38 research outputs found
Measuring the Surface Thermal Structure of the Sea off Brittany by Ship and Aircraft
During the months of September and October 1975 the âLaboratoire d âOcĂŠanographie Physique de lâUniversitĂŠ de Bretagne Occidentaleâ (LOP) and the âLaboratoire de MĂŠtĂŠorologie Dynamique du C.N.R.S.â (LMD) made a joint study of surface temperatures and their variability over the continental plateau off the westernmost point of Brittany. Between 18 September and 28 October scientists from the LOP made several trips aboard the oceanographic vessel Capricorne operating a sonde for in-situ T.S.D. measurements. The LMD utilized an Aries radiometer which they themselves had designed and perfected. This was installed aboard a DC-3 aircraft that also carried pressure, humidity and temperature sensors. Our two objectives were as follows : 1. To compare the results obtained by two different techniques; 2. To obtain details of certain aspects of the microstructure of the sea surface, in particular over a frontal region. This paper thus proposes : a) To compare the results of the bathysonde measurements carried out by the LOP on Capricorne with those of a team from the â Centre OcĂŠanologique de Bretagne" (COB) embarked in the oceanographic vessel Cry os from 16 to 29 September 1975. b) To present charts derived from radiometric measurements and to compare these charts with previous ones. c) To present aspects of the fine thermal structure at the surface from a certain number of radial passes with the DC-3
AEGIS: Infrared Spectral Energy Distributions of MIPS 70micron selected sources
We present 0.5 -160 micron Spectral Energy Distributions (SEDs) of galaxies,
detected at 70microns with the Multiband Imaging Photometer for Spitzer (MIPS),
using broadband imaging data from Spitzer and ground-based telescopes.
Spectroscopic redshifts, in the range 0.2<z<1.5, have been measured as part of
the Deep Extragalactic Evolutionary Probe2 (DEEP2) project. Based on the SEDs
we explore the nature and physical properties of the sources. Using the optical
spectra we derive Hbeta and [OII]-based Star Formation Rates (SFR) which are
10-100 times lower than SFR estimates based on IR and radio. The median offset
in SFR between optical and IR is reduced by a factor of ~3 when we apply a
typical extinction corrections. We investigate mid-to-far infrared correlations
for low redshift (>0.5) and high redshift (0.5<z<1.2) bins. Using this unique
``far-infrared'' selected sample we derive an empirical mid to far-infrared
relationship that can be used to estimate the infrared energy budget of
galaxies in the high-redshift universe. Our sample can be used as a template to
translate far-infrared luminosities into bolometric luminosities for high
redshift objects.Comment: 4 pages, 5 figures, accepted for publication in AEGIS ApJL Special
Issu
3D Quantification of Ultrasound Images: Application to Mouse Embryo Imaging In Vivo
International audienceHigh frequency ultrasound imaging has become an effective tool for anatomical mice studies. This work is focused on 3D quantification of mouse embryo development to extract pertinent information of its evolution. A series of B-Scan ultrasound images was acquired at different spatial positions along the embryo. A 3D deformable model was used to segment the images. A pregnant female mouse at embryonic day 14.5 was imaged with an ATL HDI 5000, 7-15MHz linear array. The probe was moved by a step by step motor along the abdomen of the mouse. 3D segmentation results are presented including volume quantification of the embryo
Spitzer IRS Spectra of Optically Faint Infrared Sources with Weak Spectral Features
Spectra have been obtained with the low-resolution modules of the Infrared
Spectrograph (IRS) on the Spitzer Space Telescope (Spitzer) for 58 sources
having f(24 micron) > 0.75 mJy. Sources were chosen from a survey of
8.2 deg within the NOAO Deep Wide-Field Survey region in Bootes (NDWFS)
using the Multiband Imaging Photometer (MIPS) on the Spitzer Space Telescope.
Most sources are optically very faint (I > 24mag). Redshifts have previously
been determined for 34 sources, based primarily on the presence of a deep 9.7
micron silicate absorption feature, with a median z of 2.2. Spectra are
presented for the remaining 24 sources for which we were previously unable to
determine a confident redshift because the IRS spectra show no strong features.
Optical photometry from the NDWFS and infrared photometry with MIPS and the
Infrared Array Camera on the Spitzer Space Telescope (IRAC) are given, with K
photometry from the Keck I telescope for some objects. The sources without
strong spectral features have overall spectral energy distributions (SEDs) and
distributions among optical and infrared fluxes which are similar to those for
the sources with strong absorption features. Nine of the 24 sources are found
to have feasible redshift determinations based on fits of a weak silicate
absorption feature. Results confirm that the "1 mJy" population of 24 micron
Spitzer sources which are optically faint is dominated by dusty sources with
spectroscopic indicators of an obscured AGN rather than a starburst. There
remain 14 of the 58 sources observed in Bootes for which no redshift could be
estimated, and 5 of these sources are invisible at all optical wavelengths.Comment: Accepted by Ap
The star formation history of mass-selected galaxies in the COSMOS field
We explore the evolution of the specific star formation rate (SSFR) for
3.6um-selected galaxies of different M_* in the COSMOS field. The average SFR
for sub-sets of these galaxies is estimated with stacked 1.4GHz radio continuum
emission. We separately consider the total sample and a subset of galaxies (SF)
that shows evidence for substantive recent star formation in the rest-frame
optical SED. At 0.2<z<3 both populations show a strong and M_*-independent
decrease in their SSFR towards z=0.2, best described by a power- law (1+z)^n,
where n~4.3 for all galaxies and n~3.5 for SF sources. The decrease appears to
have started at z>2, at least above 4x10^10M_Sun where our conclusions are most
robust. We find a tight correlation with power-law dependence, SSFR (M_*)^beta,
between SSFR and M_* at all z. It tends to flatten below ~10^10M_Sun if
quiescent galaxies are included; if they are excluded a shallow index beta_SFG
-0.4 fits the correlation. On average, higher M_* objects always have lower
SSFRs, also among SF galaxies. At z>1.5 there is tentative evidence for an
upper SSFR-limit that an average galaxy cannot exceed. It is suggested by a
flattening of the SSFR-M_* relation (also for SF sources), but affects massive
(>10^10M_Sun) galaxies only at the highest z. Below z=1.5 there thus is no
direct evidence that galaxies of higher M_* experience a more rapid waning of
their SSFR than lower M_* SF systems. In this sense, the data rule out any
strong 'downsizing'. We combine our results with recent measurements of the
galaxy (stellar) mass function in order to determine the characteristic mass of
a SF galaxy (M_*=10^(10.6\pm0.4)M_Sun). In this sense, too, there is no
'downsizing'. Our analysis constitutes the most extensive SFR density
determination with a single technique to z=3. Recent Herschel results are
consistent with our results, but rely on far smaller samples.Comment: 37 pages, 14 figures, 7 tables; accepted for publication in the
Astrophysical Journal; High resolution versions of all figures available at
www.mpia-hd.mpg.de/homes/karim/research.htm
Spitzer IRS 16 micron Observations of the GOODS Fields
We present Spitzer 16 micron imaging of the Great Observatories Origins Deep
Survey (GOODS) fields. We survey 150 square arcminutes in each of the two GOODS
fields (North and South), to an average 3 sigma depth of 40 and 65 micro-Jy
respectively. We detect about 1300 sources in both fields combined. We validate
the photometry using the 3-24 micron spectral energy distribution of stars in
the fields compared to Spitzer spectroscopic templates. Comparison with ISOCAM
and AKARI observations in the same fields show reasonable agreement, though the
uncertainties are large. We provide a catalog of photometry, with sources cross
correlated with available Spitzer, Chandra, and HST data. Galaxy number counts
show good agreement with previous results from ISOCAM and AKARI, with improved
uncertainties. We examine the 16 to 24 micron flux ratio and find that for most
sources it lies within the expected locus for starbursts and infrared luminous
galaxies. A color cut of S_{16}/S_{24}>1.4 selects mostly sources which lie at
1.1<z<1.6, where the 24 micron passband contains both the redshifted 9.7 micron
silicate absorption and the minimum between PAH emission peaks. We measure the
integrated galaxy light of 16 micron sources, and find a lower limit on the
galaxy contribution to the extragalactic background light at this wavelength to
be 2.2\pm 0.2$ nW m^{-2} sr^{-1}.Comment: Accepted for Publication in the AJ. 53 preprint pages, including 15
figures and 8 tables. Table 1-4 are truncated in the ms.tex but are included
in full in the tar file (and will be available in the online version of the
AJ
The Evolution of the Star Formation Rate of Galaxies at 0.0 < z < 1.2
We present the 24 micron rest-frame luminosity function (LF) of star-forming
galaxies in the redshift range 0.0 < z < 0.6 constructed from 4047
spectroscopic redshifts from the AGN and Galaxy Evolution Survey of 24 micron
selected sources in the Bootes field of the NOAO Deep Wide-Field Survey. This
sample provides the best available combination of large area (9 deg^2), depth,
and statistically complete spectroscopic observations, allowing us to probe the
evolution of the 24 micron LF of galaxies at low and intermediate redshifts
while minimizing the effects of cosmic variance. In order to use the observed
24 micron luminosity as a tracer for star formation, active galactic nuclei
(AGNs) that could contribute significantly at 24 micron are identified and
excluded from our star-forming galaxy sample based on their mid-IR spectral
energy distributions or the detection of X-ray emission. The evolution of the
24 micron LF of star-forming galaxies for redshifts of z < 0.65 is consistent
with a pure luminosity evolution where the characteristic 24 micron luminosity
evolves as (1+z)^(3.8+/-0.3). We extend our evolutionary study to encompass 0.0
< z < 1.2 by combining our data with that of the Far-Infrared Deep
Extragalactic Legacy Survey. Over this entire redshift range the evolution of
the characteristic 24 micron luminosity is described by a slightly shallower
power law of (1+z)^(3.4+/-0.2). We find a local star formation rate density of
(1.09+/-0.21) x 10^-2 Msun/yr/Mpc^-3, and that it evolves as (1+z)^(3.5+/-0.2)
over 0.0 < z < 1.2. These estimates are in good agreement with the rates using
optical and UV fluxes corrected for the effects of intrinsic extinction in the
observed sources. This agreement confirms that star formation at z <~ 1.2 is
robustly traced by 24 micron observations and that it largely occurs in
obscured regions of galaxies. (Abridged)Comment: ApJ, in press, 16 pages 9 figure
Spectroscopy of luminous z>7 galaxy candidates and sources of contamination in z>7 galaxy searches
We present three bright z+ dropout candidates selected from deep
Near-Infrared (NIR) imaging of the COSMOS 2 square degree field. All three
objects match the 0.8-8um colors of other published z>7 candidates but are
three magnitudes brighter, facilitating further study. Deep spectroscopy of two
of the candidates covering 0.64-1.02um with Keck-DEIMOS and all three covering
0.94-1.10um and 1.52-1.80um with Keck-NIRSPEC detects weak spectral features
tentatively identified as Ly-alpha at z=6.95 and z=7.69 in two of the objects.
The third object is placed at z~1.6 based on a 24um and weak optical detection.
A comparison with the spectral energy distributions of known z<7 galaxies,
including objects with strong spectral lines, large extinction, and large
systematic uncertainties in the photometry yields no objects with similar
colors. However, the lambda>1um properties of all three objects can be matched
to optically detected sources with photometric redshifts at z~1.8, so the
non-detection in the i+ and z+ bands are the primary factors which favors a z>7
solution. If any of these objects are at z~7 the bright end of the luminosity
function is significantly higher at z>7 than suggested by previous studies, but
consistent within the statistical uncertainty and the dark matter halo
distribution. If these objects are at low redshift, the Lyman-Break selection
must be contaminated by a previously unknown population of low redshift objects
with very strong breaks in their broad band spectral energy distributions and
blue NIR colors. The implications of this result on luminosity function
evolution at high redshift is discussed. We show that the primary limitation of
z>7 galaxy searches with broad filters is the depth of the available optical
data.Comment: 15 Pages, 15 figures, accepted to Ap
Bars in early- and late-type disks in COSMOS
We investigate the (large-scale) bar fraction in a mass-complete sample of M
> 10^10.5 Msun disk galaxies at 0.2 < z < 0.6 in the COSMOS field. The fraction
of barred disks strongly depends on mass, disk morphology, and specific star
formation rate (SSFR). At intermediate stellar mass (10^10.5 < M < 10^11 Msun)
the bar fraction in early-type disks is much higher, at all redshifts, by a
factor ~2, than that in late-type disks. This trend is reversed at higher
stellar mass (M > 10^11 Msun), where the fraction of bars in early-type disks
becomes significantly lower, at all redshifts, than that in late-type disks.
The bar fractions for galaxies with low and high SSFRs closely follow those of
the morphologically-selected early-type and late-type populations,
respectively. This indicates a close correspondence between morphology and SSFR
in disk galaxies at these earlier epochs. Interestingly, the total bar fraction
in 10^10.5 < M < 10^11 Msun disks is built up by a factor of ~2 over the
redshift interval explored, while for M > 10^11 Msun disks it remains roughly
constant. This indicates that, already by z ~ 0.6, spectral and morphological
transformations in the most massive disk galaxies have largely converged to the
familiar Hubble sequence that we observe in the local Universe, while for
intermediate mass disks this convergence is ongoing until at least z ~ 0.2.
Moreover, these results highlight the importance of employing mass-limited
samples for quantifying the evolution of barred galaxies. Finally, the
evolution of the barred galaxy populations investigated does not depend on the
large-scale environmental density (at least, on the scales which can be probed
with the available photometric redshifts).Comment: 10 pages, 4 figures, updated to reflect version accepted by MNRA