The Effect of Local Galaxy Surface Density on Star Formation for HI selected galaxies

We present the result of investigations into two theories to explain the star formation rate-density relationship. For regions of high galaxy density, either there are fewer star forming galaxies, or galaxies capable of forming stars are present but some physical process is suppressing their star formation. We use HI Parkes All Sky Survey's (HIPASS) HI detected galaxies and infrared and radio fluxes to investigate star formation rates and efficiencies with respect to local surface density. For nearby (vel<10000 km\s) HI galaxies we find a strong correlation between HI mass and star formation rate. The number of HI galaxies decreases with increasing local surface density. For HI galaxies (1000<vel<6000 km\s) there is no significant change in the star formation rate or the efficiency of star formation with respect to local surface density. We conclude the SFR-density relation is due to a decrease in the number of HI star forming galaxies in regions of high galaxy density and not to the suppression of star formation.Comment: 17 pages, 16 figures, Accepted for publication by MNRAS 2 August 200

Galaxy threshing and the formation of ultra-compact dwarf galaxies

Recent spectroscopic and morphological observational studies of galaxies around NGC 1399 in the Fornax Cluster (Drinkwater et al. 2000b) have discovered several `ultra-compact dwarf' galaxies with intrinsic sizes of $\sim$ 100 pc and absolute $B$ band magnitudes ranging from -13 to -11 mag. In order to elucidate the origin of these enigmatic objects, we perform numerical simulations on the dynamical evolution of nucleated dwarf galaxies orbiting NGC 1399 and suffering from its strong tidal gravitational field. Adopting a plausible scaling relation for dwarf galaxies, we find that the outer stellar components of a nucleated dwarf are totally removed. This is due to them being tidally stripped over the course of several passages past the central region of NGC 1399. The nucleus, however, manages to survive. We also find that the size and luminosity of the remnant are similar to those observed for ultra-compact dwarf galaxies, if the simulated precursor nucleated dwarf has a mass of $\sim$ $10^8$ $M_{\odot}$. These results suggest that ultra-compact dwarf galaxies could have previously been more luminous dwarf spheroidal or elliptical galaxies with rather compact nuclei.Comment: 9 pages 4 figures,2001, ApJL, 552, 10

He Spoke, I Spoke: A Usage-Based Examination of Homophony in the Navajo Verb Complex

This study examines homophony between first and third person verbs and between second and third person verbs in Navajo. The typical paradigm for person-marking in Navajo has a sh- prefix for first person, a ni- prefix in second person, and a zero-marked third person. In some phonological environments, however, the first and second person pronouns are elided, producing cases of homophony between first and third and between second and third persons. I examine all cases of this in Navajo and also provide data from Jicarilla Apache, Hupa (a Pacific Coast Athabaskan language), and three Northern Athabaskan languages: Chilcotin, Koyukon, and Ahtna to provide a cross-family historical approach to this interesting phenomenon. The study is based in cognitive and functional approaches. Results indicate that there is a strong relationship between frequency and homophony in the Navajo Verb Complex and across Athabaskan languages

Substructure and Dynamics of the Fornax Cluster

We present the first dynamical analysis of a galaxy cluster to include a large fraction of dwarf galaxies. Our sample of 108 Fornax Cluster members measured with the UK Schmidt Telescope FLAIR-II spectrograph contains 55 dwarf galaxies (15.5>bJ>18.0 or -16>MB>-13.5). Hα emission shows that 36%+/-8% of the dwarfs are star forming, twice the fraction implied by morphological classifications. The total sample has a mean velocity of 1493+/-36 km s-1 and a velocity dispersion of 374+/-26 km s-1. The dwarf galaxies form a distinct population: their velocity dispersion (429+/-41 km s-1) is larger than that of the giants (308+/-30 km s-1) at the 98% confidence level. This suggests that the dwarf population is dominated by infalling objects whereas the giants are virialized. The Fornax system has two components, the main Fornax Cluster centered on NGC 1399 with cz=1478 km s-1 and σcz=370 km s-1 and a subcluster centered 3° to the southwest including NGC 1316 with cz=1583 km s-1 and σcz=377 km s-1. This partition is preferred over a single cluster at the 99% confidence level. The subcluster, a site of intense star formation, is bound to Fornax and probably infalling toward the cluster core for the first time. We discuss the implications of this substructure for distance estimates of the Fornax Cluster. We determine the cluster mass profile using the method of Diaferio, which does not assume a virialized sample. The mass within a projected radius of 1.4 Mpc is (7+/-2)×1013 Msolar, and the mass-to-light ratio is 300+/-100 Msolar/Lsolar. The mass is consistent with values derived from the projected mass virial estimator and X-ray measurements at smaller radii

A VISION FOR ASSESSMENT IN SCIENCE

This forum seeks to bring together science and mathematics colleagues and their discipline groups to collectively identify our aspirations and challenges for assessment into the next decade. The disruptions associated with COVID-19 delivery and assessment, especially exams, have resulted in both compromise and innovation at an accelerated pace. What does best-practice in assessment look like in a post-COVID era? Do we expect to revert back to our assessment practices pre-COVID, or do we see ourselves on a new path? Are exams still fit for purpose, and if not, what are the alternatives we value? Do we trust technology and what it can deliver, or is it creating more problems than solutions? To what degree do issues with academic integrity push us in particular directions? Representatives from each of the national discipline groups are invited to share key conversations that are happening at their level, and individuals are strongly encouraged to attend, and share their perspectives. Most importantly, this forum will support the Assessment Working Group commissioned by the ACDS to identify our priorities as a community, and feed this back to the Deans of Science Faculties and Schools around the country

Substructure and dynamics of the Fornax Cluster

We present the first dynamical analysis of a galaxy cluster to include a large fraction of dwarf galaxies. Our sample of 108 Fornax Cluster members measured with the UK Schmidt Telescope FLAIR-II spectrograph contains 55 dwarf galaxies (15.5>bj>18.0 or -16>Mb>-13.5). Halpha emission shows that 36+/-8 per cent of the dwarfs are star-forming, twice the fraction implied by morphological classifications. The total sample has a mean velocity of 1493+/-36 km/s and a velocity dispersion of 374+/-26 km/s. The dwarf galaxies form a distinct population: their velocity dispersion (429+/-41 km/s) is larger than that of the giants (308+/-30 km/s) at the 98 per cent confidence level. This suggests that the dwarf population is dominated by infalling objects whereas the giants are virialized. The Fornax system has two components; the main Fornax Cluster centered on NGC 1399 with mean velocity 1478 km/s and velocity dispersion 370 km/s, and a subcluster centered 3 degrees to the south-west including NGC 1316 with mean velocity 1583 km/s and velocity dispersion 377 km/s. This partition is preferred over a single cluster at the 99 per cent confidence level. The subcluster, a site of intense star formation, is bound to Fornax and probably infalling towards the cluster core for the first time. We discuss the implications of this substructure for distance estimates of the Fornax Cluster.Comment: Accepted for publication in ApJ Letters; 11 pages, uses aastex.cls (not included

The WiggleZ Dark Energy Survey: final data release and the metallicity of UV-luminous galaxies

The WiggleZ Dark Energy Survey measured the redshifts of over 200 000 ultraviolet (UV)-selected (NUV < 22.8 mag) galaxies on the Anglo-Australian Telescope. The survey detected the baryon acoustic oscillation signal in the large-scale distribution of galaxies over the redshift range 0.2 < z < 1.0, confirming the acceleration of the expansion of the Universe and measuring the rate of structure growth within it. Here, we present the final data release of the survey: a catalogue of 225 415 galaxies and individual files of the galaxy spectra. We analyse the emission-line properties of these UV-luminous Lyman-break galaxies by stacking the spectra in bins of luminosity, redshift, and stellar mass. The most luminous (−25mag < M_(FUV) < −22mag) galaxies have very broad Hβ emission from active nuclei, as well as a broad second component to the [O III] (495.9 nm, 500.7 nm) doublet lines that is blueshifted by 100 km s^(−1) , indicating the presence of gas outflows in these galaxies. The composite spectra allow us to detect and measure the temperature-sensitive [O III] (436.3 nm) line and obtain metallicities using the direct method. The metallicities of intermediate stellar mass (8.8 < log (M*/M⊙) < 10) WiggleZ galaxies are consistent with normal emission-line galaxies at the same masses. In contrast, the metallicities of high stellar mass (10 < log (M*/M⊙) < 12) WiggleZ galaxies are significantly lower than for normal emission-line galaxies at the same masses. This is not an effect of evolution as the metallicities do not vary with redshift; it is most likely a property specific to the extremely UV-luminous WiggleZ galaxies