135 research outputs found
Live-Cell Monitoring of Periodic Gene Expression in Synchronous Human Cells Identifies Forkhead Genes involved in Cell Cycle Control
We developed a system to monitor periodic luciferase activity from cell cycle-regulated promoters in synchronous cells. Reporters were driven by a minimal human E2F1 promoter with peak expression in G1/S or a basal promoter with six Forkhead DNA-binding sites with peak expression at G2/M. After cell cycle synchronization, luciferase activity was measured in live cells at 10-min intervals across three to four synchronous cell cycles, allowing unprecedented resolution of cell cycle-regulated gene expression. We used this assay to screen Forkhead transcription factors for control of periodic gene expression. We confirmed a role for FOXM1 and identified two novel cell cycle regulators, FOXJ3 and FOXK1. Knockdown of FOXJ3 and FOXK1 eliminated cell cycle-dependent oscillations and resulted in decreased cell proliferation rates. Analysis of genes regulated by FOXJ3 and FOXK1 showed that FOXJ3 may regulate a network of zinc finger proteins and that FOXK1 binds to the promoter and regulates DHFR, TYMS, GSDMD, and the E2F binding partner TFDP1. Chromatin immunoprecipitation followed by high-throughput sequencing analysis identified 4329 genomic loci bound by FOXK1, 83% of which contained a FOXK1-binding motif. We verified that a subset of these loci are activated by wild-type FOXK1 but not by a FOXK1 (H355A) DNA-binding mutant
HST Imaging of the Host Galaxies of High Redshift Radio-Loud Quasars
We present rest-frame UV and Ly-alpha images of spatially-resolved structures
around five high-redshift radio-loud quasars obtained with the WFPC2 camera on
the Hubble Space Telescope. We find that all five quasars are extended and this
"fuzz" contains ~5-40% of the total continuum flux and 15-65% of the Ly-alpha
flux within a radius of about 1.5 arcsec. The rest-frame UV luminosities of the
hosts are log lambda P_lambda = 11.9 to 12.5 solar luminosities (assuming no
internal dust extinction), comparable to the luminous radio galaxies at similar
redshifts and a factor 10 higher than both radio-quiet field galaxies at z~2-3
and the most UV-luminous low redshift starburst galaxies. The Ly-alpha
luminosities of the hosts are (in the log) approximately 44.3-44.9 erg/s which
are also similar to the those of luminous high redshift radio galaxies and
considerably larger than the Ly-alpha luminosities of high redshift field
galaxies. To generate the Ly-alpha luminosities of the hosts would require
roughly a few percent of the total observed ionizing luminosity of the quasar.
We find good alignment between the extended Ly-alpha and the radio sources,
strong evidence for jet-cloud interactions in two cases, again resembling radio
galaxies, and what is possibly the most luminous radio-UV synchrotron jet in
one of the hosts at z=2.110.Comment: 36 pages (latex, aas macros), 3 figures (3 gif and 10 postscript
files), accepted for publication in the the Astrophysical Journal Supplement
Serie
Characterization of Extragalactic 24micron Sources in the Spitzer First Look Survey
In this Letter, we present the initial characterization of extragalactic 24um
sources in the Spitzer First Look Survey (FLS) by examining their counterparts
at 8um and R-band. The color-color diagram of 24-to-8 vs. 24-to-0.7um is
populated with 18,734 sources brighter than the 3sigma flux limit of 110uJy,
over an area of 3.7sq.degrees. The 24-to-0.7um colors of these sources span
almost 4 orders of magnitudes, while the 24-to-8um colors distribute at least
over 2 orders of magnitudes. In addition to identifying ~30% of the total
sample with infrared quiescent, mostly low redshift galaxies, we also found
that: (1) 23% of the 24um sources (~1200/sq.degrees) have very red 24-to-8 and
24-to-0.7 colors and are probably infrared luminous starbursts with
L(IR)>3x10^(11)Lsun at z>1. In particular, 13% of the sample (660/sq.degrees)
are 24um detected only, with no detectable emission in either 8um or R-band.
These sources are the candidates for being ULIRGs at z>2. (2) 2% of the sample
(85/sq.degrees) have colors similar to dust reddened AGNs, like Mrk231 at
z~0.6-3. (3) We anticipate that some of these sources with extremely red colors
may be new types of sources, since they can not be modelled with any familiar
type of spectral energy distribution. We find that 17% of the 24um sources have
no detectable optical counterparts brighter than R limit of 25.5mag. Optical
spectroscopy of these optical extremely faint 24um sources would be very
difficult, and mid-infrared spectroscopy from the Spitzer would be critical for
understanding their physical nature (Abridged).Comment: Accepted for publication in ApJ (Spitzer Special Issue
Optical and Near-IR Imaging of Ultra Steep Spectrum Radio Sources - The K-z diagram of radio and optically selected galaxies
We present optical and/or near-IR images of 128 ultra steep spectrum (USS)
radio sources. Roughly half of the objects are identified in the optical images
(R 94% are detected at K<~ 22. The mean
K-magnitude is K=19.26 within a 2" diameter aperture. The distribution of R-K
colors indicates that at least 1/3 of the objects observed have very red colors
(R-K>5). The major axes of the identifications in K-band are preferentially
oriented along the radio axes, with half of them having compact morphologies.
The 22 sources with spectroscopic redshifts and K-band magnitudes follow the
K-z relation found from previous radio samples, but with a larger scatter. We
argue that this may be due to a dependence of K-magnitude on the radio power,
with the highest radio power sources inhabiting the most massive host galaxies.
We present a composite K-z diagram of radio-loud and radio-quiet galaxies,
selected from the HDF-North and the Hawaii surveys. Out to z <~ 1, the
radio-loud galaxies trace the bright envelope of the radio quiet galaxies,
while at z >~ 1, the radio-loud galaxies are >~ 2 magnitudes brighter. We argue
that this is not due to a contribution from the AGN or emission lines. This
difference strongly suggests that radio galaxies pinpoint the most massive
systems out to the highest known redshifts, probably due to the mutual
correlation of the mass of the galaxy and the radio power on the mass of the
central black hole.Comment: 39 Pages, including 10 PostScript figures. Accepted for publication
in the January 2002 Astronomical Journal. Figures 2 and 12 are available from
http://www.strw.leidenuniv.nl/~debreuck/paper
Infrared Excess Sources: Compton Thick QSOs, low luminosity Seyferts or starbursts?
We explore the nature of Infrared Excess sources (IRX), which are proposed as
candidates for luminous L_X(2-10keV)>1e43erg/s Compton Thick (N_H>2e24cm^{-2}z\approx1z\approx2$ IRX population are not Compton
Thick QSOs but low luminosity [L_X(2-10keV)<1e43erg/s], possibly Compton Thin,
AGN or dusty starbursts. It is shown that the decomposition of the AGN and
starburst contribution to the mid-IR is essential for interpreting the nature
of this population, as star-formation may dominate this wavelength regime.Comment: Accepted by MNRA
Biological Case Against Downlisting the Whooping Crane and for Improving Implementation under the Endangered Species Act
The Whooping Crane (Grus americana; WHCR) is a large, long-lived bird endemic to North America. The remnant population migrates between Aransas National Wildlife Refuge, USA, and Wood Buffalo National Park, Canada (AWBP), and has recovered from a nadir of 15-16 birds in 1941 to ~540 birds in 2022. Two ongoing reintroduction efforts in Louisiana and the Eastern Flyway together total ~150 birds. Evidence indicates the U.S. Fish and Wildlife Service (USFWS) is strongly considering downlisting the species from an endangered to a threatened status under the Endangered Species Act (ESA). We examined the current status of the WHCR through the lens of ESA threat factors, the USFWSâs Species Status Assessment (SSA) framework, and other avian downlisting actions to determine if the action is biologically warranted. Our research indicates that WHCRs are facing an intensification of most threat drivers across populations and important ranges. The AWBP is still relatively small compared to other crane species and most birds of conservation concern. To date, only one avian species has been downlisted from an endangered status with an estimated population of \u3c3,000 individuals. Representation in terms of WHCRs historic genetic, geographic, and life history variation remains limited. Also, the lack of spatial connectivity among populations, reliance of the reintroduced populations on supplementation, and continued habitat loss suggest that WHCR populations may not be resilient to large stochastic disturbances. Given that reintroduced populations are not self-sustaining, neither supplies true redundancy for the AWBP. Proposed downlisting before recovery plan population criteria have been met is objectively unwarranted 3 and reflects USFWS inconsistency across ESA actions. Only by incorporating basic quantitative criteria and added oversight into ESA listing decisions can we avoid an action as misguided as downlisting the Whooping Crane without consideration of its recovery plan criteria or ostensibly its population ecology
Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black hole research,
as seen from a purely observational standpoint. Since the early '90s, rapid
technological advances, most notably the launch of the Hubble Space Telescope,
the commissioning of the VLBA and improvements in near-infrared speckle imaging
techniques, have not only given us incontrovertible proof of the existence of
supermassive black holes, but have unveiled fundamental connections between the
mass of the central singularity and the global properties of the host galaxy.
It is thanks to these observations that we are now, for the first time, in a
position to understand the origin, evolution and cosmic relevance of these
fascinating objects.Comment: Invited Review, 114 pages. Because of space requirements, this
version contains low resolution figures. The full resolution version can be
downloaded from http://www.physics.rutgers.edu/~lff/publications.htm
Observing Supermassive Black Holes across cosmic time: from phenomenology to physics
In the last decade, a combination of high sensitivity, high spatial
resolution observations and of coordinated multi-wavelength surveys has
revolutionized our view of extra-galactic black hole (BH) astrophysics. We now
know that supermassive black holes reside in the nuclei of almost every galaxy,
grow over cosmological times by accreting matter, interact and merge with each
other, and in the process liberate enormous amounts of energy that influence
dramatically the evolution of the surrounding gas and stars, providing a
powerful self-regulatory mechanism for galaxy formation. The different
energetic phenomena associated to growing black holes and Active Galactic
Nuclei (AGN), their cosmological evolution and the observational techniques
used to unveil them, are the subject of this chapter. In particular, I will
focus my attention on the connection between the theory of high-energy
astrophysical processes giving rise to the observed emission in AGN, the
observable imprints they leave at different wavelengths, and the methods used
to uncover them in a statistically robust way. I will show how such a combined
effort of theorists and observers have led us to unveil most of the SMBH growth
over a large fraction of the age of the Universe, but that nagging
uncertainties remain, preventing us from fully understating the exact role of
black holes in the complex process of galaxy and large-scale structure
formation, assembly and evolution.Comment: 46 pages, 21 figures. This review article appears as a chapter in the
book: "Astrophysical Black Holes", Haardt, F., Gorini, V., Moschella, U and
Treves A. (Eds), 2015, Springer International Publishing AG, Cha
The First Measurements of Galaxy Clustering from IRAC Data of the Spitzer First Look Survey
We present the first results of the angular auto-correlation function of the
galaxies detected by the Infrared Array Camera (IRAC) instrument in the First
Look Survey (FLS) of the Spitzer Space Telescope. We detect significant signals
of galaxy clustering within the survey area. The angular auto-correlation
function of the galaxies detected in each of the four IRAC instrument channels
is consistent with a power-law form out to
\theta = 0.2\arcdeg, with the slope ranging from to 1.8. We
estimate the correlation amplitudes to be , , , and at
\theta=1\arcdeg for galaxies detected in the IRAC 3.6m, 4.5m,
5.8m, and 8.0m instrument channels, respectively. We compare our
measurements at 3.6m with the previous K-band measurements, and discuss
the implications of these results.Comment: Accepted for publication in the ApJ Supplements Spitzer Special
Issue; 12 pages including 3 figures and 1 tabl
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