Astro Coffee

Suggested papers for
Tue, Mar 21, 2017, Thu, Mar 23, 2017, and Fri, Mar 24, 2017 at 11:00 AM

22 Mar 2017

First Discoveries of z>6 Quasars with the DECam Legacy Survey and UKIRT Hemisphere Survey

We present the first discoveries from a survey of $z\gtrsim6$ quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg$^2$ of sky down to $z_{\rm AB}\sim23.0$, and UKIDSS and UHS, which will map the northern sky at $0<DEC<+60^{\circ}$, reaching $J_{\rm VEGA}\sim19.6$ (5-$\sigma$). The combin...

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21 Mar 2017

Testing the existence of optical linear polarization in young brown dwarfs

Linear polarization can be used as a probe of the existence of atmospheric condensates in ultracool dwarfs. Models predict that the observed linear polarization increases withthe degree of oblateness, which is inversely proportional to the surface gravity. We aimed to test the existence of optical linear polarization in a sample of bright young brown dwarfs, with spectral types between M6 and L2, observable from the Calar Alto Observatory, and cataloged previously as low gravity objects using s...

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20 Mar 2017

First results on the Epoch of Reionization from First Light with SARAS 2

Long wavelength spectral distortions in the Cosmic Microwave Background arising from the 21-cm transition in neutral Hydrogen are a key probe of Cosmic Dawn and the Epoch of Reionization. These features may reveal the nature of the first stars and ultra-faint galaxies that transformed the spin temperature and ionization state of the primordial gas. SARAS 2 is a spectral radiometer purposely designed for precision measurement of these monopole or all-sky global 21-cm spectral distortions. We use...

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16 Mar 2017

Individual Dynamical Masses of Ultracool Dwarfs

We present the full results of our decade-long astrometric monitoring programs targeting 31 ultracool binaries with component spectral types M7-T5. Joint analysis of resolved imaging from Keck and HST and unresolved astrometry from CFHT/WIRCam yields parallactic distances for all systems, robust orbit determinations for 23 systems, and photocenter orbits for 19 systems. As a result, we measure 38 precise individual masses spanning 30-115 $M_{\rm Jup}$. We determine a model-independent substella...

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16 Mar 2017

Stellar binaries in galactic nuclei: tidally stimulated mergers followed by tidal disruptions

We investigate interactions of stellar binaries in galactic nuclear clusters with a massive black hole (MBH). We consider binaries on highly eccentric orbits around the MBH that change due to random gravitational interactions with other stars in the nuclear stellar cluster. The pericenters of the orbits perform a random walk, and we consider cases where this random walk slowly brings the binary to the Hills tidal separation radius (the so-called empty loss-cone regime). However, we find that in...

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15 Mar 2017

The predicted luminous satellite populations around SMC and LMC-mass galaxies - A missing satellite problem around the LMC?

Recent discovery of many dwarf satellite galaxies in the direction of the Small and Large Magellanic Clouds (SMC and LMC) provokes questions of their origins, and what they can reveal about galaxy evolution theory. Here, we predict the satellite stellar mass function of Magellanic Cloud-mass host galaxies using abundance matching and reionization models applied to the Caterpillar simulations. Specifically focusing on the volume within 50 kpc of the LMC, we predict a mean of 4-8 satellites with ...

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22 Mar 2017

Quasars as standard candles I: The physical relation between disc and coronal emission

A tight non-linear relation exists between the X-ray and UV emission in quasars (i.e. $L_{\rm X}\propto L_{\rm UV}^{\gamma}$), with a dispersion of $\sim$0.2~dex over $\sim$3~orders of magnitude in luminosity. Here we propose a modified version of this relation which involves the broad emission lines' full-width at half maximum, $L_{\rm X}\propto L_{\rm UV}^{\hat\gamma}\upsilon_{\rm fwhm}^{\hat\beta}$. We interpret this new relation through a simple, {\it ad-hoc} model of accretion disc corona,...

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22 Mar 2017

The Planetary Mass-Radius Relation and its Dependence on Orbital Period as Measured by Transit Timing Variations and Radial Velocities

The two most common techniques for measuring planetary masses - the radial velocity (RV) and the transit timing variations (TTVs) techniques - have been observed to yield systematically different masses for planets of similar radii. Following Steffen (2016), we consider the effects of the observational biases of the two methods as a possible cause for this difference. We find that at short orbital periods ($P<11$ day), the two methods produce statistically similar results, whereas at long pe...

21 Mar 2017

A detection of wobbling Brightest Cluster Galaxies within massive galaxy clusters

A striking signal of dark matter beyond the standard model is the existence of cores in the centre of galaxy clusters. Recent simulations predict that a Brightest Cluster Galaxy (BCG) inside a cored galaxy cluster will exhibit residual wobbling due to previous major mergers, long after the relaxation of the overall cluster. This phenomena is absent with standard cold dark matter where a cuspy density profile keeps a BCG tightly bound at the centre. We test this hypothesis using cosmological sim...

12 Mar 2017

Precision Cosmology from Future Time Delays of Lensed Gravitational Wave and Electromagnetic Signals

The"standard-siren" approaches of gravitational wave cosmology appeal to the luminosity distance estimation from the GW observation which relies on the fine details of the waveform. We propose a new waveform independent strategy based on the systems where strongly lensed gravitational waves (GWs) and their electromagnetic (EM) counterparts can be detected simultaneously. With the images and redshifts observed in the EM domain combined with very precise measurements of time delays from lensed GW...

7 Mar 2017

Counting Black Holes: The Cosmic Stellar Remnant Population and Implications for LIGO

We present an empirical approach for interpreting gravitational wave signals of binary black hole mergers under the assumption that the underlying black hole population is sourced by remnants of stellar evolution. Using the observed relationship between galaxy mass and stellar metallicity, we predict the black hole count as a function of galaxy stellar mass. We show, for example, that a galaxy like the Milky Way should host millions of $\sim 30~M_\odot$ black holes and dwarf satellite galaxies ...

14 Mar 2017

Searching For Pulsars Associated With the Fermi GeV Excess

The Fermi Large Area Telescope has detected an extended region of GeV emission toward the Galactic Center that is currently thought to be powered by dark matter annihilation or a population of young and/or millisecond pulsars. In a test of the pulsar hypothesis, we have carried out an initial search of a 20 deg**2 area centered on the peak of the galactic center GeV excess. Candidate pulsars were identified as a compact, steep spectrum continuum radio source on interferometric images and follow...

13 Mar 2017

Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago

In cold dark matter cosmology, the baryonic components of galaxies are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark matter halo. In the local Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter with...


Updated 2017/03/24 11:50:40