分类： 天文学 >> 星系和宇宙学 提交时间： 2023-12-08
摘要： This paper presents a morphological investigation of the early-type spiral galaxy M81 (NGC 3031) through decomposition by fitting radial profiles of surface brightness using the software GALFIT, aimed at exploring structural components of M81 and quantifying their morphology. In this work, we adopt 6 types of decompositions with different numbers of morphological components, among which the most complicated one contains 5 components such as a bulge, a disk, a pair of outer spiral arms, a pair of inner spiral arms, and a galactic nucleus. The results show that, M81 hosts a classical bulge with the Sersic index 5.0; the morphology and the luminosity for the bulge are almost constant in the different decomposition types. The disk of M81 has the Sersic index 1.2 but the morphology and the luminosity are found sensitive to the inclusion of the inner spiral arms in the decomposition or not. The results of this work indicate that the combination of individual substructures has a considerable impact on the morphology of the galaxy as a mixture. On the basis of the results, the usability of the different types of decomposition is suggested in this work. The three-component decomposition, i.e., bulge + disk + nucleus, is applicable to statistics of large samples of galaxies; more complicated decomposition with spiral arms taken into account is suitable for precise measurements of individual galaxies in small samples. This work is based on the single-band Spitzer-The Infrared Array Camera (IRAC) 4.5 m image. In the future, we will carry out multi-wavelength decomposition, for the purpose of investigating spectral energy distributions and stellar population properties for the galactic substructures, and thereby deduce their formation history and evolution processes.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-05-24
摘要： We analyse H(z) parameter data with some conditions by using Lagrange mean value theorem in Calculus. We find that: (1) there exists at least one decelerated phase at 1 $ sigma$ confidence level in the redshift range (0.38, 0.59); (2) the equation of motion of dark energy may be less than -1 at 1 confidence level at some redshifts in the redshift range (1.3, 1.53); (3) there exists at least one accelerated phase at 1 confidence level in the redshift range (1.037, 1.944). These results may provide possible evidences for physics beyond $ Lambd ACDM.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
Qiuhan He
Ran Li
Carlos S. Frenk
James Nightingale
Shaun Cole
Nicola C. Amorisco
Richard Massey
Andrew Robertson
Amy Etherington
Aristeidis Amvrosiadis
Xiaoyue Cao
摘要： We rederive the number density of intervening line-of-sight haloes relative to lens subhaloes in galaxy-galaxy strong lensing observations, where these perturbers can generate detectable image fluctuations. Previous studies have calculated the detection limit of a line-of-sight small-mass dark halo by comparing the lensing deflection angles it would cause, to those caused by a subhalo within the lens. However, this overly simplifies the difference in observational consequences between a subhalo and a line-of-sight halo. Furthermore, it does not take into account degeneracies between an extra subhalo and the uncertain properties of the main lens. More in keeping with analyses of real-world observations, we regard a line-of-sight halo as detectable only if adding it to a smooth model generates a statistically significant improvement in the reconstructed image. We find that the number density of detectable line-of-sight perturbers has been overestimated by as much as a factor of two in the previous literature. For typical lensing geometries and configurations, very deep imaging is sensitive to twice as many line-of-sight perturbers as subhaloes, but moderate depth imaging is sensitive to only slightly more line-of-sight perturbers than subhaloes.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
摘要： In this paper we consider the effects of adding curvature in extended cosmologies involving a free-to-vary neutrino sector and different parametrizations of Dark Energy (DE). We make use of the Planck 2018 cosmic microwave background temperature and polarization data, Baryon Acoustic Oscillations and Pantheon type Ia Supernovae data. Our main result is that a non-flat Universe cannot be discarded in light of the current astronomical data, because we find an indication for a closed Universe in most of the DE cosmologies explored in this work. On the other hand, forcing the Universe to be flat can significantly bias the constraints on the equation of state of the DE component and its dynamical nature.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
摘要： Interstellar (ISM) and circumgalactic medium (CGM) around galaxies are linked to several physical processes that drive galaxy evolution. For example, the X-ray emission from the CGM gas around ellipticals has been linked to the AGN feedback occurring in the host. Upcoming telescopes such as HUBS, with ~ 1 eV resolution, can provide us with deep insights about the hot gas properties of such galaxies thus constrain these processes. In this project, we discuss X-ray emission of the ISM and CGM of elliptical galaxies simulated using MACER code. We generate X-ray emission data from the MACER simulations with various feedback models and produce mock observations for an instrument with high spectral resolution, which is a necessary step of selecting sources for the future observations with planned mission such as HUBS. More importantly, we establish connections between the physics of AGN and stellar feedback with the emission spectra from the ISM and CGM to investigate the possibility of using observations to constrain feedback models. We fit the X-ray spectra from these simulations with standard fitting procedures and compare the retrieved physical properties with their counterparts from the simulations to understand whether the future high-resolution observations can reliably reveal the properties of the gas in the galaxies.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
Y. T. Yan
C. Henkel
K. M. Menten
Y. Gong
H. Nguyen
J. Ott
A. Ginsburg
T. L. Wilson
A. Brunthaler
A. Belloche
J. S. Zhang
N. Budaiev
D.Jeff
摘要： We report the discovery of widespread maser emission in non-metastable inversion transitions of NH_3 toward various parts of the Sagittarius B2 molecular cloud/star forming region complex: We detect masers in the J,K= (6,3), (7,4), (8,5), (9,6), and (10,7) transitions toward Sgr B2(M) and Sgr B2(N), an NH_3 (6,3) maser in Sgr B2(NS), and NH_3 (7,4), (9,6), and (10,7) masers in Sgr B2(S). With the high angular resolution data of the Karl G. Jansky Very Large Array (JVLA) in A-configuration we identify 18 maser spots. Nine maser spots arise from Sgr B2(N), one from Sgr B2(NS), five from Sgr B2(M), and three in Sgr B2(S). Compared to our Effelsberg single dish data, the JVLA data indicate no missing flux. The detected maser spots are not resolved by our JVLA observations. Lower limits to the brightness temperature are >3000~K and reach up to several 10^5~K, manifesting the lines' maser nature. In view of the masers' velocity differences with respect to adjacent hot molecular cores and/or UCH{\scriptsize II} regions, it is argued that all the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCH{\scriptsize II} regions. Overall, Sgr B2 is unique in that it allows us to measure many NH_3 masers simultaneously, which may be essential to elucidate their so far poorly understood origin and excitation.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
Guang Yang
W. N. Brandt
David M. Alexander
Médéric Boquien
Qingling Ni
Casey Papovich
Justin S. Spilker
Fabio Vito
Jonelle L. Walsh
Chengpeng Zhang
摘要： Recent studies have revealed a strong relation between sample-averaged black-hole (BH) accretion rate (BHAR) and star formation rate (SFR) among bulge-dominated galaxies, i.e., lockstep BH-bulge growth, in the distant universe. This relation might be closely related to the BH-bulge mass correlation observed in the local universe. To understand further BH-bulge coevolution, we present ALMA CO(2-1) or CO(3-2) observations of 7 star-forming bulge-dominated galaxies at z=0.5-2.5. Using the ALMA data, we detect significant (>3) CO emission from 4 objects. For our sample of 7 galaxies, we measure (or constrain with upper limits) their CO line fluxes and estimate molecular gas masses (M_{gas}). We also estimate their stellar masses (M_{star}) and SFRs by modelling their spectral energy distributions (SEDs). Using these physical properties, we derive the gas-depletion timescales (t_{dep} = M_{gas}/SFR) and compare them with the bulge/BH growth timescales (t_{grow} = M_{star}/SFR \sim M_{BH}/BHAR). Our sample generally has t_{dep} shorter than t_{grow} by a median factor of ≳4, indicating that the cold gas will be depleted before significant bulge/BH growth takes place. This result suggests that the BH-bulge lockstep growth is mainly responsible for maintaining their mass relation, not creating it. We note that our sample is small and limited to z<2.5; JWST and ALMA will be able to probe to higher redshifts in the near future.
分类： 物理学 >> 地球物理学、天文学和天体物理学 分类： 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类： 天文学 >> 星系和宇宙学 提交时间： 2022-11-03
摘要： 本文以物理学中标准钟和标准尺的定义实质和爱因斯坦的相对论物理为基础，从自然哲学层次出发讨论了物理的时空观。提出在已有的时空标度的概念基础上，应该进一步明确区分时空标度和时空背景。根据爱因斯坦相对论的实际逻辑可以作如下理解，满足相对论性变化的是时空标度，而时空标度是人为地根据物质实体中发生或存在的固有物理事件定义的，时空背景作为反映时空标度的长短或大小变化的必备基础和参考背景，应该是绝对的。空间标度的长短尺度在本质上应该理解为固有物理事件在空间的绝对背景上截取的线段的长度。最后以此时空观为基础，探讨了经典力学框架下的质点动力学方程，自然地得出了新形式的质点动力学方程。新动力学方程可以直接应用到任何实际的，（相对宇宙绝对背景）无转动的参考系中。而惯性力的本质正是作用到参考物体上的真实受力。这一经典质点动力学改造的本质是修正了牛顿第二定律传统体系中存在的一个理论缺陷。然而，可能更为重要的是，在形式上具备明显优越性的新质点动力学方程反过来强烈地暗示了时空背景的绝对性。文章最后结合广义相对论的引力几何化思想，探讨了引力对时空标度的物理效应。
分类： 物理学 >> 地球物理学、天文学和天体物理学 分类： 天文学 >> 星系和宇宙学 提交时间： 2020-09-09
摘要： Motivated by recent work on rotating black hole shadow [Phys. Rev. D101, 084029 (2020)], we investigate the shadow behaviors of rotating Hayward-de Sitter black hole for static observers at a finite distance in terms of astronomical observables. This paper uses the newly introduced distortion parameter in [arXiv:2006.00685] to describe the shadow's shape quantitatively. We show that the spin parameter would distort shadows and the magnetic monopole charge would increase the degree of deformation. At the same time, the distortion could be relieved because of the cosmological constant and the distortion would increase with the distance from the black hole. Besides, the spin parameter, magnetic monopole charge and cosmological constant increase will cause the shadow to shrink.
分类： 天文学 >> 星系和宇宙学 提交时间： 2018-04-25
摘要： 本文是[1]对冲突簇的延续和推广。我们研究冲突子群中的总、暗物质密度分布和关联。就像我们对纽曼星系团所做的那样。就像Newman星系团一样，我们发现密度分布受重子相互作用和能量的影响很大。角动量通过动态摩擦从重子转移到DM。大星系团的暗物质密度剖面的内斜率通常比纳瓦罗-弗伦克-白剖面内坡，最大值为-0.79，最小值为-0.30.如在Newman星系团的情况下，斜率α之间存在一系列的相关性。暗物质剖面，以及：A.团簇的核心半径；B.有效半径Re；C.最明亮的中央星系(BCG)的质量；D.总重子质量和恒星质量星系团。我们还发现了有效半径与病毒质量之间的关系。簇的结构，它们的总密度和密度分布，以及它们之间的相关性是：在两个阶段的情况下理解。在第一个耗散阶段，BGC形成。在第二耗散相，重子团与DM的相互作用动力摩擦(DF)使DM分布趋于平缓。这两个阶段的最终结果是不同DM分布、内部斜率及几种关联的簇的形成簇的特征量
分类： 天文学 >> 星系和宇宙学 提交时间： 2018-03-27
摘要： 在本文中，我们将展示重子物理是如何解决矮星中惊人的多样性问题的。 星系旋转曲线形状。为此，我们比较了SPARC样本的星系分布。 平面V2kpc-V最后(V2kpc是星系在2 kpc时的旋转速度，V是最外层的)。 我们模拟的星系考虑了重子效应。V2kpc-V上旋转曲线中的散射 平面上，SPARC样品的分布趋势与我们模拟星系的分布基本一致。大 解决“多样性”问题的关键在于重子过程产生非自相似光晕的能力。 只有DM的模拟。我们还发现，重子效应可以再现IC 2574等星系的自转曲线。 以半径上升缓慢为特征的。通过适当的处理，可以得到多样性问题的一个解。 考虑到重子物理效应。
分类： 天文学 >> 星系和宇宙学 提交时间： 2018-03-27
摘要： 我们研究了由角动量和切向应力产生的偏离系统球对称性的方法。修正了球崩溃模型，作为非相对论成分(δc)及其病毒过密度(∆V)崩溃的线性密度阈值，在爱因斯坦-德西特和ΛCDM模型中。我们修改球面考虑切向应力项和角动量项的塌陷模型。我们发现非球面术语改变了系统的非线性演化，崩溃“自然”地停止在维数半径处。 此外，还对线性过密度参数和∆V的值进行了相应的标准球形塌陷模型修正。
分类： 天文学 >> 星系和宇宙学 提交时间： 2016-05-05
摘要： The South Galactic Cap u-band Sky Survey (SCUSS) is a deep u-band imaging survey in the south Galactic capusing the 2.3 m Bok telescope. The survey observations were completed at the end of 2013, covering an area ofabout 5000 square degrees. We release the data in the region with an area of about 4000 deg2 that is mostly coveredby the Sloan digital sky survey. The data products contain calibrated single-epoch images, stacked images,photometric catalogs, and a catalog of star proper motions derived by Peng et al. The median seeing and magnitudelimit (5σ) are about 2 0 and 23.2 mag, respectively. There are about 8 million objects having measurements ofabsolute proper motions. All the data and related documentations can be accessed through the SCUSS data releasewebsite http://batc.bao.ac.cn/Uband/data.html.Key words: catalogs – surveys – techniques: image processing – techni
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