arXiv subjects

Tyler Foster

Publications and source records attributed to Tyler Foster.

26 records · Page 2Linked to original sources

arXiv2013

Two Radio Supernova Remnants Discovered in the Outer Galaxy

We report on the discovery of two supernova remnants (SNRs) designated G152.4-2.1 and G190.9-2.2, using Canadian Galactic Plane Survey data. The aims of this paper are, first, to present evidence that favours the classification of both sources as SNRs, and, second, to describe basic parameters (integrated flux density, spectrum, and polarization) as well as properties (morphology, line-of-sight velocity, distance and physical size) to facilitate and motivate future observations. Spectral and polarization parameters are derived from multiwavelength data from existing radio surveys carried out at wavelengths between 6 and 92cm. In particular for the source G152.4-2.1 we also use new observations at 11cm done with the Effelsberg 100m telescope. The interstellar medium around the discovered sources is analyzed using 1-arcminute line data from neutral hydrogen (HI) and 45-arcsecond 12CO(J=1-0). G152.4-2.1 is a barrel shaped SNR with two opposed radio-bright polarized flanks on the North and South. The remnant, which is elongated along the Galactic plane is evolving in a more-or-less uniform medium. G190.9-2.2 is also a shell-type remnant with East and West halves elongated perpendicular to the plane, and is evolving within a low-density region bounded by dense neutral hydrogen in the North and South, and molecular (12CO) clouds in the East and West. The integrated radio continuum spectral indices are -0.65+/-0.05 and -0.66+/-0.05 for G152.4-2.1 and G190.9-2.2 respectively. Both SNRs are approximately 1 kpc distant, with G152.4-2.1 being larger (32x30 pc in diameter) than G190.9-2.2 (18x16 pc). These two remnants are the lowest surface brightness SNRs yet catalogued at 5x10^-23 W m^-2 Hz^-1 sr^-1.

astro-ph.GA↗

arXiv2012

Higher configuration operads by way of quiver Grassmannians

We introduce a construction that associates, to each finite dimensional k-vector space V, a family of projective k-varieties that comes equipped with the structure of a operad in the category of k-schemes. When dim V = 1, this operad contains, as a suboperad, the family of moduli spaces of stably marked rational curves. For general V, our operad contains the family of Chen-Gibney-Krashen moduli spaces of stably marked trees of projective spaces as a suboperad. We realize our operad as part of a larger theory that describes how to construct operads from suitable functors. Given a category C that satisfies conditions allowing us to consider the operation of "substituting a value into an argument" within C, and given any functor F on C satisfying a variant of right-exactness, we construct a version of a set-valued operad whose inputs are given by objects in C. When C happens to be the category of nonempty finite sets, we obtain operads in the classic sense. Finally, we show that in many cases it is possible to realize these operads as disjoint unions of quiver Grassmannians.

math.AG↗

arXiv2012

Know (better) your neighbour: New HI structures in Messier 33 unveiled by a multiple peak analysis of high-resolution 21-cm data

In our quest to constrain the dynamical and structural properties of Local Group spirals from high-quality interferometric data, we have performed a neutral hydrogen survey in the direction of Messier 33. Here we present a few preliminary results from the survey and show the benefits of fitting the HI spectra by multiple peaks on constraining the structure of the Messier 33 disk. In particular we report on the discovery of new inner spiral-like and outer annular structures overlaying with the well-known main HI disk of Messier 33. Possible origins of the additional outer annular structure are presented.

astro-ph.CO↗

arXiv2010

Structure and Dynamics of the Milky Way: The Evolving Picture

From the inception of radio astronomy, the study of the Interstellar Medium has been both aided and frustrated by one fact: we are right within it! Our embedded perspective is favourable to observing kinematic and structural details that are likely to remain inaccessible in external galaxies for some time, but not so to gaining a birdseye view of our Galaxy's strucutre and motions on the largest scales. The CGPS is the original survey with the ability to image both details and the "big picture". We will broadly review what we know of the Milky Way (MW), and focus on large-scale ISM structure and dynamics that the IGPS family of surveys depicts particularly well (e.g. spiral structure, the rotation curve, density waves, rolling motions, the warp & scalloping). We also highlight areas where puzzles still exist (e.g. outer spiral structure, the question of shocks and rolling motions in the MW), and offer some new insights (e.g. multiple shocks in the 2nd quadrant; a radially varying spiral pattern speed in the disc) demonstrating what is possible with current and future high-resolution 21 cm surveys.

astro-ph.GA↗

arXiv2010

A Noncommutative Version of the Natural Numbers

In this note, we construct and study an algebraic system similar to the natural numbers, but with noncommutative addition. The addition we introduce is a binary operation that commutes with itself in the sense of N. Durov. Neverheless, the multiplication in this system (defined by iterating the noncommutative addition) turns out to be associative, commutative, and distributive over addition, and the resulting system has interesting and nontrivial arithmetic.

math.QA↗

arXiv2010

Deep wide field HI imaging of Messier 31

We report on preliminary results from a new deep 21-cm survey of the Andromeda galaxy, based on observations performed with the Synthesis Telescope and the 26-m antenna at DRAO. The HI distribution and kinematics of the disc are analyzed and basic dynamical properties are derived. New HI structures are discovered, like thin HI spur-like structures and an external arm in the disc outskirts. The HI spurs are related to perturbed stellar clumps outside the main disc of M31. The external arm lies on the far, receding side of the galaxy and has no obvious counterpart in the opposite side. These HI perturbations probably result from tidal interactions with companions. It is found a dynamical mass of 4.7 +/- 0.5 x10^11 Msol enclosed within a radius R = 38 kpc and a total mass of ~1 x10^12 Msol inside the virial radius.

astro-ph.CO↗

arXiv2009

HI kinematics and dynamics of Messier 31

[Abridged] We present a new deep 21-cm survey of the Andromeda galaxy, based on high resolution observations performed with the Synthesis Telescope and the 26-m antenna at DRAO. The HI distribution and kinematics of the disc are analyzed and basic dynamical properties are given. The rotation curve is measured out to 38 kpc, showing a nuclear peak, a dip around 4 kpc, two distinct flat parts and an increase in the outermost regions. Except for the innermost regions, the axisymmetry of the gas rotation is very good. A very strong warp of the HI disc is evidenced. The central regions appear less inclined than the average disc inclination, while the outer regions appear more inclined. Mass distribution models by LCDM NFW, Einasto or pseudo-isothermal dark matter halos with baryonic components are presented. They fail to reproduce the exact shape of the rotation curve. No significant differences are measured between the various shapes of halo. The dynamical mass of M31 enclosed within a radius of 38 kpc is (4.7 +/- 0.5) x 10^11 Msol. The dark matter component is almost 4 times more massive than the baryonic mass inside this radius. A total mass of 1.0 x 10^12 Msol is derived inside the virial radius. New HI structures are discovered in the datacube, like the detection of up to five HI components per spectrum, which is very rarely seen in other galaxies. The most remarkable new HI structures are thin HI spurs and an external arm in the disc outskirts. A relationship between these spurs and outer stellar clumps is evidenced. The external arm is 32 kpc long, lies on the far side of the galaxy and has no obvious counterpart on the other side of the galaxy. Its kinematics clearly differs from the outer adjacent disc. Both these HI perturbations could result from tidal interactions with galaxy companions.

astro-ph.CO↗

arXiv2007

Extended HI Rotation Curve of M31 using deep DRAO observations

Carignan et al. (2006) recently presented an extended HI rotation curve (RC) of M31, using single dish observations from the 100m Effelsberg and Green Bank telescopes. These observations were motivated by a comparison with previous HI data from Braun (1991) which presented a decreasing rotation curve as a function of radius. The single dish data were obtained along the semi-major axis of the approaching half of the M31 HI disk and showed a flat RC at large radius, extending up to ~35 kpc (using D=780 kpc). The kinematical analysis of M31 is pursued here and new deep 21cm observations obtained at the Dominion Radio Astrophysical Observatory (DRAO) are presented. A tilted-ring model is fitted to a new HI velocity field, allowing the derivation of the position angle and inclination as a function of radius. We concentrate on the approaching half of the disk. It is shown that the disk warping of M31 does not severely contaminate the kinematics of the neutral gas. As a consequence, the RC from the single dish data is in very good agreement with the newly derived RC.

astro-ph↗