Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The formation of globular clusters and their relation to the distribution of dark matter have long puzzled astronomers. One of the most recently proposed globular cluster formation channels ties ancient star clusters to the large-scale streaming velocity of baryons relative to dark matter in the early universe. These streaming velocities affect the global infall of baryons into dark matter halos, the high-redshift halo mass function, and the earliest generations of stars. In some cases, streaming velocities may result in dense regions of dark matter-free gas that becomes Jeans unstable, potentially leading to the formation of compact star clusters. We investigate this hypothesis using cosmological hydrodynamical simulations that include a full chemical network and the formation and destruction of H<jats:sub>2</jats:sub>, a process crucial for the formation of the first stars. We find that high-density gas in regions with significant streaming velocities is indeed somewhat offset from the centers of dark matter halos, but this offset is typically significantly smaller than the virial radius. Gas outside of dark matter halos never reaches Jeans-unstable densities in our simulations. We postulate that low-level (<jats:italic>Z</jats:italic> ≈ 10<jats:sup>−3</jats:sup> <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub>) metal enrichment by Population III supernovae may enable cooling in the extra-virial regions, allowing gas outside of dark matter halos to cool to the cosmic microwave background temperature and become Jeans unstable. Follow-up simulations that include both streaming velocities and metal enrichment by Population III supernovae are needed to understand if streaming velocities provide one path for the formation of globular clusters in the early universe.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar wind magnetic fluctuations exhibit anisotropy due to the presence of a mean magnetic field in the form of the Parker spiral. Close to the Sun, direct measurements were not available until the recently launched Parker Solar Probe (PSP) mission. The nature of the anisotropy and geometry of the magnetic fluctuations play a fundamental role in dissipation processes and in the transport of energetic particles in space. Using PSP data, we present measurements of the geometry and anisotropy of the inner heliosphere magnetic fluctuations, from fluid to kinetic scales. The results are surprising and different from 1 au observations. We find that fluctuations evolve characteristically with size scale. However, unlike 1 au solar wind, at the outer scale, the fluctuations are dominated by wavevectors quasi-parallel to the local magnetic field. In the inertial range, average wavevectors become less field aligned, but still remain more field aligned than near-Earth solar wind. In the dissipation range, the wavevectors become almost perpendicular to the local magnetic field in the dissipation range, to a much higher degree than those indicated by 1 au observations. We propose that this reduced degree of anisotropy in the outer scale and inertial range is due to the nature of large-scale forcing outside the solar corona.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is speculated that there might be some linkage between interstellar aldehydes and their corresponding alcohols. Here an observational study and astrochemical modeling are coupled together to illustrate the connection between them. The ALMA cycle 4 data of a hot molecular core, G10.47+0.03, are utilized for this study. Various aldehydes (acetaldehyde, propanal, and glycolaldehyde), alcohols (methanol and ethylene glycol), and a ketone (acetone) are identified in this source. The excitation temperatures and column densities of these species were derived via the rotation diagram method assuming local thermodynamic equilibrium conditions. An extensive investigation is carried out to understand the formation of these species. Six pairs of aldehyde–alcohol are considered for this study: (i) methanal and methanol, (ii) ethanal and ethanol, (iii) propanal and 1-propanol, (iv) propenal and allyl alcohol, (v) propynal and propargyl alcohol, and (vi) glycolaldehyde and ethylene glycol. One pair of ketone–alcohol (acetone and isopropanol) and ketene–alcohol (ethenone and vinyl alcohol) are also considered. Two successive hydrogenation reactions in the ice phase are examined to form these alcohols from aldehydes, ketone, and ketene, respectively. Quantum chemical methods are extensively executed to review the ice-phase formation route and the kinetics of these species. Based on the obtained kinetic data, astrochemical modeling is employed to derive the abundances of these aldehydes, alcohols, ketone, and ketene in this source. It is seen that our model could successfully explain the observed abundances of various species in this hot molecular core.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Air-Cherenkov telescopes have detected pulsations at energies above 50 GeV from a growing number of Fermi pulsars. These include the Crab, Vela, PSR B1706−44, and Geminga, with the first two having pulsed detections above 1 TeV. In some cases, there appears to be very-high-energy (VHE) emission that is an extension of the Fermi spectra to high energies, while in other cases, additional higher-energy spectral components that require a separate emission mechanism may be present. We present results of broadband spectral modeling using global magnetospheric fields and multiple emission mechanisms that include synchro-curvature (SC) and inverse Compton scattered (ICS) radiation from accelerated particles (primaries) and synchrotron self-Compton (SSC) emission from lower-energy pairs. Our models predict three distinct VHE components: SC from primaries whose high-energy tail can extend to 100 GeV, SSC from pairs that can extend to several TeV, and ICS from primary particles accelerated in the current sheet that scatter pair synchrotron radiation, which appears beyond 10 TeV. Our models suggest that H.E.S.S.-II and MAGIC have detected the high-energy tail of the primary SC component that produces the Fermi spectrum in Vela, Geminga, and PSR B1706−44. We argue that the ICS component peaking above 10 TeV from Vela has been seen by H.E.S.S. Detection of this emission component from the Crab and other pulsars is possible with the High Altitude Water Cherenkov Observatory and Cherenkov Telescope Array, and will directly measure the maximum particle energy in pulsars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Double-diffusive systems, such as thermosolutal convection, in which the density depends on two components that diffuse at different rates, are prone to both steady and oscillatory instabilities. Such systems can evolve into layered states, in which both components, and also the density, adopt a “staircase” profile. Turbulent transport is enhanced significantly in the layered state. Here we exploit an analogy between magnetic buoyancy and thermosolutal convection in order to demonstrate the phenomenon of magnetic layering. We examine the long-term nonlinear evolution of a vertically stratified horizontal magnetic field in the so-called “diffusive regime,” where an oscillatory linear instability operates. Motivated astrophysically, we consider the case where the viscous and magnetic diffusivities are much smaller than the thermal diffusivity. We demonstrate that diffusive layering can occur even for subadiabatic temperature gradients. Magnetic layering may be relevant for stellar radiative zones, with implications for the turbulent transport of heat, magnetic field, and chemical elements.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the probable detection of energetic neutral hydrogen atoms (ENAs) at &gt;0.8 MeV in several large solar energetic particle events observed between 1997 and 2004. The low Earth orbiting SAMPEX satellite detected transient increases of quasi-trapped equatorial protons beginning typically ∼3 hr after the X-ray flare and lasting for up to several hours. Since the magnetic cutoff rigidity is &gt;10 GV at the magnetic latitude where the particles were observed, we interpret the signal as due to ENAs that penetrate Earth’s magnetic field and charge exchange in the upper atmosphere, whereupon the charged particles may become trapped. One event outside our survey period (2006 December 5) had previously reported solar flare ENAs, the only example of this phenomenon of which we are aware. Although the statistics are limited, the events we report suggest that the ENAs are produced as the flare-associated coronal mass wjection moves through the corona, as concluded previously for the 2006 December 5 event. The finding of ENAs emitted in conjunction with large solar flares opens a new avenue to understanding these events.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore the cosmic evolution of the bar length, strength, and light deficit around the bar for 379 barred galaxies at 0.2 &lt; <jats:italic>z</jats:italic> ≤ 0.835 using F814W images from the COSMOS survey. Our sample covers galaxies with stellar masses <jats:inline-formula> <jats:tex-math> <?CDATA $10.0\leqslant \mathrm{log}({M}_{* }/{M}_{\odot })\leqslant 11.4$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>10.0</mml:mn> <mml:mo>≤</mml:mo> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≤</mml:mo> <mml:mn>11.4</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2300ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and various Hubble types. The bar length is strongly related to the galaxy mass, the disk scale length (<jats:italic>h</jats:italic>), <jats:italic>R</jats:italic> <jats:sub>50</jats:sub>, and <jats:italic>R</jats:italic> <jats:sub>90</jats:sub>, where the last two are the radii containing 50% and 90% of total stellar mass, respectively. Bar length remains almost constant, suggesting little or no evolution in bar length over the last 7 Gyr. The normalized bar lengths (<jats:italic>R</jats:italic> <jats:sub>bar</jats:sub>/<jats:italic>h</jats:italic>, <jats:italic>R</jats:italic> <jats:sub>bar</jats:sub>/<jats:italic>R</jats:italic> <jats:sub>50</jats:sub>, and <jats:italic>R</jats:italic> <jats:sub>bar</jats:sub>/<jats:italic>R</jats:italic> <jats:sub>90</jats:sub>) do not show any clear cosmic evolution. Also, the bar strength (<jats:italic>A</jats:italic> <jats:sub>2</jats:sub> and <jats:italic>Q</jats:italic> <jats:sub> <jats:italic>b</jats:italic> </jats:sub>) and the light deficit around the bar reveal little or no cosmic evolution. The constancy of the normalized bar lengths over cosmic time implies that the evolution of bars and of disks is strongly linked over all times. We discuss our results in the framework of predictions from numerical simulations. We conclude there is no strong disagreement between our results and up-to-date simulations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The origin and evolution of the <jats:sup>14</jats:sup>N/<jats:sup>15</jats:sup>N ratio of Titan’s atmosphere has long been a subject of debate. Clearly a better understanding of the N isotopic fractionation mechanism would greatly help resolve this. Photodissociation of N<jats:sub>2</jats:sub> by solar radiation has been suggested to either play a negligible role in fractionating the N isotopes in Titan, due to its rather low escape velocity, or to preferentially remove <jats:sup>15</jats:sup>N through self-shielding controlled photochemical reactions. Here, we systematically measure the branching ratios of <jats:sup>14</jats:sup>N<jats:sup>15</jats:sup>N between N(<jats:sup>4</jats:sup>S)+N(<jats:sup>2</jats:sup>P) and N(<jats:sup>4</jats:sup>S)+N(<jats:sup>2</jats:sup>D) channels. We find that many of its absorption states predominantly dissociate into N(<jats:sup>4</jats:sup>S)+N(<jats:sup>2</jats:sup>P) with a strong isotope effect between <jats:sup>14</jats:sup>N<jats:sub>2</jats:sub> and <jats:sup>14</jats:sup>N<jats:sup>15</jats:sup>N. Since N atoms produced from N(<jats:sup>4</jats:sup>S)+N(<jats:sup>2</jats:sup>P) acquire velocities close to Titan’s escape velocity, these findings provide a new N isotope fractionation mechanism for Titan that has not been considered before, potentially providing important constraints on the origin and evolution of Titan’s N<jats:sub>2</jats:sub>-dominated atmosphere.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The dynamical evolution and radiative properties of luminous radio galaxies and quasars of the FR II type, are well understood. As a result, through the use of detailed modeling of the observed radio emission of such sources, one can estimate various physical parameters of the systems, including the density of the ambient medium into which the radio structure evolves. This, however, requires rather comprehensive observational information, i.e., sampling the broadband radio continua of the targets at several frequencies, and imaging their radio structures with high resolution. Such observations are, on the other hand, not always available, especially for high-redshift objects. Here, we analyze the best-fit values of the source physical parameters, derived from extensive modeling of the largest currently available sample of FR II radio sources, for which good-quality multiwavelength radio flux measurements could be collected. In the analyzed data set, we notice a significant and nonobvious correlation between the spectral index of the nonthermal radio emission continuum, and density of the ambient medium. We derive the corresponding correlation parameters, and quantify the intrinsic scatter by means of Bayesian analysis. We propose that the discovered correlation could be used as a cosmological tool to estimate the density of ambient medium for large samples of distant radio galaxies. Our method does not require any detailed modeling of individual sources, and relies on limited observational information, namely, the slope of the radio continuum between the rest-frame frequencies 0.4 and 5 GHz, possibly combined with the total linear size of the radio structure.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze 143 Type Ia supernovae (SNe Ia) observed in <jats:italic>H</jats:italic> band (1.6–1.8 <jats:italic>μ</jats:italic>m) and find that SNe Ia are intrinsically brighter in <jats:italic>H</jats:italic> band with increasing host galaxy stellar mass. We find that SNe Ia in galaxies more massive than 10<jats:sup>10.43</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> are 0.13 ± 0.04 mag brighter in <jats:italic>H</jats:italic> than SNe Ia in less massive galaxies. The same set of SNe Ia observed at optical wavelengths, after width–color–luminosity corrections, exhibit a 0.10 ± 0.03 mag offset in the Hubble residuals. We observe an outlier population (<jats:inline-formula> <jats:tex-math> <?CDATA $| {\rm{\Delta }}{H}_{\max }| \gt 0.5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">∣</mml:mo> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:msub> <mml:mrow> <mml:mi>H</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">∣</mml:mo> <mml:mo>&gt;</mml:mo> <mml:mn>0.5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2d99ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> mag) in the <jats:italic>H</jats:italic> band and show that removing the outlier population moves the mass threshold to 10<jats:sup>10.65</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> and reduces the step in <jats:italic>H</jats:italic> band to 0.08 ± 0.04 mag, but the equivalent optical mass step is increased to 0.13 ± 0.04 mag. We conclude that the outliers do not drive the brightness–host-mass correlation. Less massive galaxies preferentially host more higher-stretch SNe Ia, which are intrinsically brighter and bluer. It is only after correction for width–luminosity and color–luminosity relationships that SNe Ia have brighter optical Hubble residuals in more massive galaxies. Thus, finding that SNe Ia are intrinsically brighter in <jats:italic>H</jats:italic> in more massive galaxies is an opposite correlation to the intrinsic (pre-width–luminosity correction) optical brightness. If dust and the treatment of intrinsic color variation were the main driver of the host galaxy mass correlation, we would not expect a correlation of brighter <jats:italic>H</jats:italic>-band SNe Ia in more massive galaxies.</jats:p>