Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present environmental analyses for 13 KPNO International Spectroscopic Survey Green Pea (GP) galaxies. These galaxies were discovered via their strong [O <jats:sc>iii</jats:sc>] emission in the redshift range 0.29 &lt; <jats:italic>z</jats:italic> &lt; 0.42, and they are undergoing a major burst of star formation. A primary goal of this study is to understand what role the environment plays in driving the current star formation activity. By studying the environments around these extreme star-forming galaxies, we can learn more about what triggers their star formation processes and how they fit into the narrative of galaxy evolution. Using the Hydra multifiber spectrograph on the WIYN 3.5 m telescope, we mapped out the galaxy distribution around each of the GPs (out to ∼15 Mpc at the redshifts of the targets). Using three density analysis methodologies chosen for their compatibility with the geometry of our redshift survey, we categorized the galaxian densities of the GPs into different density regimes. We find that the GPs in our sample tend to be located in low-density environments. We find no correlation between the density and the SFRs seen in the GPs. We conclude that the environments the GPs are found in are likely not the driving factor behind their extreme star formation activity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Utilizing low-luminosity star-forming systems discovered in the H<jats:italic>α</jats:italic> Dots survey, we present spectroscopic observations undertaken using the Kitt Peak National Observatory 4 m telescope for 26 sources. With determinations of robust, “direct”-method metal abundances, we examine the properties of these dwarf systems, exploring their utility in characterizing starburst galaxies at low luminosities and stellar masses. We find that the H<jats:italic>α</jats:italic> Dots survey provides an effective new avenue for identifying star-forming galaxies in these regimes. In addition, we examine abundance characteristics and metallicity scaling relations with these sources, highlighting a flattening of both the luminosity–metallicity (<jats:italic>L</jats:italic>–<jats:italic>Z</jats:italic>) and stellar mass–metallicity (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>–<jats:italic>Z</jats:italic>) relation slopes in these regimes as compared with those utilizing samples covering wider respective dynamic ranges. These local, accessible analogs to the kinds of star-forming dwarfs common at high redshift will help shed light on the building blocks that assembled into the massive galaxies common today.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We search through an eight million cubic parsec volume surrounding the Pleiades star cluster and the Sun to identify both the current and past members of the Pleiades cluster within the Gaia EDR3 data set. We find nearly 1300 current cluster members and 289 former cluster candidates. Many of these candidates lie well in front of or behind the cluster from our point of view, so formerly they were considered cluster members, but their parallaxes put them more than 10 pc from the center of the cluster today. Over the past 100 Myr we estimate that the cluster has lost twenty percent of its mass including two massive white dwarf stars and the <jats:italic>α</jats:italic> <jats:sup>2</jats:sup> Canum Venaticorum type variable star, 41 Tau. All three white dwarfs associated with the cluster are massive (1.01–1.06 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) and have progenitors with main-sequence masses of about six solar masses. Although we did not associate any giant stars with the cluster, the cooling time of the oldest white dwarf of 60 Myr gives a firm lower limit on the age of the cluster.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>X-ray emission provides the most direct diagnostics of the energy release process in solar flares. Occasionally, a superhot X-ray source is found to be above hot flare loops of ∼10 MK temperature. While the origin of the superhot plasma is still elusive, it has conjured up an intriguing image of in situ plasma heating near the reconnection site high above the flare loops, in contrast to the conventional picture of chromospheric evaporation. Here we investigate an extremely long duration solar flare, in which EUV images show two distinct flare loop systems that appear successively along a Γ-shaped polarity inversion line (PIL). When both flare loop systems are present, the hard X-ray spectrum is found to be well fitted by combining a hot component (<jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> ∼ 12 MK) and a superhot component (<jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> ∼ 30 MK). Associated with a fast coronal mass ejection (CME), the superhot X-ray source is located at the top of the flare arcade that appears earlier, straddling and extending along the long “arm” of the Γ-shaped PIL. Associated with a slow CME, the hot X-ray source is located at the top of the flare arcade that appears later and sits astride the short “arm” of the Γ-shaped PIL. Aided by observations from a different viewing angle, we are able to verify that the superhot X-ray source is above the hot one in projection, but the two sources belong to different flare loop systems. Thus, this case study provides a stereoscopic observation explaining the coexistence of superhot and hot X-ray-emitting plasmas in solar flares.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Scattered sunlight from the interplanetary dust (IPD) cloud in our solar system presents a serious foreground challenge for spectrophotometric measurements of the extragalactic background light (EBL). In this work, we report on inferred measurements of the absolute intensity of the zodiacal light (ZL) using the novel technique of Fraunhofer line spectroscopy on the deepest 8542 Å line of the near-infrared Ca <jats:sc>ii</jats:sc> absorption triplet. The measurements are performed with the narrow band spectrometer (NBS) on board the Cosmic Infrared Background Experiment sounding rocket instrument. We use the NBS data to test the accuracy of two ZL models widely cited in the literature, the Kelsall and Wright models, which have been used in foreground removal analyses that produce high and low EBL results respectively. We find a mean reduced <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> = 3.5 for the Kelsall model and <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> = 2.0 for the Wright model. The best description of our data is provided by a simple modification to the Kelsall model, which includes a free ZL offset parameter. This adjusted model describes the data with a reduced <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> = 1.5 and yields an inferred offset amplitude of 46 ± 19 nW m<jats:sup>−2</jats:sup> sr<jats:sup>−1</jats:sup> extrapolated to 12500 Å. These measurements elude to the potential existence of a dust cloud component in the inner solar system whose intensity does not strongly modulate with the Earth’s motion around the Sun.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the luminosity suppression and its effect on the mass–radius relation and cooling evolution of highly magnetized white dwarfs. Based on the effect of magnetic field relative to gravitational energy, we suitably modify our treatment of the radiative opacity, magnetostatic equilibrium, and degenerate core equation of state to obtain the structural properties of these stars. Although the Chandrasekhar mass limit is retained in the absence of magnetic field and irrespective of the luminosity, strong central fields of about 10<jats:sup>14</jats:sup> G can yield super-Chandrasekhar white dwarfs with masses ∼2.0 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Smaller white dwarfs tend to remain super-Chandrasekhar for sufficiently strong central fields even when their luminosity is significantly suppressed to 10<jats:sup>−16</jats:sup> <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub>. Nevertheless, owing to the cooling evolution and simultaneous field decay over 10 Gyr, the limiting masses of small magnetized white dwarfs can fall to 1.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> over time. However, the majority of these systems still remain practically hidden throughout their cooling evolution because of their high fields and correspondingly low luminosities. Utilizing the stellar evolution code <jats:sc>stars</jats:sc>, we obtain close agreement with the analytical mass limit estimates, which suggests that our analytical formalism is physically motivated. Our results argue that super-Chandrasekhar white dwarfs born as a result of strong-field effects may not remain so forever. This explains their apparent scarcity, in addition to making them hard to detect because of their suppressed luminosities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the stellar populations for a sample of 161 massive, mainly quiescent galaxies at 〈<jats:italic>z</jats:italic> <jats:sub>obs</jats:sub>〉 = 0.8 with deep Keck/DEIMOS rest-frame optical spectroscopy (HALO7D survey). With the fully Bayesian framework <jats:monospace>Prospector</jats:monospace>, we simultaneously fit the spectroscopic and photometric data with an advanced physical model (including nonparametric star formation histories, emission lines, variable dust attenuation law, and dust and active galactic nucleus emission), together with an uncertainty and outlier model. We show that both spectroscopy and photometry are needed to break the dust–age–metallicity degeneracy. We find a large diversity of star formation histories: although the most massive (<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> &gt; 2 × 10<jats:sup>11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) galaxies formed the earliest (formation redshift of <jats:italic>z</jats:italic> <jats:italic> <jats:sub>f</jats:sub> </jats:italic> ≈ 5–10 with a short star formation timescale of <jats:italic>τ</jats:italic> <jats:sub>SF</jats:sub> ≲ 1 Gyr), lower-mass galaxies have a wide range of formation redshifts, leading to only a weak trend of <jats:italic>z</jats:italic> <jats:italic> <jats:sub>f</jats:sub> </jats:italic> with <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>. Interestingly, several low-mass galaxies have formation redshifts of <jats:italic>z</jats:italic> <jats:italic> <jats:sub>f</jats:sub> </jats:italic> ≈ 5–8. Star-forming galaxies evolve about the star-forming main sequence, crossing the ridgeline several times in their past. Quiescent galaxies show a wide range and continuous distribution of quenching timescales (<jats:italic>τ</jats:italic> <jats:sub>quench</jats:sub> ≈ 0–5 Gyr) with a median of <jats:inline-formula> <jats:tex-math> <?CDATA $\langle {\tau }_{\mathrm{quench}}\rangle ={1.0}_{-0.9}^{+0.8}\,\mathrm{Gyr}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:msub> <mml:mrow> <mml:mi>τ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>quench</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">〉</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.8</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.50em" /> <mml:mi>Gyr</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac449bieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and of quenching epochs of <jats:italic>z</jats:italic> <jats:sub>quench</jats:sub> ≈ 0.8–5.0 (<jats:inline-formula> <jats:tex-math> <?CDATA $\langle {z}_{\mathrm{quench}}\rangle ={1.3}_{-0.4}^{+0.7}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:msub> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>quench</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">〉</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.7</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac449bieqn2.gif" xlink:type="simple" /> </jats:inline-formula>). This large diversity of quenching timescales and epochs points toward a combination of internal and external quenching mechanisms. In our sample, rejuvenation and “late bloomers” are uncommon. In summary, our analysis supports the “grow-and-quench” framework and is consistent with a wide and continuously populated diversity of quenching timescales.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We introduce the cosmological HYPER code based on an innovative hydro-particle-mesh (HPM) algorithm for efficient and rapid simulations of gas and dark matter. For the HPM algorithm, we update the approach of Gnedin &amp; Hui to expand the scope of its application from the lower-density intergalactic medium (IGM) to the higher-density intracluster medium (ICM). While the original algorithm tracks only one effective particle species, the updated version separately tracks the gas and dark matter particles, as they do not exactly trace each other on small scales. For the approximate hydrodynamics solver, the pressure term in the gas equations of motion is calculated using robust physical models. In particular, we use a dark matter halo model, ICM pressure profile, and IGM temperature–density relation, all of which can be systematically varied for parameter-space studies. We show that the HYPER simulation results are in good agreement with the halo model expectations for the density, temperature, and pressure radial profiles. Simulated galaxy cluster scaling relations for Sunyaev–Zel’dovich (SZ) and X-ray observables are also in good agreement with mean predictions, with scatter comparable to that found in hydrodynamic simulations. HYPER also produces lightcone catalogs of dark matter halos and full-sky tomographic maps of the lensing convergence, SZ effect, and X-ray emission. These simulation products are useful for testing data analysis pipelines, generating training data for machine learning, understanding selection and systematic effects, and for interpreting astrophysical and cosmological constraints.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The near-Earth solar wind is in general super-Alfvénic and supermagnetosonic. Using all available near-Earth solar wind measurements between 1973 and 2020, we identified 30 intervals with sub-Alfvénic solar winds. The majority (83%) of the events occurred within interplanetary coronal mass ejection magnetic clouds (MCs)/driver gases. These MC sub-Alfvénic events are characterized by exceptionally low plasma densities (<jats:italic>N</jats:italic> <jats:sub>sw</jats:sub>) of ∼0.04–1.20 cm<jats:sup>−3</jats:sup>, low temperatures (<jats:italic>T</jats:italic> <jats:sub>sw</jats:sub>) of ∼0.08 × 10<jats:sup>5</jats:sup> K to 12.46 × 10<jats:sup>5</jats:sup> K, enhanced magnetic field intensities (<jats:italic>B</jats:italic> <jats:sub>0</jats:sub>) of ∼8.3–53.9 nT, and speeds (<jats:italic>V</jats:italic> <jats:sub>sw</jats:sub>) of ∼328–949 km s<jats:sup>−1</jats:sup>. The resultant high Alfvén wave speeds (<jats:italic>V</jats:italic> <jats:sub>A</jats:sub>) ranged from ∼410 to 1471 km s<jats:sup>−1</jats:sup>. This is consistent with a mechanism of the MC expansions as they propagate radially outward, causing small pockets of sub-Alfvénic wind regions within the MCs. The remainder of the sub-Alfvénic intervals (17%) occurred within the extreme trailing portions of solar wind high-speed streams (HSSs). These HSS sub-Alfvénic winds had low <jats:italic>N</jats:italic> <jats:sub>sw</jats:sub> of ∼0.04–0.97 cm<jats:sup>−3</jats:sup>, low <jats:italic>T</jats:italic> <jats:sub>sw</jats:sub> of ∼0.06 × 10<jats:sup>5</jats:sup> K to 0.46 × 10<jats:sup>5</jats:sup> K, <jats:italic>B</jats:italic> <jats:sub>0</jats:sub> of ∼6.3–18.2 nT, <jats:italic>V</jats:italic> <jats:sub>sw</jats:sub> of ∼234–388 km s<jats:sup>−1</jats:sup>, and a <jats:italic>V</jats:italic> <jats:sub>A</jats:sub> range of ∼364–626 km s<jats:sup>−1</jats:sup>. This is consistent with a mechanism of solar wind super-radial expansions in the trailing HSS regions. During sub-Alfvénic solar wind intervals, Earth's bow shock nose exhibited rapid evanescence, and the estimated geocentric magnetopause distance increased by ∼33%–86%. The inner magnetosphere was more or less unaffected by the sub-Alfvénic solar winds. No significant impact was observed in the outer radiation belt relativistic electrons, and no geomagnetic storms or substorms were triggered during the sub-Alfvénic solar wind events.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We introduce a toy model for the time–frequency structure of fast radio bursts, in which the observed emission is produced as a narrowly peaked intrinsic spectral energy distribution sweeps down in frequency across the instrumental bandpass as a power law in time. Though originally motivated by emission models that invoke a relativistic shock, the model could in principle apply to a wider range of emission scenarios. We quantify the burst’s detectability using the frequency bandwidth over which most of its signal-to-noise ratio is accumulated. We demonstrate that, by varying just a single parameter of the toy model—the power-law index <jats:italic>β</jats:italic> of the frequency drift rate—one can transform a long (and hence preferentially time-resolved) burst with a narrow time-integrated spectrum into a shorter burst with a broad power-law time-integrated spectrum. We suggest that source-to-source diversity in the value of <jats:italic>β</jats:italic> could generate the dichotomy between burst duration and frequency-bandwidth recently found by CHIME/FRB. In shock models, the value of <jats:italic>β</jats:italic> is related to the radial density profile of the external medium, which, in light of the preferentially longer duration of bursts from repeating sources, may point to diversity in the external environments surrounding repeating versus one-off FRB sources.</jats:p>