Cold gas in the center of radio-loud galaxies:New perspectives on triggering and feedback from HI absorption surveys and molecular gas

Dit proefschrift brengt het voorkomen van atomaire waterstof getraceerd door absorptie in nabijgelegen radio sterrenstelsels in kaart, leidt de eigenschappen van het gas af en bestudeert de interactie tussen atomair en moleculair gas en de actieve kern (AGN). In twee projecten wordt geprobeerd het gas in de circumnucleaire regio's te relateren aan de brandstofvoorziening en triggerende- en feedbackeffecten van het radio AGN. Het eerste project onderzoekt de aanwezigheid van HI absorptie in een steekproef van radio AGN. De eigenschappen van de lijnen worden gerelateerd aan het ontwikkelingsstadium van de radio activiteit en de eigenschappen van het circumnucleaire stof door afleidingen van de mid-infrarode kleuren van de bronnen. De eerste uitgebreide statistieken van HI uitstromen worden gepresenteerd, hoewel afgeleid van oppervlakkige observaties. Tevens worden met de bronnen waar HI absorptie niet is gedetecteerd stacking experimenten gedaan die het mogelijk maken om de algemene eigenschappen van HI in radio AGN te onderzoeken. Het tweede project is een multi-golflengte studie van een jong radio AGN (PKS B17181-649) om te begrijpen hoe koud gas radio nucleaire activiteit kan veroorzaken. Waarnemingen van HI, moleculair stikstof en koolstofmonoxide wijzen er allemaal op dat koud gas bijdraagt aan de brandstofvoorziening voor de centrale nucleaire activiteit. Ook levert dit project bewijs voor accretie van moleculaire wolken op het centrale superzware zwarte gat. Tenslotte wordt gereflecteerd op de betekenis van deze resultaten voor toekomstige onderzoeksprojecten, zoals de HI surveys van de SKA pathfinders/precursors

ALMA observations of AGN fuelling. The case of PKS1718-649

Active galactic nuclei may play a crucial role in regulating the balance between accretion and ejection of gas in a galaxy. Absorption of neutral hydrogen (HI) in radio AGN is a powerful tool to identify cold gas flowing in and out of the active nucleus and to determine the effects of the interplay between the cold gas and the nuclear activity. Recently, we observed 250 radio galaxies with the Westerbork Synthesis Radio Telescope, detecting HI gas in 20% of them. In this talk, I will show how different shapes, widths and optical depths of the HI absorption lines that we identified trace different distributions of gas, such as circumnuclear disks, and infalling and outflowing clouds. In this talk, I will also present a multi-wavelength study of the cold gas of PKSB 1718-649. In this young (~100 years) radio-AGN, we detected two HI absorption lines tracing gas that may fuel the central black hole. Follow-up SINFONI and ALMA observations allow us to detect molecular gas that may fuel the nuclear activity. In particular, against the compact radio emission of the source (r~2pc), we detect carbon monoxide (CO) gas in absorption at red-shifted velocities with respect to the systemic velocity (v = +365±22 km/s). This CO (2-1) absorption line could trace molecular clouds falling onto the central super-massive black hole. A comparison with the SINFONI observations of the H2 1-0 S(1) line shows that the clouds must be close to the black hole (r<75 pc). The physical conditions of these clouds are different from the gas at larger radii, and are in good agreement with the predictions for the conditions of the gas when cold chaotic accretion triggers an active galactic nucleus. These observations on the centre of PKS B1718-649 provide one of the best indication that a population of cold clouds is falling towards a radio AGN, likely fuelling its activity

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&

Radio Jets as Driving Mechanism of Fast Outflows: The HI View

The complex and multi-phase nature of gas outflows is one of the properties highlighted by the work in recent years on AGN-driven outflows. In particular, the cold gas is found to play a more important role than previously expected. Surprisingly, HI has been shown to be a good tracer of fast outflows. In radio AGN, we can trace these outflows by looking at HI in absorption. I will present the results from a survey (done with the Westerbork Synthesis Radio Telescope) of radio sources up to z = 0.2, which has allowed us to explore, for the first time in a systematic way, the occurrence of HI outflows. A number of new cases have been found, showing outflow velocity up to about 1000 km/s. We have followed up some interesting cases with HI observations at high spatial resolution (reaching the pc scale with VLBI). In this way, we have located the region(s) where the HI outflows occur and investigated the role of the radio jets as driving mechanism. This relatively shallow survey was done in preparation of the upcoming "blind" surveys about to start with SKA pathfinders (Apertif, ASKAP, MeerKat). These surveys will allow two important steps forward: build up much better statistics of the HI outflows, and extend this search to higher redshifts to investigate whether any evolution is seen in their occurrence and properties. I will summarise the status of these projects

Regulation der Genexpression von MYCN in humanen Neuoblastomzellen durch Transkriptionsfaktoren der E2F-Familie

Seit fast 30 Jahren ist bekannt, dass die Amplifikation und Expression des Onkogens MYCN in Neuroblastomen mit einer sehr ungünstigen Prognose für die Patienten einhergeht. Dennoch liegen die Mechanismen der Genregulation von MYCN weiterhin größtenteils im Dunkeln. Die Präsenz potentieller Bindungsstellen für E2F-Proteine im Promotor des MYCN-Gens sowie Zellkulturexperimente lieferten Hinweise auf eine Rolle der Transkriptionsfaktoren der E2F-Familie in der Regulation der N-myc-Expression. Ziel dieser Arbeit war die Beantwortung der Frage, ob E2F-Proteine notwendig sind, um eine primär hohe Expression von N-myc in Neuroblastomzellen mit Amplifikation des Onkogens aufrechtzuerhalten, und ob sie hinreichend sind, um die Transkription von MYCN in Zellen ohne endogene Expression von N-myc einzuleiten. Durch Überexpression des Tumorsuppressorproteins p16, welches zu einer Inaktivierung endogener E2F-Proteine führt, konnte die MYCN-mRNA-Menge in Neuroblastomzellen deutlich gesenkt werden. Vergleichbare Resultate wurden durch Expression von dominant negativem E2F-1 erzielt. Da in einigen Studien gezeigt werden konnte, dass Myc-Proteine ihrerseits E2F-Gene aktivieren können, nehmen wir an, in aggressiven Neuroblastomen könnte eine positive Rückkopplungsschleife zwischen E2F-Transkriptionsfaktoren auf der einen und N-myc auf der anderen Seite existieren, die die gesteigerte Aktivität des MYCN-Onkogens aufrechterhält. Stabil transfizierte E2F-ER-Fusionsproteine waren jedoch nicht in der Lage, das endogene MYCN-Gen in Neuroblastomzellen ohne Expression von N-myc anzuschalten. E2F-Proteine werden folglich für das volle Ausmaß der starken Expression von N-myc in Neuroblastomen benötigt, sind aber nicht ausreichend, um das Onkogen MYCN in Zellen ohne endogenes N-myc zu aktivieren. In der Zukunft könnte durch Verhinderung der Bindung von E2F-Proteinen an den MYCN-Promotor oder durch gentherapeutische Ansätze, die z.B. mittels viraler Infektion den Signalweg zwischen p16 und E2F rekonstruieren, die Expression von N-myc in Neuroblastomen gesenkt werden, so dass die Aggressivität der Tumore reduziert und die individuelle Prognose der Patienten verbessert werden könnte

CO(JJ=1-0) mapping survey of 64 galaxies in the Fornax cluster with the ALMA Morita array

We conduct a $^{12}$C$^{16}$O($J$=1-0) (hereafter CO) mapping survey of 64 galaxies in the Fornax cluster using the ALMA Morita array in cycle 5. CO emission is detected from 23 out of the 64 galaxies. Our sample includes dwarf, spiral and elliptical galaxies with stellar masses of $M_{\rm star}\sim10^{6.3-11.6}$~M$_\odot$. The achieved beam size and sensitivity are $15''\times8''$ and $\sim12$~mJy~beam$^{-1}$ at the velocity resolution of $\sim10$~km~s$^{-1}$, respectively. We study the cold-gas (molecular- and atomic-gas) properties of 38 subsamples with $M_{\rm star}>10^9$~M$_\odot$ combined with literature HI data. We find that: (1) the low star-formation (SF) activity in the Fornax galaxies is caused by the decrease in the cold-gas mass fraction with respect to stellar mass (hereafter, gas fraction) rather than the decrease of the SF efficiency from the cold gas; (2) the atomic-gas fraction is more heavily reduced than the molecular-gas fraction of such galaxies with low SF activity. A comparison between the cold-gas properties of the Fornax galaxies and their environmental properties suggests that the atomic gas is stripped tidally and by the ram pressure, which leads to the molecular gas depletion with an aid of the strangulation and consequently SF quenching. Pre-processes in the group environment would also play a role in reducing cold-gas reservoirs in some Fornax galaxies.Comment: 53 pages, 41 figures, accepted for publication in ApJ