New near-infrared and visual images at 2.2 /¿m and 6550 Â are presented for 46 galaxies having infrared luminosities of L IR >8.5X10 U L 0 , 60 fim flux densities greater than 1.94 Jy, and declinations greater than-35°. These galaxies make up a significant fraction of a complete, northern hemisphere sample of ultraluminous infrared galaxies. Visual and/or near-infrared imaging data now exist for 56 ultraluminous infrared galaxies out to nearly 50 000 km s _1. Of these 56 galaxies, 53 (95%) show evidence for current or past interactions. Among these systems, there are a large variety of visual morphologies, including strongly interacting pairs with apparent tidal tails, as well as single, distorted galaxies with close double nuclei. There are three galaxies which, to the limits of the imaging data, do not appear to have suffered a recent interaction or merger. Approximately 47% (25/53) of the interacting systems have double nuclei, with projected nuclear separations ranging from 0.3 to 48 kpc. Seven systems have nuclear separations larger than 10 kpc. If the 53 interacting galaxies are viewed as stages in the evolution of pairs of interacting spiral galaxies to a single, luminous AGN or starburst, the present imaging data can be used to estimate the lifetime of the bright infrared phase. Including only those sample galaxies with morphological evidence for interactions, we calculate a lower and an upper limit to the lifetime of the ultraluminous infrared phase of the sample as a whole to be 2X10 8 and 2X10 9 yr, respectively. Comparison of these dynamical estimates to models of the mergers of gas-rich galaxies and the rates at which fuel is exhausted by starbursts or AGN suggests the lifetime of the ultraluminous phase lies much closer to the smaller of these two values. Selecting galaxies based upon luminous infrared activity clearly biases the sample towards merging galaxies with small physical separations. However, the existence of pairs with large separations indicates that the ultraluminous phase may in some cases start early during the merger process. Alternatively, these systems may contain unresolved third nuclei responsible for triggering the ultraluminous activity. We briefly compare our results to recent models of merging spiral galaxies.

We present Keck high-resolution near-IR (2.2 km ; and mid-IR (12.5 km ; FWHM D FWHM D 0A .15) images of APM 08279]5255, a z \ 3.91 IR-luminous broad absorption line quasi-stellar object with 0A .4) a prodigious apparent bolometric luminosity of 5 ] 1015 the largest known in the universe. The L _ , K-band image shows that this system consists of three components, all of which are likely to be the gravitationally lensed images of the same background object, and the 12.5 km image shows a morphology consistent with such an image conÐguration. Our lens model suggests that the magniÐcation factor is D100 from the rest-frame UV to mid-IR, where most of the luminosity is released. The intrinsic bolometric luminosity and IR luminosity of APM 08279]5255 are estimated to be 5 ] 1013 and L _ 1 ] 1013 respectively. This indicates that APM 08279]5255 is intrinsically luminous, but it is not L _ , the most luminous object known. As for its dust contents, little can be determined with the currently available data because of the uncertainties associated with the dust emissivity and the possible e †ect of di †erential magniÐcation. We also suggest that the lensing galaxy is likely to be a massive galaxy at z D 3.

Accurate analysis of precision ranges to the Moon has provided several tests of gravitational theory including the Equivalence Principle, geodetic precession, parameterized post-Newtonian (PPN) parameters γ and β, and the constancy of the gravitational constant G. Since the beginning of the experiment in 1969, the uncertainties of these tests have decreased considerably as data accuracies have improved and data time span has lengthened. We are exploring the modeling improvements necessary to proceed from cm to mm range accuracies enabled by the new Apache Point Observatory Lunar Laserranging Operation (APOLLO) currently under development in New Mexico. This facility will be able to make a significant contribution to the solar system tests of fundamental and gravitational physics. In particular, the Weak and Strong Equivalence Principle tests would have a sensitivity approaching 10 −14 , yielding sensitivity for the SEP violation parameter η of ∼ 3 × 10 −5 , v 2 /c 2 general relativistic effects would be tested to better than 0.1%, and measurements of the relative change in the gravitational constant,Ġ/G, would be ∼ 0.1% the inverse age of the universe. Having this expected accuracy in mind, we discusses the current techniques, methods and existing physical models used to process the LLR data. We also identify the challenges for modeling and data analysis that the LLR community faces today in order to take full advantage of the new APOLLO ranging station.

Human activity and land use change impact every landscape on Earth, driving declines in many animal species while benefiting others. Species ecological and life history traits may predict success in human‐dominated landscapes such that only species with “winning” combinations of traits will persist in disturbed environments. However, this link between species traits and successful coexistence with humans remains obscured by the complexity of anthropogenic disturbances and variability among study systems. We compiled detection data for 24 mammal species from 61 populations across North America to quantify the effects of (1) the direct presence of people and (2) the human footprint (landscape modification) on mammal occurrence and activity levels. Thirty‐three percent of mammal species exhibited a net negative response (i.e., reduced occurrence or activity) to increasing human presence and/or footprint across populations, whereas 58% of species were positively associated with increasing disturbance. However, apparent benefits of human presence and footprint tended to decrease or disappear at higher disturbance levels, indicative of thresholds in mammal species’ capacity to tolerate disturbance or exploit human‐dominated landscapes. Species ecological and life history traits were strong predictors of their responses to human footprint, with increasing footprint favoring smaller, less carnivorous, faster‐reproducing species. The positive and negative effects of human presence were distributed more randomly with respect to species trait values, with apparent winners and losers across a range of body sizes and dietary guilds. Differential responses by some species to human presence and human footprint highlight the importance of considering these two forms of human disturbance separately when estimating anthropogenic impacts on wildlife. Our approach provides insights into the complex mechanisms through which human activities shape mammal communities globally, revealing the drivers of the loss of larger predators in human‐modified landscapes.

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Lunar laser ranging (LLR) has for decades stood at the forefront of tests of gravitational physics, including tests of the equivalence principle (EP). Current LLR results on the EP achieve a sensitivity of Δa/a ≈ 10−13 based on few-centimeter data/model fidelity. A recent push in LLR, called APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) produces millimeter-quality data. This paper demonstrates the few-millimeter range precision achieved by APOLLO, leading to an expectation that LLR will be able to extend EP sensitivity by an order-of-magnitude to Δa/a ∼ 10−14, once modeling efforts improve to this level.

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In [1], we point out that a gravitomagnetic term in the equation of motion used to dynamically determine the precise shape of the lunar orbit is also responsible for the "frame-dragging" precession of a gyroscope near a massive rotating body. In the former case, the gravitomagnetic interaction between the moving masses of Earth and Moon-as evaluated in the solar system barycenter (SSB) frame-leads to orbital amplitude contributions at the six meter level. Part of the gravitomagnetic interaction plays a role in producing the necessary Lorentz contraction of the orbit in this frame. In the case of a gyroscope, the same interaction between mass elements moving within the macroscopic bodies produces the gyroscope precession. The physics is the same for both, the difference being in the distribution of mass currents.The SSB frame is chosen for lunar laser ranging (LLR) analysis for a variety of practical reasons [2]-not least of which that it is the most convenient asymptotically inertial reference frame for solar system dynamical analyses. The lunar and planetary orbits and the lunar rotation are determined by a simultaneous numerical integration of the post-Newtonian differential equation of motion and evaluation of light propagation times between the moving Earth and Moon [3].The six-meter gravitomagnetic influences on the lunar orbit in the SSB frame appear as cos D and cos 2D signatures, where D is the synodic phase. The post-Newtonian model, as implemented in the way described above, fits decades of LLR data in these modes to 4 mm and 8 mm accuracy, respectively. Therefore, any isolated modification of the gravitomagnetic term is limited to ≈ 0.1% the strength prescribed by general relativity [1].The gravitomagnetic term in the equation of motion is just one of several velocity-dependent contributions to the whole [4]. It is physically unrealistic to adjust the strength of a single interaction term without simultaneously examining changes to other terms in the velocity transformation package. Self-consistent transformations of the velocity-dependent terms from one frame to another in a metric framework have been worked out [5], and strongly constrained by experiment at well below the 0.1% level relevant to this discussion [6,7].It is clear that the choice of reference frame affects the lunar orbit shape needed to fit the LLR ranging dataand specifically the gravitomagnetic interaction's contribution to that frame-dependent orbit [8]. Also clear is that current successful LLR analysis performed in the SSB frame requires inclusion of general relativity's prescribed gravitomagnetism. Therefore, this interaction cannot be arbitrarily adjusted-alone or together with other aspects of post-Newtonian gravity-without considering the impact of such adjustments on LLR as well as on the variety of other relevant observations such as ranging to Mars and Mercury, binary pulsar pulse arrival times, etc.