分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2023-12-15 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Environments play an important role in galaxy formation and evolution, particularly in regulating the content of neutral gas. However, current H i surveys have limitations in their depth, which prevents them from adequately studying low H i content galaxies in high-density regions. In this study, we address this issue by employing the Five-hundred-meter Aperture Spherical radio Telescope with extensive integration times to complement the relatively shallow Arecibo Legacy Fast Arecibo L-band Feed Array H i survey. This approach allows us to explore the gas content of dwarf galaxies across various environments. We observe a positive relationship between H i mass and stellar mass in dwarf galaxies, with a well-defined upper boundary for H i mass that holds true in both observations and simulations. Furthermore, we find a decrease in the H i-to-stellar mass ratio (MH I/M*) as the density of the environment increases, irrespective of whether it is determined by the proximity to the nearest group or the projected number density. Comparing our observations to simulations, we note a steeper slope in the relationship, indicating a gradual gas-stripping process in the observational data. Additionally, we find that the scaling relation between the MH I/M* and optical properties can be improved by incorporating galaxy environments.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present results from an HI counterpart search using the HI Parkes All Sky Survey (HIPASS) for a sample of low surface brightness galaxies (LSBGs) and ultradiffuse galaxies (UDGs) identified from the Dark Energy Survey (DES). We aimed to establish the redshifts of the DES LSBGs to determine the UDG fraction and understand their properties. Out of 409 galaxies investigated, none were unambiguously detected in HI. Our study was significantly hampered by the high spectral rms of HIPASS and thus in this paper we do not make any strong conclusive claims but discuss the main trends and possible scenarios our results reflect. The overwhelming number of non-detections suggest that: (A) Either all the LSBGs in the groups, blue or red, have undergone environment aided pre-processing and are HI deficient or the majority of them are distant galaxies, beyond the HIPASS detection threshold. (B) The sample investigated is most likely dominated by galaxies with HI masses typical of dwarf galaxies. Had there been Milky Way (MW) size (R_e) galaxies in our sample, with proportionate HI content, they would have been detected, even with the limitations imposed by the HIPASS spectral quality. This leads us to infer that if some of the LSBGs have MW size optical diameters, their HI content is possibly in the dwarf range. More sensitive observations using the SKA precursors in future may resolve these questions.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Lili Gui
Chuanshuo Wang
Fei Ding
Hao Chen
Xiaosheng Xiao
Sergey I. Bozhevolnyi
Xiaoguang Zhang
Kun Xu
摘要： Wavelength-tunable vortex fiber lasers that could generate beams carrying orbital angular momentum (OAM) hold great interest in large-capacity optical communications. The wavelength tunability of conventional vortex fiber lasers is however limited by the range of 35 nm due to narrow bandwidth and/or insertion loss of mode conversion components. Optical metasurfaces apart from being compact planar components can flexibly manipulate light with high efficiency in a broad wavelength range. Here, we propose and demonstrate for the first time, to the best of our knowledge, a metasurface-assisted vortex fiber laser that can directly generate OAM beams with changeable topological charges. Due to the designed broadband gap-surface plasmon metasurface, combined with an intracavity tunable filter, the laser enables OAM beam with center wavelength continuously tunable from 1015 nm to 1075 nm, nearly twice of other vortex fiber lasers ever reported. The metasurface can be designed at will to satisfy requirements for either low pump threshold or high slope efficiency of the laser. Furthermore, the cavity-metasurface configuration can be extended to generate higher-order OAM beams or more complex structured beams in different wavelength regions, which greatly broadens the possibilities for developing low-cost and high-quality structured-beam laser sources.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Small-scale magnetic fields are not only the fundamental element of the solar magnetism, but also closely related to the structure of the solar atmosphere. The observations have shown that there is a ubiquitous tangled small-scale magnetic field with a strength of 60 $\sim$ 130\,G in the canopy forming layer of the quiet solar photosphere. On the other hand, the multi-dimensional MHD simulations show that the convective overshooting expels the magnetic field to form the magnetic canopies at a height of about 500\,km in the upper photosphere. However, the distribution of such small-scale ``canopies" in the solar photosphere cannot be rigorously constrained by either observations and numerical simulations. Based on stellar standard models, we identify that these magnetic canopies can act as a global magnetic-arch splicing layer, and find that the reflections of the solar p-mode oscillations at this magnetic-arch splicing layer results in significant improvement on the discrepancy between the observed and calculated p-mode frequencies. The location of the magnetic-arch splicing layer is determined at a height of about 630\,km, and the inferred strength of the magnetic field is about 90\,G. These features of the magnetic-arch splicing layer derived independently in the present study are quantitatively in agreement with the presence of small-scale magnetic canopies as those obtained by the observations and 3-D MHD simulations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Pu Kai Wang
Chih-Yun Chen
Hsiang-Chieh Hsu
Mu-Hsin Chang
Wei Tai Liu
Hui-Kuan Fang
Ting-Chou Wu
Wen-Hao Chen
Chin Cheng Tsai
Alfred Bing-Chih Chen
Yi Yang
摘要： The development of CubeSat and more frequent launch chances of sounding rockets are a total game changer to the space program, and it allows us to build space instruments to be more achievable and affordable. Therefore, it gives us a good opportunity to build a small cosmic ray detector which has capabilities to measure the flux, direction, and even energy of cosmic rays at the height above the limitation of balloon experiments, and it may open a new door for building a constellation of detectors to study cosmic ray physics. Compact Scintillator Array Detector (ComSAD) is dedicated for the sounding rocket mission of Taiwan's National Space Organization. In paper, we present the idea, design, and performance of ComSAD which is also suitable for CubeSat missions in the future.
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