310 research outputs found
Development of high power transferred electron effect devices for X-band and Ku-band oscillators
High power transferred electron effect devices for superhigh frequency oscillator
Cluster galaxies 10 billion years ago
Cl J1449+0856 is a spectroscopically confirmed galaxy cluster at z ~ 2. The detection of a faint, extended X-ray emission, suggestive of an already evolved, partially relaxed structure, puts this system among the most distant "established” clusters rather than in the realm of z≳2 proto-clusters. This gives us a chance of studying galaxies in an evolved overdense environment very close to their formation epoch, and in particular to trace the evolution of early-type galaxies in clusters back to ten billion years ag
The [CII] 158 m emission line as a gas mass tracer in high redshift quiescent galaxies
Many efforts have been done in recent years to probe the gas fraction
evolution of massive quiescent galaxies (QGs); however, a clear picture has not
yet been established. Recent spectroscopic confirmations at z>3 offer the
chance to measure the residual gas reservoirs of massive galaxies a few
hundreds of Myr after their death and to study how fast quenching proceeds in a
highly star-forming Universe. Even so, stringent constraints at z2 remain
hardly accessible with ALMA when adopting molecular gas tracers commonly used
for the quenched population. In this letter, we propose overcoming this impasse
by using the carbon [CII] 158 m emission line to systematically probe the
gaseous budget of unlensed QGs at z>2.8, when these galaxies could still host
non-negligible star formation on an absolute scale and when the line becomes
best observable with ALMA (Bands 8 and 7). So far predominantly used for
star-forming galaxies, this emission line is the best choice to probe the gas
budget of spectroscopically confirmed QGs at , reaching 2-4 and 13-30
times deeper than dust continuum (ALMA band 7) and CO(2-1)/(1-0) (VLA
K-K bands), respectively, at fixed integration time. Exploiting
archival ALMA observations, we place conservative 3 upper limits on the
molecular gas fraction (f) of ADF22-QG1
(f<21%), ZF-COS-20115 (f<3.2%), two of the
best-studied high-z QGs in the literature, and GS-9209 (f<72%),
the most distant massive QG discovered to date. The deep upper limit found for
ZF-COS-20115 is 3 times lower than previously anticipated for high-z QGs
suggesting, at best, the existence of a large scatter in the f
distribution of the first QGs. Lastly, we discuss the current limitations of
the method and propose ways to mitigate some of them by exploiting ALMA bands 9
and 10.Comment: 7 pages, 2 figures. A&A Letters in pres
Formation epochs, star formation histories and sizes of massive early-type galaxies in cluster and field environments at z=1.2: insights from the rest-frame UV
We derive stellar masses, ages and star formation histories of massive
early-type galaxies in the z=1.237 RDCS1252.9-2927 cluster and compare them
with those measured in a similarly mass-selected sample of field contemporaries
drawn from the GOODS South Field. Robust estimates of these parameters are
obtained by comparing a large grid of composite stellar population models with
8-9 band photometry in the rest-frame NUV, optical and IR, thus sampling the
entire relevant domain of emission of the different stellar populations.
Additionally, we present new, deep -band photometry of both fields, giving
access to the critical FUV rest-frame, in order to constrain empirically the
dependence on the environment of the most recent star formation processes. We
find that early-type galaxies, both in the cluster and in the field, show
analogous optical morphologies, follow comparable mass vs. size relation, have
congruent average surface stellar mass densities and lie on the same Kormendy
relation. We also that a fraction of early-type galaxies in the field employ
longer timescales, , to assemble their mass than their cluster
contemporaries. Hence we conclude that, while the formation epoch of early-type
only depends on their mass, the environment does regulate the timescales of
their star formation histories. Our deep -band imaging strongly supports
this conclusions. It shows that cluster galaxies are at least 0.5 mag fainter
than their field contemporaries of similar mass and optical-to-infrared colors,
implying that the last episode of star formation must have happened more
recently in the field than in the cluster.Comment: 20pages, 10 figures. to appear on Ap
On the Initial Mass Function and tilt of the Fundamental Plane of massive early-type galaxies
We investigate the most plausible stellar Initial Mass Function (IMF) and the
main origin of the tilt of the Fundamental Plane (FP) for old, massive
early-type galaxies. We consider a sample of 13 bright galaxies of the Coma
cluster and combine our results with those obtained from a sample of 57 lens
galaxies in the same luminous mass range. We estimate the luminous mass and
stellar mass-to-light ratio values of the sample galaxies by fitting their SDSS
multi-band photometry with composite stellar population models computed with
different dust-free, solar-metallicity templates and IMFs. We compare these
measurements and those derived from two-component orbit-based dynamical
modelling. The photometric and dynamical luminous mass estimates of the
galaxies in our sample are consistent, within the errors, if a Salpeter IMF is
adopted. On the contrary, with a Kroupa or Chabrier IMF the two luminous mass
diagnostics differ at a more than 4 \sigma level. For the massive Coma
galaxies, their stellar mass-to-light ratio scales with luminous mass as the
corresponding effective quantities are observed to scale on the FP. This
indicates that the tilt of the FP is primarily caused by stellar population
properties. We conclude that old, massive lens and non-lens early-type galaxies
obey the same luminous and dynamical scaling relations, favour a Salpeter IMF,
and suggest a stellar population origin for the tilt of the FP. The validity of
these results for samples of early-type galaxies with different age and mass
properties still remains to be tested.Comment: 5 pages, 2 figures, accepted by MNRA
Star Formation Histories in a Cluster Environment at z~0.84
We present a spectrophotometric analysis of galaxies belonging to the
dynamically young, massive cluster RX J0152.7-1357 at z~0.84, aimed at
understanding the effects of the cluster environment on the star formation
history (SFH) of cluster galaxies and the assembly of the red-sequence (RS). We
use VLT/FORS spectroscopy, ACS/WFC optical and NTT/SofI near-IR data to
characterize SFHs as a function of color, luminosity, morphology, stellar mass,
and local environment from a sample of 134 spectroscopic members. In order to
increase the signal-to-noise, individual galaxy spectra are stacked according
to these properties. Moreover, the D4000, Balmer, CN3883, Fe4383 and C4668
indices are also quantified. The SFH analysis shows that galaxies in the blue
faint-end of the RS have on average younger stars (Delta t ~ 2 Gyr) than those
in the red bright-end. We also found, for a given luminosity range, differences
in age (Delta t ~ 0.5 - 1.3 Gyr) as a function of color, indicating that the
intrinsic scatter of the RS may be due to age variations. Passive galaxies in
the blue faint-end of the RS are preferentially located in the low density
areas of the cluster, likely being objects entering the RS from the "blue
cloud". It is likely that the quenching of the star formation of these RS
galaxies is due to interaction with the intracluster medium. Furthermore, the
SFH of galaxies in the RS as a function of stellar mass reveals signatures of
"downsizing" in the overall cluster.Comment: 36 pages, 5 tables, 14 figures. Accepted for publication in The
Astrophysical Journa
CBLAST-Low 2001 pilot study mooring deployment cruise and data report ; FV Nobska, June 4 to August 17, 2001
During the summer of 2001, several moorings and cruises were used as part of the CBLAST-Low (Coupled Boundary Layer Air-Sea
Transfer under low wind conditions) pilot experiment in the North Atlantic, south of Martha’s Vineyard Island, MA, USA. Six
subsurface tide gauges were deployed around the study site for a period of approximately 3 months during the summer of 2001.
Further, two surface buoys equipped with meteorological instrumentation and subsurface arrays that measured temperature,
conductivity and velocity were deployed during the months of July and August 2001. For a short intensive operating period during
July 2001, a newly manufactured three-dimensional mooring designed to sample three-dimensional properties of the upper ocean was
deployed for a period of 6 days. During the Intensive Operating Period (IOP) along-shelf and across-shelf
conductivity-temperature-depth (CTD) sections were completed as well as a drifting array designed to passively collect data from the
upper water column released for approximately 24 hours. This report describes the instrumentation and type of moorings deployed by
the Woods Hole Oceanographic Institution Upper Ocean Processes (WHOI UOP) group as well as data return and quality from the
CBLAST-Low 2001 pilot study. This is summarized in graphical and tabular form in this report.Funding provided by the Office of Naval Research under Contract No. N00014-01-1-0029
and from the Secretary of the Navy / CNO Chair Grant No. N00014-99-1-0090
The Red Sequence of High-Redshift Clusters: a Comparison with Cosmological Galaxy Formation Models
We compare the results from a semi-analytic model of galaxy formation with
spectro-photometric observations of distant galaxy clusters observed in the
range 0.8< z< 1.3. We investigate the properties of their red sequence (RS)
galaxies and compare them with those of the field at the same redshift. In our
model we find that i) a well-defined, narrow RS is obtained already by z= 1.2;
this is found to be more populated than the field RS, analogously to what
observed and predicted at z=0; ii) the predicted U-V rest-frame colors and
scatter of the cluster RS at z=1.2 have average values of 1 and 0.15
respectively, with a cluster-to-cluster variance of 0.2 and 0.06, respectively.
The scatter of the RS of cluster galaxies is around 5 times smaller than the
corresponding field value; iii) when the RS galaxies are considered, the mass
growth histories of field and cluster galaxies at z=1.2 are similar, with 90 %
of the stellar mass of RS galaxies at z=1.2 already formed at cosmic times
t=2.5 Gyr, and 50 % at t=1 Gyr; v) the predicted distribution of stellar ages
of RS galaxies at z=1.2 peaks at 3.7 Gyr for both cluster and field
populations; however, for the latter the distribution is significantly skewed
toward lower ages. When compared with observations, the above findings show an
overall consistency, although the average value 0.07 of the observed cluster RS
scatter (U-V colors) at z=1.2 is smaller than the corresponding model central
value. We discuss the physical origin and the significance of the above results
in the framework of cosmological galaxy formation.Comment: 14 pages, accepted for publication in ApJ. Updated one referenc
Multi-wavelength study of XMMU J2235.3-2557: the most massive galaxy cluster at z > 1
[Abridged] XMMU J2235.3-2557 is one of the most distant X-ray selected
clusters, spectroscopically confirmed at z=1.39. We characterize the galaxy
populations of passive members, the thermodynamical properties of the hot gas,
its metal abundance and the total mass of the system using imaging data with
HST/ACS (i775 and z850 bands) and VLT/ISAAC (J and K_s bands), extensive
spectroscopic data obtained with VLT/FORS2, and deep Chandra observations. Out
of a total sample of 34 spectroscopically confirmed cluster members, we
selected 16 passive galaxies within the central 2' (or 1 Mpc) with ACS
coverage, and inferred star formation histories for a sub-sample of galaxies
inside and outside the core by modeling their spectro-photometric data with
spectral synthesis models, finding a strong mean age radial gradient. Chandra
data show a regular elongated morphology, closely resembling the distribution
of core galaxies, with a significant cool core. We measure a global X-ray
temperature of kT=8.6(-1.2,+1.3) keV (68% c.l.). By detecting the rest-frame
6.7 keV Iron K line, we measure a metallicty Z= 0.26(+0.20,-0.16) Zsun. In the
likely hypothesis of hydrostatic equilibrium, we obtain a total mass of Mtot(<1
Mpc)=(5.9+-1.3)10^14 Msun. Overall, our analysis implies that XMM2235 is the
hottest and most massive bona-fide cluster discovered to date at z>1, with a
baryonic content, both its galaxy population and intra-cluster gas, in a
significantly advanced evolutionary stage at 1/3 of the current age of the
Universe.Comment: 9 pages, 8 figures, accepted for publication in A&A (v2:
typos/language style corrections, updated references
Soil Phosphorus Uptake by Continuously Cropped Lupinus albus: A New Microcosm Design
When grown in soils with sparingly available phosphorus (P), white lupin (Lupinus albus L.) forms special root structures, called cluster roots, which secrete large amounts of organic acids and concomitantly acidify the rhizosphere. Many studies dealing with the understanding of this P acquisition strategy have been performed in short time experiments either in hydroponic cultures or in small microcosm designs with sand or sand:soil mixtures. In the present study, we applied an experimental design which came nearer to the natural field conditions: we performed a one-year experiment on large microcosms containing 7kg of soil and allowing separation of rhizosphere soil and bulk soil. We planted six successive generations of lupins and analysed P uptake, organic P desorption, phosphatase activities and organic acid concentrations in different soil samples along a spatio-temporal gradient. We compared the rhizosphere soil samples of cluster (RSC) and non-cluster roots (RSNC) as well as the bulk soil (BS) samples. A total shoot biomass of 55.69 ± 1.51g(d.w.)y−1 was produced and P uptake reached 220.59 ± 5.99mgy−1. More P was desorbed from RSC than from RSNC or BS (P < 0.05). RSC and RSNC showed a higher activity of acid and alkaline phosphatases than BS samples and a higher acid phosphatase activity was observed in RSC than in RSNC throughout the one-year experiment. Fumarate was the most abundant organic acid in all rhizosphere soil samples. Citrate was only present in detectable amounts in RSC while malate and fumarate were recovered from both RSC and RSNC. Almost no organic acids could be detected in the BS samples. Our results demonstrated that over a one-year cultivation period in the absence of an external P supply, white lupin was able to acquire phosphate from the soil and that the processes leading to this P uptake took place preferentially in the rhizosphere of cluster root
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