| 1. |
- Alatalo, K., et al.
(författare)
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Evidence of boosted 13CO/12CO ratio in early-type galaxies in dense environments
- 2015
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 450:4, s. 3874-3885
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Tidskriftsartikel (refereegranskat)abstract
- We present observations of 13CO(1-0) in 17 Combined Array for Research in Millimeter Astronomy ATLAS3D early-type galaxies (ETGs), obtained simultaneously with 12CO(1-0) observations. The 13CO in six ETGs is sufficiently bright to create images. In these six sources, we do not detect any significant radial gradient in the 13CO/12CO ratio between the nucleus and the outlying molecular gas. Using the 12CO channel maps as 3D masks to stack the 13CO emission, we are able to detect 15/17 galaxies to >3σ (and 12/17 to at least 5σ) significance in a spatially integrated manner. Overall, ETGs show a wide distribution of 13CO/12CO ratios, but Virgo cluster and group galaxies preferentially show a 13CO/12CO ratio about two times larger than field galaxies, although this could also be due to a mass dependence, or the CO spatial extent (RCO/Re). ETGs whose gas has a morphologically settled appearance also show boosted 13CO/12CO ratios. We hypothesize that this variation could be caused by (i) the extra enrichment of gas from molecular reprocessing occurring in low-mass stars (boosting the abundance of 13C to 12C in the absence of external gas accretion), (ii) much higher pressure being exerted on the mid-plane gas (by the intracluster medium) in the cluster environment than in isolated galaxies, or (iii) all but the densest molecular gas clumps being stripped as the galaxies fall into the cluster. Further observations of 13CO in dense environments, particularly of spirals, as well as studies of other isotopologues, should be able to distinguish between these hypotheses.
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| 2. |
- Kaiser, Eurika, et al.
(författare)
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Cluster-based reduced-order modelling of a mixing layer
- 2014
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 754, s. 365-414
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Tidskriftsartikel (refereegranskat)abstract
- We propose a novel cluster-based reduced-order modelling (CROM) strategy for unsteady flows. CROM combines the cluster analysis pioneered in Gunzburger’s group (Burkardt, Gunzburger & Lee, Comput. Meth. Appl. Mech. Engng, vol. 196, 2006a, pp. 337–355) and transition matrix models introduced in fluid dynamics in Eckhardt’s group (Schneider, Eckhardt & Vollmer, Phys. Rev. E, vol. 75, 2007, art. 066313). CROM constitutes a potential alternative to POD models and generalises the Ulam–Galerkin method classically used in dynamical systems to determine a finite-rank approximation of the Perron–Frobenius operator. The proposed strategy processes a time-resolved sequence of flow snapshots in two steps. First, the snapshot data are clustered into a small number of representative states, called centroids, in the state space. These centroids partition the state space in complementary non-overlapping regions (centroidal Voronoi cells). Departing from the standard algorithm, the probabilities of the clusters are determined, and the states are sorted by analysis of the transition matrix. Second, the transitions between the states are dynamically modelled using a Markov process. Physical mechanisms are then distilled by a refined analysis of the Markov process, e.g. using finite-time Lyapunov exponent (FTLE) and entropic methods. This CROM framework is applied to the Lorenz attractor (as illustrative example), to velocity fields of the spatially evolving incompressible mixing layer and the three-dimensional turbulent wake of a bluff body. For these examples, CROM is shown to identify non-trivial quasi-attractors and transition processes in an unsupervised manner. CROM has numerous potential applications for the systematic identification of physical mechanisms of complex dynamics, for comparison of flow evolution models, for the identification of precursors to desirable and undesirable events, and for flow control applications exploiting nonlinear actuation dynamics.
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| 3. |
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| 4. |
- Obara, K., et al.
(författare)
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Large eddy simulation of a tornado flow around a train
- 2019
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Ingår i: ERCOFTAC Series. - Cham : Springer International Publishing. - 1382-4309 .- 2215-1826. ; 25, s. 587-593
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- A tornado is a destructive rotating column of air extending from a cloud to the ground. It may kill people and damage property. Also there are possibilities of derailment of trains. Some train-turnover accidents are suspected to have been caused by tornadoes in Japan. For instance, a train of the JR Uestu line was overturned by a gust in 2005. According to the accident analysis, a tornado or downburst probably generated the gust (Aircraft and railway accidents investigation commission: Railway accident analysis report RA2008 -4 (2008), (in Japanese), [1]). In 2006, a train of the JR Nippo line was overturned by a tornado (Aircraft and railway accidents investigation commission: Railway accident analysis report RA2008 -6 (2008), (in Japanese), [2]).
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| 5. |
- Schmidt, K. B., et al.
(författare)
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Three-Dimensional Optimal Spectral Extraction (TDOSE) from integral field spectroscopy
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 628
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Tidskriftsartikel (refereegranskat)abstract
- The amount of integral field spectrograph (IFS) data has grown considerably over the last few decades. The demand for tools to analyze such data is therefore bigger now than ever. We present a flexible Python tool for Three-Dimensional Optimal Spectral Extraction (TDOSE) from IFS data cubes. TDOSE works on any three-dimensional data cube and bases the spectral extractions on morphological reference image models. By default, these models are generated and composed of multiple multivariate Gaussian components, but can also be constructed with independent modeling tools and be provided as input to TDOSE. In each wavelength layer of the IFS data cube, TDOSE simultaneously optimizes all sources in the morphological model to minimize the difference between the scaled model components and the IFS data. The flux optimization produces individual data cubes containing the scaled three-dimensional source models. This allows the efficient de-blending of flux in both the spatial and spectral dimensions of the IFS data cubes, and extraction of the corresponding one-dimensional spectra. TDOSE implicitly requires an assumption about the two-dimensional light distribution. We describe how the flexibility of TDOSE can be used to mitigate and correct for deviations from the input distribution. Furthermore, we present an example of how the three-dimensional source models generated by TDOSE can be used to improve two-dimensional maps of physical parameters like velocity, metallicity, or star formation rate when flux contamination is a problem. By extracting TDOSE spectra of similar to 150 [OII] emitters from the MUSE-Wide survey we show that the median increase in line flux is similar to 5% when using multi-component models as opposed to single-component models. However, the increase in recovered line emission in individual cases can be as much as 50%. Comparing the TDOSE model-based extractions of the MUSE-Wide [OII] emitters with aperture spectra, the TDOSE spectra provides a median flux (S/N) increase of 9% (14%). Hence, TDOSE spectra optimize the S/N while still being able to recover the total emitted flux.
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| 6. |
- Urrutia, T., et al.
(författare)
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The MUSE-Wide Survey : survey description and first data release
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 624
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Tidskriftsartikel (refereegranskat)abstract
- We present the MUSE-Wide survey, a blind, 3D spectroscopic survey in the CANDELS/GOODS-S and CANDELS/COSMOS regions. The final survey will cover 100 x 1 arcmin(2) MUSE fields. Each MUSE-Wide pointing has a depth of one hour and hence targets more extreme and more luminous objects over ten times the area of the MUSE-Deep fields. The legacy value of MUSE-Wide lies in providing spectroscopy of everything without photometric pre-selection. We describe the data reduction, post-processing and PSF characterization of the first 44 CANDELS /GOODS-S MUSE-Wide pointings released with this publication. Using a 3D matched filtering approach we detect 1602 emission line sources, including 479 Lyman-alpha (Ly alpha) emitting galaxies with redshifts 2.9 less than or similar to z less than or similar to 6.3. We cross-matched the emission line sources to existing photometric catalogs, finding almost complete agreement in redshifts (photometric and spectroscopic) and stellar masses for our low redshift (z < 1.5) emitters. At high redshift, we only find similar to 55% matches to photometric catalogs. We encounter a higher outlier rate and a systematic offset of Delta z similar or equal to 0.2 when comparing our MUSE redshifts with photometric redshifts from the literature. Cross-matching the emission line sources with X-ray catalogs from the Chandra Deep Field South, we find 127 matches, mostly in agreement with the literature redshifts, including ten objects with no prior spectroscopic identification. Stacking X-ray images centered on our Ly alpha emitters yields no signal; the Ly alpha population is not dominated by even low luminosity AGN. Other cross-matches of our emission-line catalog to radio and submillimeter data, yielded far lower numbers of matches, most of which already were covered by the X-ray catalog. A total of 9205 photometrically selected objects from the CANDELS survey lie in the MUSE-Wide footprint, of which we provide optimally extracted 1D spectra. We are able to determine the spectroscopic redshift of 98% of 772 photometrically selected galaxies brighter than 24th F775W magnitude. All the data in the first data release - datacubes, catalogs, extracted spectra, maps - are available on the MUSE-Wide data release webpage.
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