arXiv subjects

Swayamtrupta Panda

Publications and source records attributed to Swayamtrupta Panda.

At least 109 records · Page 6Linked to original sources

arXiv2020

Scatter Analysis Along the Multidimensional Radius-Luminosity Relations for Reverberation-Mapped Mg II Sources

The usage of the radius-luminosity (R-L) relation for the determination of black hole masses across the cosmic history as well as its application for cosmological studies motivates us to analyze its scatter, which has recently increased significantly both for the optical (H$β$) and UV (Mg II) lines. To this purpose, we determined the scatter along the R-L relation for an up-to-date reverberation-mapped Mg II sample. Studying linear combinations of the luminosity at 3000 A with independent parameters such as the Full Width at Half Maximum (FWHM), Fe II strength (R$_\mathrm{FeII}$), and the fractional variability ($F\mathrm{_{var}}$) for the whole sample, we get only a small decrease in the scatter ($σ{_{\rm rms}}=0.29-0.30$ dex). Linear combinations with the dimensionless accretion rate ($\dot{\mathcal{M}}$) and the Eddington ratio ($α_\mathrm{Edd}$) lead to significant reductions of the scatter ($σ_{\rm rms}\sim 0.1$ dex), albeit both suffering from the inter-dependency on the observed time-delay. After the division into two sub-samples considering the median value of the $\dot{\mathcal{M}}$ in the full sample, we find that the scatter decreases significantly for the highly accreting sub-sample. In particular, the smallest scatter of $σ{_{\rm rms}}=0.17$ dex is associated with the independent parameter R$_\mathrm{FeII}$, followed by the combination with $F\mathrm{_{var}}$, with $σ{_{\rm rms}}=0.19$ dex. Both of these independent observationally-inferred parameters are in turn correlated with $\dot{\mathcal{M}}$ and $α_\mathrm{Edd}$. These results suggest that the large scatter along the R-L relation is driven $\textit{mainly}$ by the accretion rate intensity.

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arXiv2020

Quasar main sequence in the UV plane

Active galaxies form a clear pattern in the optical plane showing the correlation between the Full Width Half Maximum (FWHM) of the H$β$ line and the ratio of the Equivalent Width (EW) of the optical FeII emission and the EW(H$β$). This pattern is frequently refereed to as the quasar main sequence. In this paper we study the UV plane showing FWHM of the MgII line against the ratio of EW of UV FeII emission to EW(MgII). We show that the UV plane trends are different, with the underlying strong correlation between FWHM(MgII) and EW(MgII). This correlation is entirely driven by the choice of the continuum used to measure EW(MgII). If we correct for the strong curvature in the UV continuum related to the character of emission expected from accretion disk, the behavior of the FWHM vs. EW for MgII becomes similar to the behaviour of H$β$. Such a similarity is expected since both lines belong to the Low Ionization group of emission lines and come from a similar region. Such a similarity and weak coupling between FWHM and EW of the corresponding line is then also consistent with the Broad Line Region model based on the presence of dust in the accretion disk atmosphere.

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arXiv2020

The CaFe Project: Optical Fe II and Near-Infrared Ca II triplet emission in active galaxies: (I) Photoionization modelling

Optical Fe II emission is a strong feature in quasar spectra originating in the broad-line region (BLR). The difficulty in understanding the complex Fe II pseudo-continuum has led us to search for other reliable, simpler ionic species such as Ca II. In this first part of the series, we confirm the strong correlation between the strengths of two emission features, the optical Fe II and the NIR Ca II, both from observations and photoionization modelling. With the inclusion of an up-to-date compilation of observations with both optical Fe II and NIR Ca II measurements, we span a wider and more extended parameter space and confirm the common origin of these two spectral features with our photoionization models using CLOUDY. Taking into account the effect of dust into our modelling, we constrain the BLR parameter space (primarily, in terms of the ionization parameter and local cloud density) as a function of the strengths of Fe II and Ca II emission.

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arXiv2020

Time-delay measurement of MgII broad line response for the highly-accreting quasar HE 0413-4031: Implications for the MgII-based radius-luminosity relation

We present the monitoring of the AGN continuum and MgII broad line emission for the quasar HE 0413-4031 ($z=1.38$) based on the six-year monitoring by the South African Large Telescope (SALT). We managed to estimate a time-delay of $302.6^{+28.7}_{-33.1}$ days in the rest frame of the source using seven different methods: interpolated cross-correlation function (ICCF), discrete correlation function (DCF), $z$-transformed DCF, JAVELIN, two estimators of data regularity (Von Neumann, Bartels), and $χ^2$ method. This time-delay is below the value expected from the standard radius-luminosity relation. However, based on the monochromatic luminosity of the source and the SED modelling, we interpret this departure as the shortening of the time-delay due to the higher accretion rate of the source, with the inferred Eddington ratio of $\sim 0.4$. The MgII line luminosity of HE 0413-4031 responds to the continuum variability as $L_{\rm line}\propto L_{\rm cont}^{0.43\pm 0.10}$, which is consistent with the light-travel distance of the location of MgII emission at $R_{\rm out} \sim 10^{18}\,{\rm cm}$. Using the data of 10 other quasars, we confirm the radius-luminosity relation for broad MgII line, which was previously determined for broad H$β$ line for lower-redshift sources. In addition, we detect a general departure of higher-accreting quasars from this relation in analogy to H$β$ sample. After the accretion-rate correction of the light-travel distance, the MgII-based radius-luminosity relation has a small scatter of only $0.10$ dex.

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arXiv2019

FeII emission in NLS1s -- originating from denser regions with higher abundances?

The interpretation of the main sequence of quasars has become a frontier subject in the last years. The consider the effect of a highly flattened, axially symmetric geometry for the broad-line region (BLR) on the parameters related to the distribution of quasars along their Main Sequence. We utilize the photoionization code CLOUDY to model the BLR, assuming `un-constant' virial factor with a strong dependence on the viewing angle. We show the preliminary results of the analysis to highlight the co-dependence of the Eigenvector 1 parameter, R$_{\mathrm{FeII}}$ on the broad H$β$ FWHM (i.e. the line dispersion) and the inclination angle ($θ$), assuming fixed values for the Eddington ratio ($\mathrm{L_{bol}}/\mathrm{L_{Edd}}$), black hole mass ($\mathrm{M_{BH}}$) and spectral energy distribution (SED) shape. We consider four cases with changing cloud density (n$\rm{_{H}}$) and composition. Understanding the FeII emitting region is crucial as this knowledge can be extended to the use of quasars as distance indicators for Cosmology.

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arXiv2019

FeII strength in NLS1s -- dependence on the viewing angle and FWHM

We address the effect of orientation of the accretion disk plane and the geometry of the broad-line region (BLR) in the context of understanding the distribution of quasars along their Main Sequence. We utilize the photoionization code CLOUDY to model the BLR, incorporating the `un-constant' virial factor. We show the preliminary results of the analysis to highlight the co-dependence of the Eigenvector 1 parameter, $\mathrm{R_{FeII}}$ on the broad H$β$ FWHM (i.e. the line dispersion) and the inclination angle ($θ$), assuming fixed values for the Eddington ratio ($\mathrm{L_{bol}}/\mathrm{L_{Edd}}$), black hole mass ($\mathrm{M_{BH}}$), spectral energy distribution (SED) shape, cloud density (n$\rm{_{H}}$) and composition.

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arXiv2019

Current and future applications of Reverberation-mapped quasars in Cosmology

Reverberation mapping technique is an important milestone in AGN demographics, kinematics and the structure of the Broad Line Region (BLR) based on the time-delay response between the continuum and emission line. The time delay is directly related to the size of BLR which is related to the continuum luminosity of the source, producing the well-known Radius-Luminosity (RL) relation. The majority of sources have been monitored for their H$β$ emission line in low redshift sources ($z<0.1$), while there are some attempts using the MgII line for higher redshifts. We present a recent MgII monitoring for the quasar CTS C30.10 ($z=0.90$) observed with the 10-meter SALT, for which RL scaling based on MgII holds within measurement and time-delay uncertainties. One of the most important advantages of reverberation mapping technique is the independent determination to the distant source, and considering the large range of redshifts and luminosities found in AGNs, their application to cosmology is promising. However, recently it has been found that highly accreting sources show the time delays shorter than expected from RL relation. We propose correction for this effect using a sample of 117 H$β$ reverberating-mapped AGNs with $0.02<z<0.9$, recovering the low scatter along with the relation. We are able to determine the cosmological constants, $Ω_m$ and $Ω_Λ$ within 2$σ$ confidence level. We present the first steps in modelling of light curves for H$β$ and MgII and discuss the quasar selection in the context of photometric reverberation mapping with Large Synoptic Survey Telescope (LSST). With the onset of the LSST era, we expect a huge rise in the overall quasar counts and redshift range covered ($z\lesssim 7.0$), which will provide a better constraint of AGN properties with cosmological purposes.

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arXiv2019

Explaining the Broad-line Region through photoionisation modelling

Broad-line regions (BLR) are one of the main components that constitute the phenomenological picture of active galaxies near the vicinity of the accreting supermassive black holes. Both theoretical and observational studies have shown that the BLR is made of dense, ionized gas clumps that have a strong virialized distribution at parsec-scale distances from the nuclei. Using a theoretically motivated photoionized gas model, I constrain the ionisation parameter (U) and cloud density (n$_{\rm{H}}$) as a function of the strength of the FeII emission. Recent observations in the reverberation mapping studies have contested the standard radius-luminosity relation showing increased dispersion in the relation, in particular, after the inclusion of highly accreting quasars. I incorporate the departure coefficient that accounts for this dispersion. This departure term in terms of the dimensionless accretion rate ($\dot{\mathcal{M}}$) and Eddington ratio ($L\mathrm{_{bol}}/L\mathrm{_{Edd}}$), also includes the virial factor that accounts for the BLR geometry. I then combine the fundamental plane relation for the BLR to connect the FeII strength (R$_{\rm{FeII}}$) in terms of U and n$_{\rm{H}}$ using selected values for the shape of the broad H$β$ profile.

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arXiv2019

Generating AGN spectra for LSST: First steps

In the near future, the arrival of new surveys promises a significant increment in the number of quasars (QSO) at large redshift ranges. This will help to constrain the dark energy models using quasars. The Large Synoptic Survey Telescope (LSST) will cover over 10 million QSO in six photometric bands during its 10-year run. QSO will be monitored and subsequently analysed using the photometric reverberation mapping technique. Oncoming LSST data will decrease the uncertainties in the dark energy determination using reverberating--mapped sources, particularly at high redshifts. We present the first steps in modelling of light curves for H$β$ and MgII and discuss the quasar selection in the context of photometric reverberation mapping with LSST. With the onset of the LSST era, we expect a huge rise in the overall quasar counts and redshift range covered ($z\leq7.0$), which will provide a better constraint of AGN properties with cosmological purposes.

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arXiv2019

Quasar Main Sequence: a line or a plane?

A quasar main sequence is widely believed to reveal itself through objects represented in a plane spanned by two parameters: the full-width at half-maximum (FWHM) of H$β$, and the ratio of Fe II to H$β$ equivalent width. This sequence is related to the application to quasar properties of principal component analysis (PCA), which reveals that the main axis of variance (Eigenvector 1) is co-directional with a strong anti-correlation between these two measurements. We aim to determine whether the dominance of two Eigenvectors, originally discovered over two decades ago, is replicated in newer high-quality quasar samples. If so, we aim to test if a non-linear approach is an improvement on the linear PCA method by finding two new parameters which represent a more accurate projection of the variances than the Eigenvectors recovered from PCA. We selected quasars from the XSHOOTER archive and a major quasar catalog to build high quality samples. These samples were tested with PCA. We find that the new high-quality samples do indeed have two dominant Eigenvectors as originally discovered. Subsequently we find that the fitting of a non-linear decay curve to the main sequence allows a new plane spanned by linearly independent axes to be defined, based on the distance along the decay curve as the main axis and the distance of each quasar datapoint from the curve as the secondary axis respectively. The results show that it is possible to define a new plane based on the quasar main sequence which accounts for the majority of the variance. The most likely candidate for the new main axis is an anti-correlation with black hole mass. In this case the secondary axis likely represents luminosity. However, given the results of previous studies, inclination angle likely plays a role in H$β$ width.

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arXiv2019

A catalogue of 108 extended planetary nebulae observed by GALEX

We present the ultraviolet (UV) imaging observation of planetary nebulae (PNe) using archival data of Galaxy Evolution Explorer (GALEX). We found 358 PNe detected by GALEX in near-UV (NUV). We have compiled a catalogue of 108 extended PNe with sizes greater than 8 00 and provided the angular diameters for all the 108 extended PNe in NUV and 28 in FUV from the GALEX images considering 3σ surface brightness level above the background. Of the 108 PNe, 74 are elliptical, 24 are circular and 10 are bipolar in NUV with most being larger in the UV than in the radio, Hα or optical. We derived luminosities for 33 PNe in FUV (L FUV ) and 89 PNe in NUV (L NUV ) and found that most of the sources are very bright in UV. The FUV emission of the GALEX band includes contribution from prominent emission lines N IV] (1487 Å), CIV (1550 Å), and O III] (1661 Å) whereas the NUV emission includes C III] (1907 Å) and C II (2325 Å) for PNe of all excitation classes. The other emission lines seen in low excitation PNe are O IV] (1403 Å) and N III(1892 Å) in FUV, and O II (2470 Å) and Mg II (2830 Å) in NUV. Similarly the emission lines O V (1371 Å) and He II (1666 Å) strongly contribute in FUV for high and medium excitation PNe but not for low excitation PNe. A mixture of other emission lines seen in all excitation PNe. We have also provided images of 34 PNe in NUV and 9 PNe in FUV.

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arXiv2019

Quasars from LSST as dark energy tracers: first steps

In the near future, new surveys promise a significant increase in the number of quasars (QSO) at large redshifts. This will help to constrain the dark energy models using quasars. The Large Synoptic Survey Telescope (LSST) will cover over 10 million QSO in six photometric bands during its 10-year run. QSO will be monitored and subsequently analyzed using the photometric reverberation mapping (RM) technique. In low-redshift quasars, the combination of reverberation-mapped and spectroscopic results have provided important progress. However, there are still some facts which have to be taken into account for future results. It has been found that super-Eddington sources show time delays shorter than the expected from the well-known Radius-Luminosity ($R\mathrm{_{Hβ}}-L_{5100}$) relation. Using a sample of 117 H$β$ reverberation-mapped AGN with $0.02<z<0.9$, we propose a correction by the accretion rate effect recovering the classical $R\mathrm{_{Hβ}}-L_{5100}$ relation. We determined the cosmological constants, which are in agreement with $Λ$-Cold Dark Matter model within 2$σ$ confidence level, which is still not suitable for testing possible departures from the standard model. Upcoming LSST data will decrease the uncertainties in the dark energy determination using reverberation-mapped sources, particularly at high redshifts. We show the first steps in the modeling of the expected light curves for H$β$ and MgII.

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arXiv2019

Can reverberation-measured quasars be used for cosmology?

Quasars have been proposed as a new class of standard candles analogous to Supernovae, as their large redshift range and high luminosities make them excellent candidates. Reverberation mapping (RM) method enables to estimate the distance to the source from the time delay measurement of the emission lines with respect to the continuum, since the time delay depends on the absolute luminosity of the source. This radius-luminosity (RL) relation exhibits a low scatter and it was thus proposed for cosmological purposes. However, in recent years the increase in the studied sample, and in particular the inclusion of highly accreting QSO has increased the dispersion in the RL relation, with many objects showing time delays shorter than the expected. Using H$β$ RM measurements for 117 sources with $0.002<z<0.9$ and $41.5<\mathrm{log}~L_{5100}<45.9$, we find a correction for the time delay based on the dimensionless accretion rate considering the virial factor anti-correlated with the FWHM of H$β$. This correction decreases the scattering in the accretion parameters compared with the typical value used, which is directly reflected by suppressing the RL relation dispersion. We also confirm the anti-correlation between the excess of variability and the accretion parameters. With this correction we are able to build the Hubble diagram and estimate the cosmological constants $Ω_m$ and $Ω_Λ$, which are consistent with the standard cosmological model at 2$σ$ confidence level. Therefore, RM results can be used to constrain cosmological models in the future.

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arXiv2019

Main trends of the quasar main sequence -- effect of viewing angle

We address the effect of the viewing angle of the accretion disk plane and the geometry of the broad-line region (BLR) with the goal of interpreting the distribution of quasars along the main sequence (MS). We utilize photoionization code CLOUDY to model the BLR FeII emission, incorporating the grossly underestimated role of the form factor (f). We recover the dependence of the strength of the FeII emission in the optical (R$_{\rm{FeII}}$) on L$_{\rm{bol}}$/L$_{\rm{Edd}}$ ratio and related observational trends - as a function of the spectral energy distribution (SED) shape, cloud density, composition and intra-cloud dynamics, assumed following prior observational constraints. With this approach, we are now able to explain the diversity of quasars and the change of the quasar properties along the Main Sequence (MS). Our approach also explains the rarity of the highest FeII emitters known as the extreme xA sources and can be used as a predictive tool in future reverberation mapping studies of Type-1 AGNs. This approach further justifies the use of quasars as `cosmological probes'.

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arXiv2019

The Quasar Main Sequence explained by the combination of Eddington ratio, metallicity and orientation

We address the effect of orientation of the accretion disk plane and the geometry of the broad-line region (BLR) as part of an effort to understand the distribution of quasars in the optical plane of the quasar main sequence. We utilize the photoionization code CLOUDY to model the BLR incorporating the grossly underestimated form factor ($f$). Treating the aspect of viewing angle appropriately, we confirm the dependence of the $R_{\mathrm{FeII}}$ sequence on Eddington ratio and on the related observational trends - as a function of the SED shape, cloud density and composition, verified from prior observations. Sources with $R_{\mathrm{FeII}}$ in the range 1 -- 2 (about 10\% of all quasars, the so-called extreme Population A [xA] quasars) are explained as sources of high, and possibly extreme Eddington ratio along the $R_{\mathrm{FeII}}$ sequence. This result has important implication for the exploitation of xA sources as distance indicators for Cosmology. $\mathrm{FeII}$ emitters with $R_{\mathrm{FeII}} > 2$ are very rare (<1\% of all type 1 quasars). Our approach also explains the rarity of these highest $\mathrm{FeII}$ emitters as extreme xA sources and constrains the viewing angle ranges with increasing H$β$ FWHM.

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arXiv2019

CLOUDY view of the warm corona

Bright active galaxies show a range of properties but many of these properties are correlated which has led to the concept of the Quasar Main Sequence. We test whether our current understanding of the quasar structure allows to reproduce the pattern observed in the optical plane formed by the kinematic line width of H$β$ and the relative importance of the Fe II optical emission. We performed simulations of the H$β$ and Fe II production using the code CLOUDY and well justified assumptions about the broad band spectra, distance of the emission line region, and the cloud properties. We show that the presence of the warm corona is an important element of the broad band spectrum which decreases the dependence of the relative Fe II emissivity on the Eddington ratio, and allows to reproduce the rare cases of the particularly strong Fe II emitters. Results are sensitive to the adopted cloud distance, and strong Fe II emission can be obtain either by adopting strongly super-solar metallicity, or much shorter distance than traditionally obtained from reverberation mapping. We modeled in a similar way the UV plane defined by the Mg II line and Fe II UV pseudo-continuum, but here our approach is less successful, in general overproducing the Fe II strength. We found that the Fe II optical and UV emissivity depend in a different way on the turbulent velocity and metallicity, and the best extension of the model in order to cover both planes is to allow very large turbulent velocities in the Broad Line Region clouds.

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arXiv2019

Time delay measurement of Mg II line in CTS C30.10 with SALT

We report 6 yr monitoring of a distant bright quasar CTS C30.10 (z = 0.90052) with the Southern African Large Telescope (SALT). We measured the rest-frame time-lag of $562\pm 2$ days between the continuum variations and the response of the Mg II emission line, using the Javelin approach. More conservative approach, based on five different methods, imply the time delay of $564^{+109}_{-71}$ days. This time delay, combined with other available measurements of Mg II line delay, mostly for lower redshift sources, shows that the Mg II line reverberation implies a radius-luminosity relation very similar to the one based on a more frequently studied H$β$ line.

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arXiv2018

Strong FeII emission in NLS1s: An unsolved mystery

The work initially started as a test to retrace the Shen & Ho (2014) Quasar Main Sequence diagram where they claimed that the parameter RFeII, which defines the Eigenvector 1 (EV1) is driven by the Eddington ratio alone. We subsequently construct a refined (error and redshift limited) sample from the original Shen et al. 2011 QSO catalogue. Based on our hypothesis - the main driver of the Quasar Main Sequence is the maximum of the accretion disk temperature defined by the Big Blue Bump on the Spectral Energy Distribution. We select the four extreme sources that have RFeII $\geq$ 4.0 and use the SED modelling code CIGALE to fit the multi-band photometric data for these sources. We also perform detailed spectral fitting including the FeII pseudo-continuum to estimate and compare the value of RFeII for them. We show the metallicity dependent FeII strength in the context of this study.

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