分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Searching in the MaNGA IFU survey, I identify 9 galaxies that have strong Balmer absorption lines and weak nebular emission lines measured from the spectra integrated over the entire IFUs. The spectral features measured from the bulk of the stellar light make these galaxies local analogs of high-redshift spectroscopically-selected post-starburst galaxies, thus, proxies to understand the mechanisms producing post-starburst galaxies at high-redshifts. I present the distributions of absorption-line indices and emission-line strengths, as well as stellar kinematics of these local post-starburst galaxies. Almost all local post-starburst galaxies have central compact emission-line regions at the central $<1$ kpc, mostly powered by weak star-formation activities. The age-sensitive absorption line indices EW(H$\delta$) and Dn4000 indicate that the stellar populations at the outskirts are older. Toy stellar population synthesis models suggest that the entire galaxies are experiencing a rapid decline of star formation with residual star-formation activities at the centers. These features demand that most post-starburst galaxies are the aftermath of highly dissipative processes that drive gas into centers, invoke centrally-concentrated star formation, then quench the galaxies. Meanwhiles, when measurable, post-starburst galaxies have the directions of maximum stellar velocity gradients align with photometric major axes, which suggest against major mergers being the principal driving mechanism, while gas-rich minor mergers are plausible. While directly obtaining the same quality of spatially-resolved spectra of high-redshift post-starburst galaxies is very difficult, finding proper local counterparts provides an alternative to understand quenching processes in the distant Universe.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： In this study, we theoretically and numerically investigate the resonant modes and reflectance of an optical grating consisting of a wavy dielectric slab by applying the spectral element method. The presence of the wavy shape transforms the waveguide modes into leaky resonant modes. A few resonant modes with specific longitudinal wave number have infinitely large Q factor, while the other resonant modes have finite Q factor. For the leaky resonant mode with zero longitudinal wave number, the Q factor is inversely proportional to the amplitude of the wavy shape. An array of multiple low-Q wavy gratings has a high reflectance in a large bandwidth. A double-layer wavy grating forms a Fabry-Perot cavity, which hosts Fabry-Perot bound states in the continuum (BICs) at the resonant frequency. The Q-factor of the Fabry-Perot cavity can be tuned by adjusting the distance between the two wavy slabs. The wavy shape could be generated by a vibrational wave in a flat dielectric slab so that the BICs mode and wideband reflectance could be controlled on-demand.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： We present nonlinear optical four-wave mixing in a silicon nanodisk dimer metasurface. Under the oblique incident plane waves, the designed metasurface exhibits a multi-resonant feature with simultaneous excitations of three quasi-bound states in the continuum (BIC). Through employing these quasi-BICs with maximizing electric field energy at the input bump wavelengths, significant enhancement of third-order nonlinear processes including third-harmonic generation, degenerate and non-degenerate four-wave mixing are demonstrated, giving rise to ten new frequencies in the visible wavelengths. This work may lead to a new frontier of ultracompact optical mixer for applications in optical circuitry, ultrasensitive sensing, and quantum nanophotonics.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The sample of time-delay gravitational lenses appropriate for studying the geometry of the Universe continues to grow as dedicated campaigns, such as the Dark Energy Survey, the VST ATLAS survey, and the Large Synoptic Survey Telescope, complete their census of high-redshift sources. This catalog now includes hundreds of strong lensing systems, at least 31 of which have reasonably accurate time delay measurements. In this paper, we use them to compare the predictions of two competing Friedmann-Lemaitre-Robertson-Walker models: flat LCDM, characterized by two adjustable parameters (H_0 and Omega_m), and the R_h=ct universe (with H_0 as the single free variable). Over the past decade, the latter has accounted for the data better than the standard model, most recently the emergence of well-formed galaxies discovered by JWST at cosmic dawn. Here we show that the current sample of time-delay lenses favours R_h=ct with a likelihood of ~84% versus ~16% for the standard model. This level of accuracy will greatly improve as the ongoing surveys uncover many thousands additional lens systems over the next several years.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Kirchhoff s law is one of the most fundamental law in thermal radiation. The violation of traditional Kirchhoff s law provides opportunities for higher energy conversion efficiency. Various micro-structures have been proposed to realize single-band nonreciprocal thermal emitters. However, dual-band nonreciprocal thermal emitters remain barely investigated. In this paper, we introduce magneto-optical material into a cascading one-dimensional (1-D) magnetophotonic crystal (MPC) heterostructure composed of two 1-D MPCs and a metal layer. Assisted by the nonreciprocity of the magneto-optical material and the coupling effect of two optical Tamm states (OTSs), a dual-band nonreciprocal lithography-free thermal emitter is achieved. The emitter exhibits strong dual-band nonreciprocal radiation at the wavelengths of 15.337 um and 15.731 um when the external magnetic field is 3 T and the angle of incidence is 56 degree. Besides, the magnetic field distribution is also calculated to confirm that the dual-band nonreciprocal radiation originates from the coupling effect between two OTSs. Our work may pave the way for constructing dual-band and multi-band nonreciprocal thermal emitters.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： In this work, the hyperbolic phonon polaritons (HPPs) in ultrathin hBN sheets are numerically studied. The dispersion relation and distribution of electric field are calculated to confirm the excitation of HPPs. Besides, the coupling effect between HPPs of two ultrathin hBN sheets are investigated. When the distance between two hBN sheets are smaller than the propagation length of the HPPs in the air, the HPPs can be strongly coupled. Therefore, the photon tunneling probability can be greatly enhanced. The split of the HPPs is similar to that of the surface waves, and such phenomenon is well explained in this work. We believe that this work will deepen our understanding of the HPPs in ultrathin hyperbolic materials. In addition, the knowledge about the HPPs will help us understand the near-field radiative heat transfer between hyperbolic materials.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Tailoring optical nonlinear effects (e.g. harmonic generation, sum-frequency mixing, etc.) in the recently emerging all-dielectric platform is important for both the fundamental science and industrial development of high-efficiency, ultrafast, and miniaturized photonic devices. In this work, we propose a novel paradigm for dynamically switchable high-harmonic generation in Silicon nanodimer metasurfaces by exploiting polarization-controlled dual bound states in the continuum (BIC). Owing to the high-quality factor of BIC resonances, efficient harmonic signals including the third-harmonic generation and fifth-harmonic generation from a direct process as well as a cascaded process by degenerate four-wave mixing are obtained. Moreover, the BICs and their resonantly enhanced harmonics can be switched on or off with high selectivity respect to the fundamental pump polarization. Compared with previous reports, our work provide a simple but effective tuning strategy by fully exploring the structural symmetry and polarization degree of freedom rather than resorting to additional external stimuli, which would have great advantages in smart designing tunable and switchable nonlinear light source for chip-scale applications.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： To violate Kirchhoff s law is very important in the areas of thermal radiation. However, due to the weak nonreciprocity in natural materials, it is necessary to engineer novel structures to break the balance between emission and absorption. In this work, we introduce magneto-optical material into Fibonacci photonic crystals. Assisted by the nonreciprocity of the magneto-optical material and the excitation of Tamm plasmon polaritons, strong nonreciprocal thermal radiation can be realized. The difference between absorption and emission at wavelength of 16 {\mu}m can reach 0.9 at the incident angle of 60o. The distributions of the magnetic field are also calculated to verify the underlying physical origin. By engineering the parameters of the structure, it is found that strong nonreciprocal thermal radiation can be achieved at shorter wavelength and smaller incident angle. The results indicate that the Fibonacci magnetophotonic crystals are the promising candidate to engineer the nonreciprocal emission for various requirements.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Einstein's theory of general relativity (GR) has been precisely tested on solar system scales, but extragalactic tests are still poorly performed. In this work, we use a newly compiled sample of galaxy-scale strong gravitational lenses to test the validity of GR on kiloparsec scales. In order to solve the circularity problem caused by the preassumption of a specific cosmological model based on GR, we employ the distance sum rule in the Friedmann-Lema\^{\i}tre-Robertson-Walker metric to directly estimate the parameterized post-Newtonian (PPN) parameter $\gamma_{\rm PPN}$ and the cosmic curvature $\Omega_k$ by combining observations of strong lensing and Type Ia supernovae. This is the first simultaneous measurement of $\gamma_{\rm PPN}$ and $\Omega_k$ without any assumptions about the contents of the universe or the theory of gravity. Our results show that $\gamma_{\rm PPN}=1.11^{+0.11}_{-0.09}$ and $\Omega_{k}=0.48^{+1.09}_{-0.71}$, indicating a strong degeneracy between the two quantities. The measured $\gamma_{\rm PPN}$, which is consistent with the prediction of 1 from GR, provides a precise extragalactic test of GR with a fractional accuracy better than 9.0\%. If a prior of the spatial flatness (i.e., $\Omega_{k}=0$) is adopted, the PPN parameter constraint can be further improved to $\gamma_{\rm PPN}=1.07^{+0.07}_{-0.07}$, representing a precision of 6.5\%. On the other hand, in the framework of GR (i.e., $\gamma_{\rm PPN}=1$), our results are still marginally compatible with zero curvature ($\Omega_k=-0.12^{+0.48}_{-0.36}$), supporting no significant deviation from a flat universe.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Chiral response is of tremendous importance to many fields, such as analytical chemistry, polarization manipulation and biological sensing. Here, a chiral metasurface based on rectangular holes is systematically investigated. The results show that the chirality is closely related to the size and the orientation of resonance unit. It is found that the period of the structure is always smaller than the wavelength at which chirality appears, which will provide a good basis for the design of chiral structures. More importantly, the CD is highly sensitive to the orientation of resonance unit. By adjusting the rotation angle, it is not only possible to invert the CD, but also to change the symmetry of the structure to realize the regulation of chirality. The chirality can be significantly enhanced in the proposed structure, and the maximum of circular dichroism (CD) can reach 0.76. To better understand the physical mechanism, the distributions of electric field for LCP and RCP waves are also discussed as well. This work will not only deepen the understanding of chiral metasurfaces, but also provide guidance for the design of similar chiral structures.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Metasurface-mediated bound states in the continuum (BIC) provides a versatile platform for light manipulation at subwavelength dimension with diverging radiative quality factor and extreme optical localization. In this work, we employ magnetic dipole quasi-BIC resonance in asymmetric silicon nanobar metasurfaces to realize giant Goos-H\"anchen (GH) shift enhancement by more than three orders of wavelength. In sharp contrast to GH shift based on the Brewster dip or transmission-type resonance, the maximum GH shift here is located at the reflection peak with unity reflectance, which can be conveniently detected in the experiment. By adjusting the asymmetric parameter of metasurfaces, the $Q$-factor and GH shift can be modulated accordingly. More interestingly, it is found that GH shift exhibits an inverse quadratic dependence on the asymmetric parameter. Furthermore, we design an ultrasensitive environmental refractive index sensor based on the quasi-BIC enhanced GH shift, with a maximum sensitivity of 1.5$\times$10$^{7}$ $\mu$m/RIU. Our work not only reveals the essential role of BIC in engineering the basic optical phenomena, but also suggests the way for pushing the performance limits of optical communication devices, information storage, wavelength division de/multiplexers, and ultrasensitive sensors.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-09-17
摘要： We embed the flipped SU(5) models into the SO(10) models. After the SO(10) gauge symmetry is broken down to the flipped SU(5)譛(1)X gauge symmetry, we can split the five/one-plets and ten-plets in the spinor 16 and 16 Higgs fields via the stable sliding singlet mechanism. As in the flipped SU(5) models, these ten-plet Higgs fields can break the flipped SU(5) gauge symmetry down to the Standard Model gauge symmetry. The doublet-triplet splitting problem can be solved naturally by the missing partner mechanism, and the Higgsino-exchange mediated proton decay can be suppressed elegantly. Moreover, we show that there exists one pair of the light Higgs doublets for the electroweak gauge symmetry breaking. Because there exist two pairs of additional vector-like particles with similar intermediate-scale masses, the SU(5) and U(1)X gauge couplings can be unified at the GUT scale which is reasonably (about one or two orders) higher than the SU(2)L �SU(3)C unification scale. Furthermore, we briefly discuss the simplest SO(10) model with flipped SU(5) embedding, and point out that it can not work without fine-tuning.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The mergers of supermassive black hole binaries (SMBHBs) can serve as standard sirens: the gravitational wave (GW) analog of standard candles. The upcoming space-borne GW detectors will be able to discover such systems and estimate their luminosity distances precisely. Unfortunately, weak gravitational lensing can induce significant errors in the measured distance of these standard sirens at high redshift, severely limiting their usefulness as precise distance probes. The uncertainty due to weak lensing can be reduced if the lensing magnification of the siren can be estimated independently, a procedure called 'delensing'. With the help of up-to-date numerical simulations, here we investigate how much the weak-lensing errors can be reduced using convergence maps reconstructed from shear measurements. We also evaluate the impact of delensing on cosmological parameter estimation with bright standard sirens. We find that the weak-lensing errors for sirens at $z_s = 2.9$ can be reduced by about a factor of two on average, but to achieve this would require expensive ultra-deep field observations for every siren. Such an approach is likely to be practical in only limited cases, and the reduction in the weak-lensing error is therefore likely to be insufficient to significantly improve the cosmological parameter estimation. We conclude that performing delensing corrections is unlikely to be worthwhile, in contrast to the more positive expectations presented in previous studies. For delensing to become more practicable and useful in the future will require significant improvements in the resolution/depth of the weak-lensing surveys themselves and/or the accuracy of the methods to reconstruct convergence maps from these surveys.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The mergers of supermassive black hole binaries (SMBHBs) can serve as standard sirens: the gravitational wave (GW) analog of standard candles. The upcoming space-borne GW detectors will be able to discover such systems and estimate their luminosity distances precisely. Unfortunately, weak gravitational lensing can induce significant errors in the measured distance of these standard sirens at high redshift, severely limiting their usefulness as precise distance probes. The uncertainty due to weak lensing can be reduced if the lensing magnification of the siren can be estimated independently, a procedure called 'delensing'. With the help of up-to-date numerical simulations, here we investigate how much the weak-lensing errors can be reduced using convergence maps reconstructed from shear measurements. We also evaluate the impact of delensing on cosmological parameter estimation with bright standard sirens. We find that the weak-lensing errors for sirens at $z_s = 2.9$ can be reduced by about a factor of two on average, but to achieve this would require expensive ultra-deep field observations for every siren. Such an approach is likely to be practical in only limited cases, and the reduction in the weak-lensing error is therefore likely to be insufficient to significantly improve the cosmological parameter estimation. We conclude that performing delensing corrections is unlikely to be worthwhile, in contrast to the more positive expectations presented in previous studies. For delensing to become more practicable and useful in the future will require significant improvements in the resolution/depth of the weak-lensing surveys themselves and/or the accuracy of the methods to reconstruct convergence maps from these surveys.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Long gamma-ray bursts (GRBs) have been discussed as a potential tool to probe the cosmic star formation rate (SFR) for a long time. Some studies found an enhancement in the GRB rate relative to the galaxy-inferred SFR at high redshifts, which indicates that GRBs may not be good tracers of star formation. However, in these studies, the GRB rate measured at any redshift is an average over all galaxies at that epoch. A deep understanding of the connection between GRB production and environment also needs to characterize the population of GRB host galaxies directly. Based on a complete sample of GRB hosts, we constrain the stellar-mass function (SMF) of GRB hosts, and examine redshift evolution in the GRB host population. Our results confirm that a strong redshift evolution in energy (with an evolution index of $\delta=2.47^{+0.73}_{-0.89}$) or in density ($\delta=1.82^{+0.22}_{-0.59}$) is needed in order to account for the observations. The GRB host SMF can be well described by the Schechter function with a power-law index $\xi\approx-1.10$ and a break mass $M_{b,0}\approx4.9\times10^{10}$ ${\rm M}_\odot$, independent of the assumed evolutionary effects. This is the first formulation of the GRB host SMF. The observed discrepancy between the GRB rate and the galaxy-inferred SFR may also be explained by an evolving SMF.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Long gamma-ray bursts (GRBs) have been discussed as a potential tool to probe the cosmic star formation rate (SFR) for a long time. Some studies found an enhancement in the GRB rate relative to the galaxy-inferred SFR at high redshifts, which indicates that GRBs may not be good tracers of star formation. However, in these studies, the GRB rate measured at any redshift is an average over all galaxies at that epoch. A deep understanding of the connection between GRB production and environment also needs to characterize the population of GRB host galaxies directly. Based on a complete sample of GRB hosts, we constrain the stellar-mass function (SMF) of GRB hosts, and examine redshift evolution in the GRB host population. Our results confirm that a strong redshift evolution in energy (with an evolution index of $\delta=2.47^{+0.73}_{-0.89}$) or in density ($\delta=1.82^{+0.22}_{-0.59}$) is needed in order to account for the observations. The GRB host SMF can be well described by the Schechter function with a power-law index $\xi\approx-1.10$ and a break mass $M_{b,0}\approx4.9\times10^{10}$ ${\rm M}_\odot$, independent of the assumed evolutionary effects. This is the first formulation of the GRB host SMF. The observed discrepancy between the GRB rate and the galaxy-inferred SFR may also be explained by an evolving SMF.
分类： 物理学 >> 核物理学 提交时间： 2016-08-30
Xue-Feng Wu
He Gao
Jun-Jie Wei
Xi-Long Fan
Peter M´esz´aros
Bing Zhang
Zi-Gao Dai
Shuang-Nan Zhang
Zong-Hong Zhu
摘要： A conservative constraint on the Einstein Equivalence Principle (EEP) can be obtained under the assumption that the observed time delay between correlated particles from astronomical sources is dominated by the gravitational fields through which they move. Current limits on the EEP are mainly based on the observed time delays of photons with different energies, and it is highly desirable to develop more accurate tests involving different types of particles. The detection by the advanced LIGO/VIRGO systems of gravitational waves (GWs) will provide attractive candidates for constraining the EEP, which would further extend the tested particle species to the gravitons, with potentially higher accuracy. Considering the capabilities of the advanced LIGO/VIRGO network and the source direction uncertainty, we show that the joint detection of GWs and electromagnetic signals can potentially probe the EEP to an accuracy of 10−11, which is several orders of magnitude tighter than previous limits.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Lance Taylor
Rachel Bezanson
Arjen van der Wel
Alan Pearl
Eric F. Bell
Francesco D'Eugenio
Marijn Franx
Michael V. Maseda
Adam Muzzin
David Sobral
Caroline Straatman
Katherine E. Whitaker
Po-Feng Wu
摘要： We present the first direct spectroscopic measurement of the stellar velocity dispersion function (VDF) for massive quiescent and star-forming galaxies at $0.6 100$ km s$^{-1}$) and extend to star-forming galaxies. We are largely consistent with the high-sigma tail measured from BOSS, and we find that the VDF remains constant from the median redshift of LEGA-C, $z\sim0.8$, to the present day.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Po-Feng Wu
Dylan Nelson
Arjen van der Wel
Annalisa Pillepich
Stefano Zibetti
Rachel Bezanson
Francesco D'Eugenio
Anna Gallazzi
Camilla Pacifici
Caroline M. S. Straatman
Ivana Barišić
Eric F. Bell
Michael V. Maseda
Adam Muzzin
David Sobral
Katherine E. Whitaker
摘要： We present the first comparison of observed stellar continuum spectra of high-redshift galaxies and mock galaxy spectra generated from hydrodynamical simulations. The mock spectra are produced from the IllustrisTNG TNG100 simulation combined with stellar population models and take into account dust attenuation and realistic observational effects (aperture effects and noise). We compare the simulated $D_n4000$ and EW(H$\delta$) of galaxies with $10.5 \leq \log(M_\ast/M_\odot) \leq 11.5$ at $0.6 \leq z \leq 1.0$ to the observed distributions from the LEGA-C survey. TNG100 globally reproduces the observed distributions of spectral indices, implying that the age distribution of galaxies in TNG100 is generally realistic. Yet there are small but significant differences. For old galaxies, TNG100 shows small $D_n4000$ when compared to LEGA-C, while LEGA-C galaxies have larger EW(H$\delta$) at fixed $D_n4000$. There are several possible explanations: 1) LEGA-C galaxies have overall older ages combined with small contributions (a few percent in mass) from younger ($<1$~Gyr) stars, while TNG100 galaxies may not have such young sub-populations; 2) the spectral mismatch could be due to systematic uncertainties in the stellar population models used to convert stellar ages and metallicities to observables. In conclusion, the latest cosmological galaxy formation simulations broadly reproduce the global age distribution of galaxies at $z\sim1$ and, at the same time, the high quality of the latest observed and simulated datasets help constrain stellar population synthesis models as well as the physical models underlying the simulations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jian Ge
Hui Zhang
Weicheng Zang
Hongping Deng
Shude Mao
Ji-Wei Xie
Hui-Gen Liu
Ji-Lin Zhou
Kevin Willis
Chelsea Huang
Steve B. Howell
Fabo Feng
Jiapeng Zhu
Xinyu Yao
Beibei Liu
Masataka Aizawa
Wei Zhu
Ya-Ping Li
Bo Ma
Quanzhi Ye
摘要： We propose to develop a wide-field and ultra-high-precision photometric survey mission, temporarily named "Earth 2.0 (ET)". This mission is designed to measure, for the first time, the occurrence rate and the orbital distributions of Earth-sized planets. ET consists of seven 30cm telescopes, to be launched to the Earth-Sun's L2 point. Six of these are transit telescopes with a field of view of 500 square degrees. Staring in the direction that encompasses the original Kepler field for four continuous years, this monitoring will return tens of thousands of transiting planets, including the elusive Earth twins orbiting solar-type stars. The seventh telescope is a 30cm microlensing telescope that will monitor an area of 4 square degrees toward the galactic bulge. This, combined with simultaneous ground-based KMTNet observations, will measure masses for hundreds of long-period and free-floating planets. Together, the transit and the microlensing telescopes will revolutionize our understandings of terrestrial planets across a large swath of orbital distances and free space. In addition, the survey data will also facilitate studies in the fields of asteroseismology, Galactic archeology, time-domain sciences, and black holes in binaries.
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