3D Lyman-alpha radiation transfer. I. Understanding Lyman-alpha line profile morphologies

Using a Monte Carlo technique, we have developed a 3D lyman-alpha radiation transfer code allowing for prescribed arbitrary hydrogen density, ionisation, temperature structures, and dust distribution, and arbitrary velocity fields and UV photon sources. We have examined the lyman-alpha line profiles predicted for several simple geometrical configurations and their dependence on the main input parameters. Overall, we find line profiles reaching from doubly peaked symmetric emission to symmetric Voigt (absorption) in static configurations with increasing dust content, and asymmetric red-(blue-) shifted emission lines with a blue (red) counterpart ranging from absorption to emission (with increasing line/continuum strength) in expanding (infalling) media. The following results are of interest for the interpretation of lya profiles from galaxies. 1/ Standard lya absorption line fitting of global spectra of galaxies may lead to an underestimate of the true hydrogen column density in certain geometrical conditions. 2/ Normal (inverted) P-Cygni like lya profiles can be obtained in expanding (infalling) media from objects without any intrinsic lya emission, as a natural consequence of radiation transfer effects. 3/ The formation and the detailed shape of lya profiles resulting from expanding shells has been thoroughly revised: for sufficiently large column densities, the position of the main lya emission peak is redshifted by twice the expansion velocity.This is in excellent agreement with the observations of z~3 LBGs. This finding indicates also that large scale, fairly symmetric shell structures must be a good description for the outflows in LBGs.(shortened abstract)Comment: 20 pages, 20 figures, accepted to A&

Interception of virtual throws reveals predictive skills based on the visual processing of throwing kinematics

Predicting the outcome of observed actions is fundamental for efficient interpersonal interactions. This is evident in interceptive sports, where predicting the future ball trajectory could make apart success and fail. We quantitatively assessed the predictive abilities of non-trained adults intercepting thrown balls in immersive virtual reality. Participants performed better when they could see the complete throwing action in addition to the ball flight, and they were able to move toward the correct direction when the ball flight was occluded. In both cases, performance varies with the individual motor style of the thrower. These results prove that humans can effectively predict the unfolding of complex full-body actions, with no need to extensively practice them, and that such predictions are exploited online to optimize interactive motor performance. This suggests that humans hold a functional knowledge of how actions recurrent in the human motor repertoire map into the changes brought to the environment

The sense of body ownership relaxes temporal constraints for multisensory integration

Experimental work on body ownership illusions showed how simple multisensory manipulation can generate the illusory experience of an artificial limb as being part of the own-body. This work highlighted how own-body perception relies on a plastic brain representation emerging from multisensory integration. The flexibility of this representation is reflected in the short-term modulations of physiological states and perceptual processing observed during these illusions. Here, we explore the impact of ownership illusions on the temporal dimension of multisensory integration. We show that, during the illusion, the temporal window for integrating touch on the physical body with touch seen on a virtual body representation, increases with respect to integration with visual events seen close but separated from the virtual body. We show that this effect is mediated by the ownership illusion. Crucially, the temporal window for visuotactile integration was positively correlated with participants' scores rating the illusory experience of owning the virtual body and touching the object seen in contact with it. Our results corroborate the recently proposed causal inference mechanism for illusory body ownership. As a novelty, they show that the ensuing illusory causal binding between stimuli from the real and fake body relaxes constraints for the integration of bodily signals

The visibility of Lyman Alpha Emitters during reionization

We present the first Lyman Alpha Emitter (LAE) study that combines: (i) cosmological SPH simulations run using GADGET-2, (ii) radiative transfer simulations (CRASH), and (iii) a previously developed LAE model. This complete LAE model accounts for the intrinsic LAE Lyman Alpha/continuum luminosity, dust enrichment and Lyman Alpha transmission through the intergalactic medium (IGM), to quantify the effects of reionization, dust and velocity fields on the Lyman Alpha and UV Luminosity Functions (LF). We find that a model neglecting dust sorely fails to reproduce either the slope or the magnitude of the observed Lyman Alpha and UV LFs. Clumped dust is required to simultaneously fit the observed UV and Lyman Alpha LFs, such that the intrinsic Lyman Alpha-to-continuum luminosity is enhanced by a factor f_alpha/f_c ~ 1.5 (3.7) excluding (including) peculiar velocities. The higher value including velocity fields arises since LAEs reside in large potential wells and inflows decrease their Lyman Alpha transmission. For the first time, a degeneracy is found between the the ionization state of the IGM and the clumping of dust inside high-redshift galaxies. The Lyman Alpha LF at z ~ 5.7 can be well reproduced (to within a 5 sigma error) by a wide range of IGM average neutral hydrogen fraction, 3.4/10^3 to 0.16, provided that the increase in the Lyman Alpha transmission through a more ionized IGM is compensated by a decrease in the Lyman Alpha escape fraction from the galaxy due to dust absorption. The physical properties of LAEs are presented, along with a discussion of the assumptions adopted.Comment: Submitted to MNRAS, comments welcom

Effect of Intergalactic Medium on the Observability of Lyman Alpha Emitters during Cosmic Reionization

We perform a systematic study of how the inhomogeneities in the Inter-Galactic Medium (IGM) affect the observability of Lyman Alpha Emitters (LAEs) around the Epoch of Reionization. We focus on the IGM close to the galaxies as the detailed ionization distribution and velocity fields of this region could significantly influence the scattering of Ly-alpha photons off neutral H atoms as they traverse the IGM after escaping from the galaxy. We simulate the surface brightness (SB) maps and spectra of more than 100 LAEs at z=7.7 as seen by an observer at z=0. To achieve this, we extract the source properties of galaxies and their surrounding IGM from cosmological simulations of box sizes 5-30 Mpc/h and follow the coupled radiative transfer of ionizing and Ly-alpha radiation through the IGM using CRASH-alpha. We find that the simulated SB profiles are extended and their detailed structure is affected by inhomogeneities in the IGM, especially at high neutral fractions. The detectability of LAEs and the fraction of the flux observed depend heavily on the shape of the SB profile and the SB threshold (SB_th) of the observational campaign. Only ultradeep observations (e.g. SB_th ~ 10^-23 ergs/s/cm^2/arcsec^2) would be able to obtain the true underlying mass-luminosity relation and luminosity functions of LAEs. The details of our results depend on whether Ly-alpha photons are significantly shifted in the galaxy to longer wavelengths, the mean ionization fraction in the IGM and the clustering of ionizing sources. These effects can lead to an easier escape of Ly-alpha photons with less scattering in the IGM and a concentrated SB profile similar to the one of a point source. Finally, we show that the SB profiles are steeper at high ionization fraction for the same LAE sample which can potentially be observed from the stacked profile of a large number of LAEs.Comment: 22 pages, 23 figures, 2 tables, Accepted by MNRAS. Minor change

Cosmological Radiative Transfer Codes Comparison Project I: The Static Density Field Tests

Radiative transfer simulations are now at the forefront of numerical astrophysics. They are becoming crucial for an increasing number of astrophysical and cosmological problems; at the same time their computational cost has come to the reach of currently available computational power. Further progress is retarded by the considerable number of different algorithms (including various flavours of ray-tracing and moment schemes) developed, which makes the selection of the most suitable technique for a given problem a non-trivial task. Assessing the validity ranges, accuracy and performances of these schemes is the main aim of this paper, for which we have compared 11 independent RT codes on 5 test problems: (0) basic physics, (1) isothermal H II region expansion and (2) H II region expansion with evolving temperature, (3) I-front trapping and shadowing by a dense clump, (4) multiple sources in a cosmological density field. The outputs of these tests have been compared and differences analyzed. The agreement between the various codes is satisfactory although not perfect. The main source of discrepancy appears to reside in the multi-frequency treatment approach, resulting in different thicknesses of the ionized-neutral transition regions and different temperature structure. The present results and tests represent the most complete benchmark available for the development of new codes and improvement of existing ones. To this aim all test inputs and outputs are made publicly available in digital form.Comment: 32 pages, 39 figures (all color), comments welcom

Musculoskeletal manifestations in children with Behçet's syndrome: data from the AIDA Network Behçet's Syndrome Registry

This study aims to describe musculoskeletal manifestations (MSM) in children with Behçet's syndrome (BS), their association with other disease manifestations, response to therapy, and long-term prognosis. Data were retrieved from the AIDA Network Behçet's Syndrome Registry. Out of a total of 141 patients with juvenile BS, 37 had MSM at disease onset (26.2%). The median age at onset was 10.0 years (IQR 7.7). The median follow-up duration was 21.8 years (IQR 23.3). Recurrent oral (100%) and genital ulcers (67.6%) and pseudofolliculitis (56.8%) were the most common symptoms associated with MSM. At disease onset, 31 subjects had arthritis (83.8%), 33 arthralgia (89.2%), and 14 myalgia (37.8%). Arthritis was monoarticular in 9/31 cases (29%), oligoarticular in 10 (32.3%), polyarticular in 5 (16.1%), axial in 7 (22.6%). Over time, arthritis became chronic-recurrent in 67.7% of cases and 7/31 patients had joint erosions (22.6%). The median Behçet's Syndrome Overall Damage Index was 0 (range 0-4). Colchicine was inefficacious for MSM in 4/14 cases (28.6%), independently from the type of MSM (p = 0.46) or the concomitant therapy (p = 0.30 for cDMARDs, p = 1.00 for glucocorticoids); cDMARDs and bDMARDs were inefficacious for MSM in 6/19 (31.4%) and 5/12 (41.7%) cases. The presence of myalgia was associated with bDMARDs inefficacy (p = 0.014). To conclude, MSM in children with BS are frequently associated with recurrent ulcers and pseudofolliculitis. Arthritis is mostly mono- or oligoarticular, but sacroiliitis is not unusual. Prognosis of this subset of BS is overall favorable, though the presence of myalgia negatively affects response to biologic therapies. ClinicalTrials.gov Identifier: NCT05200715 (registered on December 18, 2021)

MetalCRASH: cosmological radiative transfer through metals in CRASH

MetalCRASH is a new variant of the cosmological radiative transfer code CRASH[1 -4] . MetalCRASH extends the classical treatment of the cosmological gas composed by H and He to the most relevant metals (C,O,Si) observed in the IGM. The new software is implemented as a pipeline, integrating the radiative transfer capabilities of CRASH with the photoionization code Cloudy[7] . The reliability and applicability of the method is discussed in the context of one idealized test. A real application is presented to show the rich set of metal ionization states provided by MetalCRASH