Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Observations of low-order <jats:sup>12</jats:sup>C<jats:sup>16</jats:sup>O transitions represent the most direct way to study galaxies’ cold molecular gas, the fuel of star formation. Here we present the first detection of CO(<jats:italic>J</jats:italic> = 2 → 1) in a galaxy lying on the main-sequence of star-forming galaxies at <jats:italic>z</jats:italic> &gt; 6. Our target, G09-83808 at <jats:italic>z</jats:italic> = 6.03, has a short depletion timescale of <jats:italic>τ</jats:italic> <jats:sub>dep</jats:sub> ≈ 50 Myr and a relatively low gas fraction of <jats:italic>M</jats:italic> <jats:sub>gas</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> ≈ 0.30 that contrasts with those measured for lower-redshift main-sequence galaxies. We conclude that this galaxy is undergoing a starburst episode with a high star formation efficiency that might be the result of gas compression within its compact rotating disk. Its starburst-like nature is further supported by its high star formation rate surface density, thus favoring the use of the Kennicutt–Schmidt relation as a more precise diagnostic diagram. Without further significant gas accretion, this galaxy would become a compact, massive quiescent galaxy at <jats:italic>z</jats:italic> ∼ 5.5. In addition, we find that the calibration for estimating interstellar medium masses from dust continuum emission satisfactorily reproduces the gas mass derived from the CO(2 → 1) transition (within a factor of ∼2). This is in line with previous studies claiming a small redshift evolution in the gas-to-dust ratio of massive, metal-rich galaxies. In the absence of gravitational amplification, this detection would have required of order 1000 hr of observing time. The detection of cold molecular gas in unlensed star-forming galaxies at high redshifts is thus prohibitive with current facilities and requires a tenfold improvement in sensitivity, such as that envisaged for the Next-Generation Very Large Array .</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Sub-relativistic materials launched during the merger of binary compact objects and the core collapse of massive stars acquire velocity structures when expanding in a stratified environment. The remnant (either a spinning magnetized neutron star (NS) or a central black hole) from the compact object or core collapse could additionally inject energy into the afterglow via spin-down luminosity or/and by accreting fallback material, producing a refreshed shock, modifying the dynamics, and leading to rich radiation signatures at distinct timescales and energy bands with contrasting intensities. We derive the synchrotron light curves evolving in a stratified environment when a power-law velocity distribution parameterizes the energy of the shock, and the remnant continuously injects energy into the blast wave. As the most relevant case, we describe the latest multiwavelength afterglow observations (≳900 days) of the GW170817/GRB 170817A event via a synchrotron afterglow model with energy injection of a sub-relativistic material. The features of the remnant and the synchrotron emission of the sub-relativistic material are consistent with a spinning magnetized NS and the faster <jats:italic>blue</jats:italic> kilonova afterglow, respectively. Using the multiband observations of some short bursts with evidence of kilonovae, we provide constraints on the expected afterglow emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present observations of a solar magnetic network region in the millimeter continuum with the Atacama Large Millimeter/submillimeter Array (ALMA) and in the Ca 8542 and Na 5896 Å spectral lines with the Interferometric Bidimensional Spectrometer (IBIS). Our goal is to compare the measurement of local gas temperatures provided by ALMA with the temperature diagnostics provided by non-LTE inversions using the STockholm inversion Code (STiC). In performing these inversions, we find that using column mass as the reference height scale, rather than optical depth, provides more reliable atmospheric profiles above the temperature minimum and that the treatment of non-LTE hydrogen ionization brings the inferred chromospheric temperatures into better agreement with the ALMA measurements. The Band 3 brightness temperatures are higher but well correlated spatially with the inversion-derived temperatures at the height of formation of the Ca 8542 line core. The Band 6 temperatures instead do not show good correlations with the temperatures at any specific layer in the inverted atmospheres. We then performed inversions that included the millimeter-continuum intensities as an additional constraint. Incorporating Band 3 generally resulted in atmospheres showing a strong temperature rise in the upper atmosphere, while including Band 6 led to significant regions of anomalously low temperatures at chromospheric heights. This is consistent with the idea that the Band 6 emission can come from a combination of heights ranging from the temperature minimum to upper chromosphere. The poor constraints on the chromospheric electron density with existing inversion codes introduces difficulties in determining the height(s) of formation of the millimeter continuum as well as uncertainties in the temperatures derived from the spectral lines.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The chemical composition of the solar corona is different from that of the solar photosphere, with the strongest variation being observed in active regions (ARs). Using data from the Extreme Ultraviolet (EUV) Imaging Spectrometer (EIS) on Hinode, we present a survey of coronal elemental composition as expressed in the first ionization potential (FIP) bias in 28 ARs of different ages and magnetic flux content, which are at different stages in their evolution. We find no correlation between the FIP bias of an AR and its total unsigned magnetic flux or age. However, there is a weak dependence of FIP bias on the evolutionary stage, decreasing from 1.9 to 2.2 in ARs with spots to 1.5–1.6 in ARs that are at more advanced stages of the decay phase. FIP bias shows an increasing trend with average magnetic flux density up to 200 G, but this trend does not continue at higher values. The FIP bias distribution within ARs has a spread between 0.4 and 1. The largest spread is observed in very dispersed ARs. We attribute this to a range of physical processes taking place in these ARs, including processes associated with filament channel formation. These findings indicate that, while some general trends can be observed, the processes influencing the composition of an AR are complex and specific to its evolution, magnetic configuration, or environment. The spread of FIP bias values in ARs shows a broad match with that previously observed in situ in the slow solar wind.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Simulations of the turbulent cascade forming in the solar wind, including cross helicity, commonly adopt a homogeneous setup, not taking into account wind expansion. Here we want to assess the predictions of decaying 3D compressible (low Mach number) MHD simulations, respectively homogeneous and with expansion, in order to examine which is the most fruitful approach to understanding the turbulent cascade in the solar wind. We follow turbulent evolution during 10 nonlinear turnover times, considering several initial values of the initial spectral slope and cross helicity. In the expanding case, the transverse sizes of the plasma volume are stretched by a factor of 5 during the simulation, corresponding to traveling from 0.2 up to 1 au. In homogeneous simulations, the relative cross helicity rises, and the Elsässer spectra <jats:italic>E</jats:italic> <jats:sub>±</jats:sub> show “pinning,” with a steep dominant spectrum and flat subdominant spectrum, the final spectral indices depending on cross helicity but not initial indices. With expansion, the relative cross helicity decreases, and dominant and subdominant spectra share the same index, with the index relaxing to an asymptotic value that generally depends on the initial index. The absence of pinning, as well as the decrease of relative cross helicity, probably both rely on the permanent injection by expansion of an excess of magnetic energy at the largest scales, equivalent to injecting subdominant energy. Also, spectra generally steepen when initially starting flatter than <jats:italic>k</jats:italic> <jats:sup>−5/3</jats:sup> but stop evolving at a finite time/distance.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a targeted search for continuous gravitational waves (GWs) from 236 pulsars using data from the third observing run of LIGO and Virgo (O3) combined with data from the second observing run (O2). Searches were for emission from the <jats:italic>l</jats:italic> = <jats:italic>m</jats:italic> = 2 mass quadrupole mode with a frequency at only twice the pulsar rotation frequency (single harmonic) and the <jats:italic>l</jats:italic> = 2, <jats:italic>m</jats:italic> = 1, 2 modes with a frequency of both once and twice the rotation frequency (dual harmonic). No evidence of GWs was found, so we present 95% credible upper limits on the strain amplitudes <jats:italic>h</jats:italic> <jats:sub>0</jats:sub> for the single-harmonic search along with limits on the pulsars’ mass quadrupole moments <jats:italic>Q</jats:italic> <jats:sub>22</jats:sub> and ellipticities <jats:italic>ε</jats:italic>. Of the pulsars studied, 23 have strain amplitudes that are lower than the limits calculated from their electromagnetically measured spin-down rates. These pulsars include the millisecond pulsars J0437−4715 and J0711−6830, which have spin-down ratios of 0.87 and 0.57, respectively. For nine pulsars, their spin-down limits have been surpassed for the first time. For the Crab and Vela pulsars, our limits are factors of ∼100 and ∼20 more constraining than their spin-down limits, respectively. For the dual-harmonic searches, new limits are placed on the strain amplitudes <jats:italic>C</jats:italic> <jats:sub>21</jats:sub> and <jats:italic>C</jats:italic> <jats:sub>22</jats:sub>. For 23 pulsars, we also present limits on the emission amplitude assuming dipole radiation as predicted by Brans-Dicke theory.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations with the Fermi Large Area Telescope (LAT) of the gamma-ray source 4FGL J1702.7−5655, previously classified as a candidate millisecond pulsar, show highly significant modulation at a period of 0.2438033 days (∼5.85 hr). Further examination of the folded light curve indicates the presence of narrow eclipses, suggesting that this is a redback binary system. An examination of the long-term properties of the modulation over 13 years of LAT observations indicates that the orbital modulation of the gamma rays changed from a simple eclipse before early 2013 to a broader, more easily detected quasi-sinusoidal modulation. In addition, the time of the eclipse shifts to ∼0.05 later in phase. This change in the orbital modulation properties, however, is not accompanied by a significant overall change in gamma-ray flux or spectrum. The quasi-sinusoidal component peaks ∼0.5 out of phase with the eclipse, which would indicate inferior conjunction of the compact object in the system. Swift X-ray Telescope observations reveal a possible X-ray counterpart within the LAT error ellipse. However, radio observations obtained with the Australia Telescope Compact Array do not detect a source in the region. 4FGL J1702.7−5655 appears to have changed its state in 2013, perhaps related to changes in the intrabinary shock in the system. We compare the properties of 4FGL J1702.7−5655 to those of other binary millisecond pulsars that have exhibited orbital modulation in gamma-rays.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We introduce a new method for detecting ultra-diffuse galaxies by searching for over-densities in intergalactic globular cluster populations. Our approach is based on an application of the log-Gaussian Cox process, which is a commonly used model in the spatial statistics literature but rarely used in astronomy. This method is applied to the globular cluster data obtained from the PIPER survey, a Hubble Space Telescope imaging program targeting the Perseus cluster. We successfully detect all confirmed ultra-diffuse galaxies with known globular cluster populations in the survey. We also identify a potential galaxy that has no detected diffuse stellar content. Preliminary analysis shows that it is unlikely to be merely an accidental clump of globular clusters or other objects. If confirmed, this system would be the first of its kind. Simulations are used to assess how the physical parameters of the globular cluster systems within ultra-diffuse galaxies affect their detectability using our method. We quantify the correlation of the detection probability with the total number of globular clusters in the galaxy and the anticorrelation with increasing half-number radius of the globular cluster system. The Sérsic index of the globular cluster distribution has little impact on detectability.</jats:p>