785 research outputs found
Ly-alpha emitters: blue dwarfs or supermassive ULIRGs? Evidence for a transition with redshift
The traditional view that Ly-alpha emission and dust should be mutually
exclusive has been questioned more and more often; most notably, the
observations of Ly-alpha emission from ULIRGs seem to counter this view. In
this paper we seek to address the reverse question. How large a fraction of
Ly-alpha selected galaxies are ULIRGs? Using two samples of 24/25 Ly-alpha
emitting galaxies at z = 0.3/2.3, we perform this test, including results at z
= 3.1, and find that, whereas the ULIRG fraction at z = 3.1 is very small, it
systematically increases towards lower redshifts. There is a hint that this
evolution may be quite sudden and that it happens around a redshift of z ~ 2.5.
After measuring the infrared luminosities of the Ly-alpha emitters, we find
that they are in the normal to ULIRG range in the lower redshift sample, while
the higher redshift galaxies all have luminosities in the ULIRG category. The
Ly-alpha escape fractions for these infrared bright galaxies are in the range
1-100 % in the z = 0.3 galaxies, but are very low in the z = 2.3 galaxies, 0.4
% on average. The unobscured star formation rates are very high, ranging from
500 to more than 5000 M_sun/yr, and the dust attenuation derived are in the
range 0.0 < A_V < 3.5.Comment: 5 pages, 5 figures, 1 table, published in A&A, 508, L2
Infrared Imaging of GRB 970508
We have observed the field of the gamma-ray burst GRB 970508 at infrared wavelengths (2.2 μm) and have found a variable source coincident with the visible transient thought to be associated with the burst. The source was decaying in brightness with Ks magnitudes of 18.2±0.1, 18.8±0.1, and 19.0±0.3 mag on May 13.25, 16.25, and 20.21 UT, respectively. A 1 σ upper limit of K=21.3 mag was obtained for the brightness of the source on June 14.27 UT. The infrared light curve during this period is consistent with a ~t^(-1.2) power law, similar to the visible light curve. We do not find evidence for extended structure around the burst, as has been claimed for GRB 970228, and we obtain an upper limit of 0.04L_* for the luminosity of an underlying galaxy at the position of the infrared transient
Application of Resonance Perturbation Theory to Dynamics of Magnetization in Spin Systems Interacting with Local and Collective Bosonic Reservoirs
We apply our recently developed resonance perturbation theory to describe the
dynamics of magnetization in paramagnetic spin systems interacting
simultaneously with local and collective bosonic environments. We derive
explicit expressions for the evolution of the reduced density matrix elements.
This allows us to calculate explicitly the dynamics of the macroscopic
magnetization, including characteristic relaxation and dephasing time-scales.
We demonstrate that collective effects (i) do not influence the character of
the relaxation processes but merely renormalize the relaxation times, and (ii)
significantly modify the dephasing times, leading in some cases to a
complicated (time inhomogeneous) dynamics of the transverse magnetization,
governed by an effective time-dependent magnetic field
What fraction of stars formed in infrared galaxies at high redshift?
Star formation happens in two types of environment: ultraviolet-bright
starbursts (like 30 Doradus and HII galaxies at low redshift and Lyman-break
galaxies at high redshift) and infrared-bright dust-enshrouded regions (which
may be moderately star-forming like Orion in the Galaxy or extreme like the
core of Arp 220). In this work I will estimate how many of the stars in the
local Universe formed in each type of environment, using observations of
star-forming galaxies at all redshifts at different wavelengths and of the
evolution of the field galaxy population.Comment: 7 pages, 0 figs, to appear in proceedings of "Starbursts - From 30
Doradus to Lyman break galaxies", edited by Richard de Grijs and Rosa M.
Gonzalez Delgado, published by Kluwe
Assessment of spatio-temporal vegetation dynamics in tropical arid ecosystem of India using MODIS time-series vegetation indices
In the present study, we analyzed spatio-temporal vegetation dynamics to identify and delineate the vegetation stress zones in
tropical arid ecosystem of Anantapuramu district, Andhra Pradesh, India, using Normalized Difference Vegetation Index
(NDVI), Vegetation Condition Index (VCI), and Vegetation Anomaly Index (VAI) derived from time-series Moderate
Resolution Imaging Spectroradiometer (MODIS) 16-day products (MOD13Q1) at 250 m spatial resolution for the growing
season (June to September) of 19 years during 2000 to 2018. The 1-month Standardized Precipitation Index (SPI) was computed
for 30 years (1989 to 2018) to quantify the precipitation deficit/surplus regions and assess its influence on vegetation dynamics.
The growing season mean NDVI and VCI were correlated with growing season mean 1-month SPI of dry (2003) and wet (2007)
years to analyze the spatio-temporal vegetation dynamics. The correlation analysis between SPI and NDVI for dry year (2003)
showed strong positive correlation (r = 0.89). Analysis of VAI for dry year (2003) indicates that the central, western, and southwestern
parts of the district reported high vegetation stress with VAI of less than − 2.0. This might be due to the fact that central
and south-western parts of the district are more prone to droughts than the other parts of the district. The correlation analysis of
SPI, NDVI, and VCI distinctly shows the impact of rainfall on vegetation dynamics. The study clearly demonstrates the
robustness of NDVI, VCI, and VAI derived from time-series MODIS data in monitoring the spatio-temporal vegetation dynamics
and delineate vegetation stress zones in tropical arid ecosystem of India
Development of a novel 3D culture system for screening features of a complex implantable device for CNS repair
Tubular scaffolds which incorporate a variety of micro- and nanotopographies have a wide application potential in tissue engineering especially for the repair of spinal cord injury (SCI). We aim to produce metabolically active differentiated tissues within such tubes, as it is crucially important to evaluate the biological performance of the three-dimensional (3D) scaffold and optimize the bioprocesses for tissue culture. Because of the complex 3D configuration and the presence of various topographies, it is rarely possible to observe and analyze cells within such scaffolds in situ. Thus, we aim to develop scaled down mini-chambers as simplified in vitro simulation systems, to bridge the gap between two-dimensional (2D) cell cultures on structured substrates and three-dimensional (3D) tissue culture. The mini-chambers were manipulated to systematically simulate and evaluate the influences of gravity, topography, fluid flow, and scaffold dimension on three exemplary cell models that play a role in CNS repair (i.e., cortical astrocytes, fibroblasts, and myelinating cultures) within a tubular scaffold created by rolling up a microstructured membrane. Since we use CNS myelinating cultures, we can confirm that the scaffold does not affect neural cell differentiation. It was found that heterogeneous cell distribution within the tubular constructs was caused by a combination of gravity, fluid flow, topography, and scaffold configuration, while cell survival was influenced by scaffold length, porosity, and thickness. This research demonstrates that the mini-chambers represent a viable, novel, scale down approach for the evaluation of complex 3D scaffolds as well as providing a microbioprocessing strategy for tissue engineering and the potential repair of SCI
The Cosmic Far-Infrared Background Buildup Since Redshift 2 at 70 and 160 microns in the COSMOS and GOODS fields
The Cosmic Far-Infrared Background (CIB) at wavelengths around 160 {\mu}m
corresponds to the peak intensity of the whole Extragalactic Background Light,
which is being measured with increasing accuracy. However, the build up of the
CIB emission as a function of redshift, is still not well known. Our goal is to
measure the CIB history at 70 {\mu}m and 160 {\mu}m at different redshifts, and
provide constraints for infrared galaxy evolution models. We use complete deep
Spitzer 24 {\mu}m catalogs down to about 80 {\mu}Jy, with spectroscopic and
photometric redshifts identifications, from the GOODS and COSMOS deep infrared
surveys covering 2 square degrees total. After cleaning the Spitzer/MIPS 70
{\mu}m and 160 {\mu}m maps from detected sources, we stacked the far-IR images
at the positions of the 24 {\mu}m sources in different redshift bins. We
measured the contribution of each stacked source to the total 70 and 160 {\mu}m
light, and compare with model predictions and recent far-IR measurements made
with Herschel/PACS on smaller fields. We have detected components of the 70 and
160 {\mu}m backgrounds in different redshift bins up to z ~ 2. The contribution
to the CIB is maximum at 0.3 <= z <= 0.9 at 160{\mu}m (and z <= 0.5 at 70
{\mu}m). A total of 81% (74%) of the 70 (160) {\mu}m background was emitted at
z < 1. We estimate that the AGN relative contribution to the far-IR CIB is less
than about 10% at z < 1.5. We provide a comprehensive view of the CIB buildup
at 24, 70, 100, 160 {\mu}m. IR galaxy models predicting a major contribution to
the CIB at z < 1 are in agreement with our measurements, while our results
discard other models that predict a peak of the background at higher redshifts.
Our results are available online http://www.ias.u-psud.fr/irgalaxies/ .Comment: Accepted in Astronomy & Astrophysic
The SED of Low-Luminosity AGNs at high-spatial resolution
The inner structure of AGNs is expected to change below a certain luminosity
limit. The big blue bump, footprint of the accretion disk, is absent for the
majority of low-luminosity AGNs (LLAGNs). Moreover, recent simulations suggest
that the torus, a keystone in the Unified Model, vanishes for nuclei with L_bol
< 10^42 erg/s. However, the study of LLAGN is a complex task due to the
contribution of the host galaxy, which light swamps these faint nuclei. This is
specially critical in the IR range, at the maximum of the torus emission, due
to the contribution of the old stellar population and/or dust in the nuclear
region. Adaptive optics imaging in the NIR (VLT/NaCo) together with diffraction
limited imaging in the mid-IR (VLT/VISIR) permit us to isolate the nuclear
emission for some of the nearest LLAGNs in the Southern Hemisphere. These data
were extended to the optical/UV range (HST), radio (VLA, VLBI) and X-rays
(Chandra, XMM-Newton, Integral), in order to build a genuine spectral energy
distribution (SED) for each AGN with a consistent spatial resolution (< 0.5")
across the whole spectral range. From the individual SEDs, we construct an
average SED for LLAGNs sampled in all the wavebands mentioned before. Compared
with previous multiwavelength studies of LLAGNs, this work covers the mid-IR
and NIR ranges with high-spatial resolution data. The LLAGNs in the sample
present a large diversity in terms of SED shapes. Some of them are very well
described by a self-absorbed synchrotron (e.g. NGC 1052), while some other
present a thermal-like bump at ~1 micron (NGC 4594). All of them are
significantly different when compared with bright Seyferts and quasars,
suggesting that the inner structure of AGNs (i.e. the torus and the accretion
disk) suffers intrinsic changes at low luminosities.Comment: 8 pages, 5 figures. To appear in the proceedings of "Astrophysics at
High Angular Resolution" (AHAR 2011
The role of the LIRG and ULIRG phases in the evolution of Ks-selected galaxies
We investigate the role of the luminous infrared galaxy (LIRG) and
ultra-luminous infrared galaxy (ULIRG) phases in the evolution of Ks-selected
galaxies and, in particular, Extremely Red Galaxies (ERGs). With this aim, we
compare the properties of a sample of 2905 Ks<21.5 (Vega mag) galaxies in the
GOODS/CDFS with the sub-sample of those 696 sources which are detected at 24
microns. We find that LIRGs constitute 30% of the galaxies with stellar mass
M>1x10^{11} Msun assembled at redshift z=0.5. A minimum of 65% of the galaxies
with M>2.5x10^{11} Msun at z~2-3 are ULIRGs at those redshifts. 60% of the
ULIRGs in our sample have the characteristic colours of ERGs. Conversely, 40%
of the ERGs with stellar mass M>1.3x10^{11} Msun at 1.5<z<2.0 and a minimum of
52% of those with the same mass cut at 2.0<z<3.0 are ULIRGs. The average
optical/near-IR properties of the massive ERGs at similar redshifts that are
identified with ULIRGs and that are not have basically no difference,
suggesting that both populations contain the same kind of objects in different
phases of their lives.
LIRGs and ULIRGs have an important role in galaxy evolution and mass
assembly, and, although they are only able to trace a fraction of the massive
(M>1x10^{11} Msun) galaxies present in the Universe at a given time, this
fraction becomes very significant (>50%) at redshifts z>~2.Comment: Accepted for publication in A&A. 9 pages, 6 figure
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