Hintze Centre for Astrophysical Surveys

Abstract:

We present the H I emission project within the MIGHTEE survey, currently being carried out with the newly commissioned MeerKAT radio telescope. This is one of the first deep, blind, medium-wide interferometric surveys for neutral hydrogen (H I) ever undertaken, extending our knowledge of H I emission to z = 0.6. The science goals of this medium-deep, medium-wide survey are extensive, including the evolution of the neutral gas content of galaxies over the past 5 billion years. Simulations predict nearly 3000 galaxies over 0 <  z <  0.4 will be detected directly in H I, with statistical detections extending to z = 0.6. The survey allows us to explore H I as a function of galaxy environment, with massive groups and galaxy clusters within the survey volume. Additionally, the area is large enough to contain as many as 50 local galaxies with H I mass < 108 M⊙, which allows us to study the low-mass galaxy population. The 20 deg2 main survey area is centred on fields with exceptional multi-wavelength ancillary data, with photometry ranging from optical through far-infrared wavelengths, supplemented with multiple spectroscopic campaigns. We describe here the survey design and the key science goals. We also show first results from the Early Science observations, including kinematic modelling of individual sources, along with the redshift, H I, and stellar mass ranges of the sample to date.

Abstract:

We estimate the total population of near-Earth objects (NEOs) in the solar system using an extensive, "solarsystem-to-pixels"fake-asteroid simulation to debias detections of real NEOs by the ATLAS survey. Down to absolute magnitudes H = 25 and 27.6 (diameters of ~34 and 10 m, respectively, for 15% albedo), we find total populations of (3.72 ± 0.49) × 105 and (1.59 ± 0.45) × 107 NEOs, respectively. Most of the plausible sources of error tend toward underestimation, so the true populations are likely larger. We find the distribution of H magnitudes steepens for NEOs fainter than H ~ 22.5, making small asteroids more common than extrapolation from brighter H mags would predict. Our simulation indicates a strong bias against detecting small but dangerous asteroids that encounter Earth with high relative velocities - i.e., asteroids in highly inclined and/or eccentric orbits. Worldwide NEO discovery statistics indicate this bias affects global NEO detection capability to the point that an observational census of small asteroids in such orbits is probably not currently feasible. Prompt and aggressive followup of NEO candidates, combined with closer collaborations between segments of the global NEO community, can increase detection rates for these dangerous objects.