15 research outputs found
A candidate redshift z ~ 10 galaxy and rapid changes in that population at an age of 500 Myr
Searches for very-high-redshift galaxies over the past decade have yielded a
large sample of more than 6,000 galaxies existing just 900-2,000 million years
(Myr) after the Big Bang (redshifts 6 > z > 3; ref. 1). The Hubble Ultra Deep
Field (HUDF09) data have yielded the first reliable detections of z ~ 8
galaxies that, together with reports of a gamma-ray burst at z ~ 8.2 (refs 10,
11), constitute the earliest objects reliably reported to date. Observations of
z ~ 7-8 galaxies suggest substantial star formation at z > 9-10. Here we use
the full two-year HUDF09 data to conduct an ultra-deep search for z ~ 10
galaxies in the heart of the reionization epoch, only 500 Myr after the Big
Bang. Not only do we find one possible z ~ 10 galaxy candidate, but we show
that, regardless of source detections, the star formation rate density is much
smaller (~10%) at this time than it is just ~200 Myr later at z ~ 8. This
demonstrates how rapid galaxy build-up was at z ~ 10, as galaxies increased in
both luminosity density and volume density from z ~ 8 to z ~ 10. The 100-200
Myr before z ~ 10 is clearly a crucial phase in the assembly of the earliest
galaxies.Comment: 41 pages, 14 figures, 2 tables, Nature, in pres
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An Ultra Deep Field survey with WFIRST
Studying the formation and evolution of galaxies at the earliest cosmic
times, and their role in reionization, requires the deepest imaging possible.
Ultra-deep surveys like the HUDF and HFF have pushed to mag \mAB30,
revealing galaxies at the faint end of the LF to 911 and
constraining their role in reionization. However, a key limitation of these
fields is their size, only a few arcminutes (less than a Mpc at these
redshifts), too small to probe large-scale environments or clustering
properties of these galaxies, crucial for advancing our understanding of
reionization. Achieving HUDF-quality depth over areas 100 times larger
becomes possible with a mission like the Wide Field Infrared Survey Telescope
(WFIRST), a 2.4-m telescope with similar optical properties to HST, with a
field of view of 1000 arcmin, 100 the area of the
HST/ACS HUDF.
This whitepaper motivates an Ultra-Deep Field survey with WFIRST, covering
100300 the area of the HUDF, or up to 1 deg, to
\mAB30, potentially revealing thousands of galaxies and AGN at the
faint end of the LF, at or beyond \,\,910 in the epoch of
reionization, and tracing their LSS environments, dramatically increasing the
discovery potential at these redshifts.
(Note: This paper is a somewhat expanded version of one that was submitted as
input to the Astro2020 Decadal Survey, with this version including an Appendix
(which exceeded the Astro2020 page limits), describing how the science drivers
for a WFIRST Ultra Deep Field might map into a notional observing program,
including the filters used and exposure times needed to achieve these depths.
Nutritional ketosis alters fuel preference and thereby endurance performance in athletes
Ketosis, the metabolic response to energy crisis, is a mechanism to sustain life by altering oxidative fuel selection. Often overlooked for its metabolic potential, ketosis is poorly understood outside of starvation or diabetic crisis. Thus, we studied the biochemical advantages of ketosis in humans using a ketone ester-based form of nutrition without the unwanted milieu of endogenous ketone body production by caloric or carbohydrate restriction. In five separate studies of 39 high-performance athletes, we show how this unique metabolic state improves physical endurance by altering fuel competition for oxidative respiration. Ketosis decreased muscle glycolysis and plasma lactate concentrations, while providing an alternative substrate for oxidative phosphorylation. Ketosis increased intramuscular triacylglycerol oxidation during exercise, even in the presence of normal muscle glycogen, co-ingested carbohydrate and elevated insulin. These findings may hold clues to greater human potential and a better understanding of fuel metabolism in health and disease
From Nearby Low Luminosity AGN to High Redshift Radio Galaxies: Science Interests with Square Kilometre Array
We present detailed science cases that a large fraction of the Indian AGN
community is interested in pursuing with the upcoming Square Kilometre Array
(SKA). These interests range from understanding low luminosity active galactic
nuclei in the nearby Universe to powerful radio galaxies at high redshifts.
Important unresolved science questions in AGN physics are discussed. Ongoing
low-frequency surveys with the SKA pathfinder telescope GMRT, are highlighted.Comment: To appear in Journal of Astrophysics and Astronomy (JOAA) special
issue on "Science with the SKA: an Indian perspective
AGN Feedback in Elliptical Galaxies: Numerical Simulations
The importance of feedback (radiative and mechanical) from massive black
holes at the centers of elliptical galaxies is not in doubt, given the well
established relation among black hole mass and galaxy optical luminosity. Here,
with the aid of high-resolution hydrodynamical simulations, we discuss how this
feedback affects the hot ISM of isolated elliptical galaxies of different mass.
The cooling and heating functions include photoionization plus Compton heating,
the radiative transport equations are solved, and the mechanical feedback due
to the nuclear wind is also described on a physical basis; star formation is
considered. In the medium-high mass galaxies the resulting evolution is highly
unsteady. At early times major accretion episodes caused by cooling flows in
the recycled gas produced by stellar evolution trigger AGN flaring: relaxation
instabilities occur so that duty cycles are small enough to account for the
very small fraction of massive ellipticals observed to be in the QSO-phase,
when the accretion luminosity approaches the Eddington luminosity. At low
redshift all models are characterized by smooth, very sub-Eddington mass
accretion rates. The mass accumulated by the central black hole is limited to
range observed today, even though the mass lost by the evolving stellar
population is roughly two order of magnitude larger than the black hole masses
observed in elliptical galaxies.Comment: 20 pages, 4 (low-resolution) figures. Abbreviated version of the
article to appear in book "Hot Interstellar Matter in Elliptical Galaxies",
D.-W. Kim and S. Pellegrini eds., Astrophysics and Space Science Library
(ASSL), Springe
The evolution of diverse biological responses to DNA damage: insights from yeast and p53
The cellular response to ionizing radiation provides a conceptual framework for understanding how a yeast checkpoint system, designed to make binary decisions between arrest and cycling, evolved in a way as to allow reversible arrest, senescence or apoptosis in mammals. We propose that the diversity of responses to ionizing radiation in mammalian cells is possible because of the addition of a new regulatory control module involving the tumour-suppressor gene p53. We review the complex mechanisms controlling p53 activity and discuss how the p53 regulatory module enables cells to grow, arrest or die by integrating DNA damage checkpoint signals with the response to normal mitogenic signalling and the aberrant signalling engendered by oncogene activation