ORCID Profile
0000-0002-9405-0687
Current Organisations
University of Western Australia
,
International Centre for Radio Astronomy Research
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Publisher: Springer Science and Business Media LLC
Date: 26-06-2020
DOI: 10.1007/S42532-020-00053-4
Abstract: Self-isolating with my wife, I feel gratitude and compassion for all those supporting us, particularly those who regularly deliver our food and our immediate family members who check on us frequently. My compassion goes out to those on the “frontline”, particularly my niece and her daughter who are both nurses in a major hospital and who developed and recovered from COVID-19 symptoms. More broadly, I recognise that there are many communities that have had to cope with both geophysical and socio-politically created disasters while facing the COVID-19 pandemic, among then some young women bee-keepers in Uganda. In the UK context, I have great concern that severe funding cuts for regional and local public health services and disaster planning handicapped the country’s response to coronavirus and may have been a factor in the UK’s high coronavirus death rate. I see both positive and negative changes in air pollution and urban nature in our towns and cities, but also am concerned that we collectively may lose sight of the greater crises of climate change and species extinction. We have to work for a better future by taking forward the opportunities and lessons from our reactions to the pandemic. This leads to compassion for the yet unborn, our grandchildren’s children, who might enter a less habitable, more unequal less collaborative world than the imperfect one we now enjoy.
Publisher: Springer Science and Business Media LLC
Date: 09-2020
DOI: 10.1007/S42532-020-00067-Y
Abstract: The global COVID-19 pandemic is affecting everyone, but in many different ways, stimulating contrasting reactions and responses: opportunities for some, difficulties for many. A simple survey of how in idual workers in urban ecology have been coping with COVID-19 constraints found ergent responses to COVID-19 on people’s activities, both within countries and between continents. Many academics felt frustrated at being unable to do fieldwork, but several saw opportunities to change ways of working and review their engagement with the natural world. Some engaging with social groups found new ways of sharing ideas and developing aspirations without face-to-face contact. Practitioners creating and managing urban greenspaces had to devise ways to work and travel while maintaining social distancing. Many feared severe funding impacts from changed local government priorities. Around the world, the COVID-19 pandemic has lified issues, such as environmental injustice, disaster preparation and food security, that have been endemic in most countries across the global south in modern times. However, developing and sustaining the strong community spirit shown in many places will speed economic recovery and make cities more resilient against future geophysical and people-made disasters. Significantly, top-down responses and one-size-fits-all solutions, however good the modelling on which they are based, are unlikely to succeed without the insights that local knowledge and community understanding can bring. We all will have to look at disaster preparation in a more comprehensive, caring and consistent way in future.
Publisher: Oxford University Press (OUP)
Date: 17-01-2020
Abstract: We present an analysis of asymmetries in global H i spectra from the extended GALEX Arecibo SDSS Survey (xGASS), a stellar mass-selected and gas fraction-limited survey which is representative of the H i properties of galaxies in the local Universe. We demonstrate that the asymmetry in a H i spectrum is strongly linked to its signal-to-noise meaning that, contrary to what was done in previous works, asymmetry distributions for different s les cannot be compared at face value. We develop a method to account for noise-induced asymmetry and find that the typical galaxy detected by xGASS exhibits higher asymmetry than what can be attributed to noise alone, with 37 per cent of the s le showing asymmetry greater than 10 per cent at an 80 per cent confidence level. We find that asymmetric galaxies contain, on average, 29 per cent less H i mass compared to their symmetric counterparts matched in both stellar mass and signal-to-noise. We also present clear evidence that satellite galaxies, as a population, exhibit more asymmetric H i spectra than centrals and that group central galaxies show a slightly higher rate of H i asymmetries compared to isolated centrals. All these results support a scenario in which environmental processes, in particular those responsible for gas removal, are the dominant driver of asymmetry in xGASS.
Publisher: Oxford University Press (OUP)
Date: 15-10-2020
Abstract: Observations of the cold neutral atomic hydrogen (H i) in and around disc galaxies have revealed that spatial and kinematic asymmetries are common place, and are reflected in the global H i spectra. We use the TNG100 box from the IllustrisTNG suite of cosmological simulations to study the conditions under which these asymmetries may arise in current theoretical galaxy formation models. We find that more than 50 per cent of the s le has at least a 10 per cent difference in integrated flux between the high- and low-velocity half of the spectrum, thus the typical TNG100 galaxy has an H i profile that is not fully symmetric. We find that satellite galaxies are a more asymmetric population than centrals, consistent with observational results. Using halo mass as a proxy for environment, this trend appears to be driven by the satellite population within the virial radius of haloes more massive than 1013 M⊙, typical of medium/large groups. We show that, while the excess of H i asymmetry in group satellites is likely driven by ram pressure, the bulk of the asymmetric H i profiles observed in TNG100 are driven by physical processes able to affect both the central and satellite populations. Our results highlight how asymmetries are not driven solely by environment, and multiple physical processes can produce the same asymmetric shape in global H i spectra.
Publisher: Oxford University Press (OUP)
Date: 28-07-2016
Publisher: Oxford University Press (OUP)
Date: 22-11-2019
Abstract: Using Hubble Space Telescope ACS/WFC data we present the photometry and spatial distribution of resolved stellar populations of four fields within the extended ultraviolet disc (XUV disc) of M83. These observations show a clumpy distribution of main-sequence stars and a mostly smooth distribution of red giant branch stars. We constrain the upper end of the initial mass function (IMF) in the outer disc using the detected population of main-sequence stars and an assumed constant star formation rate (SFR) over the last 300 Myr. By comparing the observed main-sequence luminosity function to simulations, we determine the best-fitting IMF to have a power-law slope α = −2.35 ± 0.3 and an upper mass limit $M_{\\rm u}=25_{-3}^{+17} \\, \\mathrm{M}_\\odot$. This IMF is consistent with the observed H $\\rm \\alpha$ emission, which we use to provide additional constraints on the IMF. We explore the influence of deviations from the constant SFR assumption, finding that our IMF conclusions are robust against all but strong recent variations in SFR, but these are excluded by causality arguments. These results, along with our similar studies of other nearby galaxies, indicate that some XUV discs are deficient in high-mass stars compared to a Kroupa IMF. There are over one hundred galaxies within 5 Mpc, many already observed with HST, thus allowing a more comprehensive investigation of the IMF, and how it varies, using the techniques developed here.
Publisher: Oxford University Press (OUP)
Date: 16-12-2022
Abstract: Observations of the neutral atomic hydrogen (${\\rm H\\, {\\small I}}$) gas in galaxies are predominantly spatially unresolved, in the form of a global ${\\rm H\\, {\\small I}}$ spectral line. There has been substantial work on quantifying asymmetry in global ${\\rm H\\, {\\small I}}$ spectra (‘global ${\\rm H\\, {\\small I}}$ asymmetry’), but due to being spatially unresolved, it remains unknown what physical regions of galaxies the asymmetry traces, and whether the other gas phases are affected. Using optical integral field spectrograph (IFS) observations from the Sydney AAO Multi-object IFS (SAMI) survey for which global ${\\rm H\\, {\\small I}}$ spectra are also available (SAMI-${\\rm H\\, {\\small I}}$), we study the connection between asymmetry in galaxies’ ionized and neutral gas reservoirs to test if and how they can help us better understand the origin of global ${\\rm H\\, {\\small I}}$ asymmetry. We reconstruct the global Hα spectral line from the IFS observations and find that while some global Hα asymmetries can arise from disturbed ionized gas kinematics, the majority of asymmetric cases are driven by the distribution of Hα-emitting gas. When compared to the ${\\rm H\\, {\\small I}}$, we find no evidence for a relationship between the global Hα and ${\\rm H\\, {\\small I}}$ asymmetry. Further, a visual inspection reveals that cases where galaxies have qualitatively similar Hα and ${\\rm H\\, {\\small I}}$ spectral profiles can be spurious, with the similarity originating from an irregular 2D Hα flux distribution. Our results highlight that comparisons between global Hα and ${\\rm H\\, {\\small I}}$ asymmetry are not straightforward, and that many global ${\\rm H\\, {\\small I}}$ asymmetries trace disturbances that do not significantly impact the central regions of galaxies.
Publisher: SAGE Publications, Inc.
Date: 2010
Publisher: Oxford University Press (OUP)
Date: 07-12-2022
Abstract: We present SAMI-H i, a survey of the atomic hydrogen content of 296 galaxies with integral field spectroscopy available from the SAMI Galaxy Survey. The s le spans nearly 4 dex in stellar mass ($M_\\star = 10^{7.4}-10^{11.1}~ \\rm M_\\odot$), redshift z & 0.06, and includes new Arecibo observations of 153 galaxies, for which we release catalogues and H i spectra. We use these data to compare the rotational velocities obtained from optical and radio observations and to show how systematic differences affect the slope and scatter of the stellar-mass and baryonic Tully–Fisher relations. Specifically, we show that $\\rm H\\alpha$ rotational velocities measured in the inner parts of galaxies (1.3 effective radii in this work) systematically underestimate H i global measurements, with H i/$\\rm H\\alpha$ velocity ratios that increase at low stellar masses, where rotation curves are typically still rising and $\\rm H\\alpha$ measurements do not reach their plateau. As a result, the $\\rm H\\alpha$ stellar mass Tully–Fisher relation is steeper (when M⋆ is the independent variable) and has larger scatter than its H i counterpart. Interestingly, we confirm the presence of a small fraction of low-mass outliers of the $\\rm H\\alpha$ relation that are not present when H i velocity widths are used and are not explained by ‘aperture effects’. These appear to be highly disturbed systems for which $\\rm H\\alpha$ widths do not provide a reliable estimate of the rotational velocity. Our analysis reaffirms the importance of taking into account differences in velocity definitions as well as tracers used when interpreting offsets from the Tully–Fisher relation, at both low and high redshifts and when comparing with simulations.
Publisher: Oxford University Press (OUP)
Date: 15-04-2021
Abstract: Observations have revealed that disturbances in the cold neutral atomic hydrogen (H i) in galaxies are ubiquitous, but the reasons for these disturbances remain unclear. While some studies suggest that asymmetries in integrated H i spectra (global H i asymmetry) are higher in H i-rich systems, others claim that they are preferentially found in H i-poor galaxies. In this work, we utilize the Arecibo Legacy Fast ALFA (ALFALFA) and extended GALEX Arecibo SDSS Survey (xGASS) surveys, plus a s le of post-merger galaxies, to clarify the link between global H i asymmetry and the gas properties of galaxies. Focusing on star-forming galaxies in ALFALFA, we find that elevated global H i asymmetry is not associated with a change in the H i content of a galaxy, and that only the galaxies with the highest global H i asymmetry show a small increase in specific star formation rate (sSFR). However, we show that the lack of a trend with H i content is because ALFALFA misses the ‘gas-poor’ tail of the star-forming main-sequence. Using xGASS to obtain a s le of star-forming galaxies that is representative in both sSFR and H i content, we find that global H i asymmetric galaxies are typically more gas-poor than symmetric ones at fixed stellar mass, with no change in sSFR. Our results highlight the complexity of the connection between galaxy properties and global H i asymmetry. This is further confirmed by the fact that even post-merger galaxies show both symmetric and asymmetric H i spectra, demonstrating that merger activity does not always lead to an asymmetric global H i spectrum.
Publisher: Oxford University Press
Date: 03-02-2011
Publisher: American Astronomical Society
Date: 12-2022
Abstract: We measure the molecular-to-atomic gas ratio, R mol , and the star formation rate (SFR) per unit molecular gas mass, SFE mol , in 38 nearby galaxies selected from the Virgo Environment Traced in CO (VERTICO) survey. We stack ALMA 12 CO ( J = 2−1) spectra coherently using H i velocities from the VIVA survey to detect faint CO emission out to galactocentric radii r gal ∼ 1.2 r 25 . We determine the scale lengths for the molecular and stellar components, finding a ∼3:5 relation compared to ∼1:1 in field galaxies, indicating that the CO emission is more centrally concentrated than the stars. We compute R mol as a function of different physical quantities. While the spatially resolved R mol on average decreases with increasing radius, we find that the mean molecular-to-atomic gas ratio within the stellar effective radius R e , R mol ( r R e ), shows a systematic increase with the level of H i , truncation and/or asymmetry (H I perturbation). Analysis of the molecular- and the atomic-to-stellar mass ratios within R e , R ⋆ mol ( r R e ) and R ⋆ atom ( r R e ) , shows that VERTICO galaxies have increasingly lower R ⋆ atom ( r R e ) for larger levels of H I perturbation (compared to field galaxies matched in stellar mass), but no significant change in R ⋆ m o l ( r R e ) . We also measure a clear systematic decrease of the SFE mol within R e , SFE mol ( r R e ), with increasingly perturbed H i . Therefore, compared to field galaxies from the field, VERTICO galaxies are more compact in CO emission in relation to their stellar distribution, but increasingly perturbed atomic gas increases their R mol and decreases the efficiency with which their molecular gas forms stars.
Publisher: Oxford University Press (OUP)
Date: 24-04-2018
Publisher: EDP Sciences
Date: 07-2023
DOI: 10.1051/0004-6361/202346599
Abstract: We analyse cold-gas distributions in Virgo cluster galaxies using resolved observations of CO(2-1), which traces molecular hydrogen (H 2 ), and H I from the Virgo Environment Traced In CO (VERTICO) and VLA Imaging of Virgo in Atomic Gas (VIVA) surveys. From a theoretical perspective, it is expected that environmental processes in clusters will have a stronger influence on diffuse atomic gas compared to the relatively dense molecular gas component, and that these environmental perturbations can compress the cold interstellar medium in cluster galaxies, leading to elevated star formation. In this work we observationally test these predictions for star-forming satellite galaxies within the Virgo cluster. We ided our Virgo galaxy s le into H I -normal, H I -tailed, and H I -truncated classes and show, unsurprisingly, that the H I -tailed galaxies have the largest quantitative H I asymmetries. We also compared Virgo galaxies to a control s le of non-cluster galaxies and find that the former, on average, have H I asymmetries that are 40 ± 10% larger than the latter. There is less separation between control, H I -normal, H I -tailed, and H I -truncated galaxies in terms of H 2 asymmetries, and on average, Virgo galaxies have H 2 asymmetries that are only marginally (20 ± 10%) larger than the control s le. We find a weak correlation between H I and H 2 asymmetries over our entire s le, but a stronger correlation for the galaxies that are strongly impacted by environmental perturbations. Finally, we ided the discs of the H I -tailed Virgo galaxies into a leading half and trailing half according to the observed tail direction. We find evidence for excess molecular gas mass on the leading halves of the disc. This excess molecular gas is accompanied by an excess in the star formation rate such that the depletion time is, on average, unchanged.
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.14
Abstract: The quenching of cluster satellite galaxies is inextricably linked to the suppression of their cold interstellar medium (ISM) by environmental mechanisms. While the removal of neutral atomic hydrogen (H i ) at large radii is well studied, how the environment impacts the remaining gas in the centres of galaxies, which are dominated by molecular gas, is less clear. Using new observations from the Virgo Environment traced in CO survey (VERTICO) and archival H i data, we study the H i and molecular gas within the optical discs of Virgo cluster galaxies on 1.2-kpc scales with spatially resolved scaling relations between stellar ( $\\Sigma_{\\star}$ ), H i ( $\\Sigma_{\\text{H}\\,{\\small\\text{I}}}$ ), and molecular gas ( $\\Sigma_{\\text{mol}}$ ) surface densities. Adopting H i deficiency as a measure of environmental impact, we find evidence that, in addition to removing the H i at large radii, the cluster processes also lower the average $\\Sigma_{\\text{H}\\,{\\small\\text{I}}}$ of the remaining gas even in the central $1.2\\,$ kpc. The impact on molecular gas is comparatively weaker than on the H i , and we show that the lower $\\Sigma_{\\text{mol}}$ gas is removed first. In the most H i -deficient galaxies, however, we find evidence that environmental processes reduce the typical $\\Sigma_{\\text{mol}}$ of the remaining gas by nearly a factor of 3. We find no evidence for environment-driven elevation of $\\Sigma_{\\text{H}\\,{\\small\\text{I}}}$ or $\\Sigma_{\\text{mol}}$ in H i -deficient galaxies. Using the ratio of $\\Sigma_{\\text{mol}}$ -to- $\\Sigma_{\\text{H}\\,{\\small\\text{I}}}$ in in idual regions, we show that changes in the ISM physical conditions, estimated using the total gas surface density and midplane hydrostatic pressure, cannot explain the observed reduction in molecular gas content. Instead, we suggest that direct stripping of the molecular gas is required to explain our results.
Publisher: American Astronomical Society
Date: 10-2023
Publisher: SAGE Publications, Inc.
Date: 2010
Publisher: MDPI AG
Date: 20-08-2021
DOI: 10.20944/PREPRINTS202108.0422.V1
Abstract: Recovery of forest after logging can be tested in many ways: the presence of particular species of fauna or flora, the similarity of the bio ersity of the recovering forest to that on neighbouring areas of undisturbed forest or the characteristics of soils and streams whose conditions may have drastically changed during logging. Three cases of rainforest recovery after logging and clearance from Australia and Borneo exhibit different starting and different goals for recovery. Faunal indicators of recovery vary with size and with species dependence of the rainforest. Endemic forest species may have difficulty in recovering. Tree species richness and abundance may recover in two decades, but canopy closure takes longer. Compacted soils may retain low infiltration capacities for many decades. This ersity in recovery rates is confirmed when compared with those used elsewhere. Because the starting points for recovery vary, from damage by tropical cyclones and landslides, to clearance for shifting cultivation, pasture or agriculture, to post-logging conditions, universal indicators may be inappropriate. The desired endpoints of recovery also range from a & wilderness& state to a National Park for human enjoyment, bio ersity preservation, safeguarding rights of traditional forest-dwelling peoples, or a second round of selective logging.
Publisher: Informa UK Limited
Date: 03-09-2021
Location: Australia
No related grants have been discovered for Adam Watts.