WMAP pontforrások mint lehetséges űr-VLBI kalibrátorok

A WMAP 5 év alatt gyűjtött adatait használtam egy olyan új – fényes és kompakt kvazárokat tartalmazó – katalógus összeállításához, mely a jövőben mm-VLBI megfigyelésekre lesz használható. A WMAP pontforrások közül összegyűjtöttem az ismert VLBI célpontokat, összevetettem őket az eddigi VLBI katalógusokkal, majd almintákat hoztam létre aszerint, hogy az illető források szerepelnek-e vagy sem a WMAP pontforrásai között. A 41, 61 és 94 GHz frekvencián mért fluxussűrűségek alapján kiszámolt színképindexekből elkészítettem a teljes katalógus, valamint egyes alminták fluxussűrűség- és színképindex-hisztogramjait, majd a többi katalógussal való átfedés térképét. A munka egyik célja olyan új források megjelölése, amelyeket VLBI technikával 86 GHz frekvencián meg lehetne figyelni. A WMAP listából kiválogattam azokat a forrásokat, amelyeket még nem vizsgáltak 86 GHz-en, és a fluxussűrűségük 1 Jy felett van, valamint a földi hálózatok lefedettsége miatt azokat, amelyek deklinációja –40°-nál magasabb (hasonló módszert használtak az eddigi legteljesebb 86 GHz-es VLBI felmérésben). Az új katalógus létrehozásához nyilvános adatbázisok segítségével elvégeztem az objektumok optikai azonosítását, majd a forrásokhoz szélesebb sávban készült rádióspektrumokat, valamint korábbi alacsonyabb frekvencián készített VLBI képeket kerestem. A jövőben a jobb felbontást és nagyobb érzékenységet lehetővé tevő űr-VLBI műholdak – mint pl. az ASTRO-G – az általam összegyűjtött fényes kvazárokat a halványabb objektumok megfigyeléséhez kalibrátorokként is használhatják majd

Kinematics and physical conditions of HI in nearby radio sources. The last survey of the old Westerbork Synthesis Radio Telescope

We present an analysis of the properties of neutral hydrogen (HI) in 248 nearby (0.0230$mJy and for which optical spectroscopy is available. The observations were carried out with the Westerbork Synthesis Radio Telescope as the last large project before the upgrade of the telescope with phased array feed receivers (Apertif). The sample covers almost four orders of magnitude in radio power from$\log\,P_{\rm 1.4 \,GHz}=22.5$W Hz$^{-1}$and$26.2$W Hz$^{-1}$. We detect HI in absorption in$27\% \pm 5.5\%$of the objects. The distribution and kinematics of the absorbing HI gas appear to depend on radio power, the properties of the radio continuum emission, and the dust content of the sources. Among the sources where HI is detected, gas with kinematics deviating from regular rotation is more likely found as the radio power increases. In these cases, the HI profile is often asymmetric with a significant blue-shifted component. This is particularly common for sources with$\log\,P_{\rm 1.4 \, GHz}>24$W Hz$^{-1}$, where the radio emission is small, possibly because these radio sources are young. The same is found for sources that are bright in the mid-infrared, i.e. sources rich in heated dust. In these sources, the HI is outflowing likely under the effect of the interaction with the radio emission. Conversely, in dust-poor galaxies, and in sources with extended radio emission, at all radio powers we only detect HI distributed in a rotating disk. Stacking experiments show that in sources for which we do not detect HI in absorption directly, the HI has a column density that is lower than$3.5\times 10^{17} (T_{ \rm spin}/c_f)$cm$^{-2}$. We use our results to predict the number and type of HI absorption lines that will be detected by the upcoming surveys of the Square Kilometre Array precursors and pathfinders (Apertif, MeerKAT, and ASKAP).Comment: 22 pages, 15 figures, 4 tables, accepted for publication in A&

An accurate low-redshift measurement of the cosmic neutral hydrogen density

Using a spectral stacking technique, we measure the neutral hydrogen (HI) properties of a sample of galaxies at $z < 0.11$ across 35 pointings of the Westerbork Synthesis Radio Telescope (WSRT). The radio data contains 1,895 galaxies with redshifts and positions known from the Sloan Digital Sky Survey (SDSS). We carefully quantified the effects of sample bias, aperture used to extract spectra, sidelobes and weighting technique and use our data to provide a new estimate for the cosmic HI mass density. We find a cosmic HI mass density of $\Omega_{\rm HI} = (4.02 \pm 0.26)\times 10^{-4} h_{70}^{-1}$ at $\langle z\rangle = 0.066$, consistent with measurements from blind HI surveys and other HI stacking experiments at low redshifts. The combination of the small interferometer beam size and the large survey volume makes our result highly robust against systematic effects due to confusion at small scales and cosmic variance at large scales. Splitting into three sub-samples with $\langle z\rangle$ = 0.038, 0.067 and 0.093 shows no significant evolution of the HI gas content at low redshift.Comment: 17 pages, 24 figure

xGASS: total cold gas scaling relations and molecular-to-atomic gas ratios of galaxies in the local Universe

We present the extended GALEX Arecibo SDSS Survey (xGASS), a gas fraction-limited census of the atomic hydrogen (H I) gas content of 1179 galaxies selected only by stellar mass (M⋆ = 109–1011.5 M⊙) and redshift (0.01 < z < 0.05). This includes new Arecibo observations of 208 galaxies, for which we release catalogues and H I spectra. In addition to extending the GASS H I scaling relations by one decade in stellar mass, we quantify total (atomic+molecular) cold gas fractions and molecular-to-atomic gas mass ratios, Rmol, for the subset of 477 galaxies observed with the IRAM 30 m telescope. We find that atomic gas fractions keep increasing with decreasing stellar mass, with no sign of a plateau down to log M⋆/M⊙ = 9. Total gas reservoirs remain H I-dominated across our full stellar mass range, hence total gas fraction scaling relations closely resemble atomic ones, but with a scatter that strongly correlates with Rmol, especially at fixed specific star formation rate. On average, Rmol weakly increases with stellar mass and stellar surface density μ⋆, but individual values vary by almost two orders of magnitude at fixed M⋆ or μ⋆. We show that, for galaxies on the star-forming sequence, variations of Rmol are mostly driven by changes of the H I reservoirs, with a clear dependence on μ⋆. Establishing if galaxy mass or structure plays the most important role in regulating the cold gas content of galaxies requires an accurate separation of bulge and disc components for the study of gas scaling relations