Bright Beacons Research Articles

Bright Beacons? ALMA Non-detection of a Supposedly Bright [O i] 63 μm Line in a Redshift-6 Dusty Galaxy

Abstract We report a non-detection of the [O i] 63 μm emission line from the z = 6.03 galaxy G09.83808 using ALMA Band 9 observations, refuting the previously claimed detection with APEX by Rybak et al.; the new upper limit on the [O i] 63 μm flux is almost 20-times lower. [O i] 63 μm line could be a powerful tracer of neutral gas in the Epoch of Reionization: yet our null result shows that detecting [O i] 63 μm from z ≥ 6 galaxies is more challenging than previously hypothesized.

Strongly Lensed Supermassive Black Hole Binaries as Nanohertz Gravitational-wave Sources

Supermassive black hole binary systems (SMBHBs) should be the most powerful sources of gravitational waves (GWs) in the universe. Once pulsar timing arrays (PTAs) detect the stochastic GW background from their cosmic merger history, searching for individually resolvable binaries will take on new importance. Since these individual SMBHBs are expected to be rare, here we explore how strong gravitational lensing can act as a tool for increasing their detection prospects by magnifying fainter sources and bringing them into view. Unlike for electromagnetic waves, when the geometric optics limit is nearly always valid, for GWs the wave-diffraction-interference effects can become important when the wavelength of the GWs is larger than the Schwarzchild radius of the lens, i.e., . For the GW frequency range explored in this work, the geometric optics limit holds. We investigate GW signals from SMBHBs that might be detectable with current and future PTAs under the assumption that quasars serve as bright beacons that signal a recent merger. Using the black hole mass function derived from quasars and a physically motivated magnification distribution, we expect to detect a few strongly lensed binary systems out to z ≈ 2. Additionally, for a range of fixed magnifications 2 ≤ μ ≤ 100, strong lensing adds up to ∼30 more detectable binaries for PTAs. Finally, we investigate the possibility of observing both time-delayed electromagnetic signals and GW signals from these strongly lensed binary systems—that will provide us with unprecedented multi-messenger insights into their orbital evolution.

Spectroscopy of QUBRICS quasar candidates: 1672 new redshifts and a golden sample for the Sandage test of the redshift drift

ABSTRACT The QUBRICS (QUasars as BRIght beacons for Cosmology in the Southern hemisphere) survey aims at constructing a sample of the brightest quasars with $z \lower.5ex\hbox{$\,\, \buildrel\gt \over \sim \,\,$}2.5$, observable with facilities in the Southern Hemisphere. QUBRICS makes use of the available optical and IR wide-field surveys in the South and of Machine Learning techniques to produce thousands of bright quasar candidates of which only a few hundred have been confirmed with follow-up spectroscopy. Taking advantage of the recent Gaia Data Release 3, which contains 220 million low-resolution spectra, and of a newly developed spectral energy distribution fitting technique, designed to combine the photometric information with the Gaia spectroscopy, it has been possible to measure 1672 new secure redshifts of QUBRICS candidates, with a typical uncertainty of σz = 0.02. This significant progress of QUBRICS brings it closer to (one of) its primary goals: providing a sample of bright quasars at redshift 2.5 < z < 5 to perform the Sandage test of the cosmological redshift drift. A Golden Sample of seven quasars is presented that makes it possible to carry out this experiment in about 1500 h of observation in 25 yr, using the ANDES spectrograph at the 39m ELT, a significant improvement with respect to previous estimates.

The probabilistic random forest applied to the QUBRICS survey: improving the selection of high-redshift quasars with synthetic data

ABSTRACT Several recent works have focused on the search for bright, high-z quasars (QSOs) in the South. Among them, the QUasars as BRIght beacons for Cosmology in the Southern hemisphere (QUBRICS) survey has now delivered hundreds of new spectroscopically confirmed QSOs selected by means of machine learning algorithms. Building upon the results obtained by introducing the probabilistic random forest (PRF) for the QUBRICS selection, we explore in this work the feasibility of training the algorithm on synthetic data to improve the completeness in the higher redshift bins. We also compare the performances of the algorithm if colours are used as primary features instead of magnitudes. We generate synthetic data based on a composite QSO spectral energy distribution. We first train the PRF to identify QSOs among stars and galaxies, then separate high-z quasar from low-z contaminants. We apply the algorithm on an updated data set, based on SkyMapper DR3, combined with Gaia eDR3, 2MASS, and WISE magnitudes. We find that employing colours as features slightly improves the results with respect to the algorithm trained on magnitude data. Adding synthetic data to the training set provides significantly better results with respect to the PRF trained only on spectroscopically confirmed QSOs. We estimate, on a testing data set, a completeness of $\sim 86{{\ \rm per\ cent}}$ and a contamination of $\sim 36{{\ \rm per\ cent}}$. Finally, 206 PRF-selected candidates were observed: 149/206 turned out to be genuine QSOs with z > 2.5, 41 with z < 2.5, 3 galaxies and 13 stars. The result confirms the ability of the PRF to select high-z quasars in large data sets.

Near-infrared spectroscopy of extreme BAL QSOs from the QUBRICS bright quasar survey

ABSTRACT We report on the spectral confirmation of 18 quasi-stellar object (QSO) candidates from the QUasars as BRIght beacons for Cosmology in the Southern hemisphere (QUBRICS) survey, previously observed in the optical band, for which we acquired new spectroscopic data in the near-infrared band with the Folded-port InfraRed Echellette (FIRE) spectrograph at the Magellan Baade telescope. In most cases, further observations were prompted by the peculiar nature of the targets, whose optical spectra displayed unexpected absorption features. All candidates have been confirmed as bona fide QSOs, with average emission redshift z ≃ 2.1. The analysis of the emission and absorption features in the spectra, performed with astrocook and QSFit, reveals that the large majority of these objects are broad absorption line (BAL) QSOs, with almost half of them displaying strong Fe ii absorption (typical of the so-called FeLoBAL QSOs). The detection of such a large fraction of rare objects (which are estimated to account for less than 1 per cent of the general QSO population) is interpreted as an unexpected (yet favourable) consequence of the particular candidate selection procedure adopted within the QUBRICS survey. The measured properties of FeLoBAL QSOs observed so far provide no evidence that they are a manifestation of a particular stage in active galactic nucleus (AGN) evolution. In this paper, we present an explorative analysis of the individual QSOs, to serve as a basis for a further, more detailed investigation.

The Spectroscopic Follow-up of the QUBRICS Bright Quasar Survey

Abstract We present the results of the spectroscopic follow-up of the QUasars as BRIght beacons for Cosmology in the Southern Hemisphere (QUBRICS; Calderone et al. 2019) survey. The selection method is based on a machine-learning approach applied to photometric catalogs, covering an area of ∼12,400 deg2 in the Southern Hemisphere. The spectroscopic observations started in 2018 and identified 55 new, high-redshift (z ≥ 2.5), bright (i ≤ 18) quasi-stellar objects (QSOs), with the catalog published in late 2019. Here we report the current status of the survey, bringing the total number of bright QSOs at z ≥ 2.5 identified by QUBRICS to 224. The success rate of the QUBRICS selection method, in its most recent training, is estimated to be 68%. The predominant contaminant turns out to be lower-z QSOs at z < 2.5. This survey provides a unique sample of bright QSOs at high z available for a number of cosmological investigations. In particular, carrying out the redshift drift measurements (Sandage Test) in the Southern Hemisphere, using the High Resolution Spectrograph at the 39 m Extremely Large Telescope appears to be possible with less than 2500 hr of observations spread over 30 targets in 25 yr.

An insider's view on how Ki-67, the bright beacon of cell proliferation, became very popular. A tribute to Johannes Gerdes (1950-2016).

An insider's view on how Ki-67, the bright beacon of cell proliferation, became very popular. A tribute to Johannes Gerdes (1950-2016).

High redshift gamma-ray bursts as a probe of the early universe and first stars

Gamma-ray bursts (GRBs) are the most violent explosions in the universe. Thanks totheir extreme brightness, GRBs can be detected up to the edge of the visible universe.As bright beacons in the deep universe, high-redshift GRBs have been considered as an ideal tool toexplore the properties of the early universe: including the dark energy and cosmological parameters,star formation rate, first stars, the reionization and metal enrichment history of the universe.So the detection of high-$z$ GRBs has important scientific significance. Compared to currentmissions, Einstein Probe has a higher sensitivity and a wider field-of-view, operating the softX-ray band (0.5–4 keV), which would be suitable for the detection of high-$z$ GRBs. With itsobservational mode and ability, we compute the expected detection rate of high-$z$ GRBs byEinstein Probe by means of a observational tested population synthesis model of Swift GRBs.Our results show that the detection rates are expected to be about 20 events $\\rm~yr^{-1}$ $\\rm~sr^{-1}$for $z>6$ bursts, 6 events $\\rm~yr^{-1}$ $\\rm~sr^{-1}$ for $z>8$ bursts, and 1 events $\\rm~yr^{-1}$$\\rm~sr^{-1}$ for $z>12$ bursts, respectively. Over the 3 yr lifetime of the mission,Einstein Probe will able to detect about 65 GRBs at $z>6$, including $\\sim20$ GRBs at $z>8$ and$\\sim3$ GRBs at $z>12$. In sum, Einstein Probe would significantly improve the detection of high-$z$GRBs, and these abundant observational information would probably reveal some scientific mysteries ofthe early universe.

Accuracy enhancement of navigation images using blind restoration method

Optical navigation is one of the most promising technologies in the area of deep space autonomous navigation. However, since the optical images are strict motion blurred images, it is difficult to extract the lines of sight (LOS) to the beacons to reckon the spacecraft attitude and orbital position during the deep space cruise phase. This paper proposes a new blind restoration approach to effectively recover the clear image. We use a modified median filter to eliminate the black and white noises, and also, construct a blind estimation model, built on the sparsity of the gradient of navigation image, to estimate the global point spread function (PSF). Moreover, we select a few bright beacons to recover the motion blurred image, where the average value of the beacon centroid is adopted to calculate the relative position for the optical navigation. We present the simulation and actual image restoration experiment to demonstrate the accuracy and consistency of the relative position of the recovered navigation image of the proposed method. We show that the proposed method presents superior performance in comparison with the multiple cross correlation method. The estimated PSF is close to real PSF and the distributed energy of the beacon is concentrated ensuring a high SNR, where the accuracy of the relative position is higher than 0.1 pixel.

Rayleigh beacon for measuring the surface profile of a radio telescope.

Millimeter-wavelength Rayleigh scattering from water droplets in a cloud is proposed as a means of generating a bright beacon for measuring the surface profile of a radio telescope. A λ=3 mm transmitter, with an output power of a few watts, illuminating a stratiform cloud, can generate a beacon with the same flux as Mars in 10GHz bandwidth, but the beacon has a narrow line width, so it is extremely bright. The key advantage of the beacon is that it can be used at any time, and positioned anywhere in the sky, as long as there are clouds.

Notes from the Field: Planting, Nurturing, and Watching Things Grow

Editors' Note: We invited a sample of AJPM's Editorial Board, supplement guest editors, and longtime colleagues and contributors to share their experiences and impressions of the impact of AJPM on their respective domains. We were particularly fond of Ken Powell's analogy to being "tenders of the planted seed"--as planters, weeders, and harvesters--watching and nurturing the growth of AJPM, and have elected to lead with his commentary.

Active Galactic Nuclei under the scrutiny of CTA

Active Galactic Nuclei (hereafter AGN) produce powerful outflows which offer excellent conditions for efficient particle acceleration in internal and external shocks, turbulence, and magnetic reconnection events. The jets as well as particle accelerating regions close to the supermassive black holes (hereafter SMBH) at the intersection of plasma inflows and outflows, can produce readily detectable very high energy gamma-ray emission. As of now, more than 45 AGN including 41 blazars and 4 radiogalaxies have been detected by the present ground-based gamma-ray telescopes, which represents more than one third of the cosmic sources detected so far in the VHE gamma-ray regime. The future Cherenkov Telescope Array (CTA) should boost the sample of AGN detected in the VHE range by about one order of magnitude, shedding new light on AGN population studies, and AGN classification and unification schemes. CTA will be a unique tool to scrutinize the extreme high-energy tail of accelerated particles in SMBH environments, to revisit the central engines and their associated relativistic jets, and to study the particle acceleration and emission mechanisms, particularly exploring the missing link between accretion physics, SMBH magnetospheres and jet formation. Monitoring of distant AGN will be an extremely rewarding observing program which will inform us about the inner workings and evolution of AGN. Furthermore these AGN are bright beacons of gamma-rays which will allow us to constrain the extragalactic infrared and optical backgrounds as well as the intergalactic magnetic field, and will enable tests of quantum gravity and other “exotic” phenomena.

The Contested Meaning of 9/11

The terror attacks of September 11, 2001, have been a recurrent theme — sometimes implicit, often front and center — of U.S. politics throughout the past decade. How to interpret and understand them has been a crucial question. In the tragedy’s immediate aftermath, the George W. Bush administration struck a theme that resonated with the American public: the attacks constituted an outoftheblue declaration of war against an unsuspecting and entirely innocent victim, namely, the United States. “America was targeted for attack because we’re the brightest beacon for freedom and opportunity in the world,” the president told the nation on the evening of the attacks, as he promised a “war against terrorism.”1 This initial historicizing of the 9/11 attacks soon became embedded in other official speeches and documents and in the public mind. It possessed not only a congenial explanatory power but also an enormous power to mobilize. It fueled a war in Afghanistan and subsequently, with leaps of logic, the invasion and occupation of Iraq. Powerful as it has been, the official instanthistory understanding of the attacks of 9/11 was never without its challenges. A segment of the population has at times contested even the basic facts of the events. Partisan divide has arisen over the extent to which the Bush administration failed to heed warnings of an impending attack. And most persistently, the claim that the terror attacks constituted acts of

Beacons of Hope? The Impact of Imposed Democracy on Regional Peace, Democracy, and Prosperity

In 2003, American policymakers linked the democratization of Iraq with greater peace, democracy, and prosperity in the Middle East. We elaborate this regional-level policy argument theoretically and test it empirically on a global sample of states for the twentieth century. We differentiate the impact of fully and weakly democratic externally imposed polities (“bright” versus “dim” beacons, respectively) on regional interstate war, democratization, and economic growth. We conclude that (1) bright beacons reduce, while dim beacons increase war; (2) bright beacons do not stimulate democratization, while dim beacons undermine democratization; and (3) bright beacons stimulate prosperity, while dim beacons undermine prosperity.

Lessons in Morality and Mortality

Lessons in Morality and Mortality

LRP: a bright beacon at the blood-brain barrier

Ever more unexpected roles for the LDL receptor gene family in a variety of cellular signaling pathways continue to emerge. Three recent studies now add another function to this collection. By interacting with active tissue-type plasminogen activator, LDL receptor–related protein appears to control permeability of the blood-brain barrier, vascular tone, and the expression of MMPs. All of these parameters impact upon postischemic infarct size following stroke. These novel findings are discussed in the context of known mechanisms of signaling by the LDL receptor family.

Cosmic Mystery Objects Start to Yield Secrets

At a recent workshop, researchers presented evidence that the mysterious flashes of high-energy radiation known as cosmic gamma ray bursts are surprisingly frequent--one pops off somewhere in the universe every single minute--and that the bursts may be closer kin to normal supernova explosions than scientists had assumed. Soon, experts hope, these bright beacons might be used to study the first generation of stars, the origin of the large-scale structure of the universe, the history of the cosmic star-formation rate, and the chemical evolution of the universe.

Peering into review.

Peering into review.