36 research outputs found
Direct Measurement of Neutron-Star Recoil in the Oxygen-Rich Supernova Remnant Puppis A
A sequence of three Chandra X-ray Observatory High Resolution Camera images
taken over a span of five years reveals arc-second-scale displacement of RX
J0822-4300, the stellar remnant (presumably a neutron star) near the center of
the Puppis A supernova remnant. We measure its proper motion to be
0.165+/-0.025 arcsec/yr toward the west-southwest. At a distance of 2 kpc, this
corresponds to a transverse space velocity of ~1600 km/s. The space velocity is
consistent with the explosion center inferred from proper motions of the
oxygen-rich optical filaments, and confirms the idea that Puppis A resulted
from an asymmetric explosion accompanied by a kick that imparted roughly
3*10^49 ergs of kinetic energy (some 3 percent of the kinetic energy for a
typical supernova) to the stellar remnant. We discuss constraints on
core-collapse supernova models that have been proposed to explain neutron star
kick velocities
Peculiar motions of the gas at the centre of the barred galaxy UGC 4056
We derive the circular velocity curves of the gaseous and stellar discs of
UGC 4056, a giant barred galaxy with an active galactic nucleus (AGN). We
analyse UGC 4056 using the 2D spectroscopy obtained within the framework of the
Mapping Nearby Galaxies at APO (MaNGA) survey. Using images and the colour
index g-r from the Sloan Digital Sky Survey (SDSS), we determined the tilt of
the galaxy, which allows us to conclude that the galaxy rotates clockwise with
trailing spiral arms. We found that the gas motion at the central part of the
UGC 4056 shows peculiar features. The rotation velocity of the gaseous disc
shows a bump within around three kiloparsecs while the rotation velocity of the
stellar disc falls smoothly to zero with decreasing galactocentric distance. We
demonstrate that the peculiar radial velocities in the central part of the
galaxy may be caused by the inflow of the gas towards the nucleus of the
galaxy. The unusual motion of the gas takes place at the region with the
AGN-like radiation and can be explained by the gas response to the bar
potential.Comment: 11 pages, 10 figures, 1 table, accepted for publication in A&
Properties of galaxies with an offset between the position angles of the major kinematic and photometric axes
We derive the photometric, kinematic, and abundance characteristics of 18 star-forming MaNGA galaxies with fairly regular velocity fields and surface brightness distributions and with a large offset between the measured position angles of the major kinematic and photometric axes, Delta PA greater than or similar to 20 degrees. The aim is to examine if there is any other distinctive characteristic common to these galaxies. We found morphological signs of interaction in some (in 11 out of 18) but not in all galaxies. The observed velocity fields show a large variety; the maps of the isovelocities vary from an hourglass-like appearance to a set of straight lines. The position angles of the major kinematic axes of the stellar and gas rotations are close to each other. The values of the central oxygen abundance, radial abundance gradient, and star formation rate are distributed within the intervals defined by galaxies with small (no) Delta PA of similar mass. Thus, we do not find any specific characteristic common to all galaxies with large Delta PA. Instead, the properties of these galaxies are similar to those of galaxies with small (no) Delta PA. This suggests that either the reason responsible for the large Delta PA does not influence other characteristics or the galaxies with large Delta PA do not share a common origin, they can, instead, originate through different channels
Observations of the neutral hydrogen surrounding the radio quiet neutron star RX J0822-4300 in Puppis A
We have observed the HI distribution in an area 40' x 40' around the neutron
star candidate RX J0822-4300, which is located in the supernova remnant Puppis
A. The observations of the 21 cm line were obtained with the Australia
Telescope Compact Array (ATCA) and were combined with single dish data from the
Southern Galactic Plane Survey. The spatial resolution is 90", and the velocity
resolution, 1 km/s . A sensitivity of ~ 0.7 K was achieved. The results
revealed a double lobed feature of reduced emission at +16 km/s, centered on
the central compact object (CCO), and aligned with an HI hole blueshifted by 13
km/s. The HI depressions have probably been created by the sweeping up of ~ 2
solar masses. The alignement between the lobes and the optical expansion centre
of Puppis A suggests that the CCO could be ejecting two opposite jets. The
velocity at which the two lobes are best defined allowed us to confirm that the
distance to Puppis A is 2.2 kpc, based on a systemic velocity of +16 km/s. The
hydrogen column density computed using this systemic velocity is consistent
with estimates from models for X-ray spectra, thus reinforcing our conclusion
that the kinematic distance is 2.2 k pc.Comment: 8 pages, 2 ps/eps figures, plus 1 gif figure and 4 jpg figures,
MNRAS, in press. Full postscript version with all 7 figures is available at
http://www.physics.usyd.edu.au/~simonj/puppis.ps.g
Oxygen and nitrogen abundances of HII regions in six spiral galaxies
Spectroscopic observations of 63 HII regions in six spiral galaxies (NGC 628,
NGC 783, NGC 2336, NGC 6217, NGC 7331, and NGC 7678) were carried out with the
6-meter telescope (BTA) of Russian Special Astrophysical Observatory with the
Spectral Camera attached to the focal reducer SCORPIO in the multislit mode
with a dispersion of 2.1A/pixel and a spectral resolution of 10A. These
observations were used to estimate the oxygen and nitrogen abundances and the
electron temperatures in HII regions through the recent variant of the strong
line method (NS calibration). The parameters of the radial distribution (the
extrapolated central intercept value and the gradient) of the oxygen and
nitrogen abundances in the disks of spiral galaxies NGC 628, NGC 783, NGC 2336,
NGC 7331, and NGC 7678 have been determined. The abundances in the NGC 783, NGC
2336, NGC 6217, and NGC 7678 are measured for the first time. Galaxies from our
sample follow well the general trend in the luminosity - central metallicity
diagram for spiral and irregular galaxies.Comment: 11 pages, 7 figures, 6 tables. Accepted for publication in MNRA
The IMF in Starbursts
The history of the IMF in starburst regions is reviewed. The IMFs are no
longer believed to be top-heavy, although some superstar clusters, whether in
starburst regions or not, could be. General observations of the IMF are
discussed to put the starburst results in perspective. Observed IMF variations
seem to suggest that the IMF varies a little with environment in the sense that
denser and more massive clusters produce more massive stars, and perhaps more
brown dwarfs too, compared to intermediate mass stars.Comment: 8 pages, to be published in ``Starbursts: from 30 Doradus to Lyman
Break Galaxies,'' held at Institute of Astronomy, Cambridge University, UK,
September 6-10, 2004. Kluwer Academic Publishers, edited by Richard de Grijs
and Rosa M. Gonzalez Delgad