29 research outputs found
The Evolution of Molecular Gas Fraction Traced by the CO Tully-Fisher Relation
Carbon monoxide (CO) observations show a luminosityline-width correlation
that evolves with redshift. We present a method to use CO measurements alone to
infer the molecular gas fraction () and constrain the COH
conversion factor (). We compile from the literature spatially
integrated low- CO observations of six galaxy populations, including a total
of 449 galaxies between . The CO data of each population
provide an estimate of the -normalized mean molecular gas
fraction (). The redshift evolution of the
luminosityline-width correlation thus indicates an evolution of . We use a Bayesian-based Monte-Carlo Markov Chain sampler
to derive the posterior probability distribution functions of for these galaxy populations, accounting for random
inclination angles and measurement errors in the likelihood function. We find
that the molecular gas fraction evolves rapidly with redshift, with , for both normal star-forming and
starburst galaxies. Furthermore, the evolution trend agrees well with that
inferred from the Kennicutt-Schmidt relation and the star-forming main
sequence. Finally, at normal star-forming galaxies require a
larger than starburst galaxies to match their
molecular gas fractions, but at both star-forming types exhibit
sub-Galactic values and normal star-forming galaxies appear
more gas-rich than starbursts. Future applications of this method include
calibrating Tully-Fisher relations without inclination correction and inferring
the evolution of the atomic gas fraction with HI observations.Comment: 8 pages, 3 figures, 1 table. Accepted by ApJ Letter
Diversifying bioenergy crops increases yield and yield stability by reducing weed abundance
Relationships between species diversity, productivity, temporal stability of productivity, and plant invasion have been well documented in grasslands, and these relationships could translate to improved agricultural sustainability. However, few studies have explored these relationships in agricultural contexts where fertility and weeds are managed. Using 7 years of biomass yield and species composition data from 12 species mixture treatments varying in native species diversity, we found that species richness increased yield and interannual yield stability by reducing weed abundance. Stability was driven by yield as opposed to temporal variability of yield. Nitrogen fertilization increased yield but at the expense of yield stability. We show how relationships between diversity, species asynchrony, invasion, productivity, and stability observed in natural grasslands can extend into managed agricultural systems. Increasing bioenergy crop diversity can improve farmer economics via increased yield, reduced yield variability, and reduced inputs for weed control, thus promoting perennial vegetation on agricultural lands
The Subarcsecond Mid-Infrared View of Local Active Galactic Nuclei. IV. The L- and M-band Imaging Atlas
We present the largest currently existing subarcsecond 3-5 m atlas of
119 local () active galactic nuclei (AGN). This atlas includes AGN of
5 subtypes: 22 are Seyfert 1; 5 are intermediate Seyferts; 46 are Seyfert 2; 26
are LINERs; and 20 are composites/starbursts. Each AGN was observed with VLT
ISAAC in the - and/or -bands between 2000 and 2013. We detect at
3 confidence 92 sources in the -band and 83 sources in the -band.
We separate the flux into unresolved nuclear flux and resolved flux through
two-Gaussian fitting. We report the nuclear flux, extended flux, apparent size,
and position angle of each source, giving upper-limits for sources
which are undetected. Using WISE W1- and W2-band photometry we derive relations
predicting the nuclear and fluxes for Sy1 and Sy2 AGN based on their
W1-W2 color and WISE fluxes. Lastly, we compare the measured mid-infrared
colors to those predicted by dusty torus models SKIRTOR, CLUMPY, CAT3D, and
CAT3D-WIND, finding best agreement with the latter. We find that models
including polar winds best reproduce the 3-5m colors, indicating that
winds are an important component of dusty torus models. We find that several
AGN are bluer than models predict. We discuss several explanations for this and
find that it is most plausibly stellar light contamination within the ISAAC
-band nuclear fluxes.Comment: Main Text: 22 pages, 9 figures, 3 tables. Accepted by Ap
Why Chromatic Imaging Matters
During the last two decades, the first generation of beam combiners at the
Very Large Telescope Interferometer has proved the importance of optical
interferometry for high-angular resolution astrophysical studies in the near-
and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u-v
coverage per pointing increases significantly, providing an opportunity to use
reconstructed images as powerful scientific tools. Therefore, interferometric
imaging is already a key feature of the new generation of VLTI instruments, as
well as for other interferometric facilities like CHARA and JWST. It is thus
imperative to account for the current image reconstruction capabilities and
their expected evolutions in the coming years. Here, we present a general
overview of the current situation of optical interferometric image
reconstruction with a focus on new wavelength-dependent information,
highlighting its main advantages and limitations. As an Appendix we include
several cookbooks describing the usage and installation of several state-of-the
art image reconstruction packages. To illustrate the current capabilities of
the software available to the community, we recovered chromatic images, from
simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we
aim at showing the importance of selecting good regularization functions and
their impact on the reconstruction.Comment: Accepted for publication in Experimental Astronomy as part of the
topical collection: Future of Optical-infrared Interferometry in Europ
SDSS-IV MaNGA: Galaxy Pair Fraction and Correlated Active Galactic Nuclei
We have identified 105 galaxy pairs at z ~ 0.04 with the MaNGA integral-field
spectroscopic data. The pairs have projected separations between 1 kpc and 30
kpc, and are selected to have radial velocity offsets less than 600 km/s and
stellar mass ratio between 0.1 and 1. The pair fraction increases with both the
physical size of the integral-field unit and the stellar mass, consistent with
theoretical expectations. We provide the best-fit analytical function of the
pair fraction and find that ~3% of M* galaxies are in close pairs. For both
isolated galaxies and paired galaxies, active galactic nuclei (AGN) are
selected using emission-line ratios and H_alpha equivalent widths measured
inside apertures at a fixed physical size. We find AGNs in ~24% of the paired
galaxies and binary AGNs in ~13% of the pairs. To account for the selection
biases in both the pair sample and the MaNGA sample, we compare the AGN
comoving volume densities with those expected from the mass- and
redshift-dependent AGN fractions. We find a strong (~5x) excess of binary AGNs
over random pairing and a mild (~20%) deficit of single AGNs. The binary AGN
excess increases from ~2x to ~6x as the projected separation decreases from
10-30 kpc to 1-10 kpc. Our results indicate that pairing of galaxies preserves
the AGN duty cycle in individual galaxies but increases the population of
binary AGNs through correlated activities. We suggest tidally-induced
galactic-scale shocks and AGN cross-ionization as two plausible channels to
produce low-luminosity narrow-line-selected binary AGNs.Comment: ApJ in press. Matched to accepted version. The pair catalog is
provided in the Appendi
The dusty heart of Circinus II. Scrutinizing the LM-band dust morphology using MATISSE
In this paper we present the first-ever - and -band interferometric
observations of Circinus, building upon a recent -band analysis. We used
these observations to reconstruct images and fit Gaussian models to the and
bands. Our findings reveal a thin edge-on disk whose width is marginally
resolved and is the spectral continuation of the disk imaged in the band to
shorter wavelengths. Additionally, we find a point-like source in the and
bands that, based on the -band spectral energy distribution fit,
corresponds to the -band point source. We also demonstrate that there is no
trace of direct sightlines to hot dust surfaces in the circumnuclear dust
structure of Circinus. By assuming the dust is present, we find that
obscuration of A mag is necessary to reproduce the
measured fluxes. Hence, the imaged disk could play the role of the obscuring
"torus" in the unified scheme of active galactic nuclei. Furthermore, we
explored the parameter space of the disk + hyperbolic cone radiative transfer
models and identify a simple modification at the base of the cone. Adding a
cluster of clumps just above the disk and inside the base of the hyperbolic
cone provides a much better match to the observed temperature distribution in
the central aperture. This aligns well with the radiation-driven fountain
models that have recently emerged. Only the unique combination of sensitivity
and spatial resolution of the VLTI allows such models to be scrutinized and
constrained in detail. We plan to test the applicability of this detailed dust
structure to other MATISSE-observed active galactic nuclei in the future.Comment: Main article: 12 pages, 6 figures. Accepted for publication in A&A.
arXiv admin note: text overlap with arXiv:2205.0157
Grassland Resistance and Resilience after Drought Depends on Management Intensity and Species Richness
The degree to which biodiversity may promote the stability of grasslands in the light of climatic variability, such as prolonged summer drought, has attracted considerable interest. Studies so far yielded inconsistent results and in addition, the effect of different grassland management practices on their response to drought remains an open question. We experimentally combined the manipulation of prolonged summer drought (sheltered vs. unsheltered sites), plant species loss (6 levels of 60 down to 1 species) and management intensity (4 levels varying in mowing frequency and amount of fertilizer application). Stability was measured as resistance and resilience of aboveground biomass production in grasslands against decreased summer precipitation, where resistance is the difference between drought treatments directly after drought induction and resilience is the difference between drought treatments in spring of the following year. We hypothesized that (i) management intensification amplifies biomass decrease under drought, (ii) resistance decreases with increasing species richness and with management intensification and (iii) resilience increases with increasing species richness and with management intensification
Moving in the anthropocene: global reductions in terrestrial mammalian movements
Animal movement is fundamental for ecosystem functioning and species survival, yet the effects of the anthropogenic footprint on animal movements have not been estimated across species. Using a unique GPS-tracking database of 803 individuals across 57 species, we found that movements of mammals in areas with a comparatively high human footprint were on average one-half to one-third the extent of their movements in areas with a low human footprint. We attribute this reduction to behavioral changes of individual animals and to the exclusion of species with long-range movements from areas with higher human impact. Global loss of vagility alters a key ecological trait of animals that affects not only population persistence but also ecosystem processes such as predator-prey interactions, nutrient cycling, and disease transmission
Primate responses to changing environments in the anthropocene
Most primates have slow life-histories and long generation times. Because environmental change is occurring at an unprecedented rate, gene-based adaptations are unlikely to evolve fast enough to offer successful responses to these changes. The paper reviews the most common types of habitat/landscape alterations, the extent of human-primate interactions, and the impact of climate change. It demonstrates how understanding behavioural flexibility as a response to environmental change will be crucial to optimize conservation efforts by constructing informed management plans. Comparisons across species, space, and time can be used to draw generalizations about primate responses to environmental change while considering their behavioural flexibility