scholarly journals A deep learning approach to quasar continuum prediction

2021 ◽  
Vol 502 (3) ◽  
pp. 3510-3532
Author(s):  
Bin Liu ◽  
Rongmon Bordoloi
Keyword(s):  
Deep Learning ◽  
Wavelength Range ◽  
Rest Frame ◽  
Hubble Space Telescope ◽  
Signal To Noise Ratio ◽  
Sloan Digital Sky Survey ◽  
Astronomical Surveys ◽  
Forest Region ◽  
Quasar Spectra ◽  
Gradual Evolution

ABSTRACT We present a novel intelligent quasar continuum neural network (iQNet), predicting the intrinsic continuum of any quasar in the rest-frame wavelength range of $1020 \, {\mathring{\rm A}}\le \lambda _{\text{rest}} \le 1600 \, {\mathring{\rm A}}$. We train this network using high-resolution Hubble Space Telescope/Cosmic Origin Spectrograph ultraviolet quasar spectra at low redshift (z ∼ 0.2) from the Hubble Spectroscopic Legacy Archive (HSLA), and apply it to predict quasar continua in different astronomical surveys. We utilize the HSLA quasar spectra that are well defined in the rest-frame wavelength range of [1020, 1600] Å with an overall median signal-to-noise ratio of at least 5. The iQNet model achieves a median absolute fractional flux error of 2.24 per cent on the training quasar spectra, and 4.17 per cent on the testing quasar spectra. We apply iQNet and predict the continua of ∼3200 Sloan Digital Sky Survey Data Release 16 quasar spectra at higher redshift (2 < z ≤ 5) and measure the redshift evolution of mean transmitted flux (〈F〉) in the Ly α forest region. We measure a gradual evolution of 〈F〉 with redshift, which we characterize as a power-law fit to the effective optical depth of the Ly α forest. Our measurements are broadly consistent with other estimates of 〈F〉 in the literature but provide a more accurate measurement as we are directly measuring the quasar continuum where there is minimum contamination from the Ly α forest. This work proves that the deep learning iQNet model can predict the quasar continuum with high accuracy and shows the viability of such methods for quasar continuum prediction.

scholarly journals Solving the conundrum of intervening strong Mg II absorbers towards gamma-ray bursts and quasars

2017 ◽  
Vol 608 ◽  
pp. A84 ◽  
Author(s):  
L. Christensen ◽  
S. D. Vergani ◽  
S. Schulze ◽  
N. Annau ◽  
J. Selsing ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Rest Frame ◽  
Gamma Ray ◽  
Incidence Rates ◽  
Gamma Ray Bursts ◽  
Sloan Digital Sky Survey ◽  
High Spectral Resolution ◽  
Data Sets ◽  
Quasar Spectra ◽  
Width Distribution

Previous studies have shown that the incidence rate of intervening strong Mg ii absorbers towards gamma-ray bursts (GRBs) were a factor of 2–4 higher than towards quasars. Exploring the similar sized and uniformly selected legacy data sets XQ-100 and XSGRB, each consisting of 100 quasar and 81 GRB afterglow spectra obtained with a single instrument (VLT/X-shooter), we demonstrate that there is no disagreement in the number density of strong Mg ii absorbers with rest-frame equivalent widths \hbox{$W_{\rm r}^{\lambda2796}>1$} Å towardsGRBs and quasars in the redshift range 0.1 ≲ z ≲ 5. With large and similar sample sizes, and path length coverages of Δz = 57.8 and 254.4 for GRBs and quasars, respectively, the incidences of intervening absorbers are consistent within 1σ uncertainty levels at all redshifts. For absorbers at z < 2.3, the incidence towards GRBs is a factor of 1.5 ± 0.4 higher than the expected number of strong Mg ii absorbers in Sloan Digital Sky Survey (SDSS) quasar spectra, while for quasar absorbers observed with X-shooter we find an excess factor of 1.4 ± 0.2 relative to SDSS quasars. Conversely, the incidence rates agree at all redshifts with reported high-spectral-resolution quasar data, and no excess is found. The only remaining discrepancy in incidences is between SDSS Mg ii catalogues and high-spectral-resolution studies. The rest-frame equivalent-width distribution also agrees to within 1σ uncertainty levels between the GRB and quasar samples. Intervening strong Mg ii absorbers towards GRBs are therefore neither unusually frequent, nor unusually strong.

ANALISIS SENSITIVITAS VIDEO MPEG-4 BERDASARKAN STRUKTUR FRAME PADA TRANSMISI DVB-T

2020 ◽  
Vol 25 (2) ◽  
pp. 86-97
Author(s):  
Sandy Suryo Prayogo ◽  
Tubagus Maulana Kusuma
Keyword(s):  
Deep Learning ◽  
Bit Error Rate ◽  
Error Rate ◽  
Signal To Noise Ratio ◽  
Similarity Index ◽  
Structural Similarity ◽  
Signal To Noise ◽  
Structural Similarity Index ◽  
Noise Ratio

DVB merupakan standar transmisi televisi digital yang paling banyak digunakan saat ini. Unsur terpenting dari suatu proses transmisi adalah kualitas gambar dari video yang diterima setelah melalui proses transimisi tersebut. Banyak faktor yang dapat mempengaruhi kualitas dari suatu gambar, salah satunya adalah struktur frame dari video. Pada tulisan ini dilakukan pengujian sensitifitas video MPEG-4 berdasarkan struktur frame pada transmisi DVB-T. Pengujian dilakukan menggunakan simulasi matlab dan simulink. Digunakan juga ffmpeg untuk menyediakan format dan pengaturan video akan disimulasikan. Variabel yang diubah dari video adalah bitrate dan juga group-of-pictures (GOP), sedangkan variabel yang diubah dari transmisi DVB-T adalah signal-to-noise-ratio (SNR) pada kanal AWGN di antara pengirim (Tx) dan penerima (Rx). Hasil yang diperoleh dari percobaan berupa kualitas rata-rata gambar pada video yang diukur menggunakan metode pengukuran structural-similarity-index (SSIM). Dilakukan juga pengukuran terhadap jumlah bit-error-rate BER pada bitstream DVB-T. Percobaan yang dilakukan dapat menunjukkan seberapa besar sensitifitas bitrate dan GOP dari video pada transmisi DVB-T dengan kesimpulan semakin besar bitrate maka akan semakin buruk nilai kualitas gambarnya, dan semakin kecil nilai GOP maka akan semakin baik nilai kualitasnya. Penilitian diharapkan dapat dikembangkan menggunakan deep learning untuk memperoleh frame struktur yang tepat di kondisi-kondisi tertentu dalam proses transmisi televisi digital.

Frame-Level Signal-to-Noise Ratio Estimation Using Deep Learning

2020 ◽  
Author(s):  
Hao Li ◽  
DeLiang Wang ◽  
Xueliang Zhang ◽  
Guanglai Gao
Keyword(s):  
Deep Learning ◽  
Signal To Noise Ratio ◽  
Ratio Estimation ◽  
Signal To Noise ◽  
Noise Ratio

scholarly journals Galaxy spin direction distribution in HST and SDSS show similar large-scale asymmetry

2020 ◽  
Vol 37 ◽  
Author(s):  
Lior Shamir
Keyword(s):  
Large Scale ◽  
Spiral Galaxies ◽  
Hubble Space Telescope ◽  
Gravitational Interaction ◽  
Large Data ◽  
Sloan Digital Sky Survey ◽  
Data Sets ◽  
Dipole Axis ◽  
Data Set ◽  
The Asymmetry

Abstract Several recent observations using large data sets of galaxies showed non-random distribution of the spin directions of spiral galaxies, even when the galaxies are too far from each other to have gravitational interaction. Here, a data set of $\sim8.7\cdot10^3$ spiral galaxies imaged by Hubble Space Telescope (HST) is used to test and profile a possible asymmetry between galaxy spin directions. The asymmetry between galaxies with opposite spin directions is compared to the asymmetry of galaxies from the Sloan Digital Sky Survey. The two data sets contain different galaxies at different redshift ranges, and each data set was annotated using a different annotation method. The results show that both data sets show a similar asymmetry in the COSMOS field, which is covered by both telescopes. Fitting the asymmetry of the galaxies to cosine dependence shows a dipole axis with probabilities of $\sim2.8\sigma$ and $\sim7.38\sigma$ in HST and SDSS, respectively. The most likely dipole axis identified in the HST galaxies is at $(\alpha=78^{\rm o},\delta=47^{\rm o})$ and is well within the $1\sigma$ error range compared to the location of the most likely dipole axis in the SDSS galaxies with $z>0.15$ , identified at $(\alpha=71^{\rm o},\delta=61^{\rm o})$ .

scholarly journals The need for a multi-purpose, optical–NIR space facility after HST and JWST

2021 ◽  
Author(s):  
Knud Jahnke ◽  
Oliver Krause ◽  
Hans-Walter Rix ◽  
Frédéric Courbin ◽  
Adriano Fontana ◽  
...  
Keyword(s):  
Wavelength Range ◽  
Hubble Space Telescope ◽  
Hubble Constant ◽  
White Paper ◽  
Space Mission ◽  
General Purpose ◽  
List Type ◽  
Space Telescope ◽  
Readiness Level ◽  
Visible Wavelengths

AbstractIn the early 2030s, after the end of operations for the epochal Hubble Space Telescope and the long-anticipated James Webb Space Telescope, astrophysics will lose access to a general purpose high-spatial resolution space observatory to cover the UV–optical–NIR wavelength range with a variety of imaging bandpasses and high-multiplexing mid-resolution spectroscopy. This will greatly impact astrophysical “discovery space” at visible wavelengths, in stark contrast to progress at most other wavelengths enabled by groundbreaking new facilities between 2010 and 2030. This capability gap will foreseeably limit progress in a number of fundamental research directions anticipated to be pressing in the 2030’s and beyond such as: What are the histories of star formation and cosmic element production in nearby galaxies? What can we learn about the nature of dark matter from dwarf galaxies? What is the local value of the Hubble Constant? A multi-purpose optical–NIR imaging and multiplexed spectroscopy Workhorse Camera (HWC) onboard NASA’s 4m-class Habitable Exoplanet Observatory (HabEx) space mission would provide access to these required data. HabEx is currently under study by NASA for the US Decadal Survey on Astronomy and Astrophysics 2020, and if selected would launch around 2035. Aside from its direct imaging of Earth-like exoplanets, it will have a general-observatory complement of instrumentation. The versatile Workhorse Camera will provide imaging and R$\sim $ ∼ 1000 spectroscopy from 370nm to 1800nm, diffraction-limited over the whole wavelength range, with simultaneous observations of the visible and NIR. Spectroscopic multiplexing will be achieved through microshutter arrays. All necessary HWC technology is already at Technology Readiness Level 5, hence technological risks are low. HWC has a rough-order-of-magnitude (ROM) cost of 300 M€, and could be European-funded within the cost envelope of an ESA S-class mission in the Voyage 2050 program, with matching funds by national funding agencies to construct HWC by a European instrument consortium. This White Paper is intended to put a European HabEx Workhorse Camera into ESA’s considerations. If ESA shares the wide interest and if HabEx were to be selected by NASA, there would be ample time to identify interested institutes for a European instrument consortium, including MPIA, to design, finance, and build the HabEx Workhorse Camera.

scholarly journals Computing 3D Phase-Type Holograms Based on Deep Learning Method

Photonics ◽  
2021 ◽  
Vol 8 (7) ◽  
pp. 280
Author(s):  
Huadong Zheng ◽  
Jianbin Hu ◽  
Chaojun Zhou ◽  
Xiaoxi Wang
Keyword(s):  
Deep Learning ◽  
Signal To Noise Ratio ◽  
Contrast Ratio ◽  
Angular Spectrum ◽  
Structural Similarity ◽  
Computational Time ◽  
Experimental Investigations ◽  
Training Strategy ◽  
Holographic Display ◽  
Phase Type

Computer holography is a technology that use a mathematical model of optical holography to generate digital holograms. It has wide and promising applications in various areas, especially holographic display. However, traditional computational algorithms for generation of phase-type holograms based on iterative optimization have a built-in tradeoff between the calculating speed and accuracy, which severely limits the performance of computational holograms in advanced applications. Recently, several deep learning based computational methods for generating holograms have gained more and more attention. In this paper, a convolutional neural network for generation of multi-plane holograms and its training strategy is proposed using a multi-plane iterative angular spectrum algorithm (ASM). The well-trained network indicates an excellent ability to generate phase-only holograms for multi-plane input images and to reconstruct correct images in the corresponding depth plane. Numerical simulations and optical reconstructions show that the accuracy of this method is almost the same with traditional iterative methods but the computational time decreases dramatically. The result images show a high quality through analysis of the image performance indicators, e.g., peak signal-to-noise ratio (PSNR), structural similarity (SSIM) and contrast ratio. Finally, the effectiveness of the proposed method is verified through experimental investigations.

scholarly journals Survey of Gravitationally Lensed Objects in HSC Imaging (SuGOHI) – VII. Discovery and confirmation of three strongly lensed quasars†

2021 ◽  
Vol 502 (1) ◽  
pp. 1487-1493
Author(s):  
Anton T Jaelani ◽  
Cristian E Rusu ◽  
Issha Kayo ◽  
Anupreeta More ◽  
Alessandro Sonnenfeld ◽  
...  
Keyword(s):  
Spectroscopic Data ◽  
Point Sources ◽  
Sloan Digital Sky Survey ◽  
Early Type ◽  
Blue Point ◽  
X Ray ◽  
Quasar Spectra ◽  
Strategic Program ◽  
Early Type Galaxy

ABSTRACT We present spectroscopic confirmation of three new two-image gravitationally lensed quasars, compiled from existing strong lens and X-ray catalogues. Images of HSC J091843.27–022007.5 show a red galaxy with two blue point sources at either side, separated by 2.26 arcsec. This system has a source and a lens redshifts zs = 0.804 and zℓ = 0.459, respectively, as obtained by our follow-up spectroscopic data. CXCO J100201.50+020330.0 shows two point sources separated by 0.85 arcsec on either side of an early-type galaxy. The follow-up spectroscopic data confirm the fainter quasar has the same redshift with the brighter quasar from the Sloan Digital Sky Survey (SDSS) fiber spectrum at zs = 2.016. The deflecting foreground galaxy is a typical early-type galaxy at a redshift of zℓ = 0.439. SDSS J135944.21+012809.8 has two point sources with quasar spectra at the same redshift zs = 1.096, separated by 1.05 arcsec, and fits to the HSC images confirm the presence of a galaxy between these. These discoveries demonstrate the power of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP)’s deep imaging and wide sky coverage. Combined with existing X-ray source catalogues and follow-up spectroscopy, the HSC-SSP provides us unique opportunities to find multiple-image quasars lensed by a foreground galaxy.

scholarly journals EEG Emotion Classification Using an Improved SincNet-Based Deep Learning Model

2019 ◽  
Vol 9 (11) ◽  
pp. 326 ◽  
Author(s):  
Hong Zeng ◽  
Zhenhua Wu ◽  
Jiaming Zhang ◽  
Chen Yang ◽  
Hua Zhang ◽  
...  
Keyword(s):  
Deep Learning ◽  
Speaker Recognition ◽  
Classification Accuracy ◽  
Deep Neural Network ◽  
Signal To Noise Ratio ◽  
Single Subject ◽  
Emotion Classification ◽  
Eeg Signals ◽  
Electroencephalogram Eeg ◽  
Deep Learning Model

Deep learning (DL) methods have been used increasingly widely, such as in the fields of speech and image recognition. However, how to design an appropriate DL model to accurately and efficiently classify electroencephalogram (EEG) signals is still a challenge, mainly because EEG signals are characterized by significant differences between two different subjects or vary over time within a single subject, non-stability, strong randomness, low signal-to-noise ratio. SincNet is an efficient classifier for speaker recognition, but it has some drawbacks in dealing with EEG signals classification. In this paper, we improve and propose a SincNet-based classifier, SincNet-R, which consists of three convolutional layers, and three deep neural network (DNN) layers. We then make use of SincNet-R to test the classification accuracy and robustness by emotional EEG signals. The comparable results with original SincNet model and other traditional classifiers such as CNN, LSTM and SVM, show that our proposed SincNet-R model has higher classification accuracy and better algorithm robustness.

scholarly journals Searching for Mg ii absorbers in and around galaxy clusters

2021 ◽  
Vol 503 (3) ◽  
pp. 4309-4319
Author(s):  
Jong Chul Lee ◽  
Ho Seong Hwang ◽  
Hyunmi Song
Keyword(s):  
Galaxy Clusters ◽  
Detection Rate ◽  
Massive Star ◽  
Sloan Digital Sky Survey ◽  
Number Density ◽  
Cluster Galaxies ◽  
Star Forming ◽  
Quasar Spectra ◽  
Sky Survey ◽  
The Galaxy

ABSTRACT To study environmental effects on the circumgalactic medium (CGM), we use the samples of redMaPPer galaxy clusters, background quasars, and cluster galaxies from the Sloan Digital Sky Survey (SDSS). With ∼82 000 quasar spectra, we detect 197 Mg ii absorbers in and around the clusters. The detection rate per quasar is 2.7 ± 0.7 times higher inside the clusters than outside the clusters, indicating that Mg ii absorbers are relatively abundant in clusters. However, when considering the galaxy number density, the absorber-to-galaxy ratio is rather low inside the clusters. If we assume that Mg ii absorbers are mainly contributed by the CGM of massive star-forming galaxies, a typical halo size of cluster galaxies is smaller than that of field galaxies by 30 ± 10 per cent. This finding supports that galaxy haloes can be truncated by interaction with the host cluster.

Dissecting quasars with the J-PAS narrow-band photometric survey

2019 ◽  
Vol 15 (S356) ◽  
pp. 12-16
Author(s):  
Silvia Bonoli ◽  
Giorgio Calderone ◽  
Raul Abramo ◽  
Jailson Alcaniz ◽  
Narciso Benitez ◽  
...  
Keyword(s):  
Emission Line ◽  
Wavelength Range ◽  
Software Package ◽  
Narrow Band ◽  
Active Galaxies ◽  
Emission Lines ◽  
Low Resolution ◽  
Strong Emission ◽  
Optical Wavelength ◽  
Quasar Spectra

AbstractThe J-PAS survey will soon start observing thousands of square degrees of the Northern Sky with its unique set of 56 narrow band filters covering the entire optical wavelength range, providing, effectively, a low resolution spectra for every object detected. Active galaxies and quasars, thanks to their strong emission lines, can be easily identified and characterized with J-PAS data. A variety of studies can be performed, from IFU-like analysis of local AGN, to clustering of high-z quasars. We also expect to be able to extract intrinsic physical quasar properties from the J-PAS pseudo-spectra, including continuum slope and emission line luminosities. Here we show the first attempts of using the QSFit software package to derive the properties for 22 quasars at 0.8 < z < 2 observed by the miniJPAS survey, the first deg2 of J-PAS data obtained with an interim camera. Results are compared with the ones obtained by applying the same software to SDSS quasar spectra.

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