877 research outputs found
VLA 1.4GHz observations of the GOODS-North Field: Data Reduction and Analysis
We describe deep, new, wide-field radio continuum observations of the Great
Observatories Origins Deep Survey -- North (GOODS-N) field. The resulting map
has a synthesized beamsize of ~1.7" and an r.m.s. noise level of ~3.9uJy/bm
near its center and ~8uJy/bm at 15', from phase center. We have cataloged 1,230
discrete radio emitters, within a 40' x 40' region, above a 5-sigma detection
threshold of ~20uJy at the field center. New techniques, pioneered by Owen &
Morrison (2008), have enabled us to achieve a dynamic range of 6800:1 in a
field that has significantly strong confusing sources. We compare the 1.4-GHz
(20-cm) source counts with those from other published radio surveys. Our
differential counts are nearly Euclidean below 100uJy with a median source
diameter of ~1.2". This adds to the evidence presented by Owen & Morrison
(2008) that the natural confusion limit may lie near ~1uJy. If the Euclidean
slope of the counts continues down to the natural confusion limit as an
extrapolation of our log N - log S, this indicates that the cutoff must be
fairly sharp below 1uJy else the cosmic microwave background temperature would
increase above 2.7K at 1.4 GHz.Comment: Accepted for publication in ApJS. 16 pages, 19 figures. Radio data
and source list can be found at http://www.ifa.hawaii.edu/~morrison/GOODSN
Dust Obscuration in Lyman Break Galaxies at z~4
Measuring star formation rates (SFRs) in high-z galaxies with their
rest-frame ultraviolet (UV) continuum can be uncertain because of dust
obscuration. Prior studies had used the submillimeter emission at 850 um to
determine the intrinsic SFRs of rest-frame UV selected galaxies, but the
results suffered from the low sensitivity and poor resolution (~15''). Here, we
use ultradeep Very Large Array 1.4 GHz images with ~1''-2'' resolutions to
measure the intrinsic SFRs. We perform stacking analyses in the radio images
centered on ~3500 Lyman break galaxies (LBGs) at z~4 in the Great Observatories
Origins Deep Survey-North and South fields selected with Hubble Space
Telescope/Advanced Camera for Surveys data. The stacked radio flux is very low,
0.08+/-0.15 uJy, implying a mean SFR of 6+/-11 M/yr. This is comparable to the
uncorrected mean UV SFRs of 5 M/yr, implying that the z~4 LBGs have little dust
extinction. The low SFR and dust extinction support the previous results that
z~4 LBGs are in general not submillimeter galaxies. We further show that there
is no statistically significant excess of dust-hidden star-forming components
within ~22 kpc from the LBGs.Comment: 6 pages, 3 figures, and 2 tables. Accepted to the Astrophysical
Journal (ApJ
Regulatory Considerations in the Design and Manufacturing of Implantable 3DâPrinted Medical Devices
Threeâdimensional (3D) printing, or additive manufacturing, technology has rapidly penetrated the medical device industry over the past several years, and innovative groups have harnessed it to create devices with unique composition, structure, and customizability. These distinctive capabilities afforded by 3D printing have introduced new regulatory challenges. The customizability of 3Dâprinted devices introduces new complexities when drafting a design control model for FDA consideration of market approval. The customizability and unique build processes of 3Dâprinted medical devices pose unique challenges in meeting regulatory standards related to the manufacturing quality assurance. Consistent material powder properties and optimal printing parameters such as build orientation and laser power must be addressed and communicated to the FDA to ensure a quality build. Postprinting considerations unique to 3Dâprinted devices, such as cleaning, finishing and sterilization are also discussed. In this manuscript we illustrate how such regulatory hurdles can be navigated by discussing our experience with our group's 3Dâprinted bioresorbable implantable device.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/115990/1/cts12315.pd
Multicolour correlative imaging using phosphor probes
Correlative light and electron microscopy exploits the advantages of optical methods, such as multicolour probes and their use in hydrated live biological samples, to locate functional units, which are then correlated with structural details that can be revealed by the superior resolution of electron microscopes. One difficulty is locating the area imaged by the electron beam in the much larger optical field of view. Multifunctional probes that can be imaged in both modalities and thus register the two images are required. Phosphor materials give cathodoluminescence (CL) optical emissions under electron excitation. Lanthanum phosphate containing thulium or terbium or europium emits narrow bands in the blue, green and red regions of the CL spectrum; they may be synthesised with very uniform-sized crystals in the 10- to 50-nm range. Such crystals can be imaged by CL in the electron microscope, at resolutions limited by the particle size, and with colour discrimination to identify different probes. These materials also give emissions in the optical microscope, by
multiphoton excitation. They have been deposited on the surface of glioblastoma cells and imaged by CL. Gadolinium oxysulphide doped with terbium emits green photons by either ultraviolet or electron excitation. Sixty-nanometre crystals of this phosphor have been imaged in the atmospheric scanning electron microscope (JEOL ClairScope). This probe and microscope combination allow correlative imaging in hydrated samples. Phosphor probes should prove to be very useful in correlative light and electron microscopy, as fiducial
markers to assist in image registration, and in high/super resolution imaging studies
The Cluster of Galaxies Surrounding Cygnus A
We report optical imaging and spectroscopy of 41 galaxies in a 22 arcmin
square region surrounding Cygnus A. The results show that there is an extensive
rich cluster associated with Cygnus A of Abell richness at least 1 and possibly
as high as 4. The velocity histogram has two peaks, one centered on Cygnus A,
and a more significant peak redshifted by about 2060 km/s from the velocity of
Cygnus A. The dynamical centroid of the spatial distribution is also shifted
somewhat to the NW. However, statistical tests show only weak evidence that
there are two distinct clusters. The entire system has a velocity dispersion of
1581 km/s which is slightly larger than other, well studied, examples of rich
clusters.Comment: 11 pages LaTeX, 1 table, 3 postscript figures. Accepted for
publication in Ap.J. Letter
The Herschel view of the dominant mode of galaxy growth from z=4 to the present day
We present an analysis of the deepest Herschel images in four major extragalactic fields GOODS-North, GOODS-South, UDS and COSMOS obtained within the GOODS-Herschel and CANDELS-Herschel key programs. The picture provided by 10497 individual far-infrared detections is supplemented by the stacking analysis of a mass-complete sample of 62361 star-forming galaxies from the CANDELS-HST H band-selected catalogs and from two deep ground-based Ks band-selected catalogs in the GOODS-North and the COSMOS-wide fields, in order to obtain one of the most accurate and unbiased understanding to date of the stellar mass growth over the cosmic history. We show, for the first time, that stacking also provides a powerful tool to determine the dispersion of a physical correlation and describe our method called "scatter stacking" that may be easily generalized to other experiments. We demonstrate that galaxies of all masses from z=4 to 0 follow a universal scaling law, the so-called main sequence of star-forming galaxies. We find a universal close-to-linear slope of the logSFR-logM* relation with evidence for a flattening of the main sequence at high masses (log(M*/Msun) > 10.5) that becomes less prominent with increasing redshift and almost vanishes by z~2. This flattening may be due to the parallel stellar growth of quiescent bulges in star-forming galaxies. Within the main sequence, we measure a non varying SFR dispersion of 0.3 dex. The specific SFR (sSFR=SFR/M*) of star-forming galaxies is found to continuously increase from z=0 to 4. Finally we discuss the implications of our findings on the cosmic SFR history and show that more than 2/3 of present-day stars must have formed in a regime dominated by the main sequence mode. As a consequence we conclude that, although omnipresent in the distant Universe, galaxy mergers had little impact in shaping the global star formation history over the last 12.5 Gyr
Polycyclic Aromatic Hydrocarbon and Mid-Infrared Continuum Emission in a z > 4 Submillimeter Galaxy
We report the detection of 6.2 ÎŒm polycyclic aromatic hydrocarbon (PAH) and rest-frame 4-7 ÎŒm continuum emission in the z = 4.055 submillimeter galaxy GN20, using the Infrared Spectrograph on board the Spitzer Space Telescope. This represents the first detection of PAH emission at z > 4. The strength of the PAH emission feature is consistent with a very high star formation rate of ~1600 Mâ yr^(â1). We find that this intense starburst powers at least ~1/3 of the faint underlying 6 ÎŒm continuum emission, with an additional, significant (and perhaps dominant) contribution due to a power-law-like hot dust source, which we interpret to likely be a faint, dust-obscured active galactic nucleus (AGN). The inferred 6 ÎŒm AGN continuum luminosity is consistent with a sensitive upper limit on the hard X-ray emission as measured by the Chandra X-Ray Observatory if the previously undetected AGN is Compton-thick. This is in agreement with the finding at optical/infrared wavelengths that the galaxy and its nucleus are heavily dust-obscured. Despite the strong power-law component enhancing the mid-infrared continuum emission, the intense starburst associated with the photon-dominated regions that give rise to the PAH emission appears to dominate the total energy output in the infrared. GN20 is one of the most luminous starburst galaxies known at any redshift, embedded in a rich protocluster of star-forming galaxies. This investigation provides an improved understanding of the energy sources that power such exceptional systems, which represent the extreme end of massive galaxy formation at early cosmic times
Early Science with the Large Millimeter Telescope: COOL BUDHIES I - a pilot study of molecular and atomic gas at z~0.2
An understanding of the mass build-up in galaxies over time necessitates
tracing the evolution of cold gas (molecular and atomic) in galaxies. To that
end, we have conducted a pilot study called CO Observations with the LMT of the
Blind Ultra-Deep H I Environment Survey (COOL BUDHIES). We have observed 23
galaxies in and around the two clusters Abell 2192 (z = 0.188) and Abell 963 (z
= 0.206), where 12 are cluster members and 11 are slightly in the foreground or
background, using about 28 total hours on the Redshift Search Receiver (RSR) on
the Large Millimeter Telescope (LMT) to measure the CO J = 1 --> 0
emission line and obtain molecular gas masses. These new observations provide a
unique opportunity to probe both the molecular and atomic components of
galaxies as a function of environment beyond the local Universe. For our sample
of 23 galaxies, nine have reliable detections (S/N3.6) of the CO
line, and another six have marginal detections (2.0 < S/N < 3.6). For the
remaining eight targets we can place upper limits on molecular gas masses
roughly between and . Comparing our results to other
studies of molecular gas, we find that our sample is significantly more
abundant in molecular gas overall, when compared to the stellar and the atomic
gas component, and our median molecular gas fraction lies about above
the upper limits of proposed redshift evolution in earlier studies. We discuss
possible reasons for this discrepancy, with the most likely conclusion being
target selection and Eddington bias.Comment: MNRAS, submitte
American Astronomical Society logo iop-2016.png Nature of Faint Radio Sources in GOODS-North and GOODS-South Fields. I. Spectral Index and RadioâFIR Correlation
We present the first results from the deep and wide 5 GHz radio observations of the Great Observatories Origins Deep Survey (GOODS)-North (Ï = 3.5 ÎŒJy beamâ1, synthesized beam size Ξ = 147 Ă 142, and 52 sources over 109 arcmin2) and GOODS-South (Ï = 3.0 ÎŒJy beamâ1, Ξ = 098 Ă 045, and 88 sources over 190 arcmin2) fields using the Karl G. Jansky Very Large Array. We derive radio spectral indices α between 1.4 and 5 GHz using the beam-matched images and show that the overall spectral index distribution is broad even when the measured noise and flux bias are considered. We also find a clustering of faint radio sources around α = 0.8, but only within S 5 GHz \u3c 150 ÎŒJy. We demonstrate that the correct radio spectral index is important for deriving accurate rest-frame radio power and analyzing the radioâFIR correlation, and adopting a single value of α = 0.8 leads to a significant scatter and a strong bias in the analysis of the radioâFIR correlation, resulting from the broad and asymmetric spectral index distribution. When characterized by specific star formation rates, the starburst population (58%) dominates the 5 GHz radio source population, and the quiescent galaxy population (30%) follows a distinct trend in spectral index distribution and the radioâFIR correlation. Lastly, we offer suggestions on sensitivity and angular resolution for future ultra-deep surveys designed to trace the cosmic history of star formation and AGN activity using radio continuum as a probe
Nature of Faint Radio Sources in GOODS-North and GOODS-South Fields â I. Spectral Index and Radio-FIR Correlation
We present the first results from the deep and wide 5 GHz radio observations of the Great Observatories Origins Deep Survey (GOODS)-North (Ï = 3.5 ÎŒJy beamâ1, synthesized beam size Ξ = 147 Ă 142, and 52 sources over 109 arcmin2) and GOODS-South (Ï = 3.0 ÎŒJy beamâ1, Ξ = 098 Ă 045, and 88 sources over 190 arcmin2) fields using the Karl G. Jansky Very Large Array. We derive radio spectral indices α between 1.4 and 5 GHz using the beam-matched images and show that the overall spectral index distribution is broad even when the measured noise and flux bias are considered. We also find a clustering of faint radio sources around α = 0.8, but only within S 5 GHz \u3c 150 ÎŒJy. We demonstrate that the correct radio spectral index is important for deriving accurate rest-frame radio power and analyzing the radioâFIR correlation, and adopting a single value of α = 0.8 leads to a significant scatter and a strong bias in the analysis of the radioâFIR correlation, resulting from the broad and asymmetric spectral index distribution. When characterized by specific star formation rates, the starburst population (58%) dominates the 5 GHz radio source population, and the quiescent galaxy population (30%) follows a distinct trend in spectral index distribution and the radioâFIR correlation. Lastly, we offer suggestions on sensitivity and angular resolution for future ultra-deep surveys designed to trace the cosmic history of star formation and AGN activity using radio continuum as a probe
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