The Suzaku view of highly-ionised outflows in AGN: I - Statistical detection and global absorber properties (1211.5810v1)

Abstract: We present the results of a new spectroscopic study of Fe K-band absorption in Active Galactic Nuclei (AGN). Using data obtained from the Suzaku public archive we have performed a statistically driven blind search for Fe XXV Hea and/or Fe XXVI Lyb absorption lines in a large sample of 51 type 1.0-1.9 AGN. Through extensive Monte Carlo simulations we find statistically significant absorption is detected at E>6.7 keV in 20/51 sources at the P(MC)>95% level, which corresponds to ~40% of the total sample. In all cases, individual absorption lines are detected independently and simultaneously amongst the two (or three) available XIS detectors which confirms the robustness of the line detections. The most frequently observed outflow phenomenology consists of two discrete absorption troughs corresponding to Fe XXV Hea and Fe XXVI Lyb at a common velocity shift. From xstar fitting the mean column density and ionisation parameter for the Fe K absorption components are log(NH/cm^{-2})~23 and log(xi/erg cm s^{-1})~4.5, respectively. Measured outflow velocities span a continuous range from <1,500 km/s up to ~100,000 km/s, with mean and median values of ~0.1c and ~0.056c, respectively. The results of this work are consistent with those recently obtained using XMM-Newton and independently provides strong evidence for the existence of very highly-ionised circumnuclear material in a significant fraction of both radio-quiet and radio-loud AGN in the local universe.

Analysis of FeK-band Absorption in Active Galactic Nuclei Using Suzaku Data

The paper examines the presence of highly-ionized outflows in Active Galactic Nuclei (AGN) through a detailed spectroscopic analysis of FeK-band absorption lines using Suzaku observations. With a focus on the detection of Fexxv Heα and Fexxvi Lyα absorption lines, this research assesses the statistical significance and global properties of absorbers across different types of AGN.

Methodological Approach

The researchers conducted a blind search across 51 Suzaku observed type 1 to 1.9 AGNs to identify statistically significant absorption features at energies above 6.7 keV. Through extensive Monte Carlo simulations, absorption was detected in approximately 40% of the sample. Spectral fitting was carried out using the xstar photoionization code, which allowed the determination of column densities and ionization parameters. Absorbers were categorized based on their velocities, ranging from <1500 km/s to near-relativistic speeds of 0.1c, with averaged results indicating a median velocity of 0.056c.

Key Findings

• Global Detection Rate: The paper finds that highly-ionized Fexxv and Fexxvi absorption lines are prevalent in ∼40% of the analyzed AGN sample, corroborating previous detections via XMM-Newton data.
• Absorber Characteristics: The absorbers exhibit column densities from 21.5 < log(N_H/cm^−2) < 24 and ionization parameters within 2.5 < log(ξ/erg cm s^−1) < 6, values consistent with known profiles of highly-ionized outflows detected by other observatories.
• Velocity Insights: FeK absorbers show a wide range of velocities up to 100,000 km/s, highlighting their systematic differences from typical soft X-ray absorbers. The identification of ultra-fast outflows (UFOs) remains prominent, constituting a substantial fraction of detected phenomena.

Implications and Future Work

The prevalence of high-ionization FeK-band absorption features supports the notion of highly-ionized circumnuclear material playing a critical role in AGN dynamics. The paper provides observational evidence consistent with theoretical models that predict the formation and potential feedback effects of such outflows. However, future high-resolution X-ray observations, possibly from missions like Astro-H, could offer more precise discrimination of emission and absorption features at lower velocities, enhancing further insights into AGN composition and behavior.

Conclusions

This investigation affirms the consistency of Suzaku-derived measurements with previous studies utilizing XMM-Newton, reinforcing the understanding of AGN wind characteristics and their impact on galaxy evolution. While the paper successfully elucidates the statistical occurrences of high-velocity absorbers, ongoing and future studies are necessary to explore the interplay between outflow dynamics and host galaxies' evolution on cosmological scales.