5,364 research outputs found

    The evolutionary state of young protoplanetary disks

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    Observations of protoplanetary disks have been focused on low-mass, classical T-Tauri stars and on intermediate mass Herbig Ae/Be stars. The observations of the Herbig stars have introduced a bias in the intermediate mass range since they exclude the earlier stages of disk evolution. The heaviest T-Tauri stars, the intermediate mass T-Tauri stars (IMTT stars), with spectral type from F to early K and with masses ≥1.5 M☉, are the younger precursors of the Herbig stars. To get a complete picture of the evolution of protoplanetary disks IMTT stars needs to be studied. Many IMTT stars have already been included in samples of classical T-Tauri stars where they are the most massive stars in the samples. This thesis seeks to remove some of this bias by focusing on the IMTT stars and observations of the disks around them. This thesis presents the research of a sample of 49 identified IMTT stars with infrared access. Their disks are compared with those of the known Herbig Ae/Be stars to examine their evolutionary status. The thesis also presents spatially resolved near-infrared scattered light observations of the IMTT star RY Tau. Using radiative transfer modelling the observations are recreated and features reminiscent of a dusty disk wind is assessed.Finally, it presents near-infrared spatially resolved scattered light observations of 23 optically bright stars in the Orion high mass star forming region. The observations are analysed in context of the stellar parameters, stellar multiplicity and the environment of a high star forming region

    Mass classification of dark matter perturbers of stellar tidal streams

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    Stellar streams formed by tidal stripping of progenitors orbiting around the Milky Way are expected to be perturbed by encounters with dark matter subhalos. Recent studies have shown that they are an excellent proxy to infer properties of the perturbers, such as their mass. Here we present two different methodologies that make use of the fully non-Gaussian density distribution of stellar streams: a Bayesian model selection based on the probability density function (PDF) of stellar density, and a likelihood-free gradient boosting classifier. While the schemes do not assume a specific dark matter model, we are mainly interested in discerning the primordial black holes cold dark matter (PBH CDM) hypothesis form the standard particle dark matter one. Therefore, as an application we forecast model selection strength of evidence for cold dark matter clusters of masses 103–105M⊙ and 105–109M⊙, based on a GD-1-like stellar stream and including realistic observational errors. Evidence for the smaller mass range, so far under-explored, is particularly interesting for PBH CDM. We expect weak to strong evidence for model selection based on the PDF analysis, depending on the fiducial model. Instead, the gradient boosting model is a highly efficient classifier (99% accuracy) for all mass ranges here considered. As a further test of the robustness of the method, we reach similar conclusions when performing forecasts further dividing the largest mass range into 105–107M⊙ and 107–109M⊙ range

    Tidal debris from Omega Centauri discovered with unsupervised machine learning

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    The gravitational interactions between the Milky Way and in-falling satellites offer a wealth of information about the formation and evolution of our Galaxy. In this paper, we explore the high-dimensionality of the GALAH DR3 plus Gaia eDR3 data set to identify new tidally stripped candidate stars of the nearby star cluster Omega Centauri (ωCen\omega\,\mathrm{Cen}). We investigate both the chemical and dynamical parameter space simultaneously, and identify cluster candidates that are spatially separated from the main cluster body, in regions where contamination by halo field stars is high. Most notably, we find candidates for ωCen\omega\,\mathrm{Cen} scattered in the halo extending to more than 5050^{\circ} away from the main body of the cluster. Using a grid of simulated stellar streams generated with ωCen\omega\,\mathrm{Cen} like orbital properties, we then compare the on sky distribution of these candidates to the models. The results suggest that if ωCen\omega\,\mathrm{Cen} had a similar initial mass as its present day mass, then we can place a lower limit on its time of accretion at tacc>7_{\mathrm{acc}} > 7 Gyr ago. Alternatively, if the initial stellar mass was significantly larger, as would be expected if ωCen\omega\,\mathrm{Cen} is the remnant core of a dwarf Galaxy, then we can constrain the accretion time to tacc>4_{\mathrm{acc}} > 4 Gyr ago. Taken together, these results are consistent with the scenario that ωCen\omega\,\mathrm{Cen} is the remnant core of a disrupted dwarf galaxy.Comment: 22 pages, 19 figures, 2 tables, accepted for publication in MNRA

    SPYGLASS. IV. New Stellar Survey of Recent Star Formation within 1 kpc

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    Young stellar populations provide a powerful record that traces millions of years of star formation history in the solar neighborhood. Using a revised form of the SPYGLASS young star identification methodology, we produce an expanded census of nearby young stars (Age <50<50 Myr). We then use the HDBSCAN clustering algorithm to produce a new SPYGLASS Catalog of Young Associations (SCYA), which reveals 116 young associations within 1 kpc. More than 25\% of these groups are largely new discoveries, as 20 are substantively different from any previous definition, and 10 have no equivalent in the literature. The new associations reveal a yet undiscovered demographic of small associations with little connection to larger structures. Some of the groups we identify are especially unique for their high transverse velocities, which can differ from the solar velocity by 30-50 km s1^{-1}, and for their positions, which can reach up to 300 pc above the galactic plane. These features may suggest a unique origin, matching existing evidence of infalling gas parcels interacting with the disk ISM. Our clustering also suggests links between often-separated populations, hinting to direct structural connections between Orion Complex and Perseus OB2, and between the subregions of Vela. The \sim30 Myr old Cepheus-Hercules association is another emerging large-scale structure, with a size and population comparable to Sco-Cen. Cep-Her and other similarly-aged structures are also found clustered along extended structures perpendicular to known spiral arm structure, suggesting that arm-aligned star formation patterns have only recently become dominant in the solar neighborhood.Comment: Accepted to ApJ. 34 Pages, 14 Figures, 4 Tables in AASTEX63 format. Online-only catalog files and interactive figures are available in the ancillary dat

    The progenitors of the intra-cluster light and intra-cluster globular clusters in galaxy groups and clusters

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    We use the IllustrisTNG50 cosmological hydrodynamical simulation, complemented by a catalog of tagged globular clusters, to investigate the properties and build up of two extended luminous components: the intra-cluster light (ICL) and the intra-cluster globular clusters (ICGC). We select the 39 most massive groups and clusters in the box, spanning the range of virial masses 5×1012<M200/M<2×10145 \times 10^{12} < \rm M_{200}/\rm M_{\odot} < 2 \times 10^{14}. We find good agreement between predictions from the simulations and current observational estimates of the fraction of mass in the ICL and its radial extension. The stellar mass of the ICL is only 10%20%\sim10\%-20\% of the stellar mass in the central galaxy but encodes useful information on the assembly history of the group or cluster. About half the ICL in all our systems is brought in by galaxies in a narrow stellar mass range, M=10101011M_*=10^{10}-10^{11} M\rm M_{\odot}. However, the contribution of low-mass galaxies (M<1010M_*<10^{10} M\rm M_{\odot}) to the build-up of the ICL varies broadly from system to system, 5%45%\sim 5\%-45\%, a feature that might be recovered from the observable properties of the ICL at z=0z=0. At fixed virial mass, systems where the accretion of dwarf galaxies plays an important role have shallower metallicity profiles, less metal content and a lower stellar mass in the ICL than systems where the main contributors are more massive galaxies. We show that intra-cluster GCs are also good tracers of this history, representing a valuable alternative when diffuse light is not detectable

    RXCJ1111.6+4050 galaxy cluster: the observational evidence of a transitional fossil group

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    We present a detailed kinematical and dynamical study of the galaxy cluster RXCJ1111.6+4050 (RXCJ1111), at z = 0.0756 using 104 new spectroscopic redshifts of galaxies observed at the TNG 3.5m telescope and SDSS DR16 public archive. Our analysis is performed in a multiwavelength context in order to study and compare mainly optical and X-ray properties using XMM-Newton data. We find that RXCJ1111 is a galaxy cluster showing a velocity distribution with clear deviations from Gaussianity, that we are able to explain by the presence of a substructure within the cluster. The two cluster components show velocity dispersions of 644±56644 \pm 56 km/s and 410±123410 \pm 123 km/s, which yield dynamical masses of M200_{200}=1.9±0.4×10141.9 \pm 0.4 \times10^{14} M_{\odot} and 0.6±0.4×10140.6 \pm 0.4 \times 10^{14} M_{\odot} for the main system and substructure, respectively. RXCJ1111 presents an elongation in the North-South direction and a gradient of 250-350 km/s/Mpc in the velocity field, suggest that the merger axis between the main system and substructure is slightly tilted with respect to the line-of-sight. The substructure is characterized by a magnitude gap Δm121.8\Delta m_{12} \ge 1.8, so it fits the "fossil-like" definition of a galaxy group. Mass estimates derived from X-ray and optical are in good agreement when two galaxy components are considered separately. We propose a 3D merging model and find that the fossil group is in an early phase of collision with the RXCJ1111 main cluster and almost aligned with the line-of-sight. This merging model would explain the slight increase found in the TX_X with respect to what we would expect for relaxed clusters. Due to the presence of several brightest galaxies, after this collision, the substructure would presumably lose its fossil condition. Therefore, RXCJ1111 represents the observational evidence that the fossil stage of a system can be temporary and transitional.Comment: 16 pages, 11 figures, 3 tables and 1 appendi

    Peering into the Dark: Investigating dark matter and neutrinos with cosmology and astrophysics

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    The LCDM model of modern cosmology provides a highly accurate description of our universe. However, it relies on two mysterious components, dark matter and dark energy. The cold dark matter paradigm does not provide a satisfying description of its particle nature, nor any link to the Standard Model of particle physics. I investigate the consequences for cosmological structure formation in models with a coupling between dark matter and Standard Model neutrinos, as well as probes of primordial black holes as dark matter. I examine the impact that such an interaction would have through both linear perturbation theory and nonlinear N-body simulations. I present limits on the possible interaction strength from cosmic microwave background, large scale structure, and galaxy population data, as well as forecasts on the future sensitivity. I provide an analysis of what is necessary to distinguish the cosmological impact of interacting dark matter from similar effects. Intensity mapping of the 21 cm line of neutral hydrogen at high redshift using next generation observatories, such as the SKA, would provide the strongest constraints yet on such interactions, and may be able to distinguish between different scenarios causing suppressed small scale structure. I also present a novel type of probe of structure formation, using the cosmological gravitational wave signal of high redshift compact binary mergers to provide information about structure formation, and thus the behaviour of dark matter. Such observations would also provide competitive constraints. Finally, I investigate primordial black holes as an alternative dark matter candidate, presenting an analysis and framework for the evolution of extended mass populations over cosmological time and computing the present day gamma ray signal, as well as the allowed local evaporation rate. This is used to set constraints on the allowed population of low mass primordial black holes, and the likelihood of witnessing an evaporation

    Milky Way White Dwarfs as Sub-GeV to Multi-TeV Dark Matter Detectors

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    We show that Milky Way white dwarfs are excellent targets for dark matter (DM) detection. Using Fermi and H.E.S.S. Galactic center gamma-ray data, we investigate sensitivity to DM annihilating within white dwarfs into long-lived or boosted mediators and producing detectable gamma rays. Depending on the Galactic DM distribution, we set new constraints on the spin-independent scattering cross section down to 1045104110^{-45}-10^{-41} cm2^2 in the sub-GeV DM mass range, which is multiple orders of magnitude stronger than existing limits. For a generalized NFW DM profile, we find that our white dwarf constraints exceed spin-independent direct detection limits across most of the sub-GeV to multi-TeV DM mass range, achieving sensitivities as low as about 104610^{-46} cm2^2. In addition, we improve earlier versions of the DM capture calculation in white dwarfs, by including the low-temperature distribution of nuclei when the white dwarf approaches crystallization. This yields smaller capture rates than previously calculated by a factor of a few up to two orders of magnitude, depending on white dwarf size and the astrophysical system.Comment: 29 pages, 5 figure

    Galaxies Going Bananas: Inferring the 3D Geometry of High-Redshift Galaxies with JWST-CEERS

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    The 3D geometry of high-redshift galaxies remains poorly understood. We build a differentiable Bayesian model and use Hamiltonian Monte Carlo to efficiently and robustly infer the 3D shapes of star-forming galaxies in JWST-CEERS observations with logM/M=9.010.5\log M_*/M_{\odot}=9.0-10.5 at z=0.58.0z=0.5-8.0. We reproduce previous results from HST-CANDELS in a fraction of the computing time and constrain the mean ellipticity, triaxiality, size and covariances with samples as small as 50\sim50 galaxies. We find high 3D ellipticities for all mass-redshift bins suggesting oblate (disky) or prolate (elongated) geometries. We break that degeneracy by constraining the mean triaxiality to be 1\sim1 for logM/M=9.09.5\log M_*/M_{\odot}=9.0-9.5 dwarfs at z>1z>1 (favoring the prolate scenario), with significantly lower triaxialities for higher masses and lower redshifts indicating the emergence of disks. The prolate population traces out a ``banana'' in the projected b/alogab/a-\log a diagram with an excess of low b/ab/a, large loga\log a galaxies. The dwarf prolate fraction rises from 25%\sim25\% at z=0.51.0z=0.5-1.0 to 5080%\sim50-80\% at z=38z=3-8. If these are disks, they cannot be axisymmetric but instead must be unusually oval (triaxial) unlike local circular disks. We simultaneously constrain the 3D size-mass relation and its dependence on 3D geometry. High-probability prolate and oblate candidates show remarkably similar S\'ersic indices (n1n\sim1), non-parametric morphological properties and specific star formation rates. Both tend to be visually classified as disks or irregular but edge-on oblate candidates show more dust attenuation. We discuss selection effects, follow-up prospects and theoretical implications.Comment: Submitted to ApJ, main body is 35 pages of which ~half are full-page figures, comments welcom

    Cloud fragmentation and chemical evolution of the high-mass star-forming region G327.3-0.6

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    In the struggle to understand how stars form in a cluster, it is important to study the morphology, kinematics and chemistry of the star-forming clouds. This thesis focuses on the high-mass star-forming region G327.3-0.6, which is a 3 pc filament at a distance of 3.3 kpc, hosting one hot molecular core and a set of cold dense cores. It was observed with the Atacama Large Millimetre/Sub-millimetre Array (ALMA) at 1.3 mm with high resolution 2". The data were self-calibrated to improve the signal to noise ratio by a factor of 2. The dendrogram algorithm together with the background subtraction were adopted to determine 66 compact cores. Minimum spanning tree determined a median core separation at 0.15pc and possible hierarchical fragmentation, which was supported by the two-point correlation function. Core mass function (CMF) was fitted with an index of -0.83, which is a hint of high-mass star-forming regions. The fragmentation in the filament was dominated by thermal support in small scale (~0.15pc) and by turbulence in large scale (~0.4pc). With toolbox XCLASS, 26 molecules and 39 isotopes were identified in the hot core spectrum, and a temperature of 270K was derived. The temperature error is around 60%. The moment maps were derived for 42 molecular transitions and analyzed by the Histogram of Oriented Gradient (HOG), indicating correlations between DCN and continuum, SiO and H2CO/CH3OH. Principal component analysis (PCA) and clustering algorithm were applied to the average spectra of each core to classify the evolutionary stages. Four groups are found with chemical and physical distinctions, suggesting the excitation temperature of CH3OH to be a good evolutionary indicator. The infrared environment is complex and may associated with photon-dissociation regions (PDRs)
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