| 1. |
- Grasha, K., et al.
(författare)
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The spatial relation between young star clusters and molecular clouds in M51 with LEGUS
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 483:4, s. 4707-4723
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Tidskriftsartikel (refereegranskat)abstract
- We present a study correlating the spatial locations of young star clusters with those of molecular clouds in NGC 5194, in order to investigate the time-scale over which clusters separate from their birth clouds. The star cluster catalogues are from the Legacy ExtraGalactic UV Survey (LEGUS) and the molecular clouds from the Plateau de Bure Interefrometer Arcsecond Whirpool Survey (PAWS). We find that younger star clusters are spatially closer to molecular clouds than older star clusters. The median age for clusters associated with clouds is 4 Myr, whereas it is 50 Myr for clusters that are sufficiently separated from a molecular cloud to be considered unassociated. After similar to 6 Myr, the majority of the star clusters lose association with their molecular gas. Younger star clusters are also preferentially located in stellar spiral arms where they are hierarchically distributed in kpc-size regions for 50-100 Myr before dispersing. The youngest star clusters are more strongly clustered, yielding a two-point correlation function with alpha = -0.28 +/- 0.04, than the giant molecular cloud (GMCs) (alpha = -0.09 +/- 0.03) within the same PAWS field. However, the clustering strength of the most massive GMCs, supposedly the progenitors of the young clusters for a star formation efficiency of a few percent, is comparable (alpha = -0.35 +/- 0.05) to that of the clusters. We find a galactocentric dependence for the coherence of star formation, in which clusters located in the inner region of the galaxy reside in smaller star-forming complexes and display more homogeneous distributions than clusters further from the centre. This result suggests a correlation between the survival of a cluster complex and its environment.
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| 2. |
- Messa, Matteo, et al.
(författare)
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The young star cluster population of M51 with LEGUS - I. A comprehensive study of cluster formation and evolution
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 473:1, s. 996-1018
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Tidskriftsartikel (refereegranskat)abstract
- Recently acquired WFC3 UV (F275W and F336W) imaging mosaics under the Legacy Extragalactic UV Survey (LEGUS), combined with archival ACS data of M51, are used to study the young star cluster (YSC) population of this interacting system. Our newly extracted source catalogue contains 2834 cluster candidates, morphologically classified to be compact and uniform in colour, for which ages, masses and extinction are derived. In this first work we study the main properties of the YSC population of the whole galaxy, considering a mass-limited sample. Both luminosity and mass functions follow a power-law shape with slope -2, but at high luminosities and masses a dearth of sources is observed. The analysis of the mass function suggests that it is best fitted by a Schechter function with slope -2 and a truncation mass at 1.00 +/- 0.12 x 10(5) M-circle dot . Through Monte Carlo simulations, we confirm this result and link the shape of the luminosity function to the presence of a truncation in the mass function. A mass limited age function analysis, between 10 and 200 Myr, suggests that the cluster population is undergoing only moderate disruption. We observe little variation in the shape of the mass function at masses above 1 x 10(4) M-circle dot over this age range. The fraction of star formation happening in the form of bound clusters in M51 is similar to 20 per cent in the age range 10-100 Myr and little variation is observed over the whole range from 1 to 200 Myr.
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| 3. |
- Novikova, P. Y., et al.
(författare)
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Sequencing of the genus Arabidopsis identifies a complex history of nonbifurcating speciation and abundant trans-specific polymorphism
- 2016
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 48:9, s. 1077-1082
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Tidskriftsartikel (refereegranskat)abstract
- The notion of species as reproductively isolated units related through a bifurcating tree implies that gene trees should generally agree with the species tree and that sister taxa should not share polymorphisms unless they diverged recently and should be equally closely related to outgroups. It is now possible to evaluate this model systematically. We sequenced multiple individuals from 27 described taxa representing the entire Arabidopsis genus. Cluster analysis identified seven groups, corresponding to described species that capture the structure of the genus. However, at the level of gene trees, only the separation of Arabidopsis thaliana from the remaining species was universally supported, and, overall, the amount of shared polymorphism demonstrated that reproductive isolation was considerably more recent than the estimated divergence times. We uncovered multiple cases of past gene flow that contradict a bifurcating species tree. Finally, we showed that the pattern of divergence differs between gene ontologies, suggesting a role for selection. © 2016 Nature America, Inc. All rights reserved.
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| 4. |
- Burt, Richard K., et al.
(författare)
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New autoimmune diseases after autologous hematopoietic stem cell transplantation for multiple sclerosis
- 2021
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Ingår i: Bone Marrow Transplantation. - : Springer Nature. - 0268-3369 .- 1476-5365. ; 56:7, s. 1509-1517
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Forskningsöversikt (refereegranskat)abstract
- Secondary autoimmune diseases (2ndADs), most frequently autoimmune cytopenias (AICs), were first described after allogeneic hematopoietic stem cell transplantation (HSCT) undertaken for malignant and hematological indications, occurred at a prevalence of similar to 5-6.5%, and were attributed to allogeneic immune imbalances in the context of graft versus host disease, viral infections, and chronic immunosuppression. Subsequently, 2ndADs were reported to complicate roughly 2-14% of autologous HSCTs performed for an autoimmune disease. Alemtuzumab in the conditioning regimen has been identified as a risk for development of 2ndADs after either allogeneic or autologous HSCT and is consistent with the high rates of 2ndADs when using alemtuzumab as monotherapy. Due to the significant consequences but variable incidence, depending on conditioning regimen, of 2ndADs and similarity in known immune reconstitution kinetics after autologous HSCT for autoimmune diseases and after alemtuzumab monotherapy, we propose that an imbalance between B and T lineage regeneration early after HSCT may underlie the pathogenesis of 2ndADs.
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