Galactic Centers near and far - Sub-millimeter Observations of three Seyfert galaxies and the Galactic Center

The evolution of galaxies in terms of mass accretion and matter transport is still an open topic in research. My thesis consists of two parts that are bridged by a common theme: the properties of the interstellar medium interstellar matter (ISM) and star formation in centers of galaxies, studied in the (sub-)mm wavelength regime. The first part of my thesis deals with the results from Submillimeter Array (SMA) ob- servations of molecular gas (low CO transitions) at sub-kpc (∼3′′) resolution of three Seyfert 1 galaxies from the ’low-luminosity quasi stellar object (LLQSO) sample’, which covers a redshift range of z ∼ 0.01 - 0.06. The goal of the LLQSO sample is investigate the signs of internal or external triggers enhanced activity (i.e., star formation and accretion onto the supermassive black hole (SMBH)) in the centers of galaxies and their frequency with respect to the nuclear activity. Two sources, HE 0433-1028 and HE 1108-2813, were observed in 12CO(2–1) and 13CO(2–1) and the third, HE 1029-1831, in 12CO(3–2) and HCO+(4–3) line emission. In- triguingly, in all three galaxies the molecular gas accumulates at the center within a radius ~ 20 in the central region, indicating them to be warm and/or turbulent. Strikingly, also the 12CO(3–2)/(1–0) line luminosity ratio in HE 1029-1831 suggests a higher excitation phase with r31 ∼ 1, apart from the cold or diffuse gas phase implied by r21 ∼ 0.5 for all three of them. From this, together with the Luminous Infrared Galaxy (LIRG) typical infrared luminosities of L_IR ≥ 10^11 L⊙, I conclude that the emission in the centers of these Seyferts is strongly affected by diffuse gas due to violent star formation. Indeed, the centers of these galaxies seem to contain a circumnuclear starburst with minimum molecular gas mass and starformation rate (SFR) surface densities around Σ_mol = 70 - 540 M⊙ pc−2 and Σ_SFR = 1.3 - 3.8 M⊙ kpc−2 yr−1. Therefore, the galaxies’ ISM state is likely to be better described by a mass conversion factor typical for Ultraluminous Infrared Galaxies (ULIRGs), as suggested by the dynamical and dust masses. My work on these data shows how much information on the state of the molecular gas can already be obtained from these medium spatial resolutions, i.e. on 0.5 - 1 kpc-scales. The second part covers interferometric continuum and line emission data from the Atacama Large Millimeter/submillimeter Array (ALMA) of the inner 4 parsec (approximately 100′′) surrounding the SMBH, Sagittarius A* (Sgr A*), at the Galactic Center (GC). It is a region of extreme conditions not only in terms of intense IR to UV radiation from the nuclear stellar/star cluster (NSC) and X-ray emission from a population of stellar remnants and Sgr A*, but especilly in terms of turbulence and shocks due to stellar winds and tidal shear. Furthermore, it comprises several overlapping molecular and ionized structures that can be studied in term of feeding inflow and star formation potential. Its proximity makes the GC a unique laboratory for our understanding of galactic nuclei and galaxy evolution on the smallest accessible scales. I present serendipitous detections of line emission towards Sgr A* and its environment with ALMA in band 3, 6, and 7. This up to now highest resolution (<0.75′′) view of the GC in the sub-millimeter (sub-mm) domain shows molecular gas at projected distances 1′′ from the SMBH. Among the highlights are: the very first 340 GHz map of the minispiral, the very first and highly resolved detection of sub-mm molecular emission in the immedi- ate vicinity of the SMBH, and the highly resolved structures of circumnuclear disk (CND) features, especially of a region comprising a methanol class I maser closest to the SMBH. The emission in H39α and of the 100 GHz continuum imply a uniform electron temper- ature around Te ∼ 6000 K for the minispiral. Sgr A* has a spectral index (S ∝ ν^α) of α ∼ 0.5 at 100 - 250 GHz and α ∼ 0.0 at 230 - 340 GHz. The spectral indices of the luminous objects in the inner minispiral tend to -0.1 indication Bremsstrahlung emission, while the minispiral exterior shows the growing importance of the dust component with increasing frequency. The clumpy molecular gas distribution is represented best by the CS emission. Further species detected are H13CO+, HC3N, SiO, SO, C2H, CH3OH, 13CS and N2H+. Most of the emission can be found at positive velocities and in a region limited by the sources IRS 3 and 7, and the minispiral Bar and Northern Arm. For some few regions in the field, the molecular emission appears at velocities of up to 200 km s−1. Probably, this central association (CA) of clouds is an infalling group of clouds composed of denser cloud cores and diffuse gas. I cal- culated three times higher CS/X (X: any other observed molecule) ratios for the CA than for the CND which hints at a combination of higher excitation - by a temperature gradient and/or IR-pumping - and abundance enhancement due to UV- and/or X-ray emission. Assuming the NSC as the cause, CA must be closer to the center than the CND is to the center. Within the CND itself, I discerned two interesting regions: One region emits in lines of all molecular species and higher energy levels observed in this and earlier studies. Further- more, it harbours a methanol class I maser. The other region shows line ratios similar to the CA. Beyond the CND, I discover that the largest accumulations of traditionally quies- cent gas tracer N2H+ match the largest infared (IR) dark clouds in the field. The previously detected methanol class I masers in these infrared dark clouds (IRDCs) coincide with the methanol emission observed by ALMA. I conclude, that all of these special regions should be investigated in more detail in the context of hot/cold core and extreme photon dominated region (PDR)/X-ray dominated region (XDR) chemistry and consequent star formation in the GC. My work on these ALMA Cycle 0 data give a prospect on the many riddles to solve - and to discover - thanks to the superb resolution of the current ALMA facility.