645 research outputs found
Frontier Fields: High-Redshift Predictions and Early Results
The Frontier Fields program is obtaining deep Hubble and Spitzer Space
Telescope images of new "blank" fields and nearby fields gravitationally lensed
by massive galaxy clusters. The Hubble images of the lensed fields are
revealing nJy sources (AB mag > 31), the faintest galaxies yet observed. In
this paper, we present high-redshift (z > 6) number count predictions for the
full program and candidates in three of the first Hubble Frontier Fields
images. The full program will transform our understanding of galaxy evolution
in the first 600 million years (z > 9). Where previous programs yielded perhaps
a dozen z > 9 candidates, the Frontier Fields may yield ~70 (~6 per field). We
base this estimate on an extrapolation of luminosity functions observed between
4 < z < 8 and gravitational lensing models submitted by the community. However,
in the first two deep infrared Hubble images obtained to date, we find z ~ 8
candidates but no strong candidates at z > 9. This might suggest a deficit of
faint z > 9 galaxies as also reported in the Ultra Deep Field (even while
excesses of brighter z > 9 galaxies were reported in shallower fields). At
these redshifts, cosmic variance (field-to-field variation) is expected to be
significant (greater than +/-50%) and include clustering of early galaxies
formed in overdensities. The full Frontier Fields program will significantly
mitigate this uncertainty by observing six independent sightlines each with a
lensing cluster and nearby blank field.Comment: Submitted for publication in the Astrophysical Journal. 15 pages, 17
figure
CLASH: Discovery of a Bright z~6.2 Dwarf Galaxy Quadruply Lensed by MACS J0329.6-0211
We report the discovery of a z_{phot}=6.18^{+0.05}_{-0.07} (95% confidence
level) dwarf galaxy, lensed into four images by the galaxy cluster MACS
J0329.6-0211 (z_{l}=0.45). The galaxy is observed as a high-redshift dropout in
HST/ACS/WFC3 CLASH and Spitzer/IRAC imaging. Its redshift is securely
determined due to a clear detection of the Lyman-break in the 18-band
photometry, making this galaxy one of the highest-redshift multiply-lensed
objects known to date with an observed magnitude of F125W=24.00\pm0.04 AB mag
for its highest-magnified image. We also present the first strong-lensing
analysis of this cluster uncovering 15 additional multiply-imaged candidates of
five lower-redshift sources spanning the range z_{s}~2-4. The mass model
independently supports the high photometric redshift and reveals magnifications
of 11.6^{+8.9}_{-4.1}, 17.6^{+6.2}_{-3.9}, 3.9^{+3.0}_{-1.7}, and
3.7^{+1.3}_{-0.2}, respectively, for the four images of the high-redshift
galaxy. With this we construct a source image with a physical resolution of
~200 pc when the universe was ~0.9 Gyr old, where the z~6.2 galaxy occupies a
source-plane area of approximately 2.2 kpc^{2}. Modeling the observed spectral
energy distribution using population synthesis models, we find a demagnified
stellar mass of ~10^{9} {M}_{sun}, subsolar metallicity (Z/Z_{sun}~0.5), low
dust content (A_{V}~0.1 mag), a demagnified star formation rate (SFR) of ~3.2
{M}_{sun} yr^{-1}, and a specific SFR of ~3.4 Gyr^{-1}, all consistent with the
properties of local dwarf galaxies.Comment: 6 pages, 1 table, 4 figures, accepted for publication in ApJ Letters;
v3: minor changes including shortened text and figure
SeeGH – A software tool for visualization of whole genome array comparative genomic hybridization data
BACKGROUND: Array comparative genomic hybridization (CGH) is a technique which detects copy number differences in DNA segments. Complete sequencing of the human genome and the development of an array representing a tiling set of tens of thousands of DNA segments spanning the entire human genome has made high resolution copy number analysis throughout the genome possible. Since array CGH provides signal ratio for each DNA segment, visualization would require the reassembly of individual data points into chromosome profiles. RESULTS: We have developed a visualization tool for displaying whole genome array CGH data in the context of chromosomal location. SeeGH is an application that translates spot signal ratio data from array CGH experiments to displays of high resolution chromosome profiles. Data is imported from a simple tab delimited text file obtained from standard microarray image analysis software. SeeGH processes the signal ratio data and graphically displays it in a conventional CGH karyotype diagram with the added features of magnification and DNA segment annotation. In this process, SeeGH imports the data into a database, calculates the average ratio and standard deviation for each replicate spot, and links them to chromosome regions for graphical display. Once the data is displayed, users have the option of hiding or flagging DNA segments based on user defined criteria, and retrieve annotation information such as clone name, NCBI sequence accession number, ratio, base pair position on the chromosome, and standard deviation. CONCLUSIONS: SeeGH represents a novel software tool used to view and analyze array CGH data. The software gives users the ability to view the data in an overall genomic view as well as magnify specific chromosomal regions facilitating the precise localization of genetic alterations. SeeGH is easily installed and runs on Microsoft Windows 2000 or later environments
The Highest Resolution Mass Map of Galaxy Cluster Substructure To Date Without Assuming Light Traces Mass: LensPerfect Analysis of Abell 1689
We present a strong lensing mass model of Abell 1689 which resolves
substructures ~25 kpc across (including about ten individual galaxy subhalos)
within the central ~400 kpc diameter. We achieve this resolution by perfectly
reproducing the observed (strongly lensed) input positions of 168 multiple
images of 55 knots residing within 135 images of 42 galaxies. Our model makes
no assumptions about light tracing mass, yet we reproduce the brightest visible
structures with some slight deviations. A1689 remains one of the strongest
known lenses on the sky, with an Einstein radius of RE = 47.0" +/- 1.2" (143
+3/-4 kpc) for a lensed source at zs = 2. We find a single NFW or Sersic prole
yields a good fit simultaneously (with only slight tension) to both our strong
lensing (SL) mass model and published weak lensing (WL) measurements at larger
radius (out to the virial radius). According to this NFW fit, A1689 has a mass
of Mvir = 2.0 +0.5/-0.3 x 10^15 Msun / h70 (M200 = 1.8 +0.4/-0.3 x 10^15 Msun /
h70) within the virial radius rvir = 3.0 +/- 0.2 Mpc / h70 (r200 = 2.4
+0.1/-0.2 Mpc / h70), and a central concentration cvir = 11.5 +1.5/-1.4 (c200 =
9.2 +/- 1.2). Our SL model prefers slightly higher concentrations than previous
SL models, bringing our SL+WL constraints in line with other recent
derivations. Our results support those of previous studies which find A1689 has
either an anomalously large concentration or significant extra mass along the
line of sight (perhaps in part due to triaxiality). If clusters are generally
found to have higher concentrations than realized in simulations, this could
indicate they formed earlier, perhaps as a result of early dark energy.Comment: 27 pages, 17 figures, submitted to ApJ. See
http://www.its.caltech.edu/~coe/LPA1689/ for complete set of color multiple
images (observed and delensed) and more. Comments welcome at
http://scirate.com/who.php?id=1005.xxxx&what=comments (insert arXiv number at
xxxx; free & easy registration
Not In Our Backyard: Spectroscopic Support for the CLASH z=11 Candidate MACS0647-JD
We report on our first set of spectroscopic Hubble Space Telescope
observations of the z~11 candidate galaxy strongly lensed by the
MACSJ0647.7+7015 galaxy cluster. The three lensed images are faint and we show
that these early slitless grism observations are of sufficient depth to
investigate whether this high-redshift candidate, identified by its strong
photometric break at ~1.5 micron, could possibly be an emission line galaxy at
a much lower redshift. While such an interloper would imply the existence of a
rather peculiar object, we show here that such strong emission lines would
clearly have been detected. Comparing realistic, two-dimensional simulations to
these new observations we would expect the necessary emission lines to be
detected at >5 sigma while we see no evidence for such lines in the dispersed
data of any of the three lensed images. We therefore exclude that this object
could be a low redshift emission line interloper, which significantly increases
the likelihood of this candidate being a bona fide z~11 galaxy.Comment: 14 Pages. 6 Figures. 2nd revised version. Accepted. To appear in ApJ.
Please contact [email protected] for comments on this pape
The bright-end galaxy candidates at z ~ 9 from 79 independent HST fields
We present a full data analysis of the pure-parallel Hubble Space Telescope
(HST) imaging observations in the Brightest of Reionizing Galaxies Survey
(BoRG[z9]) in Cycle 22. The medium-deep exposures with five HST/WFC3IR+UVIS
filter bands from 79 independent sightlines (~370 arcmin^2) provide the least
biased determination of number density for z>9 bright galaxies against cosmic
variance. After a strict two-step selection for candidate galaxies, including
dropout color and photometric redshift analyses, and revision of previous BoRG
candidates, we identify one source at z~10 and two sources at z~9. The z~10
candidate shows evidence of line-of-sight lens magnification (mu~1.5), yet it
appears surprisingly luminous (MUV ~ -22.6\pm0.3 mag), making it one of the
brightest candidates at z > 8 known (~ 0.3 mag brighter than the z = 8.68
galaxy EGSY8p7, spectroscopically confirmed by Zitrin and collaborators). For z
~ 9 candidates, we include previous data points at fainter magnitudes and find
that the data are well fitted by a Schechter luminosity function with alpha ~
-2.1, MUV ~ -21.5 mag, and log phi ~ -4.5 Mpc^-3mag^-1, for the first time
without fixing any parameters. The inferred cosmic star formation rate density
is consistent with unaccelerated evolution from lower redshift.Comment: 18pages, 7figures, 6tables. accepted to the Astrophysical Journa
Large fragment Bst DNA polymerase for whole genome amplification of DNA from formalin-fixed paraffin-embedded tissues
BACKGROUND: Formalin-fixed paraffin-embedded (FFPE) tissues represent the largest source of archival biological material available for genomic studies of human cancer. Therefore, it is desirable to develop methods that enable whole genome amplification (WGA) using DNA extracted from FFPE tissues. Multiple-strand Displacement Amplification (MDA) is an isothermal method for WGA that uses the large fragment of Bst DNA polymerase. To date, MDA has been feasible only for genomic DNA isolated from fresh or snap-frozen tissue, and yields a representational distortion of less than threefold. RESULTS: We amplified genomic DNA of five FFPE samples of normal human lung tissue with the large fragment of Bst DNA polymerase. Using quantitative PCR, the copy number of 7 genes was evaluated in both amplified and original DNA samples. Four neuroblastoma xenograft samples derived from cell lines with known N-myc gene copy number were also evaluated, as were 7 samples of non-small cell lung cancer (NSCLC) tumors with known Skp2 gene amplification. In addition, we compared the array comparative genomic hybridization (CGH)-based genome profiles of two NSCLC samples before and after Bst MDA. A median 990-fold amplification of DNA was achieved. The DNA amplification products had a very high molecular weight (> 23 Kb). When the gene content of the amplified samples was compared to that of the original samples, the representational distortion was limited to threefold. Array CGH genome profiles of amplified and non-amplified FFPE DNA were similar. CONCLUSION: Large fragment Bst DNA polymerase is suitable for WGA of DNA extracted from FFPE tissues, with an expected maximal representational distortion of threefold. Amplified DNA may be used for the detection of gene copy number changes by quantitative realtime PCR and genome profiling by array CGH
The Bright End of the z~9 and z~10 UV Luminosity Functions using all five CANDELS Fields
The deep, wide-area (~800-900 arcmin**2) near-infrared/WFC3/IR + Spitzer/IRAC
observations over the CANDELS fields have been a remarkable resource for
constraining the bright end of high redshift UV luminosity functions (LFs).
However, the lack of HST 1.05-micron observations over the CANDELS fields has
made it difficult to identify z~9-10 sources robustly, since such data are
needed to confirm the presence of an abrupt Lyman break at 1.2 microns. We
report here on the successful identification of many such z~9-10 sources from a
new HST program (z9-CANDELS) that targets the highest-probability z~9-10 galaxy
candidates with observations at 1.05 microns, to search for a robust
Lyman-break at 1.2 microns. The potential z~9-10 candidates are preselected
from the full HST, Spitzer/IRAC S-CANDELS observations, and the
deepest-available ground-based optical+near-infrared observations. We
identified 15 credible z~9-10 galaxies over the CANDELS fields. Nine of these
galaxies lie at z~9 and 5 are new identifications. Our targeted follow-up
strategy has proven to be very efficient in making use of scarce HST time to
secure a reliable sample of z~9-10 galaxies. Through extensive simulations, we
replicate the selection process for our sample (both the preselection and
follow-up) and use it to improve current estimates for the volume density of
bright z~9 and z~10 galaxies. The volume densities we find are 5(-2)(+3)x and
8(-3)(+9)x lower, respectively, than found at z~8. When compared with the
best-fit evolution (i.e., dlog_{10} rho(UV)/dz=-0.29+/-0.02) in the UV
luminosities densities from z~8 to z~4 integrated to 0.3L*(z=3) (-20 mag),
these luminosity densities are 2.6(-0.9)(+1.5)x and 2.2(-1.1)(+2.0)x lower,
respectively, than the extrapolated trends. Our new results are broadly
consistent with the "accelerated evolution" scenario at z>8, as seen in many
theoretical models.Comment: 23 pages, 15 figures, 7 tables, updated to match the version in
press, including some minor textual corrections identified at the proof stag
- …