The galactic magnetic field in the quasar 3C216

Multifrequency polarimetric observations made with the Very Long Baseline Array of the quasar 3C216 reveal the presence of Faraday rotation measures (RMs) in excess of 2000 rad/m**2 in the source rest frame, in the arc of emission located at ~ 140 mas from the core. Rotation measures in the range -300 - +300 rad/m**2 are detected in the inner 5 mas (~30 parsecs). while the rotation measures near the core can be explained as due to a magnetic field in the narrow line region, we favor the interpretation for the high RM in the arc as due to a ``local'' Faraday screen, produced in a shock where the jet is deflected by the interstellar medium of the host galaxy. Our results indicate that a galacit magnetic field of the order of 50 microGauss on a scale greater than 100 pc must be present in the galactic medium.Comment: 23 pages, 3 tables, 11 figures. To appear on The Astronomical Journal, November 1999 Issu

The COINS Sample - VLBA Identifications of Compact Symmetric Objects

We present results of multifrequency polarimetric VLBA observations of 34 compact radio sources. The observations are part of a large survey undertaken to identify CSOs Observed in the Northern Sky (COINS). Compact Symmetric Objects (CSOs) are of particular interest in the study of the physics and evolution of active galaxies. Based on VLBI continuum surveys of ~2000 compact radio sources, we have defined a sample of 52 CSOs and CSO candidates. In this paper, we identify 18 previously known CSOs, and introduce 33 new CSO candidates. We present continuum images at several frequencies and, where possible, images of the polarized flux density and spectral index distributions for the 33 new candidates and one previously known but unconfirmed source. We find evidence to support the inclusion of 10 of these condidates into the class of CSOs. Thirteen candidates, including the previously unconfirmed source, have been ruled out. Eleven sources require further investigation. The addition of the 10 new confirmed CSOs increases the size of this class of objects by 50%.Comment: 24 pages, incl 8 figures. Accepted for publication in ApJ. Figure quality degraded in the interests of space, full gzipped PS version also available at http://www.ee.nmt.edu/~apeck/papers

Probing the Magnetized Interstellar Medium Surrounding the Planetary Nebula Sh 2-216

We present 1420 MHz polarization images of a 2.5 X 2.5 degree region around the planetary nebula (PN) Sh 2-216. The images are taken from the Canadian Galactic Plane Survey (CGPS). An arc of low polarized intensity appears prominently in the north-east portion of the visible disk of Sh 2-216, coincident with the optically identified interaction region between the PN and the interstellar medium (ISM). The arc contains structural variations down to the ~1 arcminute resolution limit in both polarized intensity and polarization angle. Several polarization-angle "knots" appear along the arc. By comparison of the polarization angles at the centers of the knots and the mean polarization angle outside Sh 2-216, we estimate the rotation measure (RM) through the knots to be -43 +/- 10 rad/m^2. Using this estimate for the RM and an estimate of the electron density in the shell of Sh 2-216, we derive a line-of-sight magnetic field in the interaction region of 5.0 +/- 2.0 microG. We believe it more likely the observed magnetic field is interstellar than stellar, though we cannot completely dismiss the latter possibility. We interpret our observations via a simple model which describes the ISM magnetic field around Sh 2-216, and comment on the potential use of old PNe as probes of the magnetized ISM.Comment: 25 pages, 4 figures. Accepted for publication in the Astrophysical Journa

Self-Generated Magnetic Fields in Galactic Cooling Flows

Interstellar magnetic fields in elliptical galaxies are assumed to have their origin in stellar fields that accompany normal mass loss from an evolving population of old stars. The seed fields are amplified by interstellar turbulence driven by stellar mass loss and supernova events. These disordered fields are further amplified by time-dependent compression in the inward moving galactic cooling flow and are expected to dominate near the galactic core. Under favorable circumstances, fields similar in strength to those observed $B \sim 1-10~(r/10~kpc)^{-1.2}\mu$G can be generated solely from these natural galactic processes. In general the interstellar field throughout elliptical galaxies is determined by the outermost regions in the interstellar gas where the turbulent dynamo process can occur. Because of the long hydrodynamic flow times in galactic cooling flows, currently observed magnetic fields may result from periods of intense turbulent field amplification that occurred in the outer galaxy in the distant past. Particularly strong fields in ellipticals may result from ancient galactic mergers or shear turbulence introduced at the boundary between the interstellar gas and ambient cluster gas.Comment: 21 pages in AASTEX LaTeX with 2 figures; accepted by Astrophysical Journa

Revisiting critical literacy in the digital age

In an age of environmental crisis, financial instability, widespread migration, and political extremism, the case for critical literacy is pressing. Navigating criticality in the digital age, however, is challenging, not least because digital media, digital devices, and digital architectures are implicated in broader social, cultural, commercial, and political activity. Critical literacy in this context needs to do more than focus on the significance of texts within networks of humans. The authors developed a model designed to support a relational approach to critical literacy, drawing on a sociomaterial perspective to consider how broader social‐material networks help generate meanings that may amplify, undermine, or contradict the activities of individuals and groups. The authors end with questions that provide a starting point for broadening the scope of critical literacy in education to reflect on relationships among people, texts, and materials across time and spaces

The New Generation Planetary Population Synthesis (NGPPS). IV. Planetary systems around low-mass stars

Context. Previous theoretical works on planet formation around low-mass stars have often been limited to large planets and individual systems. As current surveys routinely detect planets down to terrestrial size in these systems, models have shifted toward a more holistic approach that reflects their diverse architectures. Aims. Here, we investigate planet formation around low-mass stars and identify differences in the statistical distribution of modeled planets. We compare the synthetic planet populations to observed exoplanets and we discuss the identified trends. Methods. We used the Generation III Bern global model of planet formation and evolution to calculate synthetic populations, while varying the central star from Solar-like stars to ultra-late M dwarfs. This model includes planetary migration, N-body interactions between embryos, accretion of planetesimals and gas, and the long-term contraction and loss of the gaseous atmospheres. Results. We find that temperate, Earth-sized planets are most frequent around early M dwarfs (0.3 M⊙–0.5 M⊙) and that they are more rare for Solar-type stars and late M dwarfs. The planetary mass distribution does not linearly scale with the disk mass. The reason behind this is attributed to the emergence of giant planets for M⋆ ≥ 0.5 M⊙, which leads to the ejection of smaller planets. Given a linear scaling of the disk mass with stellar mass, the formation of Earth-like planets is limited by the available amount of solids for ultra-late M dwarfs. For M⋆ ≥ 0.3 M⊙, however, there is sufficient mass in the majority of systems, leading to a similar amount of Exo-Earths going from M to G dwarfs. In contrast, the number of super-Earths and larger planets increases monotonically with stellar mass. We further identify a regime of disk parameters that reproduces observed M-dwarf systems such as TRAPPIST-1. However, giant planets around late M dwarfs, such as GJ 3512b, only form when type I migration is substantially reduced. Conclusions. We are able to quantify the stellar mass dependence of multi-planet systems using global simulations of planet formation and evolution. The results fare well in comparison to current observational data and predict trends that can be tested with future observations