49 research outputs found
Polarized radio emission of cluster galaxies
No full textGalaxien, die Teil eines Galaxienhaufens werden, erfahren beim Einfall in dessen Zentrum den sogenannten Staudruck. Dieser drückt das vorhandene Gas in der Galaxie in die entgegengesetzte Richtung des Einfalls und beschleunigt damit die Entwicklung der Galaxie. Über Multiwellenlängenbeobachtungen ist herausgefunden worden, dass in den verlagerten Gasschweifen effektiv Sterne gebildet werden. Um ein allgemeines Verständnis dieses Phänomens zu erlangen, welches eine Vielzahl an Galaxien im Universum betrifft, wurde zum ersten Mal die Struktur und den Einfluss der Magnetfelder in solchen Gasschweifen studiert.
Mithilfe einer Beispielgalaxie konnte ein geordnetes Magnetfeld entlang des Gasschweifes gemessen werden. Dieses stimmt mit Windtunnelsimulationen gleicher Galaxien überein, indem das Magnetfeld von dem intergalaktischen Medium aufgesammelt wird. Ein solches Magnetfeld kann das rausgedrückte, kalte Gas vor Evaporation schützen und somit die Bildung von Sternen begünstigen.Galaxies that become part of a galaxy cluster experience the so-called ram pressure when they fall into its center. This pushes the existing gas in the galaxy in the opposite direction of the incidence and thus accelerates the evolution of the galaxy. It has been found via multi-wavelength observations that stars are effectively formed in the displaced gas tails. To gain a general understanding of this phenomenon, which affects a large number of galaxies in the Universe, the structure and influence of magnetic fields in such gas tails has been studied for the first time.
Using an example galaxy, an ordered magnetic field was measured along the gas tail. This agrees with wind tunnel simulations of identical galaxies in that the magnetic field is collected by the intergalactic medium. Such a magnetic field can protect the pushed out cold gas from evaporation and thus favor the formation of stars
Trabajo, amor y esperanza : el ancla contra la idea suicida de Louisa May Alcott
No full text1 archivo PDF (14 páginas)Louisa May Alcott, mejor conocida como la autora de Little Women, diez
años antes de ser famosa y debido a la desesperante situación familiar, tuvo
una idea suicida a la que se sobrepuso gracias al ancla del trabajo, el amor y
la esperanza que la acompañaron con fuerza el resto de sus días. En dos de
sus obras (aunque no para niños) Love & Self-Love (1859) y Work: A Story
of Experience (1872), retoma la idea del suicidio, pero fundamentalmente
las razones para no llevarlo a cabo. En su diario de 1858, de manera somera,
se puede leer acerca de ese momento de su existencia y su determinación
para transformarlo.
Louisa May Alcott, known as the author of Little Women, had a suicidal
idea ten years before being that famous. It was due to the distressing familiar
situation she was living, but she was able to overcome from such
idea due to the “anchor” of work, love and hope that accompanied her for
the rest of her life. In two of her novels (although not for children): Love &
Self-Love (1859) and Work: A Story of Experience (1872), she looks back to
the suicidal idea, but above all to the reasons for not to commit it. In her
journal of 1858, it is possible to have a glimpse of that moment in her life
and her courage to transform it.
Palabras clave / Key words: Louisa May Alcott, ideas suicidas, religión, diario,
amor y amor propio / Louisa May Alcott, suicidal ideas, religion, journals,
Love and Self-Love. tyvlx
Role of Magnetic Fields in Ram Pressure Stripped Galaxies
No full textRam-pressure stripping is a crucial evolutionary driver for cluster galaxies and jellyfish galaxies characterized by very extended tails of stripped gas, and they are the most striking examples of it in action. Recently, those extended tails are found to show ongoing star formation, raising the question of how the stripped, cold gas can survive long enough to form new stars outside the stellar disk. In this study, we summarize the most recent results achieved within the GASP collaboration to provide a holistic explanation for this phenomenon. We focus on two textbook examples of jellyfish galaxies, JO206 and JW100, for which, via multi-wavelength observations from radio to X-ray and numerical simulations, we have explored the different gas phases (neutral, molecular, diffuse-ionized, and hot). Based on additional multi-phase gas studies, we now propose a scenario of stripped tail evolution including all phases that are driven by a magnetic draping sheath, where the intracluster turbulent magnetized plasma condenses onto the galaxy disk and tail and produces a magnetized interface that protects the stripped galaxy tail gas from evaporation. In such a scenario, the accreted environmental plasma can cool down and eventually join the tail gas, hence providing additional gas to form stars. The implications of our findings can shed light on the more general scenario of draping, condensation, and cooling of hot gas surrounding cold clouds that is fundamental in many astrophysical phenomena
Evidence for Mixing between ICM and Stripped ISM by the Analysis of the Gas Metallicity in the Tails of Jellyfish Galaxies
No full textHydrodynamical simulations show that the ram pressure stripping in galaxy clusters fosters a strong interaction between stripped interstellar medium (ISM) and the surrounding medium, with the possibility of intracluster medium (ICM) cooling into cold gas clouds. Exploiting the MUSE observation of three jellyfish galaxies from the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey, we explore the gas metallicity of star-forming clumps in their gas tails. We find that the oxygen abundance of the stripped gas decreases as a function of the distance from the parent galaxy disk; the observed metallicity profiles indicate that more than 40% of the most metal-poor stripped clouds are constituted by cooled ICM, in qualitative agreement with simulations that predict mixing between the metal-rich ISM and the metal-poor ICM
Walk on the Low Side: LOFAR explores the low-frequency radio emission of GASP jellyfish galaxies
No full textJellyfish galaxies, characterized by long filaments of stripped interstellar
medium extending from their disks, are the prime laboratories to study the
outcomes of ram pressure stripping. At radio wavelengths, they often show
unilateral emission extending beyond the stellar disk, and an excess of radio
luminosity with respect to that expected from their current star formation
rate. We present new 144 MHz images provided by the LOFAR Two-metre Sky Survey
for a sample of six galaxies from the GASP survey. These galaxies are
characterized by a high global luminosity at 144 MHz ( W
Hz), in excess compared to their ongoing star formation rate. The
comparison of radio and H images smoothed with a Gaussian beam
corresponding to 10 kpc reveals a sub-linear spatial correlation between
the two emissions with an average slope . In their stellar disk we
measure , which is close to the radio-to-star formation linear
relation. We speculate that, as a consequence of the ram pressure, in these
jellyfish galaxies the cosmic rays transport is more efficient than in normal
galaxies. Radio tails typically have higher radio-to-H ratios than the
disks, thus we suggest that the radio emission is boosted by the electrons
stripped from the disks. In all galaxies, the star formation rate has decreased
by a factor within the last yr. The observed radio emission
is consistent with the past star formation, so we propose that this recent
decline may be the cause of their radio luminosity-to-star formation rate
excess.Comment: 22 pages, 7 figures. Accepted for publication on ApJ on 24/08/202
Lectura etnocrítica como herramienta analítica interdisciplinaria e interseccional
No full textThe main theoretical and methodological assumptions of ethnocriticism are presented as an analytical tool of an interdisciplinary and intersectional nature that conceives the text as an ethnotext and culture as an ethnoculture. This ethnotext condenses meaning, knowledge, and the crossover of approaches that leads to the materialization of different points of view and discriminatory ideologies. The one who anchors these ideologies in the text is its author, as it is the result of his imaginary. Aware or not, the author screens, in his esthetic work, representations contradicting his ethical, political, and ideological proposal. Ethnocriticism detects, analyzes and denounces those ideological biases.Se exponen los presupuestos esenciales teóricos y metodológicos de la etnocrítica, herramienta analítica interdisciplinar e interseccional que concibe al texto como etnotexto y a la cultura como etnocultura. Este etnotexto es un condensador de sentidos, de saberes y entrecruzamiento de enfoques, cuestión que lo lleva a materializar diversos puntos de vista e ideologías discriminatorias. Quien ancla tales ideologías en el texto es el autor, al ser desbordado por el imaginario y, de manera consciente o inconsciente, filtra en su proyecto estético representaciones que desdicen su proyecto ético, político e ideológico. La etnocrítica detecta, analiza y denuncia esos sesgos
Lectura etnocrítica como herramienta analítica interdisciplinaria e interseccional
No full textThe main theoretical and methodological assumptions of ethnocriticism are presented as an analytical tool of an interdisciplinary and intersectional nature that conceives the text as an ethnotext and culture as an ethnoculture. This ethnotext condenses meaning, knowledge, and the crossover of approaches that leads to the materialization of different points of view and discriminatory ideologies. The one who anchors these ideologies in the text is its author, as it is the result of his imaginary. Aware or not, the author screens, in his esthetic work, representations contradicting his ethical, political, and ideological proposal. Ethnocriticism detects, analyzes and denounces those ideological biases.Se exponen los presupuestos esenciales teóricos y metodológicos de la etnocrítica, herramienta analítica interdisciplinar e interseccional que concibe al texto como etnotexto y a la cultura como etnocultura. Este etnotexto es un condensador de sentidos, de saberes y entrecruzamiento de enfoques, cuestión que lo lleva a materializar diversos puntos de vista e ideologías discriminatorias. Quien ancla tales ideologías en el texto es el autor, al ser desbordado por el imaginario y, de manera consciente o inconsciente, filtra en su proyecto estético representaciones que desdicen su proyecto ético, político e ideológico. La etnocrítica detecta, analiza y denuncia esos sesgos
Multi-epoch variability of AT 2000ch (SN 2000ch) in NGC 3432
No full textContext. AT 2000ch is a highly variable massive star and supernova imposter in NGC 3432 first detected in 2000. It is similar and often compared to SN 2009ip, and it is therefore expected to undergo a core-collapse supernova (SN) – a SN imposter of similar brightness – in the near future.
Aims. We characterize the long-term variability of AT 2000ch in the radio and optical regimes with archival data reaching back to the year 1984. We use these newly reduced observations in addition to observations in the literature to restrict the mass-loss rates of AT 2000ch at multiple epochs based on different approaches, and to infer the general properties of its circumstellar nebula with respect to the detected radio brightness.
Methods. We extend the known optical light curve of AT 2000ch up to the beginning of 2022 by performing point spread function (PSF) photometry on archival data from the Palomar Transient Factory and the Zwicky Transient Facility. We reduced archival radio continuum observations obtained with the Very Large Array using standard calibration and imaging methods and complemented these with pre-reduced CHANG-E
GASP XXXIX: MeerKAT hunts Jellyfish in A2626
No full textWe present MeerKAT H I observations of six jellyfish candidate galaxies (JFCGs) in the galaxy cluster, A2626. Two of the six galaxies JW100 and JW103, which were identified as JFCGs from B-band images, are confirmed as jellyfish galaxies (JFGs). Both of the JFGs have low H I content, reside in the cluster core, and move at very high velocities (~ 3σcl). The other JFCGs, identified as non-jellyfish galaxies, are H I rich, with H I morphologies revealing warps, asymmetries, and possible tidal interactions. Both the A2626 JFGs and three other confirmed JFGs from the GASP sample show that these galaxies are H I stripped but not yet quenched. We detect H I, H α, and CO(2-1) tails of similar extent (~50 kpc) in JW100. Comparing the multiphase velocity channels, we do not detect any H I or CO(2-1) emission in the northern section of the tail where H α emission is present, possibly due to prolonged interaction between the stripped gas and the intracluster medium. We also observe an anticorrelation between H I and CO(2-1), which hints at an efficient conversion of H I to H2 in the southern part of the tail. We find that both ram-pressure stripping and H I-to-H2 conversion are significant depletion channels for atomic gas. H I-to-H2 conversion is more efficient in the disc than in the tail
Bayesian decomposition of the Galactic multi-frequency sky using probabilistic autoencoders
No full textContext. All-sky observations show both Galactic and non-Galactic diffuse emission, for example from interstellar matter or the cosmic microwave background (CMB). The decomposition of the emission into different underlying radiative components is an important signal reconstruction problem.
Aims. We aim to reconstruct radiative all-sky components using spectral data, without incorporating knowledge about physical or spatial correlations.
Methods. We built a self-instructing algorithm based on variational autoencoders following three steps: (1)We stated a forward model describing how the data set was generated from a smaller set of features, (2) we used Bayes’ theorem to derive a posterior probability distribution, and (3) we used variational inference and statistical independence of the features to approximate the posterior. From this, we derived a loss function and optimized it with neural networks. The resulting algorithm contains a quadratic error norm with a self-adaptive variance estimate to minimize the number of hyperparameters. We trained our algorithm on independent pixel vectors, each vector representing the spectral information of the same pixel in 35 Galactic all-sky maps ranging from the radio to the γ-ray regime.
Results. The algorithm calculates a compressed representation of the input data. We find the feature maps derived in the algorithm’s latent space show spatial structures that can be associated with all-sky representations of known astrophysical components. Our resulting feature maps encode (1) the dense interstellar medium (ISM), (2) the hot and dilute regions of the ISM, and (3) the CMB, without being informed about these components a priori.
Conclusions. We conclude that Bayesian signal reconstruction with independent Gaussian latent space statistics is sufficient to reconstruct the dense and the dilute ISM, as well as the CMB, from spectral correlations only. The computational approximation of the posterior can be performed efficiently using variational inference and neural networks, making them a suitable approach to probabilistic data analysis
