181 research outputs found
Gas infall towards Sgr A* from the clumpy circumnuclear disk
We present the first large-scale mosaic performed with the Submillimeter
Array (SMA) in the Galactic center. We have produced a 25-pointing mosaic,
covering a ~2' x 2' area around Sgr A*. We have detected emission from two
high-density molecular tracers, HCN(4-3) and CS(7-6), the latter never before
reported in this region. The data have an angular resolution of 4.6" x 3.1",
and the spectral window coverage is from -180 km/s to 1490 km/s for HCN(4-3)
and from -1605 km/s to 129 km/s for CS(7-6). Both molecular tracers present a
very clumpy distribution along the circumnuclear disk (CND), and are detected
with a high signal-to-noise ratio in the southern part of the CND, while they
are weaker towards the northern part. Assuming that the clumps are as close to
the Galactic center as their projected distances, they are still dense enough
to be gravitationally stable against the tidal shear produced by the
supermassive black hole. Therefore, the CND is a non-transient structure. This
geometrical distribution of both tracers suggests that the southern part of the
CND is denser than the northern part. Also, by comparing the HCN(4-3) results
with HCN(1-0) results we can see that the northern and the southern parts of
the CND have different excitation levels, with the southern part warmer than
the northern. Finally, we compare our results with those obtained with the
detection of NH3, which traces the warmer and less dense material detected in
the inner cavity of the CND. We suggest that we are detecting the origin point
where a portion of the CND becomes destabilized and approaches the dynamical
center of the Milky Way, possibly being impacted by the southern streamer and
heated on its way inwards.Comment: 35 pages, 25 figures, 2 tables, accepted for publication in ApJ,
emulate-apj styl
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
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
Surviving the hole I: Spatially resolved chemistry around Sgr A*
The interstellar region within the few central parsecs around the
super-massive black hole, Sgr A* at the very Galactic center is composed by a
number of overlapping molecular structures which are subject to one of the most
hostile physical environments in the Galaxy. We present high resolution
(4"x3"~0.16x0.11 pc) interferometric observations of CN, 13CN, H2CO, SiO,
c-C3H2 and HC3N emission at 1.3 mm towards the central ~4 pc of the Galactic
center region. Strong differences are observed in the distribution of the
different molecules. The UV resistant species CN, the only species tracing all
previously identified circumnuclear disk (CND) structures, is mostly
concentrated in optically thick clumps in the rotating filaments around Sgr A*.
H2CO emission traces a shell-like structure that we interpret as the expansion
of Sgr A East against the 50 km/s and 20 km/s giant molecular clouds (GMCs). We
derive isotopic ratios 12C/13C~15-45 across most of the CND region. The densest
molecular material, traced by SiO and HC3N, is located in the southern CND. The
observed c-C3H2/HC3N ratio observed in the region is more than an order of
magnitude lower than in Galactic PDRs. Toward the central region only CN was
detected in absorption. Apart from the known narrow line-of-sight absorptions,
a 90 km/s wide optically thick spectral feature is observed. We find evidences
of an even wider (>100 km/s) absorption feature. Around 70-75% of the gas mass,
concentrated in just the 27% densest molecular clumps, is associated with
rotating structures and show evidences of association with each of the arcs of
ionized gas in the mini-spiral structure. Chemical differentiation has been
proven to be a powerful tool to disentangle the many overlapping molecular
components in this crowded and heavily obscured region.Comment: 12 pages, 22 figures. Accepted for publication in Astronomy and
Astrophysic
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
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 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/N3.6) of the 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 and . 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 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
Gas dynamics of the central few parsec region of NGC 1068 fuelled by the evolving nuclear star cluster
High resolution observations with the NIR adaptive optics integral field
spectrograph SINFONI at the VLT proved the existence of massive and young
nuclear star clusters in the centres of a sample of Seyfert galaxies. With the
help of three-dimensional high resolution hydrodynamical simulations with the
Pluto code, we follow the evolution of such clusters, focusing on stellar mass
loss. This leads to clumpy or filamentary inflow of gas on large scales (tens
of parsec), whereas a turbulent and very dense disc builds up on the parsec
scale. In order to capture the relevant physics in the inner region, we treat
this disc separately by viscously evolving the radial surface density
distribution. This enables us to link the tens of parsec scale region
(accessible via SINFONI observations) to the (sub-)parsec scale region
(observable with the MIDI instrument and via water maser emission). In this
work, we concentrate on the effects of a parametrised turbulent viscosity to
generate angular momentum and mass transfer in the disc and additionally take
star formation into account. Input parameters are constrained by observations
of the nearby Seyfert 2 galaxy NGC 1068. At the current age of its nuclear
starburst of 250 Myr, our simulations yield disc sizes of the order of 0.8 to
0.9 pc, gas masses of 1.0e6 solar masses and mass transfer rates of 0.025 solar
masses per year through the inner rim of the disc. This shows that our large
scale torus model is able to approximately account for the disc size as
inferred from interferometric observations in the mid-infrared and compares
well to the extent and mass of a rotating disc structure as inferred from water
maser observations. Several other observational constraints are discussed as
well.Comment: 13 pages, 11 figures, accepted for publication in MNRAS, updated
author list and reference
Comparative Cytotoxic Activity of Hydroxytyrosol and Its Semisynthetic Lipophilic Derivatives in Prostate Cancer Cells
A high adherence to a Mediterranean diet has been related to numerous beneficial effects in human health, including a lower incidence and mortality of prostate cancer (PCa). Olive oil is an important source of phenolic bioactive compounds, mainly hydroxytyrosol (HT), of this diet. Because of the growing interest of this compound and its derivatives as a cancer chemopreventive agent, we aimed to compare the in vitro effect of HT isolated from olive mill wastewaters and five semisynthetic alkyl ether, ester, and nitro-derivatives against prostate cancer (PCa) cell lines. The effect in cell proliferation was determined in RWPE-1, LNCaP, 22Rv1, and PC-3 cells by resazurin assay, the effect in cell migration by wound healing assay, and tumorsphere and colony formation were evaluated. The changes in key signaling pathways involved in carcinogenesis were assessed by using a phosphorylation pathway profiling array and by Western blotting. Antiproliferative effects of HT and two lipophilic derivatives [hydroxytyrosyl acetate (HT-Ac)/ethyl hydroxytyrosyl ether (HT-Et)] were significantly higher in cancerous PC-3 and 22Rv1 cells than in non-malignant RWPE-1 cells. HT/HT-Ac/HT-Et significantly reduced migration capacity in RWPE-1 and PC-3 and prostatosphere size and colony formation in 22Rv1, whereas only HT-Ac and HT-Et reduced these functional parameters in PC-3. The cytotoxic effect in 22Rv1 cells was correlated with modifications in the phosphorylation pattern of key proteins, including ERK1/2 and AKT. Consistently, HT-Ac and HT-Et decreased p-AKT levels in PC-3. In sum, our results suggest that HT and its lipophilic derivatives could be considered as potential therapeutic tools in PCa
Unleashing the Diagnostic, Prognostic and Therapeutic Potential of the Neuronostatin/GPR107 System in Prostate Cancer
Certain components of the somatostatin-system play relevant roles in Prostate Cancer (PCa), whose most aggressive phenotype (Castration-Resistant-PCa (CRPC)) remains lethal nowadays. However, neuronostatin and the G protein-coupled receptor 107 (GPR107), two novel members of the somatostatin-system, have not been explored yet in PCa. Consequently, we investigated the pathophysiological role of NST/GPR107-system in PCa. GPR107 expression was analyzed in well-characterized PCa patient′s cohorts, and functional/mechanistic assays were performed in response to GPR107-silencing and NST-treatment in PCa cells (androgen-dependent (AD: LNCaP) and androgen-independent (AI: 22Rv1/PC-3), which are cell models of hormone-sensitive and CRPC, respectively), and normal prostate cells (RWPE-1 cell-line). GPR107 was overexpressed in PCa and associated with key clinical parameters (e.g., advance stage of PCa, presence of vascular invasion and metastasis). Furthermore, GPR107-silencing inhibited proliferation/migration rates in AI-PCa-cells and altered key genes and oncogenic signaling-pathways involved in PCa aggressiveness (i.e., KI67/CDKN2D/MMP9/PRPF40A, SST5TMD4/AR-v7/In1-ghrelin/EZH2 splicing-variants and AKT-signaling). Interestingly, NST treatment inhibited proliferation/migration only in AI-PCa cells and evoked an identical molecular response than GPR107-silencing. Finally, NST decreased GPR107 expression exclusively in AI-PCa-cells, suggesting that part of the specific antitumor effects of NST could be mediated through a GPR107-downregulation. Altogether, NST/GPR107-system could represent a valuable diagnostic and prognostic tool and a promising novel therapeutic target for PCa and CRPC
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&
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