| 1. |
-
The Seventeenth Data Release of the Sloan Digital Sky Surveys : Complete Release of MaNGA, MaStar, and APOGEE-2 Data
- 2022
-
Ingår i: Astrophysical Journal Supplement Series. - : Institute of Physics (IOP). - 0067-0049 .- 1538-4365. ; 259:2
-
Tidskriftsartikel (refereegranskat)abstract
- This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 survey that publicly releases infrared spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the subsurvey Time Domain Spectroscopic Survey data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey subsurvey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated value-added catalogs. This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper, Local Volume Mapper, and Black Hole Mapper surveys.
|
|
| 2. |
- Chamba, Nushkia, et al.
(författare)
-
How to plan your astronomy research paper in ten steps
- 2022
-
Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 6:9, s. 1015-1020
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Scientific writing is an important skill for a career as a professional astrophysicist. However, very few researchers receive any formal training in how to write scientific research papers of high quality in an efficient manner. This Perspective is the first of a two-part self-help guide to scientific writing to address this skills gap. This part focusses on planning your academic research paper in astronomy. We discuss how to crystallize the ideas that underlie a research project, analyse how the paper can be constructed considering the audience and the chosen journal, and give an overview of the publishing process. Whether you are a student writing your first paper or an experienced author, you may find the ideas presented here useful.
|
|
| 3. |
- Chamba, Nushkia, et al.
(författare)
-
The edges of galaxies : Tracing the limits of star formation
- 2022
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 667
-
Tidskriftsartikel (refereegranskat)abstract
- The outskirts of galaxies have been studied from multiple perspectives for the past few decades. However, it is still unknown if all galaxies have clear-cut edges similar to everyday objects. We address this question by developing physically motivated criteria to define the edges of galaxies. Based on the gas density threshold required for star formation, we define the edge of a galaxy as the outermost radial location associated with a significant drop in either past or ongoing in situ star formation. We explore ∼1000 low-inclination galaxies with a wide range in morphology (dwarfs to ellipticals) and stellar mass (107 M⊙ < M⋆ < 1012 M⊙). The location of the edges of these galaxies (Redge) were visually identified as the outermost cutoff or truncation in their radial profiles using deep multi-band optical imaging from the IAC Stripe82 Legacy Project. We find this characteristic feature at the following mean stellar mass density, which varies with galaxy morphology: 2.9 ± 0.10 M⊙ pc−2 for ellipticals, 1.1 ± 0.04 M⊙ pc−2 for spirals, and 0.6 ± 0.03 M⊙ pc−2 for present-day star-forming dwarfs. Additionally, we find that Redge depends on its age (colour) where bluer galaxies have larger Redge at a fixed stellar mass. The resulting stellar mass–size plane using Redge as a physically motivated galaxy size measure has a very narrow intrinsic scatter (≲0.06 dex). These results highlight the importance of new deep imaging surveys to explore the growth of galaxies and trace the limits of star formation in their outskirts.
|
|
| 4. |
- Fathi, Kambiz, et al.
(författare)
-
Evolution of structure in late-type spiral galaxies. I : Ionized gas kinematics in NGC 628
- 2007
-
Ingår i: Astronomy and Astrophysics. ; 466:905
-
Tidskriftsartikel (refereegranskat)abstract
- Aims.We study two dimensional Fabry-Perot interferometric observations of the nearby face-on late-type spiral galaxy, NGC 628, in order to analyse the ionized gas component of the interstellar medium. Covering the galaxy out to a radius larger than 12 kpc, and with a spatial sampling of 1.6'', we aim to investigate the large-scale dynamics as well as feedback from individual H ii regions into their surrounding medium. Methods: The observed Hα emission distribution and kinematics are compared with auxiliary data from molecular and atomic gas observations, which display many similarities. We decompose the observed line-of-sight velocities into rotational and higher-order harmonic components, and study the role of gravitational perturbations along with that of external triggers which can disturb the kinematics and morphology of NGC 628. We calculate radial profiles of the emission-line velocity dispersion which we use to study the role of feedback from individual H ii regions. Results: We verify the presence of an inner rapidly rotating disc-like component in NGC 628, which we interpret as caused by slow secular evolution of the large-scale spiral arms and oval structure. In combination with auxiliary data, we find indication for that gas is falling in from the outer parts towards the central regions, where a nuclear ring has formed at the location of the inner Lindblad resonance radius of an an m=2 perturbation. Complementary continuum subtracted narrow band images in Hα have been used to identify 376 H ii regions with calibrated luminosities. The mean velocity dispersion for the ionized gas (even when excluding pixels belonging to H ii regions) is almost constant out to 12 kpc, although it varies from 14 to 20 km s-1, with a steady decline in the outer parts. Conclusions: We have found kinematic signatures of radial motions caused by an m=2 perturbation. Such a perturbation may well be responsible for the inflow of material forming the nuclear ring and the inner rapidly rotating disc-like structure. The latter, in turn, could help build a pseudo-bulge in NGC 628. The current paper demonstrates a number of tools that we have developed for building a solid frame work for studying the evolution of structure in spiral galaxies using two dimensional kinematic observations.
|
|
| 5. |
- Fathi, Kambiz, et al.
(författare)
-
Spiral Inflow Feeding the Nuclear Starburst in M83 : Observed in Hα Emission with the GHαFaS Fabry-Perot Interferometer
- 2008
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 675:1, s. L17-L20
-
Tidskriftsartikel (refereegranskat)abstract
- We present observations of the nearby barred starburst galaxy M83 (NGC 5236), with the new Fabry-Perot interferometer GHαFaS mounted on the 4.2 m William Herschel Telescope on La Palma. The unprecedented high-resolution observations, of 16 pc FWHM-1, of the Hα-emitting gas cover the central 2 kpc of the galaxy. The velocity field displays the dominant disk rotation with signatures of gas inflow from kpc scales down to the nuclear regions. At the inner inner Lindblad resonance radius of the main bar and centered at the dynamical center of the main galaxy disk, a nuclear (5.5 +/- 0.9) × 108 Msolar rapidly rotating disk with scale length of 60+/-20 pc has formed. The nuclear starburst is found in the vicinity as well as inside this nuclear disk, and our observations confirm that gas spirals in from the outer parts to feed the nuclear starburst, giving rise to several star formation events at different epochs, within the central 100 pc radius of M83.
|
|
| 6. |
- fathi, kambiz, et al.
(författare)
-
Structure and evolution of star-forming gas in late-type spiral galaxies
- 2007
-
Ingår i: Stellar Populations as Building Blocks of Galaxies, Proceedings.
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- We study two dimensional Fabry-Perot interferometric observations of the nearby face-on late-type spiral galaxy, NGC 628. We investigate the role of the individual HII regions together with the large-scale gravitational mechanisms which govern star formation and overall evolution in spiral galaxies. Our kinematical analysis (reinforced by literature maps in HI and CO at lower angular resolution) enables us to verify the presence of an inner rapidly rotating inner disk-like component which we attribute to long term secular evolution of the large-scale spiral arms and oval structure. We find that gas is falling in from the outer parts towards the bluer central regions. This could be an early phase in the formation of a pseudo-bulge. We find signatures of radial motions caused by an m=2 perturbation, which are likely to be responsible for the inflow of material forming the circumnuclear ring and the rapidly rotating inner structure.
|
|
| 7. |
- Holmgren, Johan, et al.
(författare)
-
An iterative k-means clustering approach for identification of bicycle impediments in an urban traffic network
- 2020
-
Ingår i: International Journal of Traffic and Transportation Management. - : International Association for Sharing Knowledge and Sustainability. - 2371-5782. ; 2:2, s. 35-42
-
Tidskriftsartikel (refereegranskat)abstract
- The bicycle has many positive effects; however, bicyclists are more vulnerablethan users of other transport modes, andthe number of bicycle related injuries and fatalities are toohigh.We present a clustering analysis aiming to support the identification of the locations ofbicyclists' perceived unsafety in an urban trafficnetwork, so-called bicycle impediments.In particular, we presentan iterative k-means clustering approach, which in contrast to standard k-means clustering, enables to remove outliers and solitary points from the data set. In our study, we used data collected by bicyclists travelling inthe city of Lund, Sweden, where each data point defines a location andtime of a bicyclist's perceived unsafety.The results of our study show that 1) clustering is a usefulapproach in order to support the identification of perceived unsafelocations forbicyclists in an urban traffic networkand2) it might bebeneficial to combine different types of clustering to support theidentification process. Furthermore, using the adjusted Rand index, our results indicate highrobustness of our iterative k-means clustering approach.
|
|
| 8. |
- Holmgren, Johan, et al.
(författare)
-
On the use of clustering analysis for identification of unsafe places in an urban traffic network
- 2020
-
Ingår i: Procedia Computer Science. - : Elsevier. - 1877-0509. ; 170, s. 187-194
-
Tidskriftsartikel (refereegranskat)abstract
- As an alternative to the car, the bicycle is considered important for obtaining more sustainable urban transport. The bicycle has many positive effects; however, bicyclists are more vulnerable than users of other transport modes, and the number of bicycle related injuries and fatalities are too high. We present a clustering analysis aiming to support the identification of the locations of bicyclists' perceived unsafety in an urban traffic network, so-called bicycle impediments. In particular, we used an iterative k-means clustering approach, which is a contribution of the current paper, and DBSCAN. In contrast to standard k-means clustering, our iterative k-means clustering approach enables to remove outliers from the data set. In our study, we used data collected by bicyclists travelling in the city of Lund, Sweden, where each data point defines a location and time of a bicyclist's perceived unsafety. The results of our study show that 1) clustering is a useful approach in order to support the identification of perceived unsafe locations for bicyclists in an urban traffic network and 2) it might be beneficial to combine different types of clustering to support the identification process. (C) 2020 The Authors. Published by Elsevier B.V.
|
|
| 9. |
- Knapen, Johan H., et al.
(författare)
-
How to write and develop your astronomy research paper
- 2022
-
Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 6:9, s. 1021-1026
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Writing is a vital component of a modern career in scientific research. But how to write correctly and effectively is often not included in the training that young astronomers receive from their supervisors and departments. We offer a step-by-step guide to tackle this deficiency, published as a set of two Perspectives. In the first, we addressed how to plan and outline your paper and decide where to publish. In this second Perspective, we describe the various sections that constitute a typical research paper in astronomy, sharing best practice for the most efficient use of each of them. We also discuss a selection of issues that often cause trouble for writers from sentence to paragraph structure-the 'writing mechanics' used to develop a manuscript. Our two-part guide is aimed primarily at MSc- and PhD-level students who face the daunting task of writing their first scientific paper, but more senior researchers or writing instructors may well find the ideas presented here useful. Writing a good scientific paper is a challenging task that benefits from training and practice. In this second Perspective in a short series, the authors share their wisdom on the process of writing a manuscript, from the most appropriate content for each section to the language to use.
|
|
| 10. |
- Knapen, Luk, et al.
(författare)
-
Identifying bicycle trip impediments by data fusion
- 2020
-
Ingår i: Procedia Computer Science. - : Elsevier. - 1877-0509. ; 170, s. 195-202
-
Tidskriftsartikel (refereegranskat)abstract
- A set of GPS traces for bicyclists and a set of notifications by bicyclists of problematic situations (spots identified by GPS records) had been collected independently. The data collection periods did not coincide but overlapped and none was contained in the other one. The aim is to use both datasets to determine an optimal action plan for problem solving given a limited budget. First, problematic locations are clustered. Each cluster corresponds to an impediment. Impediments are then associated with trips using a distance function. The aim is to find out which impediments to solve under a given budget constraint in order to maximize the number of impediment free trips. Thereto the trip set is partitioned by matching each trip with the largest set of its affecting impediments. Solving all impediments in such set induces a cost and makes the associated part of trips impediment free. An optimizer is presented and evaluated. (C) 2020 The Authors. Published by Elsevier B.V.
|
|
| 11. |
- Knapen, Luk, et al.
(författare)
-
Optimal bicycle trip impediments resolution by data fusion
- 2021
-
Ingår i: Journal of Ambient Intelligence and Humanized Computing. - : Springer. - 1868-5137 .- 1868-5145. ; 12, s. 103-120
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a method, whose purpose is to combine a set of GPS traces collected by bicyclists with a set of notifications of problematic situations to determine an optimal action plan for solving safety related problems in a traffic network. In particular, we use optimization to determine which problem locations to resolve under a given budget constraint in order to maximize the number of impediment free trips. The method aims to suggest a priority of impediments to resolve, which would be manually infeasible. The proposed method consists of two steps. First, problematic locations are clustered, where each cluster corresponds to a so-called impediment. Each impediment is associated with trips nearby using a distance function. The trip set is partitioned by matching each trip with the largest set of its affecting impediments. Solving all impediments associated with such a part induces a cost and makes the associated part of trips impediment free. The second step aims to find the set of impediments that can be solved with a given budget and that makes the maximum number of trips impediment free. A branch-and-bound optimizer for the second step is presented and evaluated. The clustering parameters affect the set of identified impediments and the extent of each of them. In order to evaluate the sensitivity of the result to the clustering parameters a technique is proposed to consistently estimate the impediment resolution cost. Our study aims to support the interactive urban designer to improve the urban bicycle road infrastructure. By providing a method to prioritize between impediments to resolve, it also aims to contribute to a safer and more attractive traffic situation for bicyclists.
|
|
| 12. |
- Moe, Morten K., et al.
(författare)
-
The structure of the fire fighting foam surfactant Forafac (R) 1157 and its biological and photolytic transformation products
- 2012
-
Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 89:7, s. 869-875
-
Tidskriftsartikel (refereegranskat)abstract
- For several decades, perfluorooctane sulfonate (PFOS) has widely been used as a fluorinated surfactant in aqueous film forming foams used as hydrocarbon fuel fire extinguishers. Due to concerns regarding its environmental persistence and toxicological effects, PFOS has recently been replaced by novel fluorinated surfactants such as Forafac (R) 1157, developed by the DuPont company. The major component of Forafac (R) 1157 is a 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB), and a link between the trade name and the exact chemical structure is presented here to the scientific community for the first time. In the present work, the structure of the 6:2 FTAB was elucidated by H-1, C-13 and F-19 nuclear magnetic resonance Spectroscopy and high-resolution mass spectrometry. Moreover, its major metabolites from blue mussel (Mytilus edulis) and turbot (Scophthalmus maximus) and its photolytic transformation products were identified. Contrary to what has earlier been observed for PFOS, the 6:2 FTAB was extensively metabolized by blue mussel and turbot exposed to Forafac (R) 1157. The major metabolite was a deacetylated betaine species, from which mono- and di-demethylated metabolites also were formed. Another abundant metabolite was the 6:2 fluorotelomer sulfonamide. In another experiment, Forafac (R) 1157 was subjected to UV-light induced photolysis. The experimental conditions aimed to simulate Arctic conditions and the deacetylated species was again the primary transformation product of 6:2 FTAB. A 6:2 fluorotelomer sulfonamide was also formed along with a non-identified transformation product. The environmental presence of most of the metabolites and transformation products was qualitatively demonstrated by analysis of soil samples taken in close proximity to an airport fire training facility.
|
|
| 13. |
- Peletier, R. F., et al.
(författare)
-
Stars and gas in the inner parts of galaxies seen in SAURON integral field observations
- 2007
-
Ingår i: New Astronomy Reviews. - : Elsevier BV. - 1387-6473. ; 51:1-2, s. 29-33
-
Tidskriftsartikel (refereegranskat)abstract
- We give two examples of spiral galaxies that show non-circular gas motions in the inner kiloparsecs, from SAURON integral field spectroscopy. We use harmonic decomposition of the velocity field of the ionized gas to study the underlying mass distribution, employing linear theory. The higher order harmonic terms and the main kinematic features of the observed data are consistent with an analytically constructed simple bar model. We also present maps of a number of strong absorption lines in M 100, derive simple stellar populations and correlate them with features in the gas kinematics.
|
|
