Tyler Foster

H I KINEMATICS AND DYNAMICS OF MESSIER 31

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 the Dominion Radio Astrophysical Observatory. The H I distribution and kinematics of the disk are analyzed and basic dynamical properties are given. The rotation curve is measured out to 38 kpc, showing a nuclear peak at 340 km s–1, a dip at 202 km s–1 around 4 kpc, two distinct flat parts at 264 km s–1 and 230 km s–1, and an increase to 275 km s–1 in the outermost regions. Except for the innermost regions, the axisymmetry of the gas rotation is very good. A very strong warp of the H I disk is evidenced. The central regions appear less inclined than the average disk inclination of 74°, while the outer regions appear more inclined. Mass distribution models by ΛCDM Navarro-Frenk-White, 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) × 1011 ☉. The dark matter component is almost four times more massive than the baryonic mass inside this radius. A total mass of 1.0 × 1012 ☉ is derived inside the virial radius. The spectral structure of the observations is very complex, with sometimes up to five H I components detected per spectrum, which is very rarely seen in other galaxies. New H I structures are discovered in the datacube. The most remarkable new features are an external arm and thin H I spurs in the disk 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 disk. Both these H I perturbations could result from tidal interactions with galaxy companions like NGC 205.

A Thorough Investigation of the Distance to the Supernova Remnant CTB109 and Its Pulsar AXP J2301+5852

CTB109 is one of only three Galactic supernova remnants (SNRs) known to harbor an anomalous X-ray pulsar or magnetar. That makes this SNR an object of great importance and a prime target for high-energy astrophysics studies. Those studies rely heavily on the assumed distance to CTB109. There have been three major distance determinations over the last decade, all of which report completely different results. While chaotic distance determinations in the literature are not uncommon for SNRs as a class of object, the wild discrepancy in the distance to CTB109 makes it especially important to revisit and firmly resolve once and for all. In this Letter we bring to bear all available observational information and present a synthesis of evidence that consistently locates CTB109 within or close to the Perseus arm spiral shock, at a distance of 3.2 {+-} 0.2 kpc.

Discovery of a new faint radio SNR G108.2-0.6

A new faint and large shell-type radio Supernova Remnant (SNR) G108.2−0.6 has been discovered in the Canadian Galactic Plane Survey (CGPS). The SNR shows an elliptical shell-type structure at 1420 MHz, and has a 408–1420 MHz TT-plot spectral index of α = −0.5 ± 0. 1( S ν∝ν α ), typical of a shell-type SNR. The remnant’s flux density at 1420 MHz is 6.6 ± 0. 7J y, and at 408 MHz is 11.5 ± 1.2 Jy. Both of these are corrected for compact sources. An integrated spectral index of −0.45 ± 0.13 is determined. This new SNR has among the lowest surface brightness of any known remnants (Σ1 GHz = 2.4 × 10 −22 Wm −2 Hz −1 sr −1 ). 21 cm Stokes Q and U CGPS data (plus preliminary Effelsberg Q and U maps) show some suggestive features that correlate with total power. H i observations show structures associated with G108.2−0.6 in the radial velocity range −53 to −58 km s −1 , and indicate it is located in the Perseus arm shock at a distance of 3.2 ± 0.6 kpc. At this distance the diameter of G108.2−0.6 is 58 pc. IRAS maps (12, 25, 60 and 100 µm) of the new SNR show rich infrared emission surrounding G108.2−0.6.

THE ENORMOUS OUTER GALAXY H II REGION CTB 102

We present new radio recombination line observations of the previously unstudied H II region CTB 102. Line parameters are extracted and physical parameters describing the gas are calculated. We estimate the distance to CTB 102 to be 4.3 kpc. Through comparisons with H I and 1.42 GHz radio continuum data, we estimate the size of CTB 102 to be 100-130 pc, making it one of the largest H II regions known, comparable to the W4 complex. A stellar wind blown bubble model is presented as the best explanation for the observed morphology, size, and velocities.

XMM-Newton, Chandra, and CGPS observations of the Supernova Remnants G85.4+0.7 and G85.9–0.6

We present an XMM-Newton detection of two low radio surface brightness supernova remnants (SNRs), G85.4+0.7 and G85.9–0.6, discovered with the Canadian Galactic Plane Survey (CGPS). High-resolution XMM-Newton images revealing the morphology of the diffuse emission, as well as discrete point sources, are presented and correlated with radio and Chandra images. The new data also permit a spectroscopic analysis of the diffuse emission regions, and a spectroscopic and timing analysis of the point sources. Distances have been determined from H I and CO data to be 3.5 ± 1.0 kpc for SNR G85.4+0.7 and 4.8 ± 1.6 kpc for SNR G85.9–0.6. The SNR G85.4+0.7 is found to have a temperature of ~12-13 MK and a 0.5-2.5 keV luminosity of ~(1–4) × 1033D23.5 erg s−1 (where D3.5 is the distance in units of 3.5 kpc), with an electron density ne of ~(0.07–0.16) (fD3.5)−1/2 cm−3 (where f is the volume filling factor) and a shock age of ~(9–49) (fD3.5)1/2 kyr. The SNR G85.9–0.6 is found to have a temperature of ~15-19 MK and a 0.5-2.5 keV luminosity of ~(1–4) × 1034D24.8 erg s−1 (where D4.8 is the distance in units of 4.8 kpc), with an electron density ne of ~(0.04–0.10) (fD4.8)−1/2 cm−3 and a shock age of ~(12–42) (fD4.8)1/2 kyr. Based on the data presented here, none of the point sources appears to be the neutron star associated with either SNR.

Revealing the Galactic H II Region G84.9+0.5 through 5 GHz Continuum and Polarization Emission and a Voigt Profile Analysis of Radio Recombination Line Observations

We present new λ = 6 cm radio observations (Stokes I, Q, and U and hydrogen recombination line) of the Galactic object G84.9+0.5, previously classified as a supernova remnant. Radio recombination line (RRL) emission near 6 cm is detected in deep GBT observations, and we are able to separate the 7.6 mK line detected from this object (appearing at vLSR = -40 km s-1) from the line emitted by ionized gas of W80 in the foreground (Tl = 5.4 mK; vLSR ~ 0 km s-1) along the same line of sight (LOS). Detection of RRL emission from G84.9+0.5 and the absence of polarized emission at 6 cm imply that this object is an H II region. Rather than a Gaussian, a Voigt function better describes the extended line profile of G84.9+0.5, which has a low-level wing extending into its negative-velocity end. A Monte Carlo analysis of noisy synthetic spectra is presented, and it is concluded the wing is not spurious. Two physical explanations for the wing (pressure broadening and an outflow of gas) are considered. We favor that of a champagne-type outflow in the gas flowing along the inside wall of a known molecular cloud in the vicinity of the nebula (at -40 km s-1), making G84.9+0.5 a blister type H II region viewed face-on. We find Te = 9900 K and ne = 20 cm-3 from a non-LTE analysis of the peak toward the RRL, and a total H II mass of 440 M☉. A distance of 4.9 kpc is determined for this object. An IR analysis using MSX and 2MASS data is presented, showing H II region colors for G84.9+0.5 and identifying a possible exciting star for this H II region.

G181.1+9.5, a new high-latitude low-surface brightness supernova remnant

Context. More than 90% of the known Milky Way supernova remnants (SNRs) are within 5° of the Galactic plane. The discovery of the new high-latitude SNR G181.1+9.5 will give us the opportunity to learn more about the environment and magnetic field at the interface between disk and halo of our Galaxy. Aims. We present the discovery of SNR G181.1+9.5, a new high-latitude SNR, serendipitously discovered in an ongoing survey of the Galactic anti-centre High-Velocity Cloud complex, observed with the DRAO Synthesis Telescope in the 21 cm radio continuum and H i spectral line. Methods. We use radio continuum observations (including the linearly polarized component) at 1420 MHz (observed with the DRAO ST) and 4850 MHz (observed with the Effelsberg 100-m radio telescope) to map G181.1+9.5 and determine its nature as a SNR. High-resolution 21 cm H i line observations and H i emission and absorption spectra reveal the physical characteristics of its local interstellar environment. Finally, we estimate the basic physical parameters of G181.1+9.5 using models for highly-evolved SNRs. Results. G181.1+9.5 has a circular shell-like morphology with a radius of about 16 pc at a distance of 1.5 kpc some 250 pc above the mid-plane. The radio observations reveal highly linearly polarized emission with a non-thermal spectrum. Archival ROSAT X-ray data reveal high-energy emission from the interior of G181.1+9.5 indicative of the presence of shock-heated ejecta. The SNR is in the advanced radiative phase of SNR evolution, expanding into the HVC inter-cloud medium with a density of n HI ≈ 1 cm -3 . Basic physical attributes of G181.1+9.5 calculated with radiative SNR models show an upper-limit age of 16 000 yr, a swept-up mass of more than 300 M ⊙ , and an ambient density in agreement with that estimated from H i observations. Conclusions. G181.1+9.5 shows all characteristics of a typical mature shell-type SNR, but its observed faintness is unusual and requires further study.

Extended H I 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.