分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitationally lensed extragalactic sources are often subject to statistical microlensing by stars in the galaxy or cluster lens. Accurate models of the flux statistics are required for inferring source and lens properties from flux observations. We derive an accurate semi-analytic approximation for calculating the mean and variance of the magnification factor, which are applicable to Gaussian source profiles and arbitrary non-uniform macro lens models, and hence can save the need to perform expensive numerical simulations. The results are given as single and double lens-plane integrals with simple, non-oscillatory integrands, and hence are fast computable using common Monte Carlo integrators. Employing numerical ray-shooting experiments, we examine the case of a highly magnified source near a macro fold caustic, and demonstrate the excellent accuracy of this semi-analytic approximation in the regime of multiple micro images. Additionally, we point out how the maximum persistent magnification achievable near a macro caustic is fundamentally limited by the masses and number density of the foreground microlenses, in addition to the source's physical size.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Correlated red noise recently reported from pulsar timing observations may be an indication of stochastic gravitational waves emitted by cosmic strings that formed during a primordial phase transition near the Grand Unification energy scale. Unfortunately, known probes of cosmic strings, namely the Cosmic Microwave Background anisotropies and string lensing of extragalactic galaxies, are not sensitive enough for low string tensions of $G\mu = 10^{-10}-10^{-7}$ that are needed to explain this putative signal. We show that strong gravitational lensing of Fast Radio Bursts (FRBs) by cosmic strings is a potentially unambiguous avenue to probe that range of string tension values. The image pair of string lensing are expected to have identical magnification factor and parity, and have a typical time delay of $\sim 10^2\,\,(G\,\mu/10^{-8})^2$ seconds. The unique spectral fingerprint of each FRB, as well as the possibility to detect correlations in the time series of the electric field of the radio waves, will enable verification of the string lensing interpretation. Very-Long-Baseline Interferometry (VLBI) observations can spatially resolve the image pair and provide a lower bound on the string tension based on the image separation. We calculate the FRB lensing rate as a function of FRB detection number for several different models of the FRB redshift distribution. We find that a survey detecting $\sim 10^5$ FRBs, in line with estimates for the detection rate of the forthcoming survey CHORD, can uncover a strong lensing event for a string tension of $G\mu \simeq 10^{-7}$. Larger FRB surveys, such as Phase 2 of the Square Kilometre Array (SKA), have the potential to significantly improve the sensitivity on the string tension to $G\mu \simeq 10^{-9}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Just like light, gravitational waves (GWs) are deflected and magnified by gravitational fields as they propagate through the Universe. However, their low frequency, phase coherence and feeble coupling to matter allow for distinct lensing phenomena, such as diffraction and central images, that are challenging to observe through electromagnetic sources. Here we explore how these phenomena can be used to probe features of gravitational lenses. We focus on two variants of the singular isothermal sphere, with 1) a variable slope of the matter density and 2) a central core. We describe the imprints of these features in the wave- and geometric-optics regimes, including the prospect of detecting central images. We forecast the capacity of LISA and advanced LIGO to study strongly lensed signals and measure the projected lens mass, impact parameter and slope or core size. A broad range of lens masses allows all parameters to be measured with precision up to $\sim 1/{\rm SNR}$, despite large degeneracies. Thanks to wave-optics corrections, all parameters can be measured, even when no central image forms. Although GWs are sensitive to projected quantities, we compute the probability distribution of lens redshift, virial mass and projection scale given a cosmology. As an application, we consider the prospect of constraining self-interacting and ultra-light dark matter, showing the regions of parameter space accessible to strongly-lensed GWs. The distinct GW signatures will enable novel probes of fundamental physics and astrophysics, including the properties of dark matter and the central regions of galactic halos.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational wave (GW) astronomy offers the potential to probe the wave-optics regime of gravitational lensing. Wave optics (WO) effects are relevant at low frequencies, when the wavelength is comparable to the characteristic lensing time delay multiplied by the speed of light, and are thus often negligible for electromagnetic signals. Accurate predictions require computing the conditionally convergent diffraction integral, which involves highly oscillatory integrands and is numerically difficult. We develop and implement several methods to compute lensing predictions in the WO regime valid for general gravitational lenses. First, we derive approximations for high and low frequencies, obtaining explicit expressions for several analytic lens models. Next, we discuss two numerical methods suitable in the intermediate frequency range: 1) Regularized contour flow yields accurate answers in a fraction of a second for a broad range of frequencies. 2) Complex deformation is slower, but requires no knowledge of solutions to the geometric lens equation. Both methods are independent and complement each other. We verify sub-percent accuracy for several lens models, which should be sufficient for applications to GW astronomy in the near future. Apart from modelling lensed GWs, our method will also be applicable to the study of plasma lensing of radio waves and tests of gravity.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Seth Olsen
Javier Roulet
Horng Sheng Chia
Liang Dai
Tejaswi Venumadhav
Barak Zackay
Matias Zaldarriaga
摘要： We map the likelihood of GW190521, the heaviest detected binary black hole (BBH) merger, by sampling under different mass and spin priors designed to be uninformative. We find that a source-frame total mass of $\sim$$150 M_{\odot}$ is consistently supported, but posteriors in mass ratio and spin depend critically on the choice of priors. We confirm that the likelihood has a multi-modal structure with peaks in regions of mass ratio representing very different astrophysical scenarios. The unequal-mass region ($m_2 / m_1 < 0.3$) has an average likelihood $\sim$$e^6$ times larger than the equal-mass region and a maximum likelihood $\sim$$e^2$ larger. Using ensembles of samples across priors, we examine the implications of qualitatively different BBH sources that fit the data. We find that the equal-mass solution has poorly constrained spins and at least one black hole mass that is difficult to form via stellar collapse due to (pulsational) pair instability. The unequal-mass solution can avoid this mass gap entirely but requires a negative effective spin and a precessing primary. Both of these scenarios are more easily produced by dynamical formation channels than field binary co-evolution. Drawing representative samples from each region of the likelihood map, we find a sensitive comoving volume-time $\mathcal{O}(10)$ times larger in the mass gap region than the gap-avoiding region. Accounting for this distance effect, the likelihood still reverses the advantage to favor the gap-avoiding scenario by a factor of $\mathcal{O}(100)$ before including mass and spin priors. Posterior samplers can be driven away from this high-likelihood region by common prior choices meant to be uninformative, making GW190521 parameter inference sensitive to the choice of mass and spin priors. This may be a generic issue for similarly heavy events given current detector sensitivity and waveform degeneracies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Strong lensing offers a precious opportunity for studying the formation and early evolution of super star clusters that are rare in our cosmic backyard. The Sunburst Arc, a lensed Cosmic Noon galaxy, hosts a young super star cluster with escaping Lyman continuum radiation. Analyzing archival HST images and emission line data from VLT/MUSE and X-shooter, we construct a physical model for the cluster and its surrounding photoionized nebula. We confirm that the cluster is $\sim 3\mbox{--}4\,$Myr old, is extremely massive $M_\star \sim 10^7\,M_\odot$ and yet has a central component as compact as several parsecs, and we find a metallicity $Z=(0.26\pm0.03)\,Z_\odot$. The cluster is surrounded by $\gtrsim 10^5\,M_\odot$ of dense clouds that have been pressurized to $P\sim 10^9\,{\rm K}\,{\rm cm}^{-3}$ by perhaps stellar radiation at within ten parsecs. These should have large neutral columns $N_{\rm HI} > 10^{22.5}\,{\rm cm}^{-2}$ to survive rapid ejection by radiation pressure. The clouds are likely dusty as they show gas-phase depletion of silicon, and may be conducive to secondary star formation if $N_{\rm HI} > 10^{24}\,{\rm cm}^{-2}$ or if they sink further toward the cluster center. Detecting strong ${\rm N III]}\lambda\lambda$1750,1752, we infer heavy nitrogen enrichment $\log({\rm N/O})=-0.23^{+0.08}_{-0.11}$. This requires efficiently retaining $\gtrsim 500\,M_\odot$ of nitrogen in the high-pressure clouds from massive stars heavier than $60\,M_\odot$ up to 4 Myr. We suggest a physical origin of the high-pressure clouds from partial or complete condensation of slow massive star ejecta, which may have important implication for the puzzle of multiple stellar populations in globular clusters.
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： 2017-11-10
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Massimo Pascale
Brenda L. Frye
Jose Diego
Lukas J. Furtak
Adi Zitrin
Tom Broadhurst
Christopher J. Conselice
Liang Dai
Leonardo Ferreira
Nathan J. Adams
Jeremy Lim
Ashish K. Meena
Stephen M. Wilkins
Rachana Bhatawdekar
Nicholas Foo
Patrick Kelly
Wenlei Chen
Patrick Kamieneski
Rogier A. Windhorst
摘要： The first deep field images from the James Webb Space Telescope (JWST) of the galaxy cluster SMACS~J0723.3-7327 reveal a wealth of new lensed images at uncharted infrared wavelengths, with unprecedented depth and resolution. Here we securely identify 14 new sets of multiply imaged galaxies totalling 42 images, adding to the five sets of bright and multiply-imaged galaxies already known from Hubble Space Telescope data. We find examples of arcs crossing critical curves, allowing detailed community follow-up, such as JWST spectroscopy for precise redshift determinations, and measurements of the chemical abundances and of the detailed internal gas dynamics of very distant, young galaxies. One such arc contains a pair of compact knots that are magnified by a factor of hundreds, and features a microlensed transient. We also detect an Einstein cross candidate only visible thanks to JWST's superb resolution. Our parametric lens model is available through the following link: https://www.dropbox.com/sh/gwup2lvks0jsqe5/AAC2RRSKce0aX-lIFCc9vhBXa?dl=0, and will be regularly updated using additional spectroscopic redshifts. The model is constrained by 16 of these sets of multiply imaged galaxies, three of which have spectroscopic redshifts, and reproduces the multiple images to better than an rms of $0.5^{\prime \prime}$, allowing for accurate magnification estimates of high-redshift galaxies. The intracluster light extends beyond the cluster members, exhibiting large-scale features that suggest a significant past dynamical disturbance. This work represents a first taste of the enhanced power JWST will have for lensing-related science.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jose M. Diego
Ashish K. Meena
Nathan J. Adams
Tom Broadhurst
Liang Dai
Dan Coe
Brenda Frye
Patrick Kelly
Anton M. Koekemoer
Massimo Pascale
S. P. Willner
Erik Zackrisson
Adi Zitrin
Rogier A. Windhorst
Seth H. Cohen
Rolf A. Jansen
Jake Summers
Scott Tompkins
Christopher J. Conselice
Simon P. Driver
摘要： The first JWST data on the massive colliding cluster El Gordo confirm 23 known families of multiply lensed images and identify 8 new members of these families. Based on these families, which have been confirmed spectroscopically by MUSE, we derived an initial lens model. This model guided the identification of 37 additional families of multiply lensed galaxies, among which 28 are entirely new systems, and 9 were previously known. The initial lens model determined geometric redshifts for the 37 new systems. The geometric redshifts agree reasonably well with spectroscopic or photometric redshifts when those are available. The geometric redshifts enable two additional models that include all 60 families of multiply lensed galaxies spanning a redshift range $20.8$ and has an estimated virial mass close the maximum mass allowed by standard cosmological models. The JWST images also reveal the presence of small-mass perturbers that produce small lensing distortions. The smallest of these is consistent with being a dwarf galaxy at $z=0.87$ and has an estimated mass of $3.8\times10^9$~\Msol, making it the smallest substructure found at $z>0.5$. The JWST images also show several candidate caustic-crossing events. One of them is detected at high significance at the expected position of the critical curve and is likely a red supergiant star at $z=2.1878$. This would be the first red supergiant found at cosmological distances. The cluster lensing should magnify background objects at $z>6$, making more of them visible than in blank fields of similar size, but there appears to be a deficiency of such objects.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Brenda L. Frye
Massimo Pascale
Nicholas Foo
Reagen Leimbach
Nikhil Garuda
Paulina Soto Robles
Jake Summers
Carlos Diaz
Patrick Kamieneski
Lukas Furtak
Seth Cohen
Jose Diego
Benjamin Beauchesne
Rogier Windhorst
Steve Willner
Anton M. Koekemoer
Adi Zitrin
Gabriel Caminha
Karina Caputi
Dan Coe
摘要： The massive galaxy cluster El Gordo ($z=0.87$) imprints multitudes of gravitationally lensed arcs onto James Webb Space Telescope (JWST) Near-Infrared Camera (NIRCam) images. Eight bands of NIRCam imaging were obtained in the Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS) program (GTO #1176). PSF-matched photometry across a suite of Hubble Space Telescope (HST) and NIRCam filters gives new photometric redshifts. We confirm 54 known image multiplicities and find two new ones and construct a lens model based on the light-traces-mass method. The mass within 500kpc estimated from the lens model is $\sim$$7.0\times10^{14}$M$_{\odot}$ with a mass ratio between the southeastern and northwestern components of $\sim$unity, similar to recent works. A statistical search for substructures recovers only these two components, which are each tightly bound kinematically and are separated in radial velocity by ~300 km s$^{-1}$. We identify a candidate member of a known 4-member $z=4.32$ galaxy overdensity by its model-predicted and photometric redshifts. These five members span a physical extent of $\sim$60 kpc and exhibit multiple components consistent with satellite associations. Thirteen additional candidates selected by spectroscopic/photometric constraints are small and faint, with a mean apparent brightness corrected for lensing magnification that is $\sim$2.2 mag fainter than M*. NIRCam imaging admits a wide range of brightnesses and morphologies for these candidates, suggesting a more diverse galaxy population may be underlying this rare view of a strongly-lensed galaxy overdensity.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Rogier A. Windhorst
Seth H. Cohen
Rolf A. Jansen
Jake Summers
Scott Tompkins
Christopher J. Conselice
Simon P. Driver
Haojing Yan
Dan Coe
Brenda Frye
Norman Grogin
Anton Koekemoer
Madeline A. Marshall
Rosalia O'Brien
Nor Pirzkal
Aaron Robotham
Russell E. Ryan,
Christopher N. A. Willmer
Timothy Carleton
Jose M. Diego
摘要： We give an overview and describe the rationale, methods, and first results from NIRCam images of the JWST "Prime Extragalactic Areas for Reionization and Lensing Science" ("PEARLS") project. PEARLS uses up to eight NIRCam filters to survey several prime extragalactic survey areas: two fields at the North Ecliptic Pole (NEP); seven gravitationally lensing clusters; two high redshift proto-clusters; and the iconic backlit VV 191 galaxy system to map its dust attenuation. PEARLS also includes NIRISS spectra for one of the NEP fields and NIRSpec spectra of two high-redshift quasars. The main goal of PEARLS is to study the epoch of galaxy assembly, AGN growth, and First Light. Five fields, the JWST NEP Time-Domain Field (TDF), IRAC Dark Field (IDF), and three lensing clusters, will be observed in up to four epochs over a year. The cadence and sensitivity of the imaging data are ideally suited to find faint variable objects such as weak AGN, high-redshift supernovae, and cluster caustic transits. Both NEP fields have sightlines through our Galaxy, providing significant numbers of very faint brown dwarfs whose proper motions can be studied. Observations from the first spoke in the NEP TDF are public. This paper presents our first PEARLS observations, their NIRCam data reduction and analysis, our first object catalogs, the 0.9-4.5 $\mu$m galaxy counts and Integrated Galaxy Light. We assess the JWST sky brightness in 13 NIRCam filters, yielding our first constraints to diffuse light at 0.9-4.5 {\mu}m. PEARLS is designed to be of lasting benefit to the community.
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