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Register a new userChandra Observations of Excess Fe K$alpha$ Line Emission in Galaxies with High Star Formation Rates: X-ray Reflection on Galaxy Scales?
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In active galactic nuclei (AGN), fluorescent Fe K$alpha$ (iron) line emission is generally interpreted as originating from obscuring material around a supermassive black hole (SMBH) on the scale of a few parsecs (pc). However, recent Chandra studies indicate the existence of iron line emission extending to kpc scales in the host galaxy. The connection between iron line emission and large-scale material can be spatially resolved directly only in nearby galaxies, but could be inferred in more distant AGNs by a connection between line emission and star-forming gas and dust that is more extended than the pc-scale torus. Here we present the results from a stacking analysis and X-ray spectral fitting performed on sources in the Chandra Deep Field South (CDFS) 7 Ms observations. From the deep stacked spectra, we select sources with stellar mass $log(M_*/M_odot)>10$ at $0.5<z<2$, obtaining 25 sources with high infrared luminosity ($ {rm SFR}_{rm FIR} geq 17;M_{odot};{rm yr}^{-1}$) and 32 sources below this threshold. We find that the equivalent width of the iron line EW(Fe) is a factor of three higher with 3$sigma$ significance for high infrared luminosity measured from Herschel observations, indicating a connection between iron line emission and star-forming material on galaxy scales. We show that there is no significant dependence in EW(Fe) on $M_*$ or X-ray luminosity, suggesting the reflection of AGN X-ray emission over large scales in their host galaxies may be widespread.
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We present the spatial analysis of five Compton thick (CT) active galactic nuclei (AGNs), including MKN 573, NGC 1386, NGC 3393, NGC 5643, and NGC 7212, for which high resolution Chandra observations are available. For each source, we find hard X-ray emission (>3 keV) extending to ~kpc scales along the ionization cone, and for some sources, in the cross-cone region. This collection represents the first, high-signal sample of CT AGN with extended hard X-ray emission for which we can begin to build a more complete picture of this new population of AGN. We investigate the energy dependence of the extended X-ray emission, including possible dependencies on host galaxy and AGN properties, and find a correlation between the excess emission and obscuration, suggesting a connection between the nuclear obscuring material and the galactic molecular clouds. Furthermore, we find that the soft X-ray emission extends farther than the hard X-rays along the ionization cone, which may be explained by a galactocentric radial dependence on the density of molecular clouds due to the orientation of the ionization cone with respect to the galactic disk. These results are consistent with other CT AGN with observed extended hard X-ray emission (e.g., ESO 428-G014 and the Ma et al. 2020 CT AGN sample), further demonstrating the ubiquity of extended hard X-ray emission in CT AGN.
Recent observations of nearby Compton thick (CT) active galactic nuclei (AGNs) with Chandra have resolved hard (>3 keV) X-ray emission extending out from the central supermassive black hole to kiloparsec scales, challenging the long-held belief that the characteristic hard X-ray continuum and fluorescent Fe K lines originate in the inner ~parsec due to the excitation of obscuring material. In this paper we present the results of the most recent Chandra ACIS-S observations of NGC 7212, a CT AGN in a compact group of interacting galaxies, with a total effective exposure of ~150 ks. We find ~20 percent of the observed emission is found outside of the central ~kiloparsec, with ~17 percent associated with the soft X-rays, and ~3 percent with hard X-ray continuum and Fe K line. This emission is extended both along the ionization cone and in the cross-cone direction up to ~3.8 kpc scales. The spectrum of NGC 7212 is best represented by a mixture of thermal and photoionization models that indicate the presence of complex gas interactions. These observations are consistent with what is observed in other CT AGN (e.g., ESO 428-G014, NGC 1068), providing further evidence that this may be a common phenomenon. High-resolution observations of extended CT AGN provide an especially valuable environment for understanding how AGN feedback impacts host galaxies on galactic scales.
We present the first unambiguous evidence of a broad (Gaussian width ~330 eV) component of the iron K-alpha fluorescent emission line in the X-ray obscured Narrow Line Seyfert 1 Galaxy NGC5506. This is the main results of a spectroscopic monitoring campaign on this source performed with the XMM-Newton observatory between February 2001 and January 2009. The broad line lacks extreme redwards skewness. If modelled with a relativistic component, the profile of the line is consistent with a flat emissivity radial dependence (alpha~1.9). The disk inclination (~40 degrees) is nominally larger then typically observed in unobscured AGN, in agreement with most measurements of broadened iron lines in Seyfert 2 galaxies. The quality of the data allows us to decompose the full iron emission line complex, and to study its long-term (timescales of weeks to years) variability pattern. The intensity of the neutral and narrow iron K-alpha core remains constant during the monitoring campaign. This indicates that the optically thick gas responsible for the non-relativistic reprocessing of the primary AGN continuum in NGC5506 is probably located in the torus rather than in the optical Broad Line Region.
Hyper-luminous infrared galaxies (HyLIRGs) lie at the extreme luminosity end of the IR galaxy population with $L_{rm IR}>10^{13}$L$_odot$. They are thought to be closer counterparts of the more distant sub-mm galaxies, and should therefore be optimal targets to study the most massive systems in formation. We present deep $Chandra$ observations of IRAS~F15307+3252 (100ks), a classical HyLIRG located at $z=$0.93 and hosting a radio-loud AGN ($L_{rm 1.4 GHz}sim3.5times10^{25}$ W/Hz). The $Chandra$ images reveal the presence of extended ($r=160$ kpc), asymmetric X-ray emission in the soft 0.3-2.0 keV band that has no radio counterpart. We therefore argue that the emission is of thermal origin originating from a hot intragroup or intracluster medium virializing in the potential. We find that the temperature ($sim2$ keV) and bolometric X-ray luminosity ($sim3times10^{43}$ erg s$^{-1}$) of the gas follow the expected $L_{rm X-ray}-T$ correlation for groups and clusters, and that the gas has a remarkably short cooling time of $1.2$ Gyrs. In addition, VLA radio observations reveal that the galaxy hosts an unresolved compact steep-spectrum (CSS) source, most likely indicating the presence of a young radio source similar to 3C186. We also confirm that the nucleus is dominated by a redshifted 6.4 keV Fe K$alpha$ line, strongly suggesting that the AGN is Compton-thick. Finally, Hubble images reveal an over-density of galaxies and sub-structure in the galaxy that correlates with soft X-ray emission. This could be a snapshot view of on-going groupings expected in a growing cluster environment. IRAS~F15307+3252 might therefore be a rare example of a group in the process of transforming into a cluster.
Narrow-line Seyfert 1 galaxies (NLS1s) is one of the few classes of active galactic nuclei (AGN) harboring powerful relativistic jets and detected in $gamma$ rays. NLS1s are well-known X-ray sources. While in non-jetted sources the origin of this X-ray emission may be a hot corona surrounding the accretion disk, in jetted objects, especially beamed ones, the contribution of corona and relativistic jet is difficult to disentangle without a proper sampling of the hard X-ray emission. For this reason, we observed with textit{NuSTAR} the first four NLS1s detected at high energy $gamma$ rays. These data, along with textit{XMM-Newton} and textit{Swift/XRT} observations, confirmed that X rays originate both in the jet and in the accretion disk corona. Time variability in hard X rays furthermore suggests that, as observed in flat-spectrum radio quasars, the dissipation region during flares could change its position from source to source, and it can be located both inside and outside the broad-line region. We find that jetted NLS1s, and other blazars as well, seem not to follow the classical fundamental plane of black hole activity, which therefore should be used as a black hole mass estimator in blazars with extreme care only. Our results strengthen the idea according to which $gamma$-NLS1s are smaller and younger version of flat-spectrum radio quasars, in which both a Seyfert and a blazar component co-exist.
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