Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>NGC 6240 is a luminous infrared galaxy in the local universe in the midst of a major merger. We analyze high-resolution interferometric observations of warm molecular gas using CO <jats:italic>J</jats:italic> = 3–2 and 6–5 in the central few kpc of NGC 6240 taken by the Atacama Large Millimeter Array. Using these CO line observations, we model the density distribution and kinematics of the molecular gas between the nuclei of the galaxies. Our models suggest that a disk model represents the data poorly. Instead, we argue that the observations are consistent with a tidal bridge between the two nuclei. We also observe high-velocity redshifted gas that is not captured by the model. These findings shed light on small-scale processes that can affect galaxy evolution and the corresponding star formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A strong super-Alfvénic drift of energetic particles (or cosmic rays) in a magnetized plasma can amplify the magnetic field significantly through nonresonant streaming instability (NRSI). While the traditional analysis is done for an ion current, here we use kinetic particle-in-cell simulations to study how the NRSI behaves when it is driven by electrons or by a mixture of electrons and positrons. In particular, we characterize the growth rate, spectrum, and helicity of the unstable modes, as well the level of the magnetic field at saturation. Our results are potentially relevant for several space/astrophysical environments (e.g., electron strahl in the solar wind, at oblique nonrelativistic shocks, around pulsar wind nebulae), and also in laboratory experiments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetohydrodynamic (MHD) turbulence is an important agent of energetic particle acceleration. Focusing on the compressible properties of magnetic turbulence, we adopt the test particle method to study the particle acceleration from Alfvén, slow, and fast modes in four turbulence regimes that may appear in a realistic astrophysical environment. Our studies show that (1) the second-order Fermi mechanism drives the acceleration of particles in the cascade processes of three modes by particle-turbulence interactions, regardless of whether the shock wave appears; (2) not only can the power spectra of maximum-acceleration rates reveal the inertial range of compressible turbulence, but also recover the scaling and energy ratio relationship between the modes; (3) fast mode dominates the acceleration of particles, especially in the case of super-Alfvénic and supersonic turbulence, slow mode dominates the acceleration for sub-Alfvénic turbulence in the very-high-energy range, and the acceleration of Alfvén mode is significant at the early stage of the acceleration; (4) particle acceleration from three modes results in a power-law distribution in the certain range of evolution time. From the perspective of particle-wave mode interaction, this paper promotes the understanding for both the properties of turbulence and the behavior of particle acceleration, which will help provide insight into astrophysical processes involved in MHD turbulence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Over the past two decades scientists have significantly improved our understanding of the transport of energetic particles across a mean magnetic field. Due to test-particle simulations, as well as powerful nonlinear analytical tools, our understanding of this type of transport is almost complete. However, previously developed nonlinear analytical theories do not always agree perfectly with simulations. Therefore, a correction factor <jats:italic>a</jats:italic> <jats:sup>2</jats:sup> was incorporated into such theories with the aim to balance out inaccuracies. In this paper a new analytical theory for perpendicular transport is presented. This theory contains the previously developed unified nonlinear transport theory, the most advanced theory to date, in the limit of small Kubo number turbulence. New results have been obtained for two-dimensional turbulence. In this case, the new theory describes perpendicular diffusion as a process that is sub-diffusive while particles follow magnetic field lines. Diffusion is restored as soon as the turbulence transverse complexity becomes important. For long parallel mean-free paths, one finds that the perpendicular diffusion coefficient is a reduced field line random walk limit. For short parallel mean-free paths, on the other hand, one gets a hybrid diffusion coefficient that is a mixture of collisionless Rechester &amp; Rosenbluth and fluid limits. Overall, the new analytical theory developed in the current paper is in agreement with heuristic arguments. Furthermore, the new theory agrees almost perfectly with previously performed test-particle simulations without the need of the aforementioned correction factor <jats:italic>a</jats:italic> <jats:sup>2</jats:sup> or any other free parameter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Galactic synchrotron emission exhibits large angular scale features known as radio spurs and loops. Determining the physical size of these structures is important for understanding the local interstellar structure and for modeling the Galactic magnetic field. However, the distance to these structures is either under debate or entirely unknown. We revisit a classical method of finding the location of radio spurs by comparing optical polarization angles with those of synchrotron emission as a function of distance. We consider three tracers of the magnetic field: stellar polarization, polarized synchrotron radio emission, and polarized thermal dust emission. We employ archival measurements of optical starlight polarization and Gaia distances and construct a new map of polarized synchrotron emission from WMAP and Planck data. We confirm that synchrotron, dust emission, and stellar polarization angles all show a statistically significant alignment at high Galactic latitude. We obtain distance limits to three regions toward Loop I of 112 ± 17 pc, 135 ± 20 pc, and &lt;105 pc. Our results strongly suggest that the polarized synchrotron emission toward the North Polar Spur at <jats:italic>b</jats:italic> &gt; 30° is local. This is consistent with the conclusions of earlier work based on stellar polarization and extinction, but in stark contrast with the Galactic center origin recently revisited on the basis of X-ray data. We also obtain a distance measurement toward part of Loop IV (180 ± 15 pc) and find evidence that its synchrotron emission arises from chance overlap of structures located at different distances. Future optical polarization surveys will allow the expansion of this analysis to other radio spurs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of the influence of magnetic field strength and morphology in Type Ia supernovae and their late-time light curves and spectra. In order to both capture self-consistent magnetic field topologies and evolve our models to late times, a two-stage approach is taken. We study the early deflagration phase (∼1 s) using a variety of magnetic field strengths and find that the topology of the field is set by the burning, independent of the initial strength. We study late-time (∼1000 days) light curves and spectra with a variety of magnetic field topologies and infer magnetic field strengths from observed supernovae. Lower limits are found to be 10<jats:sup>6</jats:sup> G. This is determined by the escape, or lack thereof, of positrons that are tied to the magnetic field. The first stage employs 3D MHD and a local burning approximation and uses the code Enzo. The second stage employs a hybrid approach, with 3D radiation and positron transport and spherical hydrodynamics. The second stage uses the code HYDRA. In our models, magnetic field amplification remains small during the early deflagration phase. Late-time spectra bear the imprint of both magnetic field strength and morphology. Implications for alternative explosion scenarios are discussed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on the large volume Gaia Early Data Release 3 and LAMOST Data Release 5 data, we estimate the bias-corrected binary fractions of the field late G and early K dwarfs. A stellar locus outlier method is used in this work, which works well for binaries of various periods and inclination angles with single-epoch data. With a well-selected, distance-limited sample of about 90,000 GK dwarfs covering wide stellar chemical abundances, it enables us to explore the binary fraction variations with different stellar populations. The average binary fraction is 0.42 ± 0.01 for the whole sample. Thin-disk stars are found to have a binary fraction of 0.39 ± 0.02, thick-disk stars have a higher one of 0.49 ± 0.02, while inner halo stars possibly have the highest binary fraction. For both the thin- and thick-disk stars, the binary fractions decrease toward higher [Fe/H], [<jats:italic>α</jats:italic>/H], and [M/H] abundances. However, the suppressing impacts of [Fe/H], [<jats:italic>α</jats:italic>/H], and [M/H] are more significant for the thin-disk stars than those for the thick-disk stars. For a given [Fe/H], a positive correlation between [<jats:italic>α</jats:italic>/Fe] and the binary fraction is found for the thin-disk stars. However, this tendency disappears for the thick-disk stars. We suspect that it is likely related to the different formation histories of the thin and thick disks. Our results provide new clues for theoretical works on binary formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have estimated flux densities of several pulsars from radio interferometric observations mainly at 325 MHz using the Giant Metrewave Radio Telescope. The new observations allowed us to update the spectral nature of the observed pulsars, and in six sources we identified relatively high frequency turnovers, which can be classified as new GHz-peaked spectrum (GPS) pulsars. For such objects the turnover in the spectrum is most likely caused by absorption in the immediate vicinity of the pulsar (or in the interstellar medium). We modeled the turnover spectra using the thermal free–free absorption model and the physical parameters obtained from the fits enabled us to identify the environments that could potentially be responsible for the observed absorption, such as pulsar wind nebulae, supernova remnant nebulae or H <jats:sc>ii</jats:sc> regions. The discovery of 6 new GPS pulsars brings the total number of such objects to 33 and we discuss the properties of the entire sample.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Cosmology Large Angular Scale Surveyor (CLASS) is a four-telescope array observing the largest angular scales (2≲ <jats:italic>ℓ</jats:italic> ≲ 200) of the cosmic microwave background (CMB) polarization. These scales encode information about reionization and inflation during the early universe. The instrument stability necessary to observe these angular scales from the ground is achieved through the use of a variable-delay polarization modulator as the first optical element in each of the CLASS telescopes. Here, we develop a demodulation scheme used to extract the polarization timestreams from the CLASS data and apply this method to selected data from the first 2 yr of observations by the 40 GHz CLASS telescope. These timestreams are used to measure the 1/<jats:italic>f</jats:italic> noise and temperature-to-polarization (<jats:italic>T</jats:italic> → <jats:italic>P</jats:italic>) leakage present in the CLASS data. We find a median knee frequency for the pair-differenced demodulated linear polarization of 15.12 mHz and a <jats:italic>T</jats:italic> → <jats:italic>P</jats:italic> leakage of &lt;3.8 × 10<jats:sup>−4</jats:sup> (95% confidence) across the focal plane. We examine the sources of 1/<jats:italic>f</jats:italic> noise present in the data and find the component of 1/<jats:italic>f</jats:italic> due to atmospheric precipitable water vapor (PWV) has an amplitude of <jats:inline-formula> <jats:tex-math> <?CDATA $203\pm 12\,\mu {{\rm{K}}}_{\mathrm{RJ}}\sqrt{{\rm{s}}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>203</mml:mn> <mml:mo>±</mml:mo> <mml:mn>12</mml:mn> <mml:mspace width="0.50em" /> <mml:mi>μ</mml:mi> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>RJ</mml:mi> </mml:mrow> </mml:msub> <mml:msqrt> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:msqrt> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2235ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> for 1 mm of PWV when evaluated at 10 mHz; accounting for ∼17% of the 1/<jats:italic>f</jats:italic> noise in the central pixels of the focal plane. The low levels of <jats:italic>T</jats:italic> → <jats:italic>P</jats:italic> leakage and 1/<jats:italic>f</jats:italic> noise achieved through the use of a front-end polarization modulator are requirements for observing of the largest angular scales of the CMB polarization by the CLASS telescopes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Braneworld models with induced gravity exhibit phantom-like behavior of the effective equation of state of dark energy. They can, therefore, naturally accommodate higher values of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>, preferred by recent local measurements while satisfying the cosmic microwave background constraints. We test the background evolution in such phantom braneworld scenarios with the current observational data sets. We find that the phantom braneworld prefers a higher value of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> even without the R19 prior, thereby providing a much better fit to the local measurements. Although this braneworld model cannot fully satisfy all combinations of cosmological observables, among existing dark energy candidates the phantom brane provides one of the most compelling explanations of cosmic evolution.</jats:p>