3,945 research outputs found
Assessing the Impact of Retreat Mechanisms in a Simple Antarctic Ice Sheet Model Using Bayesian Calibration
The response of the Antarctic ice sheet (AIS) to changing climate forcings is
an important driver of sea-level changes. Anthropogenic climate change may
drive a sizeable AIS tipping point response with subsequent increases in
coastal flooding risks. Many studies analyzing flood risks use simple models to
project the future responses of AIS and its sea-level contributions. These
analyses have provided important new insights, but they are often silent on the
effects of potentially important processes such as Marine Ice Sheet Instability
(MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well
justified and result in more parsimonious and transparent model structures.
This raises the question of how this approximation impacts hindcasts and
projections. Here, we calibrate a previously published and relatively simple
AIS model, which neglects the effects of MICI and regional characteristics,
using a combination of observational constraints and a Bayesian inversion
method. Specifically, we approximate the effects of missing MICI by comparing
our results to those from expert assessments with more realistic models and
quantify the bias during the last interglacial when MICI may have been
triggered. Our results suggest that the model can approximate the process of
MISI and reproduce the projected median melt from some previous expert
assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the
observed data during the last interglacial period and our mean projection is
roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year
2100. These results suggest that missing MICI and/or regional characteristics
can lead to a low-bias during warming period AIS melting and hence a potential
low-bias in projected sea levels and flood risks.Comment: v1: 16 pages, 4 figures, 7 supplementary files; v2: 15 pages, 4
figures, 7 supplementary files, corrected typos, revised title, updated
according to revisions made through publication proces
Variable Hard X-ray Emission from the Candidate Accreting Black Hole in Dwarf Galaxy Henize 2-10
We present an analysis of the X-ray spectrum and long-term variability of the
nearby dwarf starburst galaxy Henize 2-10. Recent observations suggest that
this galaxy hosts an actively accreting black hole with mass ~10^6 M_sun. The
presence of an AGN in a low-mass starburst galaxy marks a new environment for
active galactic nuclei (AGNs), with implications for the processes by which
"seed" black holes may form in the early Universe. In this paper, we analyze
four epochs of X-ray observations of Henize 2-10, to characterize the long-term
behavior of its hard nuclear emission. We analyze observations with Chandra
from 2001 and XMM-Newton from 2004 and 2011, as well as an earlier, less
sensitive observation with ASCA from 1997. Based on detailed analysis of the
source and background, we find that the hard (2-10 keV) flux of the putative
AGN has decreased by approximately an order of magnitude between the 2001
Chandra observation and exposures with XMM-Newton in 2004 and 2011. The
observed variability confirms that the emission is due to a single source. It
is unlikely that the variable flux is due to a supernova or ultraluminous X-ray
source, based on the observed long-term behavior of the X-ray and radio
emission, while the observed X-ray variability is consistent with the behavior
of well-studied AGNs.Comment: 7 pages, 4 figures, 2 tables; accepted for publication in Ap
Progress and bottlenecks in the early domestication of the perennial oilseed Silphium integrifolium, a sunflower substitute
Silflower (Silphium integrifolium Michx.) is in the early stages of domestication as a perennial version of oilseed sunflower, its close relative. Grain crops with deep perennial root systems will provide farmers with new alternatives for managing soil moisture and limiting or remediating soil erosion, fertilizer leaching, and loss of soil biota. Several cycles of selection for increased seed production potential following initial germplasm evaluation in 2002 have provided opportunities to document the botany and ecology of this relatively obscure species, to compare agronomic practices for improving its propagation and management, and to evaluate the differences between semi-domesticated and wild accessions that have accrued over this time through intentional and unintentional genetic processes. Key findings include: domestication has increased aboveground biomass at seedling and adult stages; seed yield has increased more, achieving modest improvement in harvest index. Harvest index decreases with nitrogen fertilization. Silflower acquires nitrogen and water from greater depth than typical crops. In agricultural silflower stands within its native range, we found that Puccinia silphii (rust) and Eucosma giganteana (moth) populations build up to unacceptable levels, but we also found genetic variation for traits contributing to resistance or tolerance. Breeding or management for reduced height and vegetative plasticity should be top priorities for future silflower research outside its native range.Fil: Vilela, Alejandra Elena. Museo PaleontolĂłgico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: González Paleo, Luciana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Museo PaleontolĂłgico Egidio Feruglio; ArgentinaFil: Turner, Kathryn. The Land Institute; Estados UnidosFil: Peterson, Kelsey. The Land Institute; Estados UnidosFil: Ravetta, Damián AndrĂ©s. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Museo PaleontolĂłgico Egidio Feruglio; ArgentinaFil: Crews, Timothy E.. The Land Institute; Estados UnidosFil: Van Tassel, David. The Land Institute; Estados Unido
Caucasian Infants’ Attentional Orienting to Own- and Other-Race Faces
Infants show preferential attention toward faces and detect faces embedded within complex naturalistic scenes. Newborn infants are insensitive to race, but rapidly develop differential processing of own- and other-race faces. In the present study, we investigated the development of attentional orienting toward own- and other-race faces embedded within naturalistic scenes. Infants aged six-, nine- and twelve-months did not show differences in the speed of orienting to own- and other race faces, but other-race faces held infants’ visual attention for longer. We also found a clear developmental progression in attentional capture and holding, with older infants orienting to faces faster and fixating them for longer. Results are interpreted within the context of the two-process model of face processing
Global Properties of Neutral Hydrogen in Compact Groups
Compact groups of galaxies provide a unique environment to study the
evolution of galaxies amid frequent gravitational encounters. These nearby
groups have conditions similar to those in the earlier universe when galaxies
were assembled and give us the opportunity to witness hierarchical formation in
progress. To understand how the compact group environment affects galaxy
evolution, we examine the gas and dust in these groups. We present new
single-dish GBT neutral hydrogen (HI) observations of 30 compact groups and
define a new way to quantify the group HI content as the HI-to-stellar mass
ratio of the group as a whole. We compare the HI content with mid-IR indicators
of star formation and optical [g-r] color to search for correlations between
group gas content and star formation activity of individual group members.
Quiescent galaxies tend to live in HI-poor groups, and galaxies with active
star formation are more commonly found in HI-rich groups. Intriguingly, we also
find "rogue" galaxies whose star formation does not correlate with group HI
content. In particular, we identify three galaxies (NGC 2968 in RSCG 34, KUG
1131+202A in RSCG 42, and NGC 4613 in RSCG 64) whose mid-IR activity is
discrepant with the HI. We speculate that this mismatch between mid-IR activity
and HI content is a consequence of strong interactions in this environment that
can strip HI from galaxies and abruptly affect star-formation. Ultimately,
characterizing how and on what timescales the gas is processed in compact
groups will help us understand the interstellar medium in complex, dense
environments similar to the earlier Universe.Comment: Accepted to A
The Infrared Properties of Super Star Clusters: Predictions from Three-Dimensional Radiative Transfer Models
With high-resolution infrared data becoming available that can probe the
formation of high-mass stellar clusters for the first time, models that make
testable predictions of these objects are necessary. We utilize a
three-dimensional radiative transfer code, including a hierarchically clumped
medium, to study the earliest stages of super star cluster evolution. We
explore a range of parameter space in geometric sequences that mimic the
evolution of an embedded super star cluster. The inclusion of a hierarchically
clumped medium can make the envelope porous, in accordance with previous models
and supporting observational evidence. The infrared luminosity inferred from
observations can differ by a factor of two from the true value in the clumpiest
envelopes depending on the viewing angle. The infrared spectral energy
distribution also varies with viewing angle for clumpy envelopes, creating a
range in possible observable infrared colors and magnitudes, silicate feature
depths and dust continua. General observable features of cluster evolution
differ between envelopes that are relatively opaque or transparent to
mid-infrared photons. The [70]-[160] color can be used to determine star
formation efficiency; the Spitzer IRAC/MIPS [8.0]-[24] color is able to
constrain Rin and Rout values; and the IRAC [3.6]-[5.8] color is sensitive to
the fraction of the dust distributed in clumps. Finally, in a comparison of
these models to data of ultracompact HII regions, we find good agreement,
suggesting that these models are physically relevant, and will provide useful
diagnostic ability for datasets of resolved, embedded SSCs with the advent of
high-resolution infrared telescopes like JWST.Comment: ApJ, accepted, to be published in the 729 -1 issue. 17 pages with 18
figure
The Importance of Nebular Continuum and Line Emission in Observations of Young Massive Star Clusters
In this spectroscopic study of infant massive star clusters, we find that
continuum emission from ionized gas rivals the stellar luminosity at optical
wavelengths. In addition, we find that nebular line emission is significant in
many commonly used broad-band HST filters including the F814W I-band, the F555W
V-band and the F435W B-band. Two young massive clusters (YMCs) in NGC 4449 were
targeted for spectroscopic observations after Reines et al. (2008a) discovered
an F814W I-band excess in their photometric study of radio-detected clusters in
the galaxy. The spectra were obtained with the Dual Imaging Spectrograph on the
3.5 m APO telescope. We supplement these data with HST and SDSS photometry. By
comparing our data to the Starburst99 and GALEV models, we find that nebular
continuum emission competes with the stellar light in our observations and that
the relative contribution is largest in the U- and I-bands, where the Balmer
and Paschen jumps are located. The spectra also exhibit strong line emission
including the [SIII] 9069,9532 lines in the HST F814W I-band. We find that the
combination of nebular continuum and line emission can account for the F814W
I-band excess found by Reines et al. (2008a). In an effort to provide a
benchmark for estimating the impact of ionized gas emission on photometric
observations of YMCs, we compute the relative contributions of the stellar
continuum, nebular continuum, and emission lines to the total flux of a 3
Myr-old cluster through various HST filter/instrument combinations, including
filters in the WFC3. We urge caution when comparing observations of YMCs to
evolutionary synthesis models since nebular emission can have a large impact on
magnitudes and colors of young (< 5 Myr) clusters, significantly affecting
inferred properties such as ages, masses and extinctions. (Abridged)Comment: 13 pages, 11 figures, Accepted for Publication in Ap
- …