ABSTRACT
We present sofia 2, the fully automated 3D source finding pipeline for the WALLABY extragalactic H i survey with the Australian SKA Pathfinder (ASKAP). sofia 2 is a reimplementation of parts ...of the original sofia pipeline in the c programming language and makes use of OpenMP for multithreading of the most time-critical algorithms. In addition, we have developed a parallel framework called sofia-X that allows the processing of large data cubes to be split across multiple computing nodes. As a result of these efforts, sofia 2 is substantially faster and comes with a much reduced memory footprint compared to its predecessor, thus allowing the large WALLABY data volumes of hundreds of gigabytes of imaging data per epoch to be processed in real time. The source code has been made publicly available to the entire community under an open-source licence. Performance tests using mock galaxies injected into genuine ASKAP data suggest that in the absence of significant imaging artefacts sofia 2 is capable of achieving near-100 per cent completeness and reliability above an integrated signal-to-noise ratio (SNR) of about 5–6. We also demonstrate that sofia 2 generally recovers the location, integrated flux, and w20 line width of galaxies with high accuracy. Other parameters, including the peak flux density and w50 line width, are more strongly biased due to the influence of the noise on the measurement. In addition, very faint galaxies below an integrated SNR of about 10 may get broken up into multiple components, thus requiring a strategy to identify fragmented sources and ensure that they do not affect the integrity of any scientific analysis based on the sofia 2 output.
We used the Australia Telescope Compact Array to map a large field of approximately 2°× 2° around the Sculptor group galaxy NGC 300 in the 21-cm line emission of neutral hydrogen. We achieved a 5σ H ...i column density sensitivity of 1019 cm−2 over a spectral channel width of 8 km s−1 for emission filling the 180 × 88 arcsec2 synthesized beam. The corresponding H i mass sensitivity is 1.2 × 105 M⊙, assuming a distance of 1.9 Mpc. For the first time, the vast H i disc of NGC 300 has been mapped over its entire extent at a moderately high spatial resolution of about 1 kpc.
NGC 300 is characterized by a dense inner H i disc, well aligned with the optical disc of 290° orientation angle, and an extended outer H i disc with a major axis of more than 1° on the sky (equivalent to a diameter of about 35 kpc) and a different orientation angle of 332°. A significant fraction (about 43 per cent) of the total detected H i mass of 1.5 × 109 M⊙ resides within the extended outer disc. We fitted a tilted ring model to the velocity field of NGC 300 to derive the rotation curve out to a radius of 18.4 kpc, almost twice the range of previous rotation curve studies. The rotation curve rises to a maximum velocity of almost 100 km s−1 and then gently decreases again in the outer disc beyond a radius of about 10 kpc. Mass models fitted to the derived rotation curve yield good fits for Burkert and NFW dark matter halo models, whereas pseudo-isothermal halo models and Modified Newtonian Dynamics (MOND)-based models both struggle to cope with the declining rotation curve.
We also observe significant asymmetries in the outer H i disc of NGC 300, in particular near the edge of the disc, which are possibly due to ram-pressure stripping of gas by the intergalactic medium (IGM) of the Sculptor group. Our estimates show that ram-pressure stripping can occur under reasonable assumptions on the density of the IGM and the relative velocity of NGC 300. The asymmetries in the gas disc suggest a proper motion of NGC 300 towards the south-east. At the same time, our data exclude IGM densities of significantly higher than 10−5 cm−3 in the vicinity of NGC 300, as otherwise the outer gas disc would have been stripped.
Accurate parametrization of galaxies detected in the 21-cm H i emission is of fundamental importance to the measurement of commonly used indicators of galaxy evolution, including the Tully–Fisher ...relation and the H i mass function. Here, we propose a new analytic function, named the ‘busy function’, that can be used to accurately describe the characteristic double-horn H i profile of many galaxies. The busy function is a continuous, differentiable function that consists of only two basic functions, the error function, erf(x), and a polynomial, |x|
n
, of degree n ≥ 2. We present the basic properties of the busy function and illustrate its great flexibility in fitting a wide range of H i profiles from the Gaussian profiles of dwarf galaxies to the broad, asymmetric double-horn profiles of spiral galaxies. Applications of the busy function include the accurate and efficient parametrization of observed H i spectra of galaxies and the construction of spectral templates for simulations and matched-filtering algorithms. We demonstrate the busy function's power by automatically fitting it to the H i spectra of 1000 galaxies from the HI Parkes All-Sky Survey (HIPASS) Bright Galaxy Catalog, using our own c/c++ implementation, and comparing the resulting parameters with the catalogued ones. We also present two methods for determining the uncertainties of observational parameters derived from the fit.
Context. The formation of high mass stars and clusters occurs in giant molecular clouds. Objects in evolved stages of massive star formation such as protostars, hot molecular cores, and ultracompact ...HII regions have been studied in more detail than earlier, colder objects. Further progress thus requires the analysis of the time before massive protostellar objects can be probed by their infrared emission. With this in mind, the APEX Telescope Large Area Survey of the whole inner Galactic plane at 870 μm (ATLASGAL) has been carried out to provide a global view of cold dust and star formation at submillimetre wavelengths. Aims. We derive kinematic distances to a large sample of massive cold dust clumps from their measured line velocities. We estimate masses and sizes of ATLASGAL sources, for which the kinematic distance ambiguity is resolved. Methods. The ATLASGAL sample is divided into groups of sources, which are located close together, mostly within a radius of 2 pc, and have velocities in a similar range with a median velocity dispersion of ~1 km s-1. We use NH3, N2H+, and CS velocities to calculate near and far kinematic distances to those groups. Results. We obtain 296 groups of ATLASGAL sources in the first quadrant and 393 groups in the fourth quadrant, which are coherent in space and velocity. We analyse HI self-absorption and HI absorption to resolve the kinematic distance ambiguity to 689 complexes of submm clumps. They are associated with 12CO emission probing large-scale structure and 13CO (1–0) line as well as the 870 μm dust continuum on a smaller scale. We obtain a scale height of ~28 ± 2 pc and displacement below the Galactic midplane of ~−7 ± 1 pc. Within distances from 2 to 18 kpc ATLASGAL clumps have a broad range of gas masses with a median of 1050 M⊙ as well as a wide distribution of radii with a median of 0.4 pc. Their distribution in galactocentric radii is correlated with spiral arms. Conclusions. Using a statistically significant ATLASGAL sample we derive a power-law exponent of −2.2 ± 0.1 of the clump mass function. This is consistent with the slope derived for clusters and with that of the stellar initial mass function. Examining the power-law index for different galactocentric distances and various source samples shows that it is independent of environment and evolutionary phase. Fitting the mass-size relationship by a power law gives a slope of 1.76 ± 0.01 for cold sources such as IRDCs and warm clumps associated with HII regions.
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We present new multiwavelength scaling relations between the neutral hydrogen content (H i) and the stellar properties of nearby galaxies selected from the H i Parkes All-Sky Survey (HIPASS). We use ...these new scaling relations to investigate the environmental dependence of the H i content of galaxies. We find that galaxies in high-density environments tend to have on average less H i than galaxies with the same stellar mass in low-density environments. Our new H i scaling relations allow us to identify individual galaxies, as well as group/cluster environments, that have an ‘anomalous’ H i content. We map the global distribution of H i-deficient and H i-excess galaxies on the sky and compare it to the large-scale structure of galaxies. We find galaxy clusters to be H i deficient, and we identify that the regions surrounding clusters tend to be H i excess. Finally, we demonstrate the potential of using H i scaling relations to predict future H i surveys based on an optical redshift survey. We apply our scaling relations to 16 709 galaxies in the 6dF Galaxy Survey that lie in the HIPASS volume and compare our predictions to the measurements. We find that scaling relations are a good method to estimate the outcome of H i surveys.
We present deep, intermediate-resolution, optical spectroscopy of 136 genuine UV-bright regions located in both the inner and outer regions of NGC 1512. This galaxy is in close interaction with the ...blue compact dwarf galaxy NGC 1510 and possesses two prominent H i arms where extended ultraviolet complexes are found. Our data were taken using 2dF/AAOmega at the 3.9 m Anglo-Australian Telescope and are combined with the H i data from Local Volume H i
Survey and Galaxy Evolution Explorer UV data. We detect ionized gas in 82 per cent of the complexes, many of them located between 1 and 6.6 R
25. We found significant differences between regions along the Arm 1 – 8.25 ≲ 12+log(O/H) ≲ 8.45 –, and knots located in the external debris of Arm 2, –8.40 ≲ 12+log(O/H) ≲ 8.60–. Considering a radial and an azimuthal gradient following the H i arms, we confirm that Arm 2 has experienced an enhancement in star formation because of the interaction with NGC 1510 and flattened the radial metallicity at large radii. Arm 1 appears to retain the original and poorly disturbed radial distribution. We trace the kinematics of the system up to 78 kpc using the Hα emission, which matches well that provided by the H i. We estimate that the gas existing at large galactocentric radii had a metallicity of 12+log(O/H) ∼ 8.1 before the interaction started around 400 Myr ago. The metals within the H i gas are very likely not coming from the inner regions of NGC 1512 but probably from material accreted during minor mergers or outflow-enriched intergalactic medium gas during the life of the galaxy.
Gas and star formation in the Circinus galaxy For, B.-Q; Koribalski, B. S; Jarrett, T. H
Monthly Notices of the Royal Astronomical Society,
21 September 2012, Volume:
425, Issue:
3
Journal Article
Peer reviewed
Open access
Abstract
We present a detailed study of the Circinus galaxy, investigating its star formation, dust and gas properties, both in the inner and outer disc. To achieve this, we obtained high-resolution ...Spitzer mid-infrared images with the IRAC (3.6, 5.8, 4.5 and 8.0 μm) and MIPS (24 and 70 μm) instruments and sensitive H i data from the Australia Telescope Compact Array and the 64-m Parkes telescope. These were supplemented by CO maps from the Swedish-ESO Submillimetre Telescope. Because Circinus is hidden behind the Galactic plane, we demonstrate the careful removal of foreground stars as well as large- and small-scale Galactic emission from the Spitzer images. We derive a visual extinction of A
V = 2.1 mag from the spectral energy distribution of the Circinus galaxy and total stellar and gas masses of 9.5 × 1010 and 9 × 109 M⊙, respectively. Using various wavelength calibrations, we find obscured global star formation rates between 3 and 8 M⊙ yr−1. Star-forming regions in the inner spiral arms of Circinus, which are rich in H i, are beautifully unveiled in the Spitzer 8 μm image. The latter is dominated by polycyclic aromatic hydrocarbon (PAH) emission from heated interstellar dust. We find a good correlation between the 8 μm emission in the arms and regions of dense H i gas. The (PAH 8 μm)/24 μm surface brightness ratio shows significant variations across the disc of Circinus.
Here, we describe the Compact Array Broad-band Backend (CABB) and present first results obtained with the upgraded Australia Telescope Compact Array (ATCA). The 16-fold increase in observing ...bandwidth, from 2 × 128 to 2 × 2048 MHz, high-bit sampling and the addition of 16 zoom windows (each divided into further 2048 channels) provide major improvements for all ATCA observations. The benefits of the new system are: (1) hugely increased radio continuum and polarization sensitivity as well as image fidelity; (2) substantially improved capability to search for and map emission and absorption lines over large velocity ranges; (3) simultaneous multi-line and continuum observations; (4) increased sensitivity, survey speed and dynamic range due to high-bit sampling and (5) high-velocity resolution, while maintaining full polarization output. The new CABB system encourages all observers to make use of both spectral line and continuum data to achieve their full potential.
Given the dramatic increase of the ATCA capabilities in all bands (ranging from 1.1 to 105 GHz) CABB enables scientific projects that were not feasible before the upgrade, such as simultaneous observations of multiple spectral lines, on-the-fly mapping, fast follow-up of radio transients (e.g. the radio afterglow of new supernovae) and maser observation at high-velocity resolution and full polarization. The first science results presented here include wide-band spectra, high dynamic-range images and polarization measurements, highlighting the increased capability and discovery potential of the ATCA.
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The pre-merging system of galaxy clusters Abell 3391-Abell 3395 located at a mean redshift of 0.053 has been observed at 1 GHz in an ASKAP/EMU Early Science observation as well as in X-rays with ...eROSITA. The projected separation of the X-ray peaks of the two clusters is ~50′ or ~3.1 Mpc. Here we present an inventory of interesting radio sources in this field around this cluster merger. While the eROSITA observations provide clear indications of a bridge of thermal gas between the clusters, neither ASKAP nor MWA observations show any diffuse radio emission coinciding with the X-ray bridge. We derive an upper limit on the radio emissivity in the bridge region of 〈
J
〉
1 GHz
< 1.2 × 10
−44
W Hz
−1
m
−3
. A non-detection of diffuse radio emission in the X-ray bridge between these two clusters has implications for particle-acceleration mechanisms in cosmological large-scale structure. We also report extended or otherwise noteworthy radio sources in the 30 deg
2
field around Abell 3391-Abell 3395. We identified 20 Giant Radio Galaxies, plus 7 candidates, with linear projected sizes greater than 1 Mpc. The sky density of field radio galaxies with largest linear sizes of >0.7 Mpc is ≈1.7 deg
−2
, three times higher than previously reported. We find no evidence for a cosmological evolution of the population of Giant Radio Galaxies. Moreover, we find seven candidates for cluster radio relics and radio halos.
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