2,169 research outputs found
The effects of halo alignment and shape on the clustering of galaxies
We investigate the effects of halo shape and its alignment with larger scale
structure on the galaxy correlation function. We base our analysis on the
galaxy formation models of Guo et al., run on the Millennium Simulations. We
quantify the importance of these effects by randomizing the angular positions
of satellite galaxies within haloes, either coherently or individually, while
keeping the distance to their respective central galaxies fixed. We find that
the effect of disrupting the alignment with larger scale structure is a ~2 per
cent decrease in the galaxy correlation function around r=1.8 Mpc/h. We find
that sphericalizing the ellipsoidal distributions of galaxies within haloes
decreases the correlation function by up to 20 per cent for r<1 Mpc/h and
increases it slightly at somewhat larger radii. Similar results apply to power
spectra and redshift-space correlation functions. Models based on the Halo
Occupation Distribution, which place galaxies spherically within haloes
according to a mean radial profile, will therefore significantly underestimate
the clustering on sub-Mpc scales. In addition, we find that halo assembly bias,
in particular the dependence of clustering on halo shape, propagates to the
clustering of galaxies. We predict that this aspect of assembly bias should be
observable through the use of extensive group catalogues.Comment: 8 pages, 6 figures. Accepted for publication in MNRAS. Minor changes
relative to v1. Note: this is an revised and considerably extended
resubmission of http://arxiv.org/abs/1110.4888; please refer to the current
version rather than the old on
Mineralogy and geochemistry of Late Archean and Paleoproterozoic granites and pegmatites in the Northern Penokean terrane of Marquette and Dickinson Counties, Michigan
This thesis focuses on mineralogy, geochemistry, and origin of eight pegmatites and two spatially associated granites of Late Archean and Paleoproterozoic ages located in Marquette and Dickinson Counties, Michigan. Biotite geochemistry reveals that both granites and all pegmatites are peraluminous and have an orogenic signature. However, bulk composition reveals the Humboldt granite is a peraluminous A-type granite and the Bell Creek granite is a peraluminous mix between I-, S-, and A-type granites. The Republic Mine pegmatite appears to be geochemically similar to the Bell Creek granite and Grizzly pegmatite. The Crockley pegmatite is genetically related to the Humboldt granite. The Groveland Mine, Sturgeon River, and Hwy69 pegmatites appear to be a product of the Peavy Pond Complex being contaminated with the Marquette Range Super Group. Contamination and anatexis have made classification of the granites and pegmatites problematic. The Grizzly should be classified as a primitive LCT-type even though this pegmatite lacks characteristic enrichment associated with LCT pegmatites. Mineralogical geochemistry reveals that the Republic Mine is relatively more primitive than other pegmatites and should be classified as a primitive Mixed-type pegmatite. Groveland Mine has mineralogy and geochemistry not normally associated with NYF-type pegmatites and should be classified as Mixed. The Crockley pegmatite should be classified as NYF-type with a primitive LCT overprint. Dolfin, Hwy69, Sturgeon River, and Black River pegmatites should be classified as Rare Element, REE, NYF-type, although the Black River has slight tantalum enrichment expressed in columbite group minerals
The contribution of massive haloes to the matter power spectrum in the presence of AGN feedback
The clustering of matter, as measured by the matter power spectrum, informs
us about dark matter and cosmology, as well as baryonic effects on the
distribution of matter in the universe. Using cosmological hydrodynamical
simulations from the cosmo-OWLS and BAHAMAS simulation projects, we investigate
the contribution of power in haloes with various masses, defined by particles
within some overdensity region, to the full power spectrum, as well as the
power ratio between baryonic and dark matter only (DMO) simulations for a
matched (between simulations) and an unmatched set of haloes. We find that the
presence of AGN feedback suppresses the power on all scales for haloes of all
masses examined (), by ejecting matter from within
to and potentially beyond in massive
haloes (), and likely
impeding the growth of lower-mass haloes as a consequence. A lower AGN feedback
temperature drastically changes the behaviour of high-mass haloes
(), damping the
effects of AGN feedback at small scales, .
For , group-sized haloes
() dominate the power spectrum, while on
smaller scales the combined contributions of lower-mass haloes to the full
power spectrum rise above that of the group-sized haloes. Finally, we present a
model for the power suppression due to feedback, which combines observed mean
halo baryon fractions with halo mass fractions and halo-matter cross-spectra
extracted from dark matter only simulations to predict the power suppression to
percent-level accuracy down to without
any free parameters.Comment: 20 pages, 11 figures. Submitted to MNRA
The impact of baryonic processes on the two-point correlation functions of galaxies, subhaloes and matter
The observed clustering of galaxies and the cross-correlation of galaxies and
mass provide important constraints on both cosmology and models of galaxy
formation. Even though the dissipation and feedback processes associated with
galaxy formation are thought to affect the distribution of matter, essentially
all models used to predict clustering data are based on collisionless
simulations. Here, we use large hydrodynamical simulations to investigate how
galaxy formation affects the autocorrelation functions of galaxies and
subhaloes, as well as their cross-correlation with matter. We show that the
changes due to the inclusion of baryons are not limited to small scales and are
even present in samples selected by subhalo mass. Samples selected by subhalo
mass cluster ~10% more strongly in a baryonic run on scales r > 1Mpc/h, and
this difference increases for smaller separations. While the inclusion of
baryons boosts the clustering at fixed subhalo mass on all scales, the sign of
the effect on the cross-correlation of subhaloes with matter can vary with
radius. We show that the large-scale effects are due to the change in subhalo
mass caused by the strong feedback associated with galaxy formation and may
therefore not affect samples selected by number density. However, on scales r <
r_vir significant differences remain after accounting for the change in subhalo
mass. We conclude that predictions for galaxy-galaxy and galaxy-mass clustering
from models based on collisionless simulations will have errors greater than
10% on sub-Mpc scales, unless the simulation results are modified to correctly
account for the effects of baryons on the distributions of mass and satellites.Comment: 15 pages, 9 figures. Replaced to match the version accepted by MNRA
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