We present the stellar kinematics in the central 2'' of the luminous elliptical galaxy M87 (NGC 4486), using laser adaptive optics to feed the Gemini telescope integral-field spectrograph, ...Near-infrared Integral Field Spectrograph (NIFS). The velocity dispersion rises to 480 km s--1 at 02. We combine these data with extensive stellar kinematics out to large radii to derive a black hole mass equal to (6.6 ? 0.4) X 109 M , using orbit-based axisymmetric models and including only the NIFS data in the central region. Including previously reported ground-based data in the central region drops the uncertainty to 0.25 X 109 M with no change in the best-fit mass; however, we rely on the values derived from the NIFS-only data in the central region in order to limit systematic differences. The best-fit model shows a significant increase in the tangential velocity anisotropy of stars orbiting in the central region with decreasing radius, similar to that seen at the centers of other core galaxies. The black hole mass is insensitive to the inclusion of a dark halo in the models--the high angular resolution provided by the adaptive optics breaks the degeneracy between black hole mass and stellar mass-to-light ratio. The present black hole mass is in excellent agreement with the Gebhardt & Thomas value, implying that the dark halo must be included when the kinematic influence of the black hole is poorly resolved. This degeneracy implies that the black hole masses of luminous core galaxies, where this effect is important, may need to be re-evaluated. The present value exceeds the prediction of the black hole-dispersion and black hole-luminosity relations, both of which predict about 1 X 109 M for M87, by close to twice the intrinsic scatter in the relations. The high end of the black hole correlations may be poorly determined at present.
We explore the use of principal component analysis (PCA) to characterize high-fidelity simulations and interferometric observations of the millimeter emission that originates near the horizons of ...accreting black holes. We show mathematically that the Fourier transforms of eigenimages derived from PCA applied to an ensemble of images in the spatial domain are identical to the eigenvectors of PCA applied to the ensemble of the Fourier transforms of the images, which suggests that this approach may be applied to modeling the sparse interferometric Fourier-visibilities produced by an array such as the Event Horizon Telescope. We also show that the simulations in the spatial domain can themselves be compactly represented with a PCA-derived basis of eigenimages, which allows for detailed comparisons to be made between variable observations and time-dependent models, as well as for detection of outliers or rare events within a time series of images. Furthermore, we demonstrate that the spectrum of PCA eigenvalues is a diagnostic of the power spectrum of the structure and, hence, of the underlying physical processes in the simulated and observed images.
Abstract
The sparse interferometric coverage of the Event Horizon Telescope (EHT) poses a significant challenge for both reconstruction and model fitting of black hole images.
PRIMO
is a new ...principal components analysis-based algorithm for image reconstruction that uses the results of high-fidelity general relativistic, magnetohydrodynamic simulations of low-luminosity accretion flows as a training set. This allows the reconstruction of images that are consistent with the interferometric data and that live in the space of images that is spanned by the simulations.
PRIMO
follows Monte Carlo Markov Chains to fit a linear combination of principal components derived from an ensemble of simulated images to interferometric data. We show that
PRIMO
can efficiently and accurately reconstruct synthetic EHT data sets for several simulated images, even when the simulation parameters are significantly different from those of the image ensemble that was used to generate the principal components. The resulting reconstructions achieve resolution that is consistent with the performance of the array and do not introduce significant biases in image features such as the diameter of the ring of emission.
Abstract
We present a new reconstruction of the Event Horizon Telescope (EHT) image of the M87 black hole from the 2017 data set. We use
PRIMO
, a novel dictionary-learning-based algorithm that uses ...high-fidelity simulations of accreting black holes as a training set. By learning the correlations between the different regions of the space of interferometric data, this approach allows us to recover high-fidelity images even in the presence of sparse coverage and reach the nominal resolution of the EHT array. The black hole image comprises a thin bright ring with a diameter of 41.5 ± 0.6
μ
as and a fractional width that is at least a factor of 2 smaller than previously reported. This improvement has important implications for measuring the mass of the central black hole in M87 based on the EHT images.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted)We present stellar kinematics and orbit superposition models for the central regions of four brightest cluster galaxies, based upon ...integral-field spectroscopy at Gemini, Keck, and McDonald Observatories. Our integral-field data span radii from <100 pc to tens of kiloparsecs, comparable to the effective radius of each galaxy. We report black hole masses, M sub(diamonds) of ... for NGC 4889, ... for NGC 3842, and ... for NGC 7768, with errors representing 68% confidence limits. For NGC 2832, we report an upper limit of M sub(diamonds) < 9.0 x 10 super(9) M sub(middot in circle). Our models of each galaxy include a dark matter halo, and we have tested the dependence of M sub(diamonds) on the model dark matter profile. Stellar orbits near the center of each galaxy are tangentially biased, on comparable spatial scales to the galaxies' photometric cores. We find possible photometric and kinematic evidence for an eccentric torus of stars in NGC 4889, with a radius of nearly 1 kpc. We compare our measurements of M sub(diamonds) to the predicted black hole masses from various fits to the relations between M sub(diamonds) and stellar velocity dispersion (sigma), luminosity (L), or stellar mass (Mlow *). Still, the black holes in NGC 4889 and NGC 3842 are significantly more massive than all sigma-based predictions and most L-based predictions. The black hole in NGC 7768 is consistent with a broader range of predictions.
Programs to observe evolution in the M unk - sigma or M unk - L. relations typically compare black hole masses, M unk, in high-redshift galaxies selected by nuclear activity to M unk in local ...galaxies selected by luminosity L or velocity dispersion sigma . Because active galactic nucleus luminosity can depend on M unk, selection effects are different for the two samples, potentially producing a false signal of evolution. Cosmic scatter in the M unk relations means that the mean log L or log sigma among galaxies that host a black hole of given V. may be substantially different than the log L or log sigma obtained from inverting the M unk - L or M unk - sigma relations for the same nominal M unk. The bias is strongest at high M unk, where the luminosity and dispersion functions of galaxies fall rapidly. The most massive black holes occur more often as rare outliers in galaxies of modest mass than in the even rarer high-mass galaxies, which would otherwise be the sole location of such black holes in the absence of cosmic scatter. Because of this bias, M unk will typically appear to be too large in the distant sample for a given L or sigma . For the largest black holes and the largest plausible cosmic scatter, the bias can reach a factor of 3 in M unk for the M unk - sigma relation and 9 for the M unk - L relation. Unfortunately, the cosmic scatter is not known well enough to correct for the bias. Measuring evolution of the M unk relations requires object selection to be precisely defined and exactly the same at all redshifts.
Black hole (BH) masses predicted from the M unk- sigma relationship conflict with predictions from the M unk-L relationship for high-luminosity galaxies, such as brightest cluster galaxies (BCGs). ...The M unk-L relationship predicts that some BCGs may harbor BHs with M unk approaching 10 super(10) M unk, while the M unk- sigma relationship always predicts M unk < 3 x 10 super(0) M unk. we argue that the M unk-L relationship is a plausible description for galaxies of high luminosity. If the cores in central stellar density are formed by binary BHs, the inner core cusp radius, r gamma , may be an independent witness of M unk. Using central structural parameters derived from a large sample of early-type galaxies observed by HST, we argue that L is superior to sigma as an indicator of r gamma . Further, the r gamma -M unk relationship for 11 core galaxies with measured M unk appears to be consistent with the M unk-L relationship for BCGs. BCGs have large cores appropriate for their large luminosities that may be difficult to generate with the more modest BH masses inferred from the M unk- sigma relationship. M unk similar to M would be expected for BCGs, if they were formed in dissipationless mergers, which should preserve the ratio of BH to stellar mass, M. This scenario appears to be consistent with the slow increase in sigma with L and the more rapid increase in effective radii with L seen in BCGs as compared to less luminous galaxies. If BCGs have large BHs commensurate with their luminosities, then the local BH mass function for M unk > 3 x 10 super(0) M unk would be nearly an order of magnitude richer than that inferred from the M unk- sigma relationship. The volume density of the most luminous QSOs may favor the M unk-L relationship.
Re-ionization of the intergalactic medium occurred in the early Universe at redshift z ≈ 6-11, following the formation of the first generation of stars. Those young galaxies (where the bulk of stars ...formed) at a cosmic age of less than about 500 million years (z ≲ 10) remain largely unexplored because they are at or beyond the sensitivity limits of existing large telescopes. Understanding the properties of these galaxies is critical to identifying the source of the radiation that re-ionized the intergalactic medium. Gravitational lensing by galaxy clusters allows the detection of high-redshift galaxies fainter than what otherwise could be found in the deepest images of the sky. Here we report multiband observations of the cluster MACS J1149+2223 that have revealed (with high probability) a gravitationally magnified galaxy from the early Universe, at a redshift of z = 9.6 ± 0.2 (that is, a cosmic age of 490 ± 15 million years, or 3.6 per cent of the age of the Universe). We estimate that it formed less than 200 million years after the Big Bang (at the 95 per cent confidence level), implying a formation redshift of ≲14. Given the small sky area that our observations cover, faint galaxies seem to be abundant at such a young cosmic age, suggesting that they may be the dominant source for the early re-ionization of the intergalactic medium.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Dunes on Pluto Telfer, Matt W; Parteli, Eric J R; Radebaugh, Jani ...
Science (American Association for the Advancement of Science),
06/2018, Letnik:
360, Številka:
6392
Journal Article
Recenzirano
Odprti dostop
The surface of Pluto is more geologically diverse and dynamic than had been expected, but the role of its tenuous atmosphere in shaping the landscape remains unclear. We describe observations from ...the New Horizons spacecraft of regularly spaced, linear ridges whose morphology, distribution, and orientation are consistent with being transverse dunes. These are located close to mountainous regions and are orthogonal to nearby wind streaks. We demonstrate that the wavelength of the dunes (~0.4 to 1 kilometer) is best explained by the deposition of sand-sized (~200 to ~300 micrometer) particles of methane ice in moderate winds (<10 meters per second). The undisturbed morphology of the dunes, and relationships with the underlying convective glacial ice, imply that the dunes have formed in the very recent geological past.
Observations suggest that the effective radii of high-redshift massive spheroids are as much as a factor of ∼6 smaller than low-redshift galaxies of comparable mass. Given the apparent absence of ...low-redshift counterparts, this has often been interpreted as indicating that the high-density, compact red galaxies must be ‘puffed up’ by some mechanism. We compare the ensemble of high-redshift observations with large samples of well-observed, low-redshift ellipticals. At the same physical radii, the stellar surface mass densities of low- and high-redshift systems are comparable. Moreover, the abundance of high surface density material at low redshift is comparable to or larger than that observed at z > 1–2, consistent with the continuous buildup of spheroids over this time. The entire population of compact, high-redshift red galaxies may be the progenitors of the high-density cores of present-day ellipticals, with no need for a decrease in stellar density from z= 2 to 0. The primary difference between low- and high-redshift systems is thus the observed low-density material at large radii in low-redshift spheroids (rather than the high-density material in high-redshift spheroids). Such low-density material may either (1) assemble at z < 2 or (2) be present, but not yet detected, at z > 2. Mock observations of low-redshift massive systems suggest that the amount of low-density material at high redshifts is indeed significantly less than that at z= 0. However, deeper observations will be important in constraining the exact amount (or lack thereof) and distribution of this material, and how it builds up with redshift. We show that, without deep observations, the full extent of such material even at low redshifts can be difficult to determine, in particular if the mass profile is not exactly a single Sersic profile. We discuss the implications of our results for physical models of galaxy evolution.
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