112 research outputs found
NICMOS Imaging of the Nuclei of Arp 220
We report high resolution imaging of the ultraluminous infrared galaxy Arp
220 at 1.1, 1.6, and 2.22 microns with NICMOS on the HST. The
diffraction-limited images at 0.1--0.2 arcsecond resolution clearly resolve
both nuclei of the merging galaxy system and reveal for the first time a number
of luminous star clusters in the circumnuclear envelope. The morphologies of
both nuclei are strongly affected by dust obscuration, even at 2.2 microns :
the primary nucleus (west) presents a crescent shape, concave to the south and
the secondary (eastern) nucleus is bifurcated by a dust lane with the southern
component being very reddened. In the western nucleus, the morphology of the
2.2 micron emission is most likely the result of obscuration by an opaque disk
embedded within the nuclear star cluster. The morphology of the central
starburst-cluster in the western nucleus is consistent with either a
circumnuclear ring of star formation or a spherical cluster with the bottom
half obscured by the embedded dust disk. Comparison of cm-wave radio continuum
maps with the near-infrared images suggests that the radio nuclei lie in the
dust disk on the west and near the highly reddened southern component of the
eastern complex. The radio nuclei are separated by 0.98 arcseconds
(corresponding to 364 pc at 77 Mpc) and the half-widths of the infrared nuclei
are approximately 0.2-0.5 arcseconds. At least 8, unresolved infrared sources
-- probably globular clusters -- are also seen in the circumnuclear envelope at
radii 2-7 arcseconds . Their near-infrared colors do not significantly
constrain their ages.Comment: LaTex, 15 pages with 1 gif figure and 5 postscript figures. ApJL
accepte
Transverse and longitudinal correlation functions in the Intergalactic Medium from 32 close pairs of high-redshift quasars
We present the transverse flux correlation function of the Lyman-alpha forest
in quasar absorption spectra at z~2.1 from VLT-FORS and VLT-UVES observations
of a total of 32 pairs of quasars; 26 pairs with separations in the range
0.6<theta<4 arcmin and 6 pairs with 4<theta<10 arcmin. Correlation is detected
at the 3sigma level up to separations of the order of ~4 arcmin (or ~4.4 h^{-1}
Mpc comoving at z=2.1 for Omega_{m}=0.3 and Omega_{Lambda}=0.7). We have,
furthermore, measured the longitudinal correlation function at a somewhat
higher mean redshift (z=2.39) from 20 lines of sight observed with high
spectral resolution and high signal-to-noise ratio with VLT-UVES. We compare
the observed transverse and longitudinal correlation functions to that obtained
from numerical simulations and illustrate the effect of spectral resolution,
thermal broadening and peculiar motions. The shape and correlation length of
the correlation functions are in good agreement with those expected from
absorption by the filamentary and sheet-like structures in the photoionized
warm intergalactic medium predicted in CDM-like models for structures
formation. Using a sample of 139 C_{iv} systems detected along the lines of
sight toward the pairs of quasars we also investigate the transverse
correlation of metals on the same scales. The observed transverse correlation
function of intervening C_{iv} absorption systems is consistent with that of a
randomly distributed population of absorbers. This is likely due to the small
number of pairs with separation less than 2 arcmin. We detect, however, a
significant overdensity of systems in the sightlines towards the quartet
Q0103-294A&B, Q0102-2931 and Q0102-293 which extends over the redshift range
1.5<z<2.2 and an angular scale larger than 10 arcmin.Comment: accepted for publication in MNRAS, Appendix B and C will be published
online onl
A multivalent DNA aptamer specific for the B-cell receptor on human lymphoma and leukemia
Long-term survival still eludes most patients with leukemia and non-Hodgkin’s lymphoma. No approved therapies target the hallmark of the B cell, its mIgM, also known as the B-cell receptor (BCR). Aptamers are small oligonucleotides that can specifically bind to a wide range of target molecules and offer some advantages over antibodies as therapeutic agents. Here, we report the rational engineering of aptamer TD05 into multimeric forms reactive with the BCR that may be useful in biomedical applications. Systematic truncation of TD05 coupled with modification with locked nucleic acids (LNA) increased conformational stability and nuclease resistance. Trimeric and tetrameric versions with optimized polyethyleneglycol (PEG) linker lengths exhibited high avidity at physiological temperatures both in vitro and in vivo. Competition and protease studies showed that the multimeric, optimized aptamer bound to membrane-associated human mIgM, but not with soluble IgM in plasma, allowing the possibility of targeting leukemias and lymphomas in vivo. The B-cell specificity of the multivalent aptamer was confirmed on lymphoma cell lines and fresh clinical leukemia samples. The chemically engineered aptamers, with significantly improved kinetic and biochemical features, unique specificity and desirable pharmacological properties, may be useful in biomedical applications
Transverse Sizes of CIV Absorption Systems Measured from Multiple QSO Sightlines
We present tomography of the circum-galactic metal distribution at redshift
1.7 to 4.5 derived from echellete spectroscopy of binary quasars. We find CIV
systems at similar redshifts in paired sightlines more often than expected for
sightline-independent redshifts. As the separation of the sightlines increases
from 36 kpc to 907 kpc, the amplitude of this clustering decreases. At the
largest separations, the CIV systems cluster similar to Lyman-break galaxies
(Adelberger et al. 2005a). The CIV systems are significantly less correlated
than these galaxies, however, at separations less than R_1 ~ 0.42 +/- 0.15 h-1
comoving Mpc. Measured in real space, i.e., transverse to the sightlines, this
length scale is significantly smaller than the break scale estimated from the
line-of-sight correlation function in redshift space (Scannapieco et al.
2006a). Using a simple model, we interpret the new real-space measurement as an
indication of the typical physical size of enriched regions. We adopt this size
for enriched regions and fit the redshift-space distortion in the line-of-sight
correlation function. The fitted velocity kick is consistent with the peculiar
velocity of galaxies as determined by the underlying mass distribution and
places an upper limit on the outflow (or inflow) speed of metals. The implied
time scale for dispersing metals is larger than the typical stellar ages of
Lyman-break galaxies (Shapley et al. 2001), and we argue that enrichment by
galaxies at z > 4.3 played a greater role in dispersing metals. To further
constrain the growth of enriched regions, we discuss empirical constraints on
the evolution of the CIV correlation function with cosmic time. This study
demonstrates the potential of tomography for measuring the metal enrichment
history of the circum-galactic medium.Comment: 22 pages, 15 figures, 1 tabl
NICMOS Imaging of Infrared-Luminous Galaxies
We present near-infrared images obtained with the HST NICMOS camera for a
sample of 9 luminous (LIGs: L_IR (8-1000 microns) >~ 10^11 L_sun) and 15
ultra-luminous (ULIGS: L_IR >~ 10^12 L_sun) infrared galaxies. The sample
includes representative systems classified as warm (f_25/f_60 > 0.2) and cold
(f_25/f_60 <~ 0.2) based on the mid-infrared colors and systems with nuclear
emission lines classified as HII (i.e. starburst), QSO, Seyfert and LINER. The
morphologies of the sample galaxies are diverse and provide further support for
the idea that they are created by the collision or interactions of spiral
galaxies. Although no new nuclei are seen in the NICMOS images, the NICMOS
images do reveal new spiral structures, bridges, and circumnuclear star
clusters...Comment: LaTex, 27 pages with 14 gif and 4 jpg figures, AJ, in press, contour
figures of the NICMOS images can be viewed at
http://nedwww.ipac.caltech.edu/level5/Scoville/frames.htm
A slitless spectroscopic survey for quasars near quasars
We present the results of the Quasars near Quasars (QNQ) survey, a CCD-based
slitless spectroscopic survey for faint V<22 quasars at 1.7<z<3.6 on 18
26.2'x33.5' fields centred on bright quasars at 2.76<z<4.69. In total 169
quasar candidates with emission lines were selected from the extracted
flux-calibrated spectra on the basis of well-defined automatic selection
criteria followed by visual inspection and verification. With follow-up
spectroscopy of 81 candidates that were likely to reside at z>1.7 we were able
to confirm 80 new quasars at 0.580<z<3.586 on 16 of our fields. 64 of the newly
discovered quasars are located at z>1.7. The overall high success rate implies
that most of the remaining 88 candidates are quasars as well, although the
majority of them likely resides at z<1.7 on the basis of the observed line
shapes and strengths. Due to the insufficient depth of the input source
catalogues needed for extraction of the slitless spectra our survey is not well
defined in terms of limiting magnitude for faint 2.5<z<3.6 quasars whose Lyman
alpha emission is detectable well beyond V=22, albeit at a continuum S/N<1.
While not useful for characterising the evolving space density of quasars, our
sample provides many new closely spaced quasar sightlines around intensely
studied quasars for further investigations on the three-dimensional
distribution of the intergalactic medium.Comment: 18 pages, 16 figures, accepted by A&A, includes Table 2 from online
material, full paper with appendices containing additional figures and tables
available at http://www.aip.de/People/gworseck/qnqpaper/qnqpaper_final.pd
Large-scale structure in the Lyman-alpha forest II: analysis of a group of ten QSOs
The spatial distribution of Ly-alpha forest absorption systems towards ten
QSOs has been analysed to search for large-scale structure over the redshift
range 2.2 < z < 3.4. The QSOs form a closely spaced group on the sky and are
concentrated within a 1 deg^2 field. We have employed a technique based on the
first and second moments of the transmission probability density function which
is capable of identifying and assessing the significance of regions of over- or
underdense Ly-alpha absorption. We find evidence for large-scale structure in
the distribution of Ly-alpha forest absorption at the > 99 per cent confidence
level. In individual spectra we find overdense Ly-alpha absorption on scales of
up to 1200 km s^-1. There is also strong evidence for correlated absorption
across line of sight pairs separated by < 3 h^-1 proper Mpc (q_0 = 0.5). For
larger separations the cross-correlation signal becomes progressively less
significant.Comment: 15 pages, LaTeX, 6 Postscript figures, accepted for publication in
MNRA
Coincident, 100 kpc-scale damped Lyman alpha absorption towards a binary QSO: how large are galaxies at z ~ 3?
We report coincident damped Lyman alpha (DLA) and sub-DLA absorption at z =
2.66 and z = 2.94 towards the z ~ 3 13.8 arcsecond separation binary quasar
SDSS 1116+4118 AB. At the redshifts of the absorbers, this angular separation
corresponds to a proper transverse separation of ~ 110 kpc. A third absorber, a
sub-DLA at z = 2.47, is detected towards SDSS 1116+4118 B, but no corresponding
high column density absorber is present towards SDSS 1116+4118 A. We use high
resolution galaxy simulations and a clustering analysis to interpret the
coincident absorption and its implications for galaxy structure at z ~ 3. We
conclude that the common absorption in the two lines of sight is unlikely to
arise from a single galaxy, or a galaxy plus satellite system, and is more
feasibly explained by a group of two or more galaxies with separations ~ 100
kpc. The impact of these findings on single line of sight observations is also
discussed; we show that abundances of DLAs may be affected by up to a few
tenths of a dex by line of sight DLA blending. From a Keck ESI spectrum of the
two quasars, we measure metal column densities for all five absorbers and
determine abundances for the three absorbers with log N(HI) > 20. For the two
highest N(HI) absorbers, we determine high levels of metal enrichment,
corresponding to 1/3 and 1/5 solar. These metallicities are amongst the highest
measured for DLAs at any redshift and are consistent with values measured in
Lyman break galaxies at 2 < z < 3. For the DLA at z = 2.94 we also infer an
approximately solar ratio of alpha-to-Fe peak elements from [S/Zn] = +0.05, and
measure an upper limit for the molecular fraction in this particular line of
sight of log f(H_2)< -5.5.Comment: Accepted for publication in MNRAS. Full resolution simulation images
available in pdf copy of the manuscript at
http://www.astro.uvic.ca/~sara/1116.pd
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