Abstract
It has long been known that environment has a large effect on star formation in galaxies. There are several known plausible mechanisms to remove the cool gas needed for star formation, such ...as strangulation, harassment and ram-pressure stripping. It is unclear which process is dominant, and over what range of stellar mass. In this paper, we find evidence for suppression of the cross-correlation function between massive galaxies and less massive star-forming galaxies, giving a measure of how less likely a galaxy is to be star forming in the vicinity of a more massive galaxy. We develop a formalism for modelling environmental quenching mechanisms within the halo occupation distribution scheme. We find that at z ∼ 2 environment is not a significant factor in determining quenching of star-forming galaxies, and that galaxies are quenched with similar probabilities when they are satellites in sub-group environments, as they are globally. However, by z ∼ 0.5 galaxies are much less likely to be star forming when in a high-density (group or low-mass cluster) environment than when not. This increased probability of being quenched does not appear to have significant radial dependence within the halo at lower redshifts, supportive of the quenching being caused by the halting of fresh inflows of pristine gas, as opposed to by tidal stripping. Furthermore, by separating the massive sample into passive and star forming, we see that this effect is further enhanced when the central galaxy is passive, a manifestation of galactic conformity.
We present a series of results from a clustering analysis of the first data release of the Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey. ...VIDEO is the only survey currently capable of probing the bulk of stellar mass in galaxies at redshifts corresponding to the peak of star formation on degree scales. Galaxy clustering is measured with the two-point correlation function, which is calculated using a non-parametric kernel-based density estimator. We use our measurements to investigate the connection between the galaxies and the host dark matter halo using a halo occupation distribution methodology, deriving bias, satellite fractions, and typical host halo masses for stellar masses between 109.35 and 1010.85 M⊙, at redshifts 0.5 < z < 1.7. Our results show typical halo mass increasing with stellar mass (with moderate scatter) and bias increasing with stellar mass and redshift consistent with previous studies. We find that the satellite fraction increased towards low redshifts, from ∼5 per cent at z ∼ 1.5 to ∼20 per cent at z ∼ 0.6. We combine our results to derive the stellar mass-to-halo mass ratio for both satellites and centrals over a range of halo masses and find the peak corresponding to the halo mass with maximum star formation efficiency to be ∼2 × 1012 M⊙, finding no evidence for evolution.
Abstract
Dark matter haloes in which galaxies reside are likely to have a significant impact on their evolution. We investigate the link between dark matter haloes and their constituent galaxies by ...measuring the angular two-point correlation function of radio sources, using recently released 3 GHz imaging over ∼2 deg2 of the Cosmological Evolution Survey (COSMOS) field. We split the radio source population into star-forming galaxies (SFGs) and active galactic nuclei (AGN), and further separate the AGN into radiatively efficient and inefficient accreters. Restricting our analysis to z < 1, we find SFGs have a bias, $b = 1.5 ^{+0.1}_{-0.2}$, at a median redshift of z = 0.62. On the other hand, AGN are significantly more strongly clustered with b = 2.1 ± 0.2 at a median redshift of 0.7. This supports the idea that AGN are hosted by more massive haloes than SFGs. We also find low accretion rate AGN are more clustered (b = 2.9 ± 0.3) than high accretion rate AGN ($b = 1.8^{+0.4}_{-0.5}$) at the same redshift (z ∼ 0.7), suggesting that low accretion rate AGN reside in higher mass haloes. This supports previous evidence that the relatively hot gas that inhabits the most massive haloes is unable to be easily accreted by the central AGN, causing them to be inefficient. We also find evidence that low accretion rate AGN appear to reside in halo masses of Mh ∼ 3–4 × 1013 h−1 M⊙ at all redshifts. On the other hand, the efficient accreters reside in haloes of Mh ∼ 1–2 × 1013 h−1 M⊙ at low redshift but can reside in relatively lower mass haloes at higher redshifts. This could be due to the increased prevalence of cold gas in lower mass haloes at z ≥ 1 compared to z < 1.
Laser wakefield accelerators promise to revolutionize many areas of accelerator science. However, one of the greatest challenges to their widespread adoption is the difficulty in control and ...optimization of the accelerator outputs due to coupling between input parameters and the dynamic evolution of the accelerating structure. Here, we use machine learning techniques to automate a 100 MeV-scale accelerator, which optimized its outputs by simultaneously varying up to six parameters including the spectral and spatial phase of the laser and the plasma density and length. Most notably, the model built by the algorithm enabled optimization of the laser evolution that might otherwise have been missed in single-variable scans. Subtle tuning of the laser pulse shape caused an 80% increase in electron beam charge, despite the pulse length changing by just 1%.
ABSTRACT
Hydrodynamical cosmological simulations have recently made great advances in reproducing galaxy mass assembly over cosmic time – as often quantified from the comparison of their predicted ...stellar mass functions to observed stellar mass functions from data. In this paper, we compare the clustering of galaxies from the hydrodynamical cosmological simulated light-cone Horizon-AGN to clustering measurements from the VIDEO survey observations. Using mocks built from a VIDEO-like photometry, we first explore the bias introduced into clustering measurements by using stellar masses and redshifts derived from spectral energy distribution fitting, rather than the intrinsic values. The propagation of redshift and mass statistical and systematic uncertainties in the clustering measurements causes us to underestimate the clustering amplitude. We then find that clustering and halo occupation distribution (HOD) modelling results are qualitatively similar in Horizon-AGN and VIDEO. However, at low stellar masses, Horizon-AGN underestimates the observed clustering by up to a factor of ∼3, reflecting the known excess stellar mass to halo mass ratio for Horizon-AGN low-mass haloes, already discussed in previous works. This reinforces the need for stronger regulation of star formation in low-mass haloes in the simulation. Finally, the comparison of the stellar mass to halo mass ratio in the simulated catalogue, inferred from angular clustering, to that directly measured from the simulation validates HOD modelling of clustering as a probe of the galaxy–halo connection.
Six UK studies investigating stereotactic ablative radiotherapy (SABR) are currently open. Many of these involve the treatment of oligometastatic disease at different locations in the body. Members ...of all the trial management groups collaborated to generate a consensus document on appropriate organ at risk dose constraints. Values from existing but older reviews were updated using data from current studies. It is hoped that this unified approach will facilitate standardised implementation of SABR across the UK and will allow meaningful toxicity comparisons between SABR studies and internationally.
Modelling burning thermonuclear plasma Rose, S. J.; Hatfield, P. W.; Scott, R. H. H.
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
11/2020, Letnik:
378, Številka:
2184
Journal Article
Recenzirano
Odprti dostop
Considerable progress towards the achievement of thermonuclear burn using inertial confinement fusion has been achieved at the National Ignition Facility in the USA in the last few years. Other ...drivers, such as the Z-machine at Sandia, are also making progress towards this goal. A burning thermonuclear plasma would provide a unique and extreme plasma environment; in this paper we discuss (a) different theoretical challenges involved in modelling burning plasmas not currently considered, (b) the use of novel machine learning-based methods that might help large facilities reach ignition, and (c) the connections that a burning plasma might have to fundamental physics, including quantum electrodynamics studies, and the replication and exploration of conditions that last occurred in the first few minutes after the Big Bang.
This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 1)’.
ABSTRACT
In this paper, we present photometric redshifts for 2.7 million galaxies in the XMM-LSS and COSMOS fields, both with rich optical and near-infrared data from VISTA and HyperSuprimeCam. Both ...template fitting (using galaxy and active galactic nuclei templates within LePhare) and machine learning (using gpz) methods are run on the aperture photometry of sources selected in the Ks-band. The resulting predictions are then combined using a Hierarchical Bayesian model, to produce consensus photometric redshift point estimates and probability distribution functions that outperform each method individually. Our point estimates have a root mean square error of ∼0.08–0.09, and an outlier fraction of ∼3–4 percent when compared to spectroscopic redshifts. We also compare our results to the COSMOS2020 photometric redshifts, which contain fewer sources, but had access to a larger number of bands and greater wavelength coverage, finding that comparable photo-z quality can be achieved (for bright and intermediate luminosity sources where a direct comparison can be made). Our resulting redshifts represent the most accurate set of photometric redshifts (for a catalogue this large) for these deep multisquare degree multiwavelength fields to date.
The history and use of the Timepix detector as an educational tool is outlined. The CERN@school project which lends the Timepix technology to schools has been developing for the last ten years with ...over 300 schools involved and thousands of students. Resource materials and online support is available and schools have used the technology both to support curriculum activities and provide stimulus for student research. Student work includes research on radiation levels during a solar eclipse and a payload launched in space. Research projects with the Timepix technology have led to the development of the Langton Ultimate Cosmic ray Intensity Detector (LUCID) which has enabled students to develop an understanding of radiation in space and large scale data analysis. Feedback on the impact of these projects is discussed alongside plans for expansion of access to this technology. Possibilities for progress in the next ten years are suggested to include the gradual replacement of the Geiger Müller tube in schools with this technology. This would make invisible ionising radiation visible and transform the understanding young people have of radiation. Alongside this transformation of the teaching and learning of radioactivity there is potential for further development of student expertise in analysing data from Timepix detectors in space. The opportunities this technology offers to students in school are vast and students have valuable roles to play in the use and application of the technology over the next ten years. It is hoped that not only are these developments in the UK but also across Europe and beyond.
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