388 research outputs found
Thermal Emission from Warm Dust in the Most Distant Quasars
We report new continuum observations of fourteen z~6 quasars at 250 GHz and
fourteen quasars at 1.4 GHz. We summarize all recent millimeter and radio
observations of the sample of the thirty-three quasars known with
5.71<=z<=6.43, and present a study of the rest frame far-infrared (FIR)
properties of this sample. These quasars were observed with the Max Plank
Millimeter Bolometer Array (MAMBO) at 250 GHz with mJy sensitivity, and 30% of
them were detected. We also recover the average 250 GHz flux density of the
MAMBO undetected sources at 4 sigma, by stacking the on-source measurements.
The derived mean radio-to-UV spectral energy distributions (SEDs) of the full
sample and the 250 GHz non-detections show no significant difference from that
of lower-redshift optical quasars. Obvious FIR excesses are seen in the
individual SEDs of the strong 250 GHz detections, with FIR-to-radio emission
ratios consistent with that of typical star forming galaxies. Most 250
GHz-detected sources follow the L_{FIR}--L_{bol} relationship derived from a
sample of local IR luminous quasars (L_{IR}>10^{12}L_{\odot}), while the
average L_{FIR}/L_{bol} ratio of the non-detections is consistent with that of
the optically-selected PG quasars. The MAMBO detections also tend to have
weaker Ly\alpha emission than the non-detected sources. We discuss possible FIR
dust heating sources, and critically assess the possibility of active star
formation in the host galaxies of the z~6 quasars. The average star formation
rate of the MAMBO non-detections is likely to be less than a few hundred
M_{\odot} yr^{-1}, but in the strong detections, the host galaxy star formation
is probably at a rate of \gtrsim10^{3} M_{\odot} yr^{-1}, which dominates the
FIR dust heating.Comment: 32 pages with 6 figures; ApJ, in press; Added references; Corrected
typo
On improved fail-safe sensor distributions for a structural health monitoring system
Sensor placement optimization (SPO) is usually applied during the structural health monitoring sensor system design process to collect effective data. However, the failure of a sensor may significantly affect the expected performance of the entire system. Therefore, it is necessary to study the optimal sensor placement considering the possibility of sensor failure. In this article, the research focusses on an SPO giving a fail-safe sensor distribution, whose sub-distributions still have good performance. The performance of the fail-safe sensor distribution with multiple sensors placed in the same position will also be studied. The adopted data sets include the mode shapes and corresponding labels of structural states from a series of tests on a glider wing. A genetic algorithm is used to search for sensor deployments, and the partial results are validated by an exhaustive search. Two types of optimization objectives are investigated, one for modal identification and the other for damage identification. The results show that the proposed fail-safe sensor optimization method is beneficial for balancing the system performance before and after sensor failure
On robustness of optimal sensor placement to environmental variation for SHM
One challenge in establishing an effective structural health monitoring (SHM) system is the impact of environmental variability on damage identification. It is therefore, advantageous to consider any environmental effects when conducting sensor placement optimisation (SPO). One approach to this problem is to check the robustness of SPO technique to environmental variations and consider whether it is necessary to take account of these environmental factors as part of the optimisation process. This paper will study the robustness of an SPO method to variations in the ambient temperature of the structure. Two kinds of data, including the mode shapes and the Mahalanobis squared-distance (MSD), from tests on a glider wing structure are used as features for SPO separately. This structure was set up and tested in different health states across a series of controlled temperatures. The results show that the SPO results obtained via the mode shapes are robust to the temperature variation, while the SPO results corresponding to MSD are sensitive to temperature changes
HCN J=5-4 Emission in APM08279+5255 at z=3.91
We detect HCN J=5-4 emission from the ultraluminous quasar APM08279+5255 at
z=3.911 using the IRAM Plateau de Bure interferometer. This object is strongly
gravitationally lensed, yet still thought to be one of the most intrinsically
luminous objects in the Universe. The new data imply a line luminosity
L'_HCN(J=5-4) = 4.0+/-0.5 x 10^(10) K km/s pc^2. The ~440 km/s full width half
maximum of the HCN J=5-4 line matches that of the previously observed high-J CO
lines in this object and suggests that the emission from both species emerges
from the same region: a warm, dense circumnuclear disk. Simple radiative
transfer models suggest an enhanced abundance of HCN relative to CO in the
nuclear region of APM08279+5255, perhaps due to increased ionization, or
possibly the selective depletion of oxygen. The ratio of far-infrared
luminosity to HCN luminosity is at the high end of the range found for nearby
star forming galaxies, but comparable to that observed in the few high redshift
objects detected in the HCN J=1-0 line. This is the first clear detection of
high-J HCN emission redshifted into the 3-millimeter atmospheric window.Comment: Accepted for publication in ApJ
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Constraining the nature of two Lyα emitters detected by ALMA at z = 4.7
We report optical VLT FORS2 spectroscopy of the two Ly-alpha emitters (LAEs)
companions to the quasi-stellar object (QSO) - sub-millimetre galaxy (SMG)
system BRI1202-0725 at z = 4.7, which have recently been detected in the
[CII]158um line by the Atacama Large Millimetre/Sub-millimetre Array (ALMA). We
detect Ly-alpha emission from both sources and so confirm that these Ly-alpha
emitter candidates are physically associated with the BRI1202- 0725 system. We
also report the lack of detection of any high ionisation emission lines (N V,
Si IV, C IV and He II) and find that these systems are likely not photoionised
by the quasar, leaving in situ star formation as the main powering source of
these LAEs. We also find that both LAEs have Ly-alpha emission much broader
(1300 km/s) than the [CII] emission and broader than most LAEs. In addition,
both LAEs have roughly symmetric Ly-alpha profiles implying that both systems
are within the HII sphere produced by the quasar. This is the first time that
the proximity zone of a quasar is probed by exploiting nearby Ly-alpha
emitters. We discuss the observational properties of these galaxies in the
context of recent galaxy formation models.This work was co-funded under the Marie Curie Actions of the European Commission (FP7-COFUND).This is the final published version, which originally appeared in MNRAS and is available at http://mnras.oxfordjournals.org/content/439/2/2096
Observations by GMRT at 323 MHz of radio-loud quasars at
We present Giant Metrewave Radio Telescope (GMRT) 323 MHz radio continuum
observations toward 13 radio-loud quasars at , sampling the low-frequency
synchrotron emission from these objects. Among the 12 targets successfully
observed, we detected 10 above significance, while 2 remain
undetected. All of the detected sources appear as point sources. Combined with
previous radio continuum detections from the literature, 9 quasars have
power-law spectral energy distributions throughout the radio range; for some
the flux density drops with increasing frequency while it increases for others.
Two of these sources appear to have spectral turnover. For the power-law-like
sources, the power-law indices have a positive range between 0.18 and 0.67 and
a negative values between and . For the turnover sources, the
radio peaks around and GHz in the rest frame, the optically
thin indices are and , and the optically thick indices are 0.50
and 1.20. A magnetic field and spectral age analysis of SDSS
J114657.59+403708.6 at may indicate that the turnover is not caused by
synchrotron self-absorption, but rather by free-free absorption by the
high-density medium in the nuclear region. Alternatively, the apparent turnover
may be an artifact of source variability. Finally, we calculated the radio
loudness for our sample, which spans a very wide range from
12 to 4982.Comment: 13 pages; Accepted by A&
Comparing the direct normal form and multiple scales methods through frequency detuning
Approximate analytical methods, such as the multiple scales (MS) and direct normal form (DNF) techniques, have been used extensively for investigating nonlinear mechanical structures, due to their ability to offer insight into the system dynamics. A comparison of their accuracy has not previously been undertaken, so is addressed in this paper. This is achieved by computing the backbone curves of two systems: the single-degree-of-freedom Duffing oscillator and a non-symmetric, two-degree-of-freedom oscillator. The DNF method includes an inherent detuning, which can be physically interpreted as a series expansion about the natural frequencies of the underlying linear system and has previously been shown to increase its accuracy. In contrast, there is no such inbuilt detuning for MS, although one may be, and usually is, included. This paper investigates the use of the DNF detuning as the chosen detuning in the MS method as a way of equating the two techniques, demonstrating that the two can be made to give identical results up to ε2 order. For the examples considered here, the resulting predictions are more accurate than those provided by the standard MS technique. Wolfram Mathematica scripts implementing these methods have been provided to be used in conjunction with this paper to illustrate their practicality
Unveiling the Nature of Submillimeter Galaxy SXDF850.6
We present an 880 micron Submillimeter Array (SMA) detection of the
submillimeter galaxy SXDF850.6. SXDF850.6 is a bright source (S(850 micron) = 8
mJy) detected in the SCUBA Half Degree Extragalactic Survey (SHADES), and has
multiple possible radio counterparts in its deep radio image obtained at the
VLA. Our new SMA detection finds that the submm emission coincides with the
brightest radio emission that is found ~8" north of the coordinates determined
from SCUBA. Despite the lack of detectable counterparts in deep UV/optical
images, we find a source at the SMA position in near-infrared and longer
wavelength images. We perform SED model fits to UV-optical-IR photometry (u, B,
V, R, i', z', J, H, K, 3.6 micron, 4.5 micron, 5.8 micron, and 8.0 micron) and
to submm-radio photometry (850 micron, 880 micron, 1100 micron, and 21 cm)
independently, and we find both are well described by starburst templates at a
redshift of z ~= 2.2 (+/- 0.3). The best-fit parameters from the UV-optical-IR
SED fit are a redshift of z = 1.87 (+0.15/-0.07), a stellar mass of M_star =
2.5 +2.2/-0.3 x 10^11 M_sun, an extinction of A_V = 3.0 (+0.3/-1.0) mag, and an
age of 720 (+1880/-210) Myr. The submm-radio SED fit provides a consistent
redshift of z ~ 1.8-2.5, an IR luminosity of L_IR = (7-26) x 10^12 L_sun, and a
star formation rate of 1300-4500 M_sun/yr. These results suggest that SXDF850.6
is a mature system already having a massive amount of old stellar population
constructed before its submm bright phase and is experiencing a dusty
starburst, possibly induced by major mergers.Comment: 7 pages, 5 figures, Accepted for publication in Astrophysical Journa
Assessing the sociology of sport: On race and diaspora
© The Author(s) 2014 On the 50th anniversary of the ISSA and IRSS, a key foundational scholar on the intersection of race and sport, Ben Carrington, reflects on the field as a whole and the notion of “diaspora” in understanding race and sport. In considering the trajectory of the sociology of sport, questions are raised about whether a coherent field has ever existed. Noting relative failures in getting “mainstream sociology” to take sport seriously, the challenges ahead are for a field that is necessarily a “multifaceted” entity, and one that ironically has never been more impactful while at its weakest institutional moment. Noting the paradox between the relative little consideration given to sport in the main sociology journals in the US and UK in contrast with the sociology of sport having successfully established self-reproducing and self-referencing spaces of critical enquiry, a key challenge for the field continues to be in its search for a “scholarly place;” it is less than clear whether the banner of “the sociology of sport” continues to resonate in the face of the neo-liberal assaults on critical scholarship within higher education. The concept of “diaspora,” surprisingly ignored in the study of sport, will be increasingly important in the future as it will enable critical race scholars to problematize the often Eurocentric and teleological underpinning of globalization theory in relation to sport; considerations of diaspora will fuel more meaningful accounts of how sport reconnects geographically dispersed groups and changes identities and subjectivities in hostile circumstances
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