We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal-component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines ('late types') and more quiescent galaxies ('early types'). We measure the clustering in real space, free from any distortion of the clustering pattern owing to peculiar velocities, for a series of volume-limited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range 2<( σ / h -1 Mpc)<15 , with a marginally steeper slope for early types than late types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of ∼2.5 between L * and 4 L *. At all luminosities, however, the correlation function amplitude for the early types is ∼50 per cent higher than that of the late types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity. 相似文献
Investigation of coarse (>2 mm) heavy-mineral concentrates from the White Hills Gravel near St Arnaud in western Victoria provides new evidence for the age and provenance of this widespread palaeoplacer formation. A prominent zircon – sapphire – spinel assemblage is characteristic of Cenozoic basaltic-derived gemfields in eastern Australia, while a single diamond shows similar features to others found in alluvial deposits in northeastern Victoria and New South Wales. Dating of two suites of zircons by fission track and U – Pb (SHRIMP) methods gave overlapping ages between 67.4 ± 5.2 and 74.5 ± 6.3 Ma, indicating a maximum age of Late Cretaceous for the formation. Another suite of minerals includes tourmaline (schorl – dravite), andalusite, rutile and anatase, which are probably locally derived from contact metamorphic aureoles in Cambro-Ordovician basement metapelites intruded by Early Devonian granites. U – Pb dating of rutile grains by laser ablation ICPMS gave an age of 393 ± 10 Ma, confirming an Early Devonian age for the regional granites and associated contact metamorphism. Other phases present include pseudorutile, metamorphic corundum of various types, maghemite and hematite, which have more equivocal source rocks. A model to explain the diverse sources of these minerals invokes recycling and mixing of the far-travelled basalt-derived suite with the less mature, locally derived metamorphic suite. Some minerals have probably been recycled from Mesozoic gravels through Early Cenozoic (Paleocene – Eocene) drainage systems during various episodes of weathering, ferruginisation and erosion. Comparison between heavy-mineral assemblages in occurrences of the White Hills Gravel may allow distinction between depositional models advocating either separate drainage networks or coalescing sheets. Such assemblages may also provide evidence for the present-day divide in the Western Uplands being the youngest expression of an old (Late Mesozoic – Early Cenozoic) stable divide separating north- and south-flowing streams or a much younger feature (ca 10 Ma) which disrupted mainly south-flowing drainage. 相似文献
In this paper, we reflect on an emerging community-based partnership rooted in place-based reparative research. Braiding knowledges (Atalay, 2012) from Nbisiing Anishinaabeg communities, northern Ontario universities, and multi-scalar museums, the partnership focuses on repatriation, reparative environmental histories, and action-based research in the context of settler colonialism and climate change. We reflect on ongoing projects that attempt to put Anishinaabe gikendaasowin (knowledge) into action alongside historical geographical research. We discuss how the partnership resonates with community geography values of relationship, collaboration, equity, and reciprocity, and urge non-Indigenous geographers to acknowledge how Indigenous knowledges and approaches have shaped these ideas long before geography became a discipline. We contend that historical geographers have a deeper role to play in community geography scholarship, citing examples of two projects related to (1) repatriation of Anishinaabeg cultural heritage and (2) storymapping through historical Geographic Information Systems (HGIS). However, we argue, geographers must continue to acknowledge their own positionality in a discipline that was built through settler colonial violence and knowledge production. Finally, we reflect on the role of academic institutions in facilitating First Nation-university-museum partnerships through access to funding, space, and databases, while addressing the challenges of relying on institutional support for reparatory and decolonizing projects.
We calculate the optical b J luminosity function (LF) of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, η , which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η identifies the average emission- and absorption-line strength in the galaxy rest frame spectrum, and hence is a useful indicator of the present star formation. We use a total of 75 000 galaxies in our calculations, chosen from a sample of high signal-to-noise ratio, low-redshift galaxies observed before 2001 January. We find that there is a systematic steepening of the faint-end slope ( α ) as one moves from passive ( α =-0.54) to active ( α =-1.50) star-forming galaxies, and that there is also a corresponding faintening of the rest frame characteristic magnitude M *-5 log10( h ) (from −19.6 to −19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies [ M b J-5 log10( h ) fainter than −16.0], perhaps suggesting the presence of a significant dwarf population. The LFs presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent k -corrections, and investigate possible fibre-aperture biases. 相似文献
We demonstrate that cosmogenic nuclide surface exposure dating can be used to provide the first well-constrained age for a Fiordland bedrock surface that was created by coastal erosion and has since been uplifted. Tight clustering of 10Be and 26Al apparent exposure ages between 102-119 kyr on a terrace with strandline at 65 ± 8 m gives a last interglacial age of terrace formation of 130-120 ka, and an uplift rate of 0.52 ± 0.08 mm/yr. Apparent exposure ages from a higher (92-130 m), more incised region of remnant coastal morphology fall in the range 53-111 kyr. The anomalously low ages and large variance demonstrate that weathering and fluvial or rockfall erosion rates are too extreme at the higher sites to determine an age of coastal erosion. Sea level samples have apparent exposure ages in the range 2-11 kyr, with an uncertainty of about 3 kyr. This is consistent with surface exposure during the present sea level high-stand, indicates minimal inheritance of ancient cosmogenic nuclides, and is in accord with geomorphic arguments. Mean 26Al/10Be ratios of 6.6 for each sample set is consistent with the actively exhuming late Quaternary tectonic setting. Large boulders and gently convex rocky outcrops formed during coastal erosion preserve surfaces that are least modified during later uplift, and are hence the best sites for determining the age of coastal erosion. 相似文献
Gem corundum, a minor but persistent megacryst in east Australian basalt fields, is mined from some placer concentrations. Laser ablation, inductively coupled plasma mass spectrometry analyses and O isotope determinations on a colour range of corundum from different fields, show that chromophore (Fe, Cr, Ti, V) and genetic indicator (Ga, Mg, δ18O) values can distinguish corundum sources (magmatic, metamorphic and metasomatic) before basalt incorporation. They also characterise corundum groups from different fields. This identified two metamorphic groups, one carrying ruby at Barrington Tops, and a magmatic group distinct from those from other gem fields (lower Fe, northeast Tasmania; higher Fe, Yarrowitch). Ruby-bearing groups show clear provincial characteristics and include lower temperature spinel-facies groups (Barrington, Yarrowitch) and higher temperature garnet-facies groups (Cudgegong–Macquarie River). High Mg/Fe and Ni values in the latter approach those for corundum in diamond, and are a possible diamond indicator. The corundum derived from diverse fold-belt and felsic sources in underlying lithosphere forms a dataset for comparing corundum from other basalt fields. 相似文献