D-Scrambled Cantor Sets
For all $d \ge 3$, we provide an example of a homeomorphism of Cantor space that has an uncountable $d$-scrambled set but no $d$-scrambled Cantor set.
math.DS↗
arXiv subjects
B. Miller
Publications and source records attributed to B. Miller.
Tidal pre-conditioning and ram-pressure stripping in NGC 1427A. Deep VLT/MUSE spectroscopy and FUV-to-radio observations trace a Fornax Cluster dwarf in transformation
The early environmental transformation of low-mass cluster galaxies from gas-rich to gas-poor remains poorly constrained, partly because clear, phase-resolved observations are rare. NGC 1427A, a disturbed star-forming dwarf in the Fornax cluster, offers a favorable case for studying this process. We aim to build a spatially resolved, multi-phase picture of NGC 1427A to constrain the roles of ram-pressure stripping and tidal perturbations. We combine a deep, spatially contiguous VLT/MUSE mosaic with ancillary data from the FUV to the radio. Full-spectrum fitting of the MUSE cube yields maps of stellar kinematics, ages, metallicities, and continuum attenuation, while emission-line modeling provides ionized-gas kinematics, Balmer-decrement reddening, and star-formation-rate surface densities. Ancillary multi-wavelength data trace neutral and molecular gas, dust, and recent star formation, placing the MUSE-based results in a broader multi-phase context. We find a pronounced decoupling between stars and gas: the H I and ionized gas rotate about an axis tilted with respect to the stellar field and are globally blueshifted. Stellar and nebular attenuation, infrared dust tracers, and H I morphology indicate stripping with a strong line-of-sight component that has reached the ISM. At the same time, the asymmetric gas and dust distribution, together with structured and time-dependent star formation, points to an additional gravitational perturbation, with a recent mild fly-by by a nearby dwarf being the favored interpretation. We propose that dwarf-dwarf tidal effects have torqued and pre-conditioned the gas, while the Fornax intracluster medium is driving ram-pressure stripping that now reaches the ISM and coincides with a declining global star formation rate. This places NGC 1427A at the onset of environmental quenching, making it a useful benchmark for early cluster dwarf transformation.
astro-ph.GA↗
Strategic Scientific Plan for Gemini Observatory
We present the Strategic Scientific Plan (SSP) for the direction and activities of the Gemini Observatory in the 2020s. The overarching goal is to ensure that Gemini best uses the available resources to serve the needs of its international user community throughout the coming decade. The actionable items fall into three general categories: (1) preserving Gemini's current facilities and strengths; (2) developing instrumentation and software systems, including data pipelines, to enable new scientific capabilities that build on those strengths; (3) strategizing how visiting instruments can deliver additional valuable capabilities. We provide a high-level timeline (schematically illustrated in one figure) for the main developments discussed in this SSP. The schedule is ambitious, but in light of the recent Gemini in the Era of Multi-Messenger Astronomy (GEMMA) award from the NSF, the plan becomes achievable. Lists of milestones are given for gauging progress. As these milestones are reached and new instruments become available, some current instruments will need to be retired; we make recommendations in this regard. The final section concludes by reemphasizing the importance of a strong partnership committed to the needs of all members.
astro-ph.IM↗
How nucleation and luminosity shape faint dwarf galaxies
We study the intrinsic shapes of a sample of over 400 quiescent galaxies in the cores of the Virgo and Fornax clusters with luminosities $10^{6} \leq L_{g}/L_{\odot} \leq 10^{8}$. Similar to satellites of the Local Group and Centaurus A, these faint, low surface brightness cluster galaxies are best described as a family of thick ($C/A > 0.5$), oblate-triaxial spheroids. However, the large sample size allows us to show that the flattening of their stellar distributions depends both on luminosity and on the presence of a nuclear star cluster. Nucleated satellites are thicker at all luminosities compared to their non-nucleated counterparts, and fainter galaxies are systematically thicker as well, regardless of nucleation. Once nucleation is accounted for, we find no evidence that the environment the satellites live in plays a relevant role in setting their three-dimensional structure. We interpret both the presence of stellar nuclei and the associated thicker shapes as the result of preferential early and rapid formation, effectively making these faint nucleated galaxies the first generation of cluster satellites.
astro-ph.GA↗
The Next Generation Virgo Cluster Survey. XXIII. Fundamentals of nuclear star clusters over seven decades in galaxy mass
Using deep, high resolution optical imaging from the Next Generation Virgo Cluster Survey we study the properties of nuclear star clusters (NSCs) in a sample of nearly 400 quiescent galaxies in the core of Virgo with stellar masses $10^{5}\lesssim M_{*}/M_{\odot} \lesssim10^{12}$. The nucleation fraction reaches a peak value $f_{n}\approx90\%$ for $M_{*} \approx 10^{9} M_{\odot}$ galaxies and declines for both higher and lower masses, but nuclei populate galaxies as small as $M_{*} \approx5\times10^{5} M_{\odot}$. Comparison with literature data for nearby groups and clusters shows that at the low-mass end nucleation is more frequent in denser environments. The NSC mass function peaks at $M_{NSC}\approx7\times10^{5} M_{\odot}$, a factor 3-4 times larger than the turnover mass for globular clusters (GCs). We find a nonlinear relation between the stellar masses of NSCs and of their host galaxies, with a mean nucleus-to-galaxy mass ratio that drops to $M_{NSC}/M_{*}\approx3.6\times10^{-3}$ for $M_{*} \approx 5\times10^{9} M_{\odot}$ galaxies. Nuclei in both more and less massive galaxies are much more prominent: $M_{NSC}\propto M_{*}^{0.46}$ at the low-mass end, where nuclei are nearly 50% as massive as their hosts. We measure an intrinsic scatter in NSC masses at fixed galaxy stellar mass of 0.4 dex, which we interpret as evidence that the process of NSC growth is significantly stochastic. At low galaxy masses we find a close connection between NSCs and GC systems, including a very similar occupation distribution and comparable total masses. We discuss these results in the context of current dissipative and dissipationless models of NSC formation.
astro-ph.GA↗
The SeaQuest Spectrometer at Fermilab
The SeaQuest spectrometer at Fermilab was designed to detect oppositely-charged pairs of muons (dimuons) produced by interactions between a 120 GeV proton beam and liquid hydrogen, liquid deuterium and solid nuclear targets. The primary physics program uses the Drell-Yan process to probe antiquark distributions in the target nucleon. The spectrometer consists of a target system, two dipole magnets and four detector stations. The upstream magnet is a closed-aperture solid iron magnet which also serves as the beam dump, while the second magnet is an open aperture magnet. Each of the detector stations consists of scintillator hodoscopes and a high-resolution tracking device. The FPGA-based trigger compares the hodoscope signals to a set of pre-programmed roads to determine if the event contains oppositely-signed, high-mass muon pairs.
physics.ins-det↗
Imaging Spectroscopic Ellipsometry of Mono- and Few-layer MoS2
Micromechanically exfoliated mono- and multilayers of molybdenum disulfide (MoS2) are investigated by spectroscopic imaging ellipsometry. In combination with knife edge illumination, MoS2 flakes can be detected and classified on arbitrary flat and also transparent substrates with a lateral resolution down to 1 to 2 um. The complex dielectric functions from mono- and trilayer MoS2 are presented. They are extracted from a multilayer model to fit the measured ellipsometric angles employing an anisotropic and an isotropic fit approach. We find that the energies of the critical points of the optical constants can be treated to be independent of the utilized model, whereas the magnitude of the optical constants varies with the used model. The anisotropic model suggests a maximum absorbance for a MoS2 sheet supported by sapphire of about 14 % for monolayer and of 10 % for trilayer MoS2. Furthermore, the lateral homogeneity of the complex dielectric function for monolayer MoS2 is investigated with a spatial resolution of 2 um. Only minor fluctuations are observed. No evidence for strain, for a significant amount of disorder or lattice defects can be found in the wrinkle-free regions of the MoS2 monolayer from complementary Raman spectroscopy measurements. We assume that the minor lateral variation in the optical constants are caused by lateral modification in the van der Waals interaction presumably caused by the preparation using micromechanical exfoliation and viscoelastic stamping.
cond-mat.mes-hall↗
PSR J1930-1852: a pulsar in the widest known orbit around another neutron star
In the summer of 2012, during a Pulsar Search Collaboratory workshop, two high-school students discovered J1930$-$1852, a pulsar in a double neutron star (DNS) system. Most DNS systems are characterized by short orbital periods, rapid spin periods and eccentric orbits. However, J1930$-$1852 has the longest spin period ($P_{\rm spin}\sim$185 ms) and orbital period ($P_{\rm b}\sim$45 days) yet measured among known, recycled pulsars in DNS systems, implying a shorter than average and/or inefficient recycling period before its companion went supernova. We measure the relativistic advance of periastron for J1930$-$1852, $\dot{\omega}=0.00078$(4) deg/yr, which implies a total mass (M$_{\rm{tot}}=2.59$(4) M$_{\odot}$) consistent with other DNS systems. The $2\sigma$ constraints on M$_{\rm{tot}}$ place limits on the pulsar and companion masses ($m_{\rm p}<1.32$ M$_{\odot}$ and $m_{\rm c}>1.30$ M$_{\odot}$ respectively). J1930$-$1852's spin and orbital parameters challenge current DNS population models and make J1930$-$1852 an important system for further investigation.
astro-ph.HE↗
Definitive Sun-as-a-star p-mode frequencies: 23 years of BiSON observations
We present a list of "best possible" estimates of low-degree p-mode frequencies, from 8640 days of observations made by the Birmingham Solar-Oscillations Network (BiSON). This is the longest stretch of helioseismic data ever used for this purpose, giving exquisite precision in the estimated frequencies. Every effort has been made in the analysis to ensure that the frequency estimates are also accurate. In addition to presenting the raw best-fitting frequencies from our "peak bagging" analysis, we also provide tables of corrected frequencies pertinent to the quiet-Sun and an intermediate level of solar activity.
astro-ph.SR↗
Kinemetry: quantifying kinematic maps
We describe a new technique, kinemetry, to quantify kinematic maps of early-type galaxies in an efficient way. We present the first applications to velocity fields obtained with the integral-field spectrograph SAURON.
astro-ph↗