Australia Telescope National Facility

About: Australia Telescope National Facility is a facility organization based out in Sydney, New South Wales, Australia. It is known for research contribution in the topics: Galaxy & Pulsar. The organization has 699 authors who have published 2774 publications receiving 151507 citations. The organization is also known as: ATNF.

A Chandra X-ray survey of nearby dwarf starburst galaxies: II. Starburst properties and outflows

Abstract: We present a comprehensive comparison of the X-ray properties of a sample of eight dwarf starburst galaxies observed with Chandra (IZw18, VIIZw403, NGC1569, NGC3077, NGC4214, NGC4449, NGC5253, He2–10). In PaperI we presented in detail the data reduction and analysis of the individual galaxies. For the unresolved X-ray sources we find the following: point sources are in general located close to bright H ii regions, rims of superbubbles, or young stellar clusters. The number of X-ray point sources appears to be a function of the current star formation rate and the blue luminosity of the hosts. Ultraluminous X-ray sources are only found in those dwarf galaxies which are currently interacting. The power law index of the combined cumulative X-ray point source luminosity function is α = 0.24 ± 0.06, shallower than that of more massive starburst galaxies (α = 0.4 − 0.8) and of non-starburst galaxies (α ∼ 1.2). For those galaxies showing extended X-ray emission (6 out of the 8 galaxies), we derive the following: Superwinds develop along the steepest gradient of the H i distribution with volume densities of 0.02 −0.06cm 3 , pressures of 1 −3 ×10 5 Kcm 3 , thermal energies of 2 − 30 × 10 54 erg, and hot gas masses of 2 − 20 × 10 6 M⊙ (∼ 1 per cent of the H i masses. On global scales, the distribution of the X-ray emission looks remarkably similar to that seen in Hα (comparing azimuthal averages); locally however their distribution is clearly distinct in many cases – this can be explained by the different emission mechanisms (forward vs. reverse shocks). Mass-loading of order 1 to 5 is required to explain the differences between the amount of hot gas and and the modelled mass-loss from massive stars. The metallicity of the dwarf galaxies correlates with the diffuse X-ray luminosity and anti-correlates with the cooling time of the hot gas. The diffuse X-ray luminosity is also a function of the current star formation rate. The mechanical luminosities of the developing superwinds are energetic enough to overcome the gravitational potentials of their host galaxies. This scenario is supported by the overpressures of the hot gas compared to the ambient ISM. Extended H i envelopes such as tidal tails, however, may delay outflows on timescales exceeding those of the cooling time of the hot gas.

The nature of the optical---radio correlations for powerful radio galaxies

Abstract: The nature of the optical--radio correlations for powerful radio galaxies is investigated using spectroscopic observations of a complete sample of southern 2Jy radio sources. In line with previous work, we find that significant correlations exist between the luminosities of the [OIII]5007, [OII]3727 and Hbeta emission lines and the radio luminosity. However, our observations are not easily reconciled with the idea that these correlations are caused by the increase in the power of the photoionizing quasar as the jet power increases, with average ISM properties not changing appreciably with redshift or radio power: not only do we find that the scatter in the L_[OIII] vs. L_radio correlation is significantly larger than in L_[OII]} vs. L_radio and L_Hbeta vs. L_radio correlations, but the ionization state deduced from the emission lines does not increase with radio power as predicted by the simple, constant ISM, photionization model. We conclude that: (a) there exists a considerable range in the quasar ionizing luminosity at a given redshift; and (b) that the mean density of the emission line clouds is larger in the high redshift/high power radio sources. The latter density enhancement may either be a consequence of the increased importance of jet-cloud interactions or, alternatively, due to a higher pressure in the confining hot ISM, in the high redshift objects. Deep spectra show that many of the sources in our sample are broad line radio galaxies (BLRG). The fact that the BLRG are observed out the redshift limit of the survey, overlapping in redshift with the quasars, argues against the idea that BLRG are simply the low radio power counterparts of high power, high redshift quasars.

Pulsar spin–velocity alignment: kinematic ages, birth periods and braking indices

Abstract: This paper presents a detailed investigation of the dependence of pulsar spin-velocity alignment, which has been observed for a sample of 58 pulsars, on pulsar age. At first, our study considers only pulsar characteristic ages, resulting in no change in the degree of correlation as a function of age, up to at least 100 Myr. Subsequently, we consider a more reliable estimate of pulsar age, the kinematic age, assuming that pulsars are born near the Galactic plane. We derive kinematic ages for 52 pulsars, based on the measured pulsar proper motions and positions, by modelling the trajectory of the pulsars in a Galactic potential. The sample of 52 pulsar kinematic ages constitutes the largest number of independently estimated pulsar ages to date. Using only the 33 most reliable kinematic ages from our simulations, we revisit the evolution of spin- velocity alignment, this time as a function of kinematic age. We find that the strong correlation seen in young pulsars is completely smeared out for pulsars with kinematic ages above 10 Myr, a length of time beyond which we expect the gravitational pull of the Galaxy to have a significant effect on the directions of pulsar velocities. In the discussion, we investigate the impact of large distance uncertainties on the reliability of the calculated kinematic ages. Furthermore, we present a detailed investigation of the implications of our revised pulsar ages for the braking-index and birth-period distributions. Finally, we discuss the predictions of various SN-kick mechanisms and their compatibility with our results.

Interstellar Scintillation of the Polarized Flux Density in Quasar PKS 0405-385

Abstract: The remarkable rapid variations in radio flux density and polarization of the quasar PKS 0405-385 observed in 1996 are subject to a correlation analysis, from which characteristic timescales and amplitudes are derived. The variations are interpreted as interstellar scintillations (ISSs). The centimeter wavelength observations are in the weak scintillation regime for which models for the various auto- and cross-correlations of the Stokes parameters are derived and fitted to the observations. These are well modeled by ISS of a 30 × 22 ?as source, with about 180? rotation of the polarization angle along its long dimension. This success in explaining the remarkable intraday variability (IDVs) in polarization confirms that ISS gives rise to the IDV in this quasar. However, the fit requires the scintillations to be occurring much closer to the Earth than expected according to the standard model for the ionized interstellar medium (IISM). Scattering at distances in the range 3-30 pc is required to explain the observations. For our preferred distance of 25 pc the associated source model has a peak brightness temperature near 2 × 1013 K, which is about 25 times smaller than previously derived for this source. This reduces the implied Doppler factor in the relativistic jet, presumed responsible to ~75, which is still substantially higher than centimeter wavelength VLBI estimates for the Doppler factors in active galactic nuclei (AGNs).

The latitude dependence of the rotation measures of NVSS sources

Abstract: In this Letter I use the variation of the spread in rotation measure (RM) with Galactic latitude to separate the Galactic from the extragalactic contributions to RM. This is possible since the latter does not depend on Galactic latitude. As input data I use RMs from the catalogue by Taylor, Stil & Sunstrum, supplemented with published values for the spread in RM (‘σRM’) in specific regions on the sky. I test four models of the free-electron column density (which I will abbreviate to ‘DM∞’) of the Milky Way, and the best model builds up DM∞ on a characteristic scale of a few kpc from the Sun. σRM correlates well with DM∞. The measured σRM can be modelled as a Galactic contribution, consisting of a term σRM,MW that is amplified at smaller Galactic latitudes as 1/sin |b|, in a similar way to DM∞, and an extragalactic contribution, σRM,EG, that is independent of latitude. This model is sensitive to the relative magnitudes of σRM,MW and σRM,EG, and the best fit is produced by σRM,MW≈ 8 rad m−2 and σRM,EG≈ 6 rad m−2. The four published values for σRM as a function of latitude suggest an even larger σRM,MW contribution and a smaller σRM,EG. This result from the NVSS RMs and published σRM shows that the Galactic contribution dominates structure in RM on scales between about 1° and 10° on the sky. I work out which factors contribute to the variation of σRM with Galactic latitude, and show that the σRM,EG I derived is an upper limit. Furthermore, to explain the modelled σRM,MW requires that structure in 〈B∥〉 has a 1σ spread ≲0.4 μG.