147 research outputs found
The Conditional Colour-Magnitude Distribution: I. A Comprehensive Model of the Colour-Magnitude-Halo Mass Distribution of Present-Day Galaxies
We formulate a model of the conditional colour-magnitude distribution (CCMD)
to describe the distribution of galaxy luminosity and colour as a function of
halo mass. It consists of two populations of different colour distributions,
dubbed pseudo-blue and pseudo-red, respectively, with each further separated
into central and satellite galaxies. We define a global parameterization of
these four colour-magnitude distributions and their dependence on halo mass,
and we infer parameter values by simultaneously fitting the space densities and
auto-correlation functions of 79 galaxy samples from the Sloan Digital Sky
Survey defined by fine bins in the colour-magnitude diagram (CMD). The model
deprojects the overall galaxy CMD, revealing its tomograph along the halo mass
direction. The bimodality of the colour distribution is driven by central
galaxies at most luminosities, though at low luminosities it is driven by the
difference between blue centrals and red satellites. For central galaxies, the
two pseudo-colour components are distinct and orthogonal to each other in the
CCMD: at fixed halo mass, pseudo-blue galaxies have a narrow luminosity range
and broad colour range, while pseudo-red galaxies have a narrow colour range
and broad luminosity range. For pseudo-blue centrals, luminosity correlates
tightly with halo mass, while for pseudo-red galaxies colour correlates more
tightly (redder galaxies in more massive haloes). The satellite fraction is
higher for redder and for fainter galaxies, with colour a stronger indicator
than luminosity. We discuss the implications of the results and further
applications of the CCMD model.Comment: 32 pages, 26 figures, accepted for publication in MNRA
Non-local Attention Optimized Deep Image Compression
This paper proposes a novel Non-Local Attention Optimized Deep Image
Compression (NLAIC) framework, which is built on top of the popular variational
auto-encoder (VAE) structure. Our NLAIC framework embeds non-local operations
in the encoders and decoders for both image and latent feature probability
information (known as hyperprior) to capture both local and global
correlations, and apply attention mechanism to generate masks that are used to
weigh the features for the image and hyperprior, which implicitly adapt bit
allocation for different features based on their importance. Furthermore, both
hyperpriors and spatial-channel neighbors of the latent features are used to
improve entropy coding. The proposed model outperforms the existing methods on
Kodak dataset, including learned (e.g., Balle2019, Balle2018) and conventional
(e.g., BPG, JPEG2000, JPEG) image compression methods, for both PSNR and
MS-SSIM distortion metrics
The Magnetic Properties of 1111-type Diluted Magnetic Semiconductor (LaBa)(ZnMn)AsO in the Low Doping Regime
We investigated the magnetic properties of
(LaBa)(ZnMn)AsO with varying from 0.005 to 0.05
at an external magnetic field of 1000 Oe. For doping levels of 0.01,
the system remains paramagnetic down to the lowest measurable temperature of 2
K. Only when the doping level increases to = 0.02 does the ferromagnetic
ordering appear. Our analysis indicates that antiferromagnetic exchange
interactions dominate for 0.01, as shown by the negative Weiss
temperature fitted from the magnetization data. The Weiss temperature becomes
positive, i.e., ferromagnetic coupling starts to dominate, for 0.02.
The Mn-Mn spin interaction parameter is estimated to be in
the order of 10 K for both 0.01 (antiferromagnetic ordered state)
and 0.02 (ferromagnetic ordered state). Our results unequivocally
demonstrate the competition between ferromagnetic and antiferromagnetic
exchange interactions in carrier-mediated ferromagnetic systems.Comment: 9 pages, 3 figure
Molecular properties of PTCDA on graphene grown on a rectangular symmetry substrate
The chemical modulation associated with moiré patterns, arising at the interface of metal-supported 2D material systems, affects the interaction between molecules and 2D materials on surfaces. Since the crystallography of the support influences the interfacial chemistry of the moiré modulation, this parameter could also play a role in the graphene-molecule interaction, although studies using non-hexagonal metal supports are needed to investigate this effect. It is a key issue since graphene appears combined with organic films in most technological advances related to this material. Here, we have characterized the properties of PTCDA molecules on graphene grown on Rh(110) substrates, which exhibit a rectangular atomic packing, using scanning tunneling microscopy and spectroscopy. The results showed that PTCDA molecules are arranged on the surface into a herringbone structure exhibiting a long-range ordering, which grows continuously across substrate atomic steps edge and dislocations. The quasi-1D moiré patterns of the Gr/Rh(110) surfaces are found to provide an inert chemical landscape for the molecular arrangement. Bias voltage-dependent imaging of the orbital structure of PTCDA molecules and differential conductance spectra back up a weak molecule–substrate interaction scheme. Finally, the α-polymorph of bulk crystal PTCDA has been determined as the favored stacking configuration for bilayer molecules on Gr/Rh(110)Financial support
from the Spanish Ministerio de Economía y Competitividad (MINECO)
and Fondo Europeo de Desarrollo Regional (FEDER) under grant No.
MAT2016-77852-C2-2-R, as well as, from the Spanish Ministerio de
Ciencia e Innovacion ´ (MICINN) through the “María de Maetzu” program
for units of excellence in R&D (grant No. CEX2018-000805-M) is
gratefully acknowledged. A. J. M.-G. acknowledges funding by the
Spanish Ministerio de Ciencia e Innovacion ´ (MICINN) through Project
No. PID2020-116619GA-C22, as well as, from the Comunidad de Madrid
and the Universidad Autonoma ´ de Madrid under project SI3/PJI/2021-
0050
Constraining the HI-Halo Mass Relation From Galaxy Clustering
We study the dependence of galaxy clustering on atomic gas mass using a
sample of 16,000 galaxies with redshift in the range of
and HI mass of , drawn from the 70% complete sample
of the Arecibo Legacy Fast ALFA survey. We construct subsamples of galaxies
with above different thresholds, and make volume-limited
clustering measurements in terms of three statistics: the projected two-point
correlation function, the projected cross-correlation function with respect to
a reference sample selected from the Sloan Digital Sky Survey, and the
redshift-space monopole moment. In contrast to previous studies, which found
no/weak HI-mass dependence, we find both the clustering amplitude on scales
above a few Mpc and the bias factors to increase significantly with increasing
HI mass for subsamples with HI mass thresholds above . For HI
mass thresholds below , while the measurements have large
uncertainties caused by the limited survey volume and sample size, the inferred
galaxy bias factors are systematically lower than the minimum halo bias factor
from mass-selected halo samples. The simple halo model, in which galaxy content
is only determined by halo mass, has difficulties in interpreting the
clustering measurements of the HI-selected samples. We extend the simple model
by including the halo formation time as an additional parameter. A model that
puts HI-rich galaxies into halos that formed late can reproduce the clustering
measurements reasonably well. We present the implications of our best-fitting
model on the correlation of HI mass with halo mass and formation time, as well
as the halo occupation distributions and HI mass functions for central and
satellite galaxies. These results are compared with the predictions from
semi-analytic galaxy formation models and hydrodynamic galaxy formation
simulations.Comment: Accepted for publication in ApJ. The 2PCF measurements are available
at http://sdss4.shao.ac.cn/guoh
Lateral Heterostructures of Graphene and h-BN with Atomic Lattice Coherence and Tunable Rotational Order
In-plane heterostructures of graphene and hexagonal boron nitride (h-BN) exhibit exceptional properties, which are highly sensitive to the structure of the alternating domains. Nevertheless, achieving accurate control over their structural properties, while keeping a high perfection at the graphene-h-BN boundaries, still remains a challenge. Here, the growth of lateral heterostructures of graphene and h-BN on Rh(110) surfaces is reported. The choice of the 2D material, grown firstly, determines the structural properties of the whole heterostructure layer, allowing to have control over the rotational order of the domains. The atomic-scale observation of the boundaries demonstrates a perfect lateral matching. In-plane heterostructures floating over an oxygen layer have been successfully obtained, enabling to observe intervalley scattering processes in graphene regions. The high tuning capabilities of these heterostructures, along with their good structural quality, even around the boundaries, suggest their usage as test beds for fundamental studies aiming at the development of novel nanomaterials with tailored properties.Financial support
from the Spanish Ministerio de Economía y Competitividad (MINECO)
and Fondo Europeo de Desarrollo Regional (FEDER) under grant No.
MAT2016-77852-C2-2-R, as well as, from the Spanish Ministerio de
Ciencia e Innovación through the “María de Maetzu” program for units
of excellence in R&D (grant No. CEX2018-000805-M) was gratefully
acknowledged. A. J. M.-G. acknowledged funding by the Spanish
Ministerio de Ciencia e Innovación (MICINN through Project No.
PID2020-116619GA-C22, as well as, by the Comunidad de Madrid and
Universidad Autónoma de Madrid under Project No. SI3/PJI/2021-00500.
Funding sources: Spanish MINECO (Ref: MAT2016-77852-C2-2-R). Spanish
MICINN (Ref: PID2020-116619GA-C22). Comunidad de Madrid (CAM)
and Universidad Autónoma de Madrid (UAM) (Ref: SI3/PJI/2021-00500
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