Because of the development of large-format, wide-field cameras, microlensing surveys are now able to monitor millions of stars with sufficient cadence to detect planets. These new discoveries will span the full range of significance levels including planetary signals too small to be distinguished from the noise. At present, we do not understand where the threshold is for detecting planets. MOA-2011-BLG-293Lb is the first planet to be published from the new surveys, and it also has substantial followup observations. This planet is robustly detected in survey+followup data (∆χ 2 ∼ 5400). The planet/host mass ratio is q = 5.3 ± 0.2 × 10 −3 . The best fit projected separation is s = 0.548 ± 0.005 Einstein radii. However, due to the s ↔ s −1 degeneracy, projected separations of s −1 are only marginally disfavored at ∆χ 2 = 3. A Bayesian estimate of the host mass gives M L = 0.43 +0.27 −0.17 M ⊙ , with a sharp upper limit of M L < 1.2 M ⊙ from upper limits on the lens flux. Hence, the planet mass is m p = 2.4 +1.5 −0.9 M Jup , and the physical projected separation is either r ⊥ ≃ 1.0 AU or r ⊥ ≃ 3.4 AU. We show that survey data alone predict this solution and are able to characterize the planet, but the ∆χ 2 is much smaller (∆χ 2 ∼ 500) than with the followup data. The ∆χ 2 for the survey data alone is smaller than for any other securely detected planet. This event suggests a means to probe the detection threshold, by analyzing a large sample of events like MOA-2011-BLG-293, which have both followup data and high cadence survey data, to provide a guide for the interpretation of pure survey microlensing data.

We present CCD imaging observations of early‐type galaxies with dark lanes obtained with the Southern African Large Telescope (SALT) during its performance‐verification phase. The observations were performed in six spectral bands that span the spectral range from the near‐ultraviolet atmospheric cut‐off to the near‐infrared. We derive the extinction law by the extragalactic dust in the dark lanes in the spectral range 1.11 < λ−1 < 2.94 μm−1 by fitting model galaxies to the unextinguished parts of the image, and subtracting from these the actual images. This procedure allows the derivation, with reasonably high signal‐to‐noise ratio, of the extinction in each spectral band we used for each resolution element of the image. We also introduce an alternative method to derive the extinction values by comparing various colour‐index maps under the assumption of negligible intrinsic colour gradients in these galaxies. We than compare the results obtained using these two methods. We compare the total‐to‐selective extinction derived for these galaxies with previously obtained results and with similar extinction values of Milky Way dust to derive conclusions about the properties of extragalactic dust in different objects and conditions. We find that the extinction curves run parallel to the Galactic extinction curve, which implies that the properties of dust in the extragalactic environment are similar to those of the Milky Way, despite our original expectations. The ratio of the total V‐band extinction to the selective extinction between the V and B bands is derived for each galaxy with an average of 2.82 ± 0.38, compared to a canonical value of 3.1 for the Milky Way. The similar values imply that galaxies with well‐defined dark lanes have characteristic dust grain sizes similar to those of Galactic dust. We use total optical extinction values to estimate the dust mass for each galaxy, compare these with dust masses derived from IRAS measurements, and find them in the range 104–107 M⊙.

We report the results of multicolour observations of 30 E/S0 galaxies with dust lanes. For each galaxy we obtained broad-band images and narrow-band images using interference filters isolating the H\alpha +[NII] emission lines to derive the amount and morphology of dust and ionized gas. To improve the wavelength coverage we retrieved data from the SDSS and 2MASS and combined these with our data. Ionized gas is detected in 25 galaxies and shows in most cases a smooth morphology, although knots and filamentary structure are also observed in some objects. The extended gas distribution closely follows the dust structure, with a clear correlation between the mass of both components. An extinction law by the extragalactic dust in the dark lanes is derived and is used to estimate the dust content of the galaxies. The derived extinction law is used to correct the measured colours for intrinsic dust extinction and the data are fitted with a stellar population synthesis model. We find that the H-alpha emission and colours of most objects are consistent with the presence of an "old" stellar population (~10 Gyr) and a small fraction of a "young" population (~10-100 Myr). To check this we closely examine NGC5363, for which archival Spitzer/IRAC and GALEX data are available, as a representative dust-lane E/S0 galaxy of the sample.Comment: 28 pages, 15 figures and 10 tables. Minor corrections included to match published MNRAS version. R-band contour maps are low-resolution versions of those used in the MNRAS versio

We point out an important source of error in measurements of extragalactic Hα emission and suggest ways to reduce it. The Hα line, used for estimating star formation rates, is commonly measured by imaging in a narrow band and a wide band, both of which include the line. The image analysis relies on the accurate removal of the underlying continuum. We discuss in detail the derivation of the emission‐line’s equivalent width and flux for extragalactic extended sources, and the required photometric calibrations. We describe commonly used continuum‐subtraction procedures, and discuss the uncertainties that they introduce. Specifically, we analyse errors introduced by colour effects. We show that the errors in the measured Hα equivalent width induced by colour effects can lead to underestimates as large as 40 per cent and overestimates as large as 10 per cent, depending on the underlying galaxy’s stellar population and the continuum‐subtraction procedure used. We also show that these errors may lead to biases in results of surveys, and to the underestimation of the cosmic star formation rate at low redshifts (the low z points in the Madau plot). We suggest a method to significantly reduce these errors using a single colour measurement.

We present results from an ongoing programme to study the dust and ionized gas in E/S0 galaxies with dust lanes. Our data, together with results from previous studies of E/S0 galaxies, are used to demonstrate the close relationship between these two components. This relationship is discussed in light of our current understanding of the nature and origin of the interstellar medium (ISM), and in particular in the context of the interplay between the different multi‐temperature components. We show that focusing on dust obscured regions as tracers of the ISM, and on their properties, serves as independent evidence for the external origin of the dust and ionized gas.