Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We perform magnetohydrodynamic simulations of accreting, equal-mass binary black holes in full general relativity focusing on the impact of black hole spin on the dynamical formation and evolution of minidisks. We find that during the late inspiral the sizes of minidisks are primarily determined by the interplay between the tidal field and the effective innermost stable orbit around each black hole. Our calculations support that a minidisk forms when the Hill sphere around each black hole is significantly larger than the black hole’s effective innermost stable orbit. As the binary inspirals, the radius of the Hill sphere decreases, and minidisks consequently shrink in size. As a result, electromagnetic signatures associated with minidisks may be expected to gradually disappear prior to merger when there are no more stable orbits within the Hill sphere. In particular, a gradual disappearance of a hard electromagnetic component in the spectrum of such systems could provide a characteristic signature of merging black hole binaries. For a binary of given total mass, the timescale to minidisk “evaporation” should therefore depend on the black hole spins and the mass ratio. We also demonstrate that accreting binary black holes with spin have a higher efficiency for converting accretion power to jet luminosity. These results could provide new ways to estimate black hole spins in the future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The ∼4 km diameter main belt asteroid 6478 Gault has ejected dust intermittently since at least 2013. The character of the emission, including its episodic nature and the low speed of the ejected particles (<jats:italic>V</jats:italic> ∼ 0.15 m s<jats:sup>−1</jats:sup>), is most consistent with mass loss from a body rotating near rotational breakup. Owing to dust contamination of the nucleus signal, this conclusion had not yet been confirmed. To test this idea, we have obtained new images of Gault in 2020 August in the absence of dust. Our photometry shows a lightcurve with a very small amplitude (maximum ∼0.05 mag) and a periodicity of 2.55 ± 0.10 hr. The new observations are consistent with a model in which Gault is rotating near breakup, with centrifugal forces responsible for its episodic mass loss. Approximated as a strengthless (fluid) spherical body, the implied density is <jats:italic>ρ</jats:italic> = 1700 kg m<jats:sup>−3</jats:sup>. We use the Froude number <jats:italic>Fr</jats:italic>, defined here as the ratio between centrifugal force and gravitational force, as a way to investigate mass-loss regimes in fast-spinning asteroids and find that mass shedding starts at <jats:italic>Fr</jats:italic> ∼ 0.5.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present here a self-consistent cosmological zoom-in simulation of a triple supermassive black hole (SMBH) system forming in a complex multiple galaxy merger. The simulation is run with an updated version of our code KETJU, which is able to follow the motion of SMBHs down to separations of tens of Schwarzschild radii while simultaneously modeling the large-scale astrophysical processes in the surrounding galaxies, such as gas cooling, star formation, and stellar and AGN feedback. Our simulation produces initially an SMBH binary system for which the hardening process is interrupted by the late arrival of a third SMBH. The KETJU code is able to accurately model the complex behavior occurring in such a triple SMBH system, including the ejection of one SMBH to a kiloparsec-scale orbit in the galaxy due to strong three-body interactions as well as Lidov–Kozai oscillations suppressed by relativistic precession when the SMBHs are in a hierarchical configuration. One pair of SMBHs merges ∼3 Gyr after the initial galaxy merger, while the remaining binary is at a parsec-scale separation when the simulation ends at redshift <jats:italic>z</jats:italic> = 0. We also show that KETJU can capture the effects of the SMBH binaries and triplets on the surrounding stellar population, which can affect the binary merger timescales as the stellar density in the system evolves. Our results demonstrate the importance of dynamically resolving the complex behavior of multiple SMBHs in galactic mergers, as such systems cannot be readily modeled using simple orbit-averaged semianalytic models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The first radial alignment between Parker Solar Probe and Solar Orbiter spacecraft is used to investigate the evolution of solar wind turbulence in the inner heliosphere. Assuming ballistic propagation, two 1.5 hr intervals are tentatively identified as providing measurements of the same plasma parcels traveling from 0.1 to 1 au. Using magnetic field measurements from both spacecraft, the properties of turbulence in the two intervals are assessed. Magnetic spectral density, flatness, and high-order moment scaling laws are calculated. The Hilbert–Huang transform is additionally used to mitigate short sample and poor stationarity effects. Results show that the plasma evolves from a highly Alfvénic, less-developed turbulence state near the Sun, to fully developed and intermittent turbulence at 1 au. These observations provide strong evidence for the radial evolution of solar wind turbulence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use new Hubble Space Telescope (HST) images of nine Green Pea galaxies (GPGs) to study their resolved structure and color. The choice of filters, F555W and F850LP, together with the redshift of the galaxies (<jats:italic>z</jats:italic> ∼ 0.25), minimizes the contribution of the nebular [O <jats:sc>iii</jats:sc>] and H<jats:italic>α</jats:italic> emission lines to the broadband images. While these galaxies are typically very blue in color, our analysis reveals that it is only the dominant stellar clusters that are blue. Each GPG does clearly show the presence of at least one bright and compact star-forming region, but these are invariably superimposed on a more extended and lower surface brightness emission. Moreover, the colors of the star-forming regions are on average bluer than those of the diffuse emission, reaching up to 0.6 magnitudes bluer. Assuming that the diffuse and compact components have constant and single-burst star formation histories, respectively, the observed colors imply that the diffuse components (possibly the host galaxy of the star formation episode) have, on average, old stellar ages (&gt;1 Gyr), while the star clusters are younger than 500 Myr. While a redder stellar component is perhaps the most plausible explanation for these results, the limitations of our current data set lead us to examine possible alternative mechanisms, particularly recombination emission processes, which are unusually prominent in systems with such strong line emission. With the available data, however, it is not possible to distinguish between these two interpretations. A substantial presence of old stars would indicate that the mechanisms allowing large escape fractions in these local galaxies may be different from those at play during the reionization epoch.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent 1D core-collapse simulations indicate a nonmonotonicity of the explodability of massive stars with respect to their precollapse core masses, which is in contrast to commonly used prescriptions. In this work, we explore the implications of these results on the formation of coalescing black hole (BH)–neutron star (NS) binaries. Furthermore, we investigate the effects of natal kicks and the NS’s radius on the synthesis of such systems and potential electromagnetic counterparts (EMCs) linked to them. Models based on 1D core-collapse simulations result in a BH–NS merger detection rate ( ∼ 2.3 yr<jats:sup>−1</jats:sup>), 5–10 times larger than the predictions of “standard” prescriptions. This is primarily due to the formation of low-mass BHs via direct collapse, and hence no natal kicks, favored by the 1D simulations. The fraction of observed systems that will produce an EMC, with the supernova engine from 1D simulations, ranges from 2% to 25%, depending on the NS equation of state. Notably, in most merging systems with EMCs, the NS is the first-born compact object, as long as the NS’s radius is ≲ 12 km. Furthermore, models with negligible kicks for low-mass BHs increase the detection rate of GW190426_152155-like events to ∼ 0.6 yr<jats:sup>−1</jats:sup>, with an associated probability of EMC ≤10% for all supernova engines. Finally, models based on 1D core-collapse simulations predict a ratio of BH–NSs to binary BHs’ merger rate density that is at least twice as high as other prescriptions, but at the same time overpredicting the measured local merger density rate of binary black holes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report that Ly<jats:italic>α</jats:italic>-emitting galaxies (LAEs) may not faithfully trace the cosmic web of neutral hydrogen (H <jats:sc>i</jats:sc>), but their distribution is likely biased depending on the viewing direction. We calculate the cross-correlation function (CCF) between galaxies and Ly<jats:italic>α</jats:italic> forest transmission fluctuations on the near and far sides of the galaxies separately, for three galaxy samples at <jats:italic>z</jats:italic> ∼ 2: LAEs, [O <jats:sc>iii</jats:sc>] emitters (O3Es), and continuum-selected galaxies. We find that only LAEs have anisotropic CCFs, with the near side one showing lower signals up to <jats:italic>r</jats:italic> = 3–4 <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> comoving Mpc. This means that the average H <jats:sc>i</jats:sc> density on the near side of LAEs is lower than that on the far side by a factor of 2.1 under the fluctuating Gunn–Peterson approximation. Mock LAEs created by assigning Ly<jats:italic>α</jats:italic> equivalent width (<jats:inline-formula> <jats:tex-math> <?CDATA ${{EW}}_{{\rm{Ly}}\alpha }^{{\rm{obs}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabf04cieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) values to O3Es with an empirical relation also show similar, anisotropic CCFs if we use only objects with higher <jats:inline-formula> <jats:tex-math> <?CDATA ${{EW}}_{{\rm{Ly}}\alpha }^{{\rm{obs}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabf04cieqn2.gif" xlink:type="simple" /> </jats:inline-formula> than a certain threshold. These results indicate that galaxies on the far side of a dense region are more difficult to be detected (“hidden”) in Ly<jats:italic>α</jats:italic> because Ly<jats:italic>α</jats:italic> emission toward us is absorbed by dense neutral hydrogen. If the same region is viewed from a different direction, a different set of LAEs will be selected as if galaxies are playing hide-and-seek using H <jats:sc>i</jats:sc> gas. Care is needed when using LAEs to search for overdensities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the analysis of X-ray and optical observations of gas filaments observed in the radio source 3CR 318.1, associated with NGC 5920, the brightest cluster galaxy (BCG) of MKW 3 s, a nearby cool core galaxy cluster. This work is one of the first X-ray and optical analyses of filaments in cool core clusters carried out using MUSE observations. We aim at identifying the main excitation processes responsible for the emission arising from these filaments. We complemented the optical VLT/MUSE observations, tracing the colder gas phase, with X-ray Chandra observations of the hotter highly ionized gas phase. Using the MUSE observations, we studied the emission line intensity ratios along the filaments to constrain the physical processes driving the excitation, and, using the Chandra observations, we carried out a spectral analysis of the gas along these filaments. We found a spatial association between the X-ray and optical morphology of these filaments, which are colder and have lower metal abundance than the surrounding intracluster medium (ICM), as already seen in other BCGs. Comparing with previous results from the literature for other BCGs, we propose that the excitation process that is most likely responsible for these filaments emission is a combination of star formation and shocks, with a likely contribution from self-ionizing, cooling ICM. Additionally, we conclude that the filaments most likely originated from AGN-driven outflows in the direction of the radio jet.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent cosmological analyses (e.g., JLA, Pantheon) of Type Ia supernovae (SNe Ia) have propagated systematic uncertainties into a covariance matrix and either binned or smoothed the systematic uncertainty vectors in redshift space. We demonstrate that systematic error budgets of these analyses can be improved by a factor of ∼ 1.5 × with the use of unbinned and unsmoothed covariance matrices. To understand this, we employ a separate approach that simultaneously fits for cosmological parameters and additional self-calibrating scale parameters that constrain the size of each systematic. We show that the covariance-matrix approach and scale-parameter approach indeed yield equivalent results, implying that in both cases the data can self-calibrate certain systematic uncertainties, but that this ability is hindered when information is binned or smoothed in redshift space. We review the top systematic uncertainties in current analyses and find that the reduction of systematic uncertainties in the unbinned case depends on whether a systematic is solely degenerate with the cosmological model in redshift space or whether it can be described by additional correlations between supernova properties and luminosity. Furthermore, we show that the power of self-calibration increases with the size of the data set, which presents a tremendous opportunity for upcoming analyses of photometrically classified samples, like those of Legacy Survey of Space and Time (LSST) and the Nancy Grace Roman Telescope (NGRST). However, to take advantage of self-calibration in large, photometrically classified samples, we must first address the issue that binning is required in currently used photometric analysis methods.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have obtained sensitive dust continuum polarization observations at 850 <jats:italic>μ</jats:italic>m in the B213 region of Taurus using POL-2 on SCUBA-2 at the James Clerk Maxwell Telescope as part of the <jats:italic>B</jats:italic>-fields in STar-forming Region Observations (BISTRO) survey. These observations allow us to probe magnetic field (<jats:italic>B</jats:italic>-field) at high spatial resolution (∼2000 au or ∼0.01 pc at 140 pc) in two protostellar cores (K04166 and K04169) and one prestellar core (Miz-8b) that lie within the B213 filament. Using the Davis–Chandrasekhar–Fermi method, we estimate the <jats:italic>B</jats:italic>-field strengths in K04166, K04169, and Miz-8b to be 38 ± 14, 44 ± 16, and 12 ± 5 <jats:italic>μ</jats:italic>G, respectively. These cores show distinct mean <jats:italic>B</jats:italic>-field orientations. The <jats:italic>B</jats:italic>-field in K04166 is well ordered and aligned parallel to the orientations of the core minor axis, outflows, core rotation axis, and large-scale uniform <jats:italic>B</jats:italic>-field, in accordance with magnetically regulated star formation via ambipolar diffusion taking place in K04166. The <jats:italic>B</jats:italic>-field in K04169 is found to be ordered but oriented nearly perpendicular to the core minor axis and large-scale <jats:italic>B</jats:italic>-field and not well correlated with other axes. In contrast, Miz-8b exhibits a disordered <jats:italic>B</jats:italic>-field that shows no preferred alignment with the core minor axis or large-scale field. We found that only one core, K04166, retains a memory of the large-scale uniform <jats:italic>B</jats:italic>-field. The other two cores, K04169 and Miz-8b, are decoupled from the large-scale field. Such a complex <jats:italic>B</jats:italic>-field configuration could be caused by gas inflow onto the filament, even in the presence of a substantial magnetic flux.</jats:p>