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Emission-Line and Continuum Reverberation Mapping of the NLS1 Galaxy WPVS 48

M. A. Probst, W. Kollatschny, M. W. Ochmann, C. Sobrino Figaredo, D. Chelouche, M. Haas, S. Kaspi, L. Meerwart, T. -O. Husser

TL;DR

This study performs optical reverberation mapping of WPVS 48 with 24 SALT spectra over ~7 months to map the BLR and estimate the SMBH mass. The BLR is found to be stratified, with Balmer and He I lines lagging the continuum by about 12–16 days, while He II lags by ≤5 days, and interband continuum delays increasing with wavelength point to a diffuse BLR-origin continuum component. A BH mass of roughly $1.3\times10^7\,M_{\odot}$ is derived, yielding $L/L_{\rm Edd} \approx 0.39$, though inclination effects could raise the true mass if the system is viewed nearly face-on. The results are consistent with the BLR radius–luminosity relation for AGN and extend reverberation-mapping studies to the NLS1 subclass, highlighting the role of geometry and diffusion in AGN variability. Overall, WPVS 48 provides a coherent RM picture for a representative NLS1 and demonstrates the feasibility and value of intensive spectroscopic RM campaigns.

Abstract

WPVS 48 is a nearby narrow-line Seyfert 1 galaxy without previous analysis of the broad-line region (BLR) by means of optical spectroscopic reverberation mapping. By studying the continuum and emission line variability of WPVS 48, we aim to infer the BLR size as well as the mass of the central supermassive black hole (SMBH). We analyse data from a dedicated optical spectroscopic reverberation mapping campaign of WPVS 48 taken with the 10 m Southern African Large Telescope (SALT) at 24 epochs over a period of 7 months between December 2013 and June 2014. WPVS 48 shows variability throughout the campaign. We find a stratified BLR, where the variability amplitude of the integrated emission lines decreases with distance to the ionizing continuum source. Specifically, the variable emission of H$α$, H$β$, H$γ$, He I $\lambda5876$ originates at distances of $16.0^{+4.0}_{-2.0}$, $15.0^{+4.5}_{-1.9}$, $12.5^{+3.5}_{-2.5}$ and $14.0^{+2.5}_{-2.1}$ light-days, respectively, to the optical continuum at 5100 A. The He II $λ4686$ lag is $\lesssim 5$ days. Based on the high S/N spectra, we identify variable emission of N III $\lambda4640$ and C IV $\lambda4658$ in the line complex with He II $λ4686$. We derive interband continuum delays increasing with wavelength up to $\sim 8$ days. These delays are consistent with an additional diffuse continuum originating at the same distance as the variable Balmer emission. We derive a central black hole mass of $(1.3_{-0.6}^{+1.1})\times10^7M_{\odot}$ based on the integrated line-widths and distances of the BLR and discuss corrections for the inclination angle. This gives an Eddington ratio $L/L_{\text{Edd}}\approx 0.39$ without correction for inclination.

Emission-Line and Continuum Reverberation Mapping of the NLS1 Galaxy WPVS 48

TL;DR

This study performs optical reverberation mapping of WPVS 48 with 24 SALT spectra over ~7 months to map the BLR and estimate the SMBH mass. The BLR is found to be stratified, with Balmer and He I lines lagging the continuum by about 12–16 days, while He II lags by ≤5 days, and interband continuum delays increasing with wavelength point to a diffuse BLR-origin continuum component. A BH mass of roughly is derived, yielding , though inclination effects could raise the true mass if the system is viewed nearly face-on. The results are consistent with the BLR radius–luminosity relation for AGN and extend reverberation-mapping studies to the NLS1 subclass, highlighting the role of geometry and diffusion in AGN variability. Overall, WPVS 48 provides a coherent RM picture for a representative NLS1 and demonstrates the feasibility and value of intensive spectroscopic RM campaigns.

Abstract

WPVS 48 is a nearby narrow-line Seyfert 1 galaxy without previous analysis of the broad-line region (BLR) by means of optical spectroscopic reverberation mapping. By studying the continuum and emission line variability of WPVS 48, we aim to infer the BLR size as well as the mass of the central supermassive black hole (SMBH). We analyse data from a dedicated optical spectroscopic reverberation mapping campaign of WPVS 48 taken with the 10 m Southern African Large Telescope (SALT) at 24 epochs over a period of 7 months between December 2013 and June 2014. WPVS 48 shows variability throughout the campaign. We find a stratified BLR, where the variability amplitude of the integrated emission lines decreases with distance to the ionizing continuum source. Specifically, the variable emission of H, H, H, He I originates at distances of , , and light-days, respectively, to the optical continuum at 5100 A. The He II lag is days. Based on the high S/N spectra, we identify variable emission of N III and C IV in the line complex with He II . We derive interband continuum delays increasing with wavelength up to days. These delays are consistent with an additional diffuse continuum originating at the same distance as the variable Balmer emission. We derive a central black hole mass of based on the integrated line-widths and distances of the BLR and discuss corrections for the inclination angle. This gives an Eddington ratio without correction for inclination.

Paper Structure

This paper contains 29 sections, 8 equations, 17 figures, 13 tables.

Table of Contents

  1. Introduction
  2. Observations and data reduction
  3. Results
  4. Optical spectral observations
  5. Host galaxy contribution
  6. Identification of Bowen Fluorescence near Heii $\lambda$4686
  7. Continuum Variability
  8. Continuum Light Curves
  9. Interband continuum delays -- Univariate Analysis
  10. Interband Continuum Delays -- Bivariate Analysis
  11. Emission-Line Variability
  12. Broad-line Fluxes and Light Curves
  13. Emission-line lags and BLR size
  14. Broad-Line Profiles
  15. Narrow-Line Fluxes
  16. ...and 14 more sections

Figures (17)

  • Figure 1: Top panel: Reduced optical spectra of WPVS 48 during the variability campaign from December 2013 to June 2014. The spectra were calibrated to the same absolute [Oiii] $\lambda5007$ flux of $244 \times 10^{-15} \rm\,erg\,cm^{-2}\,s^{-1}$. The identified emission features are labelled. Bottom panel: Zoom on the continuum and the low-intensity emission lines. The conspicuous feature at $\sim 5490$ Å is a residual from night-sky emission.
  • Figure 2: Combined mean spectrum (black) and rms spectrum (red) of WPVS 48 from our campaign. The partition in the two intercalibrations (see Sect. \ref{['sec:observations']} for details) is shown with a grey dashed line. The rms spectrum was scaled to allow for a direct comparison. The analysed continuum regions and the identical pseudo-continua used for linear continuum subtraction are highlighted with blue bars below the spectra. The line integration limits are marked by the shaded areas. All emission lines of Hei are displayed in orange.
  • Figure 3: Extinction corrected B-V flux variations. The blue dashed line represents the best linear fit of the AGN slope of WPVS 48 and the red shaded area host slopes of nearby AGN.
  • Figure 4: Extinction corrected B-R flux variations. The blue dashed line represents the best linear fit of the AGN slope of WPVS 48 and the red shaded area host slopes of nearby AGN.
  • Figure 5: Detailed emission line identification in the mean spectrum close to Heii $\lambda4686$. We identify Niii $\lambda4640$ and Civ $\lambda4658$1982ApJ...261...64O and further labelled the position of the Feii $(37,\,38)$ emission bands 2022ApJS..258...38P as well as [Ariv] $\lambda\lambda4712, 4740$.
  • ...and 12 more figures