775 research outputs found
VERTICO VI: Cold-gas asymmetries in Virgo cluster galaxies
We analyze cold-gas distributions in Virgo cluster galaxies using resolved
CO(2-1) (tracing molecular hydrogen, H2) and HI observations from the Virgo
Environment Traced In CO (VERTICO) and the VLA Imaging of Virgo in Atomic Gas
(VIVA) surveys. From a theoretical perspective, it is expected that
environmental processes in clusters will have a stronger influence on diffuse
atomic gas compared to the relatively dense molecular gas component, and that
these environmental perturbations can compress the cold interstellar medium in
cluster galaxies leading to elevated star formation. In this work we
observationally test these predictions for star-forming satellite galaxies
within the Virgo cluster. We divide our Virgo galaxy sample into HI-normal,
HI-tailed, and HI-truncated classes and show, unsurprisingly, that the
HI-tailed galaxies have the largest quantitative HI asymmetries. We also
compare to a control sample of non-cluster galaxies and find that Virgo
galaxies, on average, have HI asymmetries that are 40 +/- 10 per cent larger
than the control. There is less separation between control, HI-normal,
HI-tailed, and HI-truncated galaxies in terms of H2 asymmetries, and on
average, Virgo galaxies have H2 asymmetries that are only marginally (20 +/- 10
per cent) larger than the control sample. We find a weak correlation between HI
and H2 asymmetries over our entire sample, but a stronger correlation for those
specific galaxies being strongly impacted by environmental perturbations.
Finally, we divide the discs of the HI-tailed Virgo galaxies into a leading
half and trailing half according to the observed tail direction. We find
evidence for excess molecular gas mass on the leading halves of the disc. This
excess molecular gas on the leading half is accompanied by an excess in star
formation rate such that the depletion time is, on average, unchanged.Comment: 15 pages, 8 figures, 1 table, accepted for publication in A&
VERTICO VII: Environmental quenching caused by suppression of molecular gas content and star formation efficiency in Virgo Cluster galaxies
We study how environment regulates the star formation cycle of 33 Virgo
Cluster satellite galaxies on 720 parsec scales. We present the first resolved
star-forming main sequence for cluster galaxies, dividing the sample based on
their global HI properties and comparing to a control sample of field galaxies.
HI-poor cluster galaxies have reduced star formation rate (SFR) surface
densities with respect to both HI-normal cluster and field galaxies (0.5 dex),
suggesting that mechanisms regulating the global HI content are responsible for
quenching local star formation. We demonstrate that the observed quenching in
HI-poor galaxies is caused by environmental processes such as ram pressure
stripping (RPS) simultaneously reducing molecular gas surface density and star
formation efficiency (SFE), compared to regions in HI-normal systems (by 0.38
and 0.22 dex, respectively). We observe systematically elevated SFRs that are
driven by increased molecular gas surface densities at fixed stellar mass
surface density in the outskirts of early-stage RPS galaxies, while SFE remains
unchanged with respect to the field sample. We quantify how RPS and starvation
affect the star formation cycle of inner and outer galaxy discs as they are
processed by the cluster. We show both are effective quenching mechanisms with
the key difference being that RPS acts upon the galaxy outskirts while
starvation regulates the star formation cycle throughout disc, including within
the truncation radius. For both processes, the quenching is caused by a
simultaneous reduction in molecular gas surface densities and SFE at fixed
stellar mass surface density.Comment: 17 pages, 1 table, 5 figures, accepted for publication in Ap
STROBE-X: A probe-class mission for x-ray spectroscopy and timing on timescales from microseconds to years
We describe the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X), a probeclass mission concept that will provide an unprecedented view of the X-ray sky, performing timing and spectroscopy over both a broad energy band (0.2-30 keV) and a wide range of timescales from microseconds to years. STROBE-X comprises two narrow-field instruments and a wide field monitor. The soft or low-energy band (0.2-12 keV) is covered by an array of lightweight optics (3-m focal length) that concentrate incident photons onto small solid-state detectors with CCD-level (85-175 eV) energy resolution, 100 ns time resolution, and low background rates. This technology has been fully developed for NICER and will be scaled up to take advantage of the longer focal length of STROBE-X. The higher-energy band (2-30 keV) is covered by large-area, collimated silicon drift detectors that were developed for the European LOFT mission concept. Each instrument will provide an order of magnitude improvement in effective area over its predecessor (NICER in the soft band and RXTE in the hard band). Finally, STROBE-X offers a sensitive wide-field monitor (WFM), both to act as a trigger for pointed observations of X-ray transients and also to provide high duty-cycle, high time-resolution, and high spectral-resolution monitoring of the variable X-ray sky. The WFM will boast approximately 20 times the sensitivity of the RXTE All-Sky Monitor, enabling multi-wavelength and multi-messenger investigations with a large instantaneous field of view. This mission concept will be presented to the 2020 Decadal Survey for consideration
What Makes a Better Smeller?
Olfaction is often viewed as difficult, yet the empirical evidence suggests a different picture. A closer look shows people around the world differ in their ability to detect, discriminate, and name odors. This gives rise to the question of what influences our ability to smell. Instead of focusing on olfactory deficiencies, this review presents a positive perspective by focusing on factors that make someone a better smeller. We consider three driving forces in improving olfactory ability: one's biological makeup, one's experience, and the environment. For each factor, we consider aspects proposed to improve odor perception and critically examine the evidence; as well as introducing lesser discussed areas. In terms of biology, there are cases of neurodiversity, such as olfactory synesthesia, that serve to enhance olfactory ability. Our lifetime experience, be it typical development or unique training experience, can also modify the trajectory of olfaction. Finally, our odor environment, in terms of ambient odor or culinary traditions, can influence odor perception too. Rather than highlighting the weaknesses of olfaction, we emphasize routes to harnessing our olfactory potential
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
Vertico. IV. Environmental effects on the gas distribution and star formation efficiency of virgo cluster spirals
We measure the molecular-to-atomic gas ratio, R mol, and the star formation rate (SFR) per unit molecular gas mass, SFEmol, in 38 nearby galaxies selected from the Virgo Environment Traced in CO (VERTICO) survey. We stack ALMA 12CO (J = 2−1) spectra coherently using H i velocities from the VIVA survey to detect faint CO emission out to galactocentric radii r gal ∼ 1.2 r 25. We determine the scale lengths for the molecular and stellar components, finding a ∼3:5 relation compared to ∼1:1 in field galaxies, indicating that the CO emission is more centrally concentrated than the stars. We compute R mol as a function of different physical quantities. While the spatially resolved R mol on average decreases with increasing radius, we find that the mean molecular-to-atomic gas ratio within the stellar effective radius R e , R mol(r < R e ), shows a systematic increase with the level of H i, truncation and/or asymmetry (HI perturbation). Analysis of the molecular- and the atomic-to-stellar mass ratios within R e , R⋆mol(
Mutations in TOP3A Cause a Bloom Syndrome-like Disorder
Bloom syndrome, caused by biallelic mutations in BLM, is characterized by prenatal-onset growth deficiency, short stature, an erythematous photosensitive malar rash, and increased cancer predisposition. Diagnostically, a hallmark feature is the presence of increased sister chromatid exchanges (SCEs) on cytogenetic testing. Here, we describe biallelic mutations in TOP3A in ten individuals with prenatal-onset growth restriction and microcephaly. TOP3A encodes topoisomerase III alpha (TopIIIα), which binds to BLM as part of the BTRR complex, and promotes dissolution of double Holliday junctions arising during homologous recombination. We also identify a homozygous truncating variant in RMI1, which encodes another component of the BTRR complex, in two individuals with microcephalic dwarfism. The TOP3A mutations substantially reduce cellular levels of TopIIIα, and consequently subjects’ cells demonstrate elevated rates of SCE. Unresolved DNA recombination and/or replication intermediates persist into mitosis, leading to chromosome segregation defects and genome instability that most likely explain the growth restriction seen in these subjects and in Bloom syndrome. Clinical features of mitochondrial dysfunction are evident in several individuals with biallelic TOP3A mutations, consistent with the recently reported additional function of TopIIIα in mitochondrial DNA decatenation. In summary, our findings establish TOP3A mutations as an additional cause of prenatal-onset short stature with increased cytogenetic SCEs and implicate the decatenation activity of the BTRR complex in their pathogenesis
VERTICO V: The environmentally driven evolution of the inner cold gas discs of Virgo cluster galaxies
The quenching of cluster satellite galaxies is inextricably linked to the suppression of their cold interstellar medium (ISM) by environmental mechanisms. While the removal of neutral atomic hydrogen (H I) at large radii is well studied, how the environment impacts the remaining gas in the centres of galaxies, which are dominated by molecular gas, is less clear. Using new observations from the Virgo Environment traced in CO survey (VERTICO) and archival H I data, we study the H I and molecular gas within the optical discs of Virgo cluster galaxies on 1.2-kpc scales with spatially resolved scaling relations between stellar ( Σ⋆
), H I ( ΣHI
), and molecular gas ( Σmol
) surface densities. Adopting H I deficiency as a measure of environmental impact, we find evidence that, in addition to removing the H I at large radii, the cluster processes also lower the average ΣHI
of the remaining gas even in the central 1.2
kpc. The impact on molecular gas is comparatively weaker than on the H I, and we show that the lower Σmol
gas is removed first. In the most H I-deficient galaxies, however, we find evidence that environmental processes reduce the typical Σmol
of the remaining gas by nearly a factor of 3. We find no evidence for environment-driven elevation of ΣHI
or Σmol
in H I-deficient galaxies. Using the ratio of Σmol
-to- ΣHI
in individual regions, we show that changes in the ISM physical conditions, estimated using the total gas surface density and midplane hydrostatic pressure, cannot explain the observed reduction in molecular gas content. Instead, we suggest that direct stripping of the molecular gas is required to explain our results
VERTICO III. The Kennicutt-Schmidt relation in Virgo cluster galaxies
Aims. In this Virgo Environment Traced in CO (VERTICO) science paper, we aim to study how the star formation process depends on the galactic environment and gravitational interactions in the context of galaxy evolution. We explore the scaling relation between the star formation rate surface density (ΣSFR) and the molecular gas surface density (Σmol), also known as the Kennicutt-Schmidt relation, in a subsample of Virgo cluster spiral galaxies.
Methods. We used new Atacama Compact Array and Total Power (ACA+TP) observations from the VERTICO-Atacama Large Millimeter/submillimeter Array (ALMA) Large Program at 720 pc resolution to resolve the molecular gas content, as traced by the 12CO (2 − 1) transition, across the disks of 37 spiral galaxies in the Virgo cluster. In combination with archival UV and IR observations used to determine the star formation rate (SFR), we estimated the parameters of the Kennicutt-Schmidt (KS) relation for the entire ensemble of galaxies, and within individual galaxies.
Results. We find the KS slope for the entire population to be N = 0.97 ± 0.07, with a characteristic molecular gas depletion time of 1.86 Gyr for our full sample, which is in agreement with previous work in isolated, nearby star-forming galaxies. In individual galaxies, we find that the KS slope ranges between 0.69 and 1.40, and that typical star formation efficiencies of molecular gas can vary from galaxy to galaxy by a factor of ∼4. These galaxy-to-galaxy variations account for ∼0.20 dex in scatter in the ensemble KS relation, which is characterized by a 0.42 dex scatter. In addition, we find that the HI-deficient galaxies in the Virgo cluster show a steeper resolved KS relation and lower molecular gas efficiencies than HI-normal cluster galaxies.
Conclusions. While the molecular gas content in galaxies residing in the Virgo cluster appears – to first order – to behave similarly to that in isolated galaxies, our VERTICO sample of galaxies shows that cluster environments play a key role in regulating star formation. The environmental mechanisms affecting the HI galaxy content also have a direct impact on the star formation efficiency of molecular gas in cluster galaxies, leading to longer depletion times in HI-deficient members
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