We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C II] 158 µm fine structure line and dust continuum emission from the host galaxies of five redshift 6 quasars. We also report complementary observations of 250 GHz dust continuum and CO (6-5) line emission from the z=6.00 quasar SDSS J231038.88+185519.7 using the IRAM facilities. The ALMA observations were carried out in the extended array at 0. −4 , which is comparable to the values found in other high-redshift quasar-starburst systems and local ultra-luminous infrared galaxies. The sources are marginally resolved and the intrinsic source sizes (major axis FWHM) are constrained to be 0.3 ′′ to 0.6 ′′ (i.e., 1.7 to 3.5 kpc) for the [C II] line emission and 0.2 ′′ to 0.4 ′′ (i.e., 1.2 to 2.3 kpc) for the continuum. These measurements indicate that there is vigorous star formation over the central few kpc in the quasar host galaxies. The ALMA observations also constrain the dynamical properties of the star-forming gas in the nuclear region. The intensity-weighted velocity maps of three sources show clear velocity gradients. Such velocity gradients are consistent with a rotating, gravitationally bound gas component, although they are not uniquely interpreted as such. Under the simplifying assumption of rotation, the implied dynamical masses within the [C II]-emitting regions are of order 10 10 to 10 11 M ⊙ . Given these estimates, the mass ratios between the SMBHs and the spheroidal bulge are an order of magnitude higher than the mean value found in local spheroidal galaxies, which is in agreement with results from previous CO observations of high redshift quasars.
Gravitational waves are expected to be radiated by supermassive black hole binaries formed during galaxy mergers. A stochastic superposition of gravitational waves from all such binary systems will modulate the arrival times of pulses from radio pulsars. Using observations of millisecond pulsars obtained with the Parkes radio telescope, we constrain the characteristic amplitude of this background, A c,yr , to be < 1.0×10-15 with 95% confidence. This limit excludes predicted ranges for A c,yr from current models with 91-99.7% probability. We conclude that binary evolution is either stalled or dramatically accelerated by galactic-center environments, and that higher-cadence and shorter-wavelength observations would result in an increased sensitivity to gravitational waves.Studies of the dynamics of stars and gas in nearby galaxies provide strong evidence for the ubiquity of supermassive (> 10 6 solar mass) black holes (SMBHs) (1). Observations of luminous quasars indicate that SMBHs are hosted by galaxies throughout the history of the universe (2) and affect global properties of the host galaxies (3). The prevailing dark energycold dark matter cosmological paradigm predicts that large galaxies are assembled through the hierarchical merging of smaller galaxies. The remnants of mergers can host gravitationally bound binary SMBHs with orbits decaying through the emission of gravitational waves (GWs) (4).Gravitational waves from binary SMBHs, with periods between ~ 0.1 and 30 yr (5), can be detected or constrained by monitoring, for years to decades, a set of rapidly rotating millisecond pulsars (MSPs) distributed throughout our galaxy. Radio emission beams from MSPs are observed as pulses that can be time-tagged with as small as 20 ns precision (6). When traveling across the pulsar-Earth line of sight, GWs induce variations in the arrival times of the pulses (7).The superposition of GWs from the binary SMBH population is a stochastic background (GWB), which is typically characterized by the strain-amplitude spectrum h c (f)=A c,yr [f/(1 yr -1 )] -2/3 , where f is the GW frequency, A c,yr is the characteristic amplitude of the GWB measured at f = 1 yr -1 , predicted to be A c,yr > 10 -15 (5,(8)(9)(10)(11)(12), and -2/3 is the predicted spectral index (5,(8)(9)(10)(11)(12). The GWB will add low-frequency perturbations to pulse arrival times. While the detection of the GWB would confirm the presence of a cosmological population of binary SMBHs, limits on its amplitude constrain models of galaxy and SMBH evolution (8).As part of the Parkes Pulsar Timing Array project to detect GWs (6), we have been monitoring 24 pulsars with the 64-m Parkes radio telescope. We have produced a new data set, using observations taken at a central wavelength of 10 cm and previously reported methods (6,8), that spans 11 yr, which is 3 yr longer than previous data sets analyzed at this wavelength. In addition to having greater sensitivity to the GWB because of the longer duration, the data set was improved by identifying and correc...
We present new limits on an isotropic stochastic gravitational-wave background (GWB) using a six pulsar dataset spanning 18 yr of observations from the 2015 European Pulsar Timing Array data release. Performing a Bayesian analysis, we fit simultaneously for the intrinsic noise parameters for each pulsar, along with common correlated signals including clock, and Solar System ephemeris errors, obtaining a robust 95% upper limit on the dimensionless strain amplitude A of the background of A < 3.0 × 10 −15 at a reference frequency of 1yr −1 and a spectral index of 13/3, corresponding to a background from inspiralling super-massive black hole binaries, constraining the GW energy density to Ω gw ( f )h 2 < 1.1 × 10 −9 at 2.8 nHz. We also present limits on the correlated power spectrum at a series of discrete frequencies, and show that our sensitivity to a fiducial isotropic GWB is highest at a frequency of ∼ 5×10 −9 Hz. Finally we discuss the implications of our analysis for the astrophysics of supermassive black hole binaries, and present 95% upper limits on the string tension, Gµ/c 2 , characterising a background produced by a cosmic string network for a set of possible scenarios, and for a stochastic relic GWB. For a Nambu-Goto field theory cosmic string network, we set a limit Gµ/c 2 < 1.3 × 10 −7 , identical to that set by the Planck Collaboration, when combining Planck and high-Cosmic Microwave Background data from other experiments. For a stochastic relic background we set a limit of Ω relic gw ( f )h 2 < 1.2 × 10 −9 , a factor of 9 improvement over the most stringent limits previously set by a pulsar timing array. c 0000 RAS arXiv:1504.03692v3 [astro-ph.CO] 9 Sep 2015
We report on the high-precision timing of 42 radio millisecond pulsars (MSPs) observed by the European Pulsar Timing Array (EPTA). This EPTA Data Release 1.0 extends up to mid-2014 and baselines range from 7-18 years. It forms the basis for the stochastic gravitationalwave background, anisotropic background, and continuous-wave limits recently presented by the EPTA elsewhere. The Bayesian timing analysis performed with TempoNest yields the detection of several new parameters: seven parallaxes, nine proper motions and, in the case of six binary pulsars, an apparent change of the semi-major axis. We find the NE2001 Galactic electron density model to be a better match to our parallax distances (after correction from the Lutz-Kelker bias) than the M2 and M3 models by Schnitzeler (2012). However, we measure an average uncertainty of 80% (fractional) for NE2001, three times larger than what is typically assumed in the literature. We revisit the transverse velocity distribution for a set of 19 isolated and 57 binary MSPs and find no statistical difference between these two populations. We detect Shapiro delay in the timing residuals of PSRs J1600−3053 and J1918−0642, implying pulsar and companion masses m p = 1.22 +0.5 −0.35 M ⊙ , m c = 0.21 +0.06 −0.04 M ⊙ and m p = 1.25 +0.6 −0.4 M ⊙ , m c = 0.23 +0.07 −0.05 M ⊙ , respectively. Finally, we use the measurement of the orbital period derivative to set a stringent constraint on the distance to PSRs J1012+5307 and J1909−3744, and set limits on the longitude of ascending node through the search of the annual-orbital parallax for PSRs J1600−3053 and J1909−3744.
The highly stable spin of neutron stars can be exploited for a variety of (astro-)physical investigations. In particular arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such "Pulsar Timing Arrays" (PTAs) have been set up around the world over the past decades and collectively form the "International" PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available online) is used to demonstrate the IPTA's potential of improving upon gravitational-wave limits placed by individual PTAs by a factor of ∼ 2 and provides a 2 − σ limit on the dimensionless amplitude of a stochastic GWB of 1.7 × 10 −15 at a frequency of 1 yr −1 . This is 1.7 times less constraining than the limit placed by , due mostly to the more recent, high-quality data they used. c 2015 RAS c 2015 RAS, MNRAS 000, 1-25 First IPTA Data Release 3 σJitter ∝ fJW eff 1 + m 2 I Np ,with fJ the jitter parameter, which needs to be determined experimentally (Liu et al. 2012;Shannon et al. 2014); W eff the pulse width; mI = σE/µE the modulation index, defined by the mean (µE) and standard deviation (σE) of the pulseenergy distribution; and Np = tint/P the number of pulses in the observation, which equals the total observing time divided by the pulse period. Consequently, the highest-precision timing efforts ideally require rapidly rotating pulsars (P 0.03 s) with high relatively flux densities (S1.4 GHz 0.5 mJy) and narrow pulses (δ 20%) are observed at sensitive (A eff /Tsys) telescopes with wide-bandwidth receivers (∆f ) and for long integration times (tint 30 min).
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