503 research outputs found
The Millennium Galaxy Catalogue: The nearby supermassive black hole mass function
We highlight the correlation between a galaxy's supermassive black hole mass
and the Sersic-index of the host spheroid or bulge component. From our
bulge-disk decompositions of 10 095 galaxies, drawn from the Millennium Galaxy
Catalogue, we construct the local (z < 0.18) mass function of supermassive
black holes. We compare our results to those of McLure & Dunlop (2004) and
conclude that the mass density of supermassive black holes may be marginally
higher than previously supposed. This increase is predominantly due to the
inclusion of low mass and later-type bulges. More details will be presented in
a forthcoming paper.Comment: Contributed article to the Fabulous Destiny of Galaxies meetin
Evaluation of Combustion Processes for Production of Feedstock Chemicals from Ammonium Sulfate and Ammonium Bisulfate
The combustion of ammonium bisulfate and ammonium sulfate solutions in hydrocarbon/air flames was studied under varied flame conditions. The objective of the study was to optimize the recovery of sulfur value from aqueous waste streams containing these salts. Combustion of ammonium sulfates yielded different sulfur species such as sulfur dioxide (SO2 ), hydrogen sulfide (H2S), and carbonyl sulfide (COS). The types of sulfur species obtained and their yields were dependent on the flame stoichiometry. When combustion was carried out in stochiometric flames or in flames with excess oxygen, the sulfur present in the salts was quantitatively converted to SO2 . However, these flames also produced nitrogen oxides (NOx ) above the 200ppm level. Combustion of ammonium sulfates in the sub-stoichiometric (oxygen-deficient) flames resulted in the formation of reduced sulfur species, particularly H2S. This species accounted for nearly 90% of the total sulfur present in the salts. Introduction of a secondary air stream in cooler regions of the combustor led to quantitative oxidation of H2 S and other reduced species such as COS to SO2. The SO2 obtained through the secondary oxidation contained nitrogen oxides at comparably lower levels
The Millennium Galaxy Catalogue: The connection between close pairs and asymmetry; implications for the galaxy merger rate
We compare the use of galaxy asymmetry and pair proximity for measuring
galaxy merger fractions and rates for a volume limited sample of 3184 galaxies
with -21 < M(B) -5 log h < -18 mag. and 0.010 < z < 0.123 drawn from the
Millennium Galaxy Catalogue. Our findings are that:
(i) Galaxies in close pairs are generally more asymmetric than isolated
galaxies and the degree of asymmetry increases for closer pairs. At least 35%
of close pairs (with projected separation of less than 20 h^{-1} kpc and
velocity difference of less than 500 km s^{-1}) show significant asymmetry and
are therefore likely to be physically bound.
(ii) Among asymmetric galaxies, we find that at least 80% are either
interacting systems or merger remnants. However, a significant fraction of
galaxies initially identified as asymmetric are contaminated by nearby stars or
are fragmented by the source extraction algorithm. Merger rates calculated via
asymmetry indices need careful attention in order to remove the above sources
of contamination, but are very reliable once this is carried out.
(iii) Close pairs and asymmetries represent two complementary methods of
measuring the merger rate. Galaxies in close pairs identify future mergers,
occurring within the dynamical friction timescale, while asymmetries are
sensitive to the immediate pre-merger phase and identify remnants.
(iv) The merger fraction derived via the close pair fraction and asymmetries
is about 2% for a merger rate of (5.2 +- 1.0) 10^{-4} h^3 Mpc^{-3} Gyr^{-1}.
These results are marginally consistent with theoretical simulations (depending
on the merger time-scale), but imply a flat evolution of the merger rate with
redshift up to z ~1.Comment: 10 pages, 10 figures, emulateapj format. ApJ, accepte
The Millennium Galaxy Catalogue: On the natural sub-division of galaxies
The distribution of global photometric, spectroscopic, structural and
morphological parameters for a well defined sample of 350 nearby galaxies has
been examined. The usual trends were recovered demonstrating that E/S0 galaxies
are redder, more quiescent, more centrally concentrated and possess larger
Sersic indices than later type galaxies.
Multivariate statistical analyses were performed to examine the distribution
of all parameters simultaneously. The main result of these analyses was the
existence of only two classes of galaxies, corresponding closely to early and
late types. Linear discriminant analysis was able to reproduce the
classifications of early and late types galaxies with high success, but further
refinement of galaxy types was not reproduced in the distribution of observed
galaxy properties. A principal components analysis showed that the major
variance of the parameter set corresponded to a distinction between early and
late types, highlighting the importance of the distinction. A hierarchical
clustering analysis revealed only two clear natural classes within the
parameter set, closely corresponding to early and late types. Early and late
types are clearly distinct and the distinction is of fundamental importance. In
contrast, late types from Sa to Irr are smoothly distributed throughout the
parameter space.
A population of galaxies classified by eye as elliptical/lenticular, and
exhibiting concentration indices similar to early-types were found to have a
significant star-formation activity. These galaxies are preferentially faint,
suggesting they are low-mass systems.Comment: Accepted for publication in MNRAS. 17 pages, 12 figure
The Millennium Galaxy Catalogue: morphological classification and bimodality in the colour-concentration plane
Using 10 095 galaxies (B < 20 mag) from the Millennium Galaxy Catalogue, we
derive B-band luminosity distributions and selected bivariate brightness
distributions for the galaxy population. All subdivisions extract highly
correlated sub-sets of the galaxy population which consistently point towards
two overlapping distributions. A clear bimodality in the observed distribution
is seen in both the rest-(u-r) colour and log(n) distributions. The rest-(u-r)
colour bimodality becomes more pronounced when using the core colour as opposed
to global colour. The two populations are extremely well separated in the
colour-log(n) plane. Using our sample of 3 314 (B < 19 mag) eyeball classified
galaxies, we show that the bulge-dominated, early-type galaxies populate one
peak and the bulge-less, late-type galaxies occupy the second. The early- and
mid-type spirals sprawl across and between the peaks. This constitutes
extremely strong evidence that the fundamental way to divide the luminous
galaxy population is into bulges and discs and that the galaxy bimodality
reflects the two component nature of galaxies and not two distinct galaxy
classes. We argue that these two-components require two independent formation
mechanisms/processes and advocate early bulge formation through initial
collapse and ongoing disc formation through splashback, infall and
merging/accretion. We calculate the B-band luminosity-densities and
stellar-mass densities within each subdivision and estimate that the z ~ 0
stellar mass content in spheroids, bulges and discs is 35 +/- 2 per cent, 18
+/- 7 and 47 +/- 7 per cent respectively. [Abridged]Comment: Accepted for publication in MNRAS, 23 pages, 17 figures. Comments
welcome. MGC website is at: http://www.eso.org/~jliske/mgc
Quantifying cosmic variance
We determine an expression for the cosmic variance of any "normal" galaxy
survey based on examination of M* +/- 1 mag galaxies in the SDSS DR7 data cube.
We find that cosmic variance will depend on a number of factors principally:
total survey volume, survey aspect ratio, and whether the area surveyed is
contiguous or comprised of independent sight-lines. As a rule of thumb cosmic
variance falls below 10% once a volume of 10^7h_0.7^-3Mpc^3 is surveyed for a
single contiguous region with a 1:1 aspect ratio. Cosmic variance will be lower
for higher aspect ratios and/or non-contiguous surveys. Extrapolating outside
our test region we infer that cosmic variance in the entire SDSS DR7 main
survey region is ~7% to z < 0.1. The equation obtained from the SDSS DR7 region
can be generalised to estimate the cosmic variance for any density measurement
determined from normal galaxies (e.g., luminosity densities, stellar mass
densities and cosmic star-formation rates) within the volume range 10^3 to 10^7
h^-3_0.7Mpc^3. We apply our equation to show that 2 sightlines are required to
ensure cosmic variance is <10% in any ASKAP galaxy survey (divided into dz ~0.1
intervals, i.e., ~1 Gyr intervals for z <0.5). Likewise 10 MeerKAT sightlines
will be required to meet the same conditions. GAMA, VVDS, and zCOSMOS all
suffer less than 10% cosmic variance (~3%-8%) in dz intervals of 0.1, 0.25, and
0.5 respectively. Finally we show that cosmic variance is potentially at the
50-70% level, or greater, in the HST Ultra Deep Field depending on assumptions
as to the evolution of clustering. 100 or 10 independent sightlines will be
required to reduce cosmic variance to a manageable level (<10%) for HST ACS or
HST WFC3 surveys respectively (in dz ~ 1 intervals). Cosmic variance is
therefore a significant factor in the z>6 HST studies currently underway.Comment: Accepted for publication in MNRA
The ugrizYJHK luminosity distributions and densities from the combined MGC, SDSS and UKIDSS LAS datasets
We combine data from the MGC, SDSS and UKIDSS LAS surveys to produce
ugrizYJHK luminosity functions and densities from within a common, low redshift
volume (z<0.1, ~71,000 h_1^-3 Mpc^3 for L* systems) with 100 per cent
spectroscopic completeness. In the optical the fitted Schechter functions are
comparable in shape to those previously reported values but with higher
normalisations (typically 0, 30, 20, 15, 5 per cent higher phi*-values in u, g,
r, i, z respectively over those reported by the SDSS team). We attribute these
to differences in the redshift ranges probed, incompleteness, and adopted
normalisation methods. In the NIR we find significantly different Schechter
function parameters (mainly in the M* values) to those previously reported and
attribute this to the improvement in the quality of the imaging data over
previous studies. This is the first homogeneous measurement of the
extragalactic luminosity density which fully samples both the optical and
near-IR regimes. Unlike previous compilations that have noted a discontinuity
between the optical and near-IR regimes our homogeneous dataset shows a smooth
cosmic spectral energy distribution (CSED). After correcting for dust
attenuation we compare our CSED to the expected values based on recent
constraints on the cosmic star-formation history and the initial mass function.Comment: 17 pages, 13 figures, Accepted in MNRAS: 2010 January 18; in original
form 2009 August 1
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