Astro Coffee

Suggested papers for
Tue, Jun 07, 2016 at 03:00 PM and Thu, Jun 09, 2016 at 02:00 PM

6 Jun 2016

Massive Black Hole Binary Mergers in Dynamical Galactic Environments

Gravitational Waves (GW) have now been detected from stellar-mass black hole binaries, and the first observations of GW from Massive Black Hole (MBH) Binaries are expected within the next decade. Pulsar Timing Arrays (PTA), which can measure the years long periods of GW from MBHB, have excluded many standard predictions for the amplitude of a stochastic GW Background (GWB). We use coevolved populations of MBH and galaxies from hydrodynamic, cosmological simulations ('Illustris') to calculate a ...

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3 Jun 2016

Lyman-alpha and CIII] Emission in z=7-9 Galaxies: Accelerated Reionization Around Luminous Star Forming Systems?

We discuss new Keck/MOSFIRE spectroscopic observations of four luminous galaxies at z~7-9 selected to have intense optical line emission by Roberts-Borsani et al. (2016). Previous follow-up has revealed Lyman-alpha in two of the four galaxies. Our new MOSFIRE observations confirm that Lyman-alpha is present in the entire sample. We detect Lyman-alpha emission in COS-zs7-1, confirming its redshift as z=7.154, and we detect Lyman-alpha in EGS-zs8-2 at z=7.477, verifying a tentative detection pres...

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3 Jun 2016

Unification of the Fundamental Plane and Super-Massive Black Holes Masses

According to the Virial Theorem, all gravitational systems in equilibrium sit on a plane in the 3D parameter space defined by their mass, size and second moment of the velocity tensor. While these quantities cannot be directly observed, there are suitable proxies: the luminosity Lk, half-light radius Re and dispersion sigma_e. These proxies indeed lie on a very tight Fundamental Plane (FP). How do the black holes in the centers of galaxies relate to the FP? Their masses are known to exhibit no ...

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4 Jun 2016

The Unusual Galactic Center Radio Source N3

Here we report on new, multi-wavelength radio observations of the unusual point source "N3" that appears to be located in the vicinity of the Galactic Center. VLA observations between 2 and 50 GHz reveal that N3 is a compact and bright source (56 mJy at 10 GHz) with a non-thermal spectrum superimposed upon the non-thermal radio filaments (NTFs) of the Radio Arc. Our highest frequency observations place a strict upper limit of 65 x 28 mas on the size of N3. We compare our observations to those o...

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3 Jun 2016

Variability in the Near-Infrared Synchrotron Emission From Cassiopeia A

We present multi-epoch Ks band imaging of the supernova remnant Cassiopeia A (Cas A). The morphology of the emission in this band is generally diffuse and filamentary, consistent with synchrotron radiation observed at radio wavelengths. However, in one region to the southwest of the remnant, compact knots of emission appear to be entrained in the ejecta and have the same proper motion as ejecta observed at similar projected radii. The presence of these knots suggests that material with high mag...

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30 May 2016

Radio Counterparts of Compact Binary Mergers detectable in Gravitational Waves: A Simulation for an Optimized Survey

Mergers of binary neutron stars and black hole-neutron star binaries produce gravitational-wave (GW) emission and outflows with significant kinetic energies. These outflows result in radio emissions through synchrotron radiation of accelerated electrons in shocks formed with the circum-merger medium. We explore the detectability of these synchrotron generated radio signals by follow-up observations of GW merger events lacking a detection of electromagnetic counterparts in other wavelengths. We ...

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1 Jun 2016

A deep ALMA image of the Hubble Ultra Deep Field

We present the results of the first, deep ALMA imaging covering the full 4.5 sq arcmin of the Hubble Ultra Deep Field (HUDF) as previously imaged with WFC3/IR on HST. Using a mosaic of 45 pointings, we have obtained a homogeneous 1.3mm image of the HUDF, achieving an rms sensitivity of 35 microJy, at a resolution of 0.7 arcsec. From an initial list of ~50 >3.5sigma peaks, a rigorous analysis confirms 16 sources with flux densities S(1.3) > 120 microJy. All of these have secure galaxy coun...

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10 May 2016

#FoundThem - 21st Century Pre-Search and Post-Detection SETI Protocols for Social and Digital Media

The transmission of news stories in global culture has changed fundamentally in the last three decades. The general public are alerted to breaking stories on increasingly rapid timescales, and the discussion/distortion of facts by writers, bloggers, commenters and Internet users can also be extremely fast. The narrative of a news item no longer belongs to a small cadre of conventional media outlets, but is instead synthesised to some level by the public as they select where and how they consume...

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10 May 2016

viXra: Repulsive Force Proportional to Energy Density as an Origin of Dark Energy

An X-particle with repulsive force proportional to energy density is postulated as an origin of dark energy. Like photon, the particle has only relativistic mass (zero rest mass), and acts like a particle that has a definite position and momentum. It creates spaces between them by forces of gravitational attraction and repulsion, where the repulsive force is postulated to be proportional to energy density. The model could be applied to explain the Lambda-CDM model of dark energy which is fillin...

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25 May 2016

The Prevalence and Impact of Wolf-Rayet Stars in Emerging Massive Star Clusters

We investigate Wolf-Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR star...

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7 Jun 2016

Detection of solar-like oscillations in relics of the Milky Way: asteroseismology of K giants in M4 using data from the NASA K2 mission

Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens of thousands of field stars. Tests against independent estimates of these properties are however scarce, especially in the metal-poor regime. Here, we report the detection of solar-like oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular cluster M4. The detections were made in photometric observations from the K2 Mission during its Campaign 2. Making use...

1 Jun 2016

Spectroscopic Measurements of the Far-Ultraviolet Dust Attenuation Curve at z~3

We present the first measurements of the shape of the far-ultraviolet (far-UV; lambda=950-1500 A) dust attenuation curve at high redshift (z~3). Our analysis employs rest-frame UV spectra of 933 galaxies at z~3, 121 of which have very deep spectroscopic observations (>7 hrs) at lambda=850-1300 A, with the Low Resolution Imaging Spectrograph on the Keck Telescope. By using an iterative approach in which we calculate the ratios of composite spectra in different bins of continuum color excess, ...

6 Jun 2016

BICEP2 / Keck Array VIII: Measurement of gravitational lensing from large-scale B-mode polarization

We present measurements of polarization lensing using the 150 GHz maps which include all data taken by the BICEP2 & Keck Array CMB polarization experiments up to and including the 2014 observing season (BK14). Despite their modest angular resolution ($\sim 0.5^\circ$), the excellent sensitivity ($\sim 3\mu$K-arcmin) of these maps makes it possible to directly reconstruct the lensing potential using only information at larger angular scales ($\ell\leq 700$). From the auto-spectrum of the rec...

6 Jun 2016

Formation of Massive Black Holes in Galactic Nuclei: Runaway Tidal Encounters

Nuclear star clusters (NSCs) and supermassive black holes (SMBHs) both inhabit galactic nuclei, coexisting in a range of bulge masses, but excluding each other in the largest or smallest galaxies. We propose that the transformation of NSCs into SMBHs occurs via runaway tidal captures, once NSCs exceed a certain critical central density and velocity dispersion. The bottleneck in this process, as with all collisional runaways, is growing the first e-fold in black hole mass. The growth of a stella...

3 Jun 2016

An improved analysis of GW150914 using a fully spin-precessing waveform model

This paper presents updated estimates of source parameters for GW150914, a binary black-hole coalescence event detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) on September 14, 2015 [1]. Reference presented parameter estimation [2] of the source using a 13-dimensional, phenomenological precessing-spin model (precessing IMRPhenom) and a 11-dimensional nonprecessing effective-one-body (EOB) model calibrated to numerical-relativity simulations, which forces spin alignment...

1 Jun 2016

Q1549-C25: A Clean Source of Lyman-Continuum Emission at $z=3.15$

We present observations of Q1549-C25, an ~L* star-forming galaxy at z=3.15 for which Lyman-continuum (LyC) radiation is significantly detected in deep Keck/LRIS spectroscopy. We find no evidence for contamination from a lower-redshift interloper close to the line of sight in the high signal-to-noise spectrum of Q1549-C25. Furthermore, the morphology of Q1549-C25 in V_606, J_125, and H_160 Hubble Space Telescope (HST) imaging reveals that the object consists of a single, isolated component withi...


Updated 2016/06/09 14:42:55

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