Radio source extraction with ProFound Hale, C L; Robotham, A S G; Davies, L J M ...
Monthly notices of the Royal Astronomical Society,
08/2019, Letnik:
487, Številka:
3
Journal Article
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Abstract
In the current era of radio astronomy, continuum surveys observe a multitude of objects with complex morphologies and sizes, and are not limited to observing point sources. Typical radio ...source extraction software generates catalogues by using Gaussian components to form a model of the emission. This may not be well suited to complicated jet structures and extended emission, particularly in the era of interferometers with a high density of short baselines, which are sensitive to extended emission. In this paper, we investigate how the optically motivated source detection package ProFound (Robotham et al. 2018) may be used to model radio emission of both complicated and point-like radio sources. We use a combination of observations and simulations to investigate how ProFound compares to other source extractor packages used for radio surveys. We find that ProFound can accurately recover both the flux densities of simulated Gaussian sources as well as extended radio galaxies. ProFound can create models that trace the complicated nature of these extended galaxies, which we show is not necessarily the case with other source extraction software. Our work suggests that our knowledge of the emission from extended radio objects may be both over or under-estimated using traditional software. We suggest that ProFound offers a useful alternative to the fitting of Gaussian components for generating catalogues from current and future radio surveys. Furthermore, ProFound’s multiwavelength capabilities will be useful in investigating radio sources in combination with multiwavelength data.
We explore how the group environment may affect the evolution of star-forming galaxies. We select 1197 Galaxy And Mass Assembly groups at 0.05 ≤ z ≤ 0.2 and analyze the projected phase space (PPS) ...diagram, i.e., the galaxy velocity as a function of projected group-centric radius, as a local environmental metric in the low-mass halo regime 1012 ≤ (M200/M ) < 1014. We study the properties of star-forming group galaxies, exploring the correlation of star formation rate (SFR) with radial distance and stellar mass. We find that the fraction of star-forming group members is higher in the PPS regions dominated by recently accreted galaxies, whereas passive galaxies dominate the virialized regions. We observe a small decline in specific SFR of star-forming galaxies toward the group center by a factor ∼1.2 with respect to field galaxies. Similar to cluster studies, we conclude for low-mass halos that star-forming group galaxies represent an infalling population from the field to the halo and show suppressed star formation.
A full appreciation of the role played by gas metallicity (Z), star formation rate (SFR) and stellar mass (M
*) is fundamental to understanding how galaxies form and evolve. The connections between ...these three parameters at different redshifts significantly affect galaxy evolution, and thus provide important constraints for galaxy evolution models. Using data from the Sloan Digital Sky Survey-Data Release 7 (SDSS-DR7) and the Galaxy and Mass Assembly (GAMA) surveys, we study the relationships and dependences between SFR, Z and M
*, as well as the Fundamental Plane for star-forming galaxies. We combine both surveys using volume-limited samples up to a redshift of z 0.36. The GAMA and SDSS surveys complement each other when analysing the relationships between SFR, M
* and Z. We present evidence for SFR and metallicity evolution to z ∼ 0.2. We study the dependences between SFR, M
*, Z and specific SFR (SSFR) on the M
*-Z, M
*-SFR, M
*-SSFR, Z-SFR and Z-SSFR relations, finding strong correlations between all. Based on those dependences, we propose a simple model that allows us to explain the different behaviour observed between low- and high-mass galaxies. Finally, our analysis allows us to confirm the existence of a Fundamental Plane, for which M
* = f(Z, SFR) in star-forming galaxies.
Galaxy and Mass Assembly (GAMA) is a project to study galaxy formation and evolution, combining imaging data from ultraviolet to radio with spectroscopic data from the AAOmega spectrograph on the ...Anglo-Australian Telescope. Using data from Phase 1 of GAMA, taken over three observing seasons, and correcting for various minor sources of incompleteness, we calculate galaxy luminosity functions (LFs) and their evolution in the ugriz passbands.
At low redshift, z < 0.1, we find that blue galaxies, defined according to a magnitude-dependent but non-evolving colour cut, are reasonably well fitted over a range of more than 10 magnitudes by simple Schechter functions in all bands. Red galaxies, and the combined blue plus red sample, require double power-law Schechter functions to fit a dip in their LF faintwards of the characteristic magnitude M* before a steepening faint end. This upturn is at least partly due to dust-reddened disc galaxies.
We measure the evolution of the galaxy LF over the redshift range 0.002 < z < 0.5 both by using a parametric fit and by measuring binned LFs in redshift slices. The characteristic luminosity L* is found to increase with redshift in all bands, with red galaxies showing stronger luminosity evolution than blue galaxies. The comoving number density of blue galaxies increases with redshift, while that of red galaxies decreases, consistent with prevailing movement from blue cloud to red sequence. As well as being more numerous at higher redshift, blue galaxies also dominate the overall luminosity density beyond redshifts z≃ 0.2. At lower redshifts, the luminosity density is dominated by red galaxies in the riz bands, and by blue galaxies in u and g.
Abstract
We explore the constraints that can be placed on the evolutionary time-scales for typical low-redshift galaxies evolving from the blue cloud through the green valley and on to the red ...sequence. We utilize galaxies from the GAMA survey with 0.1 < z < 0.2 and classify them according to the intrinsic (u* − r*) colours of their stellar populations, as determined by fits to their multiwavelength spectral energy distributions. Using these fits to also determine stellar population ages and star formation time-scales, we argue that our results are consistent with a green valley population dominated by galaxies that are simply decreasing their star formation (running out of gas) over a time-scale of 2–4 Gyr which are seen at a specific epoch in their evolution (approximately 1.6 e-folding times after their peak in star formation). If their fitted star formation histories are extrapolated forward, the green galaxies will further redden over time, until they attain the colours of a passive population. In this picture, no specific quenching event which cuts-off their star formation is required, though it remains possible that the decline in star formation in green galaxies may be expedited by internal or external forces. However, there is no evidence that green galaxies have recently changed their star formation time-scales relative to their previous longer term star formation histories.
Scaling relations between supermassive black hole mass, M
BH, and host galaxy properties are a powerful instrument for studying their co-evolution. A complete picture involving all of the black hole ...scaling relations, in which each relation is consistent with the others, is necessary to fully understand the black hole-galaxy connection. The relation between M
BH and the central light concentration of the surrounding bulge, quantified by the Sérsic index n, may be one of the simplest and strongest such relations, requiring only uncalibrated galaxy images. We have conducted a census of literature Sérsic index measurements for a sample of 54 local galaxies with directly measured M
BH values. We find a clear M
BH-n relation, despite an appreciable level of scatter due to the heterogeneity of the data. Given the current M
BH-L
sph and the L
sph-n relations, we have additionally derived the expected
M
BH-n relations, which are marginally consistent at the 2σ level with the observed relations. Elliptical galaxies and the bulges of disc galaxies are each expected to follow two distinct bent
M
BH-n relations due to the Sérsic/core-Sérsic divide. For the same central light concentration, we predict that M
BH in the Sérsic bulges of disc galaxies are an order magnitude higher than in Sérsic elliptical galaxies if they follow the same M
BH-L
sph relation.
ABSTRACT
How do galaxy properties (such as stellar mass, luminosity, star formation rate, and morphology) and their evolution depend on the mass of their host dark matter halo? Using the Galaxy and ...Mass Assembly group catalogue, we address this question by exploring the dependence on host halo mass of the luminosity function (LF) and stellar mass function (SMF) for grouped galaxies subdivided by colour, morphology, and central/satellite. We find that spheroidal galaxies in particular dominate the bright and massive ends of the LF and SMF, respectively. More massive haloes host more massive and more luminous central galaxies. The satellites LF and SMF, respectively, show a systematic brightening of characteristic magnitude, and increase in characteristic mass, with increasing halo mass. In contrast to some previous results, the faint-end and low-mass slopes show little systematic dependence on halo mass. Semi-analytic models and simulations show similar or enhanced dependence of central mass and luminosity on halo mass. Faint and low-mass simulated satellite galaxies are remarkably independent of halo mass, but the most massive satellites are more common in more massive groups. In the first investigation of low-redshift LF and SMF evolution in group environments, we find that the red/blue ratio of galaxies in groups has increased since redshift z ≈ 0.3 relative to the field population. This observation strongly suggests that quenching of star formation in galaxies as they are accreted into galaxy groups is a significant and ongoing process.
ABSTRACT
We present the Australian Square Kilometre Array Pathfinder (ASKAP) observations of the Galaxy and Mass Assembly (GAMA)-23h field. The survey was carried out at 887.5 MHz and covers an ∼83 ...square deg field. We imaged the calibrated visibility data, taken as part of the Evolutionary Mapping of Universe Early Science Programme, using the latest version of the ASKAPSoft pipeline. The final mosaic has an angular resolution of 10 arcsec and a central rms noise of around 38 $\mu$Jy beam−1. The derived radio source catalogue has 39 812 entries above a peak flux density threshold of 5σ. We searched for the radio source host galaxy counterparts using the GAMA spectroscopic (with an i-band magnitude limit of 19.2 mag) and multiwavelength catalogues that are available as part of the collaboration. We identified hosts with GAMA spectroscopic redshifts for 5934 radio sources. We describe the data reduction, imaging, and source identification process, and present the source counts. Thanks to the wide area covered by our survey, we obtain very robust counts down to 0.2 mJy. ASKAP’s exceptional survey speed, providing efficient, sensitive, and high-resolution mapping of large regions of the sky in conjunction with the multiwavelength data available for the GAMA23 field, allowed us to discover 63 giant radio galaxies. The data presented here demonstrate the excellent capabilities of ASKAP in the pre-SKA era.
Experimental introduction of RNA into cells can be used in certain biological systems to interfere with the function of an endogenous gene,. Such effects have been proposed to result from a simple ...antisense mechanism that depends on hybridization between the injected RNA and endogenous messenger RNA transcripts. RNA interference has been used in the nematode Caenorhabditis elegans to manipulate gene expression,. Here we investigate the requirements for structure and delivery of the interfering RNA. To our surprise, we found that double-stranded RNA was substantially more effective at producing interference than was either strand individually. After injection into adult animals, purified single strands had at most a modest effect, whereas double-stranded mixtures caused potent and specific interference. The effects of this interference were evident in both the injected animals and their progeny. Only a few molecules of injected double-stranded RNA were required per affected cell, arguing against stochiometric interference with endogenous mRNA and suggesting that there could be a catalytic or amplification component in the interference process.
ABSTRACT
We present the dust mass function (DMF) of 15 750 galaxies with redshift $z$ < 0.1, drawn from the overlapping area of the GAMA and H-ATLAS surveys. The DMF is derived using the density ...corrected Vmax method, where we estimate Vmax using: (i) the normal photometric selection limit (pVmax) and (ii) a bivariate brightness distribution (BBD) technique, which accounts for two selection effects. We fit the data with a Schechter function, and find $M^{*}=(4.65 \pm 0.18)\times 10^{7}\,h^2_{70}\, \mathrm{ M}_{\odot }$, α = (−1.22 ± 0.01), $\phi ^{*}=(6.26 \pm 0.28)\times 10^{-3}\,h^3_{70}\,\rm Mpc^{-3}\,dex^{-1}$. The resulting dust mass density parameter integrated down to 104 M⊙ is Ωd = (1.11 ± 0.02) × 10−6 which implies the mass fraction of baryons in dust is $f_{m_\mathrm{ b}}=(2.40\pm 0.04)\times 10^{-5}$; cosmic variance adds an extra 7–17 per cent uncertainty to the quoted statistical errors. Our measurements have fewer galaxies with high dust mass than predicted by semi-analytic models. This is because the models include too much dust in high stellar mass galaxies. Conversely, our measurements find more galaxies with high dust mass than predicted by hydrodynamical cosmological simulations. This is likely to be from the long time-scales for grain growth assumed in the models. We calculate DMFs split by galaxy type and find dust mass densities of Ωd = (0.88 ± 0.03) × 10−6 and Ωd = (0.060 ± 0.005) × 10−6 for late types and early types, respectively. Comparing to the equivalent galaxy stellar mass functions (GSMF) we find that the DMF for late types is well matched by the GSMF scaled by (8.07 ± 0.35) × 10−4.
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