108 research outputs found
Türk-Ermeni ilişkileri
Taha Toros Arşivi, Dosya No: 77/A-Ermeniler. Not: Gazetenin"Düşünenlerin Düşüncesi" köşesinde yayımlanmıştır.İstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033
New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign
Understanding cosmic reionization requires the identification and
characterization of early sources of hydrogen-ionizing photons. The 2012 Hubble
Ultra Deep Field (UDF12) campaign has acquired the deepest infrared images with
the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time,
systematically explored the galaxy population deep into the era when cosmic
microwave background (CMB) data indicates reionization was underway. The UDF12
campaign thus provides the best constraints to date on the abundance,
luminosity distribution, and spectral properties of early star-forming
galaxies. We synthesize the new UDF12 results with the most recent constraints
from CMB observations to infer redshift-dependent ultraviolet (UV) luminosity
densities, reionization histories, and electron scattering optical depth
evolution consistent with the available data. Under reasonable assumptions
about the escape fraction of hydrogen ionizing photons and the intergalactic
medium clumping factor, we find that to fully reionize the universe by redshift
z~6 the population of star-forming galaxies at redshifts z~7-9 likely must
extend in luminosity below the UDF12 limits to absolute UV magnitudes of
M_UV\sim -13 or fainter. Moreover, low levels of star formation extending to
redshifts z~15-25, as suggested by the normal UV colors of z\simeq7-8 galaxies
and the smooth decline in abundance with redshift observed by UDF12 to
z\simeq10, are additionally likely required to reproduce the optical depth to
electron scattering inferred from CMB observations.Comment: Version accepted by ApJ (originally submitted Jan 5, 2013). The UDF12
website can be found at http://udf12.arizona.ed
PANORAMIC - A Pure Parallel Wide Area Legacy Imaging Survey at 1-5 Micron
Where HST has characterized the UV universe to z=6-7 and beyond, JWST is designed to take the crucial next step and characterize the UV universe to z=12-15 (a factor of 2 in expansion rate), at only ~300 Myr after the Big Bang where we expect the first galaxies to form. Additionally, JWST for the first time allows studies of the restframe optical emission to z=10, a huge leap from the current z=3 (HST). To fully capitalize on JWST's unparalleled imaging AND spectroscopic capabilities, it is critical, however, to find the most precious intrinsically luminous candidate galaxies early in the mission. Large area imaging is thus needed from day one. Here, we propose to exploit the unique opportunity offered by pure parallel observing to efficiently obtain such a wide-area reference survey over 0.4 sq degrees in 6 NIRCam filters. By probing 7x larger area than any other currently planned (GTO/ERS) program our survey will probe a unique discovery space with unprecedented imaging at 1-5micron. These data overcome two major outstanding limitations in our current extragalactic census using yet-undiscovered populations: (1) the brightest and most distant sources that ended the cosmic Dark Ages at z>9 and (2) red sources at
A deep radio view of the evolution of the cosmic star formation rate density from a stellar-mass-selected sample in VLA-COSMOS
We present the 1.4 GHz radio luminosity functions (RLFs) of galaxies in the Cosmic Evolution Survey (COSMOS) field, measured above and below the 5σ detection threshold, using a Bayesian model-fitting technique. The radio flux densities from Very Large Array (VLA)-COSMOS 3-GHz data are extracted at the position of stellar-mass-selected galaxies. We fit a local RLF model, which is a combination of active galactic nuclei and star-forming galaxies (SFGs), in 10 redshift bins with a pure luminosity evolution model. Our RLF exceeds previous determinations at low radio luminosities at z 1.5. We investigate the effects of stellar mass on the total RLF by splitting our sample into low (108.5 ≤ M/M⊙ ≤ 1010) and high (M>1010M⊙) stellar-mass subsets. We find that the SFRD is dominated by sources in the high stellar masses bin, at all redshifts
The UV Luminosity Function of Star-forming Galaxies via Dropout Selection at Redshifts z ~ 7 and 8 from the 2012 Ultra Deep Field Campaign
We present a catalog of high-redshift star-forming galaxies selected to lie within the redshift range z ≃ 7-8 using the Ultra Deep Field 2012 (UDF12), the deepest near-infrared (near-IR) exposures yet taken with the Hubble Space Telescope (HST). As a result of the increased near-IR exposure time compared to previous HST imaging in this field, we probe ~0.65 (0.25) mag fainter in absolute UV magnitude, at z ~ 7 (8), which increases confidence in a measurement of the faint end slope of the galaxy luminosity function. Through a 0.7 mag deeper limit in the key F105W filter that encompasses or lies just longward of the Lyman break, we also achieve a much-refined color-color selection that balances high redshift completeness and a low expected contamination fraction. We improve the number of dropout-selected UDF sources to 47 at z ~ 7 and 27 at z ~ 8. Incorporating brighter archival and ground-based samples, we measure the z ≃ 7 UV luminosity function to an absolute magnitude limit of M_(UV) = –17 and find a faint end Schechter slope of ɑ =-1.87^(+0.18)_(-0.17). Using a similar color-color selection at z ≃ 8 that takes our newly added imaging in the F140W filter into account, and incorporating archival data from the HIPPIES and BoRG campaigns, we provide a robust estimate of the faint end slope at z ≃ 8, ɑ =-1.94^(+0.21)_(-0.24). We briefly discuss our results in the context of earlier work and that derived using the same UDF12 data but with an independent photometric redshift technique
Characterising the evolving -band luminosity function using the UltraVISTA, CANDELS and HUDF surveys
We present the results of a new study of the K-band galaxy luminosity
function (KLF) at redshifts z<3.75, based on a nested combination of the
UltraVISTA, CANDELS and HUDF surveys. The large dynamic range in luminosity
spanned by this new dataset (3-4 dex over the full redshift range) is
sufficient to clearly demonstrate for the first time that the faint-end slope
of the KLF at z>0.25 is relatively steep (-1.3<alpha<-1.5 for a single
Schechter function), in good agreement with recent theoretical and
phenomenological models. Moreover, based on our new dataset we find that a
double Schechter function provides a significantly improved description of the
KLF at z0.25 the evolution of the KLF is remarkably smooth,
with little or no evolution evident at faint (M_K>-20.5) or bright magnitudes
(M_K<-24.5). Instead, the KLF is seen to evolve rapidly at intermediate
magnitudes, with the number density of galaxies at M_K~-23 dropping by a factor
of ~5 over the redshift interval 0.25<z<3.75. Motivated by this, we explore a
simple description of the evolving KLF based on a double Schechter function
with fixed faint-end slopes (alpha_1=-0.5, alpha_2=-1.5) and a shared
characteristic magnitude (M_K*). According to this parameterisation, the
normalisation of the component which dominates the faint-end of the KLF remains
approximately constant, with phi*_2 decreasing by only a factor of ~2 between
z~0 and z~3.25. In contrast, the component which dominates the bright end of
the KLF at low redshifts evolves dramatically, becoming essentially negligible
by z~3. Finally, we note that within this parameterisation, the observed
evolution of M_K* between z~0 and z~3.25 is entirely consistent with M_K*
corresponding to a constant stellar mass of M*~5x10^10 Msun at all redshifts.Comment: 18 pages, 10 figures, accepted for publication in MNRA
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