Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>A theory of electron injection into diffusive shock acceleration (DSA) for the generation of cosmic-ray electrons at collisionless shocks is presented. We consider a recently proposed particle acceleration mechanism called stochastic shock drift acceleration (SSDA). We find that SSDA may be understood as a diffusive particle acceleration mechanism at an oblique shock of finite thickness. More specifically, it is described by a solution to the diffusion–convection equation for particles with the characteristic diffusion length comparable to the shock thickness. On the other hand, the same equation yields the standard DSA if the diffusion length is much longer than the thickness. Although SSDA predicts, in general, a spectral index steeper than DSA, it is much more efficient for low-energy electron acceleration and is favorable for injection. The injection threshold energy corresponds to the transition energy between the two different regimes. It is of the order of 0.1–1 MeV in typical interstellar and interplanetary conditions if the dissipation scale of turbulence around the shock is determined by the ion inertial length. The electron injection is more efficient at high <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{{\rm{A}}}/\cos {\theta }_{{Bn}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">A</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi>cos</mml:mi> <mml:msub> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">Bn</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4f49ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:italic>M</jats:italic> <jats:sub>A</jats:sub> and <jats:italic>θ</jats:italic> <jats:sub> <jats:italic>Bn</jats:italic> </jats:sub> are the Alfvén Mach number and the shock obliquity, respectively. The theory suggests that efficient acceleration of electrons to ultrarelativistic energies will be more easily realized at high Mach number, young supernova remnant shocks, but not at weak or moderate shocks in the heliosphere unless the upstream magnetic field is nearly perpendicular to the shock normal.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The bulk chemical composition and interior structure of rocky exoplanets are fundamentally important to understand their long-term evolution and potential habitability. Observations of the chemical compositions of solar system rocky bodies and of other planetary systems have increasingly shown a concordant picture that the chemical composition of rocky planets reflects that of their host stars for refractory elements, whereas this expression breaks down for volatiles. This behavior is explained by devolatilization during planetary formation and early evolution. Here we apply a devolatilization model calibrated with solar system bodies to the chemical composition of our nearest Sun-like stars—<jats:italic>α</jats:italic> Centauri A and B—to estimate the bulk composition of any habitable-zone rocky planet in this binary system (“<jats:italic>α</jats:italic>-Cen-Earth”). Through further modeling of likely planetary interiors and early atmospheres, we find that, compared to Earth, such a planet is expected to have (i) a reduced (primitive) mantle that is similarly dominated by silicates, albeit enriched in carbon-bearing species (graphite/diamond); (ii) a slightly larger iron core, with a core mass fraction of <jats:inline-formula> <jats:tex-math> <?CDATA ${38.4}_{-5.1}^{+4.7}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>38.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>5.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>4.7</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4e8cieqn1.gif" xlink:type="simple" /> </jats:inline-formula> wt% (see Earth’s 32.5 ± 0.3 wt%); (iii) an equivalent water-storage capacity; and (iv) a CO<jats:sub>2</jats:sub>–CH<jats:sub>4</jats:sub>–H<jats:sub>2</jats:sub>O-dominated early atmosphere that resembles that of Archean Earth. Further taking into account its ∼25% lower intrinsic radiogenic heating from long-lived radionuclides, an ancient <jats:italic>α</jats:italic>-Cen-Earth (∼1.5–2.5 Gyr older than Earth) is expected to have less efficient mantle convection and planetary resurfacing, with a potentially prolonged history of stagnant-lid regimes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on five years of 3–5 <jats:italic>μ</jats:italic>m photometry measurements obtained by warm Spitzer to track the dust debris emission in the terrestrial zone of HD 166191 in combination with simultaneous optical data. We show that the debris production in this young (∼10 Myr) system increased significantly in early 2018 and reached a record high level (almost double by mid 2019) by the end of the Spitzer mission (early 2020), suggesting intense collisional activity in its terrestrial zone likely due to either initial assembling of terrestrial planets through giant impacts or dynamical shake-up from unseen planet-mass objects or recent planet migration. This intense activity is further highlighted by detecting a star-size dust clump, passing in front of the star, in the midst of its infrared brightening. We constrain the minimum size and mass of the clump using multiwavelength transit profiles and conclude that the dust clump is most likely created by a large impact involving objects of several hundred kilometers in size with an apparent period of 142 days (i.e., 0.62 au, assuming a circular orbit). The system’s evolutionary state (right after the dispersal of its gas-rich disk) makes it extremely valuable to learn about the process of terrestrial-planet formation and planetary architecture through future observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the discovery of a giant cloud of ionized gas in the field of the starbursting galaxy M82. Emission from the cloud is seen in H<jats:italic>α</jats:italic> and [N <jats:sc>ii</jats:sc>] <jats:italic>λ</jats:italic>6583 in data obtained though a small pathfinder instrument used to test the key ideas that will be implemented in the Dragonfly Spectral Line Mapper, an upcoming ultranarrow-bandpass imaging version of the Dragonfly Telephoto Array. The discovered cloud has a shell-like morphology with a linear extent of 0.°8 and is positioned 0.°6 northwest of M82. At the heliocentric distance of the M81 group, the cloud’s longest angular extent corresponds to 55 kpc and its projected distance from the nucleus of M82 is 40 kpc. The cloud has an average H<jats:italic>α</jats:italic> surface brightness of 2 × 10<jats:sup>−18</jats:sup> <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{erg}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}\,{\mathrm{arcsec}}^{-2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>erg</mml:mi> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>arcsec</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac50b6ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. The [N <jats:sc>ii</jats:sc>]<jats:italic> λ</jats:italic>6583/H<jats:italic>α</jats:italic> line ratio varies from [N <jats:sc>ii</jats:sc>]/H<jats:italic>α</jats:italic> ∼ 0.2 to [N <jats:sc>ii</jats:sc>]/H<jats:italic>α</jats:italic> ∼ 1.0 across the cloud, with higher values found in its eastern end. Follow-up spectra obtained with Keck LRIS confirm the existence of the cloud and yield line ratios of [N <jats:sc>ii</jats:sc>]<jats:italic> λ</jats:italic>6583/H<jats:italic>α</jats:italic> = 0.340 ± 0.003 and [S <jats:sc>ii</jats:sc>] <jats:italic>λλ</jats:italic>6716, 6731/H<jats:italic>α</jats:italic> = 0.64 ± 0.03 in the cloud. This giant cloud of material could be lifted from M82 by tidal interactions or by its powerful starburst. Alternatively, it may be gas infalling from the cosmic web, potentially precipitated by the superwinds of M82. Deeper data are needed to test these ideas further. The upcoming Dragonfly Spectral Line Mapper will have 120 lenses, 40× more than in the pathfinder instrument used to obtain the data presented here.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We address the nature and origin of a spiral disk at the center of NGC 1275, the giant elliptical galaxy at the center of the Perseus cluster, that spans a radius of ∼5 kpc. By comparing stellar absorption lines measured in long-slit optical spectra with synthetic spectra for single stellar populations, we find that fitting of these lines requires two stellar populations: (i) a very young population that peaks in radial velocity at ±250 km s<jats:sup>−1</jats:sup> of the systemic velocity within a radius of ∼720 pc of the nucleus, a 1<jats:italic>σ</jats:italic> velocity dispersion significantly lower than 140 km s<jats:sup>−1</jats:sup>, and an age of 0.15 ± 0.05 Gyr; and (ii) a very old population having a constant radial velocity with a radius corresponding to the systemic velocity, a much broader velocity dispersion of ∼250 km s<jats:sup>−1</jats:sup>, and an age of around 10 Gyr. We attribute the former to a post-starburst population associated with the spiral disk, and the latter to the main stellar body of NGC 1275 along the same sight line. If the spiral disk is the remnant of a cannibalized galaxy, then its progenitor would have had to retain an enormous amount of gas in the face of intensive ram-pressure stripping so as to form a total initial mass in stars of ∼3 × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. More likely, the central spiral originally comprised a gaseous body accreted over the distant past from a residual cooling flow, before experiencing a starburst ∼0.15 Gyr ago to form its stellar body.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We address the nature and origin of super star clusters (SSCs) discovered by Holtzman et al. within a radius of ∼5 kpc from the center of NGC 1275, the giant elliptical galaxy at the center of the Perseus Cluster. We show that, in contrast with the much more numerous population of SSCs subsequently discovered up to ∼30 kpc from the center of this galaxy, the central SSC population have maximal masses an order of magnitude higher and a mass function with a shallower power-law slope. Furthermore, whereas the outer SSC population have ages spanning a few Myr to at least ∼1 Gyr, the central SSC population have ages strongly concentrated around ∼500 Myr with a 1<jats:italic>σ</jats:italic> dispersion of ∼100 Myr. These SSCs share a close spatial and temporal relationship with the “central spiral,” which also has a radius ∼5 kpc centered on NGC 1275 and a characteristic stellar age of ∼150 Myr. We argue that both the central SSC population and the central spiral formed from gas deposited by a residual cooling flow, with the SSCs forming first followed by the formation of the stellar body of the central spiral ∼300–400 Myr later. The ages of the central SSC population imply that they are able to withstand very strong tidal fields near the center of NGC 1275, making them genuine progenitor globular clusters. Evidently, a spiral disk hosting progenitor globular clusters has recently formed at the center of a giant elliptical galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on observations of the candidate Be/X-ray binary (BeXRB) IGR J18219−1347 with the Swift/X-ray Telescope, the Nuclear Spectroscopic Telescope ARray, and the Neutron Star Interior Composition Explorer during Type-I outbursts in 2020 March and June. Our timing analysis revealed the spin period of a neutron star with <jats:italic>P</jats:italic> <jats:sub>spin</jats:sub> = 52.46 s. This periodicity, combined with the known orbital period of 72.4 days, indicates that the system is a BeXRB. Furthermore, by comparing the spectral energy distribution of the infrared counterpart to that of known BeXRBs, we confirm this classification and set a distance of approximately 10–15 kpc for the source. The broadband X-ray spectrum (1.5–50 keV) of the source is described by an absorbed power law with a photon index Γ ∼ 0.5 and a cutoff energy at ∼13 keV.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use data from the first six encounters of the Parker Solar Probe and employ the partial variance of increments (PVI) method to study the statistical properties of coherent structures in the inner heliosphere with the aim of exploring physical connections between magnetic field intermittency and observable consequences such as plasma heating and turbulence dissipation. Our results support proton heating localized in the vicinity of, and strongly correlated with, magnetic structures characterized by PVI ≥ 1. We show that, on average, such events constitute ≈19% of the data set, though variations may occur depending on the plasma parameters. We show that the waiting time distribution (WT) of identified events is consistent across all six encounters following a power-law scaling at lower WTs. This result indicates that coherent structures are not evenly distributed in the solar wind but rather tend to be tightly correlated and form clusters. We observe that the strongest magnetic discontinuities, PVI ≥ 6, usually associated with reconnection exhausts, are sites where magnetic energy is locally dissipated in proton heating and are associated with the most abrupt changes in proton temperature. However, due to the scarcity of such events, their relative contribution to energy dissipation is minor. Taking clustering effects into consideration, we show that smaller scale, more frequent structures with PVI between 1 ≲ PVI ≲ 6 play a major role in magnetic energy dissipation. The number density of such events is strongly associated with the global solar wind temperature, with denser intervals being associated with higher <jats:italic>T</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We quantify galaxy overdensities around three high-redshift quasars with known [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub> companions: PJ231–20 (<jats:italic>z</jats:italic> = 6.59), PJ308–21 (<jats:italic>z</jats:italic> = 6.24), and J0305–3150 (<jats:italic>z</jats:italic> = 6.61). Recent SCUBA2 imaging revealed the presence of 17 submillimeter galaxies (SMGs) with sky separations 0.′7 &lt; <jats:italic>θ</jats:italic> &lt; 2.′4 from these three quasars. We present ALMA Band 6 follow-up observations of these SCUBA2-selected SMGs to confirm their nature and redshift. We also search for continuum-undetected [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub> emitters in the ALMA pointings and make use of archival MUSE observations to search for Ly<jats:italic>α</jats:italic> emitters (LAEs) associated with the quasars. While most of the SCUBA2-selected sources are detected with ALMA in the continuum, no [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub> line emission could be detected, indicating that they are not at the quasar redshifts. Based on the serendipitous detection of CO 7–6 and [C <jats:sc>i</jats:sc>]<jats:sub>809 <jats:italic>μ</jats:italic>m</jats:sub> emission lines, we find that four SMGs in the field of PJ231–20 are at <jats:italic>z</jats:italic> ∼ 2.4, which is coincident with the redshift of an Mg <jats:sc>ii</jats:sc> absorber in the quasar rest-frame UV spectrum. We report the discovery of two LAEs within &lt;0.6 cMpc of PJ231–20 at the same redshift, indicating an LAE overdensity around this quasar. Taken together, these observations provide new constraints on the large-scale excess of Ly<jats:italic>α</jats:italic>- and [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub>-emitting galaxies around <jats:italic>z</jats:italic> &gt; 6 quasars and suggest that only wide-field observations, such as MUSE, ALMA, or JWST mosaics, can reveal a comprehensive picture of large-scale structure around quasars in the first billion years of the universe.</jats:p>