Simulations of the Origin and Fate of the Galactic Center Cloud G2

We investigate the origin and fate of the recently discovered gas cloud G2 close to the Galactic Center. Our hydrodynamical simulations focussing on the dynamical evolution of the cloud in combination with currently available observations favor two scenarios: a Compact Cloud which started around the year 1995 and a Spherical Shell of gas, with an apocenter distance within the disk(s) of young stars and a radius of a few times the size of the Compact Cloud. The former is able to explain the detected signal of G2 in the position-velocity diagram of the Br gamma emission of the year 2008.5 and 2011.5 data. The latter can account for both, G2's signal as well as the fainter extended tail-like structure G2t seen at larger distances from the black hole and smaller velocities. In contrast, gas stripped from a compact cloud by hydrodynamical interactions is not able to explain the location of the detected G2t emission in the observed position-velocity diagrams. This favors the Spherical Shell Scenario and might be a severe problem for the Compact Cloud as well as the so-called Compact Source Scenario. From these first idealized simulations we expect a roughly constant feeding of the supermassive black hole through a nozzle-like structure over a long period, starting shortly after the closest approach in 2013.51 for the Compact Cloud. If the matter accretes in the hot accretion mode, we do not expect a significant boost of the current activity of Sgr A* for the Compact Cloud model, but a boost of the average infrared and X-ray luminosity by roughly a factor of 80 for the Spherical Shell scenario with order of magnitude variations on a timescale of a few months. The near-future evolution of the cloud will be a sensitive probe of the conditions of the gas distribution in the milli-parsec environment of the massive black hole in the Galactic Center.Comment: 16 pages, 16 figures, accepted by Ap

BUDHIES IV:Deep 21-cm neutral Hydrogen, optical, and UV imaging data of Abell 963 and Abell 2192 at z ≃ 0.2

In this paper, we present data from the Blind Ultra-Deep H I Environmental Survey (BUDHIES), which is a blind 21-cm H I spectral line imaging survey undertaken with the Westerbork Synthesis Radio Telescope. Two volumes were surveyed, each with a single pointing and covering a redshift range of 0.164 < z < 0.224. Within these two volumes, this survey targeted the clusters Abell 963 and Abell 2192, which are dynamically different and offer unique environments to study the process of galaxy evolution within clusters. With an integration time of 117 × 12 h on Abell 963 and 72 × 12 h on Abell 2192, a total of 166 galaxies were detected and imaged in H I. While the clusters themselves occupy only 4 per cent of the 73 400 Mpc3 surveyed by BUDHIES, most of the volume consists of large-scale structures in which the clusters are embedded, including foreground and background overdensities and voids. We present the data processing and source detection techniques and counterpart identification based on a wide-field optical imaging survey using the Isaac Newton Telescope and deep ultraviolet (UV) Galaxy Evolution Explorer (GALEX) imaging. Finally, we present H I and optical catalogues of the detected sources as well as atlases of their global H I properties, which include integrated column density maps, position-velocity diagrams, global H I profiles, and optical and UV images of the H I sources

Early Science with the Large Millimeter Telescope: COOL BUDHIES I - a pilot study of molecular and atomic gas at z~0.2

An understanding of the mass build-up in galaxies over time necessitates tracing the evolution of cold gas (molecular and atomic) in galaxies. To that end, we have conducted a pilot study called CO Observations with the LMT of the Blind Ultra-Deep H I Environment Survey (COOL BUDHIES). We have observed 23 galaxies in and around the two clusters Abell 2192 (z = 0.188) and Abell 963 (z = 0.206), where 12 are cluster members and 11 are slightly in the foreground or background, using about 28 total hours on the Redshift Search Receiver (RSR) on the Large Millimeter Telescope (LMT) to measure the $^{12}$CO J = 1 --> 0 emission line and obtain molecular gas masses. These new observations provide a unique opportunity to probe both the molecular and atomic components of galaxies as a function of environment beyond the local Universe. For our sample of 23 galaxies, nine have reliable detections (S/N$\geq$3.6) of the $^{12}$CO line, and another six have marginal detections (2.0 < S/N < 3.6). For the remaining eight targets we can place upper limits on molecular gas masses roughly between $10^9$ and $10^{10} M_\odot$. Comparing our results to other studies of molecular gas, we find that our sample is significantly more abundant in molecular gas overall, when compared to the stellar and the atomic gas component, and our median molecular gas fraction lies about $1\sigma$ above the upper limits of proposed redshift evolution in earlier studies. We discuss possible reasons for this discrepancy, with the most likely conclusion being target selection and Eddington bias.Comment: MNRAS, submitte

Simulations of Direct Collisions of Gas Clouds with the Central Black Hole

We perform numerical simulations of clouds in the Galactic Centre (GC) engulfing the nuclear super-massive black hole and show that this mechanism leads to the formation of gaseous accretion discs with properties that are similar to the expected gaseous progenitor discs that fragmented into the observed stellar disc in the GC. As soon as the cloud hits the black hole, gas with opposite angular momentum relative to the black hole collides downstream. This process leads to redistribution of angular momentum and dissipation of kinetic energy, resulting in a compact gaseous accretion disc. A parameter study using thirteen high resolution simulations of homogeneous clouds falling onto the black hole and engulfing it in parts demonstrates that this mechanism is able to produce gaseous accretion discs that could potentially be the progenitor of the observed stellar disc in the GC. A comparison of simulations with different equations of state (adiabatic, isothermal and full cooling) demonstrates the importance of including a detailed thermodynamical description. However the simple isothermal approach already yields good results on the radial mass transfer and accretion rates, as well as disc eccentricities and sizes. We find that the cloud impact parameter strongly influences the accretion rate whereas the impact velocity has a small affect on the accretion rate.Comment: 21 pages, 18 figures, Accepted for publication in MNRA

Dense Gas in Nearby Galaxies: XVII. The Distribution of Ammonia in NGC253, Maffei2 and IC342

The central few 100 pc of galaxies often contain large amounts of molecular gas. The chemical and physical properties of these extragalactic star formation regions differ from those in galactic disks, but are poorly constrained. This study aims to develop a better knowledge of the spatial distribution and kinetic temperature of the dense neutral gas associated with the nuclear regions of three prototypical spiral galaxies, NGC253, IC342, and Maffei2. VLA CnD and D configuration measurements have been made of three ammonia (NH3) inversion transitions. The (J,K)=(1,1) and (2,2) transitions of NH3 were imaged toward IC342 and Maffei2. The (3,3) transition was imaged toward NGC253. The entire flux obtained from single-antenna measurements is recovered for all three galaxies observed. Derived lower limits to the kinetic temperatures determined for the giant molecular clouds in the centers of these galaxies are between 25 and 50K. There is good agreement between the distributions of NH3 and other H2 tracers, such as rare CO isotopologues or HCN, suggesting that NH3 is representative of the distribution of dense gas. The "Western Peak" in IC342 is seen in the (6,6) line but not in lower transitions, suggesting maser emission in the (6,6) transition.Comment: 13 pages, 8 figures, latex format, accepted by A&

Mapping photodissociation and shocks in the vicinity of Sgr A*

We have obtained maps of the molecular emission within the central five arcminutes (12 pc) of the Galactic center (GC) in selected molecular tracers: SiO(2-1), HNCO(5_{0,5}-4_{0,4}), and the J=1-->0 transition of H^{13}CO+, HN^{13}C, and C^{18}O at an angular resolution of 30" (1.2 pc). The mapped region includes the circumnuclear disk (CND) and the two surrounding giant molecular clouds (GMCs) of the Sgr A complex, known as the 20 and 50 km s^{-1} molecular clouds.Additionally, we simultaneously observed the J=2-1 and 3-2 transitions of SiO toward selected positions to estimate the physical conditions of the molecular gas. The SiO(2-1) and H^{13}CO+(1-0) emission covers the same velocity range and presents a similar distribution. In contrast, HNCO(5-4) emission appears in a narrow velocity range mostly concentrated in the 20 and 50 km s^{-1} GMCs. The HNCO column densities and fractional abundances present the highest contrast, with difference factors of $\geq$60 and 28, respectively. Their highest values are found toward the cores of the GMCs, whereas the lowest ones are measured at the CND. SiO abundances do not follow this trend, with high values found toward the CND, as well as the GMCs. By comparing our abundances with those of prototypical Galactic sources we conclude that HNCO, similar to SiO, is ejected from grain mantles into gas-phase by nondissociative C-shocks. This results in the high abundances measured toward the CND and the GMCs. However, the strong UV radiation from the Central cluster utterly photodissociates HNCO as we get closer to the center, whereas SiO seems to be more resistant against UV-photons or it is produced more efficiently by the strong shocks in the CND. Finally, we discuss the possible connections between the molecular gas at the CND and the GMCs using the HNCO/SiO, SiO/CS, and HNCO/CS intensity ratios as probes of distance to the Central cluster.Comment: 26 pages plus 2 appendixes with additional figures. 17 figures in total. Accepted for publication in A&

Traces of past activity in the Galactic Centre

The Milky Way centre hosts a supermassive Black Hole (BH) with a mass of ~4*10^6 M_Sun. Sgr A*, its electromagnetic counterpart, currently appears as an extremely weak source with a luminosity L~10^-9 L_Edd. The lowest known Eddington ratio BH. However, it was not always so; traces of "glorious" active periods can be found in the surrounding medium. We review here our current view of the X-ray emission from the Galactic Center (GC) and its environment, and the expected signatures (e.g. X-ray reflection) of a past flare. We discuss the history of Sgr A*'s past activity and its impact on the surrounding medium. The structure of the Central Molecular Zone (CMZ) has not changed significantly since the last active phase of Sgr A*. This relic torus provides us with the opportunity to image the structure of an AGN torus in exquisite detail.Comment: Invited refereed review. Chapter of the book: "Cosmic ray induced phenomenology in star forming environments" (eds. Olaf Reimer and Diego F. Torres

Effectiveness, safety/tolerability of OBV/PTV/r ± DSV in patients with HCV genotype 1 or 4 with/without HIV-1 co-infection, chronic kidney disease (CKD) stage IIIb/V and dialysis in Spanish clinical practice – preliminary data Vie-KinD study

Poster presentatio

Star Formation and Dynamics in the Galactic Centre

The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A., 'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201