55285186
SLUG – Stochastically Lighting Up Galaxies – II. Quantifying the effects of stochasticity on star formation rate indicators
The integrated light of a stellar population, measured through photometric filters that are sensitive to the presence of young stars, is often used to infer the star formation rate (SFR) for that population. However, these techniques rely on an assumption that star formation is a continuous process, whereas in reality stars form in discrete spatially and temporally correlated structures. This discreteness causes the light output to undergo significant time-dependent fluctuations, which, if not accounted for, introduce systematic errors in the inferred SFRs due to the intrinsic distribution of luminosities at any fix SFR. We use SLUG a code that Stochastically Lights Up Galaxies, to simulate galaxies undergoing stochastic star formation. We then use these simulations to present a quantitative analysis of these effects and provide tools for calculating probability distribution functions of SFRs given a set of observations. We show that, depending on the SFR tracer used, stochastic fluctuations can produce non-trivial errors at SFRs as high as 1  M⊙ yr−1 and biases ≳ 0.5 dex at the lowest SFRs. We emphasize that due to the stochastic behaviour of blue SFR tracers, one cannot assign a deterministic single value to the SFR of an individual galaxy, but we suggest methods by which future analyses that rely on integrated-light indicators can properly account for these stochastic effects.
15537902
The Lick AGN Monitoring Project 2011: Reverberation Mapping of Markarian 50
The Lick AGN Monitoring Project 2011 observing campaign was carried out over the course of 11 weeks in spring 2011. Here we present the first results from this program, a measurement of the broad-line reverberation lag in the Seyfert 1 galaxy Mrk 50. Combining our data with supplemental observations obtained prior to the start of the main observing campaign, our data set covers a total duration of 4.5 months. During this time, Mrk 50 was highly variable, exhibiting a maximum variability amplitude of a factor of ~4 in the U-band continuum and a factor of ~2 in the Hβ line. Using standard cross-correlation techniques, we find that Hβ and Hγ lag the V-band continuum by τ_(cen) = 10.64^(+0.82)_(–0.93) and 8.43^(+1.30)_(–1.28) days, respectively, while the lag of He II λ4686 is unresolved. The Hβ line exhibits a symmetric velocity-resolved reverberation signature with shorter lags in the high-velocity wings than in the line core, consistent with an origin in a broad-line region (BLR) dominated by orbital motion rather than infall or outflow. Assuming a virial normalization factor of f = 5.25, the virial estimate of the black hole mass is (3.2 ± 0.5) × 10^7 M_☉. These observations demonstrate that Mrk 50 is among the most promising nearby active galaxies for detailed investigations of BLR structure and dynamics.
118174601
SLUG: A new way to Stochastically Light Up Galaxies
We present SLUG, a new code to "Stochastically Light Up Galaxies". SLUG populates star clusters by randomly drawing stars from an initial mass function (IMF) and then following their time evolution with stellar models and an observationally-motivated prescription for cluster disruption. For a choice of star formation history, metallicity, and IMF, SLUG outputs synthetic photometry for clusters and field stars with a proper treatment of stochastic star formation. SLUG generates realistic distributions of star clusters, demonstrating the range of properties that result from finite sampling of an IMF and a random distribution of ages. The simulated data sets provide a quantitative means to address open problems in studies of star formation in galaxies and clusters, such as a test for IMF variations that are suggested by the systematic deficiency in the H-alpha/UV ratio in outer disks or in dwarf galaxies. SLUG will be made publicly available through the website this http URL
44837884
SLUG—STOCHASTICALLY LIGHTING UP GALAXIES. I. METHODS AND VALIDATING TESTS
The effects of stochasticity on the luminosities of stellar populations are an often neglected but crucial element for understanding populations in the low-mass or the low star formation rate regime. To address this issue, we present SLUG, a new code to "Stochastically Light Up Galaxies." SLUG synthesizes stellar populations using a Monte Carlo technique that properly treats stochastic sampling including the effects of clustering, the stellar initial mass function, star formation history, stellar evolution, and cluster disruption. This code produces many useful outputs, including (1) catalogs of star clusters and their properties such as their stellar initial mass distributions and their photometric properties in a variety of filters, (2) two dimensional histograms of color-magnitude diagrams of every star in the simulation, and (3) the photometric properties of field stars and the integrated photometry of the entire simulated galaxy. After presenting the SLUG algorithm in detail, we validate the code through comparisons with STARBURST99 in the well-sampled regime, and with observed photometry of Milky Way clusters. Finally, we demonstrate SLUG's capabilities by presenting outputs in the stochastic regime. SLUG is publicly distributed through the Web site http://sites.google.com/site/runslug/.
33202267
Generalized field theoretical approach to general relativity and conserved quantities in anti–de Sitter spacetimes
A new prescription to calculate the total energies and angular momenta of asymptotically $(d+1)$-dimensional anti\char21{}de Sitter spacetimes is proposed. The method is based on an extension of the field theoretical approach to general relativity to the case where there is an effective cosmological constant. A $(d\ensuremath{-}1)$ form $\ensuremath{\Omega}$ is exhibited which, when integrated on asymptotic $(d\ensuremath{-}1)$-dimensional boundary surfaces, yields the values of those conserved quantities. The calculations are gauge independent once asymptotic conditions are not violated. Total energies and angular momenta of some known solutions in four and five dimensions are calculated agreeing with standard results.
118072730
Construction and test of the prototype chamber for region 1 of the LHCb muon station 2
A four gapMWPC prototypefor region 1 of the muonstation2, with non-staggered wires,wasbuilt andtested.Theconstructiondetailsandthetestresultsarepresented. 1 Intr oduction TheLHCb muonsystem[1] will useMulti-Wire ProportionalChambers(MWPC) for thefour regionsof stations2 and3, for regions3 and4 of station1 andfor regions1 and2 of stations4 and5. Thechambersvary in sizefor thedifferentstationsandregionsandthey have different readoutpadsizesin thoseregions(see[2] for moredetails). In this note,theconstructionof a MWPC prototypefor region 1 of station2 is described.The prototypeis an exact realization of a chamberfor this region. It hasfour symmetricgasgapsandthe characteristicslisted in table1. Table1: Somechamberparametersandoperationconditions. GasGapsize(mm) 5 Anode-Cathodespacing(mm) 2.5 Wire Diameter( m) 30 Sensiti vearea(mm ) 300 250 Wire pitch (mm) 1.5 Wire padsize(mm ) 6.3 250 Wire length(mm) 257 Cathodepadsize(mm ) 37.5 31.3 Wire Tension(gf) 60 10 NominalGasmixture (40%50%10%) Wire nominalpotential(V) 3150 The chamberhasa combinedreadoutof wire andcathodepadsasa consequenceof the requiredgranularity. 2 Chamber Construction The prototypewasbuilt in Rio (CEFET-RJ andLAPE/IF-UFRJ)with PCB-honeycomb-PCB panelsas describedin the Muon SystemTDR [1]. The panels’flatnesswas measured(INMETRO1 andBargoa2) to be within m, which is betterthanthe requiredspecifications (see[3]). Thewire fixation barswerealsomeasuredandgluedto thecathodepanels.Theanodeto cathodedistancewasinsuredbymeansof aprecisesteelspacerfixedto thosebars,during thegluing of thewires. For thepresentprototypethewire fixation barswerenot machinedto have a noseon theedgeswhich wasdonefor thepreviousprototypesto avoid dischar ges[3]. The resultsfor the dark currentandthe sparklimit show that this noseis not necessary . The darkcurrentmeasuredwasof theorderof thenA andthesparklimit wasof about3.45kV. The wiring wasdonein a latheasshown in thepictureof figure1. The wire tensionwas guaranteedusinga calibrateddevice asshown in figure 2. This device hasa DC motor that keepsthewire undertensionby applyinga torqueon thereel. TheDC voltageappliedto the motorwascalibratedwith a60gf weight. 1InstitutoNacionaldeMetrologia,Normalizaç̃aoe QualidadeIndustrial,Rio deJaneiro 2BargoaConectores, Rio deJaneiro
121956644
A fast voltage preamplifier for use with MWPCs
Abstract We report the development of a voltage preamplifier for use with ionizing particles detection. It has been designed to match the requirements of a test station for muon Multiwire Proportional Chambers (MWPC) of the LHCb experiment at CERN. Simulation results and bench test measurements are presented, which exhibit the main circuit features: gain close to 500, rise time below 20 ns, bandwidth exceeding 30 MHz, input noise lower than 10 nV / Hz . Other results that demonstrate the applicability of the device in other contexts, specially with X-Ray imaging systems based on position sensitive detectors and proportional counters, are presented.
118403419
A method to identify and characterise binary candidates - a study of CoRoT data
The analysis of the CoRoT space mission data was performed aiming to test a method that selects, among the several light curves observed, the transiting systems that likely host a low-mass star orbiting the main target. The method identifies stellar companions by fitting a model to the observed transits. Applying this model, that uses equations like Kepler's third law and an empirical mass-radius relation, it is possible to estimate the mass and radius of the primary and secondary objects as well as the semimajor axis and inclination angle of the orbit. We focus on how the method can be used in the characterisation of transiting systems having a low-mass stellar companion with no need to be monitored with radial-velocity measurements or ground-based photometric observations. The model, which provides a good estimate of the system parameters, is also useful as a complementary approach to select possible planetary candidates. A list of confirmed binaries together with our estimate of their parameters are presented. The characterisation of the first twelve detected CoRoT exoplanetary systems was also performed and agrees very well with the results of their respective announcement papers. The comparison with confirmed systems validates our method, specially when the radius of the secondary companion is smaller than 1.5 Rjup, in the case of planets, or larger than 2 Rjup, in the case of low-mass stars. Intermediate situations are not conclusive.
118654190
Maximum Entropy Principle and the Higgs boson mass
A successful connection between Higgs boson decays and the Maximum Entropy Principle is presented. Based on the information theory inference approach we determine the Higgs boson mass as MH=125.04±0.25GeV, a value fully compatible to the LHC measurement. This is straightforwardly obtained by taking the Higgs boson branching ratios as the target probability distributions of the inference, without any extra assumptions beyond the Standard Model. Yet, the principle can be a powerful tool in the construction of any model affecting the Higgs sector. We give, as an example, the case where the Higgs boson has an extra invisible decay channel within a Higgs portal model.