226 research outputs found
Galaxy And Mass Assembly (GAMA) : refining the local galaxy merger rate using morphological information
KRVS acknowledges the Science and Technology Facilities Council (STFC) for providing funding for this project, as well as the Government of Catalonia for a research travel grant (ref. 2010 BE-00268) to begin this project at the University of Nottingham. PN acknowledges the support of the Royal Society through the award of a University Research Fellowship and the European Research Council, through receipt of a Starting Grant (DEGAS-259586).We use the Galaxy And Mass Assembly (GAMA) survey to measure the local Universe mass-dependent merger fraction and merger rate using galaxy pairs and the CAS (concentration, asymmetry, and smoothness) structural method, which identifies highly asymmetric merger candidate galaxies. Our goals are to determine which types of mergers produce highly asymmetrical galaxies and to provide a new measurement of the local galaxy major merger rate. We examine galaxy pairs at stellar mass limits down to M* = 108âMâ with mass ratios of 4:1) the lower mass companion becomes highly asymmetric, whereas the larger galaxy is much less affected. The fraction of highly asymmetric paired galaxies which have a major merger companion is highest for the most massive galaxies and drops progressively with decreasing mass. We calculate that the mass-dependent major merger fraction is fairly constant at âŒ1.3â2 perâcent within 109.5 < M* < 1011.5âMâ, and increases to âŒ4 perâcent at lower masses. When the observability time-scales are taken into consideration, the major merger rate is found to approximately triple over the mass range we consider. The total comoving volume major merger rate over the range 108.0 < M* < 1011.5âMâ is (1.2 ± 0.5) à 10â3 h370 Mpcâ3 Gyrâ1.Publisher PDFPeer reviewe
DustPedia: Multiwavelength photometry and imagery of 875 nearby galaxies in 42 ultraviolet-microwave bands
Aims. The DustPedia project is capitalising on the legacy of the Herschel Space Observatory, using cutting-edge modelling techniques to study dust in the 875 DustPedia galaxies â representing the vast majority of extended galaxies within 3000âkmâs-1 that were observed by Herschel. This work requires a database of multiwavelength imagery and photometry that greatly exceeds the scope (in terms of wavelength coverage and number of galaxies) of any previous local-Universe survey.
Methods. We constructed a database containing our own custom Herschel reductions, along with standardised archival observations from GALEX, SDSS, DSS, 2MASS, WISE, Spitzer, and Planck. Using these data, we performed consistent aperture-matched photometry, which we combined with external supplementary photometry from IRAS and Planck.
Results. We present our multiwavelength imagery and photometry across 42 UV-microwave bands for the 875 DustPedia galaxies. Our aperture-matched photometry, combined with the external supplementary photometry, represents a total of 21â857 photometric measurements. A typical DustPedia galaxy has multiwavelength photometry spanning 25 bands. We also present the Comprehensive & Adaptable Aperture Photometry Routine (CAAPR), the pipeline we developed to carry out our aperture-matched photometry. CAAPR is designed to produce consistent photometry for the enormous range of galaxy and observation types in our data. In particular, CAAPR is able to determine robust cross-compatible uncertainties, thanks to a novel method for reliably extrapolating the aperture noise for observations that cover a very limited amount of background. Our rich database of imagery and photometry is being made available to the community
From the cell membrane to the nucleus: unearthing transport mechanisms for Dynein
Mutations in the motor protein cytoplasmic dynein have been found to cause Charcot-Marie-Tooth disease, spinal muscular atrophy, and severe intellectual disabilities in humans. In mouse models, neurodegeneration is observed. We sought to develop a novel model which could incorporate the effects of mutations on distance travelled and velocity. A mechanical model for the dynein mediated transport of endosomes is derived from first principles and solved numerically. The effects of variations in model parameter values are analysed to find those that have a significant impact on velocity and distance travelled. The model successfully describes the processivity of dynein and matches qualitatively the velocity profiles observed in experiments
The evolution of quiescent galaxies at high redshift (z > 1.4)
We have studied the evolution of high redshift quiescent galaxies over an
effective area of ~1.7 deg^2 in the COSMOS field. Galaxies have been divided
according to their star-formation activity and the evolution of the different
populations has been investigated in detail. We have studied an IRAC (mag_3.6 <
22.0) selected sample of ~18000 galaxies at z > 1.4 with multi-wavelength
coverage. We have derived accurate photometric redshifts (sigma=0.06) and other
important physical parameters through a SED-fitting procedure. We have divided
our sample into actively star-forming, intermediate and quiescent galaxies
depending on their specific star formation rate. We have computed the galaxy
stellar mass function of the total sample and the different populations at
z=1.4-3.0. We have studied the properties of high redshift quiescent galaxies
finding that they are old (1-4 Gyr), massive (log(M/M_sun)~10.65), weakly star
forming stellar populations with low dust extinction (E(B-V) < 0.15) and small
e-folding time scales (tau ~ 0.1-0.3 Gyr). We observe a significant evolution
of the quiescent stellar mass function from 2.5 < z < 3.0 to 1.4 < z < 1.6,
increasing by ~ 1 dex in this redshift interval. We find that z ~ 1.5 is an
epoch of transition of the GSMF. The fraction of star-forming galaxies
decreases from 60% to 20% from z ~ 2.5-3.0 to z ~ 1.4-1.6 for log(M/M_sun) >
11, while the quiescent population increases from 10% to 50% at the same
redshift and mass intervals. We compare the fraction of quiescent galaxies
derived with that predicted by theoretical models and find that the Kitzbichler
& White (2007) model is the one that better reproduces the data. Finally, we
calculate the stellar mass density of the star-forming and quiescent
populations finding that there is already a significant number of quiescent
galaxies at z > 2.5 (rho~6.0 MsunMpc^-3).Comment: 17 pages, 20 figures, 5 tables. Accepted for publication in MNRA
The bimodality of the 10k zCOSMOS-bright galaxies up to z ~ 1: a new statistical and portable classification based on the optical galaxy properties
Our goal is to develop a new and reliable statistical method to classify
galaxies from large surveys. We probe the reliability of the method by
comparing it with a three-dimensional classification cube, using the same set
of spectral, photometric and morphological parameters.We applied two different
methods of classification to a sample of galaxies extracted from the zCOSMOS
redshift survey, in the redshift range 0.5 < z < 1.3. The first method is the
combination of three independent classification schemes, while the second
method exploits an entirely new approach based on statistical analyses like
Principal Component Analysis (PCA) and Unsupervised Fuzzy Partition (UFP)
clustering method. The PCA+UFP method has been applied also to a lower redshift
sample (z < 0.5), exploiting the same set of data but the spectral ones,
replaced by the equivalent width of H. The comparison between the two
methods shows fairly good agreement on the definition on the two main clusters,
the early-type and the late-type galaxies ones. Our PCA-UFP method of
classification is robust, flexible and capable of identifying the two main
populations of galaxies as well as the intermediate population. The
intermediate galaxy population shows many of the properties of the green valley
galaxies, and constitutes a more coherent and homogeneous population. The
fairly large redshift range of the studied sample allows us to behold the
downsizing effect: galaxies with masses of the order of Msun
mainly are found in transition from the late type to the early type group at
, while galaxies with lower masses - of the order of Msun -
are in transition at later epochs; galaxies with Msun did not
begin their transition yet, while galaxies with very large masses ( Msun) mostly completed their transition before .Comment: 16 pages, 14 figures, accepted for publication in A&
Galaxy and mass assembly (GAMA): refining the local galaxy merger rate using morphological information
We use the Galaxy And Mass Assembly (GAMA) survey to measure the local Universe mass dependent merger fraction and merger rate using galaxy pairs and the CAS structural method, which identifies highly asymmetric merger candidate galaxies. Our goals are to determine which types of mergers produce highly asymmetrical galaxies, and to provide a new measurement of the local galaxy major merger rate. We examine galaxy pairs at stellar mass limits down to with mass ratios of 4:1) the lower mass companion becomes highly asymmetric, while the larger galaxy is much less affected. The fraction of highly asymmetric paired galaxies which have a major merger companion is highest for the most massive galaxies and drops progressively with decreasing mass. We calculate that the mass dependent major merger fraction is fairly constant at between , and increases to at lower masses. When the observability time scales are taken into consideration, the major merger rate is found to approximately triple over the mass range we consider. The total co-moving volume major merger rate over the range is Mpc Gyr
The SWIRE-VVDS-CFHTLS surveys: stellar mass assembly over the last 10 Gyears. Evidence for a major build up of the red sequence between z=2 and z=1
(abridged abstract) We present an analysis of the stellar mass growth over
the last 10 Gyrs using a large 3.6 selected sample. We split our sample
into active (blue) and quiescent (red) galaxies. Our measurements of the K-LFs
and LD evolution support the idea that a large fraction of galaxies is already
assembled at . Based on the analysis of the evolution of the stellar
mass-to-light ratio (in K-band) for the spectroscopic sub-sample, we derive the
stellar mass density for the entire sample. We find that the global evolution
of the stellar mass density is well reproduced by the star formation rate
derived from UV dust corrected measurements. Over the last 8Gyrs, we observe
that the stellar mass density of the active population remains approximately
constant while it gradually increases for the quiescent population over the
same timescale. As a consequence, the growth of the stellar mass in the
quiescent population must be due to the shutoff of star formation in active
galaxies that migrate into the quiescent population. From to , we
observe a major build-up of the quiescent population with an increase by a
factor of 10 in stellar mass, suggesting that we are observing the epoch when
an increasing fraction of galaxies are ending their star formation activity and
start to build up the red sequence.Comment: Accepted to A&A with major changes. 1 table and 13 figure
Do Employment Quotas Explain the Occupational Choices of Disadvantaged Minorities in India?
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
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