bluuebunny/crossref_metadata_2025_split huggingface dataset:
Young stellar disks formed by the collision of a molecular cloud with a circumnuclear disk at the Galactic center
Authors: Alig C. , Schartmann M. , Burkert A. , Dolag K. 
Published: May 2014

AbstractWe suggest a new formation mechanism for the inclined, sub-parsec scale and counterrotating stellar disks observed around the central black hole in the Milky Way Galactic center. The simulation of a single molecular cloud crashing into a circumnuclear ring of gas leads to the inflow of multiple streams of gas towards the central parsec region. The time delayed arrival of those streams forms multiple, sub-parsec scale accretion disks, with angular momentum depending on the ratio of cloud and circumnuclear ring material. These accretion disks could then be the progenitors which fragmented into the observed stellar disks. A similar event might have also led to the creation of the so-called minispiral in the Galactic center.
Cloud-cloud collision in the Sgr B2 molecular cloud complex
Authors: Tsuboi Masato , Miyazaki Atsushi , Handa Toshihiro 
Published: May 2014

AbstractWe present results from a high-resolution wide-field imaging observation of the central molecular zone (CMZ) in H13CO+J = (1 − 0) and SiO v=0, J = (2−1) emission lines by using the Nobeyama 45-m telescope in order to depict the high-density molecular gas mass distribution and explore molecular gas affected by interstellar shocks. We found a candidate for ongoing cloud-cloud collision in the Sgr B2 complex. This is identified as a hollow paraboloid-like structure in the l−b−v data cube of both emission lines. The central part of the feature is denser and warmer than the outer envelope and contains a vast amount of shocked molecular gas. These properties are consistent with those expected from simulations of cloud-cloud collisions in the CMZ.
Young stars in the Galactic center
Authors: Lu Jessica R. , Ghez Andrea M. , Morris Mark R. , Clarkson Will , Stolte Andrea , Do Tuan , Yelda Sylvana , Anderson Jay 
Published: May 2014

AbstractThe central parsec of our Galaxy hosts not only a supermassive black hole, but also a large population of young stars (age <6 Myr) whose presence is puzzling given how inhospitable the region is for star formation. The strong tidal forces require gas densities many orders of magnitude higher than is found in typical molecular clouds. Kinematic observations of this young nuclear cluster show complex structures, including a well-defined inner disk, but also a substantial off-disk population. Spectroscopic and photometric measurements indicate the initial mass function (IMF) differs significantly from the canonical IMF found in the solar neighborhood. These observations have led to a number of proposed star formation scenarios, such as an infalling massive star cluster, a single infalling molecular cloud, or cloud-cloud collisions. I will review recent works on the young stars in the central parsec and discuss connections with young nuclear star clusters in other galaxies, such as M31, and with star formation in the larger central molecular zone.
The Milky Way nuclear star cluster beyond 1 pc
Authors: Feldmeier A. , Neumayer N. , Seth A. , de Zeeuw P. T. , Schödel R. , Lützgendorf N. , Kissler-Patig M. , Nishiyama S. , Walcher C. J. 
Published: May 2014

AbstractWithin the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster, forming a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ∼75% of nearby galaxies. It is, however, not fully understood how nuclear clusters form. Because the Milky Way nuclear star cluster is at a distance of only 8 kpc, we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster a reference object for understanding the structure and assembly history of all nuclear star clusters.We have obtained an unparalleled data set using the near-infrared long-slit spectrograph ISAAC (VLT) in a novel drift-scan technique to construct an integral-field spectroscopic map of the central ∼10 × 8 pc of our Galaxy. To complement our data set we also observed fields out to a distance of ∼19 pc along the Galactic plane to disentangle the influence of the nuclear stellar disk.From this data set we extract a stellar kinematic map using the CO bandheads and an emission line kinematic map using H2 emission lines. Using the stellar kinematics, we set up a kinematic model for the Milky Way nuclear star cluster to derive its mass and constrain the central Galactic potential. Because the black hole mass in the Milky Way is precisely known, this kinematic data set will also serve as a benchmark for testing black hole mass modeling techniques used in external galaxies.
Unveiling the massive stars in the Galactic center
Authors: Dong H. , Mauerhan J. , Morris M. R. , Wang Q. D. , Cotera A. 
Published: May 2014

AbstractWe present our recent efforts to unveil and understand the origin of massive stars outside the three massive star clusters in the Galactic center. From our Hubble/NICMOS survey of the Galactic center, we have identified 180 Paschen-α emitting sources, most of which should be evolved massive stars with strong optically thin stellar winds. Recently, we obtained Gemini GNIRS/NIFS H- and K-band spectra of eight massive stars near the Arches cluster. From their radial velocities, ages and masses, we suggest that in our sample, two stars are previous members of the Arches cluster, while other two stars embedded in the H1/H2 Hii regions formed in-situ.
New orbital analysis of stars at the Galactic center using speckle holography and orbital priors
Authors: Boehle Anna , Schödel Rainer , Meyer Leo , Ghez Andrea M. 
Published: May 2014

AbstractWe present initial results of a study that has more than doubled the time baseline for astrometric measurements of faint stars orbiting the supermassive black hole (SMBH) at the Galactic center. The advent of adaptive optics has enabled stars as faint as K = 19 mag to be tracked at 50 mas resolution for the last decade. While similar resolution images exist from the prior decade, they were obtained from speckle imaging data analyzed with the technique of shift-and-add, which limited detections to stars brighter than K = 16 mag. By improving the speckle data analysis technique with speckle holography and using prior orbital knowledge, we are now able to track stars as faint as ∼18 mag at 50 mas resolution through the early Keck speckle data sets (1995-2005). This methodology has already led to the detection of two short-period stars never previously seen in speckle images, such that our data now spans their full orbits. We can now better constrain the orbital parameters of all stars in the intriguing “S-star cluster,” which will ultimately give us insight into the origin of these stars and be used to probe the curvature of space-time in the unexplored regime near a SMBH.
Observations of NIR polarized light from Sagittarius A*
Authors: Shahzamanian B. , Eckart A. , Zamaninasab M. , Witzel G. , Sabha N. 
Published: May 2014

AbstractWe present a brief overview of results obtained from near-infrared polarized observations of Sgr A*, which is associated with the supermassive black hole at the center of the Milky Way. The observations have been carried out using the NACO adaptive optics instrument at the VLT UT4 in the infrared Ks-band from 2004 to 2012. Several polarized flares have been observed in this time interval which allow us to determine the statistical properties of NIR linearly polarized light from Sgr A*. Linear polarization at 2.2 μm and its variations can help us to constrain the physical conditions of the accretion process around this supermassive black hole.
Radio emission from the bow shock of G2
Authors: Crumley P. , Kumar P. 
Published: May 2014

AbstractThe radio flux from the synchrotron emission of electrons accelerated in the forward bow shock of G2 is expected to have peaked when the forward shock passes close to the pericenter from the Galactic center, around autumn of 2013. This radio flux is model dependent. We find that if G2 were to be a momentum-supported bow shock of a faint star with a strong wind, the radio synchrotron flux from the forward-shock heated ISM is well below the quiescent radio flux of Sgr A*. By contrast, if G2 is a diffuse cloud, the radio flux is predicted to be much larger than the quiescent radio flux and therefore should have already been detected or will be detected shortly. No such radiation has been observed to date. Radio measurements can reveal the nature of G2 well before G2 completes its periapsis passage.
The Galactic center X-ray transients AX J1745.6–2901 and GRS 1741–2853
Authors: Degenaar N. , Wijnands R. , Reynolds M. T. , Miller J. M. , Kennea J. , Gehrels N. 
Published: May 2014

AbstractAX J1745.6–2901 and GRS 1741–2853 are two transient neutron star low-mass X-ray binaries that are located within ≃ 10′ from the Galactic center. Multi-year monitoring observations with the Swift/XRT has exposed several accretion outbursts from these objects. We report on their updated X-ray light curves and renewed activity that occurred in 2010–2013.
3D moving mesh simulations of Galactic center cloud G2
Authors: Fragile P. C. , Anninos P. , Murray S. D. 
Published: May 2014

AbstractUsing three-dimensional, moving-mesh simulations, we investigate the future evolution of the recently discovered gas cloud G2 traveling through the galactic center. From our simulations we expect an average feeding rate onto Sgr A* in the range of (5−19) × 10−8M⊙ yr−1 beginning in 2014. This accretion varies by less than a factor of three on timescales ∼ 1 month, and shows no more than a factor of 10 difference between the maximum and minimum observed rates within any given model. These rates are comparable to the current estimated accretion rate in the immediate vicinity of Sgr A*, although they represent only a small (< 10%) increase over the current expected feeding rate at the effective inner boundary of our simulations (racc = 750 RS ∼ 1015 cm). We also explore multiple possible equations of state to describe the gas. In examining the Br-γ light curves produced from our simulations, we find that all of our isothermal models predict significant (factor of 10) enhancements in the luminosity of G2 as it approaches pericenter, in conflict with observations. Models that instead allow the cloud to heat as it is compressed do better at matching observations.
Multiple accretion events as a trigger for Sagittarius A* activity
Authors: Kunneriath D. , Czerny B. , Karas V. , Das T. K. 
Published: May 2014

AbstractThe Galactic center supermassive black hole is surrounded by orbiting clouds of gas. These clumps of gas may collide with each other, losing angular momentum and plunging towards the center. Observations of X-ray reflection from molecular clouds surrounding the Galactic center show evidence for enhanced activity of Sagittarius A* during the past few hundred years. These observations enable us to place constraints on the nature of past accretion events responsible for this enhanced activity. We model the source intrinsic luminosity of Sgr A* using multiple accretion events occurring at various moments in time, characterized by a range of angular momentum We also applied our scheme to the case of G2 cloud in the Galactic center.
Hydrodynamical simulations of G2 interpreted as a diffuse gas cloud
Authors: Schartmann M. , Burkert A. , Ballone A. , Alig C. , Gillessen S. , Genzel R. , Eisenhauer F. , Fritz T. 
Published: May 2014

AbstractRecently the gas and dust cloud “G2” was discovered on a highly eccentric orbit around the massive black hole in the Galactic center. The orbit will bring the cloud as close as 2400 Schwarzschild radii to Sgr A* beginning of 2014. With the help of hydrodynamical simulations using the PLUTO code, we investigate possible origins and the fate of the cloud in the coming years. In this proceedings article, we concentrate on a scenario where G2 is interpreted as a diffuse gas cloud and show its detailed evolution in the observable position-velocity diagrams. We further elaborate on the problem of the tail emission which might or might not be related to the G2 cloud.
Feeding and feedback in nearby AGN – comparison with the Milky Way center
Authors: Storchi-Bergmann T. 
Published: May 2014

AbstractI discuss feeding and feedback processes observed in the inner few hundred parsecs of nearby active galaxies using integral field spectroscopy at spatial resolutions of a few to tens of parsecs. Signatures of feedback include outflows from the nucleus with velocities ranging from 200 to 1000 km s−1, with mass outflow rates between 0.5 and a few M⊙ yr−1. Signatures of feeding include the observation of gas inflows along nuclear spirals and filaments, with velocities ranging from 50 to 100 km s−1 and mass flow rates from 0.1 to ∼1 M⊙ yr−1. These rates are 2–3 orders of magnitude larger than the mass accretion rate to the supermassive black hole (SMBH). These inflows can thus lead, during less than one activity cycle, to the accumulation of enough gas in the inner few hundred parsecs, to trigger the formation of new stars, leading to the growth of the galaxy bulge. Young to intermediate age stars have indeed been found in circumnuclear rings around a number of Active Galactic Nuclei (AGN). In particular, one of these rings, with radius of ≈ 100 pc is observed in the Seyfert 2 galaxy NGC 1068, and is associated to an off-centered molecular ring, very similar to that observed in the Milky Way (MW). On the basis of an evolutionary scenario in which gas falling into the nuclear region triggers star formation followed by the triggering of nuclear activity, we speculate that, in the case of the MW, molecular gas has already accumulated within the inner ≈ 100 pc to trigger the formation of new stars, as supported by the presence of blue stars close to the galactic center. A possible increase in the star-formation rate in the nuclear region will then be followed, probably tens of millions of years later, by the triggering of nuclear activity in Sgr A*.
Daily monitor of Sagittarius A* at 22 GHz with the Japanese VLBI Network
Authors: Tsuboi M. , Asaki Y. , Yonekura Y. , Miyamoto Y. , Kaneko H. , Seta M. , Nakai N. , Kameya O. , Miyoshi M. , Takaba H. , Wakamatsu K. , Fukuzaki Y. , Morimitsu T. , Uehara K. , Sekido M. , Oka T. , Takekawa S. , Omodaka T. , Handa T. , Takumi A. 
Published: May 2014

AbstractWe have been monitoring the flux density of Sagittarius A* (Sgr A*) at 22 GHz since DOY=42 (11 Feb. 2013) with a sub-array of the Japanese VLBI Network in order to search the increase of 22-GHz emission from Sgr A* induced by the interaction of the G2 cloud with the accretion disk. The flux densities observed until DOY=322 (18 Nov. 2013) are consistent with the previously observed values before the approaching of the cloud. We have detected no large flare during this period.
Sturm und Drang: The turbulent, magnetic tempest in the Galactic center
Authors: Lacki Brian C. 
Published: May 2014

AbstractThe Galactic center central molecular zone (GCCMZ) bears similarities with extragalactic starburst regions, including a high supernova (SN) rate density. As in other starbursts like M82, the frequent SNe can heat the ISM until it is filled with a hot (∼ 4 × 107 K) superwind. Furthermore, the random forcing from SNe stirs up the wind, powering Mach 1 turbulence. I argue that a turbulent dynamo explains the strong magnetic fields in starbursts, and I predict an average B ∼70 μG in the GCCMZ. I demonstrate how the SN driving of the ISM leads to equipartition between various pressure components in the ISM. The SN-heated wind escapes the center, but I show that it may be stopped in the Galactic halo. I propose that the Fermi bubbles are the wind's termination shock.
Detecting gravitational waves from the Galactic center with pulsar timing
Authors: Ray Alak , Kocsis Bence , Zwart Simon Portegies 
Published: May 2014

AbstractBlack holes orbiting the supermassive black hole (SMBH) Sgr A* in the Galactic center (GC) of the Milky Way generate gravitational waves (GW). The resulting spectrum, due to stars and black holes (BHs), is continuous below 40 nHz while individual BHs within about 200 AU of the central SMBH stick out in the spectrum at higher frequencies. The GWs can be detected by timing radio pulsars within a few parsecs of this region. Future observations with the Square Kilometer Array of such pulsars with sufficient timing accuracy may be sensitive to signals from intermediate mass BHs (IMBH) in a 3 year observation baseline. The recent detection of radio pulsations from the magnetar SGR J1745–29 very near the GC opens up the possibilities of detecting millisecond pulsars (which can be used as probes of the GWs) through lines of sight with only moderate pulse and angular broadening due to scattering.
First results from the NuSTAR “mini-survey” of the Galactic center region
Authors: Hailey Charles J. ,   the NuSTAR Team
Published: May 2014

AbstractOne of the major science objectives of the Nuclear Spectroscopic Telescope Array (NuSTAR) observatory is to perform the first sub-arcminute, hard X-ray survey of several square degrees of the Galactic plane, centered on a region near the Galactic center. As a prelude to the full survey, which began in July 2013, NuSTAR conducted a ∼500 ks, 0.3 × 0.4° “mini-survey” focused on Sgr A* and its environs. We present analysis of several candidate pulsar wind nebulae and filaments, which are revealed to be intense sources of X-ray emission at >10 keV.
The origin of the Galactic center diffuse X-ray emission investigated by near-infrared imaging and polarimetric observations
Authors: Nishiyama Shogo , Yasui Kazuki , Nagata Tetsuya , Yoshikawa Tatsuhito , Uchiyama Hideki , Tamura Motohide 
Published: May 2014

AbstractThe origin of the Galactic center diffuse X-ray emission (GCDX) is still under intense investigation. We have found a clear excess in a longitudinal GCDX profile over a stellar number density profile in the nuclear bulge region, suggesting a significant contribution of diffuse, interstellar hot plasma to the GCDX. We have estimated that contributions of an old stellar population to the GCDX are ∼50% and ∼20% in the nuclear stellar disk and nuclear star cluster, respectively. Our near-infrared polarimetric observations show that the GCDX region is permeated by a large scale, toroidal magnetic field. Together with observed magnetic field strengths in nearly energy equipartition, the interstellar hot plasma could be confined by the toroidal magnetic field.
Mixed lineage kinases activate MEK independently of RAF to mediate resistance to RAF inhibitors
Authors: Marusiak Anna A. , Edwards Zoe C. , Hugo Willy , Trotter Eleanor W. , Girotti Maria R. , Stephenson Natalie L. , Kong Xiangju , Gartside Michael G. , Fawdar Shameem , Hudson Andrew , Breitwieser Wolfgang , Hayward Nicholas K. , Marais Richard , Lo Roger S. , Brognard John 
Published: May 2014

AbstractRAF inhibitor therapy yields significant reductions in tumour burden in the majority of V600E-positive melanoma patients; however, resistance occurs within 2–18 months. Here we demonstrate that the mixed lineage kinases (MLK1–4) are MEK kinases that reactivate the MEK/ERK pathway in the presence of RAF inhibitors. Expression of MLK1–4 mediates resistance to RAF inhibitors and promotes survival in V600E-positive melanoma cell lines. Furthermore, we observe upregulation of the MLKs in 9 of 21 melanoma patients with acquired drug resistance. Consistent with this observation, MLKs promote resistance to RAF inhibitors in mouse models and contribute to acquired resistance in a cell line model. Lastly, we observe that a majority of MLK1 mutations identified in patients are gain-of-function mutations. In summary, our data demonstrate a role for MLKs as direct activators of the MEK/ERK pathway with implications for melanomagenesis and resistance to RAF inhibitors.
Relativistic Quantum Metrology: Exploiting relativity to improve quantum measurement technologies
Authors: Ahmadi Mehdi , Bruschi David Edward , Sabín Carlos , Adesso Gerardo , Fuentes Ivette 
Published: May 2014

AbstractWe present a framework for relativistic quantum metrology that is useful for both Earth-based and space-based technologies. Quantum metrology has been so far successfully applied to design precision instruments such as clocks and sensors which outperform classical devices by exploiting quantum properties. There are advanced plans to implement these and other quantum technologies in space, for instance Space-QUEST and Space Optical Clock projects intend to implement quantum communications and quantum clocks at regimes where relativity starts to kick in. However, typical setups do not take into account the effects of relativity on quantum properties. To include and exploit these effects, we introduce techniques for the application of metrology to quantum field theory. Quantum field theory properly incorporates quantum theory and relativity, in particular, at regimes where space-based experiments take place. This framework allows for high precision estimation of parameters that appear in quantum field theory including proper times and accelerations. Indeed, the techniques can be applied to develop a novel generation of relativistic quantum technologies for gravimeters, clocks and sensors. As an example, we present a high precision device which in principle improves the state-of-the-art in quantum accelerometers by exploiting relativistic effects.
Using embryonic stem cells to understand how glycosaminoglycans regulate differentiation
Authors: Holley Rebecca J. , Meade Kate A. , Merry Catherine L.R. 
Published: May 2014

Differentiation and subsequent specialization of every cell within an organism is an intricate interwoven process. A complex network of signalling pathways eventually leads to the specification of a multitude of different cell types able to function co-operatively. HS (heparan sulfate) is a highly sulfated linear polysaccharide that resides at the pericellular cell–matrix interface where it dictates the binding and activity of a large number of proteins, including growth factors and morphogens such as members of the FGF (fibroblast growth factor) and BMP (bone morphogenetic protein) families. Embryonic stem cells derived from mice with mutations in components of the HS biosynthetic pathway provide an opportunity to dissect the contribution of HS to signalling pathways critical for regulating stem cell maintenance and differentiation. In addition to improving our understanding of signalling mechanisms, this knowledge enables the selection of exogenous HS saccharides to improve the efficiency and selectivity of directed differentiation protocols, offering a cost-effective alternative to high concentrations of expensive growth factors to drive differentiation towards a particular therapeutically relevant cell type.
Foix-Alajouanine Syndrome Presenting as Acute Cauda Equina Syndrome: A Case Report
Authors: Menon K. Venugopal , Sorour Tamer M. M. , Raniga Sameer B. 
Published: May 2014

Study Design Case report. Objective Present a case of Foix-Alajouanine syndrome that presented as acute cauda equina syndrome and discuss the pathophysiology and management. Methods An adult male patient developed sudden onset of back pain and leg pain with weakness of the lower limbs and bladder/bowel dysfunction typical of cauda equina syndrome. Emergency magnetic resonance imaging revealed no compressive lesion in the spine but showed tortuous flow voids and end-on blood vessels in the peridural region suggesting spinal arteriovenous malformation resulting in Foix-Alajouanine syndrome. Results The case was managed by endovascular embolization with excellent results. The pathophysiology, imaging features, management, and literature review of the syndrome is discussed. Conclusion The authors conclude that this condition may be an important differential diagnosis for cauda equina syndrome.