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Comments on measurements of inter-stellar magnetic fields in the bar region of the galaxy NGC1097, as presented by Beck et al in the January 28, 1999 issue of `Nature.' Focus on the direction of gas flow in the galaxy and the location of regions of gas compression; Belief that gas flows inward along lanes to fuel bursts of star formation in a ring of dense molecular gas known as the circumnuclear ring; Effects of gas inflow in barred galaxies; Measurement of polarized radio synchrotron emission.

The center of the nearby galaxy NGC 253 hosts a population of more than a dozen super star clusters (SSCs) that are still in the process of forming. The majority of the star formation of the burst is concentrated in these SSCs, and the starburst is powering a multiphase outflow from the galaxy. In this work, we measure the 350 GHz dust continuum emission toward the center of NGC 253 at 47 mas (0.8 pc) resolution using data from the Atacama Large Millimeter/submillimeter Array. We report the detection of 350 GHz (dust) continuum emission in the outflow for the first time, associated with the prominent South-West streamer. In this feature, the dust emission has a width of ≈8 pc, is located at the outer edge of the CO emission, and corresponds to a molecular gas mass of ∼(8â€"17)Ă—106 M ⊙. In the starburst nucleus, we measure the resolved radial profiles, sizes, and molecular gas masses of the SSCs. Compared to previous work at the somewhat lower spatial resolution, the SSCs here break apart into smaller substructures with radii 0.4â€"0.7 pc. In projection, the SSCs, dust, and dense molecular gas appear to be arranged as a thin, almost linear, structure roughly 155 pc in length. The morphology and kinematics of this structure can be well explained as gas following x 2 orbits at the center of a barred potential. We constrain the morpho-kinematic arrangement of the SSCs themselves, finding that an elliptical, angular-momentum-conserving ring is a good description of both the morphology and kinematics of the SSCs. [ABSTRACT FROM AUTHOR]

Rotation curves of galaxies probe their total mass distributions, including dark matter. Dwarf galaxies are excellent systems to investigate the dark matter density distribution, as they tend to have larger fractions of dark matter compared to higher mass systems. The core-cusp problem describes the discrepancy found in the slope of the dark matter density profile in the centres of galaxies (β*) between observations of dwarf galaxies (shallower cores) and dark matter-only simulations (steeper cusps). We investigate β* in six nearby spiral dwarf galaxies for which high-resolution CO J  = 1–0 data were obtained with ALMA (Atacama Large Millimeter/submillimeter Array). We derive rotation curves and decompose the mass profile of the dark matter using our CO rotation curves as a tracer of the total potential and 4.5  |$\mu$| m photometry to define the stellar mass distribution. We find 〈β*〉 = 0.6 with a standard deviation of ±0.1 among the galaxies in this sample, in agreement with previous measurements in this mass range. The galaxies studied are on the high stellar mass end of dwarf galaxies and have cuspier profiles than lower mass dwarfs, in agreement with other observations. When the same definition of the slope is used, we observe steeper slopes than predicted by the FIRE and NIHAO simulations. This may signal that these relatively massive dwarfs underwent stronger gas inflows towards their centres than predicted by these simulations, that these simulations overpredict the frequency of accretion or feedback events, or that a combination of these or other effects are at work. [ABSTRACT FROM AUTHOR]

We examine the formation of clusters of galaxies in numerical simulations of a QUMOND cosmogony with massive sterile neutrinos. Clusters formed in these exploratory simulations develop higher velocities than those found in ACDM simulations. The bulk motions of clusters attain ~1000 km s-1 by low redshift, comparable to observations whereas ACDM simulated clusters tend to fall short. Similarly, high pairwise velocities are common in cluster-cluster collisions like the Bullet Cluster. There is also a propensity for the most massive clusters to be larger in QUMOND and to appear earlier than in ACDM, potentially providing an explanation for "pink elephants" like El Gordo. However, it is not obvious that the cluster mass function can be recovered. [ABSTRACT FROM AUTHOR]

Employing analytical and numerical tools, we expound the Galactic epicycle theory to describe the kinematic evolution of stellar, gravitationally unbound associations in the vicinity of the Sun. We estimate the limits of applicability of the analytical epicycle approximation and harmonic vertical motion by numerical integration of test orbits with an axisymmetric potential. We consider mainly early times when the associations are not too stretched out by differential Galactic rotation. If the member stars are ejected from a compact parental molecular cloud simultaneously, but with different velocities of ejection, the association remains as an entity for a long time. However, at a given time, individual velocities may vary widely among the members. The systematic differences of individual velocities does not allow one to apply the classical convergent point method even to young associations only several million years old. We demonstrate, however, that certain coordinate- and age-dependent corrections can be applied to the proper motions as observed in order to ‘rectify’ them and retrieve a common convergent point. This method can be used for determining the Oort's constants A and B, and for estimating the vertical frequency in the local part of the Galaxy and the expansion ages of nearby associations. In combination with the global convergence mapping technique, it can be used to search for yet-undiscovered nearby associations using the Hipparcos and Tycho-2 catalogues. [ABSTRACT FROM AUTHOR]

We present an empirical relation between the cold gas surface density (Σgas) and the optical extinction (AV) in a sample of 103 galaxies from the Extragalactic Database for Galaxy Evolution (EDGE) survey. This survey provides CARMA interferometric CO observations for 126 galaxies included in the Calar Alto Legacy Integral Field Area (CALIFA) survey. The matched, spatially resolved nature of these data sets allows us to derive the Σgas– AV  relation on global, radial, and kpc (spaxel) scales. We determine AV  from the Balmer decrement (H α/H β). We find that the best fit for this relation is |$\Sigma _{\rm gas}\,(\rm {M_\odot \,pc}^{-2}) \sim 26 \times {\rm \mathit{ A}_\mathit{ V}} \,(\rm mag)$|⁠ , and that it does not depend on the spatial scale used for the fit. However, the scatter in the fits increases as we probe smaller spatial scales, reflecting the complex relative spatial distributions of stars, gas, and dust. We investigate the Σgas/ AV  ratio on radial and spaxel scales as a function of |$\mathrm{EW(H\,\alpha)}$|⁠. We find that at larger values of |$\mathrm{EW({H\,\alpha })}$| (i.e. actively star-forming regions) this ratio tends to converge to twice the value expected for a foreground dust screen geometry (∼30 |$\mathrm{M_{\odot } \, pc^{-2} \, mag^{-1}}$|⁠). On radial scales, we do not find a significant relation between the Σgas/ AV  ratio and the ionized gas metallicity. We contrast our estimates of Σgas using AV  with compilations in the literature of the gas fraction on global and radial scales as well as with well-known scaling relations such as the radial star formation law and the Σgas–Σ* relation. These tests show that optical extinction is a reliable proxy for estimating Σgas in the absence of direct sub/millimeter observations of the cold gas. [ABSTRACT FROM AUTHOR]

This article includes the following "mini-articles" about applications and examples of computing in astronomy: "Visualizing the Universe: Using Modern Graphics Cards to Understand the Physical World," by F. Alexander Bogert, Nicholas Smith, and John Holdener; "Visualizing Big Data in Astronomy: The Automated Movie Production Environment Distribution and Display (AMPED) Pipeline," by Eric M. De Jong; "Supporting Distributed, Collaborative Review and Classification of Fast Transient Events," by Andrew F. Hart, Luca Cinquini, Shakeh E. Khudikyan, David R. Thompson, Chris A. Mattmann, Kiri Wagstaff, Joseph Lazio, and Dayton L. Jones; "Big Data Technologies at JPL," by Dayton L. Jones; and "The Astrophysics Source Code Library: ascl.net," by Alice Allen, Lior Shamir, and Peter Teuben. [ABSTRACT FROM PUBLISHER]

ABSTRACT The isolation, simple apparent structure and low luminosity of the nearby spiral galaxy NGC 6503 make it an ideal candidate for an in-depth kinematic and photometric study. We introduce a new publicly available code, D iskF it, that implements procedures for fitting non-axisymmetries in either kinematic or photometric data. We use D iskF it to analyse new Hα and CO velocity field data as well as H i kinematics from Greisen et al. to search for non-circular motions in the disc of NGC 6503. We find NGC 6503 to have remarkably regular gas kinematics that are well described by rotation only. We also use D iskF it and a new Ks-band image of NGC 6503 to constrain photometric models of the disc, bar and bulge. We find the galaxy to be photometrically dominated by the disc. We find NGC 6503 to contain a faint bar and an exponential bulge which together contribute only ∼5 per cent of the total galaxy light. The combination of our kinematic and photometric D iskF it models suggests that NGC 6503 contains a weak, end-on bar that may have produced its Type II surface brightness profile but is unlikely to be responsible for its strong σ-drop. [ABSTRACT FROM AUTHOR]

The inner regions of barred galaxies contain substructures such as off-axis shocks, nuclear rings, and nuclear spirals. These substructures may affect star formation, and control the activity of a central black hole (BH) by determining the mass inflow rate. We investigate the formation and properties of such substructures using high-resolution, grid-based hydrodynamic simulations. The gaseous medium is assumed to be infinitesimally thin, isothermal, and non-self-gravitating. The stars and dark matter are represented by a static gravitational potential with four components: a stellar disk, a bulge, a central BH, and a bar. To investigate various galactic environments, we vary the gas sound speed, cs, as well as the mass of the central BH, MBH. Once the flow has reached a quasi-steady state, off-axis shocks tend to move closer to the bar major axis as cs increases. Nuclear rings shrink in size with increasing cs, but are independent of MBH, suggesting that the ring position is not determined by the Lindblad resonances. Rings in low-cs models are narrow since they are occupied largely by gas on x2-orbits and well decoupled from nuclear spirals, while they become broad because of large thermal perturbations in high-cs models. Nuclear spirals persist only when either cs is small or MBH is large; they would otherwise be destroyed completely by the ring material on eccentric orbits. The shape and strength of nuclear spirals depend sensitively on cs and MBH such that they are leading if both cs and MBH are small, weak trailing if cs is small and MBH is large, and strong trailing if both cs and MBH are large. While the mass inflow rate toward the nucleus is quite small in low-cs models because of the presence of a narrow nuclear ring, it becomes larger than 0.01 M⊙ yr-1 when cs is large, providing a potential explanation of nuclear activity in Seyfert galaxies. [ABSTRACT FROM AUTHOR]

We summarize the main results from MODEST-1, the first workshop on MOdeling DEnse STellar systems. Our goal is to go beyond traditional population synthesis models, by introducing dynamical interactions between single stars, binaries, and multiple systems. The challenge is to define and develop a software framework to enable us to combine in one simulation existing computer codes in stellar evolution, stellar dynamics, and stellar hydrodynamics. With this objective, the workshop brought together experts in these three fields, as well as other interested astrophysicists and computer scientists. We report here our main conclusions, questions and suggestions for further steps toward integrating stellar evolution and stellar (hydro)dynamics. [Copyright &y& Elsevier]

We present observations of N2H+ (J = 1 → 0), HCO+ (J = 1 → 0), and HCN (J = 1 → 0) toward the Serpens Main molecular cloud from the CARMA Large Area Star Formation Survey (CLASSy). We mapped 150 arcmin2 of Serpens Main with an angular resolution of ∼7″. The gas emission is concentrated in two subclusters (the NW and SE subclusters). The SE subcluster has more prominent filamentary structures and more complicated kinematics compared to the NW subcluster. The majority of gas in the two subclusters has subsonic to sonic velocity dispersions. We applied a dendrogram technique with N2H+(1-0) to study the gas structures; the SE subcluster has a higher degree of hierarchy than the NW subcluster. Combining the dendrogram and line fitting analyses reveals two distinct relations: a flat relation between nonthermal velocity dispersion and size, and a positive correlation between variation in velocity centroids and size. The two relations imply a characteristic depth of 0.15 pc for the cloud. Furthermore, we have identified six filaments in the SE subcluster. These filaments have lengths of ∼0.2 pc and widths of ∼0.03 pc, which is smaller than a characteristic width of 0.1 pc suggested by Herschel observations. The filaments can be classified into two types based on their properties. The first type, located in the northeast of the SE subcluster, has larger velocity gradients, smaller masses, and nearly critical mass-per-unit-length ratios. The other type, located in the southwest of the SE subcluster, has the opposite properties. Several YSOs are formed along two filaments which have supercritical mass per unit length ratios, while filaments with nearly critical mass-per-unit-length ratios are not associated with YSOs, suggesting that stars are formed on gravitationally unstable filaments. [ABSTRACT FROM AUTHOR]

We present details of the CARMA Large Area Star Formation Survey (CLASSy), while focusing on observations of Barnard 1. CLASSy is a CARMA Key Project that spectrally imaged N2H+, HCO+, and HCN (J = 1 → 0 transitions) across over 800 square arcminutes of the Perseus and Serpens Molecular Clouds. The observations have angular resolution near 7″ and spectral resolution near 0.16 km s–1. We imaged ∼150 square arcminutes of Barnard 1, focusing on the main core, and the B1 Ridge and clumps to its southwest. N2H+ shows the strongest emission, with morphology similar to cool dust in the region, while HCO+ and HCN trace several molecular outflows from a collection of protostars in the main core. We identify a range of kinematic complexity, with N2H+ velocity dispersions ranging from ∼0.05 to 0.50 km s–1 across the field. Simultaneous continuum mapping at 3 mm reveals six compact object detections, three of which are new detections. A new, non-binary dendrogram algorithm is used to analyze dense gas structures in the N2H+ position-position-velocity (PPV) cube. The projected sizes of dendrogram-identified structures range from about 0.01 to 0.34 pc. Size-linewidth relations using those structures show that non-thermal line-of-sight velocity dispersion varies weakly with projected size, while rms variation in the centroid velocity rises steeply with projected size. Comparing these relations, we propose that all dense gas structures in Barnard 1 have comparable depths into the sky, around 0.1-0.2 pc; this suggests that overdense, parsec-scale regions within molecular clouds are better described as flattened structures rather than spherical collections of gas. Science-ready PPV cubes for Barnard 1 molecular emission are available for download. [ABSTRACT FROM AUTHOR]