Abstract
ABSTRACT High-resolution soft X-ray spectroscopy of the prototype accretion disk wind quasar, PDS 456, is presented. Here, the XMM-Newton reflection grating spectrometer spectra are analyzed from the large 2013–2014 XMM-Newton campaign, consisting of five observations of approximately 100 ks in length. During the last observation (OBS. E), the quasar is at a minimum flux level, and broad absorption line (BAL) profiles are revealed in the soft X-ray band, with typical velocity widths of km s−1. During a period of higher flux in the third and fourth observations (OBS. C and D, respectively), a very broad absorption trough is also present above 1 keV. From fitting the absorption lines with models of photoionized absorption spectra, the inferred outflow velocities lie in the range . The absorption lines likely originate from He and H-like neon and L-shell iron at these energies. A comparison with earlier archival data of PDS 456 also reveals a similar absorption structure near 1 keV in a 40 ks observation in 2001, and generally the absorption lines appear most apparent when the spectrum is more absorbed overall. The presence of the soft X-ray BALs is also independently confirmed by an analysis of the XMM-Newton EPIC spectra below 2 keV. We suggest that the soft X-ray absorption profiles could be associated with a lower ionization and possibly clumpy phase of the accretion disk wind, where the latter is known to be present in this quasar from its well-studied iron K absorption profile and where the wind velocity reaches a typical value of 0.3c.
Highlights
The masses of supermassive black holes (SMBHs, with MBH = 106–109M ) are known to correlate with galaxy bulge mass (Magorrian et al 1998) and even more tightly with the stellar velocity dispersion on kiloparsec scales; this is the socalled M –s relation (Ferrarese & Merritt 2000; Gebhardt et al 2000)
The optical and near-infrared spectra show Balmer and Paschen lines with broad wings, while in the Hubble Space Telescope (HST)/STIS UV spectrum the C IV l1549 Å emission line is blueshifted by ∼5000 km s−1, and a tentative absorption trough extends from ∼14,000 to 24,000 km s−1 blueward of the Lyα rest-frame energy (O’Brien et al 2005)
No direct measurement is available for the mass of the central black hole, but this can be estimated from the SMBH–host galaxy scaling relations to be ~(1–2) ́ 109M (Nardini et al 2015), implying that the black hole in PDS 456 is accreting at a substantial fraction of the Eddington rate
Summary
A potential mechanism responsible for this coevolution came with the discovery of extremely energetic outflows from the black holes powering the most luminous active galactic nuclei (AGNs) and quasars (Chartas et al 2002, 2003; Pounds et al 2003; Reeves et al 2003; Tombesi et al 2010; Gofford et al 2013) At high redshifts, such winds would have provided the necessary mechanical feedback that both controlled the formation of stellar bulges and simultaneously regulated SMBH growth, leaving the observed M –s relation as a record of the process (Silk & Rees 1998; King 2003; Di Matteo et al 2005). All of the observations were complemented by the simultaneous high-energy spectra collected by NuSTAR, which provide a valuable broadband view that extends from the optical/UV to the hard X-ray In this campaign, Nardini et al (2015) were able to detect a persistent P-Cygni-like profile from highly ionized iron, establishing the wide-angle character of the disk wind in PDS 456.
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