777 research outputs found
Morphology and Redshifts of Extremely Red Galaxies in the GOODS/CDFS deep ISAAC field
We present the photometric redshift distribution of a sample of 198 Extremely
Red Galaxies (ERGs) with Ks3.92 (Vega), selected by Roche et al.
in 50.4 sq. arcmin of the Chandra Deep Field South (CDFS). The sample has been
obtained using ISAAC-VLT and ACS-HST GOODS public data. We also show the
results of a morphological study of the 72 brightest ERGs in the z band (z<25,
AB).Comment: 2 pages, 2 figures. To appear in the proceedings of the ESO/USM/MPE
Workshop "Multiwavelength Mapping of Galaxy Formation and Evolution", Venice,
October 13-16, 200
The stellar mass function of the most massive galaxies at 3<=z<5 in the UKIDSS Ultra Deep Survey
We have analysed a sample of 1292 4.5 micron-selected galaxies at z>=3, over
0.6 square degrees of the UKIRT Infrared Deep Survey (UKIDSS) Ultra Deep Survey
(UDS). Using photometry from the U band through 4.5 microns, we have obtained
photometric redshifts and derived stellar masses for our sources. Only two of
our galaxies potentially lie at z>5. We have studied the galaxy stellar mass
function at 3<=z<5, based on the 1213 galaxies in our catalogue with [4.5]<=
24.0. We find that: i) the number density of M > 10^11 Msun galaxies increased
by a factor > 10 between z=5 and 3, indicating that the assembly rate of these
galaxies proceeded > 20 times faster at these redshifts than at 0<z<2; ii) the
Schechter function slope alpha is significantly steeper than that displayed by
the local stellar mass function, which is both a consequence of the steeper
faint end and the absence of a pure exponential decline at the high-mass end;
iii) the evolution of the comoving stellar mass density from z=0 to 5 can be
modelled as log10 (rho_M) =-(0.05 +/- 0.09) z^2 - (0.22 -/+ 0.32) z + 8.69. At
3 10^11 Msun galaxies would be missed by optical
surveys with R<27 or z<26. Thus, our study demonstrates the importance of deep
mid-IR surveys over large areas to perform a complete census of massive
galaxies at high z and trace the early stages of massive galaxy assembly.Comment: 16 pages, 15 figures, 2 tables. Accepted for publication in MNRA
The evolution of Ks-selected galaxies in the GOODS/CDFS deep ISAAC field
We present estimated redshifts and derived properties for a sample of 1663
galaxies with Ks <= 22 (Vega), selected from 50.4 sq.arcmin of the GOODS/CDFS
field with deep ISAAC imaging, and make an extensive comparison of their
properties with those of the extremely red galaxies (ERGs) selected in the same
field. We study in detail the evolution of Ks-selected galaxies up to redshifts
z ~ 4 and clarify the role of ERGs within the total Ks-band galaxy population.
We compute the total Ks-band luminosity function (LF) and compare its evolution
with the ERG LF. Up to =2.5, the bright end of the Ks-band LF shows no
sign of decline, and is progressively well reproduced by the ERGs with
increasing redshift. We also explore the evolution of massive systems present
in our sample: up to 20%-25% of the population of local galaxies with assembled
stellar mass M>1x10^11 Msun has been formed before redshift z ~ 4, and contains
~ 45% to 70% of the stellar mass density of the Universe at that redshift.
Within our sample, the comoving number density of these massive systems is then
essentially constant down to redshift z ~ 1.5, by which point most of them have
apparently evolved into (I-Ks)-selected ERGs. The remaining massive systems
observed in the local Universe are assembled later, at redshifts z <= 1.5. Our
results therefore suggest a two-fold assembly history for massive galaxies, in
which galaxy/star formation proceeds very efficiently in high mass haloes at
very high redshift.Comment: Revised version accepted by MNRAS. 17 pages, 15 figure
Species-Specific Diversity of a Fixed Motor Pattern: The Electric Organ Discharge of Gymnotus
Understanding fixed motor pattern diversity across related species provides a window for exploring the evolution of their underlying neural mechanisms. The electric organ discharges of weakly electric fishes offer several advantages as paradigmatic models for investigating how a neural decision is transformed into a spatiotemporal pattern of action. Here, we compared the far fields, the near fields and the electromotive force patterns generated by three species of the pulse generating New World gymnotiform genus Gymnotus. We found a common pattern in electromotive force, with the far field and near field diversity determined by variations in amplitude, duration, and the degree of synchronization of the different components of the electric organ discharges. While the rostral regions of the three species generate similar profiles of electromotive force and local fields, most of the species-specific differences are generated in the main body and tail regions of the fish. This causes that the waveform of the field is highly site dependant in all the studied species. These findings support a hypothesis of the relative separation of the electrolocation and communication carriers. The presence of early head negative waves in the rostral region, a species-dependent early positive wave at the caudal region, and the different relationship between the late negative peak and the main positive peak suggest three points of lability in the evolution of the electrogenic system: a) the variously timed neuronal inputs to different groups of electrocytes; b) the appearance of both rostrally and caudally innervated electrocytes, and c) changes in the responsiveness of the electrocyte membrane
Active Electric Imaging: Body-Object Interplay and Object's “Electric Texture”
This article deals with the role of fish's body and object's geometry on determining the image spatial shape in pulse Gymnotiforms. This problem was explored by measuring local electric fields along a line on the skin in the presence and absence of objects. We depicted object's electric images at different regions of the electrosensory mosaic, paying particular attention to the perioral region where a fovea has been described. When sensory surface curvature increases relative to the object's curvature, the image details depending on object's shape are blurred and finally disappear. The remaining effect of the object on the stimulus profile depends on the strength of its global polarization. This depends on the length of the object's axis aligned with the field, in turn depending on fish body geometry. Thus, fish's body and self-generated electric field geometries are embodied in this “global effect” of the object. The presence of edges or local changes in impedance at the nearest surface of closely located objects adds peaks to the image profiles (“local effect” or “object's electric texture”). It is concluded that two cues for object recognition may be used by active electroreceptive animals: global effects (informing on object's dimension along the field lines, conductance, and position) and local effects (informing on object's surface). Since the field has fish's centered coordinates, and electrosensory fovea is used for exploration of surfaces, fish fine movements are essential to perform electric perception. We conclude that fish may explore adjacent objects combining active movements and electrogenesis to represent them using electrosensory information
Expansion of the catalytic repertoire of alcohol dehydrogenases in plant metabolism
Medium-chain alcohol dehydrogenases (ADHs) comprise a highly conserved enzyme family that catalyse the reversible reduction of aldehydes. However, recent discoveries in plant natural product biosynthesis suggest that the catalytic repertoire of ADHs has been expanded. Here we report the crystal structure of dihydroprecondylocarpine acetate synthase (DPAS), an ADH that catalyses the non-canonical 1,4-reduction of an alpha,beta-unsaturated iminium moiety. Comparison with structures of plant-derived ADHs suggest the 1,4-iminium reduction does not require a proton relay or the presence of a catalytic zinc ion in contrast to canonical 1,2-aldehyde reducing ADHs that require the catalytic zinc and a proton relay. Furthermore, ADHs that catalysed 1,2-iminium reduction required the presence of the catalytic zinc and the loss of the proton relay. This suggests how the ADH active site can be modified to perform atypical carbonyl reductions, providing insight into how chemical reactions are diversified in plant metabolism
Residual layer ozone, mixing, and the nocturnal jet in California's San Joaquin Valley
The San Joaquin Valley of California is known for
excessive ozone air pollution owing to local production combined with
terrain-induced flow patterns that channel air in from the highly populated
San Francisco Bay area and stagnate it against the surrounding mountains.
During the summer, ozone violations of the National Ambient Air Quality
Standards (NAAQS) are notoriously common, with the San Joaquin Valley having
an average of 115 violations of the current 70 ppb standard each year
between 2012 and 2016. Because regional photochemical production peaks with
actinic radiation, most studies focus on the daytime, and consequently the
nocturnal chemistry and dynamics that contribute to these summertime high-ozone events are not as well elucidated. Here we investigate the hypothesis
that on nights with a strong low-level jet (LLJ), ozone in the residual
layer (RL) is more effectively mixed down into the nocturnal boundary layer
(NBL) where it is subject to dry deposition to the surface, the rate of
which is itself enhanced by the strength of the LLJ, resulting in lower
ozone levels the following day. Conversely, nights with a weaker LLJ will
sustain RLs that are more decoupled from the surface, retaining more ozone
overnight, and thus lead to more fumigation of ozone the following mornings,
giving rise to higher ozone concentrations the following afternoon. The
relative importance of this effect, however, is strongly dependent on the
net chemical overnight loss of Ox (here [Ox] ≡ [O3]
+ [NO2]), which we show is highly uncertain, without knowing the
ultimate chemical fate of the nitrate radical (NO3). We analyze
aircraft data from a study sponsored by the California Air Resources Board
(CARB) aimed at quantifying the role of RL ozone in the high-ozone
events in this area. By formulating nocturnal scalar budgets based on pairs
of consecutive flights (the first around midnight and the second just after
sunrise the following day), we estimate the rate of vertical mixing between
the RL and the NBL and thereby infer eddy diffusion coefficients in the top
half of the NBL. The average depth of the NBL observed on the 12 pairs of
flights for this study was 210( ± 50) m. Of the average −1.3 ppb h−1
loss of Ox in the NBL during the overnight hours from midnight
to 06:00 PST, −0.2 ppb h−1 was found to be due to horizontal advection,
−1.2 ppb h−1 due to dry deposition, −2.7 ppb h−1 to chemical loss
via nitrate production, and +2.8 ppb h−1 from mixing into the NBL
from the RL. Based on the observed gradients of Ox in the top half of
the NBL, these mixing rates yield eddy diffusivity estimates ranging from
1.1 to 3.5 m2 s−1, which are found to inversely correlate with the
following afternoon's ozone levels, providing support for our hypothesis.
The diffusivity values are approximately an order of magnitude larger than
the few others reported in the extant literature for the NBL, which further
suggests that the vigorous nature of nocturnal mixing in this region, due to
the LLJ, may have an important control on daytime ozone levels.
Additionally, we propose that the LLJ is a branch of what is colloquially
referred to as the Fresno eddy, which has been previously proposed to
recirculate pollutants. However, vertical mixing from the LLJ may counteract
this effect, which highlights the importance of studying the LLJ and Fresno
eddy as a single interactive system. The synoptic conditions that are
associated with strong LLJs are found to contain deeper troughs along the
California coastline. The LLJs observed during this study had an average
centerline height of 340 m, average speed of 9.9 m s−1 (σ = 3.1 m s−1),
and a typical peak timing around 23:00 PST. A total of 7 years of
915 MHz radioacoustic sounding system and surface air quality network data
show an inverse correlation between the jet strength and ozone the following
day, further suggesting that air quality models need to forecast the
strength of the LLJ in order to more accurately predict ozone violations.</p
Light-Scattering Observation Of Surface Acoustic Modes In High-Order Brillouin Zones Of A Si(001) Grating
In Brillouin light-scattering (BLS) measurements of an ion-milled Si(001) surface grating with grating wavelength Lambda(G) =0.35 mu m, we have observed numerous high-order zone-folded surface acoustic modes between the second and third zone boundaries associated with the grating. A surprisingly intense signal from a zone-folded longitudinal resonance was observed in the absence of direct hybridization with the Rayleigh modes. The relative intensities of all of the modes have been calculated by allowing for coupling between modes related by up to two grating reciprocal-lattice vectors, and for a grating profile with nonzero first and second Fourier amplitudes. The Fourier amplitudes inferred from the BLS measurements and calculations agree very well with those obtained from a direct measurement of the grating profile using atomic-force microscopy
A population of z> 2 far-infrared Herschel-spire-selected starbursts
We present spectroscopic observations for a sample of 36 Herschel-SPIRE
250-500um selected galaxies (HSGs) at 2<z<5 from the Herschel Multi-tiered
Extragalactic Survey (HerMES). Redshifts are confirmed as part of a large
redshift survey of Herschel-SPIRE-selected sources covering ~0.93deg^2 in six
extragalactic legacy fields. Observations were taken with the Keck I Low
Resolution Imaging Spectrometer (LRIS) and the Keck II DEep Imaging
Multi-Object Spectrograph (DEIMOS). Precise astrometry, needed for
spectroscopic follow-up, is determined by identification of counterparts at
24um or 1.4GHz using a cross-identification likelihood matching method.
Individual source luminosities range from log(L_IR/Lsun)=12.5-13.6
(corresponding to star formation rates 500-9000Msun/yr, assuming a Salpeter
IMF), constituting some of the most intrinsically luminous, distant infrared
galaxies yet discovered. We present both individual and composite rest-frame
ultraviolet spectra and infrared spectral energy distributions (SEDs). The
selection of these HSGs is reproducible and well characterized across large
areas of sky in contrast to most z>2 HyLIRGs in the literature which are
detected serendipitously or via tailored surveys searching only for high-z
HyLIRGs; therefore, we can place lower limits on the contribution of HSGs to
the cosmic star formation rate density at (7+-2)x10^(-3)Msun/yr h^3Mpc^(-3) at
z~2.5, which is >10% of the estimated total star formation rate density (SFRD)
of the Universe from optical surveys. The contribution at z~4 has a lower limit
of 3x10^(-3)Msun/yr h^3 Mpc^(-3), ~>20% of the estimated total SFRD. This
highlights the importance of extremely infrared-luminous galaxies with high
star formation rates to the build-up of stellar mass, even at the earliest
epochs.Comment: 25 pages, 10 figures; ApJ accepte
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