147 research outputs found
Simulating non-axisymmetric flows in disc galaxies
We present a two-step method to simulate and study non-circular motions in
strongly barred galaxies. The first step is to constrain the initial parameters
using a Bayesian analysis of each galaxy's azimuthally averaged rotation curve,
the 3.6 surface brightness, and the gas surface density. The second
step is to generate equilibrium models using the GalactICS code and evolve them
via GADGET-2. The bar strengths and mock velocity maps of the resulting
snapshots are compared to observations in order to determine the best
representation of the galaxy. We test our method on the unbarred galaxy NGC
3621 and the barred galaxies NGC 1300 and NGC 1530. NGC 3621 provides a
validation of our method of generating initial conditions. NGC 1530 has an
intermediate bar orientation that allows for a comparison to DiskFit. Finally
NGC 1300 has a bar oriented parallel to the galaxy's major axis, where other
algorithms tend to fail. Our models for NGC 3621 and NGC 1530 are comparable to
those obtained using commonly available algorithms. Moreover, we have produced
one of the first mass distribution models for NGC 1300.Comment: 19 pages, 15 figures, 5 tables, accepted for publication in A&
Measuring Galaxy Asymmetries in 3D
One of the commonly used non-parametric morphometric statistics for galaxy
profiles and images is the asymmetry statistic. With an eye to current and
upcoming large neutral hydrogen (HI) surveys, we develop a 3D version of the
asymmetry statistic that can be applied to datacubes. This statistic is more
resilient to variations due to the observed geometry than 1D asymmetry
measures, and can be successfully applied to lower spatial resolutions (3-4
beams across the galaxy major axis) than the 2D statistic. We have also
modified the asymmetry definition from an `absolute difference' version to a
`squared difference' version that removes much of the bias due to noise
contributions for low signal-to-noise observations. Using a suite of mock
asymmetric cubes we show that the background-corrected, squared difference 3D
asymmetry statistic can be applied to many marginally resolved galaxies in
large wide-area HI surveys such as WALLABY on the Australian SKA Pathfinder
(ASKAP).Comment: 14 pages, Accepted to MNRA
ASymba: HI global profile asymmetries in the Simba simulation
Asymmetry in the spatially integrated, 1D HI global profiles of galaxies can
inform us on both internal (e.g. outflows) and external (e.g. mergers, tidal
interactions, ram pressure stripping) processes that shape galaxy evolution.
Understanding which of these primarily drive HI profile asymmetry is of
particular interest. In the lead-up to SKA pathfinder and SKA HI emission
surveys, hydrodynamical simulations have proved to be a useful resource for
such studies. Here we present the methodology behind, as well as first results,
of ASymba: Asymmetries in HI of Simba galaxies, the first time this simulation
suite has been used for this type of study. We generate mock observations of
the HI content of these galaxies and calculate the profile asymmetries using
three different methods. We find that has the strongest
correlation with all asymmetry measures, with weaker correlations also found
with the number of mergers a galaxy has undergone, and gas and galaxy rotation.
We also find good agreement with the xGASS sample, in that galaxies with highly
asymmetric profiles tend to have lower HI gas fractions than galaxies with
symmetric profiles, and additionally find the same holds in sSFR parameter
space. For low HI mass galaxies, it is difficult to distinguish between
asymmetric and symmetric galaxies, but this becomes achievable in the high HI
mass population. These results showcase the potential of ASymba and provide the
groundwork for further studies, including comparison to upcoming large HI
emission surveys.Comment: 17 pages, 10 figures, 2 tables. Accepted in MNRA
Involvement of microbial mats in early fossilization by decay delay and formation of impressions and replicas of vertebrates and invertebrates
Microbial mats have been hypothesized to improve the persistence and the preservation of organic remains during fossilization processes. We test this hypothesis with long-term experiments (up to 5.5âyears) using invertebrate and vertebrate corpses.Once placed on mats,the microbial community coats the corpses and forms a three-dimensional sarcophagus composed of microbial cells and exopolymeric substances (EPS). This coverage provides a template for i) moulding superficial features, resulting in negative impressions, and ii) generating replicas.The impressions of fly setulae, fish scales and frog skin verrucae are shaped mainly by small cells in an EPS matrix. Microbes also replicate delicate structures such as the three successive layers that compose a fish eye.The sarcophagus protects the body integrity, allowing the persistence of inner organs such as the ovaries and digestive apparatus in flies,the swim bladder and muscles in fish, and the bone marrow in frog legs.This study brings strong experimental evidence to the idea that mats favour metazoan fossilization by moulding, replicating and delaying decay. Rapid burial has classically been invoked as a mechanism to explain exceptional preservation. However, mats may play a similar role during early fossilization as they can preserve complex features for a long timeThis work, which is part of the research projects CGL2013-42643P and the research grant supporting M. Iniesto were funded by the Spanish Ministry of Economy and Competitiveness. The SEM facility at IMPMC was supported by Region Ile de France grant SESAME 2006 I-07-593/R, INSU-CNRS, INP-CNRS, and University Pierre et Marie Curie, Paris. SEM analyses performed for this study were supported by a grant from the Foundation Simone et Cino Del Duca (PI: K. Benzerara). Some SEM observations were also conducted at SIdI UAM (Madrid). Environmental SEM observations were performed at the MNCN (Madrid
WALLABY Pilot Survey: Hydra Cluster Galaxies UV and HI morphometrics
Galaxy morphology in atomic hydrogen (HI) and in the ultra-violet (UV) are
closely linked. This has motivated their combined use to quantify morphology
over the full H i disk for both H i and UV imaging. We apply galaxy
morphometrics: Concentration, Asymmetry, Gini, M20 and
Multimode-Intensity-Deviation statistics to the first moment-0 maps of the
WALLABY survey of galaxies in the Hydra cluster center. Taking advantage of
this new HI survey, we apply the same morphometrics over the full HI extent on
archival GALEX FUV and NUV data to explore how well HI truncated, extended
ultraviolet disk (XUV) and other morphological phenomena can be captured using
pipeline WALLABY data products. Extended HI and UV disks can be identified
relatively straightforward from their respective concentration. Combined with
WALLABY HI, even the shallowest GALEX data is sufficient to identify XUV disks.
Our second goal is to isolate galaxies undergoing ram-pressure stripping in the
H i morphometric space. We employ four different machine learning techniques, a
decision tree, a k-nearest neighbour, a support-vector machine, and a random
forest. Up to 80% precision and recall are possible with the Random Forest
giving the most robust results.Comment: 17 figures, 12 figures, 7 tables, accepted by MNRA
WALLABY Pilot Survey: the Potential Polar Ring Galaxies NGC~4632 and NGC~6156
We report on the discovery of two potential polar ring galaxies (PRGs) in the
WALLABY Pilot Data Release 1 (PDR1). These untargetted detections,
cross-matched to NGC 4632 and NGC 6156, are some of the first galaxies where
the Hi observations show two distinct components. We used the iDaVIE virtual
reality software to separate the anomalous gas from the galactic gas and find
that the anomalous gas comprises ~ 50% of the total H i content of both
systems. We have generated plausible 3D kinematic models for each galaxy
assuming that the rings are circular and inclined at 90 degrees to the galaxy
bodies. These models show that the data are consistent with PRGs, but do not
definitively prove that the galaxies are PRGs. By projecting these models at
different combinations of main disk inclinations, ring orientations, and
angular resolutions in mock datacubes, we have further investigated the
detectability of similar PRGs in WALLABY. Assuming that these galaxies are
indeed PRGs, the detectability fraction, combined with the size distribution of
WALLABY PDR1 galaxies, implies an incidence rate of ~ 1% - 3%. If this rate
holds true, the WALLABY survey will detect hundreds of new polar ring galaxies.Comment: Accepted to MNRAS -- Corrected Table
WALLABY Pilot Survey: HI in the host galaxy of a Fast Radio Burst
We report on the commensal ASKAP detection of a fast radio burst (FRB),
FRB20211127I, and the detection of neutral hydrogen (HI) emission in the FRB
host galaxy, WALLABYJ131913-185018 (hereafter W13-18). This collaboration
between the CRAFT and WALLABY survey teams marks the fifth, and most distant,
FRB host galaxy detected in HI, not including the Milky Way. We find that
W13-18 has a HI mass of = 6.5 10 M, a
HI-to-stellar mass ratio of 2.17, and coincides with a continuum radio source
of flux density at 1.4 GHz of 1.3 mJy. The HI global spectrum of W13-18 appears
to be asymmetric, albeit the HI observation has a low S/N, and the galaxy
itself appears modestly undisturbed. These properties are compared to the early
literature of HI emission detected in other FRB hosts to date, where either the
HI global spectra were strongly asymmetric, or there were clearly disrupted HI
intensity map distributions. W13-18 lacks sufficient S/N to determine whether
it is significantly less asymmetric in its HI distribution than previous
examples of FRB host galaxies. However, there are no strong signs of a major
interaction in the HI or optical image of the host galaxy that would stimulate
a burst of star formation and hence the production of putative FRB progenitors
related to massive stars and their compact remnants.Comment: 13 pages, 5 figures. Published in Ap
STREGA: STRucture and Evolution of the GAlaxy - I : Survey overview and first results
STREGA (STRucture and Evolution of the GAlaxy) is a guaranteed time survey being performed at the VST (the ESO Very Large Telescope Survey Telescope) to map about 150 square degrees in the Galactic halo, in order to constrain the mechanisms of galactic formation and evolution. The survey is built as a 5 yr project, organized in two parts: a core programme to explore the surrounding regions of selected stellar systems and a second complementary part to map the southern portion of the Fornax orbit and extend the observations of the core programme. The adopted stellar tracers are mainly variable stars (RR Lyraes and long-period variables) and main-sequence turn-off stars for which observations in the g, r, i bands are obtained. We present an overview of the survey and some preliminary results for three observing runs that have been completed. For the region centred on Ï Cen (37 deg^2), covering about three tidal radii, we also discuss the detected stellar density radial profile and angular distribution, leading to the identification of extratidal cluster stars. We also conclude that the cluster tidal radius is about 1.2 deg, in agreement with values in the literature based on the Wilson model.Peer reviewedFinal Accepted Versio
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