight into the dynamical processes shaping the Galactic disk. Their orientations record how and where the stellar energy input, the Galactic fountain process, the cosmic ray diffusion, and the gas accretion have molded the diffuse interstellar medium in the Galactic plane

Radio continuum emission in the northern Galactic plane: Sources and spectral indices from the THOR survey

Radio continuum surveys of the Galactic plane can find and characterize HII regions, supernova remnants (SNRs), planetary nebulae (PNe), and extragalactic sources. A number of surveys at high angular resolution (<25") at different wavelengths exist to study the interstellar medium (ISM), but no comparable high-resolution and high-sensitivity survey exists at long radio wavelengths around 21cm. We observed a large fraction of the Galactic plane in the first quadrant of the Milky Way (l=14.0-67.4deg and |b| < 1.25deg) with the Karl G. Jansky Very Large Array (VLA) in the C-configuration covering six continuum spectral windows. These data provide a detailed view on the compact as well as extended radio emission of our Galaxy and thousands of extragalactic background sources. We used the BLOBCAT software and extracted 10916 sources. After removing spurious source detections caused by the sidelobes of the synthesised beam, we classified 10387 sources as reliable detections. We smoothed the images to a common resolution of 25" and extracted the peak flux density of each source in each spectral window (SPW) to determine the spectral indices $\alpha$ (assuming $I(\nu)\propto\nu^\alpha$). By cross-matching with catalogs of HII regions, SNRs, PNe, and pulsars, we found radio counterparts for 840 HII regions, 52 SNRs, 164 PNe, and 38 pulsars. We found 79 continuum sources that are associated with X-ray sources. We identified 699 ultra-steep spectral sources ($\alpha < -1.3$) that could be high-redshift galaxies. Around 9000 of the sources we extracted are not classified specifically, but based on their spatial and spectral distribution, a large fraction of them is likely to be extragalactic background sources. More than 7750 sources do not have counterparts in the SIMBAD database, and more than 3760 sources do not have counterparts in the NED database

ALMA Uncovers Highly Filamentary Structure toward the Sgr E Region

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 H ii regions. We present 12CO(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