分类： 天文学 >> 天体物理学 提交时间： 2023-02-21
Weicheng Zang
Youn Kil Jung
Hongjing Yang
Xiangyu Zhang
Andrzej Udalski
Jennifer C. Yee
Andrew Gould
Shude Mao
摘要： We present the analysis of seven microlensing planetary events with planet/host mass ratios q < 10^{-4}: KMT-2017-BLG-1194, KMT-2017-BLG-0428, KMT-2019-BLG-1806, KMT-2017-BLG-1003, KMT-2019-BLG-1367, OGLE-2017-BLG-1806, and KMT-2016-BLG-1105. They were identified by applying the Korea Microlensing Telescope Network (KMTNet) AnomalyFinder algorithm to 2016--2019 KMTNet events. A Bayesian analysis indicates that all the lens systems consist of a cold super-Earth orbiting an M or K dwarf. Together with 17 previously published and three that will be published elsewhere, AnomalyFinder has found a total of 27 planets that have solutions with q < 10^{-4} from 2016--2019 KMTNet events, which lays the foundation for the first statistical analysis of the planetary mass-ratio function based on KMTNet data. By reviewing the 27 planets, we find that the missing planetary caustics problem in the KMTNet planetary sample has been solved by AnomalyFinder. We also find a desert of high-magnification planetary signals (A≳65), and a follow-up project for KMTNet high-magnification events could detect at least two more q < 10^{-4} planets per year and form an independent statistical sample.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The connection between halo gas acquisition through the circumgalactic medium (CGM) and galaxy star formation has long been studied. In this series of two papers, we put this interplay within the context of the galaxy environment on large scales (several hundreds of kpc), which, to a certain degree, maps out various paths for galaxy interactions. We use the IllustrisTNG-100 simulation to demonstrate that the large-scale environment modulates the circumgalactic gas angular momentum, resulting in either enhanced (Paper I) or suppressed (Paper II) star formation inside a galaxy. In this paper (Paper I), we show that the large-scale environment around a star-forming galaxy is often responsible for triggering new episodes of star formation. Such an episodic star formation pattern is well synced with a pulsating motion of the circumgalactic gas, which, on the one hand receives angular momentum modulations from the large-scale environment, yielding in-spiralling gas to fuel the star-forming reservoir, while, on the other hand, is affected by the feedback activities from the galaxy centre. As a result, a present-day star-forming galaxy may have gone through several cycles of star-forming and quiescent phases during its evolutionary history, with the circumgalactic gas carrying out a synchronized cadence of "breathing in and out" motions out to $\sim 100$ kpc.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Shengdong Lu
Dandan Xu
Sen Wang
Yunchong Wang
Shude Mao
Xiaoyang Xia
Mark Vogelsberger
Lars Hernquist
摘要： Galaxy morphologies, kinematics, and stellar populations are thought to be linked to each other. However, both simulations and observations have pointed out mismatches therein. In this work, we study the nature and origin of the present-day quenched, bulge-dominated, but dynamically cold galaxies within a stellar mass range of $10.3\,\leqslant\,\log\,M_{\ast}/\mathrm{M_{\odot}}\,\leqslant\,11.2$ in the IllustrisTNG-100 Simulation. We compare these galaxies with a population of normal star-forming dynamically cold disc galaxies and a population of normal quenched dynamically hot elliptical galaxies within the same mass range. The populations of the present-day quenched and bulge-dominated galaxies (both being dynamically cold and hot) used to have significantly higher star-formation rates and flatter morphologies at redshift of $z\sim 2$. They have experienced more frequent larger mass-ratio mergers below $z \sim 0.7$ in comparison to their star-forming disc counterparts, which is responsible for the formation of their bulge-dominated morphologies. The dynamically cold populations (both being star-forming and quenched) have experienced more frequent prograde and tangential mergers especially below $z \sim 1$, in contrast to the dynamically hot ellipticals, which have had more retrograde and radial mergers. Such different merging histories can well explain the differences on the cold and hot dynamical status among these galaxies. We point out that the real-world counterparts of these dynamically cold and hot bulge-dominated quenched populations are the fast- and slow-rotating early-type galaxies, respectively, as seen in observations and hence reveal the different evolution paths of these two distinct populations of early-type galaxies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： There is a population of stars with velocities in excess of 500 km s$^{-1}$ relative to the Galactic center. Many, perhaps most, of these hyper-velocity stars (HVSs) are B stars, similar to the disk and S stars in a nuclear cluster around a super-massive black hole (SMBH) near $\rm Sgr~A^{\star}$. In the paper I of this series, we showed that the eccentricity of the stars emerged from a hypothetical disk around the SMBH can be rapidly excited by the secular perturbation of its intermediate-mass companion (IMC), and we suggested IRS 13E as a potential candidate for the IMC. Here, we show that this process leads to an influx of stars on parabolic orbits to the proximity of $\rm Sgr~A^{\star}$ on a secular timescale of a few Myr. This timescale is much shorter than the diffusion timescale into the lost cone through either the classical or the resonant relaxation. Precession of the highly-eccentric stars' longitude of periastron, relative to that of the IMC, brings them to its proximity within a few Myr. The IMC's gravitational perturbation scatters a fraction of the stars from nearly parabolic to hyperbolic orbits, with respect to the SMBH. Their follow-up close encounters with the SMBH induce them to escape with hyper-velocity. This scenario is a variant of the hypothesis proposed by Hills based on the anticipated breakup of some progenitor binary stars in the proximity of the SMBH, and its main objective is to account for the limited lifespan of the known HVSs. We generalize our previous numerical simulations of this process with a much wider range of orbital configurations. We demonstrate the robustness and evaluate the efficiency of this channel of HVS formation. From these numerical simulations, we infer observable kinematic properties for the HVSs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Shengdong Lu
Dandan Xu
Sen Wang
Zheng Cai
Chuan He
C. Kevin Xu
Xiaoyang Xia
Shude Mao
Volker Springel
Lars Hernquist
摘要： The gas needed to sustain star formation in galaxies is supplied by the circumgalactic medium (CGM), which in turn is affected by accretion from large scales. In a series of two papers, we examine the interplay between a galaxy's ambient CGM and central star formation within the context of the large-scale environment. We use the IllustrisTNG-100 simulation to show that the influence exerted by the large-scale galaxy environment on the CGM gas angular momentum results in either enhanced (Paper I) or suppressed (Paper II, this paper) star formation inside a galaxy. We find that for present-day quenched galaxies, both the large-scale environments and the ambient CGM have always had higher angular momenta throughout their evolutionary history since at least $z=2$, in comparison to those around present-day star-forming disk galaxies, resulting in less efficient gas inflow into the central star-forming gas reservoirs. A sufficiently high CGM angular momentum, as inherited from the larger-scale environment, is thus an important factor in keeping a galaxy quenched, once it is quenched. The process above naturally renders two key observational signatures: (1) a coherent rotation pattern existing across multiple distances from the large-scale galaxy environment, to the circumgalactic gas, to the central stellar disk; and (2) an anti-correlation between galaxy star-formation rates and orbital angular momenta of interacting galaxy pairs or groups.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yunchong Wang
Shude Mao
Mark Vogelsberger
Volker Springel
Lars Hernquist
Risa Wechsler
Tsinghua
Stanford
MIT
MPA
Harvard
SLAC
摘要： Early-type galaxies (ETGs) possess total density profiles close to isothermal, which can lead to non-Gaussian line-of-sight velocity dispersion (LOSVD) under anisotropic stellar orbits. However, recent observations of local ETGs in the MASSIVE Survey reveal outer kinematic structures at $1.5 R_{\mathrm{eff}}$ (effective radius) that are inconsistent with fixed isothermal density profiles; the authors proposed varying density profiles as an explanation. We aim to verify this conjecture and understand the influence of stellar assembly on these kinematic features through mock ETGs in IllustrisTNG. We create mock Integral-Field-Unit observations to extract projected stellar kinematic features for 207 ETGs with stellar mass $M_{\ast}\geqslant 10^{11} \mathrm{M_{\odot}}$ in TNG100-1. The mock observations reproduce the key outer ($1.5R_{\mathrm{eff}}$) kinematic structures in the MASSIVE ETGs, including the puzzling positive correlation between velocity dispersion profile outer slope $\gamma_{\mathrm{outer}}$ and the kurtosis $h_{4}$'s gradient. We find that $h_{4}$ is uncorrelated with stellar orbital anisotropy beyond $R_{\mathrm{eff}}$; instead we find that the variations in $\gamma_{\mathrm{outer}}$ and outer $h_{4}$ (a good proxy for $h_{4}$ gradient) are both driven by variations of the density profile at the outskirts across different ETGs. These findings corroborate the proposed conjecture and rule out velocity anisotropy as the origin of non-Gaussian outer kinematic structure in ETGs. We also find that the outer kurtosis and anisotropy correlate with different stellar assembly components, with the former related to minor mergers or flyby interactions while the latter is mainly driven by major mergers, suggesting distinct stellar assembly origins that decorrelates the two quantities.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Weicheng Zang
Youn Kil Jung
Hongjing Yang
Xiangyu Zhang
Andrzej Udalski
Jennifer C. Yee
Andrew Gould
Shude Mao
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Kyu-Ha Hwang
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
Chung-Uk Lee
摘要： We present the analysis of seven microlensing planetary events with planet/host mass ratios $q < 10^{-4}$: KMT-2017-BLG-1194, KMT-2017-BLG-0428, KMT-2019-BLG-1806, KMT-2017-BLG-1003, KMT-2019-BLG-1367, OGLE-2017-BLG-1806, and KMT-2016-BLG-1105. They were identified by applying the Korea Microlensing Telescope Network (KMTNet) AnomalyFinder algorithm to 2016--2019 KMTNet events. A Bayesian analysis indicates that all the lens systems consist of a cold super-Earth orbiting an M or K dwarf. Together with 17 previously published and three that will be published elsewhere, AnomalyFinder has found a total of 27 planets that have solutions with $q < 10^{-4}$ from 2016--2019 KMTNet events, which lays the foundation for the first statistical analysis of the planetary mass-ratio function based on KMTNet data. By reviewing the 27 planets, we find that the missing planetary caustics problem in the KMTNet planetary sample has been solved by AnomalyFinder. We also find a desert of high-magnification planetary signals ($A \gtrsim 65$), and a follow-up project for KMTNet high-magnification events could detect at least two more $q < 10^{-4}$ planets per year and form an independent statistical sample.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Galaxy is found to be in disequilibrium based on recent findings of the North/South (N/S) asymmetry and the phase mixing signatures, such as a phase spiral (snail) structure in the vertical phase space ($z-V_{z}$). We show that the N/S asymmetry in a tracer population of dwarfs may be quantitatively modeled with a simple phase snail model superimposed on a smooth equilibrium background. As the phase snail intersects with the $z$ axis, the number density is enhanced, and the velocity dispersion ($\sigma_{z}$) is decreased relative to the other side of the Galactic plane. Fitting only to the observed asymmetric N/S $\sigma_{z}$ profiles, we obtain reasonable parameters for the phase space snail and the potential utilized in modeling the background, despite the complex dependence of the model on the potential parameters and the significant selection effects of the data. Both the snail shape and the N/S number density difference given by our best-fit model are consistent with previous observations. The equilibrium background implies a local dark matter density of $0.0151^{+0.0050}_{-0.0051}$ ${\rm M}_{\odot}\,{\rm pc}^{-3}$. The vertical bulk motion of our model is similar to the observation, but with a $\sim$1.2 $\rm km\,s^{-1}$ shift. Our work demonstrates the strong correlation between the phase space snail and the N/S asymmetry. Future observational constraints will facilitate more comprehensive snail models to unravel the Milky Way potential and the perturbation history encoded in the snail feature.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Knowing the conserved quantities that a galaxy's stellar orbits conform to is important in helping us understand the stellar distribution and structures within the galaxy. Isolating integrals of motion and resonances are particularly important, non-isolating integrals less so. We compare the behavior and results of two methods for counting the number of conserved quantities, one based on the correlation integral approach and the other a more recent method using machine learning. Both methods use stellar orbit trajectories in phase space as their only input, and we create such trajectories from theoretical spherical, axisymmetric and triaxial model galaxies. The orbits have known isolating integrals and resonances. We find that neither method is fully effective in recovering the numbers of these quantities, nor in determining the number of non-isolating integrals. From a computer performance perspective, we find the correlation integral approach to be the faster. Determining the algebraic formulae of (multiple) conserved quantities from the trajectories has not been possible due to the lack of an appropriate symbolic regression capability. Notwithstanding the shortcomings we have noted, it may be that the methods are usable as part of a trajectory analysis tool kit.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Weicheng Zang
Kyu-Ha Hwang
Andrzej Udalski
Tianshu Wang
Wei Zhu
Takahiro Sumi
Jennifer C. Yee
Andrew Gould
Shude Mao
Xiangyu Zhang
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Youn Kil Jung
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
摘要： In order to exhume the buried signatures of "missing planetary caustics" in the KMTNet data, we conducted a systematic anomaly search to the residuals from point-source point-lens fits, based on a modified version of the KMTNet EventFinder algorithm. This search reveals the lowest mass-ratio planetary caustic to date in the microlensing event OGLE-2019-BLG-1053, for which the planetary signal had not been noticed before. The planetary system has a planet-host mass ratio of $q = (1.25 \pm 0.13) \times 10^{-5}$. A Bayesian analysis yields estimates of the mass of the host star, $M_{\rm host} = 0.61_{-0.24}^{+0.29}~M_\odot$, the mass of its planet, $M_{\rm planet} = 2.48_{-0.98}^{+1.19}~M_{\oplus}$, the projected planet-host separation, $a_\perp = 3.4_{-0.5}^{+0.5}$ au, and the lens distance of $D_{\rm L} = 6.8_{-0.9}^{+0.6}$ kpc. The discovery of this very low mass-ratio planet illustrates the utility of our method and opens a new window for a large and homogeneous sample to study the microlensing planet-host mass-ratio function down to $q \sim 10^{-5}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Weicheng Zang
Hongjing Yang
Cheongho Han
Chung-Uk Lee
Andrzej Udalski
Andrew Gould
Shude Mao
Xiangyu Zhang
Wei Zhu
Michael D. Albrow
Sun-Ju Chung
Kyu-Ha Hwang
Youn Kil Jung
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
摘要： We report the complete statistical planetary sample from the prime fields ($\Gamma \geq 2~{\rm hr}^{-1}$) of the 2019 Korea Microlensing Telescope Network (KMTNet) microlensing survey. We develop the optimized KMTNet AnomalyFinder algorithm and apply it to the 2019 KMTNet prime fields. We find a total of 14 homogeneously selected planets and report the analysis of three planetary events, KMT-2019-BLG-(1042,1552,2974). The planet-host mass ratios, $q$, for the three planetary events are $6.34 \times 10^{-4}, 4.89 \times 10^{-3}$ and $6.18 \times 10^{-4}$, respectively. A Bayesian analysis indicates the three planets are all cold giant planets beyond the snow line of their host stars. The 13 planets are basically uniform in $\log q$ over the range $-5.0 < \log q < -1.5$. This result suggests that the planets below $q_{\rm break} = 1.7 \times 10^{-4}$ proposed by the MOA-II survey may be more common than previously believed. This work is an early component of a large project to determine the KMTNet mass-ratio function, and the whole sample of 2016--2019 KMTNet events should contain about 120 planets.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ling Zhu
Glenn van de Ven
Ryan Leaman
Annalisa Pillepich
Lodovico Coccato
Yuchen Ding
Jesús Falcón-Barroso
Enrichetta Iodice
Ignacio Martin Navarro
Francesca Pinna
Enrico Maria Corsini
Dimitri A. Gadotti
Katja Fahrion
Mariya Lyubenova
Shude Mao
Richard McDermid
Adriano Poci
Marc Sarzi
Tim de Zeeuw
摘要： We report the discovery of ancient massive merger events in the early-type galaxies NGC 1380 and NGC 1427, members of the Fornax galaxy cluster. Both galaxies have been observed by the MUSE IFU instrument on the VLT, as part of the Fornax3D project. By fitting recently-developed population-orbital superposition models to the observed surface brightness as well as stellar kinematic, age, and metallicity maps, we obtain the stellar orbits, age and metallicity distributions of each galaxy. We then decompose each galaxy into multiple orbital-based components, including a dynamically hot inner stellar halo component which is identified as the relic of past massive mergers. By comparing to analogues from cosmological galaxy simulations, chiefly TNG50, we find that the formation of such a hot inner stellar halo requires the merger with a now-destroyed massive satellite galaxy of $3.7_{-1.5}^{+2.7} \times 10^{10}$ Msun (about $1/5$ of its current stellar mass) in the case of NGC 1380 and of $1.5_{-0.7}^{+1.6} \times10^{10}$ Msun (about $1/4$ of its current stellar mass) in the case of NGC 1427. Moreover, we infer that the last massive merger in NGC 1380 happened $\sim10$ Gyr ago based on the stellar age distribution of the re-grown dynamically cold disk, whereas the merger in NGC 1427 ended $t\lesssim 8$ Gyr ago based on the stellar populations in its hot inner stellar halo. The major merger event in NGC 1380 is the first one with both merger mass and merger time quantitatively inferred in a galaxy beyond the Local Volume. Moreover, it is the oldest and most massive merger uncovered in nearby galaxies so far.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
D. Specht
R. Poleski
M. T. Penny
E. Kerins
I. McDonald
Chung-Uk Lee
A. Udalski
I. A. Bond
Y. Shvartzvald
Weicheng Zang
R. A. Street
D. W. Hogg
B. S. Gaudi
T. Barclay
G. Barentsen
S. B. Howell
F. Mullally
C. B. Henderson
S. T. Bryson
D. A. Caldwell
摘要： We present K2-2016-BLG-0005Lb, a densely sampled, planetary binary caustic-crossing microlensing event found from a blind search of data gathered from Campaign 9 of the Kepler K2 mission (K2C9). K2-2016-BLG-0005Lb is the first bound microlensing exoplanet discovered from space-based data. The event has caustic entry and exit points that are resolved in the K2C9 data, enabling the lens--source relative proper motion to be measured. We have fitted a binary microlens model to the Kepler data, and to simultaneous observations from multiple ground-based surveys. Whilst the ground-based data only sparsely sample the binary caustic, they provide a clear detection of parallax that allows us to break completely the microlensing mass--position--velocity degeneracy and measure the planet's mass directly. We find a host mass of $0.58\pm0.04 ~{\rm M}_\odot$ and a planetary mass of $1.1\pm0.1 ~{\rm M_J}$. The system lies at a distance of $5.2\pm0.2~$kpc from Earth towards the Galactic bulge, more than twice the distance of the previous most distant planet found by Kepler. The sky-projected separation of the planet from its host is found to be $4.2\pm0.3~$au which, for circular orbits, deprojects to a host separation $a = 4.4^{+1.9}_{-0.4}~$au and orbital period $P = 13^{+9}_{-2}~$yr. This makes K2-2016-BLG-0005Lb a close Jupiter analogue orbiting a low-mass host star. According to current planet formation models, this system is very close to the host mass threshold below which Jupiters are not expected to form. Upcoming space-based exoplanet microlensing surveys by NASA's Nancy Grace Roman Space Telescope and, possibly, ESA's Euclid mission, will provide demanding tests of current planet formation models.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Weicheng Zang
Youn Kil Jung
Hongjing Yang
Xiangyu Zhang
Andrzej Udalski
Jennifer C. Yee
Andrew Gould
Shude Mao
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Kyu-Ha Hwang
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
Chung-Uk Lee
摘要： We present the analysis of seven microlensing planetary events with planet/host mass ratios $q < 10^{-4}$: KMT-2017-BLG-1194, KMT-2017-BLG-0428, KMT-2019-BLG-1806, KMT-2017-BLG-1003, KMT-2019-BLG-1367, OGLE-2017-BLG-1806, and KMT-2016-BLG-1105. They were identified by applying the Korea Microlensing Telescope Network (KMTNet) AnomalyFinder algorithm to 2016--2019 KMTNet events. A Bayesian analysis indicates that all the lens systems consist of a cold super-Earth orbiting an M or K dwarf. Together with 17 previously published and three that will be published elsewhere, AnomalyFinder has found a total of 27 planets that have solutions with $q < 10^{-4}$ from 2016--2019 KMTNet events, which lays the foundation for the first statistical analysis of the planetary mass-ratio function based on KMTNet data. By reviewing the 27 planets, we find that the missing planetary caustics problem in the KMTNet planetary sample has been solved by AnomalyFinder. We also find a desert of high-magnification planetary signals ($A \gtrsim 65$), and a follow-up project for KMTNet high-magnification events could detect at least two more $q < 10^{-4}$ planets per year and form an independent statistical sample.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Plasma lensing is the refraction of low-frequency electromagnetic rays due to cold free electrons in the universe. For sources at a cosmological distance, there is observational evidence of elongated, complex plasma structures along the line of sight requiring a multi-lens-plane description. To investigate the limits of single-plane plasma lensing, we set up a double-plane lens with a projected Gaussian electron density in each lens plane. We compare double-plane scenarios with corresponding effective single-plane configurations. Our results show how double-plane lenses can be distinguished from single-plane lenses by observables, i.e. resolved multiple image positions, relative magnifications, time delays, and pulse shapes. For plasma lensing of fast radio bursts, the observed pulse shape may be dominated by the lensing effect, allowing us to neglect the intrinsic source pulse shape to distinguish different lensing configurations. The time-domain observables turn out to be the most salient features to tell multi- and single-plane lenses apart.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The effect of ionized gas on the propagation of radio signals is known as plasma lensing. Unlike gravitational lensing, plasma lensing causes both magnification and strong de-magnification effects to background sources. We study the cross section of plasma lensing for two density profiles, the Gaussian and power-law models. In general, the cross section increases with the density gradient. Radio sources can be used to measure the free electron density along the line of sight. However, plasma lensing de-magnification causes an underestimate of the electron density. Such a bias increases with the electron density, and can be up to $\sim 15\%$ in the high density region. There is a large probability that high density clumps will be missed due to this bias. The magnification of plasma lensing can also change the luminosity function of the background sources. The number density of sources on both the high and low luminosity ends can be overestimated due to this biasing effect.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this study we demonstrate that stellar masses of galaxies (Mstar) are universally correlated through a double power law function with the product of the dynamical velocities (Ve) and sizes to one-fourth power (Re^0.25) of galaxies, both measured at the effective radii. The product VeRe^0.25 represents the fourth root of the total binding energies within effective radii of galaxies. This stellar mass-binding energy correlation has an observed scatter of 0.14 dex in log(VeRe^0.25) and 0.46 dex in log(Mstar). It holds for a variety of galaxy types over a stellar mass range of nine orders of magnitude, with little evolution over cosmic time. A toy model of self-regulation between binding energies and supernovae feedback is shown to be able to reproduce the observed slopes, but the underlying physical mechanisms are still unclear. The correlation can be a potential distance estimator with an uncertainty of 0.2 dex independent of the galaxy type.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The stellar mass-to-light ratio gradient in SDSS $r-$band $\nabla (M_*/L_r)$ of a galaxy depends on its mass assembly history, which is imprinted in its morphology and gradients of age, metallicity, and stellar initial mass function (IMF). Taking a MaNGA sample of 2051 galaxies with stellar masses ranging from $10^9$ to $10^{12}M_\odot$ released in SDSS DR15, we focus on face-on galaxies, without merger and bar signatures, and investigate the dependence of the 2D $\nabla (M_*/L_r)$ on other galaxy properties, including $M_*/L_r$-colour relationships by assuming a fixed Salpeter IMF as the mass normalization reference. The median gradient is $\nabla M_*/L_r\sim -0.1$ (i.e., the $M_*/L_r$ is larger at the centre) for massive galaxies, becomes flat around $M_*\sim 10^{10} M_{\odot}$ and change sign to $\nabla M_*/L_r\sim 0.1$ at the lowest masses. The $M_*/L_r$ inside a half light radius increases with increasing galaxy stellar mass; in each mass bin, early-type galaxies have the highest value, while pure-disk late-type galaxies have the smallest. Correlation analyses suggest that the mass-weighted stellar age is the dominant parameter influencing the $M_*/L_r$ profile, since a luminosity-weighted age is easily affected by star formation when the specific star formation rate (sSFR) inside the half light radius is higher than $10^{-3} {\rm Gyr}^{-1}$. With increased sSFR gradient, one can obtain a steeper negative $\nabla (M_*/L_r)$. The scatter in the slopes of $M_*/L$-colour relations increases with increasing sSFR, for example, the slope for post-starburst galaxies can be flattened to $0.45$ from the global value $0.87$ in the $M_*/L$ vs. $g-r$ diagram. Hence converting galaxy colours to $M_*/L$ should be done carefully, especially for those galaxies with young luminosity-weighted stellar ages, which can have quite different star formation histories.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jiyuan Zhang
Weicheng Zang
Youn Kil Jung
Hongjing Yang
Andrew Gould
Takahiro Sumi
Shude Mao
Subo Dong
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Kyu-Ha Hwang
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
摘要： We present the observations and analysis of a high-magnification microlensing planetary event, KMT-2022-BLG-0440, for which the weak and short-lived planetary signal was covered by both the KMTNet survey and follow-up observations. The binary-lens models with a central caustic provide the best fits, with a planet/host mass ratio, $q = 0.75$--$1.00 \times 10^{-4}$ at $1\sigma$. The binary-lens models with a resonant caustic and a brown-dwarf mass ratio are both excluded by $\Delta\chi^2 > 70$. The binary-source model can fit the anomaly well but is rejected by the ``color argument'' on the second source. From Bayesian analyses, it is estimated that the host star is likely a K or M dwarf located in the Galactic disk, the planet probably has a Neptune-mass, and the projected planet-host separation is $1.9^{+0.6}_{-0.7}$ or $4.6^{+1.4}_{-1.7}$ au, subject to the close/wide degeneracy. This is the third $q < 10^{-4}$ planet from a high-magnification planetary signal ($A \gtrsim 65$). Together with another such planet, KMT-2021-BLG-0171Lb, the ongoing follow-up program for the KMTNet high-magnification events has demonstrated its ability in detecting high-magnification planetary signals for $q < 10^{-4}$ planets, which are challenging for the current microlensing surveys.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Up to date, only 13 firmly established triple microlensing events have been discovered, so the occurrence rates of microlensing two-planet systems and planets in binary systems are still uncertain. With the upcoming space-based microlensing surveys, hundreds of triple microlensing events will be detected. To provide clues for future observations and statistical analyses, we initiate a project to investigate the detectability of triple-lens systems with different configurations and observational setups. As the first step, in this work we develop the simulation software and investigate the detectability of a scaled Sun-Jupiter-Saturn system with the recently proposed telescope for microlensing observation on the ``Earth 2.0 (ET)'' satellite. With the same $\Delta\chi^2$ thresholds of detecting a single planet and two planets, we find that the detectability of the scaled Sun-Jupiter-Saturn analog is about 1% and the presence of the Jovian planet suppresses the detectability of the Saturn-like planet by $\sim $13% regardless of the adopted detection $\Delta\chi^2$ threshold. This suppression probability could be at the same level as the Poisson noise of future space-based statistical samples of triple-lenses, so it is inappropriate to treat each planet separately during detection efficiency calculations.
点击量
待评议
点击量
下载量
评论
