Mean-field density functional theory of a nanoconfined classical, three-dimensional Heisenberg fluid. II. The interplay between molecular packing and orientational order

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 149, 054704 (2018) and may be found at https://doi.org/10.1063/1.5040934.As in Paper I of this series of papers [S. M. Cattes et al., J. Chem. Phys. 144, 194704 (2016)], we study a Heisenberg fluid confined to a nanoscopic slit pore with smooth walls. The pore walls can either energetically discriminate specific orientations of the molecules next to them or are indifferent to molecular orientations. Unlike in Paper I, we employ a version of classical density functional theory that allows us to explicitly account for the stratification of the fluid (i.e., the formation of molecular layers) as a consequence of the symmetry-breaking presence of the pore walls. We treat this stratification within the White Bear version (Mark I) of fundamental measure theory. Thus, in this work, we focus on the interplay between local packing of the molecules and orientational features. In particular, we demonstrate why a critical end point can only exist if the pore walls are not energetically discriminating specific molecular orientations. We analyze in detail the positional and orientational order of the confined fluid and show that reorienting molecules across the pore space can be a two-dimensional process. Last but not least, we propose an algorithm based upon a series expansion of Bessel functions of the first kind with which we can solve certain types of integrals in a very efficient manner.DFG, 65143814, GRK 1524: Self-Assembled Soft-Matter Nanostructures at Interface

Resolving stellar populations with crowded field 3D spectroscopy

(Abridged) We describe a new method to extract spectra of stars from observations of crowded stellar fields with integral field spectroscopy (IFS). Our approach extends the well-established concept of crowded field photometry in images into the domain of 3-dimensional spectroscopic datacubes. The main features of our algorithm are: (1) We assume that a high-fidelity input source catalogue already exists and that it is not needed to perform sophisticated source detection in the IFS data. (2) Source positions and properties of the point spread function (PSF) vary smoothly between spectral layers of the datacube, and these variations can be described by simple fitting functions. (3) The shape of the PSF can be adequately described by an analytical function. Even without isolated PSF calibrator stars we can therefore estimate the PSF by a model fit to the full ensemble of stars visible within the field of view. (4) By using sparse matrices to describe the sources, the problem of extracting the spectra of many stars simultaneously becomes computationally tractable. We present extensive performance and validation tests of our algorithm using realistic simulated datacubes that closely reproduce actual IFS observations of the central regions of Galactic globular clusters. We investigate the quality of the extracted spectra under the effects of crowding. The main effect of blending between two nearby stars is a decrease in the S/N in their spectra. The effect increases with the crowding in the field in a way that the maximum number of stars with useful spectra is always ~0.2 per spatial resolution element. This balance breaks down when exceeding a total source density of ~1 significantly detected star per resolution element. We close with an outlook by applying our method to a simulated globular cluster observation with the upcoming MUSE instrument at the ESO-VLT.Comment: accepted for publication in A&A, 19 pages, 19 figure

An IFU investigation of possible Lyman continuum escape from Mrk 71/NGC 2366

Mrk 71/NGC 2366 is the closest Green Pea (GP) analog and candidate Lyman Continuum (LyC) emitter. Recently, 11 LyC-leaking GPs have been detected through direct observations of the ionizing continuum, making this the most abundant class of confirmed LyC-emitters at any redshift. High resolution, multi-wavelength studies of GPs can lead to an understanding of the method(s), through which LyC escapes from these galaxies. The proximity of Mrk 71/NCG 2366 offers unprecedented detail on the inner workings of a GP analog, and enables us to identify the mechanisms of LyC escape. We use 5825-7650{\AA} integral field unit PMAS observations to study the kinematics and physical conditions in Mrk 71. An electron density map is obtained from the [S II] ratio. A fortuitous second order contamination by the [O II]3727 doublet enables the construction of an electron temperature map. Resolved maps of sound speed, thermal broadening, "true" velocity dispersion, and Mach number are obtained and compared to the high resolution magneto-hydrodynamic SILCC simulations. Two regions of increased velocity dispersion indicative of outflows are detected to the north and south of the super star cluster, knot B, with redshifted and blueshifted velocities, respectively. We confirm the presence of a faint broad kinematical component, which is seemingly decoupled from the outflow regions, and is fainter and narrower than previously reported in the literature. Within uncertainties, the low- and high-ionization gas move together. Outside of the core of Mrk 71, an increase in Mach numbers is detected, implying a decrease in gas density. Simulations suggest this drop in density can be as high as ~4 dex, down to almost optically thin levels, which would imply a non-zero LyC escape fraction along the outflows... [abridged]Comment: Accepted for publication in A&A. 17 pages, 16 figures, 4 table

Phase Transitions in Hexane Monolayers Physisorbed onto Graphite

We report the results of molecular dynamics (MD) simulations of a complete monolayer of hexane physisorbed onto the basal plane of graphite. At low temperatures the system forms a herringbone solid. With increasing temperature, a solid to nematic liquid crystal transition takes place at $T_1 = 138 \pm 2$K followed by another transition at $T_2 = 176 \pm 3$K into an isotropic fluid. We characterize the different phases by calculating various order parameters, coordinate distributions, energetics, spreading pressure and correlation functions, most of which are in reasonable agreement with available experimental evidence. In addition, we perform simulations where the Lennard-Jones interaction strength, corrugation potential strength and dihedral rigidity are varied in order to better characterize the nature of the two transitions through. We find that both phase transitions are facilitated by a ``footprint reduction'' of the molecules via tilting, and to a lesser degree via creation of gauche defects in the molecules.Comment: 18 pages, eps figures embedded, submitted to Phys. Rev.

Resolving stellar populations with integral field spectroscopy

High-performance instruments at large ground-based telescopes have made integral field spectroscopy (IFS) a powerful tool for the study of extended objects such as galaxies, nebulae, or even larger survey fields on the sky. Here, we discuss the capabilities of IFS for the study of resolved stellar populations, using the newmethod of point-spread-function-fitting crowded field IFS, analogous to the well-established technique of crowded field photometry with image sensors.We review early pioneering work with first-generation integral field spectrographs, the breakthrough achieved with the multiunit spectral explorer (MUSE) instrument at the European Organisation for Astronomical Research in the Southern Hemisphere (ESO)Very Large Telescope, the remarkable progress accomplished with MUSE in the study of globular clusters, and first results on nearby galaxies. We discuss the synergy of integral field spectrographs at 8–10 mclass telescopes with future facilities such as the extremely large telescope (ELT)

Resolving stellar populations with integral field spectroscopy

High-performance instruments at large ground-based telescopes have made integral field spectroscopy (IFS) a powerful tool for the study of extended objects such as galaxies, nebulae, or even larger survey fields on the sky. Here we discuss the capabilities of IFS for the study of resolved stellar populations, using the new method of PSF-fitting crowded field IFS, analogous to the well-established technique of crowded field photometry with image sensors. We review early pioneering work with first generation integral field spectrographs, the breakthrough achieved with the MUSE instrument at the ESO Very Large Telescope, the remarkable progress accomplished with MUSE in the study of globular clusters, and first results on nearby galaxies. We discuss the synergy of integral field spectrographs at 8-10m class telescopes with future facilities such as the Extremely Large Telescope (ELT).Comment: 6 pages, 3 figures, accepted for AN special issue for STARS2019/SMFNS201

The central dynamics of M3, M13, and M92: Stringent limits on the masses of intermediate-mass black holes

We used the PMAS integral field spectrograph to obtain large sets of radial velocities in the central regions of three northern Galactic globular clusters: M3, M13, and M92. By applying the novel technique of crowded field 3D spectroscopy, we measured radial velocities for about 80 stars within the central ~ 10 arcsec of each cluster. These are by far the largest spectroscopic datasets obtained in the innermost parts of these clusters up to now. To obtain kinematical data across the whole extent of the clusters, we complement our data with measurements available in the literature. We combine our velocity measurements with surface brightness profiles to analyse the internal dynamics of each cluster using spherical Jeans models, and investigate whether our data provide evidence for an intermediate-mass black hole in any of the clusters. The surface brightness profiles reveal that all three clusters are consistent with a core profile, although shallow cusps cannot be excluded. We find that spherical Jeans models with a constant mass-to-light ratio provide a good overall representation of the kinematical data. A massive black hole is required in none of the three clusters to explain the observed kinematics. Our 1sigma (3sigma) upper limits are 5300 M_sun (12000 M_sun) for M3, 8600 M_sun (13000 M_sun) for M13, and 980 M_sun (2700 M_sun) for M92. A puzzling circumstance is the existence of several potential high velocity stars in M3 and M13, as their presence can account for the majority of the discrepancies that we find in our mass limits compared to M92.Comment: accepted for publication in A&A, 20 pages, 15 figures, tables D1 to D6 only available at CD