It is shown that upon combining GALEX far-ultraviolet and Johnson B magnitudes a resultant FUV–B colour can be obtained that for red giant stars of luminosity classes III and II correlates well with chromospheric emission in the cores of the Mg iih and k lines. Giant stars throughout the colour range 0.8 ≤ B – V ≤ 1.6 exhibit such a phenomenon. The main result of this paper is to show that GALEX far-ultraviolet photometry can provide information about the degree of chromospheric activity among red giant stars, and as such may offer a tool for surveying the evolution of chromospheric activity from the main sequence into the red giant phases of stellar evolution.

Breakthrough Listen is a 10-yr initiative to search for signatures of technologies created by extraterrestrial civilisations at radio and optical wavelengths. Here, we detail the digital data recording system deployed for Breakthrough Listen observations at the 64-m aperture CSIRO Parkes Telescope in New South Wales, Australia. The recording system currently implements two modes: a dual-polarisation, 1.125-GHz bandwidth mode for single-beam observations, and a 26-input, 308-MHz bandwidth mode for the 21-cm multibeam receiver. The system is also designed to support a 3-GHz single-beam mode for the forthcoming Parkes ultra-wideband feed. In this paper, we present details of the system architecture, provide an overview of hardware and software, and present initial performance results.

We use Gemini Multi-Object Spectrograph integral Field Unit observations of the inner 285 × 400 pc2 region of the Seyfert 2 galaxy NGC 5643 to map the [S iii]λ9069 emission line flux distribution and kinematics, as well as the stellar kinematics, derived by fitting the Ca iiλλλ8498,8542,8662 triplet, at a spatial resolution of 45 pc. The stellar velocity field shows regular rotation, with a projected velocity of 100 km s−1 and kinematic major axis along a position angle of –36°. A ring of low stellar velocity dispersion values (∼70 km s−1), attributed to young/intermediate age stellar populations, is seen surrounding the nucleus with a radius of 50 pc. We found that the [S iii] flux distribution shows an elongated structure along the east–west direction and its kinematics is dominated by outflows within a bi-cone at an ionised gas outflow rate of 0.3 M⊙ yr−1. In addition, velocity slices across the [S iii]λ9069 emission line reveal a kinematic component attributed to rotation of gas in the plane of the galaxy.

The birth of stars and the formation of galaxies are cornerstones of modern astrophysics. While much is known about how galaxies globally and their stars individually form and evolve, one fundamental property that affects both remains elusive. This is problematic because this key property, the birth mass distribution of stars, referred to as the stellar initial mass function, is a key tracer of the physics of star formation that underpins almost all of the unknowns in galaxy and stellar evolution. It is perhaps the greatest source of systematic uncertainty in star and galaxy evolution. The past decade has seen a growing variety of methods for measuring or inferring the initial mass function. This range of approaches and evolving definitions of the quantity being measured has in turn led to conflicting conclusions regarding whether or not the initial mass function is universal. Here I review this growing wealth of approaches, and highlight the importance of considering potential initial mass function variations, reinforcing the need to carefully quantify the scope and uncertainties of measurements. I present a new framework to aid the discussion of the initial mass function and promote clarity in the further development of this fundamental field.

Merger trees harvested from cosmological N-body simulations encode the assembly histories of dark matter halos over cosmic time and are a fundamental component of semi-analytical models of galaxy formation. The ability to compare the tools used to construct merger trees, namely halo finders and tree building algorithms, in an unbiased and systematic manner is critical to assess the quality of merger trees. In this paper, we present the dendrogram, a novel method to visualise merger trees, which provides a comprehensive characterisation of a halo’s assembly history—tracking subhalo orbits, halo merger events, and the general evolution of halo properties. We show the usefulness of the dendrogram as a diagnostic tool of merger trees by comparing halo assembly simulation analysed with three different halo finders—VELOCIraptor, AHF, and Rockstar—and their associated tree builders. Based on our analysis of the resulting dendrograms, we highlight how they have been used to motivate improvements to VELOCIraptor. The dendrogram software is publicly available online, at: https://github.com/rhyspoulton/MergerTree-Dendrograms.

It has recently been shown that the abundance of cold neutral gas may follow a similar evolution as the star formation history. This is physically motivated, since stars form out of this component of the neutral gas and if the case, would resolve the long-standing issue that there is a clear disparity between the total abundance of neutral gas and star-forming activity over the history of the Universe. Radio-band 21-cm absorption traces the cold gas and comparison with the Lyman-α absorption, which traces all of the gas, provides a measure of the cold gas fraction, or the spin temperature, Tspin. The recent study has shown that the spin temperature (degenerate with the ratio of the absorber/emitter extent) appears to be anti-correlated with the star formation density, ψ*, with 1/Tspin undergoing a similar steep evolution as ψ* over redshifts of 0 ≲ z ≲ 3, whereas the total neutral hydrogen exhibits little evolution. Above z ∼ 3, where ψ* shows a steep decline with redshift, there are insufficient 21-cm data to determine whether 1/Tspin continues to follow ψ*. Knowing this is paramount in ascertaining whether the cold neutral gas does trace the star formation over the Universe’s history. We explore the feasibility of resolving this with 21-cm observations of the largest contemporary sample of reliable damped Lyman-α absorption systems and conclude that, while today’s largest radio interferometers can reach the required sensitivity at z ≲ 3.5, the Square Kilometre Array is required to probe higher redshifts.

The purpose of this paper is to determine the origin of the photometric variations of 48 Lib using the data from the STEREO and to investigate their relations with the disk structure. The photometric data comprise a period of five years from 2007 to 2011. The spectroscopic data covering the same time interval are provided from the BeSS database. The Hα lines are examined by measuring their equivalent widths and line intensities. Hα variations are then compared with those displayed by the photometric data. From the photometry, high-precision results (10−5 c d−1 in frequency and 10−4 mag in amplitude) are obtained. It is detected that the star has shown 24 frequencies, mainly clustered around the peaks at 2.48896(1) and 5.08150(2) c d−1. The analysis reveals that the photometric frequencies are not due to pulsation, but caused by the rotation, and that the remaining frequencies arise from transient activities on or just above the photosphere. Also, it is shown that the spectroscopic data exhibit a significant Hα variability, and that the Hα line variation depends on the variation of frequency and amplitude, something which has been often proposed in the literature but has never before been demonstrated observationally. This proves that the disk structure and photometric variations are related.

We describe the motivation and design details of the ‘Phase II’ upgrade of the Murchison Widefield Array radio telescope. The expansion doubles to 256 the number of antenna tiles deployed in the array. The new antenna tiles enhance the capabilities of the Murchison Widefield Array in several key science areas. Seventy-two of the new tiles are deployed in a regular configuration near the existing array core. These new tiles enhance the surface brightness sensitivity of the array and will improve the ability of the Murchison Widefield Array to estimate the slope of the Epoch of Reionisation power spectrum by a factor of ∼3.5. The remaining 56 tiles are deployed on long baselines, doubling the maximum baseline of the array and improving the array u, v coverage. The improved imaging capabilities will provide an order of magnitude improvement in the noise floor of Murchison Widefield Array continuum images. The upgrade retains all of the features that have underpinned the Murchison Widefield Array’s success (large field of view, snapshot image quality, and pointing agility) and boosts the scientific potential with enhanced imaging capabilities and by enabling new calibration strategies.