151 research outputs found
Environmental Effects on the Metal Enrichment of Low Mass Galaxies in Nearby Clusters
In this paper we study the chemical history of low-mass star-forming (SF)
galaxies in the local Universe clusters Coma, A1367, A779, and A634. The aim of
this work is to search for the imprint of the environment on the chemical
evolution of these galaxies. Galaxy chemical evolution is linked to the star
formation history (SFH), as well as to the gas interchange with the
environment, and low-mass galaxies are well known to be vulnerable systems to
environmental processes affecting both these parameters. For our study we have
used spectra from the SDSS-III DR8. We have examined the mass-metallicity
relation of cluster galaxies finding well defined sequences. The slope of these
sequences, for galaxies in low-mass clusters and galaxies at large
cluster-centric distances, follows the predictions of recent hydrodynamic
models. A flattening of this slope has been observed for galaxies located in
the core of the two more massive clusters of the sample, principally in Coma,
suggesting that the imprint of the cluster environment on the chemical
evolution of SF galaxies should be sensitive to both the galaxy mass and the
host cluster mass. The HI gas content of Coma and A1367 galaxies indicate that
low-mass SF galaxies, located at the core of these clusters, have been severely
affected by ram-pressure stripping. The observed mass-dependent enhancement of
the metal content of low-mass galaxies in dense environments seems plausible,
according to hydrodynamic simulations. This enhanced metal enrichment could be
produced by the combination of effects such as wind reaccretion, due to
pressure cofinement by the intra-cluster medium (ICM), and the truncation of
gas infall, as a result of the ram-pressure stripping. Thus, the properties of
the ICM should play an important role in the chemical evolution of low-mass
galaxies in clusters.Comment: ApJ accepted, 31 pages, 13 figure
Extreme Plasma Astrophysics
This is a science white paper submitted to the Astro-2020 and Plasma-2020
Decadal Surveys. The paper describes the present status and emerging
opportunities in Extreme Plasma Astrophysics -- a study of
astrophysically-relevant plasma processes taking place under extreme conditions
that necessitate taking into account relativistic, radiation, and QED effects.Comment: A science white paper submitted to the Astro-2020 and Plasma-2020
Decadal Surveys. 7 pages including cover page and references. Paper updated
in late March 2019 to include a several additional co-authors and references,
and a few small change
The hunt for extraterrestrial high-energy neutrino counterparts
The origin of Petaelectronvolt (PeV) astrophysical neutrinos is fundamental
to our understanding of the high-energy Universe. Apart from the technical
challenges of operating detectors deep below ice, oceans, and lakes, the
phenomenological challenges are even greater than those of gravitational waves;
the sources are unknown, hard to predict, and we lack clear signatures.
Neutrino astronomy therefore represents the greatest challenge faced by the
astronomy and physics communities thus far. The possible neutrino sources range
from accretion disks and tidal disruption events, to relativistic jets and
galaxy clusters with blazar TXS~0506+056 the most compelling association thus
far. Since that association, immense effort has been put into proving or
disproving that jets are indeed neutrino emitters, but to no avail. By
generating simulated neutrino counterpart samples, we explore the potential of
detecting a significant correlation of neutrinos with jets from active galactic
nuclei. We find that, given the existing challenges, even our best experiments
could not have produced a result. Larger programs over the next few
years will be able to detect a significant correlation only if the brightest
radio sources, rather than all jetted active galactic nuclei, are neutrino
emitters. We discuss the necessary strategies required to steer future efforts
into successful experiments.Comment: 8 pages, 1 figure, 1 table, accepted for publication in A&
Aperture effects on the oxygen abundance determinations from CALIFA data
This paper aims at providing aperture corrections for emission lines in a
sample of spiral galaxies from the Calar Alto Legacy Integral Field Area Survey
(CALIFA) database. In particular, we explore the behavior of the
log([OIII]5007/Hbeta)/([NII]6583/Halpha) (O3N2) and log[NII]6583/Halpha (N2)
flux ratios since they are closely connected to different empirical
calibrations of the oxygen abundances in star forming galaxies.
We compute median growth curves of Halpha, Halpha/Hbeta, O3N2 and N2 up to
2.5R_50 and 1.5 disk R_eff. The growth curves simulate the effect of observing
galaxies through apertures of varying radii. The median growth curve of the
Halpha/Hbeta ratio monotonically decreases from the center towards larger
radii, showing for small apertures a maximum value of ~10% larger than the
integrated one. The median growth curve of N2 shows a similar behavior,
decreasing from the center towards larger radii. No strong dependence is seen
with the inclination, morphological type and stellar mass for these growth
curves. Finally, the median growth curve of O3N2 increases monotonically with
radius. However, at small radii it shows systematically higher values for
galaxies of earlier morphological types and for high stellar mass galaxies.
Applying our aperture corrections to a sample of galaxies from the SDSS
survey at 0.02<=z<=0.3 shows that the average difference between fiber-based
and aperture corrected oxygen abundances, for different galaxy stellar mass and
redshift ranges, reaches typically to ~11%, depending on the abundance
calibration used. This average difference is found to be systematically biased,
though still within the typical uncertainties of oxygen abundances derived from
empirical calibrations. Caution must be exercised when using observations of
galaxies for small radii (e.g. below 0.5R_eff) given the high dispersion shown
around the median growth curves.Comment: Accepted for publication in Ap
Surface density of the young cluster IC 348 in the Perseus molecular cloud
The IC 348 young star cluster contains more than 300 confirmed members. It is
embedded in the Perseus molecular cloud, making any clustering analysis subject
to an extinction bias. In this work, we derive the extinction map of the cloud
and revisit the content of IC 348 through a statistical approach that uses the
2MASS data. Our goal was to address the question of the completeness of IC 348
and of young clusters in general. We performed a combined analysis of the star
color and density in this region, in order to establish the surface density map
of the cluster. We reached the conclusion that IC 348 has structures up to 25'
from the cluster center, and we estimate that about 40 members brighter than
Ks=13 mag are still unidentified. Although we cannot use our statistical method
to identify these new members individually, the surface density map gives a
strong indication of their actual location. They are distributed in the outer
regions of the cluster, where very few dedicated observations have been made so
far, which is probably why they escaped previous identification. In addition,
we propose the existence of a new embedded cluster associated to the infrared
source MSX6C G160.2784-18.4216, about 38' south of IC 348.Comment: 5 pages, 5 figures, accepted for publication in A&
Identifying crop variants with high resistant starch content to maintain healthy glucose homeostasis
Identifying dietary tools that prevent disordered insulin secretion from pancreatic ÎČâcells is an attractive strategy to combat the increasing prevalence of type 2 diabetes. Dietary resistant starch has been linked to improvements in the function of ÎČâcells, possibly via increased colonic fermentation and production of shortâchain fatty acids (SCFAs). Increasing the resistant starch content of commonly consumed foods could therefore maintain glucose homeostasis at the population level. As part of Biotechnology and Biological Sciences Research Council (BBSRC) Diet and Health Research Industry Club (DRINC) initiative, variants of Pisum sativum L. (pea) are being investigated to identify the features of pea starch that make it resistant to digestion and available for colonic fermentation and SCFA production. Parallel in vitro and in vivo studies are being conducted using both whole pea seeds and pea flour to facilitate a better understanding of how cells in the pea cotyledons are affected by processing and, in turn, how this influences starch digestibility. Trials in human volunteers are being used to monitor a full spectrum of shortâ and longâterm physiological responses relevant to pancreatic ÎČâcell function and glucose homeostasis. This project is providing new insights into variants of crops that are associated with the specific types of resistant starch that provide the best protection against defects in insulin secretion and function
The hunt for extraterrestrial high-energy neutrino counterparts
The origin of Petaelectronvolt (PeV) astrophysical neutrinos is fundamental to our understanding of the high-energy Universe. Apart from the technical challenges of operating detectors deep below ice, oceans, and lakes, the phenomenological challenges are even greater than those of gravitational waves; the sources are unknown, hard to predict, and we lack clear signatures. Neutrino astronomy therefore represents the greatest challenge faced by the astronomy and physics communities thus far. The possible neutrino sources range from accretion disks and tidal disruption events, to relativistic jets and galaxy clusters with blazar TXS 0506+056 the most compelling association thus far. Since that association, immense effort has been put into proving or disproving that jets are indeed neutrino emitters, but to no avail. By generating simulated neutrino counterpart samples, we explore the potential of detecting a significant correlation of neutrinos with jets from active galactic nuclei. We find that, given the existing challenges, even our best experiments could not have produced a > 3Ï result. Larger programs over the next few years will be able to detect a significant correlation only if the brightest radio sources, rather than all jetted active galactic nuclei, are neutrino emitters. We discuss the necessary strategies required to steer future efforts into successful experiments. </p
High-Energy Polarimetry - a new window to probe extreme physics in AGN jets
The constantly improving sensitivity of ground-based and space-borne
observatories has made possible the detection of high-energy emission (X-rays
and gamma-rays) from several thousands of extragalactic sources. Enormous
progress has been made in measuring the continuum flux enabling us to perform
imaging, spectral and timing studies. An important remaining challenge for
high-energy astronomy is measuring polarization. The capability to measure
polarization is being realized currently at X-ray energies (e.g. with IXPE),
and sensitive gamma-ray telescopes capable of measuring polarization, such as
AMEGO, AdEPT, e-ASTROGAM, etc., are being developed. These future gamma-ray
telescopes will probe the radiation mechanisms and magnetic fields of
relativistic jets from active galactic nuclei at spatial scales much smaller
than the angular resolution achieved with continuum observations of the
instrument. In this white paper, we discuss the scientific potentials of
high-energy polarimetry, especially gamma-ray polarimetry, including the
theoretical implications, and observational technology advances being made. In
particular, we will explore the primary scientific opportunities and wealth of
information expected from synergy of multi-wavelength polarimetry that will be
brought to multi-messenger astronomy.Comment: submitted to Astro2020 (Astronomy and Astrophysics Decadal Survey
A combined radio and GeV Îł-ray view of the 2012 and 2013 flares of Mrk 421
In 2012 Markarian 421 underwent the largest flare ever observed in this blazar at radio frequencies. In the present study, we start exploring this unique event and compare it to a less extreme event in 2013. We use 15âGHz radio data obtained with the Owens Valley Radio Observatory 40-m telescope, 95âGHz millimetre data from the Combined Array for Research in Millimeter-Wave Astronomy, and GeV Îł-ray data from the Fermi Gamma-ray Space Telescope. The radio light curves during the flaring periods in 2012 and 2013 have very different appearances, in both shape and peak flux density. Assuming that the radio and Îł-ray flares are physically connected, we attempt to model the most prominent sub-flares of the 2012 and 2013 activity periods by using the simplest possible theoretical framework. We first fit a one-zone synchrotron self-Compton (SSC) model to the less extreme 2013 flare and estimate parameters describing the emission region. We then model the major Îł-ray and radio flares of 2012 using the same framework. The 2012 Îł-ray flare shows two distinct spikes of similar amplitude, so we examine scenarios associating the radio flare with each spike in turn. In the first scenario, we cannot explain the sharp radio flare with a simple SSC model, but we can accommodate this by adding plausible time variations to the Doppler beaming factor. In the second scenario, a varying Doppler factor is not needed, but the SSC model parameters require fine-tuning. Both alternatives indicate that the sharp radio flare, if physically connected to the preceding Îł-ray flares, can be reproduced only for a very specific choice of parameters
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