Models of biogenic carbon (BC) flux assume that short herbivorous food chains lead to high export, whereas complex microbial or omnivorous food webs lead to recycling and low export, and that export ...of BC from the euphotic zone equals new production (NP). In the Gulf of St. Lawrence, particulate organic carbon fluxes were similar during the spring phytoplankton bloom, when herbivory dominated, and during nonbloom conditions, when microbial and omnivorous food webs dominated. In contrast, NP was 1.2 to 161 times greater during the bloom than after it. Thus, neither food web structure nor NP can predict the magnitude or patterns of BC export, particularly on time scales over which the ocean is in nonequilibrium conditions.
Among radio galaxies containing nuclear dust disks, the bipolar jet axis is generally observed to be perpendicular to the disk major axis. The FR I radio source 3C 449 is an outlier to this ...statistical majority, as it possesses a nearly parallel jet/disk orientation on the sky. We examine the 600 pc dusty disk in this galaxy with images from the Hubble Space Telescope. We find that a 1.6 km/0.7 km color map of the disk exhibits a twist in its isocolor contours (isochromes). We model the color map by integrating galactic starlight through an absorptive disk and find that the anomalous twist in the isochromes can be reproduced in the model with a vertically thin, warped disk. The model predicts that the disk is nearly perpendicular to the jet axis within 100 pc of the nucleus. We discuss physical mechanisms capable of causing such a warp. We show that precessional models or a torque on the disk arising from a possible binary black hole in the AGN causes precession on a timescale that is too long to account for the predicted disk morphology. However, we estimate that the pressure in the X-ray-emitting interstellar medium is large enough to perturb the disk, and we argue that jet-driven anisotropy in the excited ISM may be the cause of the warp. In this way, the warped disk in 3C 449 may be a new manifestation of feedback from an active galactic nucleus.
It was recently proposed that there is, in the pelagic environment, a continuum of trophic pathways ranging from the herbivorous food web to the multivorous food web, the microbial food web and the ...microbial loop. It was also suggested that combining specific ecological ratios could provide a way of assessing the dominance of planktonic food webs by specific trophic pathways. Three large data sets, collected in different but adjacent marine systems (the Scotian Shelf, off eastern Canada; the Gulf of St Lawrence; and nearshore waters of the Baie des Chaleurs, in the northwestern Gulf), are used to compute two ratios: small-sized (<5 μm) to large-sized (>5 μm) particulate phytoplankton production, and phaeopigments in small- to phaeopigments in large-sized particles. By combining the two ecological ratios it is possible to delineate successfully, in each studied system, coherent periods during the year; to interpret the combined ratios in terms of dominance by specific trophic pathways; and to show that the interpretation is consistent with additional information collected in the three systems.
We report ALMA Early Science observations of the A1835 brightest cluster galaxy (BCG) in the CO (3-2) and CO (1-0) emission lines. We detect 5 × 1010 M of molecular gas within 10 kpc of the BCG. Its ...ensemble velocity profile width of ~130 km s-1 FWHM is too narrow for the molecular clouds to be supported in the galaxy by dynamic pressure. The gas may instead be supported in a rotating, turbulent disk oriented nearly face-on. Roughly 1010 M of molecular gas is projected 3-10 kpc to the northwest and to the east of the nucleus with line-of-sight velocities lying between -250 km s-1 and 480 km s-1 with respect to the systemic velocity. The high-velocity gas may be either inflowing or outflowing. However, the absence of high-velocity gas toward the nucleus that would be expected in a steady inflow, and its bipolar distribution on either side of the nucleus, are more naturally explained as outflow. Star formation and radiation from the active galactic nucleus (AGN) are both incapable of driving an outflow of this magnitude. The location of the high-velocity gas projected behind buoyantly rising X-ray cavities and favorable energetics suggest an outflow driven by the radio AGN. If so, the molecular outflow may be associated with a hot outflow on larger scales reported by Kirkpatrick and colleagues. The molecular gas flow rate of approximately 200 M yr-1 is comparable to the star formation rate of 100-180 M yr-1 in the central disk. How radio bubbles would lift dense molecular gas in their updrafts, how much gas will be lost to the BCG, and how much will return to fuel future star formation and AGN activity are poorly understood. Our results imply that radio-mechanical (radio-mode) feedback not only heats hot atmospheres surrounding elliptical galaxies and BCGs, but it is able to sweep higher density molecular gas away from their centers.
We present 19 nearby (z < 0.3) 3CR radio galaxies imaged at low and high excitation as part of a Cycle 15 Hubble Space Telescope (HST) snapshot survey with the Advanced Camera for Surveys (ACS). ...These images consist of exposures of the H{alpha} (6563 A, plus N II contamination) and O III{lambda}5007 emission lines using narrowband linear ramp filters adjusted according to the redshift of the target. To facilitate continuum subtraction, a single-pointing 60 s line-free exposure was taken with a mediumband filter appropriate for the target's redshift. We discuss the steps taken to reduce these images independently of the automated recalibration pipeline so as to use more recent ACS flat-field data as well as to better reject cosmic rays. We describe the method used to produce continuum-free (pure line-emission) images, and present these images along with qualitative descriptions of the narrow-line region morphologies we observe. We present H{alpha}+N II and O III line fluxes from aperture photometry, finding the values to fall expectedly on the redshift-luminosity trend from a past HST/WFPC2 emission line study of a larger, generally higher redshift subset of the 3CR. We also find expected trends between emission line luminosity and total radio power, as well as a positive correlation between the size of the emission line region and redshift. We discuss the associated interpretation of these results, and conclude with a summary of future work enabled by this data set.
While supermassive black holes (BHs) are widely observed in the nearby and
distant universe, their origin remains debated with two viable formation
scenarios with light and heavy seeds. In the light ...seeding model, the first BHs
form from the collapse of massive stars with masses of $10-100 \
\rm{M_{\odot}}$, while the heavy seeding model posits the formation of
$10^{4-5} \ \rm{M_{\odot}}$ seeds from direct collapse. The detection of BHs at
redshifts $z\gtrsim10$, edging closer to their formation epoch, provides
critical observational discrimination between these scenarios. Here, we focus
on the JWST-detected galaxy, GHZ 9, at $z\approx10$ that is lensed by the
foreground cluster, Abell 2744. Based on 2.1 Ms deep Chandra observations, we
detect a candidate X-ray AGN, which is spatially coincident with the
high-redshift galaxy, GHZ 9. The BH candidate is inferred to have a bolometric
luminosity of $(1.0^{+0.5}_{-0.4})\times10^{46} \ \rm{erg \ s^{-1}}$, which
corresponds to a BH mass of $(8.0^{+3.7}_{-3.2})\times10^7 \ \rm{M_{\odot}}$
assuming Eddington-limited accretion. This extreme mass at such an early cosmic
epoch suggests the heavy seed origin for this BH candidate. Based on the
Chandra and JWST discoveries of extremely high-redshift quasars, we have
constructed the first simple AGN luminosity function extending to $z\approx10$.
Comparison of this luminosity function with theoretical models indicates an
over-abundant $z\approx10$ BH population, consistent with a
higher-than-expected seed formation efficiency.
Omega-3 fatty acids (n-3 PUFAs) are essential for the functional maturation of the brain. Westernization of dietary habits in both developed and developing countries is accompanied by a progressive ...reduction in dietary intake of n-3 PUFAs. Low maternal intake of n-3 PUFAs has been linked to neurodevelopmental diseases in Humans. However, the n-3 PUFAs deficiency-mediated mechanisms affecting the development of the central nervous system are poorly understood. Active microglial engulfment of synapses regulates brain development. Impaired synaptic pruning is associated with several neurodevelopmental disorders. Here, we identify a molecular mechanism for detrimental effects of low maternal n-3 PUFA intake on hippocampal development in mice. Our results show that maternal dietary n-3 PUFA deficiency increases microglia-mediated phagocytosis of synaptic elements in the rodent developing hippocampus, partly through the activation of 12/15-lipoxygenase (LOX)/12-HETE signaling, altering neuronal morphology and affecting cognitive performance of the offspring. These findings provide a mechanistic insight into neurodevelopmental defects caused by maternal n-3 PUFAs dietary deficiency.
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