51 research outputs found
Orange Organic Long-persistent Luminescence from an Electron Donor/Acceptor Binary System
Organic long-persistent luminescence (LPL) materials can overcome the disadvantages of inorganic LPL materials in terms of element sustainability, processability, and color tunability. However, all published electron donor/acceptor binary organic LPL systems show green emission. Here, we report an organic LPL system consisting of N,N,N\u27,N\u27-tetrakis(p-diisobutylaminophenyl)-p-phenylenediamine (TBAPD) as a donor dopant and 2,8-bis(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) as an acceptor host. The TBAPD/PPT film exhibits orange photoluminescence (CIEx, CIEy = 0.49, 0.49) and LPL (CIEx, CIEy = 0.51, 0.48)
Dust Emission as a Function of Stellar Population Age in the Nearby Galaxy M33
Dust emission at 8 micron has been extensively calibrated as an indicator of
current star formation rate for galaxies and ~kpc-size regions within galaxies.
Yet, the exact link between the 8 micron emission and the young stellar
populations in galaxies is still under question, as dust grains can be
stochastically heated also by older field stars. In order to investigate this
link, we have combined mid-infrared images from the Spitzer Space Telescope
with a published star cluster candidates catalog for the Local Group galaxy
M33. M33 is sufficiently close that the Spitzer's 8 micron images resolve
individual regions of star formation. Star clusters represent almost-single-age
stellar populations, which are significantly easier to model than more complex
mixtures of stars. We find a decrease in the 8 micron luminosity per unit
stellar mass as a function of age of the star clusters, with a large scatter
that is consistent with varying fractions of stellar light absorbed by dust.
The decrease and scatter both confirm findings based on more distant galaxies
and are well described by simple models for the dust emission of a young
stellar population. We conclude that the dust emission at 8 micron depends
sensitively on the age of the stellar population, out to at least the oldest
age analyzed here, ~400 Myr. This dependence complicates the use of the 8
micron emission as a star formation rate indicator, at least for small galactic
regions and individual star forming regions. By leveraging the Spitzer legacy,
this investigation paves the way for future explorations with the James Webb
Space Telescope.Comment: Accepted for publication on ApJ. Includes 5 figure
Influence of energy gap between charge-transfer and locally excited states on organic long persistence luminescence
Organic long-persistent luminescence (LPL) is an organic luminescence system that slowly releases stored exciton energy as light. Organic LPL materials have several advantages over inorganic LPL materials in terms of functionality, flexibility, transparency, and solution-processability. However, the molecular selection strategies for the organic LPL system still remain unclear. Here we report that the energy gap between the lowest localized triplet excited state and the lowest singlet charge-transfer excited state in the exciplex system significantly controls the LPL performance. Changes in the LPL duration and spectra properties are systematically investigated for three donor materials having a different energy gap. When the energy level of the lowest localized triplet excited state is much lower than that of the charge-transfer excited state, the system exhibits a short LPL duration and clear two distinct emission features originating from exciplex fluorescence and donor phosphorescence
Spectroscopic Observation and Analysis of HII regions in M33 with MMT: Temperatures and Oxygen Abundances
The spectra of 413 star-forming (or HII) regions in M33 (NGC 598) were
observed by using the multifiber spectrograph of Hectospec at the 6.5-m
Multiple Mirror Telescope (MMT). By using this homogeneous spectra sample, we
measured the intensities of emission lines and some physical parameters, such
as electron temperatures, electron densities, and metallicities. Oxygen
abundances were derived via the direct method (when available) and two
empirical strong-line methods, namely, O3N2 and N2. In the high-metallicity
end, oxygen abundances derived from O3N2 calibration were higher than those
derived from N2 index, indicating an inconsistency between O3N2 and N2
calibrations. We presented a detailed analysis of the spatial distribution of
gas-phase oxygen abundances in M33 and confirmed the existence of the
axisymmetric global metallicity distribution widely assumed in literature.
Local variations were also observed and subsequently associated with spiral
structures to provide evidence of radial migration driven by arms. Our O/H
gradient fitted out to 1.1 resulted in slopes of ,
, and dex utilizing abundances from
O3N2, N2 diagnostics, and direct method, respectively.Comment: Accepted for publication in Ap
Solution to the conflict between the resolved and unresolved galaxy stellar mass estimation from the perspective of JWST
By utilizing the spatially-resolved photometry of galaxies at in
the CEERS field, we estimate the resolved and unresolved stellar mass via
spectral energy distribution (SED) fitting to study the discrepancy between
them. We first compare derived from photometry with and without the
JWST wavelength coverage and find that can be overestimated by up to
0.2 dex when lacking rest-frame NIR data. The SED fitting process tends to
overestimate both stellar age and dust attenuation in the absence of rest-frame
NIR data, consequently leading to a larger observed mass-to-light ratio and
hence an elevated . With the inclusion of the JWST NIR photometry, we
find no significant disparity between the resolved and unresolved stellar mass
estimates, providing a plausible solution to the conflict between them out to
. Further investigation demonstrates that reliable
estimates can be obtained, regardless of whether they are derived from
spatially resolved or spatially unresolved photometry, so long as the reddest
filter included in the SED fitting has a rest-frame wavelength larger than
10000 \AA.Comment: 8 pages, 5 figures, accepted by Ap
The Size-Mass Relation of Post-Starburst Galaxies in the Local Universe
We present a study of the size--mass relation for local post-starburst (PSB)
galaxies at selected from the Sloan Digital Sky Survey Data
Release 8. We find that PSB galaxies with stellar mass () at
have their galaxy size smaller than or
comparable with those of quiescent galaxies (QGs). After controlling redshift
and stellar mass, the sizes of PSBs are smaller on average than
those of QGs, such differences become larger and significant towards the
low- end, especially at where PSBs can be on average smaller than QGs.
In comparison with predictions of possible PSB evolutionary pathways from
cosmological simulations, we suggest that a fast quenching of star formation
following a short-lived starburst event (might be induced by major merger)
should be the dominated pathway of our PSB sample. Furthermore, by
cross-matching with group catalogs, we confirm that local PSBs at
are more clustered than more massive ones. PSBs
resided in groups are found to be slightly larger in galaxy size and more
disk-like compared to field PSBs, which is qualitatively consistent with and
thus hints the environment-driven fast quenching pathway for group PSBs. Taken
together, our results support multiple evolutionary pathways for local PSB
galaxies: while massive PSBs are thought of as products of fast quenching
following a major merger-induced starburst, environment-induced fast quenching
should play a role in the evolution of less massive PSBs, especially at
.Comment: 16 pages, 7 figures; accepted for publication in Ap
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