arXiv subjects

Marzena Śniegowska

Publications and source records attributed to Marzena Śniegowska.

26 records · Page 2Linked to original sources

arXiv2021

High metal content of highly accreting quasars

We present an analysis of UV spectra of 13 quasars believed to belong to extreme Population A (xA) quasars, aimed at the estimation of the chemical abundances of the broad line emitting gas. Metallicity estimates for the broad line emitting gas of quasars are subject to a number of caveats, although present data suggest the possibility of an increase along the quasar main sequence along with prominence of optical Fe II emission. Extreme Population A sources with the strongest Fe II emission offer several advantages with respect to the quasar general population, as their optical and UV emission lines can be interpreted as the sum of a low-ionization component roughly at quasar rest frame (from virialized gas), plus a blueshifted excess (a disk wind), in different physical conditions. Specifically, in terms of ionization parameter, cloud density, metallicity and column density. Capitalizing on these results, we analyze the component at rest frame and the blueshifted one, exploiting the dependence (of several intensity line ratios on metallicity $Z$). We find that the validity of intensity line ratios as metallicity indicators depends on the physical conditions. We apply the measured diagnostic ratios to estimate the physical properties of sources such as density, ionization, and metallicity of the gas. Our results confirm that the two regions (the low-ionization component and the blue-shifted excess) of different dynamical conditions also show different physical conditions and suggest metallicity values that are high, and probably the highest along the quasar main sequence, with $Z \gtrsim 10 Z_{\odot}$. We found some evidence of an overabundance of Aluminium with respect to Carbon, possibly due to selective enrichment of the broad line emitting gas by supernova ejecta.

astro-ph.HE↗

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.

astro-ph.HE↗

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.

astro-ph.GA↗

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.

astro-ph.HE↗

arXiv2018

Modelling of the quasar main sequence in the optical plane

The concept of the quasar main sequence is very attractive since it stresses correlations between various parameters and implies the underlying simplicity. In the optical plane defined by the width of the H\{beta} line and the ratio of the equivalent width of the Fe II to H\{beta} observed objects form a characteristic pattern. In this paper, we use a physically motivated model to explain the distribution of quasars in the optical plane. Continuum is modelled as an accretion disk with a hard X-ray power law uniquely tight to the disk at the basis of observational scaling, and the Broad Line Region distance is determined also from observational scaling. We perform the computations of the FeII and H\{beta} line production with the code CLOUDY. We have only six free parameters for an individual source: maximum temperature of the accretion disk, Eddington ratio, cloud density, cloud column density, microturbulence, and iron abundance, and only the last four remain as global parameters in our modelling of the whole sequence. Our theoretically computed points cover well the optical plane part populated with the observed quasars, particularly if we allow for super-Solar abundance of heavy elements. Explanation of the exceptionally strong Fe II emitter requires a stronger contribution from the dark sides of the clouds. Analyzing the way how our model covers the optical plane we conclude that there is no single simple driver behind the sequence, as neither the Eddington ratio nor broad band spectrum shape plays the dominant role. Also, the role of the viewing angle in providing the dispersion of the quasar main sequence is apparently not as strong as expected.

astro-ph.HE↗

arXiv2018

Using vo tools to iNvestIgate Quasar Spectra (UNIQS)

The work initially started as a test to retrace the Shen & Ho (2014) Quasar Main Sequence diagram where they (and references therein) 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 five extreme sources that have RFeII >= 4.0 and use the SED modelling code CIGALE to fit the multi-band photometric data for these sources. Incorporating the prescription for broad emission-line species dependent virial factors, we derive the black hole masses for the entire Shen+11 catalogue and compare their distribution with the black hole masses in the original catalogue. Here, we show the results of our analysis for one of the 5 extreme sources, SDSSJ082358.30+213545.2. We also show the detailed modelling, including the Fe II pseudo-continuum to estimate and compare the value of RFeII for this object.

astro-ph.HE↗

arXiv2017

What drives the Quasar Main Sequence?

Eigenvector 1 (EV1) was found to be the dominant component behind the significant correlations for the measured parameters in quasar spectra (Boroson & Green, 1992). The parameter R$_{\mathrm{FeII}}$, which strongly correlates to the EV1, is the ${\mathrm{FeII}}$ strength, defined to be the ratio of the equivalent width of ${\mathrm{FeII}}$ to the equivalent width of ${\mathrm{Hβ}}$. This allows to construct a quasar main sequence analogous to the stellar properties driven HR diagram (Sulentic et al. 2001). We try to find the main driver behind the EV1 among the basic (theoretically motivated) parameters of an active nucleus (Eddington ratio, black hole mass, accretion rate, spin, and viewing angle). Based on theoretical modeling using the photoionization code CLOUDY (Ferland et al. 2013), we test the hypothesis that the physical driver of EV1 is the maximum of the accretion disk temperature ($\mathrm{T_{BBB}}$), reflected in the shape of the spectral energy distribution (SED). We have assumed that both H$\mathrmβ$ and Fe${\mathrm{II}}$ emission come from the Broad Line Region represented as a constant density cloud in a plane-parallel geometry. We test the effect of changing Eddington ratio on the $\mathrm{R_{FeII} - T_{BBB}}$ trends with varying mean hydrogen densities. We also test the effect of adding microturbulence that affect the line intensities on the overall $\mathrm{R_{FeII} - T_{BBB}}$ picture.

astro-ph.HE↗

arXiv2017

Testing the physical driver of Eigenvector 1 in Quasar Main Sequence

Quasars are among the most luminous sources characterized by their broad band spectra ranging from radio through optical to X-ray band, with numerous emission and absorption features. Using the Principal Component Analysis (PCA), Boroson & Green (1992) were able to show significant correlations between the measured parameters. Among the significant correlations projected, the leading component, related to Eigenvector 1 (EV1) was dominated by the anti-correlation between the Fe${\mathrm{II}}$ optical emission and [OIII] line where the EV1 alone contained 30% of the total variance. This introduced a way to define a quasar main sequence, in close analogy to the stellar main sequence in the Hertzsprung-Russel (HR) diagram (Sulentic et. al 2001). Which of the basic theoretically motivated parameters of an active nucleus (Eddington ratio, black hole mass, accretion rate, spin, and viewing angle) is the main driver behind the EV1 yet remains to be answered. We currently limit ourselves to the optical waveband, and concentrate on theoretical modelling the Fe${\mathrm{II}}$ to H$\mathrmβ$ ratio, and test the hypothesis that the physical driver of EV1 is the maximum of the accretion disk temperature, reflected in the shape of the spectral energy distribution (SED). We performed computations of the H$\mathrmβ$ and optical Fe${\mathrm{II}}$ for a broad range of SED peak position using CLOUDY photoionisation code. We assumed that both H$\mathrmβ$ and Fe${\mathrm{II}}$ emission come from the Broad Line Region represented as a constant density cloud in a plane-parallel geometry. We compare the results for two different approaches: (1) considering a fixed bolometric luminosity for the SED; (2) considering $\mathrm{L_{bol}/L_{Edd}}$ = 1.

astro-ph.HE↗