1,119 research outputs found
The Core Mass Function in the Massive Protocluster G286.21+0.17 revealed by ALMA
We study the core mass function (CMF) of the massive protocluster
G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array via 1.3~mm
continuum emission at a resolution of 1.0\arcsec\ (2500~au). We have mapped a
field of 5.3\arcmin5.3\arcmin\ centered on the protocluster clump. We
measure the CMF in the central region, exploring various core detection
algorithms, which give source numbers ranging from 60 to 125, depending on
parameter selection. We estimate completeness corrections due to imperfect flux
recovery and core identification via artificial core insertion experiments. For
masses , the fiducial dendrogram-identified CMF can be fit
with a power law of the form
with , slightly shallower than, but still consistent with, the
index of the Salpeter stellar initial mass function of 1.35.
Clumpfind-identified CMFs are significantly shallower with
. While raw CMFs show a peak near ,
completeness-corrected CMFs are consistent with a single power law extending
down to , with only a tentative indication of a shallowing
of the slope around . We discuss the implications of these
results for star and star cluster formation theories.Comment: 11 pages, accepted by Ap
The Core Mass Function Across Galactic Environments. II. Infrared Dark Cloud Clumps
We study the core mass function (CMF) within 32 dense clumps in seven
infrared dark clouds (IRDCs) with the Atacama Large Millimeter/submillimeter
Array (ALMA) via 1.3~mm continuum emission at a resolution of 1". We have
identified 107 cores with the dendrogram algorithm, with a median radius of
about 0.02 pc. Their masses range from 0.261 to 178 . After applying
completeness corrections, we fit the combined IRDC CMF with a power law of the
form and derive an index of
for and
for , which is a significantly
more top-heavy distribution than the Salpeter stellar initial mass function
(IMF) index of 1.35. We also make a direct comparison of these IRDC clump CMF
results to those measured in the more evolved protocluster G286 derived with
similar methods, which have and in
these mass ranges, respectively. These results provide a hint that, especially
for the range where completeness corrections are modest,
the CMF in high pressure, early-stage environments of IRDC clumps may be
top-heavy compared to that in the more evolved, global environment of the G286
protoclusters. However, larger samples of cores probing these different
environments are needed to better establish the robustness of this potential
CMF variation.Comment: Accepted to ApJ, 15 pages, 7 figure
Image Fusion with Contrast Improving and Feature Preserving
The goal of image fusion is to obtain a fused image that contains most significant information in all input images which were captured by different sensors from the same scene. In particular, the fusion process should improve the contrast and keep the integrity of significant features from input images. In this paper, we propose a region-based image fusion method to fuse spatially registered visible and infrared images while improving the contrast and preserving the significant features of input images. At first, the proposed method decomposes input images into base layers and detail layers using a bilateral filter. Then the base layers of the input images are segmented into regions. Third, a region-based decision map is proposed to represent the importance of every region. The decision map is obtained by calculating the weights of regions according to the gray-level difference between each region and its neighboring regions in the base layers. At last, the detail layers and the base layers are separately fused by different fusion rules based on the same decision map to generate a final fused image. Experimental results qualitatively and quantitatively demonstrate that the proposed method can improve the contrast of fused images and preserve more features of input images than several previous image fusion methods
Implications of the lens redshift distribution of strong lensing systems: cosmological parameters and the global properties of early-type galaxies
In this paper, we assemble a well-defined sample of early-type gravitational
lenses extracted from a large collection of 158 systems, and use the redshift
distribution of galactic-scale lenses to test the standard cosmological model
(CDM) and the modified gravity theory (DGP). Two additional
sub-samples are also included to account for possible selection effect
introduced by the detectability of lens galaxies. Our results show that
independent measurement of the matter density parameter () could be
expected from such strong lensing statistics. Based on future measurements of
strong lensing systems from the forthcoming LSST survey, one can expect
to be estimated at the precision of ,
which provides a better constraint on than \textit{Planck} 2015
results. Moreover, use the lens redshift test is also used to constrain the
characteristic velocity dispersion of the lensing galaxies, which is well
consistent with that derived from the optical spectroscopic observations. A
parameter is adopted to quantify the relation between the lensing-based
velocity dispersion and the corresponding stellar value. Finally, the
accumulation of detectable galactic lenses from future LSST survey would lead
to more stringent fits of , which encourages us to test
the global properties of early-type galaxies at much higher accuracy.Comment: 12 pages, accepted for publication in The European Physical Journal
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