124 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
The Millennium Galaxy Catalogue: Star counts and the Structure of the Galactic Stellar Halo
We derive a star catalogue generated from the images taken as part of the
37.5 sq. deg Millennium Galaxy Catalogue. These data, alone and together with
colours gained from the Sloan Digital Sky Survey Early Data Release, allow the
analysis of faint star counts (B(MGC) < 20) at high Galactic latitude (41 < b <
63), as a function of Galactic longitude (239 < l < 353). We focus here on the
inner stellar halo, providing robust limits on the amplitude of substructure
and on the large-scale flattening. In line with previous results, the thick
disk, an old, intermediate-metallicity population, is clearly seen in the
colour-magnitude diagram. We find that the Galactic stellar halo within ~10 kpc
(the bulk of the stellar mass) is significantly flattened, with an axial ratio
of (c/a) =0.56 +/- 0.01, again consistent with previous results. Our analysis
using counts-in-cells, angular correlation functions and the Lee 2D statistic,
confirms tidal debris from the Sagittarius dwarf but finds little evidence for
other substructure in the inner halo, at heliocentric distances of < 5 kpc.
This new quantification of the smoothness in coordinate space limits the
contribution of recent accretion/disruption to the build-up of the bulk of the
stellar halo.Comment: Accepted for publication in MNRAS (figs 16 and 17 degraded here
Detection of gravitational waves in circular particle accelerators II. Response analysis and parameter estimation using synthetic data
We simulate the response of a Storage Ring Gravitational-wave Observatory
(SRGO) to astrophysical gravitational waves (GWs), numerically obtaining its
sensitivity curve, parameter degeneracies, and optimal choices of some
controllable experiment parameters. We also generate synthetic noisy GW data
and use Markov Chain Monte Carlo (MCMC) methods to perform parameter estimation
of the source properties. With this, we show that a single SRGO could
potentially localize the GW source in the sky using Earth's rotation. Then, we
study the source sky localization area, mass and distance estimation errors as
functions of noise, data sampling rate, and observing time. Finally, we
discuss, along with its implications, the capacity of an SRGO to detect and
constrain the parameters of millihertz (mHz) GW events.Comment: This manuscript is the sequel to Phys. Rev. D 102, 122006 (2020) or
arXiv:2012.00529. This manuscript will be submitted for review and
publication to Physical Review D (PRD). 21 pages, 10 figure
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
Forecasting cosmic acceleration measurements using the Lyman- forest
We present results from end-to-end simulations of observations designed to
constrain the rate of change in the expansion history of the Universe using the
redshift drift of the Lyman- forest absorption lines along the
lines-of-sight toward bright quasars. For our simulations we take
Lyman- forest lines extracted from Keck/HIRES spectra of bright quasars
at , and compare the results from these real quasar spectra with mock
spectra generated via Monte Carlo realizations. We use the results of these
simulations to assess the potential for a dedicated observatory to detect
redshift drift, and quantify the telescope and spectrograph requirements for
these observations. Relative to Liske et al. (2008), two main refinements in
the current work are inclusion of quasars from more recent catalogs and
consideration of a realistic observing strategy for a dedicated redshift drift
experiment that maximizes . We find that using a
dedicated facility and our designed observing plan, the redshift drift can be
detected at significance in 15 years with a 25m telescope, given a
spectrograph with long term stability with and 25% total system
efficiency. To achieve this significance, the optimal number of targets is four
quasars, with observing time weighted based upon and
object visibility. This optimized strategy leads to a 9% decrease in the
telescope diameter or a 6% decrease in the required time to achieve the same
S/N as for the idealized case of uniformly distributing time to the same
quasars.Comment: 13 pages, 12 figures, accepted for publication in MNRA
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
The Millennium Galaxy Catalogue: Dynamically Close Galaxy Pairs and the Global Merger Rate
We derive the number of dynamically close companions per galaxy () and
their total luminosity () for galaxies in the Millennium Galaxy Catalogue:
is similar to the fraction of galaxies in close pairs and is directly
related to the galaxy merger rate. We find and
for galaxies with and , for galaxies with , with
. The integrated merger rate to for both samples is about 20
%, but this depends sensitively on the fraction of kinematic pairs that are
truly undergoing a merger (assumed here to be 50%), the evolution of the merger
rate (here as ) and the adopted timescale for mergers (0.2 and 0.5 Gyr
for each sample, respectively). Galaxies involved in mergers tend to be
marginally bluer than non-interacting galaxies and show an excess of both
early-type and very late-type objects and a deficiency of intermediate-type
spirals. This suggests that interactions and mergers partly drive the star
formation and morphological evolution of galaxies.Comment: 26 pages, 3 figures, AJ accepted for publicatio
Astro2020 Project White Paper: The Cosmic Accelerometer
We propose an experiment, the Cosmic Accelerometer, designed to yield
velocity precision of cm/s with measurement stability over years to
decades. The first-phase Cosmic Accelerometer, which is at the scale of the
Astro2020 Small programs, will be ideal for precision radial velocity
measurements of terrestrial exoplanets in the Habitable Zone of Sun-like stars.
At the same time, this experiment will serve as the technical pathfinder and
facility core for a second-phase larger facility at the Medium scale, which can
provide a significant detection of cosmological redshift drift on a 6-year
timescale. This larger facility will naturally provide further detection/study
of Earth twin planet systems as part of its external calibration process. This
experiment is fundamentally enabled by a novel low-cost telescope technology
called PolyOculus, which harnesses recent advances in commercial off the shelf
equipment (telescopes, CCD cameras, and control computers) combined with a
novel optical architecture to produce telescope collecting areas equivalent to
standard telescopes with large mirror diameters. Combining a PolyOculus array
with an actively-stabilized high-precision radial velocity spectrograph
provides a unique facility with novel calibration features to achieve the
performance requirements for the Cosmic Accelerometer
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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