arXiv subjects

Neeraj Gupta

Publications and source records attributed to Neeraj Gupta.

At least 37 records · Page 2Linked to original sources

arXiv2021

Spatially resolved Lyman-$α$ emission around radio bright quasars

We use Southern African Large Telescope (SALT) to perform long-slit spectroscopic observations of 23 newly discovered radio-loud quasars (RLQs) at $2.7 $1000 km/s in all, except one). Using the samples of high-$z$ radio-loud quasars and galaxies from literature, we confirm the correlation between the Ly$α$ halo luminosity and its size with radio power ($L_{\rm 420MHz}$). The same quantities are found to be correlating weakly with the projected linear size of the radio emission. Our sample is the second largest sample of RLQs being studied for the presence of diffuse Ly$α$ emission and fills in a redshift gap between previous such studies. Integral Field Spectroscopy is required to fully understand the relationship between the large scale radio emission and the overall distribution, kinematics and over density of Ly$α$ emission in the field of these RLQs.

astro-ph.GA↗

arXiv2021

FREGAN : an application of generative adversarial networks in enhancing the frame rate of videos

A digital video is a collection of individual frames, while streaming the video the scene utilized the time slice for each frame. High refresh rate and high frame rate is the demand of all high technology applications. The action tracking in videos becomes easier and motion becomes smoother in gaming applications due to the high refresh rate. It provides a faster response because of less time in between each frame that is displayed on the screen. FREGAN (Frame Rate Enhancement Generative Adversarial Network) model has been proposed, which predicts future frames of a video sequence based on a sequence of past frames. In this paper, we investigated the GAN model and proposed FREGAN for the enhancement of frame rate in videos. We have utilized Huber loss as a loss function in the proposed FREGAN. It provided excellent results in super-resolution and we have tried to reciprocate that performance in the application of frame rate enhancement. We have validated the effectiveness of the proposed model on the standard datasets (UCF101 and RFree500). The experimental outcomes illustrate that the proposed model has a Peak signal-to-noise ratio (PSNR) of 34.94 and a Structural Similarity Index (SSIM) of 0.95.

cs.CV↗

arXiv2021

The Evolutionary Map of the Universe Pilot Survey

We present the data and initial results from the first Pilot Survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The survey covers 270 \sqdeg of an area covered by the Dark Energy Survey, reaching a depth of 25--30 \ujybm\ rms at a spatial resolution of $\sim$ 11--18 arcsec, resulting in a catalogue of $\sim$ 220,000 sources, of which $\sim$ 180,000 are single-component sources. Here we present the catalogue of single-component sources, together with (where available) optical and infrared cross-identifications, classifications, and redshifts. This survey explores a new region of parameter space compared to previous surveys. Specifically, the EMU Pilot Survey has a high density of sources, and also a high sensitivity to low surface-brightness emission. These properties result in the detection of types of sources that were rarely seen in or absent from previous surveys. We present some of these new results here.

astro-ph.CO↗

arXiv2021

Lyman-$α$ emission from a WISE-selected optically faint powerful radio galaxy M151304.72-252439.7 at $z$ = 3.132

We report the detection of a large ($\sim90$ kpc) and luminous $\mathrm{Lyα}$ nebula [$L\mathrm{_{Lyα}}$ = $(6.80\pm0.08)\times 10^{44}$] $\rm{\,erg\,s^{-1}}$ around an optically faint (r$>23$ mag) radio galaxy M1513-2524 at $z\mathrm{_{em}}$=3.132. The double-lobed radio emission has an extent of 184 kpc, but the radio core, i.e., emission associated with the active galactic nucleus (AGN) itself, is barely detected. This object was found as part of our survey to identify high-$z$ quasars based on Wide-field Infrared Survey Explorer (WISE) colors. The optical spectrum has revealed $\mathrm{Lyα}$, NV, CIV and HeII emission lines with a very weak continuum. Based on long-slit spectroscopy and narrow band imaging centered on the $\mathrm{Lyα}$ emission, we identify two spatial components: a "compact component" with high velocity dispersion ($\sim 1500$$\rm{\,km\,s^{-1}}$) seen in all three lines, and an "extended component", having low velocity dispersion (i.e., 700-1000$\rm{\,km\,s^{-1}}$). The emission line ratios are consistent with the compact component being in photoionization equilibrium with an AGN. We also detect spatially extended associated $\mathrm{Lyα}$ absorption, which is blue-shifted within 250-400$\rm{\,km\,s^{-1}}$ of the $\mathrm{Lyα}$ peak. The probability of $\mathrm{Lyα}$ absorption detection in such large radio sources is found to be low ($\sim$10%) in the literature. M1513-2524 belongs to the top few percent of the population in terms of $\mathrm{Lyα}$ and radio luminosities. Deep integral field spectroscopy is essential for probing this interesting source and its surroundings in more detail.

astro-ph.GA↗

arXiv2020

OH in the diffuse interstellar medium: physical modelling and prospects with upcoming SKA precursor/pathfinder surveys

Hydroxyl ($\rm OH$) is known to form efficiently in cold gas ($T\sim 100$K) along with the molecule $\rm H_2$ and can be used as an efficient tracer of the diffuse molecular gas in the interstellar medium (ISM). Using a simple formalism describing the $\rm H\,I/H_2$ transition and a reduced network of major chemical reactions, we present a semi-analytical prescription to estimate the abundances of O-bearing molecules in the diffuse ISM. We show that predictions based on our prescription are in good agreement with the estimates obtained using the MEUDON PDR code which utilizes the full reaction network. We investigate the dependence of the relative abundances of $\rm OH/H\,I$ and $\rm OH/H_2$ on the variations of physical conditions i.e., the metallicity, number density ($n$), cosmic ray ionization rate ($ζ$) and strength of UV field ($χ$) in the medium. We find that the $\rm OH/H\,I$ abundances observed in the Galactic ISM can be reproduced by models with $n\sim 50$cm$^{-3}$, $χ\sim 1$ (Mathis field) and $ζ\sim3\times10^{-17}$s$^{-1}$, with a variation of about one dex allowed around these values. Using the constrained $\rm H_2$ column density distribution function at $z\sim3$, we estimate the $\rm OH$ column density distribution function and discuss future prospects with the upcoming large radio absorption line surveys.

astro-ph.GA↗

arXiv2020

uGMRT HI 21-cm absorption observations of two extremely inverted spectrum sources

We report the detection of HI 21-cm absorption in a member of the rare and recently discovered class of compact radio sources, 'Extremely Inverted Spectrum Extragalactic Radio Sources (EISERS)'. EISERS conceivably form a special sub-class of the inverted spectrum radio galaxies since the spectral index of the optically thick part of the spectrum for these sources crosses the synchrotron self absorption limit of $α=+2.5$ (S($ν$) $\propto$ $ν^α$). We have searched for HI absorption in two EISERS using the recently upgraded Giant Metrewave Radio Telescope (uGMRT) and detected an absorption feature in one of them. The strong associated HI absorption detected against the source J1209$-$2032 ($z$=0.4040) implies an optical depth of 0.178$\pm$0.02 corresponding to an HI column density of 34.8$\pm$2.9 $\times$10$^{20}$ cm$^{-2}$, for an assumed HI spin temperature of 100 K and covering factor of 1. This is among the highest known optical depth and HI column densities found for compact radio sources of GPC/CSS type and supports the free-free absorption model for the steeply inverted radio spectrum of this source. For the other source, J1549$+$5038 ($z$ = 2.171), no HI absorption was detected in our observations.

astro-ph.GA↗

arXiv2019

uGMRT search for cold gas at z~1-1.4 towards red quasars

We present results from our search for HI 21-cm and OH 18-cm absorption at z~1-1.4 towards red quasars showing strong MgII absorption using uGMRT. The quasars J1501+1822 and J1521+5508 show multiple strong associated MgII absorption at z~1.1 and signature of reddening in their optical spectra. We report the detection of HI 21-cm absorption towards J1521+5508 at the systemic redshift of the quasar, with N(HI) =(1.2 +/- 0.2) x 10^{20} cm^{-2} for spin temperature of 100 K and unit covering factor. The HI 21-cm absorption is offset from the blueshifted strong MgII absorbers by >~1500 km/s. We do not detect HI 21-cm absorption at the redshift of the associated MgII absorption and at the systemic redshift towards J1501+1822. We argue that lack of one-to-one correspondence between MgII and HI 21-cm absorption could be related with clumpiness of the neutral gas and the radio and optical sightlines probing different volume of the gas. We find that the presence of strong associated MgII absorption and reddening in the optical spectra of the quasars lead to an increased detection rate of associated HI 21-cm absorption at z>=1. We also report non-detection of intervening OH absorption ([OH]/[HI] <= (1-4) x 10^{-8}) at z = 1.3 towards two red quasars, J0850+5159 and J0852+3435, which show strong metal and HI 21-cm absorption and the 2175 A dust extinction bump.

astro-ph.GA↗

arXiv2019

Prevalence of neutral gas in centres of merging galaxies-II: nuclear HI and multi-wavelength properties

Using a sample of 38 radio-loud galaxy mergers at z<=0.2, we confirm the high detection rate (~84%) of HI 21-cm absorption in mergers, which is significantly higher (~4 times) than in non-mergers. The distributions of the HI column density [N(HI)] and velocity shift of the absorption with respect to the systemic redshift of the galaxy hosting the radio source in mergers are significantly different from that in non-mergers. We investigate the connection of the nuclear HI gas with various multi-wavelength properties of the mergers. While the inferred N(HI) and gas kinematics do not show strong (i.e. >=3-sigma level) correlation with galaxy properties, we find that the incidence and N(HI) of absorption tend to be slightly higher at smaller projected separations between the galaxy pairs and among the lower stellar mass-radio galaxies. The incidence, N(HI) and line width of HI absorption increase from the pre-merger to the post-merger stages. The 100% detection rate in post-mergers indicates that the neutral gas in the circumnuclear regions survives the coalescence period and is not yet quenched by the nuclear radio activity.

astro-ph.GA↗

arXiv2019

GMRT 610 MHz observations of galaxy clusters in the ACT equatorial sample

We present Giant Metrewave Radio Telescope 610 MHz observations of 14 Atacama Cosmology Telescope (ACT) clusters, including new data for nine. The sample includes 73\% of ACT equatorial clusters with $M_{500} > 5 \times 10^{14}\;M_\odot$. We detect diffuse emission in three of these (27$^{+20}_{-14}$\%): we detect a radio mini-halo in ACT-CL J0022.2$-$0036 at $z=0.8$, making it the highest-redshift mini-halo known; we detect potential radio relic emission in ACT-CL J0014.9$-$0057 ($z=0.533$); and we confirm the presence of a radio halo in low-mass cluster ACT-CL J0256.5+0006, with flux density $S_{610} = 6.3\;\pm\;0.4$ mJy. We also detect residual diffuse emission in ACT-CL J0045.9$-$0152 ($z=0.545$), which we cannot conclusively classify. For systems lacking diffuse radio emission, we determine radio halo upper limits in two ways and find via survival analysis that these limits do not significantly affect radio power scaling relations. Several clusters with no diffuse emission detection are known or suspected mergers, based on archival X-ray and/or optical measures; given the limited sensitivity of our observations, deeper observations of these disturbed systems are required in order to rule out the presence of diffuse emission consistent with known scaling relations. In parallel with our diffuse emission results, we present catalogs of individual radio sources, including a few interesting extended sources. Our study represents the first step towards probing the occurrence of diffuse emission in high-redshift ($z\gtrsim0.5$) clusters, and serves as a pilot for statistical studies of larger cluster samples with the new radio telescopes available in the pre-SKA era.

astro-ph.CO↗

arXiv2018

Prevalence of neutral gas in centres of merging galaxies

We present Giant Metrewave Radio Telescope and Very Large Array observations of HI 21-cm absorption in ten z<=0.2 galaxy mergers that host strong radio sources. Seven of these mergers show strong absorption [with N(HI) ~10^{21-22} cm^{-2}, for spin temperature of 100 K and unit covering factor], leading to a total detection rate of 83 +/- 17% in low-z radio-loud galaxy mergers. This is ~3-4 times higher than that found for intrinsic HI 21-cm absorption in low-z radio sources in general. The fraction of intrinsic absorbers that are associated with mergers increases with increasing N(HI) threshold, i.e. ~40% and 100% of the absorbers with N(HI) >10^{21} cm^{-2} and >10^{22} cm^{-2} arise from mergers, respectively. The distribution of N(HI) among the mergers is significantly different from that found in isolated systems, with mergers giving rise to six times stronger absorption on average. The fraction of redshifted absorption components (with respect to the systemic velocity of the radio source obtained from optical emission lines) among mergers is found to be higher by two to three times compared to that found for non-interacting systems. Follow-up spatially-resolved multi-wavelength spectroscopy is essential to understand the exact connection between the presence of circumnuclear neutral gas and the AGN activity in these mergers.

astro-ph.GA↗

arXiv2017

HI 21-cm absorption from $z\sim0.35$ strong MgII absorbers

We have searched for HI 21-cm absorption in 11 strong MgII systems ($W_{\rm r}$(MgII $λ2796$) $\ge 1$ Å) at $0.3<z<0.5$ using the Giant Metrewave Radio Telescope. We have detected HI 21-cm absorption in two of these. From the integrated optical depth ($\intτ~dv$) we estimate $N$(HI) = $43 \pm 2$ and $9 \pm 2$ in units of $10^{19}$ cm$^{-2}$ for the absorbers towards J1428+2103 ($z_{abs} = 0.3940$) and J1551+0713 ($z_{abs} = 0.3289$), respectively, assuming spin temperature, $T_s = 100$ K, and gas covering factor, $C_f = 1$. The velocity width of the HI absorption towards J1428+2103 and J1551+0713 indicate that the gas temperature is $<1600$ K and $<350$ K, respectively. The $3σ$ upper limits on $\intτ~dv$ in case of the HI 21-cm non-detections indicate that these MgII absorbers are likely to arise from sub-damped Lyman-$α$ systems, when we assume $T_s = 100$ K and $C_f = 1$. This is verified for one of the systems which has $N$(HI) measurement using Lyman-$α$ absorption detected in the ultraviolet spectrum. We estimate the detection rate of HI 21-cm absorption in strong MgII systems in our sample to be $0.18^{+0.24}_{-0.12}$ at $z\sim0.35$, for an integrated optical depth sensitivity of $\le 0.3$ km s$^{-1}$. Comparing with the results of HI 21-cm absorption surveys in strong MgII systems at higher redshifts from the literature, we do not find any significant evolution in the incidence and number density per unit redshift of HI 21-cm absorbers in strong MgII systems over $0.3<z<1.5$.

astro-ph.GA↗

arXiv2016

A giant radio halo in a low-mass SZ-selected galaxy cluster: ACT-CL J0256.5+0006

We present the detection of a giant radio halo (GRH) in the Sunyaev-Zel'dovich (SZ)-selected merging galaxy cluster ACT-CL J0256.5+0006 ($z = 0.363$), observed with the Giant Metrewave Radio Telescope at 325 MHz and 610 MHz. We find this cluster to host a faint ($S_{610} = 5.6 \pm 1.4$ mJy) radio halo with an angular extent of 2.6 arcmin, corresponding to 0.8 Mpc at the cluster redshift, qualifying it as a GRH. J0256 is one of the lowest-mass systems, $M_{\rm 500,SZ} = (5.0 \pm 1.2) \times 10^{14} M_\odot$, found to host a GRH. We measure the GRH at lower significance at 325 MHz ($S_{325} = 10.3 \pm 5.3$ mJy), obtaining a spectral index measurement of $α^{610}_{325} = 1.0^{+0.7}_{-0.9}$. This result is consistent with the mean spectral index of the population of typical radio halos, $α= 1.2 \pm 0.2$. Adopting the latter value, we determine a 1.4 GHz radio power of $P_{1.4\text{GHz}} = (1.0 \pm 0.3) \times 10^{24}$ W Hz$^{-1}$, placing this cluster within the scatter of known scaling relations. Various lines of evidence, including the ICM morphology, suggest that ACT-CL J0256.5+0006 is composed of two subclusters. We determine a merger mass ratio of 7:4, and a line-of-sight velocity difference of $v_\perp = 1880 \pm 280$ km s$^{-1}$. We construct a simple merger model to infer relevant time-scales in the merger. From its location on the $P_{\rm 1.4GHz}{-}L_{\rm X}$ scaling relation, we infer that we observe ACT-CL J0256.5+0006 approximately 500 Myr before first core crossing.

astro-ph.GA↗

arXiv2016

Mapping kiloparsec-scale structures in the extended HI disc of the galaxy UGC 00439 by HI 21-cm absorption

We study the properties of HI gas in the outer regions (~2r_25) of a spiral galaxy, UGC 00439 (z = 0.01769), using HI 21-cm absorption towards different components of an extended background radio source, J0041$-$0043 (z = 1.679). The radio source exhibits a compact core coincident with the optical quasar and two lobes separated by ~7 kpc, all at an impact parameter ~25 kpc. The HI 21-cm absorption detected towards the southern lobe is found to extend over ~2 kpc^2. The absorbing gas shows sub-kpc-scale structures with the line-of-sight velocities dominated by turbulent motions. Much larger optical depth variations over 4-7 kpc-scale are revealed by the non-detection of HI 21-cm absorption towards the radio core and the northern lobe, and the detection of NaI and CaII absorption towards the quasar. This could reflect a patchy distribution of cold gas in the extended HI disc. We also detect HI 21-cm emission from UGC 00439 and two other galaxies within ~150 kpc to it, that probably form an interacting group. However, no HI 21-cm emission from the absorbing gas is detected. Assuming a linear extent of ~4 kpc, as required to cover both the core and the southern lobe, we constrain the spin temperature <~300 K for the absorbing gas. The kinematics of the gas and the lack of signatures of any ongoing in situ star formation are consistent with the absorbing gas being at the kinematical minor axis and corotating with the galaxy. Deeper HI 21-cm observations would help to map in greater detail both the large- and small-scale structures in the HI gas associated with UGC 00439.

astro-ph.GA↗

arXiv2014

The Radio Relics and Halo of El Gordo, a Massive $z=0.870$ Cluster Merger

We present 610 MHz and 2.1 GHz imaging of the massive SZE-selected z=0.870 cluster merger ACT-CL J0102-4915 (El Gordo), obtained with the GMRT and the ATCA, respectively. We detect two complexes of radio relics separated by 3.4' (1.6 Mpc) along the system's NW-to-SE collision axis that have high integrated polarizations (33%) and steep spectral indices, consistent with creation via Fermi acceleration by shocks in the ICM. From the spectral index of the relics, we compute a Mach number of 2.5^{+0.7}_{-0.3} and shock speed of 2500^{+400}_{-300} km/s. With our ATCA data, we compute the Faraday depth across the NW relic and find a mean value of 11 rad/m^2 and standard deviation of 6 rad/m^2. With the integrated line-of-sight gas density derived from new Chandra observations, our Faraday depth measurement implies B_parallel~0.01 μG in the cluster outskirts. The extremely narrow shock widths in the relics (<23 kpc) prevent us from placing a meaningful constraint on |B| using cooling time arguments. In addition to the relics, we detect a large (1.1 Mpc radius), powerful (log L_1.4[W/Hz]= 25.66+-0.12) radio halo with a Bullet-like morphology. The spectral-index map of the halo shows the synchrotron spectrum is flattest near the relics, along the collision axis, and in regions of high T_gas, all locations associated with recent energy injection. The spatial and spectral correlation between the halo emission and cluster X-ray properties supports primary-electron processes like turbulent reacceleration as the halo production mechanism. The halo's integrated 610 MHz to 2.1 GHz spectral index is 1.2+-0.1, consistent with the cluster's high T_gas in view of previously established global scaling relations. El Gordo is the highest-redshift cluster known to host a radio halo and/or radio relics, and provides new constraints on the non-thermal physics in clusters at z>0.6. [abridged]

astro-ph.CO↗

arXiv2012

Associated 21-cm absorption towards the cores of radio galaxies

We present the results of Giant Metrewave Radio Telescope (GMRT) observations to detect H{\sc i} in absorption towards the cores of a sample of radio galaxies. From observations of a sample of 16 sources, we detect H{\sc i} in absorption towards the core of only one source, the FR\,II radio galaxy 3C\,452 which has been reported earlier by Gupta & Saikia (2006a). In this paper we present the results for the remaining sources which have been observed to a similar optical depth as for a comparison sample of compact steep-spectrum (CSS) and giga-hertz peaked spectrum (GPS) sources. We also compile available information on H{\sc i} absorption towards the cores of extended radio sources observed with angular resolutions of a few arcsec or better. The fraction of extended sources with detection of H{\sc i} absorption towards their cores is significantly smaller (7/47) than the fraction of H{\sc i} detection towards CSS and GPS objects (28/49). For the cores of extended sources, there is no evidence of a significant correlation between H{\sc i} column density towards the cores and the largest linear size of the sources. The distribution of the relative velocity of the principal absorbing component towards the cores of extended sources is not significantly different from that of the CSS and GPS objects. However, a few of the CSS and GPS objects have blue-shifted components $\gapp$1000 km s$^{-1}$, possibly due to jet-cloud interactions. With the small number of detections towards cores, the difference in detection rate between FR\,I (4/32) and FR\,II (3/15) sources is within the statistical uncertainties.

astro-ph.CO↗

arXiv2012

Associated H{\sc i} absorption towards the core of the radio galaxy 3C 321

We report the results of Giant Metrewave Radio Telescope (GMRT) observations of H{\sc i} absorption towards the FRII radio galaxy 3C321 (J1531+2404), which is associated with an active galaxy interacting with a companion. The absorption profile towards the radio core is well resolved and consists three components, of which the two prominent ones are red-shifted by 186 and 235 km s$^{-1}$ relative to the optical systemic velocity. The neutral hydrogen column density towards the core is estimated to be $N$(H{\sci})=9.23$\times10^{21}$(${T}_{\rm s}$/100)($f_{c}$/1.0) cm$^{-2}$, where ${T}_{\rm s}$ and $f_c$ are the spin temperature and covering factor of the background source respectively. We also present radio continuum observations of the source with both the GMRT and the Very Large Array (VLA) in order to understand the properties of a plume of emission at an angle of $\sim30^\circ$ to the source axis. This feature appears to have a steep high-frequency spectrum. The current hotspots and jet are active and seen in X-ray emission. The spectral ages of the lobes are $\lapp$26 Myr. We discuss the possibility that the plume could be relic emission due to an earlier cycle of activity.

astro-ph.GA↗

arXiv2012

A Probabilistic Transmission Expansion Planning Methodology based on Roulette Wheel Selection and Social Welfare

A new probabilistic methodology for transmission expansion planning (TEP) that does not require a priori specification of new/additional transmission capacities and uses the concept of social welfare has been proposed. Two new concepts have been introduced in this paper: (i) roulette wheel methodology has been used to calculate the capacity of new transmission lines and (ii) load flow analysis has been used to calculate expected demand not served (EDNS). The overall methodology has been implemented on a modified IEEE 5-bus test system. Simulations show an important result: addition of only new transmission lines is not sufficient to minimize EDNS.

cs.AI↗

arXiv2011

A Novel Method for Calculating Demand Not Served for Transmission Expansion Planning

Restructuring of the power market introduced demand uncertainty in transmission expansion planning (TEP), which in turn also requires an accurate estimation of demand not served (DNS). Unfortunately, the graph theory based minimum-cut maximum-flow (MCMF) approach does not ensure that electrical laws are followed. Nor can it be used for calculating DNS at individual buses. In this letter, we propose a generalized load flow based methodology for calculating DNS. This procedure is able to calculate simultaneously generation not served (GNS) and wheeling loss (WL). Importantly, the procedure is able to incorporate the effect of I2R losses, excluded in MCMF approach. Case study on a 5-bus IEEE system shows the effectiveness of the proposed approach over existing method.

cs.OH↗