2,231 research outputs found
Supermassive Black Hole Mass Functions at Intermediate Redshifts from Spheroid and AGN Luminosity Functions
Redshift evolution of supermassive black hole mass functions (BHMFs) is
investigated up to z ~ 1. BHMFs at intermediate redshifts are calculated in two
ways. One way is from early-type galaxy luminosity functions (LFs); we assume
an M_BH - L_sph correlation at a redshift by considering a passive evolution of
L_sph in the local relationship. The resultant BHMFs (spheroid-BHMFs) from LFs
of red sequence galaxies indicates a slight decrease of number density with
increasing redshift at M_BH > 10^{7.5-8} M_solar. Since a redshift evolution in
slope and zeropoint of the M_BH - L_sph relation is unlikely to be capable of
making such an evolution in BHMF, the evolution of the spheroid-BHMFs is
perhaps due mainly to the decreasing normalization in the galaxy LFs. We also
investigate how spheroid-BHMFs are affected by uncertainties existing in the
derivation in detail. The other way of deriving a BHMF is based on the
continuity equation for number density of SMBHs and LFs of active galactic
nucleus (AGN). The resultant BHMFs (AGN-BHMFs) show no clear evolution out to z
= 1 at M_BH > 10^8 M_solar, but exhibit a significant decrease with redshift in
the lower mass range. Comparison of the spheroid-BHMFs with the AGN-BHMFs
suggests that at M_BH > 10^{8} M_solar, the spheroid-BHMFs are broadly
consistent with the AGN-BHMFs out to z ~ 1. The agreement between the
spheroid-BHMFs and the AGN-BHMFs appears to support that most of the SMBHs are
already hosted by massive spheroids at z ~ 1 and they evolve without
significant mass growth since then.Comment: 13 pages, accepted for publication in MNRA
Progress in development of graded bandgap thin film solar cells with electroplated materials
Photovoltaic devices are developed mainly based on p-n or p-i-n type device structures, and these devices can utilise only a fraction of the solar spectrum. In order to further improve device parameters and move towards low-cost and high-efficiency next generation solar cells, device architectures capable of harvesting all photons available should be designed and developed. One such architecture is the fully graded bandgap device structure as proposed recently based on both n-type and p-type window layers. These designs have been experimentally tested using well researched GaAs/AlGaAs system producing impressive device parameters of open circuit voltage (Voc) ~1175 mV and fill factor (FF) ~0.85. The devices have also been experimentally tested for the evidence of impurity photovoltaic (PV) effect and impact ionisation taking place within the same device. Since these structures have been experimentally proved with a well-established semiconductor, the effort has been focussed on developing these devices using low-cost and scalable electroplated semiconductors, in order to minimise manufacturing cost. This paper reviews and summarises the work carried out during the past decade on this subject. Graded bandgap devices produced using only two or three electroplated semiconductor layers have been explored and their conversion efficiencies have gradually increased from 10.0%, through 12.8% to 15.3% for different structures. While the work is progressing along this line, the paper summarises the achievements to date
The COMBO-17 Survey: Evolution of the Galaxy Luminosity Function from 25,000 Galaxies with 0.2<z<1.2
We present a detailed empirical assessment of how the galaxy luminosity
function and stellar luminosity density evolves over the last half of the
universe's age (0.2<z<1.2) for galaxies of different spectral energy
distributions (SED). The results are based on ~25,000 galaxies (R<24) with
redshift measurements (sigma_z~0.03) and SEDs across 350..930 nm, derived from
medium-band photometry in 17 filters, observed as part of the COMBO-17 survey
(``Classifying Objects by Medium-Band Observations in 17 Filters'') over three
disjoint fields with a total area of 0.78 square degrees. Luminosity functions
(LF), binned in redshift and SED-type, are presented in the restframe passbands
of the SDSS r-band, the Johnson B-band and a synthetic UV continuum band at 280
nm. We find that the luminosity function depends strongly on SED-type at all
redshifts covered. The shape of the LF, i.e. the faint-end power-law slope,
does depend on SED type, but not on redshift. However, the redshift evolution
of the characteristic luminosity M* and density phi* depends strongly on
SED-type: (1) Early-type galaxies, defined as redder than a present-day
reference Sa spectrum, become drastically more abundant towards low redshift,
by a factor of 10 in the number density phi* from z=1.1 to now, and by a factor
of 4 in their contribution to the co-moving r-band luminosity density, j_r. (2)
Galaxies resembling present-day Sa- to Sbc-colours show a co-moving number
density and contribution to j_r that does not vary much with redshift. (3)
Galaxies with blue spectra reflecting strong star formation decrease towards
low redshift both in luminosity and density, and by a factor of 4 in their j_r
contribution. (abridged)Comment: 35 pages, 32 figures, submitted to Astronomy & Astrophysic
Mapping dusty star formation in and around a cluster at z=0.81 by wide-field imaging with AKARI
We present environmental dependence of dusty star forming activity in and
around the cluster RXJ1716.4+6708 at z=0.81 based on wide-field and
multi-wavelength observations with Suprime-Cam on the Subaru telescope and IRC
onboard the AKARI satellite. Our optical data shows that the optical colour
distribution of galaxies starts to dramatically change from blue to red at the
medium-density environment such as cluster outskirts, groups and filaments. By
combining with infrared data, we find that 15 micron galaxies tend to have
optical colours between the red sequence and the blue cloud with a tail into
the red sequence.
The spatial distribution of the 15 micron galaxies over ~200 arcmin^2 around
the cluster reveals that few 15 micron galaxies are detected in the cluster
central region. This is probably due to the low star forming activity in the
cluster core. However, interestingly, the fraction of 15 micron galaxies in the
medium-density environments is as high as in the low-density field, despite the
fact that the optical colours start to change in the medium-density
environments. Furthermore, we find that 15 micron galaxies which have optically
red colours (candidates for dusty red galaxies) and galaxies with high specific
star formation rates are also concentrated in the medium-density environment.
These results imply that the star forming activity in galaxies in groups and
filaments is enhanced due to some environmental effects specific to the
medium-density environment, and such a phenomenon is probably directly
connected to the truncation of star forming activity in galaxies seen as the
dramatic change in optical colours in such environments.Comment: 15 pages, 14 figures, accepted for publication in MNRA
Cosmic Star Formation: Constraints on the Galaxy Formation Models
We study the evolution of the cosmic star formation by computing the
luminosity density (LD) in the UV, B, J, and K bands, and the stellar mass
density (MD) of galaxies in two reference models of galaxy evolution: the pure
luminosity evolution (PLE) model developed by Calura & Matteucci (2003) and the
semi-analytical model (SAM) of hierarchical galaxy formation by Menci et al.
(2002). The former includes a detailed description of the chemical evolution of
galaxies of different morphological types with no density evolution; the latter
includes the merging histories of the galactic DM haloes, as predicted by the
hierarchical clustering scenario, but it does not contain morphological
classification nor chemical evolution. We find that at z< 1.5 both models are
consistent with the available data on the LD of galaxies in all the considered
bands. At high z, the LDs predicted in the PLE model show a peak due to the
formation of ellipticals, whereas the SAM predicts a gradual decrease of the
star formation and of the LD for z> 2.5. At such redshifts the PLE predictions
tend to overestimate the present data in the B band whereas the SAM tends to
underestimate the observed UV LD. As for the stellar MD, the PLE picture
predicts that nearly 50% and 85% of the present stellar mass are in place at
z=4 and z=1, respectively. According to the SAM, 50% and 60% of the present
stellar mass are in place at z=1.2 and z=1, respectively. Both predictions fit
the observed MD up to z=1. At z>1, the PLE model and the SAM tend to
overestimate and underestimate the observed values, respectively. We discuss
the origin of the above model results, and the role of observational
uncertainties (such as dust extinction) in comparing models with observations.Comment: 14 pages, accepted for publication in MNRA
Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes.
Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase in methylammonium bromide (MABr) molar proportion, and we spatially confined the exciton in uniform MAPbBr3 nanograins (average diameter = 99.7 nanometers) formed by a nanocrystal pinning process and concomitant reduction of exciton diffusion length to 67 nanometers. These changes caused substantial increases in steady-state photoluminescence intensity and efficiency of MAPbBr3 nanograin layers.This work was partially supported by Samsung Research Funding Center of Samsung Electronics under Project Number SRFC-MA-1402-07. A.S. was partially supported by the Engineering and Physical Sciences Research Council (UK).This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by the American Association for the Advancement of Science
Galaxy Luminosity Functions to z~1: DEEP2 vs. COMBO-17 and Implications for Red Galaxy Formation
The DEEP2 and COMBO-17 surveys are used to study the evolution of the
luminosity function of red and blue galaxies to . Schechter function
fits show that, since , dims by 1.3 mag per unit redshift
for both color classes, of blue galaxies shows little change, while
for red galaxies has formally nearly quadrupled. At face value, the
number density of blue galaxies has remained roughly constant since ,
whereas that of red galaxies has been rising. Luminosity densities support both
conclusions, but we note that most red-galaxy evolution occurs between our data
and local surveys and in our highest redshift bin, where the data are weakest.
We discuss the implications of having most red galaxies emerge after
from precursors among the blue population, taking into account the properties
of local and distant E/S0s. We suggest a ``mixed'' scenario in which some blue
galaxies have their star-formation quenched in gas-rich mergers, migrate to the
red sequence with a variety of masses, and merge further on the red sequence in
one or more purely stellar mergers. E/S0s of a given mass today will have
formed via different routes, in a manner that may help to explain the
fundamental plane and other local scaling laws.Comment: Submitted to ApJ. 73 pages, 12 figures. Part II of a two-paper
series. The entire paper is available as a single postscript file at:
http://www.ucolick.org/~cnaw/paper2_submitted.ps.g
Evolution in the Disks and Bulges of Group Galaxies since z=0.4
We present quantitative morphology measurements of a sample of optically
selected group galaxies at 0.3 < z < 0.55 using the Hubble Space Telescope
(HST) Advanced Camera for Surveys (ACS) and the GIM2D surface
brightness--fitting software package. The group sample is derived from the
Canadian Network for Observational Cosmology Field Redshift survey (CNOC2) and
follow-up Magellan spectroscopy. We compare these measurements to a similarly
selected group sample from the Millennium Galaxy Catalogue (MGC) at 0.05 < z <
0.12. We find that, at both epochs, the group and field fractional bulge
luminosity (B/T) distributions differ significantly, with the dominant
difference being a deficit of disk--dominated (B/T < 0.2) galaxies in the group
samples. At fixed luminosity, z=0.4 groups have ~ 5.5 +/- 2 % fewer
disk--dominated galaxies than the field, while by z=0.1 this difference has
increased to ~ 19 +/- 6 %. Despite the morphological evolution we see no
evidence that the group environment is actively perturbing or otherwise
affecting the entire existing disk population. At both redshifts, the disks of
group galaxies have similar scaling relations and show similar median
asymmetries as the disks of field galaxies. We do find evidence that the
fraction of highly asymmetric, bulge--dominated galaxies is 6 +/- 3 % higher in
groups than in the field, suggesting there may be enhanced merging in group
environments. We replicate our group samples at z=0.4 and z=0 using the
semi-analytic galaxy catalogues of Bower et al (2006). This model accurately
reproduces the B/T distributions of the group and field at z=0.1. However, the
model does not reproduce our finding that the deficit of disks in groups has
increased significantly since z=0.4.Comment: Accepted for publication in MNRAS. 20 pages, 17 figure
Atomic transition frequencies, isotope shifts, and sensitivity to variation of the fine structure constant for studies of quasar absorption spectra
Theories unifying gravity with other interactions suggest spatial and
temporal variation of fundamental "constants" in the Universe. A change in the
fine structure constant, alpha, could be detected via shifts in the frequencies
of atomic transitions in quasar absorption systems. Recent studies using 140
absorption systems from the Keck telescope and 153 from the Very Large
Telescope, suggest that alpha varies spatially. That is, in one direction on
the sky alpha seems to have been smaller at the time of absorption, while in
the opposite direction it seems to have been larger.
To continue this study we need accurate laboratory measurements of atomic
transition frequencies. The aim of this paper is to provide a compilation of
transitions of importance to the search for alpha variation. They are E1
transitions to the ground state in several different atoms and ions, with
wavelengths ranging from around 900 - 6000 A, and require an accuracy of better
than 10^{-4} A. We discuss isotope shift measurements that are needed in order
to resolve systematic effects in the study. The coefficients of sensitivity to
alpha-variation (q) are also presented.Comment: Includes updated version of the "alpha line" lis
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