80 research outputs found
First observational evidence of a relation between globular clusters' internal rotation and stellar masses
Several observational studies have shown that many Galactic globular clusters
(GCs) are characterised by internal rotation. Theoretical studies of the
dynamical evolution of rotating clusters have predicted that, during their
long-term evolution, these stellar systems should develop a dependence of the
rotational velocity around the cluster's centre on the mass of stars, with the
internal rotation increasing for more massive stars. In this paper we present
the first observational evidence of the predicted rotation-mass trend. In our
investigation, we exploited the Data Release 3 catalogue of
three GCs: NGC 104 (47 Tuc), NGC 5139 ( Cen) and NGC 5904 (M 5). We
found clear evidence of a cluster rotation-mass relation in 47 Tuc and M 5,
while in Cen, the dynamically youngest system among the three clusters
studied here, no such trend was detected.Comment: 6 pages, 4 figures, 1 table. Accepted for publication in MNRAS
Letter
Independent Evolution of Transcriptional Inactivation on Sex Chromosomes in Birds and Mammals
X chromosome inactivation in eutherian mammals has been thought to be tightly controlled, as expected from a mechanism that compensates for the different dosage of X-borne genes in XX females and XY males. However, many X genes escape inactivation in humans, inactivation of the X in marsupials is partial, and the unrelated sex chromosomes of monotreme mammals have incomplete and gene-specific inactivation of X-linked genes. The bird ZW sex chromosome system represents a third independently evolved amniote sex chromosome system with dosage compensation, albeit partial and gene-specific, via an unknown mechanism (i.e. upregulation of the single Z in females, down regulation of one or both Zs in males, or a combination). We used RNA-fluorescent in situ hybridization (RNA-FISH) to demonstrate, on individual fibroblast cells, inactivation of 11 genes on the chicken Z and 28 genes on the X chromosomes of platypus. Each gene displayed a reproducible frequency of 1Z/1X-active and 2Z/2X-active cells in the homogametic sex. Our results indicate that the probability of inactivation is controlled on a gene-by-gene basis (or small domains) on the chicken Z and platypus X chromosomes. This regulatory mechanism must have been exapted independently to the non-homologous sex chromosomes in birds and mammals in response to an over-expressed Z or X in the homogametic sex, highlighting the universal importance that (at least partial) silencing plays in the evolution on amniote dosage compensation and, therefore, the differentiation of sex chromosomes.This project was supported by an Australian Research Fellowship to PDW (DP0987091) and an Australian Research Council discovery project grant to PDW, JED and JAMG (DP1094868) (http://www.arc.gov.au/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
First Phase Space Portrait of a Hierarchical Stellar Structure in the Milky Way
We present the first detailed observational picture of a possible ongoing
massive cluster hierarchical assembly in the Galactic disk as revealed by the
analysis of the stellar full phase-space (3D positions and kinematics and
spectro-photometric properties) of an extended area ( diameter)
surrounding the well-known and Persei double stellar cluster in
the Perseus Arm. Gaia-EDR3 shows that the area is populated by seven co-moving
clusters, three of which were previously unknown, and by an extended and quite
massive () halo. All stars and clusters define a complex
structure with evidence of possible mutual interactions in the form of
intra-cluster over-densities and/or bridges. They share the same chemical
abundances (half-solar metallicity) and age ( Myr) within a small
confidence interval and the stellar density distribution of the surrounding
diffuse stellar halo resembles that of a cluster-like stellar system. The
combination of these evidences suggests that stars distributed within a few
degrees from and Persei are part of a common, sub-structured
stellar complex that we named LISCA I. Comparison with results obtained through
direct -body simulations suggest that LISCA I may be at an intermediate
stage of an ongoing cluster assembly that can eventually evolve in a relatively
massive (a few ) stellar system. We argue that such cluster
formation mechanism may be quite efficient in the Milky Way and disk-like
galaxies and, as a consequence, it has a relevant impact on our understanding
of cluster formation efficiency as a function of the environment and redshift.Comment: 19 pages, 8 figures, 1 table; accepted for publication in Ap
Ongoing hierarchical massive cluster assembly: the LISCA II structure in the Perseus complex
We report on the identification of a massive ( M)
sub-structured stellar system in the Galactic Perseus complex likely undergoing
hierarchical cluster assembly. Such a system comprises nine star clusters
(including the well-known clusters NGC 654 and NGC 663) and an extended and
low-density stellar halo. Gaia-DR3 and available spectroscopic data show that
all its components are physically consistent in the 6D phase-space (position,
parallax, and 3D motion), homogeneous in age (14 44 Myr), and chemical
content (half-solar metallicity). In addition, the system's global stellar
density distribution is that of typical star clusters and shows clear evidence
of mass segregation. We find that the hierarchical structure is mostly
contracting towards the center with a speed of up to km s,
while the innermost regions expand at a lower rate (about km
s) and are dominated by random motions. Interestingly, this pattern is
dominated by the kinematics of massive stars, while low-mass stars (
M) are characterized by contraction across the entire cluster. Finally,
the nine star clusters in the system are all characterized by a relatively flat
velocity dispersion profile possibly resulting from ongoing interactions and
tidal heating. We show that the observational results are generally consistent
with those found in -body simulations following the cluster violent
relaxation phase strongly suggesting that the system is a massive cluster in
the early assembly stages. This is the second structure with these properties
identified in our Galaxy and, following the nomenclature of our previous work,
we named it LISCA II.Comment: 21 pages, 24 figures, 1 table; accepted for publication in A&
Landscape of DNA methylation on the marsupial x
DNA methylation plays a key role in maintaining transcriptional silence on the inactive X chromosome of eutherian mammals. Beyond eutherians, there are limited genome wide data on DNA methylation from other vertebrates. Previous studies of X borne genes in various marsupial models revealed no differential DNA methylation of promoters between the sexes, leading to the conclusion that CpG methylation plays no role in marsupial X-inactivation. Using reduced representation bisulfite sequencing, we generated male and female CpG methylation profiles in four representative vertebrates (mouse, gray short-tailed opossum, platypus, and chicken). A variety of DNA methylation patterns were observed. Platypus and chicken displayed no large-scale differential DNA methylation between the sexes on the autosomes or the sex chromosomes. As expected, a metagene analysis revealed hypermethylation at transcription start sites (TSS) of genes subject to X-inactivation in female mice. This contrasted with the opossum, in which metagene analysis did not detect differential DNA methylation between the sexes at TSSs of genes subject to X-inactivation. However, regions flanking TSSs of these genes were hypomethylated. Our data are the first to demonstrate that, for genes subject to X-inactivation in both eutherian and marsupial mammals, there is a consistent difference between DNA methylation levels at TSSs and immediate flanking regions, which we propose has a silencing effect in both groups.This work was funded by Australian Research Council
Discovery Projects DP0987091 and DP1094868
Reversing a tyranny of cascading shoreline-protection decisions driving coastal habitat loss
Shoreline hardening is a major driver of biodiversity and habitat loss in coastal ecosystems yet remains a common approach to coastal management globally. Using surveys of waterfront residents in North Carolina, USA, we sought to identify factors influencing individual shore-protection decisions and ultimately impacting coastal ecosystems, particularly coastal wetlands. We found that neighboring shore condition was the best predictor of respondent shore condition. Respondents with hardened shorelines were more likely to have neighbors with hardened shorelines, and to report that neighbors influenced their shore-protection choices than respondents with natural shorelines. Further, respondents who expressed climate-change skepticism and preference for shoreline hardening were opposed to shoreline-hardening restrictions. Despite preferring hardening, respondents ranked wetlands as highly valuable for storm protection and other ecosystem services, suggesting a disconnect between the ecological knowledge of individuals and social norms of shore-protection decisions. However, our results also suggest that efforts to increase the installation of living shorelines have the potential to conserve and restore important coastal habitats and support biodiversity along shorelines that may otherwise be degraded by hardening. Further, encouraging waterfront-property owners who have adopted living shorelines to recommend them to neighbors may be an effective strategy to initiate and reinforce pro-conservation social norms
First Phase Space Portrait of a Hierarchical Stellar Structure in the Milky Way
We present the first detailed observational picture of a possible ongoing massive cluster hierarchical assembly in the Galactic disk as revealed by the analysis of the stellar full phase space (3D positions and kinematics and spectro-photometric properties) of an extended area (6° diameter) surrounding the well-known h and χ Persei double stellar cluster in the Perseus Arm. Gaia-EDR3 shows that the area is populated by seven comoving clusters, three of which were previously unknown, and by an extended and quite massive (M ∼ 105 M⊙) halo. All stars and clusters define a complex structure with evidence of possible mutual interactions in the form of intra-cluster overdensities and/or bridges. They share the same chemical abundances (half-solar metallicity) and age (t ∼ 20 Myr) within a small confidence interval and the stellar density distribution of the surrounding diffuse stellar halo resembles that of a cluster-like stellar system. The combination of these pieces of evidence suggests that stars distributed within a few degrees from h and χ Persei are part of a common, substructured stellar complex that we named LISCA I. Comparison with results obtained through direct N-body simulations suggest that LISCA I may be at an intermediate stage of an ongoing cluster assembly that can eventually evolve in a relatively massive (a few times 105 M⊙) stellar system. We argue that such a cluster formation mechanism may be quite efficient in the Milky Way and disk-like galaxies and, as a consequence, it has a relevant impact on our understanding of cluster formation efficiency as a function of the environment and redshift
Nonrenewable Resources, Strategic Behavior and the Hotelling Rule: An Experiment
This study uses the methods of experimental economics to investigate possible causes for the failure of the Hotelling rule for nonrenewable resources. We argue that as long as resource stocks are large enough, producers may choose to (partially) ignore the dynamic component of their production decision, shifting production to the present and focusing more on strategic behavior. We experimentally vary stock size in a nonrenewable resource duopoly setting and find that producers with large stocks indeed pay significantly less attention to variables related to dynamic optimization,leading to a failure of the Hotelling rule
Mechanisms and Evolutionary Patterns of Mammalian and Avian Dosage Compensation
A large-scale comparative gene expression study reveals the different ways in which the chromosome-wide gene dosage reductions resulting from sex chromosome differentiation events were compensated during mammalian and avian evolution
- …