Un regard sur l'évolution dynamique des régions HII géantes : interprétation des mouvements du gaz ionisé

L'interférométrie de Fabry-Pérot nous permet de quantifier les mouvements systémiques du matériel ionisé confiné à l'intérieur de deux nébuleuses géantes : la région H II galactique W 4 et la région H II géante extragalactique N GC 595. La région H II W 4 fut autrefois qualifiée de sérieuse candidate de cheminée dynamique. La cinématique Hα du gaz ionisé, obtenue à l'Observatoire du mont Mégantic, révèle que la nébuleuse est séparée en deux portions distinctes, définies par leurs étendues en latitude. W 4-sud (0° [plus petit ou égal à] b [plus petit ou égal à] 3°) est largement régie par une série d'écoulements Champagne à petite échelle résultant de la photoérosion d'agrégats moléculaires associés à la nébuleuse. Une importante partie de W4-sud, par contre, semble renfermer une composante ionisée reliée à la photoionisation de la coquille HI enveloppant l'imposante région H II. Si W4-sud nous apparaît comme le dernier stade dans la vie d'un complexe moléculaire géant, W 4-nord (3° [plus petit que] b [plus petit ou égal à] 7°) confirme la formation d'une cheminée dynamique dans la nébuleuse. Des instabilités au niveau de la portion nord de la coquille se sont vraissemblablement développées, entraînant la rupture de cette dernière. Un scénario de raréfaction domine W4-nord menant à un gradient de vitesse sud-nord à grande échelle au fur et à mesure que le matériel ionisé est éjecté. Le comportement cinématique de la composante H+ indique que l'amas stellaire IC 1805 contribue à l'ionisation du matériel interstellaire au-dessus du plan galactique. Nous proposons que les objets astronomiques similaires à W4 correspondent au chaînon manquant entre les régions H II galactiques de petite taille et les régions H II géantes extragalactiques. La région H II géante extragalactique NGC 595 se classe au second rang des nébuleuses les plus imposantes de M33, une galaxie spirale membre du Groupe Local. L'objet fut cartographié en Ha et [S II] suite à diverses missions d'observations à l'Observatoire du mont Mégantic. Les données [0 III] furent, pour leur part, obtenues au Télescope Canada-France-Hawaii par le directeur de thèse. Les observations spectro-interférométriques du gaz ionisé sont utilisées en combinaison avec des observations radio de la raie à 21 cm. Les largeurs de raie indiquent des mouvements supersoniques, un comportement régulièrement observé dans les objets extragalactiques. Ce comportement est potentiellement expliqué par le fait qu'écoulements Champagne et une forte turbulence isotrope dominent l'intérieur de la nébuleuse géante. En première approximation, il semblerait que composantes H+, 0++ et S+ ne coexistent pas spatialement. Une région au voisinage de l'amas stellaire montre un dédoublement de raies en Ha et [0 III]. Nous proposons que cette particularité spectrale résulte de bulles de vents stellaires en expansion confinées à l'intérieur d'objet. L'étude de NGC 595 nous permet de présenter la première carte bidimensionnelle en densités électroniques associée à une région H II géante extragalactique

Étude de la modularité de la synchronisation à la pulsation musicale : synchronisation sensorimotrice dans l’amusie congénitale

À l’écoute de musique, la plupart des gens ressentent naturellement l’envie de bouger au rythme de celle-ci. Bien que cette activité puisse paraitre anodine, la capacité à émettre un mouvement en synchronie avec une pulsation rythmique (ou le beat en anglais) repose sur l’interaction d’un ensemble de mécanismes complexes. L’habileté à percevoir la pulsation dans la musique, et à pouvoir prédire l’occurrence des temps marquant celle-ci, serait entre autres possible grâce à un mécanisme d’entrainement. La spécificité des processus d’entrainement à la pulsation musicale demeure cependant débattue. Afin de mieux cerner la modularité de l’entrainement au beat musical, le travail de recherche présenté dans cette thèse avait pour objectif de caractériser, chez des individus présentant une amusie congénitale, la capacité à se synchroniser à la musique, au chant et à la parole. L’amusie congénitale est un trouble d’origine neurodéveloppementale qui affecte, selon le cas, l’habileté à percevoir dans la musique les fines variations mélodiques ou la capacité à percevoir et à se synchroniser au beat. L’étude 1 visait d’abord à déterminer l’influence d’une amusie congénitale affectant le traitement des hauteurs sur la perception et la synchronisation au beat. Les résultats ont mis en évidence, dans 50 % des cas, une faible capacité à se synchroniser avec le beat de séquences rythmiques contenant ou non des variations mélodiques. Néanmoins, des cas de dissociation claire ont pu être identifiés. Ainsi, bien que dans la majorité des cas une perception des variations de hauteurs déficiente semble s’accompagner d’une capacité réduite à percevoir la pulsation musicale et s’y synchroniser, ces deux habiletés peuvent également se trouver atteintes de façon isolée. Cette dissociation se constate d’ailleurs chez les individus ayant pris part aux études subséquentes de la thèse, qui ne parviennent pas à synchroniser un mouvement simple avec le beat, tout en demeurant dans les limites de la norme à une épreuve mesurant la perception des hauteurs en contexte mélodique. Les études 2 et 3 ont été élaborées dans le but d’investiguer la modularité de l’entrainement à la pulsation musicale en regard d’hypothèses suggérant que ce mécanisme soit plutôt partagé avec d’autres domaines tels que le langage. L’étude 2 avait pour objectif de tester l’implication des processus d’entrainement au beat musical dans la synchronisation à la parole. Pour se faire, un groupe d’individus ayant une amusie congénitale touchant la synchronisation au beat et des participants neurotypiques appariés ont complété une tâche de synchronisation motrice sur des extraits de chant et de parole. Les participants devaient taper du doigt la pulsation rythmique perçue dans des phrases chantées, dites avec un rythme régulier (comparable à du rap), et énoncées de manière naturelle (rythme irrégulier). Dans ces trois conditions, les individus atteints d’amusie sont moins bien parvenus à se synchroniser, comparativement aux participants contrôles. Ce résultat suggère l’existence d’un mécanisme d’entrainement commun à la parole et à la musique. Enfin, dans l’étude 3, nous avons testé une hypothèse selon laquelle la capacité d’imitation vocale et la synchronisation au beat reposeraient en partie sur un mécanisme commun de couplage sensorimoteur. Dans cette étude, des participants ayant une difficulté à se synchroniser au beat, ainsi que des participants contrôles appariés, ont chanté une mélodie connue avec et sans paroles, d’abord de mémoire, ensuite par imitation d’un modèle, et enfin en synchronie avec le modèle et avec un métronome. Les résultats de cette étude montrent, en premier lieu, que la capacité des participants ayant un trouble de la synchronisation au beat à chanter avec justesse est comparable à la population générale. Certains participants ont tout de même pu être identifiés comme étant de mauvais chanteurs. Cependant, nous n’avons pas pu mettre en évidence d’association claire entre la justesse du chant et l’habileté à se synchroniser à une pulsation rythmique. En revanche, la faible habileté à se synchroniser au beat était généralisée à la difficulté à se synchroniser par le chant. Dans l’ensemble, les résultats de la thèse suggèrent que, dans les cas d’amusie congénitale étudiés, la capacité à produire un mouvement synchronisé à la musique émergerait d’un mécanisme plus général d’entrainement permettant la synchronisation à d’autres stimuli auditifs, y compris la parole.Music naturally compels most individuals to engage in rhythmic behaviors. We can think of someone tapping his foot or nodding his head to the beat of music. Synchronizing a movement to the beat may seem simple at first, but it is a complex behavior. At least, someone needs to be able to extract the beat and predict the timing of upcoming beats. This ability to couple movement and music could be achieved through entrainment. The specificity of beat-based entrainment to music is, however, debated. This thesis aimed to assess sensorimotor synchronization to music, singing, and speech in congenital amusia, in order to test the specificity of entrainment mechanism to musical beat. Congenital amusia refers to a neurodevelopmental disorder that can affect, depending on cases, pitch perception (pitch-based amusia) or beat perception (beat-based amusia). In the first study, individuals with pitch-based amusia were tested on their ability to perceive and to produce musical beat. The results indicated that about fifty percent of pitch-based amusic participants had associated deficits in beat production and beat perception. Still, cases of dissociation, with spared ability to synchronize to and perceive musical beat, were also identified. Therefore, findings highlight a connection between melody and rhythm processing in most cases of pitchbased amusia, although it is possible for these domains to be selectively impaired. Concurrently, cases of beat-based amusia, included in Study 2 and Study 3, had a specific impairment in their ability to synchronize a simple movement with musical beat, while performing within the normal range on a standardized measure of pitch perception. Study 2 and Study 3 had the objective to test hypotheses regarding the domain specificity of beat-based entrainment. In Study 2, entrainment to speech and music was compared in participants with beat-based amusia. Participants had to align taps to the perceived regularity in the rhythm of naturally spoken, regularly spoken (similar to rap music), and sung sentences. It was found that the amusic participants synchronized less accurately in all conditions. This result suggests that a general entrainment mechanism could maybe drive sensorimotor synchronisation to speech and music. In Study 3, we assessed the hypothesis according to which vocal imitation and beatbased synchronisation could share a common sensorimotor coupling mechanism. Here, participants had to sing a familiar song from memory, after hearing a model, with the model, and with a metronome. First, results from this study indicate that vocal-pitch abilities are similar to the general population in beat-based amusia, when singing from memory. Cases of poor-pitch singing could still be identified among amusic participants. However, no clear association between synchronization to beat and vocal-pitch abilities was found. Nonetheless, results from synchronous singing and singing with a metronome mirrored results from tapping tasks, indicating a lowered ability to synchronize with the beat across contexts in beat-based amusia. Overall, by investigating sensorimotor synchronization to music and singing in congenital amusia, this thesis work provides new evidence that sensorimotor synchronization to musical beat may be built on a domain-general entrainment mechanism that could be involved with auditory stimuli that are not beat-based, like speech

Diagnostic line ratios in the IC 1805 optical gas complex

Large HII regions, with angular dimensions exceeding 10 pc, usually enclose numerous massive O-stars. Stellar winds from such stars are expected to play a sizeable role in the dynamical, morphological and chemical evolution of the targeted nebula. Kinematically, stellar winds remain hardly observable i.e., the typical expansion velocities of wind-blown bubbles being often confused with other dynamical processes also regularly found HII regions. However, supersonic shock waves, developed by stellar winds, should favor shock excitation and leave a well-defined spectral signature in the ionized nebular content. In this work, the presence of stellar winds, observed through shock excitation, is investigated in the brightest portions of the Galactic IC 1805 nebula, a giant HII region encompassing at least 10 O-stars from main-sequence O9 to giant and supergiant O4. The use of the imaging Fourier transform spectrometer SpIOMM enabled the simultaneous acquisition of the spectral information associated to the Halpha6563A, [NII]6548, 6584A, and [SII]6716, 6731A ionic lines. Diagnostic diagrams, first introduced by Sabbadin and collaborators, were used to circumscribe portions of the nebula likely subject to shock excitation from other areas dominated by photoionization. The gas compression, expected from supersonic shocks, is investigated by comparing the pre- and post-shocked material's densities computed from the [SII]/[SII] line ratio. The typical [NII]/[NII] line ratio slightly exceeds the theoretical value of 3 expected in low-density regimes. To explain such behavior, a scenario based on collisional de-excitations affecting the [NII]6548A line is proposed.Comment: 22 pages, 19 figures, 1 table, Accepted for publication by MNRAS on November 11th 201

Atomic Hydrogen produced in M33 Photodissociation Regions

We derive total (atomic + molecular) hydrogen densities in giant molecular clouds (GMCs) in the nearby spiral galaxy M33 using a method that views the atomic hydrogen near regions of recent star formation as the product of photodissociation. Far-UV photons emanating from a nearby OB association produce a layer of atomic hydrogen on the surfaces of nearby GMCs. Our approach provides an estimate of the total hydrogen density in these GMCs from observations of the excess far-UV emission that reaches the GMC from the OB association, and the excess 21-cm radio HI emission produced after these far-UV photons convert H2 into HI on the GMC surface. The method provides an alternative approach to the use of CO emission as a tracer of H2 in GMCs, and is especially sensitive to a range of density well below the critical density for CO(1-0) emission. We describe our "PDR method" in more detail and apply it using GALEX far-UV and VLA 21-cm radio data to obtain volume densities in a selection of GMCs in the nearby spiral galaxy M33. We have also examined the sensitivity of the method to the linear resolution of the observations used; the results obtained at 20 pc are similar to those for the larger set of data at 80 pc resolution. The cloud densities we derive range from 1 to 500 cm-3, with no clear dependence on galactocentric radius; these results are generally similar to those obtained earlier in M81, M83, and M101 using the same method.Comment: Accepted for publication in MNRAS. 25 figures, 16 tables, including online-only material

Spatially resolved study of the physical properties of the ionized gas in NGC 595

We present Integral Field Spectroscopy (IFS) of NGC 595, one of the most luminous HII regions in M33. This type of observations allows studying the variation of the principal emission-line ratios across the surface of the nebula. At each position of the field of view, we fit the main emission-line features of the spectrum within the spectral range 3650-6990A, and create maps of the principal emission-line ratios for the total surface of the region. The extinction map derived from the Balmer decrement and the absorbed H-alpha luminosity show good spatial correlation with the 24 micron emission from Spitzer. We also show here the capability of the IFS to study the existence of Wolf-Rayet (WR) stars, identifying the previously catalogued WR stars and detecting a new candidate towards the north of the region. The ionization structure of the region nicely follows the H-alpha shell morphology and is clearly related to the location of the central ionizing stars. The electron density distribution does not show strong variations within the HII region nor any trend with the H-alpha emission distribution. We study the behaviour within the HII region of several classical emission-line ratios proposed as metallicity calibrators: while [NII]/Ha and [NII]/[OIII] show important variations, the R23 index is substantially constant across the surface of the nebula, despite the strong variation of the ionization parameter as a function of the radial distance from the ionizing stars. These results show the reliability in using the R23 index to characterize the metallicity of HII regions even when only a fraction of the total area is covered by the observations.Comment: 16 pages, 12 figures, published in MNRAS (replaced to match the journal version). Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, (MPIA and IAA-CSIC

Overview of the massive young star-forming complex study in infrared and X-ray (MYStIX) project

The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) seeks to characterize 20 OB-dominated young clusters and their environs at distances d ≤ 4 kpc using imaging detectors on the Chandra X-ray Observatory, Spitzer Space Telescope, and the United Kingdom InfraRed Telescope. The observational goals are to construct catalogs of star-forming complex stellar members with well-defined criteria and maps of nebular gas (particularly of hot X-ray-emitting plasma) and dust. A catalog of MYStIX Probable Complex Members with several hundred OB stars and 31,784 low-mass pre-main sequence stars is assembled. This sample and related data products will be used to seek new empirical constraints on theoretical models of cluster formation and dynamics, mass segregation, OB star formation, star formation triggering on the periphery of H II regions, and the survivability of protoplanetary disks in H II regions. This paper gives an introduction and overview of the project, covering the data analysis methodology and application to two star-forming regions: NGC 2264 and the Trifid Nebula

Neurophysiological and Behavioral Differences between Older and Younger Adults When Processing Violations of Tonal Structure in Music

Aging is associated with decline in both cognitive and auditory abilities. However, evidence suggests that music perception is relatively spared, despite relying on auditory and cognitive abilities that tend to decline with age. It is therefore likely that older adults engage compensatory mechanisms which should be evident in the underlying functional neurophysiology related to processing music. In other words, the perception of musical structure would be similar or enhanced in older compared to younger adults, while the underlying functional neurophysiology would be different. The present study aimed to compare the electrophysiological brain responses of younger and older adults to melodic incongruities during a passive and active listening task. Older and younger adults had a similar ability to detect an out-of-tune incongruity (i.e., non-chromatic), while the amplitudes of the ERAN and P600 were reduced in older adults compared to younger adults. On the other hand, out-of-key incongruities (i.e., non-diatonic), were better detected by older adults compared to younger adults, while the ERAN and P600 were comparable between the two age groups. This pattern of results indicates that perception of tonal structure is preserved in older adults, despite age-related neurophysiological changes in how melodic violations are processed

Poor Synchronization to Musical Beat Generalizes to Speech

The rhythmic nature of speech may recruit entrainment mechanisms in a manner similar to music. In the current study, we tested the hypothesis that individuals who display a severe deficit in synchronizing their taps to a musical beat (called beat-deaf here) would also experience difficulties entraining to speech. The beat-deaf participants and their matched controls were required to align taps with the perceived regularity in the rhythm of naturally spoken, regularly spoken, and sung sentences. The results showed that beat-deaf individuals synchronized their taps less accurately than the control group across conditions. In addition, participants from both groups exhibited more inter-tap variability to natural speech than to regularly spoken and sung sentences. The findings support the idea that acoustic periodicity is a major factor in domain-general entrainment to both music and speech. Therefore, a beat-finding deficit may affect periodic auditory rhythms in general, not just those for music

The Gradient-Boosting Method for Tackling High Computing Demand in Underwater Acoustic Propagation Modeling

Agent-based models return spatiotemporal information used to process time series of specific parameters for specific individuals called “agents”. For complex, advanced and detailed models, this typically comes at the expense of high computing times and requires access to important computing resources. This paper provides an example on how machine learning and artificial intelligence can help predict an agent-based model’s output values at regular intervals without having to rely on time-consuming numerical calculations. Gradient-boosting XGBoost under GNU package’s R was used in the social-ecological agent-based model 3MTSim to interpolate, in the time domain, sound pressure levels received at the agents’ positions that were occupied by the endangered St. Lawrence Estuary and Saguenay Fjord belugas and caused by anthropomorphic noise of nearby transiting merchant vessels. A mean error of 3.23 ± 3.76(1σ) dB on received sound pressure levels was predicted when compared to ground truth values that were processed using rigorous, although time-consuming, numerical algorithms. The computing time gain was significant, i.e., it was estimated to be 10-fold higher than the ground truth simulation, whilst maintaining the original temporal resolution