2,444 research outputs found
The Carnegie-Irvine Galaxy Survey. III. The Three-Component Structure of Nearby Elliptical Galaxies
Motivated by recent developments in our understanding of the formation and
evolution of massive galaxies, we explore the detailed photometric structure of
a representative sample of 94 bright, nearby elliptical galaxies, using
high-quality optical images from the Carnegie-Irvine Galaxy Survey. The sample
spans a range of environments and stellar masses, from M* = 10^{10.2} to
10^{12.0} solar mass. We exploit the unique capabilities of two-dimensional
image decomposition to explore the possibility that local elliptical galaxies
may contain photometrically distinct substructure that can shed light on their
evolutionary history. Compared with the traditional one-dimensional approach,
these two-dimensional models are capable of consistently recovering the surface
brightness distribution and the systematic radial variation of geometric
information at the same time. Contrary to conventional perception, we find that
the global light distribution of the majority (>75%) of elliptical galaxies is
not well described by a single Sersic function. Instead, we propose that local
elliptical galaxies generically contain three subcomponents: a compact (R_e < 1
kpc) inner component with luminosity fraction f ~ 0.1-0.15; an
intermediate-scale (R_e ~ 2.5 kpc) middle component with f ~ 0.2-0.25; and a
dominant (f = 0.6), extended (R_e ~ 10 kpc) outer envelope. All subcomponents
have average Sersic indices n ~ 1-2, significantly lower than the values
typically obtained from single-component fits. The individual subcomponents
follow well-defined photometric scaling relations and the stellar mass-size
relation. We discuss the physical nature of the substructures and their
implications for the formation of massive elliptical galaxies.Comment: To appear in The Astrophysical Journal; 36 pages, 2 tables, 38
figures; For the full resolution version, see:
http://users.obs.carnegiescience.edu/shuang/PaperIII.pdf ; For the atlas of
all selected models, see
http://users.obs.carnegiescience.edu/shuang/AppendixE.pd
The Carnegie-Irvine Galaxy Survey. IV. A Method to Determine the Average Mass Ratio of Mergers That Built Massive Elliptical Galaxies
Many recent observations and numerical simulations suggest that nearby
massive, early-type galaxies were formed through a "two-phase" process. In the
proposed second phase, the extended stellar envelope was accumulated through
many dry mergers. However, details of the past merger history of present-day
ellipticals, such as the typical merger mass ratio, are difficult to constrain
observationally. Within the context and assumptions of the two-phase formation
scenario, we propose a straightforward method, using photometric data alone, to
estimate the average mass ratio of mergers that contributed to the build-up of
massive elliptical galaxies. We study a sample of nearby massive elliptical
galaxies selected from the Carnegie-Irvine Galaxy Survey, using two-dimensional
analysis to decompose their light distribution into an inner, denser component
plus an extended, outer envelope, each having a different optical color. The
combination of these two substructures accurately recovers the negative color
gradient exhibited by the galaxy as whole. The color difference between the two
components ( ~ 0.10 mag; ~ 0.14 mag), based on the
slope of the M_stellar-color relation for nearby early-type galaxies, can be
translated into an estimate of the average mass ratio of the mergers. The rough
estimate, 1:5 to 1:10, is consistent with the expectation of the two-phase
formation scenario, suggesting that minor mergers were largely responsible for
building up to the outer stellar envelope of present-day massive ellipticals.
With the help of accurate photometry, large sample size, and more choices of
colors promised by ongoing and future surveys, the approach proposed here can
reveal more insights into the growth of massive galaxies during the last few
Gyr.Comment: Accepted by ApJ; 20 pages, 11 figures, 1 table; The high resolution
figures and the full table can be downloaded from here:
https://github.com/dr-guangtou/cgs_colorgra
Designing Visible Light-Cured Thiol-Acrylate Hydrogels for Studying the HIPPO Pathway Activation in Hepatocellular Carcinoma Cells
Various polymerization mechanisms have been developed to prepare peptide-immobilized poly(ethylene glycol) (PEG) hydrogels, a class of biomaterials suitable for studying cell biology in vitro. Here, a visible light mediated thiol-acrylate photopolymerization scheme is reported to synthesize dually degradable PEG-peptide hydrogels with controllable crosslinking and degradability. The influence of immobilized monothiol pendant peptide is systematically evaluated on the crosslinking of these hydrogels. Further, methods are proposed to modulate hydrogel crosslinking, including adjusting concentration of comonomer or altering the design of multifunctional peptide crosslinker. Due to the formation of thioether ester bonds, these hydrogels are hydrolytically degradable. If the dithiol peptide linkers used are susceptible to protease cleavage, these thiol-acrylate hydrogels can be designed to undergo partial proteolysis. The differences between linear and multiarm PEG-acrylate (i.e., PEGDA vs PEG4A) are also evaluated. Finally, the use of the mixed-mode thiol-acrylate PEG4A-peptide hydrogels is explored for in situ encapsulation of hepatocellular carcinoma cells (Huh7). The effects of matrix stiffness and integrin binding motif (e.g., RGDS) on Huh7 cell growth and HIPPO pathway activation are studied using PEG4A-peptide hydrogels. This visible light poly-merized thiol-acrylate hydrogel system represents an alternative to existing light-cured hydrogel platforms and shall be useful in many biomedical applications
Stimulation of ribosomal frameshifting by antisense LNA
Programmed ribosomal frameshifting is a translational recoding mechanism commonly used by RNA viruses to express two or more proteins from a single mRNA at a fixed ratio. An essential element in this process is the presence of an RNA secondary structure, such as a pseudoknot or a hairpin, located downstream of the slippery sequence. Here, we have tested the efficiency of RNA oligonucleotides annealing downstream of the slippery sequence to induce frameshifting in vitro. Maximal frameshifting was observed with oligonucleotides of 12–18 nt. Antisense oligonucleotides bearing locked nucleid acid (LNA) modifications also proved to be efficient frameshift-stimulators in contrast to DNA oligonucleotides. The number, sequence and location of LNA bases in an otherwise DNA oligonucleotide have to be carefully manipulated to obtain optimal levels of frameshifting. Our data favor a model in which RNA stability at the entrance of the ribosomal tunnel is the major determinant of stimulating slippage rather than a specific three-dimensional structure of the stimulating RNA element
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