575 research outputs found
Galaxy And Mass Assembly (GAMA) blended spectra catalogue: strong galaxy-galaxy lens and occulting galaxy pair candidates
We present the catalogue of blended galaxy spectra from the Galaxy And Mass Assembly (GAMA) survey. These are cases where light from two galaxies are significantly detected in a single GAMA fibre. Galaxy pairs identified from their blended spectrum fall into two principal classes: they are either strong lenses, a passive galaxy lensing an emission-line galaxy; or occulting galaxies, serendipitous overlaps of two galaxies, of any type. Blended spectra can thus be used to reliably identify strong lenses for follow-up observations (high-resolution imaging) and occulting pairs, especially those that are a late-type partly obscuring an early-type galaxy which are of interest for the study of dust content of spiral and irregular galaxies. The GAMA survey setup and its AUTOZ automated redshift determination were used to identify candidate blended galaxy spectra from the cross-correlation peaks. We identify 280 blended spectra with a minimum velocity separation of 600 km s−1, of which 104 are lens pair candidates, 71 emission-line-passive pairs, 78 are pairs of emission-line galaxies and 27 are pairs of galaxies with passive spectra. We have visually inspected the candidates in the Sloan Digital Sky Survey (SDSS) and Kilo Degree Survey (KiDS) images. Many blended objects are ellipticals with blue fuzz (Ef in our classification). These latter ‘Ef’ classifications are candidates for possible strong lenses, massive ellipticals with an emission-line galaxy in one or more lensed images. The GAMA lens and occulting galaxy candidate samples are similar in size to those identified in the entire SDSS. This blended spectrum sample stands as a testament of the power of this highly complete, second-largest spectroscopic survey in existence and offers the possibility to expand e.g. strong gravitational lens surveys
Quantified Morphology of HI Disks in the Universe
he upcoming new perspective of the high redshift Universe in the 21 cm line
of atomic hydrogen opens possibilities to explore topics of spiral disk
evolution, hitherto reserved for the optical regime. The growth of spiral gas
disks over Cosmic time can be explored with the new generation of radio
telescopes, notably the SKA, and its precursors, as accurately as with the
Hubble Space Telescope for stellar disks. Since the atomic hydrogen gas is the
building block of these disks, it should trace their formation accurately.
Morphology of HI disks can now equally be quantified over Cosmic time. In
studies of HST deep fields, the optical or UV morphology of high-redshift
galaxy disks have been characterized using a few quantities: concentration (C),
asymmetry (A), smoothness (S), second-order-moment (M20), the GINI coefficient
(G), and Ellipticity (E). We have applied these parameters across wavelengths
and compared them to the HI morphology over the THINGS sample. NGC 3184, an
unperturbed disk, and NGC 5194, the canonical 3:1 interaction, serve as
examples for quantified morphology. We find that morphology parameters
determined in HI are as good or better a tracer of interaction compared to
those in any other wavelength, notably in Asymmetry, Gini and M20. This opens
the possibility of using them in the parameterization pipeline for SKA
precursor catalogues to select interacting or harassed galaxies from their HI
morphology. Asymmetry, Gini and M20 may be redefined for use on data-cubes
rather than HI column density image.Comment: 6 pages, 3 figures, proceeding of the conference "Panoramic Radio
Astronomy: Wide-field 1-2 GHz research on galaxy evolution", June 02 - 05
2009, Groningen, update after small edit
Quantified HI Morphology III: Merger Visibility Times from HI in Galaxy Simulations
Major mergers of disk galaxies are thought to be a substantial driver in
galaxy evolution. To trace the fraction and the rate galaxies are in mergers
over cosmic times, several observational techniques, including morphological
selection criteria, have been developed over the last decade. We apply this
morphological selection of mergers to 21 cm radio emission line (HI) column
density images of spiral galaxies in nearby surveys. In this paper, we
investigate how long a 1:1 merger is visible in HI from N-body simulations. We
evaluate the merger visibility times for selection criteria based on four
parameters: Concentration, Asymmetry, M20, and the Gini parameter of second
order moment of the flux distribution (GM). Of three selection criteria used in
the literature, one based on Concentration and M20 works well for the HI
perspective with a merger time scale of 0.4 Gyr. Of the three selection
criteria defined in our previous paper, the GM performs well and cleanly
selects mergers for 0.69 Gyr. The other two criteria (A-M20 and C-M20), select
isolated disks as well, but perform best for face-on, gas-rich disks (T(merger)
~ 1 Gyr). The different visibility scales can be combined with the selected
fractions of galaxies in any large HI survey to obtain merger rates in the
nearby Universe. All-sky surveys such as WALLABY with ASKAP and the Medium Deep
Survey with the APETIF instrument on Westerbork are set to revolutionize our
perspective on neutral hydrogen and will provide an accurate measure of the
merger fraction and rate of the present epoch.Comment: 12 pages, 6 figures, 4 tables, accepted by MNRAS, appendix not
include
Preventie en bestrijding van slakken
Veel biologische telers proberen grondbewerking tegenwoordig tot een minimum te beperken. Dit is goed voor de bodemstructuur en het bodemleven. Maar minimale grondbewerking lijkt schade door slakken juist te bevorderen. Ook de brede inzet van groenbemesters kan de slakkenpopulatie bevorderen. Dit kan leiden tot aanzienlijke schade als gevolg van verontreiniging en vraat. In dit biokennisbericht een aantal handreikingen om opbrengstderving door slakken te beperken
The dependence of intrinsic alignment of galaxies on wavelength using KiDS and GAMA
The outer regions of galaxies are more susceptible to the tidal interactions
that lead to intrinsic alignments of galaxies. The resulting alignment signal
may therefore depend on the passband if the colours of galaxies vary spatially.
To quantify this, we measured the shapes of galaxies with spectroscopic
redshifts from the GAMA survey using deep gri imaging data from the KiloDegree
Survey. The performance of the moment-based shape measurement algorithm DEIMOS
was assessed using dedicated image simulations, which showed that the
ellipticities could be determined with an accuracy better than 1% in all bands.
Additional tests for potential systematic errors did not reveal any issues. We
measure a significant difference of the alignment signal between the g,r and
i-band observations. This difference exceeds the amplitude of the linear
alignment model on scales below 2 Mpc/h. Separating the sample into
central/satellite and red/blue galaxies, we find that that the difference is
dominated by red satellite galaxies.Comment: 16 pages, 13 figures, accepted, to appear in A&
Quantified HI Morphology II : Lopsidedness and Interaction in WHISP Column Density Maps
Lopsidedness of the gaseous disk of spiral galaxies is a common phenomenon in
disk morphology, profile and kinematics. Simultaneously, the asymmetry of a
galaxy's stellar disk, in combination with other morphological parameters, has
seen extensive use as an indication of recent merger or interaction in galaxy
samples. Quantified morphology of stellar spiral disks is one avenue to
determine the merger rate over much of the age of the Universe. In this paper,
we measure the quantitative morphology parameters for the HI column density
maps from the Westerbork observations of neutral Hydrogen in Irregular and
SPiral galaxies (WHISP). These are Concentration, Asymmetry, Smoothness, Gini,
M20, and one addition of our own, the Gini parameter of the second order moment
(GM). Our aim is to determine if lopsided or interacting disks can be
identified with these parameters. Our sample of 141 HI maps have all previous
classifications on their lopsidedness and interaction. We find that the
Asymmetry, M20, and our new GM parameter correlate only weakly with the
previous morphological lopsidedness quantification. These three parameters may
be used to compute a probability that an HI disk is morphologically lopsided
but not unequivocally to determine it. However, we do find that that the
question whether or not an HI disk is interacting can be settled well using
morphological parameters. Parameter cuts from the literature do not translate
from ultraviolet to HI directly but new selection criteria using combinations
of Asymmetry and M20 or Concentration and M20, work very well. We suggest that
future all-sky HI surveys may use these parameters of the column density maps
to determine the merger fraction and hence rate in the local Universe with a
high degree of accuracy.Comment: 12 pages, 5 figures, 1 table, accepted by MNRAS, appendix not
include
Quantified HI Morphology I: Multi-Wavelengths Analysis of the THINGS Galaxies
Galaxy evolution is driven to a large extent by interactions and mergers with
other galaxies and the gas in galaxies is extremely sensitive to the
interactions. One method to measure such interactions uses the quantified
morphology of galaxy images. Well-established parameters are Concentration,
Asymmetry, Smoothness, Gini, and M20 of a galaxy image. Thus far, the
application of this technique has mostly been restricted to restframe
ultra-violet and optical images. However, with the new radio observatories
being commissioned (MeerKAT, ASKAP, EVLA, WSRT/APERTIF, and ultimately SKA), a
new window on the neutral atomic hydrogen gas (HI) morphology of a large
numbers of galaxies will open up. The quantified morphology of gas disks of
spirals can be an alternative indicator of the level and frequency of
interaction. The HI in galaxies is typically spatially more extended and more
sensitive to low-mass or weak interactions. In this paper, we explore six
morphological parameters calculated over the extent of the stellar (optical)
disk and the extent of the gas disk for a range of wavelengths spanning UV,
Optical, Near- and Far-Infrared and 21 cm (HI) of 28 galaxies from The HI
Nearby Galaxy Survey (THINGS). Though the THINGS sample is small and contains
only a single ongoing interaction, it spans both non-interacting and
post-interacting galaxies with a wealth of multi-wavelength data. We find that
the choice of area for the computation of the morphological parameters is less
of an issue than the wavelength at which they are measured. The signal of
interaction is as good in the HI as in any of the other wavelengths in which
morphology has been used to trace the interaction rate to date, mostly
star-formation dominated ones (near- and far-ultraviolet). The Asymmetry and
M20 parameters are the ones which show the most promise as tracers of
interaction in 21 cm line observations.Comment: 16 pages, 11 figure, table 1, accepted by MNRAS, appendix not
include
The dependence of the AV prior for SN Ia on host mass and disc inclination.
Type Ia supernovae (SNe Ia) are used as ‘standard candles’ for cosmological distance scales. To fit their light-curve shape–absolute luminosity relation, one needs to assume an intrinsic colour and a likelihood of host galaxy extinction or a convolution of these, a colour distribution prior. The host galaxy extinction prior is typically assumed to be an exponential drop-off for the current supernova programmes ( P(AV)∝e−AV/τ0 role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline-table; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3eP(AV)∝e−AV/τ0P(AV)∝e−AV/τ0
). We explore the validity of this prior using the distribution of extinction values inferred when two galaxies accidentally overlap (an occulting galaxy pair). We correct the supernova luminosity distances from the SDSS-III supernova projects (SDSS-SN) by matching the host galaxies to one of three templates from occulting galaxy pairs based on the host galaxy mass and the AV-bias–prior-scale (τ0) relation from Jha et al. We find that introducing an AV prior that depends on host mass results in lowered luminosity distances for the SDSS-SN on average but it does not reduce the scatter in individual measurements. This points, in our view, to the need for many more occulting galaxy templates to match to SN Ia host galaxies to rule out this possible source of scatter in the SN Ia distance measurements. We match occulting galaxy templates based on both mass and projected radius and we find that one should match by stellar mass first with radius as a secondary consideration. We discuss the caveats of the current approach: the lack of enough radial coverage, the small sample of priors (occulting pairs with HST data), the effect of gravitationally interacting as well as occulting pairs, and whether an exponential distribution is appropriate. Our aim is to convince the reader that a library of occulting galaxy pairs observed with HST will provide sufficient priors to improve (optical) SN Ia measurements to the next required accuracy in cosmology
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