arXiv subjects

M. Vivek

Publications and source records attributed to M. Vivek.

At least 19 recordsLinked to original sources

arXiv2026

Recurrent Multi-year Mg II BAL Variability in SDSS J1333+0012

We present a long-term spectroscopic study of Broad Absorption Line (BAL) variability in the quasar J1333+0012 (\zem = 0.9197) using an extensive multi-epoch dataset spanning nearly two decades. The dataset comprises multi-epoch observations from multiple observatories, delivering nearly uniform temporal coverage of the Mg II BAL profile, with close to one spectroscopic observation per year spanning the period from 2008 to 2025. We identify recurrent multi-year variability in the BAL absorption strength, characterized by a rest-frame timescale of $\sim$4 yr. Because the well-sampled baseline covers only a small number of candidate cycles, we present J1333+0012 as a candidate quasi-periodic BAL system. In contrast, contemporaneous optical photometric light curves from CRTS, Pan-STARRS, ZTF, and PTF show no statistically significant correlated variability on comparable timescales. However, ionization-driven variability cannot be ruled out, as the observed optical continuum does not directly trace the unobserved extreme-UV ionizing continuum. The coherence of the variability across distinct velocity components, coupled with the absence of large-scale profile reshaping, is consistent with a geometric origin. We interpret the observed behavior as modulation of the line-of-sight absorption by the rotation of an inhomogeneous shielding-gas structure.

astro-ph.GA↗

arXiv2026

Detection of Quasiperiodic Oscillations in the Blazar PKS 0735+178 with TESS

We report here the detection of signatures of a quasiperiodic oscillation (QPO) and a short flare in the optical light curve of the blazar PKS 0735+178, observed in two sectors, 71 and 72, spanning around 49 days with the Transiting Exoplanet Survey Satellite. The modest flare in sector 71 lasted ~4.3 days and appears as a combination of two sub-flares. In sector 72, a transient QPO with a period ~11.2 hours is detected at local and global significance levels of 4.11$\sigma$ and 3.06$\sigma$, respectively. We used weighted wavelet z transform, Lomb-Scargle periodogram, and phase dispersion minimization analysis techniques to look for and confirm the QPO feature. We also performed a segment-wise statistical inspection of these light curves and discuss here possible mechanisms that could explain the observed flux behavior.

astro-ph.HE↗

arXiv2025

Estimating the masses of Narrow line Seyfert 1 galaxies using damped random walk method

Narrow-line Seyfert 1 galaxies (NLSy1s) are a subclass of active galactic nuclei (AGNs), commonly associated with rapidly accreting, relatively low-mass black holes ($10^6$ - $10^8 M_\odot$) hosted in spiral galaxies. Although typically considered to have high Eddington ratios, recent observations, particularly of $\gamma$-ray-emitting NLSy1s, have raised questions about their true black hole masses, with some estimates approaching those of Broad-line Seyfert 1 (BLSy1) systems. In this work, we present the recalibrated mass estimations for a large sample of NLSy1s galaxies with z $<0.8$. We apply the damped random walk (DRW) formalism to a comparison set of 1,141 NLSy1 and 1,143 BLSy1 galaxies, matched in redshift and bolometric luminosity using SDSS DR17 spectroscopy. Our analysis employs a multivariate calibration that incorporates both the Eddington ratio and the rest-frame wavelength to refine the mass estimates. We obtain median DRW-based black hole masses of $\text{log}(M_{\text{BH}}^{\text{DRW}}/M_\odot) = 6.25 \pm 0.65$ for NLSy1s and $7.07 \pm 0.67$ for BLSy1s, in agreement with their respective virial mass distributions. Furthermore, we identify strong inverse trends between the variability amplitude and both optical luminosity and FeII emission strength, consistent with a scenario where higher accretion rates suppress long-term optical variability. These findings reinforce the view that NLSy1s harbor smaller black holes and highlight the value of variability-based approaches in tracing AGN accretion properties.

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arXiv2025

Radio Follow-Up Observations of a Weak-Line Quasar Exhibiting Remarkable X-ray Variability

SDSSJ1539+3954 ($z\approx 1.935$), a radio-quiet weak-line quasar (WLQ), exhibited exceptional X-ray variability in 2019$-$2020, with its X-ray flux increasing by over 20 times from 2013 to 2019 and subsequently dropping by at least a factor of nine in 2020. Motivated by the empirical correlations between X-ray and radio emission in AGN cores, we carried out a follow-up radio study in the 0.3$-$10 GHz range using GMRT (2020, 2022, 2024) and VLA (2022), and analyzed archival VLASS 3 GHz data (2017-2023) to investigate the source's radio properties and potential connection with the X-ray behavior. Our observations reveal a compact radio source with a spectral index of -0.65$\pm$0.15 in the frequency range of 0.3$-$1.4 GHz and -1.09$\pm$0.16 in 3$-$10 GHz. While the source was undetected in VLA-FIRST (1994) and VLASS epochs, the GMRT and VLA observations show no statistically significant variability over the monitored period. The absence of detectable changes in the radio flux, despite strong X-ray variability, suggests no direct connection between the X-ray variability and the radio emission, consistent with the Thick-Disk plus Outflow (TDO) model for WLQs. However, the sensitivity limit of the surveys prevents us from drawing definitive conclusions regarding longer timescale variability between the VLA-FIRST and GMRT epochs. We further explore possible mechanisms driving the radio emission from this source. Our analysis rules out small-scale jets and coronal emission as the primary drivers of the radio emission, suggesting that extended emission from AGN winds and star formation is the more plausible mechanism.

astro-ph.GA↗

arXiv2025

X-ray selected broad absorption line quasars in SDSS-V: BALs and non-BALs span the same range of X-ray properties

Broad absorption line (BAL) quasars are often considered X-ray weak relative to their optical/UV luminosity, whether intrinsically (i.e., the coronal emission is fainter) or due to large column densities of absorbing material. The SDSS-V is providing optical spectroscopy for samples of quasar candidates identified by eROSITA as well as Chandra, XMM or Swift, making the resulting datasets ideal for characterising the BAL quasar population within an X-ray selected sample. We use the Balnicity Index (BI) to identify the BAL quasars based on absorption of the CIV $\lambda\,1549$ emission line in the optical spectra, finding 143 BAL quasars in our sample of 2317 X-ray selected quasars within $1.5\le z \le3.5$. This observed BAL fraction of $\approx$ 6 per cent is comparable to that found in optically selected samples. We also identify absorption systems via the Absorption Index (AI) which includes mini-BALs and NALs, finding 954 quasars with AI $>0$. We consider the CIV emission space (equivalent width vs. blueshift) to study the BAL outflows within the context of the radiatively driven accretion disc-wind model. X-ray selection excludes the highest outflow velocities in emission but includes the full range of absorption velocities which we suggest is consistent with the BAL gas being located further from the X-ray corona than the emitting gas. We observe both X-ray weak and X-ray strong BALs (via the optical-to-X-ray spectral slope, $\alpha_\text{ox}$) and detect little evidence for differing column densities between the BAL and non-BAL quasars, suggesting the BALs and non-BALs have the same shielding gas and intrinsic X-ray emission.

astro-ph.GA↗

arXiv2025

Transient LoBALs at high velocities: A Case of Extreme Broad Absorption Line Variability in J115636.82+085628.9

We present a multi-epoch spectroscopic study of the broad absorption line (BAL) quasar J115636.82+085628.9 (z(em) = 2.1077), based on five spectra spanning nearly two decades in the observer's frame. This source exhibits remarkable variability in both low-ionization (LoBAL: Al III and Mg II) and high-ionization (HiBAL: C IV and Si IV) absorption features. For the first time, we detect the emergence and subsequent disappearance of LoBAL troughs at high velocities (~20,000 kms$^{-1}$), coinciding with the strengthening and weakening of the corresponding HiBAL absorption. The C IV BAL profile extends from ~6,700 kms$^{-1}$ to a conservative upper limit of 30,000 kms$^{-1}$ and is composed of narrow, variable absorption features embedded within a broad, smooth envelope. Both C IV and Si IV BAL troughs exhibit dramatic equivalent width (EW) changes, among the most extreme reported to date. Notably, these EW variations are strongly anti-correlated with continuum flux changes inferred from optical photometric light curves. We interpret this variability as the result of a new absorbing flow transiting into our line of sight, increasing the shielding of a more distant, pre-existing outflow and giving rise to transient LoBAL absorption. This scenario supports a unified picture in which LoBAL and HiBAL features arise from similar outflow structures, with observed differences governed primarily by line-of-sight column densities consistent with previous findings.

astro-ph.GA↗

arXiv2025

BAL Outflows are common in Low Eddington Ratio AGN

Broad absorption line (BAL) quasars exhibit significant outflows, offering insights into active galactic nuclei (AGN) feedback. While typically associated with high Eddington ratios, BAL quasars also occur in low Eddington ratio regimes, which remain poorly understood. This study aims to compare BAL properties and variability across these regimes.We investigate the occurrence rates, absorption characteristics, and variability of BAL quasars at low and high Eddington ratios. Using the SDSS DR16 quasar catalog, we selected a redshift-matched control sample to compare low and high Eddington ratio BAL quasar sources. We first examined the BAL fraction as a function of Eddington ratio. Key absorption parameters-equivalent width, absorption line width, velocity range, and depth-were analyzed, and a multi-epoch variability study was conducted using repeat spectra, followed by a comparison of parameter distributions between the two samples. For the first time, we report an increase in BAL fraction toward low Eddington ratios, in addition to the previously known trend of high BAL fraction at high Eddington ratios. While high Eddington sources show extreme absorption features, overall distributions are statistically similar except for maximum outflow velocity. No significant variability differences were observed. The correlation between outflow velocity, Eddington ratio, and luminosity supports the role of radiation pressure in driving quasar outflows. For low Eddington ratios, additional mechanisms, such as softer SEDs, larger outflow distances, and thickened accretion disks from radiatively inefficient processes, likely drive outflow formation.

astro-ph.GA↗

arXiv2024

Spectroscopic Quasar Anomaly Detection (SQuAD) I: Rest-Frame UV Spectra from SDSS DR16

We present the results of applying anomaly detection algorithms to a quasar spectroscopic sub-sample from the SDSS DR16 Quasar Catalog, covering the redshift range 1.88 < z < 2.47. Principal Component Analysis (PCA) was employed for dimensionality reduction of the quasar spectra, followed by hierarchical K-Means clustering in a 20-dimensional PCA eigenvector hyperspace. To prevent broad absorption line (BAL) quasars from being identified as the primary anomaly group, we conducted the analysis with and without them, comparing both datasets for a clearer identification of other anomalous quasar types. We identified 1,888 anomalous quasars, categorized into 10 broad groups. The anomalous groups include C IV Peakers-quasars with extremely strong and narrow C IV emission lines; Excess Si IV emitters-quasars where the Si IV line is as strong as the C IV line; and Si IV Deficient anomalies, which exhibit significantly weaker Si IV emission compared to typical quasars. The anomalous nature of these quasars is attributed to lower Eddington ratios for C IV Peakers, super-solar metallicity for Excess Si IV emitters, and sub-solar metallicity for Si IV Deficient anomalies. Additionally, we identified four groups of BAL anomalies: Blue BALs, Flat BALs, Reddened BALs, and FeLoBALs, distinguished primarily by the strength of reddening in these sources. Further, among the non-BAL quasars, we identified three types of reddened anomaly groups classified as heavily reddened, moderately reddened, and plateau-shaped spectrum quasars, each exhibiting varying degrees of reddening. The detected anomalies are presented as a value-added catalog.

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arXiv2024

FLAME: Fitting Ly$\alpha$ Absorption lines using Machine learning

We introduce FLAME, a machine-learning algorithm designed to fit Voigt profiles to HI Lyman-alpha (Ly$\alpha$) absorption lines using deep convolutional neural networks. FLAME integrates two algorithms: the first determines the number of components required to fit Ly$\alpha$ absorption lines, and the second calculates the Doppler parameter $b$, the HI column density N$_{\rm HI}$, and the velocity separation of individual components. For the current version of FLAME, we trained it on low-redshift Ly$\alpha$ forests observed with the far-ultraviolet gratings of the Cosmic Origin Spectrograph (COS) on board the Hubble Space Telescope (HST). Using these data, we trained FLAME on $\sim$ $10^6$ simulated Voigt profiles which we forward-modeled to mimic Ly$\alpha$ absorption lines observed with HST-COS in order to classify lines as either single or double components and then determine Voigt profile-fitting parameters. FLAME shows impressive accuracy on the simulated data, identifying more than 98\% (90\%) of single (double) component lines. It determines $b$ values within $\approx \pm{8}~(15)$ km s$^{-1}$ and log $N_{\rm HI}/ {\rm cm}^2$ values within $\approx \pm 0.3~(0.8)$ for 90\% of the single (double) component lines. However, when applied to real data, FLAME's component classification accuracy drops by $\sim$ 10\%. Nevertheless, there is reasonable agreement between the $b$ and N$_{\rm HI}$ distributions obtained from traditional Voigt profile-fitting methods and FLAME's predictions. Our mock HST-COS data analysis, designed to emulate real data parameters, demonstrates that FLAME is able to achieve consistent accuracy comparable to its performance with simulated data. This finding suggests that the drop in FLAME's accuracy when used on real data primarily arises from the difficulty in replicating the full complexity of real data in the training sample.

astro-ph.CO↗

arXiv2023

How does the presence of bar affects the fueling of supermassive black holes ? An IllustrisTNG100 perspective

We conduct a statistical study of black hole masses of barred and unbarred galaxies in the IllustrisTNG100 cosmological magneto-hydrodynamical simulations. This work aims to understand the role of the bars in the growth of central supermassive black hole mass and its implications on AGN fueling. Our sample consists of 1191 barred galaxies and 2738 unbarred galaxies in the IllustrisTNG100 simulations. To have an unbiased study, we perform our analysis with an equal number of barred and unbarred galaxies by using various controlled parameters like total galaxy mass, stellar mass, gas mass, dark matter halo mass, etc. Except for the stellar mass controlling, we find that the median of the black hole mass distribution for barred galaxies is higher than that of the unbarred ones indicating that stellar mass is a key parameter influencing the black hole growth. The higher mean accretion rate of the black holes in barred galaxies, averaged since the bar forming epoch (z~2 ), explains the higher mean black hole masses in barred galaxies. Further, we also test that these results are unaffected by other environmental processes like minor/major merger histories and neighboring gas density of black hole. Although the relationship between stellar mass, bar formation, and black hole growth is complex, with various mechanisms involved, our analysis suggests that bars can play a crucial role in feeding black holes, particularly in galaxies with massive stellar disks.

astro-ph.GA↗

arXiv2022

Photometric identification of compact galaxies, stars and quasars using multiple neural networks

We present MargNet, a deep learning-based classifier for identifying stars, quasars and compact galaxies using photometric parameters and images from the Sloan Digital Sky Survey (SDSS) Data Release 16 (DR16) catalogue. MargNet consists of a combination of Convolutional Neural Network (CNN) and Artificial Neural Network (ANN) architectures. Using a carefully curated dataset consisting of 240,000 compact objects and an additional 150,000 faint objects, the machine learns classification directly from the data, minimising the need for human intervention. MargNet is the first classifier focusing exclusively on compact galaxies and performs better than other methods to classify compact galaxies from stars and quasars, even at fainter magnitudes. This model and feature engineering in such deep learning architectures will provide greater success in identifying objects in the ongoing and upcoming surveys, such as Dark Energy Survey (DES) and images from the Vera C. Rubin Observatory.

astro-ph.GA↗

arXiv2022

Fraction of broad absorption line quasars in different radio morphologies

In this study, we investigated the orientation model of Broad Absorption Line (BAL) quasars using a sample of sources that are common in Sloan Digital Sky Survey (SDSS) Data Release (DR)-16 quasar catalog and Very Large Array (VLA)-Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey. Using the radio cut-out images from the FIRST survey, we first designed a deep learning model using convolutional neural networks (CNN) to classify the quasar radio morphologies into the core-only, young jet, single lobe, or triples. These radio morphologies are further sub-classified into core-dominated and lobe-dominated sources. The CNN models can classify the sources with a high precision of >98% for all the morphological sub-classes. The average BAL fraction in the resolved core, core-dominated, and lobe-dominated quasars are consistent with the BAL fraction inferred from radio and infra-red surveys. We also present the distribution of BAL quasars as a function of quasar orientation by using the radio core-dominance as an orientation indicator. A similar analysis is performed for HiBALs, LoBALs, and FeLoBALs. All the radio morphological sub-classes and BAL sub-classes show an increase in BAL fraction at high orientation angles of the jets with respect to the line of sight. Our analysis suggests that BAL quasars are more likely to be found in viewing angles close to the equatorial plane of the quasar. However, a pure orientation model is inadequate, and a combination of orientation and evolution is probably the best way to explain the complete BAL phenomena.

astro-ph.GA↗

arXiv2021

Appearance vs Disappearance of broad absorption line troughs in quasars

We present a new set of 84 Broad absorption line (BAL) quasars ( 1.7 $<$ \zem $<$ 4.4) exhibiting an appearance of \civ BAL troughs over 0.3$-$4.8 rest-frame years by comparing the Sloan Digital Sky Survey Data Release (SDSSDR)-7, SDSSDR-12, and SDSSDR-14 quasar catalogs. We contrast the nature of BAL variability in this appearing BAL quasar sample with a disappearing BAL quasar sample studied in literature by comparing the quasar's intrinsic, BAL trough, and continuum parameters between the two samples. We find that appearing BAL quasars have relatively higher redshift and smaller probed timescales as compared to the disappearing BAL quasars. To mitigate the effect of any redshift bias, we created control samples of appearing and disappearing BAL quasars that have similar redshift distribution. We find that the appearing BAL quasars are relatively brighter and have shallower and wider BAL troughs compared to the disappearing BAL sample. The distribution of quasar continuum variability parameters between the two samples is clearly separated, with the appearance of the BAL troughs being accompanied by the dimming of the continuum and vice versa. Spectral index variations in the two samples also point to the anti-correlation between the BAL trough and continuum variations consistent with the "bluer when brighter" trend in quasars. We show that the intrinsic dust model is less likely to be a favorable scenario in explaining BAL appearance/disappearance. Our analysis suggests that the extreme variations of BAL troughs like BAL appearance/disappearance are mainly driven by changes in the ionization conditions of the absorbing gas.

astro-ph.GA↗

arXiv2020

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Large-scale Structure Catalogs for Cosmological Analysis

We present large-scale structure catalogs from the completed extended Baryon Oscillation Spectroscopic Survey (eBOSS). Derived from Sloan Digital Sky Survey (SDSS) -IV Data Release 16 (DR16), these catalogs provide the data samples, corrected for observational systematics, and random positions sampling the survey selection function. Combined, they allow large-scale clustering measurements suitable for testing cosmological models. We describe the methods used to create these catalogs for the eBOSS DR16 Luminous Red Galaxy (LRG) and Quasar samples. The quasar catalog contains 343,708 redshifts with $0.8 < z < 2.2$ over 4,808\,deg$^2$. We combine 174,816 eBOSS LRG redshifts over 4,242\,deg$^2$ in the redshift interval $0.6 < z < 1.0$ with SDSS-III BOSS LRGs in the same redshift range to produce a combined sample of 377,458 galaxy redshifts distributed over 9,493\,deg$^2$. Improved algorithms for estimating redshifts allow that 98 per cent of LRG observations result in a successful redshift, with less than one per cent catastrophic failures ($\Delta z > 1000$ ${\rm km~s}^{-1}$). For quasars, these rates are 95 and 2 per cent (with $\Delta z > 3000$ ${\rm km~s}^{-1}$). We apply corrections for trends between the number densities of our samples and the properties of the imaging and spectroscopic data. For example, the quasar catalog obtains a $\chi^2$/DoF$= 776/10$ for a null test against imaging depth before corrections and a $\chi^2$/DoF$=6/8$ after. The catalogs, combined with careful consideration of the details of their construction found here-in, allow companion papers to present cosmological results with negligible impact from observational systematic uncertainties.

astro-ph.CO↗

arXiv2020

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: BAO and RSD measurements from the anisotropic power spectrum of the Quasar sample between redshift 0.8 and 2.2

We measure the clustering of quasars of the final data release (DR16) of eBOSS. The sample contains $343\,708$ quasars between redshifts $0.8\leq z\leq2.2$ over $4699\,\mathrm{deg}^2$. We calculate the Legendre multipoles (0,2,4) of the anisotropic power spectrum and perform a BAO and a Full-Shape (FS) analysis at the effective redshift $z{\rm eff}=1.480$. The errors include systematic errors that amount to 1/3 of the statistical error. The systematic errors comprise a modelling part studied using a blind N-Body mock challenge and observational effects studied with approximate mocks to account for various types of redshift smearing and fibre collisions. For the BAO analysis, we measure the transverse comoving distance $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.60\pm{0.90}$ and the Hubble distance $D_{\rm H}(z_{\rm eff})/r_{\rm drag}=13.34\pm{0.60}$. This agrees with the configuration space analysis, and the consensus yields: $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.69\pm{0.80}$ and $D_{\rm H}(z_{\rm eff})/r_{\rm drag}=13.26\pm{0.55}$. In the FS analysis, we fit the power spectrum using a model based on Regularised Perturbation Theory, which includes Redshift Space Distortions and the Alcock-Paczynski effect. The results are $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.68\pm{0.90}$ and $D_{\rm H}(z_{\rm eff})/r_{\rm drag}=13.52\pm{0.51}$ and we constrain the linear growth rate of structure $f(z_{\rm eff})\sigma_8(z_{\rm eff})=0.476\pm{0.047}$. Our results agree with the configuration space analysis. The consensus analysis of the eBOSS quasar sample yields: $D_{\rm M}(z_{\rm eff})/r_{\rm drag}=30.21\pm{0.79}$, $D_{\rm H}(z_{\rm eff})/r_{\rm drag}=3.23\pm{0.47}$ and $f(z_{\rm eff})\sigma_8(z_{\rm eff})=0.462\pm{0.045}$ and is consistent with a flat $\Lambda {\rm CDM}$ cosmological model using Planck results.

astro-ph.CO↗

arXiv2020

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: BAO and RSD measurements from anisotropic clustering analysis of the Quasar Sample in configuration space between redshift 0.8 and 2.2

We measure the anisotropic clustering of the quasar sample from Data Release 16 (DR16) of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey (eBOSS). A sample of $343,708$ spectroscopically confirmed quasars between redshift $0.8<z<2.2$ are used as tracers of the underlying dark matter field. In comparison with DR14 sample, the final sample doubles the number of objects as well as the survey area. In this paper, we present the analysis in configuration space by measuring the two-point correlation function and decompose using the Legendre polynomials. For the full-shape analysis of the Legendre multipole moments, we measure the BAO distance and the growth rate of the cosmic structure. At an effective redshift of $z_{\rm eff}=1.48$, we measure the comoving angular diameter distance $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 30.66\pm0.88$, the Hubble distance $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 13.11\pm0.52$, and the growth rate $f\sigma_8(z_{\rm eff}) = 0.439\pm0.048$. The accuracy of these measurements is confirmed using an extensive set of mock simulations developed for the quasar sample. The uncertainties on the distance and growth rate measurements have been reduced substantially ($\sim 45\%$ and $\sim30\%$) with respect to the DR14 results. We also perform a BAO-only analysis to cross check the robustness of the methodology of the full-shape analysis. Combining our analysis with the Fourier space analysis, we arrive at $D^{\bf{c}}_{\rm M}(z_{\rm eff})/r_{\rm drag} = 30.22 \pm 0.79$, $D^{\bf{c}}_{\rm H}(z_{\rm eff})/r_{\rm drag} = 13.26 \pm 0.47$, and $f\sigma_8^{\bf{c}}(z_{\rm eff}) = 0.464 \pm 0.045$.

astro-ph.CO↗

arXiv2020

The completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Large-scale Structure Catalogues and Measurement of the isotropic BAO between redshift 0.6 and 1.1 for the Emission Line Galaxy Sample

We present the Emission Line Galaxy (ELG) sample of the extended Baryon Oscillation Spectroscopic Survey (eBOSS) from the Sloan Digital Sky Survey IV Data Release 16 (DR16). After describing the observations and redshift measurement for the 269,243 observed ELG spectra over 1170 deg$^2$, we present the large-scale structure catalogues, which are used for the cosmological analysis. These catalogues contain 173,736 reliable spectroscopic redshifts between 0.6 and 1.1, along with the associated random catalogues quantifying the extent of observations, and the appropriate weights to correct for non-cosmological fluctuations. We perform a spherically averaged baryon acoustic oscillations (BAO) measurement in configuration space, with density field reconstruction: the data 2-point correlation function shows a feature consistent with that of the BAO, providing a 3.2-percent measurement of the spherically averaged BAO distance $D_V(z_{\rm eff})/r_{\rm drag} = 18.23\pm 0.58$ at the effective redshift $z_{\rm eff}=0.845$.

astro-ph.CO↗

arXiv2020

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: measurement of the BAO and growth rate of structure of the emission line galaxy sample from the anisotropic power spectrum between redshift 0.6 and 1.1

We analyse the large-scale clustering in Fourier space of emission line galaxies (ELG) from the Data Release 16 of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey. The ELG sample contains 173,736 galaxies covering 1,170 square degrees in the redshift range $0.6 < z < 1.1$. We perform a BAO measurement from the post-reconstruction power spectrum monopole, and study redshift space distortions (RSD) in the first three even multipoles. Photometric variations yield fluctuations of both the angular and radial survey selection functions. Those are directly inferred from data, imposing integral constraints which we model consistently. The full data set has only a weak preference for a BAO feature ($1.4\sigma$). At the effective redshift $z_{\rm eff} = 0.845$ we measure $D_{\rm V}(z_{\rm eff})/r_{\rm drag} = 18.33_{-0.62}^{+0.57}$, with $D_{\rm V}$ the volume-averaged distance and $r_{\rm drag}$ the comoving sound horizon at the drag epoch. In combination with the RSD measurement, at $z_{\rm eff} = 0.85$ we find $f\sigma_8(z_{\rm eff}) = 0.289_{-0.096}^{+0.085}$, with $f$ the growth rate of structure and $\sigma_8$ the normalisation of the linear power spectrum, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 20.0_{-2.2}^{+2.4}$ and $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 19.17 \pm 0.99$ with $D_{\rm H}$ and $D_{\rm M}$ the Hubble and comoving angular distances, respectively. These results are in agreement with those obtained in configuration space, thus allowing a consensus measurement of $f\sigma_8(z_{\rm eff}) = 0.315 \pm 0.095$, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 19.6_{-2.1}^{+2.2}$ and $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 19.5 \pm 1.0$. This measurement is consistent with a flat $\Lambda$CDM model with Planck parameters.

astro-ph.CO↗