The distribution of mass within spiral galaxies:unique solutions from gas and stellar kinematics

In dit proefschrift wordt de hoeveelheid en verdeling van de verschillende dynamische componenten, gevormd door de aanwezige sterren, het aanwezige gas en de donkere materie, in 30 spiraalstelsels gelijkend op onze eigen Melkweg onderzocht. Dit onderzoek biedt inzicht in ons algemeen begrip van de vorming en evolutie van sterrenstelsels. Met behulp van optische- en radiospectroscopie heb ik de totale dynamische massa van ieder spiraalstelsel bepaald aan de hand van de rotatiekromme van de aanwezige schijf. De totale massa van de schijf volgt uit de gemeten verticale bewegingen van de sterren in de schijf, terwijl de totale massa van het atomaire en moleculaire gas direct volgt uit hun emissie in het infrarood en radio. Vervolgens heb ik de massa en verdeling van de aanwezige donkere materie bepaald door het verschil te meten tussen de totale dynamische massa en de totale massa van de overige (zichtbare) componenten. In tegenstelling tot wat algemeen wordt aangenomen, heb ik gevonden dat donkere materie een belangrijke, en zelfs dominante, component vormt, zelfs in de centra van de meest heldere spiraalstelsels. De zichtbare componenten dragen gemiddeld slechts ongeveer 30 procent bij aan de totale massa binnen een straal vergelijkbaar met de afstand van onze zon tot het centrum van ons Melkwegstelsel. De overige 70 procent van de massa is dus donker. Hieruit concludeer ik dat de lichtgevende massa van spiraalstelsels ongeveer drie keer kleiner is dan algemeen wordt aangenomen

The distribution of mass within spiral galaxies:unique solutions from gas and stellar kinematics

In dit proefschrift wordt de hoeveelheid en verdeling van de verschillende dynamische componenten, gevormd door de aanwezige sterren, het aanwezige gas en de donkere materie, in 30 spiraalstelsels gelijkend op onze eigen Melkweg onderzocht. Dit onderzoek biedt inzicht in ons algemeen begrip van de vorming en evolutie van sterrenstelsels. Met behulp van optische- en radiospectroscopie heb ik de totale dynamische massa van ieder spiraalstelsel bepaald aan de hand van de rotatiekromme van de aanwezige schijf. De totale massa van de schijf volgt uit de gemeten verticale bewegingen van de sterren in de schijf, terwijl de totale massa van het atomaire en moleculaire gas direct volgt uit hun emissie in het infrarood en radio. Vervolgens heb ik de massa en verdeling van de aanwezige donkere materie bepaald door het verschil te meten tussen de totale dynamische massa en de totale massa van de overige (zichtbare) componenten. In tegenstelling tot wat algemeen wordt aangenomen, heb ik gevonden dat donkere materie een belangrijke, en zelfs dominante, component vormt, zelfs in de centra van de meest heldere spiraalstelsels. De zichtbare componenten dragen gemiddeld slechts ongeveer 30 procent bij aan de totale massa binnen een straal vergelijkbaar met de afstand van onze zon tot het centrum van ons Melkwegstelsel. De overige 70 procent van de massa is dus donker. Hieruit concludeer ik dat de lichtgevende massa van spiraalstelsels ongeveer drie keer kleiner is dan algemeen wordt aangenomen

A Road to Success Under Construction? Examining the Constraints of Public-Private Partnerships in Sweden

Public-Private Partnerships (PPP) have been embraced across the globe the past decades, with the driving forces varying across countries. Considering the relatively scarce usage of PPP in Sweden it appears highly relevant to identify the constraints for realising PPP projects. The outcome of such a study provides better understanding on what factors could constrain countries with low utilisation, as well as what could drive PPP usage in countries with high utilisation. The purpose of this thesis is to identify the constraints of realising public-private partnerships in Sweden and suggest measures to overcome them. By assessing Sweden’s PPP readiness in the Economist Intelligence Unit’s (EIU) Infrascope index, low-scoring PPP readiness areas are identified. By combining the low-scoring areas and critical success factors for PPPs, three major areas were identified as the major constraints. These three major constraints of realising PPP projects in Sweden were identified as; insufficient evaluation, inadequate organisational support and knowledge and political resistance. The first refers to the lacking capacity of evaluating public and private alternatives. The second refers to the insufficient coordination of support and capturing and sharing of PPP knowledge. The third refers to the lack of political will to conduct PPP projects and the underlying arguments. Measures involve the establishment of a formalised and systematic evaluation tool for the first constraint. A domestic and international PPP knowledge infrastructure is recommended for the second constraint. Finally, nuancing the debate, an investigation of alternative financing forms and the establishment of a clear decision-making tool for is suggested for the third constraint

The DiskMass Survey. X. Radio synthesis imaging of spiral galaxies

We present results from 21 cm radio synthesis imaging of 28 spiral galaxies from the DiskMass Survey obtained with the VLA, WSRT, and GMRT facilities. We detail the observations and data reduction procedures and present a brief analysis of the radio data. We construct 21 cm continuum images, global HI emission-line profiles, column-density maps, velocity fields, and position-velocity diagrams. From these we determine star formation rates (SFRs), HI line widths, total HI masses, rotation curves, and azimuthally-averaged radial HI column-density profiles. All galaxies have an HI disk that extends beyond the readily observable stellar disk, with an average ratio and scatter of R_{HI}/R_{25}=1.35+/-0.22, and a majority of the galaxies appear to have a warped HI disk. A tight correlation exists between total HI mass and HI diameter, with the largest disks having a slightly lower average column density. Galaxies with relatively large HI disks tend to exhibit an enhanced stellar velocity dispersion at larger radii, suggesting the influence of the gas disk on the stellar dynamics in the outer regions of disk galaxies. We find a striking similarity among the radial HI surface density profiles, where the average, normalized radial profile of the late-type spirals is described surprisingly well with a Gaussian profile. These results can be used to estimate HI surface density profiles in galaxies that only have a total HI flux measurement. We compare our 21 cm radio continuum luminosities with 60 micron luminosities from IRAS observations for a subsample of 15 galaxies and find that these follow a tight radio-infrared relation, with a hint of a deviation from this relation at low luminosities. We also find a strong correlation between the average SFR surface density and the K-band surface brightness of the stellar disk.Comment: 22 pages + Appendix, 16 figures + Atlas, 5 tables. Accepted for publication in Astronomy & Astrophysic

The DiskMass Survey. VIII. On the Relationship Between Disk Stability and Star Formation

We study the relationship between the stability level of late-type galaxy disks and their star-formation activity using integral-field gaseous and stellar kinematic data. Specifically, we compare the two-component (gas+stars) stability parameter from Romeo & Wiegert (Q_RW), incorporating stellar kinematic data for the first time, and the star-formation rate estimated from 21cm continuum emission. We determine the stability level of each disk probabilistically using a Bayesian analysis of our data and a simple dynamical model. Our method incorporates the shape of the stellar velocity ellipsoid (SVE) and yields robust SVE measurements for over 90% of our sample. Averaging over this subsample, we find a meridional shape of sigma_z/sigma_R = 0.51^{+0.36}_{-0.25} for the SVE and, at 1.5 disk scale lengths, a stability parameter of Q_RW = 2.0 +/- 0.9. We also find that the disk-averaged star-formation-rate surface density (Sigma-dot_e,*) is correlated with the disk-averaged gas and stellar mass surface densities (Sigma_e,g and Sigma_e,*) and anti-correlated with Q_RW. We show that an anti-correlation between Sigma-dot_e,* and Q_RW can be predicted using empirical scaling relations, such that this outcome is consistent with well-established statistical properties of star-forming galaxies. Interestingly, Sigma-dot_e,* is not correlated with the gas-only or star-only Toomre parameters, demonstrating the merit of calculating a multi-component stability parameter when comparing to star-formation activity. Finally, our results are consistent with the Ostriker et al. model of self-regulated star-formation, which predicts Sigma-dot_e,*/Sigma_e,g/sqrt(Sigma_e,*). Based on this and other theoretical expectations, we discuss the possibility of a physical link between disk stability level and star-formation rate in light of our empirical results.Comment: Accepted for publication in ApJ. 15 pages, 6 figures, 2 tables. An electronic version of Table 1 is available by request, or at http://www.astro.rug.nl/~westfall/research/dmVIII_table1.tx

A MUSE map of the central Orion Nebula (M 42)

We present a new integral-field spectroscopic dataset of the central part of the Orion Nebula (M 42), observed with the MUSE instrument at the ESO VLT. We reduced the data with the public MUSE pipeline. The output products are two FITS cubes with a spatial size of ~5.9'x4.9' (corresponding to ~0.76 pc x 0.63 pc) and a contiguous wavelength coverage of 4595...9366 Angstrom, spatially sampled at 0.2". We provide two versions with a sampling of 1.25 Angstrom and 0.85 Angstrom in dispersion direction. Together with variance cubes these files have a size of 75 and 110 GiB on disk. They represent one of the largest integral field mosaics to date in terms of information content. We make them available for use in the community. To validate this dataset, we compare world coordinates, reconstructed magnitudes, velocities, and absolute and relative emission line fluxes to the literature and find excellent agreement. We derive a two-dimensional map of extinction and present de-reddened flux maps of several individual emission lines and of diagnostic line ratios. We estimate physical properties of the Orion Nebula, using the emission line ratios [N II] and [S III] (for the electron temperature $T_e$) and [S II] and [Cl III] (for the electron density $N_e$), and show two-dimensional images of the velocity measured from several bright emission lines.Comment: Resubmitted to A&A after incorporating referee comments; access to full dataset via http://muse-vlt.eu/science/data-release

The Link Between Light and Mass in Late-type Spiral Galaxy Disks

We present the correlation between the extrapolated central disk surface brightness (mu) and extrapolated central surface mass density (Sigma) for galaxies in the DiskMass sample. This mu-Sigma-relation has a small scatter of 30% at the high-surface-brightness (HSB) end. At the low surface brightness (LSB) end, galaxies fall above the mu-Sigma-relation, which we attribute to their higher dark matter content. After correcting for the dark matter, as well as for the contribution of gas and the effects of radial gradients in the disk, the LSB end falls back on the linear mu-Sigma-relation. The resulting scatter about the corrected mu-Sigma-relation is 25% at the HSB end, and about 50% at the LSB end. The intrinsic scatter in the mu-Sigma-relation is estimated to be 10% to 20%. Thus, if the surface brightness is known, the stellar surface mass density is known to within 10-20% (random error). Assuming disks have an exponential vertical distribution of mass, the average (M_L)_K is 0.24 Msun/Lsun, with an intrinsic scatter around the mean of at most 0.05 Msun/Lsun. This value for (M/L)_K is 20% smaller than we found in Martinsson et al., mainly due to the correction for dark matter applied here. This small scatter means that among the galaxies in our sample variations in scale height, vertical density profile shape, and/or the ratio of vertical over radial velocity dispersion must be small.Comment: Accepted for publication in ApJ Letter

An optical particle size spectrometer for aircraft-borne measurements in IAGOS-CARIBIC

The particle number size distribution is an important parameter to characterize the atmospheric aerosol and its influence on the Earth's climate. Here we describe a new optical particle size spectrometer (OPSS) for measurements of the accumulation mode particle number size distribution in the tropopause region on board a passenger aircraft (IAGOS-CARIBIC observatory: In-service Aircraft for a Global Observing System – Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container). A modified KS93 particle sensor from RION Co., Ltd., together with a new airflow system and a dedicated data acquisition system, is the key component of the CARIBIC OPSS. The instrument records individual particle pulse signal curves in the particle size range 130–1110 nm diameter (for a particle refractive index of 1.47-i0.006) together with a time stamp and thus allows the post-flight choice of the time resolution and the size distribution bin width. The CARIBIC OPSS has a 50 % particle detection diameter of 152 nm and a maximum asymptotic counting efficiency of 98 %. The instrument's measurement performance shows no pressure dependency and no particle coincidence for free tropospheric conditions. The size response function of the CARIBIC OPSS was obtained by a polystyrene latex calibration in combination with model calculations. Particle number size distributions measured with the new OPSS in the lowermost stratosphere agreed within a factor of 2 in concentration with balloon-borne measurements over western North America. Since June 2010 the CARIBIC OPSS is deployed once per month in the IAGOS-CARIBIC observatory