Gravitationally Lensed HI with MeerKAT

The SKA era is set to revolutionize our understanding of neutral hydrogen (HI) in individual galaxies out to redshifts of z~0.8; and in the z > 6 intergalactic medium through the detection and imaging of cosmic reionization. Direct HI number density constraints will, nonetheless, remain relatively weak out to cosmic noon (z~2) - the epoch of peak star formation and black hole accretion - and beyond. However, as was demonstrated from the 1990s with molecular line observations, this can be overcome by utilising the natural amplification afforded by strong gravitational lensing, which results in an effective increase in integration time by the square of the total magnification (\mu^2) for an unresolved source. Here we outline how a dedicated lensed HI survey will leverage MeerKAT's high sensitivity, frequency coverage, large instantaneous bandwidth, and high dynamic range imaging to enable a lasting legacy of high-redshift HI emission detections well into the SKA era. This survey will not only provide high-impact, rapid-turnaround MeerKAT science commissioning results, but also unveil Milky Way-like systems towards cosmic noon which is not possible with any other SKA precursors/pathfinders. An ambitious lensed HI survey will therefore make a significant impact from MeerKAT commissioning all the way through to the full SKA era, and provide a more complete picture of the HI history of the Universe.Comment: 15 pages, 3 figures, accepted for publication, Proceedings of Science, workshop on "MeerKAT Science: On the Pathway to the SKA", held in Stellenbosch 25-27 May 2016. Comments welcom

Towards the first detection of strongly lensed HI emission

We report interferometric observations tuned to the redshifted neutral hydrogen (HI) 21cm emission line in three strongly lensed galaxies at $z \sim 0.4$ with the Giant Metrewave Radio Telescope (GMRT). One galaxy spectrum (J1106+5228 at z=0.407) shows evidence of a marginal detection with an integrated signal-to-noise ratio of 3.8, which, if confirmed by follow-up observations, would represent the first strongly lensed and most distant individual galaxy detected in HI emission. Two steps are performed to transcribe the lensed integrated flux measurements into HI mass measurements for all three target galaxies. First, we calculate the HI magnification factor $\mu$ by applying general relativistic ray-tracing to a physical model of the source-lens system. The HI magnification generally differs from the optical magnification and depends largely on the intrinsic HI mass $M_{\rm HI}$ due to the HI mass-size relation. Second, we employ a Bayesian formalism to convert the integrated flux, amplified by the $M_{\rm HI}$-dependent magnification factor $\mu$, into a probability density for $M_{\rm HI}$, accounting for the asymmetric uncertainty due to the declining HI mass function (Eddington bias). In this way, we determine a value of $\log_{\rm 10} (M_{\rm HI}/M_\odot) = 10.2^{+0.3}_{-0.7}$ for J1106+5228, consistent with the estimate of $9.4\pm0.3$ from the optical properties of this galaxy. The HI mass of the other two sources are consistent with zero within a 95 per cent confidence interval however we still provide upper limits for both sources and a $1\sigma$ lower limit for J1250-0135 using the same formalism.Comment: Accepted by MNRAS, no changes made. 12 pages, 7 figure

The first image of the Milky Way’s central black hole and the unique enhancement Africa could offer future tests of gravity

Astronomers use a wide range of telescopes to study the universe, tuning into different parts of the electromagnetic spectrum to explore diverse astrophysical phenomena. Our eyes are sensitive to light that has a wavelength of approximately 500 nanometres. This is the region in which traditional, so-called ‘optical’ astronomy is carried out with facilities such as the Southern African Large Telescope in Sutherland. The choice of wavelength and telescope depends on the physical properties of the astronomical source of interest, e.g. hot gas at billion-degree temperatures is best studied at shorter wavelengths like X-rays. The recently launched James Webb Space Telescope will revolutionise our view of the infrared universe with a sensitivity significantly surpassing that of the Hubble Space Telescope. Another critical aspect of a telescope is the sharpness with which it can make out small details in a distant object. In this Commentary, we discuss a global network of radio telescopes known as the Event Horizon Telescope (EHT), observing light with a wavelength of 1 millimetre (mm), synthesising a much larger, earth-sized virtual telescope to achieve the sharpest detail attainable in astronomy. The primary objective of the EHT is to make images of supermassive black holes, behemoths that lie at the centres of galaxies and possess masses that range from about a million to ten billion times the mass of our own Sun

Elm Farm Research Centre Bulletin with Technical Updates from the Organic Advisory Service 80

A collection of technical, policy and research articles on organic food and food system

High-Resolution Radio Observations of Five Optically Selected Type 2 Quasars

Many low-luminosity active galactic nuclei (AGNs) contain a compact radio core which can be observed with high angular resolution using very long baseline interferometry (VLBI). Combining arcsec-scale structural information with milliarcsec-resolution VLBI imaging is a useful way to characterise the objects and to find compact cores on parsec scales. VLBI imaging could also be employed to look for dual AGNs when the sources show kpc-scale double symmetric structure with flat or inverted radio spectra. We observed five such sources at redshifts 0.36 < z < 0.58 taken from an optically selected sample of Type 2 quasars with the European VLBI Network (EVN) at 1.7 and 5 GHz. Out of the five sources, only one (SDSS J1026-0042) shows a confidently detected compact VLBI core at both frequencies. The other four sources are marginally detected at 1.7 GHz only, indicating resolved-out radio structure and steep spectra. Using first-epoch data from the ongoing Karl G. Jansky Very Large Array Sky Survey, we confirm that indeed all four of these sources have steep radio spectra on arcsec scale, contrary to the inverted spectra reported earlier in the literature. However, the VLBI-detected source, SDSS J1026-0042, has a flat integrated spectrum. Radio AGNs that show kpc-scale symmetric structures with truly flat or inverted spectra could still be promising candidates of dual AGNs, to be targeted with VLBI observations in the future.Comment: 13 pages, 2 figures, appeared in the open-access journal Symmetry (special issue: Astronomy and Symmetry

Trace Hydrogen in Minerals

Trace hydrogen in minerals most frequently occurs bonded to oxygen. The resulting water and hydroxyl (OH-) affect and play a role in a variety of mineral properties and reactions. This thesis examines the occurrence of trace hydrogen in nominally anhydrous minerals, the mechanisms by which trace hydrogen participates in reactions and controls properties, and the changes that occur in hydrogen speciation and siting as a function of temperature. The principal tool used in this study is infrared (IR) spectroscopy because of its sensitivity to the highly polar O-H bond, yielding quantitative information on concentration, and symmetry, speciation, and siting information. The speciation of trace hydrogen in garnet and low temperature natural and synthetic quartz is examined in detail. In garnet hydrogen occurs as the hydrogarnet substitution, four hydroxyl groups replacing a silicate tetrahedron. This substitution is extremely common among natural garnets. Concentrations range from 0.05 to 0.20 wt. % (as H2O) in garnets from most occurrences, including garnets from the mantle. This trace hydrogen is truly dissolved. The hydrogen found in natural and synthetic quartz formed at low temperature can occur as either hydroxyl or molecular water. The molecular water is the active participant in hydrolytic weakening of quartz, but it is not truly dissolved. It occurs as small groups of molecules (approximately 5 to 200) which were trapped during rapid growth. Two properties of minerals affected by trace hydrogen are strength and radiation response. Molecular water may be responsible for weakening of other minerals as well as quartz. Both water and hydroxyl participate in radiation response of minerals. In metamict zircon, water stabilizes local charge imbalance formed when bonds are broken. Water enters the crystal after a threshold of damage occurs, and reacts with broken bonds to form hydroxyl groups. These must reform molecular water and be expelled before recrystallization occurs during heating. In quartz, molecular water is strongly correlated with the formation of citrine color during irradiation, but inhibits the formation of the amethyst color center Fe4+. Apparently molecular hydrogen forms during radiolysis of the water, and reduces the Fe4+. Several hydroxyl sites in topaz are strongly correlated with the formation of brown color upon irradiation. The unifying theme in all these reactions is the extreme mobility of hydrogen and the ease with which different oxygen-hydrogen species may be formed in silicates. The behavior of trace hydrogen at temperatures of geologic interest has been examined using high temperature infrared spectroscopy. Direct observations of speciation, concentration, and properties have been made up to 1200°C. In muscovite there is no change in hydrogen speciation or site up to the dehydration point, as expected. However, in cordierite and beryl water reversibly partitions into a gas-like state above 400°C, and the formation of this new state controls the dehydration behavior. In topaz, hydroxyl groups have been observed converting to new sites at temperatures above 500°C. In orthoclase feldspar, one type of molecular water dehydrates at 200°C, while a second type converts irreversibly to a new hydrous species above 600°C. There is no evidence for the existence of hydrogen species other than hydroxyl and water in silicate minerals. The hydrogarnet substitution (four hydroxyl groups in a tetrahedral configuration) is common in garnets and may be important in other orthosilicates. The most common hydrous species in nominally anhydrous silicates (aside from fluid inclusions and alteration) are: small groups of trapped water molecules; individual water molecules occupying voids in the structure of minerals; hydroxyl occurring in a charge balancing role such as AlO3OH substituting for SiO4; hydroxyl neutralizing substitutional atoms, e.g., LiOH; and hydroxyl groups formed from the reaction of broken bonds with water as in radiation damaged minerals. There is no evidence for the presence of the oxonium ion, H3O+, in common minerals, and the existing evidence for the occurrence of molecular hydrogen may better be explained by the presence of water or hydroxyl groups.</p

Multiple supermassive black hole systems: SKA's future leading role

Galaxies and supermassive black holes (SMBHs) are believed to evolve through a process of hierarchical merging and accretion. Through this paradigm, multiple SMBH systems are expected to be relatively common in the Universe. However, to date there are poor observational constraints on multiple SMBHs systems with separations comparable to a SMBH gravitational sphere of influence (<< 1 kpc). In this chapter, we discuss how deep continuum observations with the SKA will make leading contributions towards understanding how multiple black hole systems impact galaxy evolution. In addition, these observations will provide constraints on and an understanding of stochastic gravitational wave background detections in the pulsar timing array sensitivity band (nanoHz -microHz). We also discuss how targets for pointed gravitational wave experiments (that cannot be resolved by VLBI) could potentially be found using the large-scale radio-jet morphology, which can be modulated by the presence of a close-pair binary SMBH system. The combination of direct imaging at high angular resolution; low-surface brightness radio-jet tracers; and pulsar timing arrays will allow the SKA to trace black hole binary evolution from separations of a galaxy virial radius down to the sub-parsec level. This large dynamic range in binary SMBH separation will ensure that the SKA plays a leading role in this observational frontier.Comment: 11 pages, 4 figures. To be published in the proceedings of "Advancing Astrophysics with the Square Kilometre Array", PoS(AASKA14)151, in pres