1,349 research outputs found
On the Stellar Kinematics and Mass of the Virgo Ultra-Diffuse Galaxy VCC 1287
Here, we present a kinematical analysis of the Virgo cluster ultra-diffuse
galaxy (UDG) VCC 1287 based on data taken with the Keck Cosmic Web Imager
(KCWI). We confirm VCC 1287's association both with the Virgo cluster and its
globular cluster (GC) system, measuring a recessional velocity of $1116 \pm 2\
\mathrm{km\ s^{-1}}19 \pm 6\
\mathrm{km\ s^{-1}}1.11^{+0.81}_{-0.81}
\times 10^{9} \ \mathrm{M_{\odot}}13^{+11}_{-11}$)
within the half light radius (4.4 kpc). This places VCC 1287 slightly above the
well established relation for normal galaxies, with a higher mass to light
ratio for its dynamical mass than normal galaxies. We use our dynamical mass,
and an estimate of GC system richness, to place VCC 1287 on the GC number --
dynamical mass relation, finding good agreement with a sample of normal
galaxies. Based on a total halo mass derived from GC counts, we then infer that
VCC 1287 likely resides in a cored or low concentration dark matter halo. Based
on the comparison of our measurements to predictions from simulations, we find
that strong stellar feedback and/or tidal effects are plausibly the dominant
mechanisms in the formation of VCC 1287. Finally, we compare our measurement of
the dynamical mass with those for other UDGs. These dynamical mass estimates
suggest relatively massive halos and a failed galaxy origin for at least some
UDGs.Comment: 13 pages, 10 figures with an additional 5 pages and 5 figures in
appendices. Accepted for publication in MNRAS. v2: with small updates from
publication formatting and a minor plotting fix for Fig. 1
Quantitatively probing propensity for structural transitions in engineered virus nanoparticles by single-molecule mechanical analysis
Viruses are increasingly being studied from the perspective of fundamental physics at the nanoscale as biologically evolved nanodevices with many technological applications. In viral particles of the minute virus of mice (MVM), folded segments of the single-stranded DNA genome are bound to the capsid inner wall and act as molecular buttresses that increase locally the mechanical stiffness of the particle. We have explored whether a quantitative linkage exists in MVM particles between their DNA-mediated stiffening and impairment of a heat-induced, virus-inactivating structural change. A series of structurally modified virus particles with disrupted capsid-DNA interactions and/or distorted capsid cavities close to the DNA-binding sites were engineered and characterized, both in classic kinetics assays and by single-molecule mechanical analysis using atomic force microscopy. The rate constant of the virus inactivation reaction was found to decrease exponentially with the increase in elastic constant (stiffness) of the regions closer to DNA-binding sites. The application of transition state theory suggests that the height of the free energy barrier of the virus-inactivating structural transition increases linearly with local mechanical stiffness. From a virological perspective, the results indicate that infectious MVM particles may have acquired the biological advantage of increased survival under thermal stress by evolving architectural elements that rigidify the particle and impair non-productive structural changes. From a nanotechnological perspective, this study provides proof of principle that determination of mechanical stiffness and its manipulation by protein engineering may be applied for quantitatively probing and tuning the conformational dynamics of virus-based and other protein-based nanoassemblies. This journal isThis work was funded by grants to M.G.M. from the Spanish Government (BIO2009-10092 and BIO2012-37649) and Comunidad de Madrid (S-505/MAT-0303) and by an institutional grant from Fundación Ramón Areces to the Centro de Biología Molecular. P.J.P.C. is the recipient of a FPI contract from the Spanish Government. M.G.M. is an associate member of the Institute for Biocomputation and Physics of Complex Systems, Zaragoza, Spain.Peer Reviewe
Bridging the gap in the mass-size relation of compact galaxies with MaNGA
We present the analysis of the full MaNGA DR17 sample to characterize its
population of compact galaxies. We focus on galaxies that fill the stellar mass
(M) gap between compact elliptical galaxies (cEs; ) and compact massive galaxies
(CMGs; ). We study their
stellar populations and kinematics to reveal how their properties depend on
stellar mass. We select compact galaxies in the MaNGA DR17 sample according to
their effective radius () and stellar mass. 37 galaxies fulfill our
selection criteria in the bridging region between cEs and CMGs. We derive their
kinematics and stellar population parameters from the stacked spectra at
1~ using a full spectral fitting routine. We then classify the selected
compact galaxies in three main groups based on their stellar population
properties. One of the groups shows characteristics compatible with relic
galaxies, i.e. galaxies that have remained mostly unchanged since their early
formation epoch (). Another group shows more extended and continuous
star formation histories (SFHs). The third group shows a low star-forming rate
at initial times, which increases at around Gyr. We compare the derived
properties of the selected galaxies with those of previously studied compact
galaxies at different mass ranges. The selected galaxies successfully fill the
mass gap between cEs and CMGs. Their properties are compatible with the
assumption that the scaling relations of compact galaxies at different mass
ranges are related, although galaxies in the first group are clear outliers in
the fundamental plane, suggesting different formation mechanisms for this relic
population.Comment: 16 pages, 14 figures, 2 table
The assembly history of the nearest S0 galaxy NGC 3115 from its kinematics out to six half-light radii
Using new and archival data, we study the kinematic properties of the nearest
field S0 galaxy, NGC 3115, out to half-light radii ()
from its stars (integrated starlight), globular clusters (GCs) and planetary
nebulae (PNe). We find evidence of three kinematic regions with an inner
transition at from a dispersion-dominated bulge
() to a fast-rotating disk (), and then an additional transition from the disk to a slowly rotating
spheroid at , as traced by the red GCs and PNe (and
possibly by the blue GCs beyond ). From comparison with
simulations, we propose an assembly history in which the original progenitor
spiral galaxy undergoes a gas-rich minor merger that results in the embedded
kinematically cold disk that we see today in NGC 3115. At a later stage, dwarf
galaxies, in mini mergers (mass-ratio 1:10), were accreted building-up the
outer slowly rotating spheroid, with the central disk kinematics largely
unaltered. Additionally, we report new spectroscopic observations of a sample
of ultra-compact dwarfs (UCDs) around NGC 3115 with the Keck/KCWI instrument.
We find that five UCDs are inconsistent with the general rotation field of the
GCs, suggesting an \textit{ex-situ} origin for these objects, i.e. perhaps the
remnants of tidally stripped dwarfs. A further seven UCDs follow the GC
rotation pattern, suggesting an \textit{in-situ} origin and, possibly a GC-like
nature.Comment: 22 pages (including 3 pages of Appendix material), 14 figures,
published in MNRA
Hierarchical spatio-temporal change-point detection
Detecting change-points in multivariate settings is usually carried out by analyzing all marginals either independently, via univariate methods, or jointly, through multivariate approaches. The former discards any inherent dependencies between different marginals and the latter may suffer from domination/masking among different change-points of distinct marginals. As a remedy, we propose an approach which groups marginals with similar temporal behaviors, and then performs group-wise multivariate change-point detection. Our approach groups marginals based on hierarchical clustering using distances which adjust for inherent dependencies. Through a simulation study we show that our approach, by preventing domination/masking, significantly enhances the general performance of the employed multivariate change-point detection method. Finally, we apply our approach to two datasets: (i) Land Surface Temperature in Spain, during the years 2000–2021, and (ii) The WikiLeaks Afghan War Diary data
Impact of genotype 1 and 2 of porcine reproductive and respiratory syndrome viruses on interferon-α responses by plasmacytoid dendritic cells
Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) infections are characterized by prolonged viremia and viral shedding consistent with incomplete immunity. Type I interferons (IFN) are essential for mounting efficient antiviral innate and adaptive immune responses, but in a recent study, North American PRRSV genotype 2 isolates did not induce, or even strongly inhibited, IFN-α in plasmacytoid dendritic cells (pDC), representing "professional IFN-α-producing cells". Since inhibition of IFN-α expression might initiate PRRSV pathogenesis, we further characterized PRRSV effects and host modifying factors on IFN-α responses of pDC. Surprisingly, a variety of type 1 and type 2 PRRSV directly stimulated IFN-α secretion by pDC. The effect did not require live virus and was mediated through the TLR7 pathway. Furthermore, both IFN-γ and IL-4 significantly enhanced the pDC production of IFN-α in response to PRRSV exposure. PRRSV inhibition of IFN-α responses from enriched pDC stimulated by CpG oligodeoxynucleotides was weak or absent. VR-2332, the prototype genotype 2 PRRSV, only suppressed the responses by 34%, and the highest level of suppression (51%) was induced by a Chinese highly pathogenic PRRSV isolate. Taken together, these findings demonstrate that pDC respond to PRRSV and suggest that suppressive activities on pDC, if any, are moderate and strain-dependent. Thus, pDC may be a source of systemic IFN-α responses reported in PRRSV-infected animals, further contributing to the puzzling immunopathogenesis of PRRS
For the common good: Measuring residents\' efforts to protect their community from drug- and sex-related harm
People in high-risk neighbourhoods try to protect their friends, neighbours, relatives and others from the social and physical risks associated with sex and drug use. This paper develops and validates a community-grounded questionnaire to measure such
‘intravention\' (health-directed efforts to protect others). An initial ethnography, including life-history interviews and focus groups, explored the forms of intravention activities engaged in by residents of Bushwick (a high-risk New York City neighbourhood). Grassroots categories of intraventions were derived and questions developed to ask about such behaviours. Face validity and adequacy of the questions were assessed by independent experts. Pre-testing was conducted, and reliability and validity were assessed. An instrument including 110 intravention items was administered to 57 community-recruited residents. Analysis focused on 57 items in 11 domain-specific subscale. All subscales had good to very good reliability; Cronbach\'s alpha ranged from .81 to .95. The subscales evidenced both convergent and discriminant validity. Although further testing of this instrument on additional populations is clearly warranted, this intravention instrument seems valid and reliable. It can be used by researchers in comparative and longitudinal studies of the causes, prevalence and affects of different intravention activities in communities. It can benefit public health practitioners by
helping them understand the environments in which they are intervening and by helping them find ways to cooperate with local neighbourhood-level health activists. Keywords: Intravention, drug prevention, harm reduction, community actions, protecting others.SAHARA-J Vol. 5 (3) 2008: pp. 144-15
Keck Cosmic Web Imager (KCWI) spectra of globular clusters and ultracompact dwarfs in the halo of M87
Using the Keck Cosmic Web Imager, we obtain spectra of several globular clusters (GCs), ultracompact dwarfs (UCDs), and the inner halo starlight of M87, at a similar projected galactocentric radius of ∼5 kpc. This enables us, for the first time, to apply the same stellar population analysis to the GCs, UCDs, and starlight consistently to derive ages, metallicities, and alpha-element abundances in M87. We find evidence for a dual stellar population in the M87 halo light, i.e. an ∼80 per cent component by mass that is old and metal-rich and a ∼20 per cent component that is old but metal-poor. Two red GCs share similar stellar populations to the halo light suggesting they may have formed contemporaneously with the dominant halo component. Three UCDs, and one blue GC, have similar stellar populations, with younger mean ages, lower metallicities, and near solar alpha-element abundances. Combined with literature data, our findings are consistent with the scenario that UCDs are the remnant nucleus of a stripped galaxy. We further investigate the discrepancy in the literature for M87\u27s kinematics at large radii, favouring a declining velocity dispersion profile. This work has highlighted the need for more self-consistent studies of galaxy haloes
Keck Cosmic Web Imager (KCWI) Spectra of Globular Clusters and Ultra Compact Dwarfs in the Halo of M87
Using the Keck Cosmic Web Imager we obtain spectra of several globular
clusters (GCs), ultra compact dwarfs (UCDs) and the inner halo starlight of
M87, at a similar projected galactocentric radius of 5 kpc. This enables
us, for the first time, to apply the same stellar population analysis to the
GCs, UCDs and starlight consistently to derive ages, metallicities and
alpha-element abundances in M87. We find evidence for a dual stellar population
in the M87 halo light, i.e an 80\% component by mass which is old and
metal-rich and a 20\% component which is old but metal-poor. Two red GCs
share similar stellar populations to the halo light suggesting they may have
formed contemporaneously with the dominant halo component. Three UCDs, and one
blue GC, have similar stellar populations, with younger mean ages, lower
metallicities and near solar alpha-element abundances. Combined with literature
data, our findings are consistent with the scenario that UCDs are the remnant
nucleus of a stripped galaxy. We further investigate the discrepancy in the
literature for M87's kinematics at large radii, favouring a declining velocity
dispersion profile. This work has highlighted the need for more self-consistent
studies of galaxy halos.Comment: 12 pages, 10 figures, accepted for publication in MNRA
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