The scatter of the spatially resolved star formation main sequence (SFMS) is investigated in order to reveal signatures about the processes of galaxy formation and evolution. We have assembled a ...sample of 355 nearby galaxies with spatially resolved H and mid-infrared fluxes from the Survey for Ionized Neutral Gas in Galaxies and the Wide-field Infrared Survey Explorer, respectively. We examine the impact of various star formation rate (SFR) and stellar mass transformations on the SFMS. Ranging from 106 to 1011.5 M and derived from color to mass-to-light ratio methods for mid-infrared bands, the stellar masses are internally consistent within their range of applicability and inherent systematic errors; a constant mass-to-light ratio also yields representative stellar masses. The various SFR estimates show intrinsic differences and produce noticeable vertical shifts in the SFMS, depending on the timescales and physics encompassed by the corresponding tracer. SFR estimates appear to break down on physical scales below 500 pc. We also examine the various sources of scatter in the spatially resolved SFMS and find morphology does not play a significant role. We identify three unique tracks across the SFMS by individual galaxies, delineated by a critical stellar mass density of log( ) ∼ 7.5. Below this scale, the SFMS shows no clear trend and is likely driven by local, stochastic internal processes. Above this scale, all spatially resolved galaxies have comparable SFMS slopes but exhibit two different behaviors, resulting likely from the rate of mass accretion at the center of the galaxy.
How do we study resilience? A systematic review le Polain de Waroux, Yann; Carignan, Marie‐Claude; del Giorgio, Olivia ...
People and nature,
04/2024, Letnik:
6, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract The concept of resilience has gained immense popularity as a way to frame social and environmental challenges. However, its empirical operationalization and the integration of social and ...ecological dimensions continue to present difficulties. In this paper, we conduct a systematic review of existing empirical studies of resilience in social, ecological and social‐ecological systems (SESs) and examine how and to what extent these studies have achieved the operationalization of the concept of resilience. We evaluate the operationalization of resilience in 463 papers based on whether they define the system of interest and disturbances, whether they define resilience, whether they evaluate resilience, and for papers focusing on SESs, whether that evaluation integrates social and ecological dimensions. We find that 51% of empirical studies do not meet at least one of these operationalization criteria, and that even those that do often lack key features for effective operationalization, such as clear system boundaries and baseline state or an effective integration of social and ecological dimensions. Of the papers examining SESs and evaluating resilience, only 54% integrate social and ecological dimensions in that evaluation. Building on these findings, we propose some design guidelines for operationalizing future empirical studies of resilience. Read the free Plain Language Summary for this article on the Journal blog.
Read the free Plain Language Summary for this article on the Journal blog.
MeerKAT-16 H i observation of the dIrr galaxy WLM Ianjamasimanana, Roger; Namumba, Brenda; Ramaila, Athanaseus J T ...
Monthly Notices of the Royal Astronomical Society,
10/2020, Letnik:
497, Številka:
4
Journal Article
Recenzirano
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ABSTRACT
We present observations and models of the kinematics and the distribution of the neutral hydrogen (H i) in the isolated dwarf irregular galaxy, Wolf-Lundmark-Melotte (WLM). We observed WLM ...with the Green Bank Telescope (GBT) and as part of the MeerKAT Early Science Programme, where 16 dishes were available. The H i disc of WLM extends out to a major axis diameter of 30 arcmin (8.5 kpc), and a minor axis diameter of 20 arcmin (5.6 kpc) as measured by the GBT. We use the MeerKAT data to model WLM using the tirific software suite, allowing us to fit different tilted-ring models and select the one that best matches the observation. Our final best-fitting model is a flat disc with a vertical thickness, a constant inclination and dispersion, and a radially varying surface brightness with harmonic distortions. To simulate bar-like motions, we include second-order harmonic distortions in velocity in the tangential and vertical directions. We present a model with only circular motions included and a model with non-circular motions. The latter describes the data better. Overall, the models reproduce the global distribution and the kinematics of the gas, except for some faint emission at the 2σ level. We model the mass distribution of WLM with pseudo-isothermal (ISO) and Navarro–Frenk–White (NFW) dark matter halo models. The NFW and the ISO models fit the derived rotation curves within the formal errors, but with the ISO model giving better reduced chi-square values. The mass distribution in WLM is dominated by dark matter at all radii.
H I Kinematics and Dynamics of Messier 31 Chemin, Laurent; Carignan, Claude; Foster, Tyler
Astrophysical journal/The Astrophysical journal,
11/2009, Letnik:
705, Številka:
2
Journal Article
Recenzirano
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We present a new deep 21 cm survey of the Andromeda galaxy, based on high-resolution observations performed with the Synthesis Telescope and the 26 m antenna at the Dominion Radio Astrophysical ...Observatory. The H I distribution and kinematics of the disk are analyzed and basic dynamical properties are given. The rotation curve is measured out to 38 kpc, showing a nuclear peak at 340 km s-1, a dip at 202 km s-1 around 4 kpc, two distinct flat parts at 264 km s-1 and 230 km s-1, and an increase to 275 km s-1 in the outermost regions. Except for the innermost regions, the axisymmetry of the gas rotation is very good. A very strong warp of the H I disk is evidenced. The central regions appear less inclined than the average disk inclination of 74 deg, while the outer regions appear more inclined. Mass distribution models by Delta *LCDM Navarro-Frenk-White, Einasto or pseudo-isothermal dark matter halos with baryonic components are presented. They fail to reproduce the exact shape of the rotation curve. No significant differences are measured between the various shapes of halo. The dynamical mass of M31 enclosed within a radius of 38 kpc is (4.7 +/- 0.5) X 1011. The dark matter component is almost four times more massive than the baryonic mass inside this radius. A total mass of 1.0 X 1012 is derived inside the virial radius. The spectral structure of the observations is very complex, with sometimes up to five H I components detected per spectrum, which is very rarely seen in other galaxies. New H I structures are discovered in the datacube. The most remarkable new features are an external arm and thin H I spurs in the disk outskirts. A relationship between these spurs and outer stellar clumps is evidenced. The external arm is 32 kpc long, lies on the far side of the galaxy, and has no obvious counterpart on the other side of the galaxy. Its kinematics clearly differs from the outer adjacent disk. Both these H I perturbations could result from tidal interactions with galaxy companions like NGC 205.
HI KINEMATICS AND DYNAMICS OF MESSIER 31 CHEMIN, Laurent; CARIGNAN, Claude; FOSTER, Tyler
The Astrophysical journal,
11/2009, Letnik:
705, Številka:
2
Journal Article
Abstract
We know that the observed H i (and H
2
) content cannot explain the SFR observed in galaxies. The only way galaxies can sustain that SFR is by accreting HI-rich dwarf galaxies or ...Inter-Galactic HI clouds. However, no observation to detect those accretion events has been conclusive so far. Instruments having the necessary sensitivity (e.g. GBT) lack the necessary spatial resolution and those with the proper resolution (e.g. VLA) lack the sensitivity. I will show that both are necessary to detect those illusive H
i
clouds. The SKA precursor MeerKAT is starting its operation as we speak and will start the Large Survey Programs at the end of 2018. FAST has started its observations in drift scan mode with CRAFTS (Commensal Radio Astronomy Fast Survey). In the near future (2019-20), the best combination to study low column density H i will be to combine the sensitivity of FAST with the spatial resolution of MeerKAT.
Mass models of 15 nearby dwarf and spiral galaxies are presented. The galaxies are selected to be homogeneous in terms of the method used to determine their distances, the sampling of their rotation ...curves (RCs) and the mass-to-light ratio (M/L) of their stellar contributions, which will minimize the uncertainties on the mass model results. Those RCs are modelled using the MOdified Newtonian Dynamics (MOND) prescription and the observationally motivated pseudo-isothermal (ISO) dark matter (DM) halo density distribution. For the MOND models with fixed M/L, better fits are obtained when the constant a
0 is allowed to vary, giving a mean value of (1.13 ± 0.50) × 10−8 cm s−2, compared to the standard value of 1.21 × 10−8 cm s−2. Even with a
0 as a free parameter, MOND provides acceptable fits (reduced
< 2) for only 60 per cent (9/15) of the sample. The data suggest that galaxies with higher central surface brightnesses tend to favour higher values of the constant a
0. This poses a serious challenge to MOND since a
0 should be a universal constant. For the DM models, our results confirm that the DM halo surface density of ISO models is nearly constant at ρ0 R
C ∼ 120 M pc−2. This means that if the M/L is determined by stellar population models, ISO DM models are left with only one free parameter, the DM halo central surface density.
One year after the site selection decision of the Square Kilometre Array (SKA), the first significant scientific results from South Africa's Karoo Array Telescope test array KAT-7 have appeared in ...the astronomical literature. This marks one of the many major milestones on the path to the SKA in Africa and highlights the commencement of cutting-edge science observations with South Africa's new radio interferometer. KAT-7 is now at a stage where it is able to respond regularly to requests from the international community for observations of specific objects. Flexible scheduling in combination with state-of-the-art receivers will make KAT-7 a very attractive radio telescope until MeerKAT comes online. The MeerKAT LSPs will continue to look to KAT-7 to test new and novel data analysis techniques ultimately designed for MeerKAT. The success of involving the next generation in novel science during the earliest phases of a new facility, certainly bodes well for the future science commissioning of MeerKAT and early science with this SKA precursor.
Mass models of 100 nearby spiral and irregular galaxies, covering morphological types from Sa to Irr, are computed using Hα rotation curves and R c-band surface brightness profiles. The kinematics ...was obtained using a scanning Fabry-Perot interferometer. One of the aims is to compare our results with those from Korsaga et al. (2018), which used mid-infrared (MIR) WISE W1 (3.4 µm) photometric data. For the analysis, the same tools were used for both bands. Pseudo-Isothermal (ISO) core and Navarro-Frenk-White (NFW) cuspy models have been used. We test Best Fit Models (BFM), Maximum Disc Models (MDM) and models for which M/L is fixed using the B-V colors. Similarly to what was found in the MIR 3.4 µm band, most of the observed rotation curves are better described by a central core density profile (ISO) than a cuspy one (NFW) when using the optical R c-band. In both bands, the dispersion in the (M/L) values is smaller for the fixed M/L fits. As for the W1 photometry, the derived DM halos' parameters depend on the morphological types. We find similar relations than those in the literature, only when we compare our results for the bulge-poor sub-sample because most of previous results were mainly based on late-type spirals. Because the dispersion in the model parameters is smaller and because stellar masses are better defined in that band, MIR photometry should be preferred, when possible, to the optical bands. It is shown that for high-z galaxies, sensible results can still be obtained without full profile decomposition.
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