Cette thèse présente l’étude d’un réseau de capteurs pour la surveillance en temps réel de la qualité des eaux souterraines. L’objectif est de réussir à communiquer dans la bande de fréquences libre à 433MHz sur plusieurs dizaines de kilomètres. Le problème majeur des bandes libres est la présence de transmissions parasites (brouilleurs). Nous avons donc, en premier lieu, mis en évidence de la présence de ces brouilleurs et étudier leur impact sur les communications. Après analyse, il s’avère que les brouilleurs sont très nombreux et puissants mais que leur répartition dans la bande est inégale. Une étude spectrale de la bande semble nécessaire, avant la mise en place du réseau, afin de transmettre dans les canaux les moins pollués. Des communications nocturnes sont également à privilégier car les brouilleurs sont moins nombreux la nuit. Nous présentons ensuite une architecture réseau, adaptée au cahier des charges et à cette bande de fréquences. Nous avons également testé un composant RF dédié aux transmissions en bande ISM. Les résultats montrent que les performances de ce composant sont faibles pour des communications longues distances en présence de brouilleurs. Un récepteur radiofréquence simple ne permet donc pas de réaliser des communications fiables dans ces conditions. Le prototype complet du réseau, développé durant ces travaux, est ensuite décrit. Pour finir, nous proposons un nouveau concept de récepteur, utilisant un réseau d’antennes phasé et un détecteur cyclostationnaire, pour pallier au problème des brouilleurs. Le but est de stocker les signaux reçus pour les traiter en temps différé à l’aide d’algorithmes de filtrage spatial. Des simulations montrent l’efficacité de ce concept. / This thesis presents the study of a wireless sensor network for real-time monitoring of groundwater quality. The aim is to successfully communicate in the free 433MHz frequency band over tens of kilometers. The main issue of free bands is the presence of radio frequency interferences (RFI). First, we have studied the properties of these RFI and there impacts on communications. This analysis shows numerous and powerful jammers but with an irregular distribution in time and frequency. In consequence, the network set-up should be based on prior analysis of the time-frequency context. In particular, night communications should be preferred. Then, we present a network architecture adapted to the given industrial specifications and the mentioned frequency band constraint. We have also tested a RF component suitable for ISM band transmissions. Results show that the component performances are low for longue range communications with RFI. With a simple radio frequency receiver, reliable communications are not possible in these conditions. Then the complete network prototype, developed during this thesis, is described. Finally, to overcome the problem due to jammers, we propose a new receiver concept. It is based on a phased antenna array and a cyclostationary detector. The aim is to detect the signal of interest among RFI and to store it for further signal processing. In particular, off-line spatial filtering techniques can used to remove RFI. Simulations show the efficiency of this concept.

We revisit the proposed extended Schmidt law, which posits that the star formation efficiency in galaxies depends on the stellar mass surface density, by investigating spatially resolved star formation rates (SFRs), gas masses, and stellar masses of star formation regions in a vast range of galactic environments, from the outer disks of dwarf galaxies, to spiral disks and to merging galaxies, as well as individual molecular clouds in M33. We find that these regions are distributed in a tight power law as Sigma(SFR) proportional to (Sigma(0.5)(star)Sigma(gas))(1.09), which is also valid for the integrated measurements of disk and merging galaxies at high-z. Interestingly, we show that star formation regions in the outer disks of dwarf galaxies with Sigma(SFR) down to 10(-5) M(circle dot)yr(-1) kpc(-2), which are outliers of both the Kennicutt-Schmidt and Silk-Elmegreen laws, also follow the extended Schmidt law. Other outliers in the Kennicutt-Schmidt law, such as extremely metal-poor star formation regions, also show significantly reduced deviation from the extended Schmidt law. These results suggest an important role for existing stars in helping to regulate star formation through the effect of their gravity on the midplane pressure in a wide range of galactic environments.

We present Herschel Spectral and Photometric Imaging Receiver (SPIRE)-Fourier Transform Spectrometer (FTS) intermediate-sampled mapping observations of the central similar to 8 kpc (similar to 150 arcsec) of M51, with a spatial resolution of 40 arcsec. We detect four (CO)-C-12 transitions (J = 4-3 to J = 7-6) and the [C i] P-3(2)-P-3(1) and P-3(1)-P-3(0) transitions. We supplement these observations with ground-based observations of (CO)-C-12 J = 1-0 to J = 3-2 and perform a two-component non-local thermodynamic equilibrium analysis. We find that the molecular gas in the nucleus and centre regions has a cool component (T-kin similar to 10-20 K) with a moderate but poorly constrained density (n(H-2) similar to 10(3)-10(6) cm(-3)), as well as significant molecular gas in a warmer (T-kin similar to 300-3000 K), lower density (n(H-2) similar to 10(1.6)-10(2.5) cm(-3)) component. We compare our CO line ratios and calculated densities along with ratios of CO to total infrared luminosity to a grid of photon-dominated region (PDR) models and find that the cold molecular gas likely resides in PDRs with a field strength of G(0) similar to 10(2). The warm component likely requires an additional source of mechanical heating, from supernovae and stellar winds or possibly shocks produced in the strong spiral density wave. When compared to similar two-component models of other star-forming galaxies published as part of the Very Nearby Galaxies Survey (Arp 220, M82 and NGC 4038/39), M51 has the lowest density for the warm component, while having a warm gas mass fraction that is comparable to those of Arp 220 and M82, and significantly higher than that of NGC 4038/39.

New detections of CCH have been made toward nine planetary nebulae (PNe), including K4-47, K3-58, K3-17, M3-28, and M4-14. Measurements of the N = 1 -> 0 and N = 3 -> 2 transitions of this radical near 87 and 262 GHz were carried out using the new 12 m and the Sub-Millimeter Telescope (SMT) of the Arizona Radio Observatory (ARO). The presence of fine and/or hyperfine structure in the spectra aided in the identification. CCH was not observed in two PNe which are sources of C-60. The planetary nebulae with positive detections represent a wide range of ages and morphologies, and all had previously been observed in HCN and HNC. Column densities for CCH in the PNe, determined from radiative transfer modeling, were N-tot(CCH) similar to 0.2-3.3 x 10(15) cm(-2), corresponding to fractional abundances with respect to H-2 of f similar to 0.2-47 x 10(-7). The abundance of CCH was found to not vary significantly with kinematic age across a time span of similar to 10,000 years, in contrast to predictions of chemical models. CCH appears to be a fairly common constituent of PNe that are carbon-rich, and its distribution may anti-correlate with that of C-60. These results suggest that CCH may be a product of C-60 photodestruction, which is known to create C-2 units. The molecule may subsequently survive the PN stage and populate diffuse clouds. The distinct, double-horned line profiles for CCH observed in K3-45 and M3-28 indicate the possible presence of a bipolar flow oriented at least partially toward the line of sight.

We describe an ultraviolet spectroscopic survey of interstellar high-velocity cloud (HVC) absorption in the strong λ1206.500 line of Si III using the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. Because the Si III line is 4-5 times stronger than O VI λ1031.926, it provides a sensitive probe of ionized gas down to column densities N Si III 5 × 1011 cm-2 at Si III equivalent width 10 m. We detect high-velocity Si III over 91% 4% of the sky (53 of 58 sight lines); 59% of the HVCs show negative local standard of rest velocities. The mean HVC column density per sight line is 〈log N Si III 〉 = 13.19±0.45, while the mean for all 90 velocity components is 12.92±0.46. Lower limits due to Si III line saturation are included in this average, so the actual mean/median values are even higher. The Si III appears to trace an extensive ionized component of Galactic halo gas at temperatures 104.0-4.5 K indicative of a cooling flow. Photoionization models suggest that typical Si III absorbers with 12.5 < log N Si III < 13.5 have total hydrogen column densities N H 1018-1019 cm-2 for gas of hydrogen density n H 0.1 cm-3 and 10% solar metallicity. With typical neutral fractions N H I/N H 0.01, these HVCs may elude even long-duration 21 cm observations at Arecibo, the EVLA, and other radio facilities. However, if Si III is associated with higher density gas, n H ≥ 1 cm-3, the corresponding neutral hydrogen could be visible in deep observations. This reservoir of ionized gas may contain 10 8M and produce a mass infall rate of 1 M yr-1 to the Galactic disk.

We present HST Goddard High Resolution Spectrograph and Space Telescope Imaging Spectrograph observations of five quasi stellar objects that probe the prominent high-velocity cloud (HVC) Complex C, covering ∼10% of the northern sky. Based upon a single sight-line measurement (Mrk 290), a metallicity [S/H] = -1.05 ± 0.12 has been associated with Complex C by Wakker et al. When coupled with its inferred distance (5 ≲ d ≲ 30 kpc) and line-of-sight velocity (v ∼ -100 to -200 km s-1), Complex C appeared to represent the first direct evidence for infalling low-metallicity gas onto the Milky Way, which could provide the bulk of the fuel for star formation in the Galaxy. We have extended the abundance analysis of Complex C to encompass five sight lines. We detect S n absorption in three targets (Mrk 290, 817, and 279); the resulting [S II/H I] values range from -0.36 (Mrk 279) to -0.48 (Mrk 817) to -1.10 (Mrk 290). Our preliminary O I FUSE analysis of the Mrk 817 sight line also supports the conclusion that metallicities as high as 0.3 times solar are encountered within Complex C. These results complicate an interpretation of Complex C as infalling low-metallicity Galactic fuel. Ionization corrections for H II and S III cannot easily reconcile the higher apparent metallicities along the Mrk 817 and Mrk 279 sight lines with that seen toward Mrk 290, since Hα emission measures preclude the existence of sufficient H II. If gas along the other lines of sight has a similar pressure and temperature to that sampled toward Mrk 290, the predicted Hα emission measures would be ∼900 mR. It may be necessary to reclassify Complex C as mildly enriched Galactic waste from the Milky Way or processed gas torn from a disrupted neighboring dwarf, as opposed to low-metallicity Galactic fuel.

Context. Measurement of the Galactic neutral atomic hydrogen (H I) column density, NH I, and brightness temperatures, T-B, is of high scientific value for a broad range of astrophysical disciplines. In the past two decades, one of the most-used legacy H I datasets has been the Leiden/Argentine/Bonn Survey (LAB). Aims. We release the H I 4 pi survey (HI4PI), an all-sky database of Galactic H I, which supersedes the LAB survey. Methods. The HI4PI survey is based on data from the recently completed first coverage of the Effelsberg-Bonn H I Survey (EBHIS) and from the third revision of the Galactic All-Sky Survey (GASS). EBHIS and GASS share similar angular resolution and match well in sensitivity. Combined, they are ideally suited to be a successor to LAB. Results. The new HI4PI survey outperforms the LAB in angular resolution (theta(FWHM) = 16'.2) and sensitivity (sigma(rms) = 43 mK). Moreover, it has full spatial sampling and thus overcomes a major drawback of LAB, which severely undersamples the sky. We publish all-sky column density maps of the neutral atomic hydrogen in the Milky Way, along with full spectroscopic data, in several map projections including HEALPix.

This thesis analyses and proposes solutions for the following PNe mysteries: 1. The missing PNe population. 100 new objects were spectroscopically observed and analysed using the INT Photometric Halpha Survey (IPHAS). 32 are PNe, 13 are possible PNe and the rest are HII regions, SNR and unclear objects. The new PNe were within the inner parts of the galactic plane. The IPHAS survey has been the deepest survey done in Halpha, and revealed objects never seen before. 2. The mixed chemistry in Galactic Bulge PNe. These GBPNe are the end-products of low-mass stars (and therefore expected to be O-rich) and belong to a metal rich population. These PNe present dual-dust chemistry, with the presence of PAHs (carbon-rich) and crystalline silicates (oxygen-rich) in their spectra. This thesis analysed 40 Galactic Bulge PNe and found a strong correlation between intensity of the PAH bands and morphology, notably a massive torus. This torus provides the dense irradiated environment needed to form the PAHs. Follow-up observations using VISIR revealed a dense dusty tori in 11 PNe. PAHs are present in the outer edges of these tori, whereas ionised material is located within the dusty tori.3. The 3He problem. Using the VLA we observed three PNe, upper-limits of their 3He abundances were estimated. The resulting evolution of 3He is only consistent with the values determined in pre-solar material and the ISM, if the PNe observed represent only 4% of the population of low-mass stars, and the remaining 96% have undergone enhanced 3He depletion.

This thesis presents new 450$\mu$m and 850$\mu$m observations of NGC3627 taken with the new SCUBA-2 with the main goal of trying to better understand the properties of gas and dust in the interstellar medium of NGC3627. We determined properties of the cold component of NGC3627's spectral energy distribution (SED) using dust models given by the Planck Collaboration, by Li and Draine, and allowing the emissivity index to be treated as a free parameter. Fitting the SED required the use of 100$\mu$m, 160$\mu$m, 250$\mu$m, 350$\mu$m, and 500$\mu$m data from the KINGFISH survey. Each of the KINGFISH observations have been passed through an extended emission filter in order to match the SCUBA-2 observations. The best fit temperatures and emissivity indices agreed with the results found in other recent studies, but our fitted masses were smaller than those of other studies due to differences in the fitted temperature and observed fluxes. After the properties of the dust emission were calculated, we implemented a method to determine the amount of molecular hydrogen present in NGC3627. The method we used involves finding a CO-to-H$_2$ conversion factor that minimizes the scatter present in dust-to-gas mass ratio. We used CO J=2-1 from the HERACLES survey and CO J=1-0 from the Nobeyama 45-m telescope to act as our molecular tracer, and HI observations of NGC3627 from the THINGS survey. The results from minimizing the dust-to-gas ratio scatter give low $\alpha_{CO}$ values, that are normally associated with U/LIRGs. The low $\alpha_{CO}$ values can be attributed to the treatment of the error associated with reported $\alpha_{CO}$. The uncertainties for $\alpha_{CO}$ reported in this thesis are a minimum estimate, and if the error associated with $\alpha_{CO}$ is large enough, then the best fit $\alpha_{CO}$ values can be considered as a lower threshold for the system. / Thesis / Master of Science (MSc)

Title: Shell-like structures in the ISM: Observation versus simulations Author: Vojtěch Sidorin (vojtech.sidorin@gmail.com)1 Department: Astronomical Institute of Charles University2 Supervisor: Prof. RNDr. Jan Palouš, DrSc. (palous@asu.cas.cz), Astronomical Institute of the Czech Academy of Sciences3 Abstract: Shell-like structures are objects found in large numbers in the inter- stellar medium (ISM). They usually appear as bubbles or segments of bubbles and are believed to result from the deposition of mass and energy into the ISM by stars, gamma-ray bursts, or high-velocity clouds. Interstellar turbulence may play a role in their creation too. These structures influence the dynamics of the ISM and are also linked to star formation. In this thesis, I review our current knowledge of the ISM, interstellar turbulence, and shell-like structures in the ISM. Then I present the research into the GLIMPSE bubble N107 conducted in collaboration with my colleagues. N107 is a dusty shell-like structure found in our Galaxy. We explored its atomic, molecular, and radio-continuum components; derived its distance (3.6 kpc), size (radius of 12 pc), and expansion velocity (8 km s−1 ); and identified 49 associated molecular clumps. Using numerical simulations, we estimated the conditions under which N107 formed and concluded...