scholarly journals How many components? Quantifying the complexity of the metallicity distribution in the Milky Way bulge with APOGEE

2020 ◽  
Vol 499 (1) ◽  
pp. 1037-1057 ◽  
Author(s):  
Alvaro Rojas-Arriagada ◽  
Gail Zasowski ◽  
Mathias Schultheis ◽  
Manuela Zoccali ◽  
Sten Hasselquist ◽  
...  
Keyword(s):  
Measurement Errors ◽  
High Redshift ◽  
Gaussian Mixture ◽  
Optimal Number ◽  
Sloan Digital Sky Survey ◽  
Individual Measurement ◽  
Rr Lyrae ◽  
Bulge Region ◽  
Evolution Experiment ◽  
Metallicity Distribution

ABSTRACT We use data of ∼13 000 stars from the Sloan Digital Sky Survey/Apache Point Observatory Galactic Evolution Experiment survey to study the shape of the bulge metallicity distribution function (MDF) within the region |ℓ| ≤ 11° and |b| ≤ 13°, and spatially constrained to RGC ≤ 3.5 kpc. We apply Gaussian mixture modelling and non-negative matrix factorization decomposition techniques to identify the optimal number and the properties of MDF components. We find that the shape and spatial variations of the MDF (at [Fe/H] ≥ −1 dex) are well represented as a smoothly varying contribution of three overlapping components located at [Fe/H] = +0.32, −0.17, and −0.66 dex. The bimodal MDF found in previous studies is in agreement with our trimodal assessment once the limitations in sample size and individual measurement errors are taken into account. The shape of the MDF and its correlations with kinematics reveal different spatial distributions and kinematical structure for the three components co-existing in the bulge region. We confirm the consensus physical interpretation of metal-rich stars as associated with the secularly evolved disc into a boxy/peanut X-shape bar. On the other hand, metal-intermediate stars could be the product of in-situ formation at high redshift in a gas-rich environment characterized by violent and fast star formation. This interpretation would help us to link a present-day structure with those observed in formation in the centre of high-redshift galaxies. Finally, metal-poor stars may correspond to the metal-rich tail of the population sampled at lower metallicity from the study of RR Lyrae stars. Conversely, they could be associated with the metal-poor tail of the early thick disc.

scholarly journals The bimodal [Mg/Fe] versus [Fe/H] bulge sequence as revealed by APOGEE DR14

2019 ◽  
Vol 626 ◽  
pp. A16 ◽  
Author(s):  
A. Rojas-Arriagada ◽  
M. Zoccali ◽  
M. Schultheis ◽  
A. Recio-Blanco ◽  
G. Zasowski ◽  
...  
Keyword(s):  
Fundamental Parameters ◽  
Elemental Abundances ◽  
Data Release ◽  
Bulge Region ◽  
Solar Metallicity ◽  
Inner Region ◽  
Clean Sample ◽  
Metallicity Distribution ◽  
Single Sequence

Context. The Galactic bulge has a bimodal metallicity distribution function: different kinematic, spatial, and, potentially, age distributions characterize the metal-poor and metal-rich components. Despite this observed dichotomy, which argues for different formation channels for those stars, the distribution of bulge stars in the α-abundance versus metallicity plane has been found so far to be a rather smooth single sequence. Aims. We use data from the fourteenth data release of the APOGEE spectroscopic survey (DR14) to investigate the distribution in the Mg abundance (as tracer of the α-elements)-versus-metallicity plane of a sample of stars selected to be in the inner region of the bulge. Methods. A clean sample has been selected from the DR14 using a set of data- and pipeline-flags to ensure the quality of their fundamental parameters and elemental abundances. An additional selection made use of computed spectro-photometric distances to select a sample of likely bulge stars as those with RGC ≤ 3.5 kpc. We adopt magnesium abundance as an α-abundance proxy for our clean sample as it has been proven to be the most accurate α-element as determined by ASPCAP, the pipeline for data products from APOGEE spectra. Results. From the distribution of our bulge sample in the [Mg/Fe]-versus-[Fe/H] plane, we found that the sequence is bimodal. This bimodality is given by the presence of a low-Mg sequence of stars parallel to the main high-Mg sequence over a range of ∼0.5 dex around solar metallicity. The two sequences merge above [Fe/H] ∼ 0.15 dex into a single sequence whose dispersion in [Mg/Fe] is larger than either of the two sequences visible at lower metallicity. This result is confirmed when we consider stars in our sample that are inside the bulge region according to trustworthy Gaia DR2 distances.

The Quest for Relics: Massive compact galaxies in the local Universe

2019 ◽  
Vol 15 (S359) ◽  
pp. 441-443
Author(s):  
F. S. Lohmann ◽  
A. Schnorr-Müller ◽  
M. Trevisan ◽  
R. Riffel ◽  
N. Mallmann ◽  
...  
Keyword(s):  
High Redshift ◽  
Control Sample ◽  
Sloan Digital Sky Survey ◽  
Integral Field Spectroscopy ◽  
Sky Survey ◽  
Size Evolution ◽  
Compact Galaxies ◽  
Minor Mergers ◽  
Significant Size ◽  
Integral Field

AbstractObservations at high redshift reveal that a population of massive, quiescent galaxies (called red nuggets) already existed 10 Gyr ago. These objects undergo a significant size evolution over time, likely due to minor mergers. In this work we present an analysis of local massive compact galaxies to assess if their properties are consistent with what is expected for unevolved red nuggets (relic galaxies). Using integral field spectroscopy (IFS) data from the MaNGA survey from the Sloan Digital Sky Survey (SDSS), we characterized the kinematics and properties of stellar populations of massive compact galaxies, and find that these objects exhibit, on average, a higher rotational support than a control sample of average sized early-type galaxies. This is in agreement with a scenario in which these objects have a quiet accretion history, rendering them candidates for relic galaxies.

scholarly journals Computing Accurate Probabilistic Estimates of One-D Entropy from Equiprobable Random Samples

Entropy ◽  
2021 ◽  
Vol 23 (6) ◽  
pp. 740
Author(s):  
Hoshin V. Gupta ◽  
Mohammad Reza Ehsani ◽  
Tirthankar Roy ◽  
Maria A. Sans-Fuentes ◽  
Uwe Ehret ◽  
...  
Keyword(s):  
Sample Size ◽  
Parameter Tuning ◽  
Gaussian Mixture ◽  
Optimal Number ◽  
Small Sample ◽  
Random Samples ◽  
Data Points ◽  
Probability Mass ◽  
Entropy Estimate ◽  
Log Normal

We develop a simple Quantile Spacing (QS) method for accurate probabilistic estimation of one-dimensional entropy from equiprobable random samples, and compare it with the popular Bin-Counting (BC) and Kernel Density (KD) methods. In contrast to BC, which uses equal-width bins with varying probability mass, the QS method uses estimates of the quantiles that divide the support of the data generating probability density function (pdf) into equal-probability-mass intervals. And, whereas BC and KD each require optimal tuning of a hyper-parameter whose value varies with sample size and shape of the pdf, QS only requires specification of the number of quantiles to be used. Results indicate, for the class of distributions tested, that the optimal number of quantiles is a fixed fraction of the sample size (empirically determined to be ~0.25–0.35), and that this value is relatively insensitive to distributional form or sample size. This provides a clear advantage over BC and KD since hyper-parameter tuning is not required. Further, unlike KD, there is no need to select an appropriate kernel-type, and so QS is applicable to pdfs of arbitrary shape, including those with discontinuous slope and/or magnitude. Bootstrapping is used to approximate the sampling variability distribution of the resulting entropy estimate, and is shown to accurately reflect the true uncertainty. For the four distributional forms studied (Gaussian, Log-Normal, Exponential and Bimodal Gaussian Mixture), expected estimation bias is less than 1% and uncertainty is low even for samples of as few as 100 data points; in contrast, for KD the small sample bias can be as large as -10% and for BC as large as -50%. We speculate that estimating quantile locations, rather than bin-probabilities, results in more efficient use of the information in the data to approximate the underlying shape of an unknown data generating pdf.

scholarly journals Predicted properties of RR Lyrae stars in the Sloan Digital Sky Survey photometric system

2006 ◽  
Vol 371 (3) ◽  
pp. 1503-1512 ◽  
Author(s):  
M. Marconi ◽  
M. Cignoni ◽  
M. Di Criscienzo ◽  
V. Ripepi ◽  
F. Castelli ◽  
...  
Keyword(s):  
Sloan Digital Sky Survey ◽  
Photometric System ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Sky Survey ◽  
Lyrae Stars

scholarly journals FIVE NEW HIGH-REDSHIFT QUASAR LENSES FROM THE SLOAN DIGITAL SKY SURVEY

2009 ◽  
Vol 137 (5) ◽  
pp. 4118-4126 ◽  
Author(s):  
Naohisa Inada ◽  
Masamune Oguri ◽  
Min-Su Shin ◽  
Issha Kayo ◽  
Michael A. Strauss ◽  
...  
Keyword(s):  
High Redshift ◽  
Sloan Digital Sky Survey ◽  
Sky Survey

Simulation of Compressor Transient Behavior Through Recurrent Neural Network Models

2005 ◽  
Vol 128 (3) ◽  
pp. 444-454 ◽  
Author(s):  
M. Venturini
Keyword(s):  
Measurement Errors ◽  
Learning Algorithm ◽  
Back Propagation ◽  
Network Models ◽  
Transient Behavior ◽  
Optimal Number ◽  
Measured Data ◽  
Outlet Temperature ◽  
Neural Network Models ◽  
Hidden Layer

In the paper, self-adapting models capable of reproducing time-dependent data with high computational speed are investigated. The considered models are recurrent feed-forward neural networks (RNNs) with one feedback loop in a recursive computational structure, trained by using a back-propagation learning algorithm. The data used for both training and testing the RNNs have been generated by means of a nonlinear physics-based model for compressor dynamic simulation, which was calibrated on a multistage axial-centrifugal small size compressor. The first step of the analysis is the selection of the compressor maneuver to be used for optimizing RNN training. The subsequent step consists in evaluating the most appropriate RNN structure (optimal number of neurons in the hidden layer and number of outputs) and RNN proper delay time. Then, the robustness of the model response towards measurement uncertainty is ascertained, by comparing the performance of RNNs trained on data uncorrupted or corrupted with measurement errors with respect to the simulation of data corrupted with measurement errors. Finally, the best RNN model is tested on field data taken on the axial-centrifugal compressor on which the physics-based model was calibrated, by comparing physics-based model and RNN predictions against measured data. The comparison between RNN predictions and measured data shows that the agreement can be considered acceptable for inlet pressure, outlet pressure and outlet temperature, while errors are significant for inlet mass flow rate.

scholarly journals The Optical/Near-IR Colours of Red Quasars

2000 ◽  
Vol 17 (1) ◽  
pp. 56-71 ◽  
Author(s):  
Paul J. Francis ◽  
Matthew T. Whiting ◽  
Rachel L. Webster
Keyword(s):  
Power Law ◽  
High Redshift ◽  
Sloan Digital Sky Survey ◽  
Spectral Energy ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Red Power ◽  
Near Ir ◽  
Sky Survey ◽  
Ir Photometry

AbstractWe present quasi-simultaneous multi-colour optical/near-IR photometry for 157 radio selected quasars, forming an unbiassed sub-sample of the Parkes Flat-Spectrum Sample. Data are also presented for 12 optically selected QSOs, drawn from the Large Bright QSO Survey. The spectral energy distributions of the radio- and optically-selected sources are quite different. The optically selected QSOs are all very similar: they have blue spectral energy distributions curving downwards at shorter wavelengths. Roughly 90% of the radio-selected quasars have roughly power-law spectral energy distributions, with slopes ranging from Fv∝v0 to Fv∝v−2. The remaining 10% have spectral energy distributions showing sharp peaks: these are radio galaxies and highly reddened quasars. Four radio sources were not detected down to magnitude limits of H ∼ 19·6. These are probably high redshift (z > 3) galaxies or quasars. We show that the colours of our red quasars lie close to the stellar locus in the optical: they will be hard to identify in surveys such as the Sloan Digital Sky Survey. If near-IR photometry is added, however, the red power-law sources can be clearly separated from the stellar locus: IR surveys such as 2MASS should be capable of finding these sources on the basis of their excess flux in the K-band.

scholarly journals The effect of dust bias on the census of neutral gas and metals in the high-redshift Universe due to SDSS-II quasar colour selection

2019 ◽  
Vol 486 (3) ◽  
pp. 4377-4397 ◽  
Author(s):  
Jens-Kristian Krogager ◽  
Johan P U Fynbo ◽  
Palle Møller ◽  
Pasquier Noterdaeme ◽  
Kasper E Heintz ◽  
...  
Keyword(s):  
Mass Density ◽  
High Redshift ◽  
Target Selection ◽  
Neutral Hydrogen ◽  
Sloan Digital Sky Survey ◽  
Selection Probability ◽  
Optical Extinction ◽  
Neutral Gas ◽  
High Redshift Universe ◽  
The Impact

ABSTRACT We present a systematic study of the impact of a dust bias on samples of damped Ly α absorbers (DLAs). This bias arises as an effect of the magnitude and colour criteria utilized in the Sloan Digital Sky Survey (SDSS) quasar target selection up until data release 7 (DR7). The bias has previously been quantified assuming only a contribution from the dust obscuration. In this work, we apply the full set of magnitude and colour criteria used up until SDSS-DR7 in order to quantify the full impact of dust biasing against dusty and metal-rich DLAs. We apply the quasar target selection algorithm on a modelled population of intrinsic colours, and by exploring the parameter space consisting of redshift, ($z_{\rm{\small QSO}}$and zabs), optical extinction, and H i column density, we demonstrate how the selection probability depends on these variables. We quantify the dust bias on the following properties derived for DLAs at z ≈ 3: the incidence rate, the mass density of neutral hydrogen and metals, and the average metallicity. We find that all quantities are significantly affected. When considering all uncertainties, the mass density of neutral hydrogen is underestimated by 10–50 per cent, and the mass density in metals is underestimated by 30–200 per cent. Lastly, we find that the bias depends on redshift. At redshift z = 2.2, the mass density of neutral hydrogen and metals might be underestimated by up to a factor of 2 and 5, respectively. Characterizing such a bias is crucial in order to accurately interpret and model the properties and metallicity evolution of absorption-selected galaxies.

scholarly journals Absolute calibration of the polarisation angle for future CMB B-mode experiments from current and future measurements of the Crab nebula

2020 ◽  
Vol 634 ◽  
pp. A100 ◽  
Author(s):  
J. Aumont ◽  
J. F. Macías-Pérez ◽  
A. Ritacco ◽  
N. Ponthieu ◽  
A. Mangilli
Keyword(s):  
Measurement Errors ◽  
Crab Nebula ◽  
Potential Effect ◽  
Energy Scale ◽  
Absolute Calibration ◽  
Systematic Effect ◽  
Individual Measurement ◽  
Microwave Frequencies ◽  
Mode Spectrum ◽  
The Crab Nebula

A tremendous international effort is currently dedicated to observing the so-called primordial B modes of the cosmic microwave background (CMB) polarisation. If measured, this faint signal, caused by the primordial gravitational wave background, would be evidence of the inflation epoch and quantify its energy scale, providing a rigorous test of fundamental physics far beyond the reach of accelerators. At the unprecedented sensitivity level that the new generation of CMB experiments aims to reach, every uncontrolled instrumental systematic effect will potentially result in an analysis bias that is larger than the much sought-after CMB B-mode signal. The absolute calibration of the polarisation angle is particularly important in this context because any associated error will end up in leakage from the much larger E modes into B modes. The Crab nebula (Tau A), with its bright microwave synchrotron emission, is one of the few objects in the sky that can be used as absolute polarisation calibrators. In this paper we review the currently best constraints on its polarisation angle from 23 to 353 GHz at typical angular scales for CMB observations from WMAP, XPOL, Planck, and NIKA data. These polarisation angle measurements are compatible with a constant angle of −88.26° ±0.27° (assuming that systematic errors are independent between frequencies and that the experiments fully capture the extent of the Crab nebula). We study the uncertainty on this mean angle under different considerations for combinations of the individual measurement errors. For each of the cases, we study the potential effect on the CMB B-mode spectrum and on the recovered r parameter through a likelihood analysis. We find that current constraints on the Crab polarisation angle, assuming it is constant through microwave frequencies, allow us to calibrate experiments with an accuracy enabling the measurement of r ∼ 0.01. On the other hand, even under the most optimistic assumptions, current constraints will lead to an important limitation for the detection of r ∼ 10−3. New realistic measurement of the Crab nebula can change this situation by strengthening the assumption of the consistency across microwave frequencies and reducing the combined error.

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