Mrk 231 is a nearby ultra-luminous IR galaxy exhibiting a kpc-scale, multi-phase AGN-driven outflow. This galaxy represents the best target to investigate in detail the morphology and energetics of ...powerful outflows, as well as their still poorly-understood expansion mechanism and impact on the host galaxy. In this work, we present the best sensitivity and angular resolution maps of the molecular disk and outflow of Mrk 231, as traced by CO(2−1) and (3−2) observations obtained with the IRAM/PdBI. In addition, we analyze archival deep Chandra and NuSTAR X-ray observations. We use this unprecedented combination of multi-wavelength data sets to constrain the physical properties of both the molecular disk and outflow, the presence of a highly-ionized ultra-fast nuclear wind, and their connection. The molecular CO(2−1) outflow has a size of ~1 kpc, and extends in all directions around the nucleus, being more prominent along the south-west to north-east direction, suggesting a wide-angle biconical geometry. The maximum projected velocity of the outflow is nearly constant out to ~1 kpc, thus implying that the density of the outflowing material must decrease from the nucleus outwards as ~r-2. This suggests that either a large part of the gas leaves the flow during its expansion or that the bulk of the outflow has not yet reached out to ~1 kpc, thus implying a limit on its age of ~1 Myr. Mapping the mass and energy rates of the molecular outflow yields \hbox{$\rm \dot {\it M}$}M˙ OF = 500−1000 M⊙ yr-1 and Ėkin,OF = 7−10 × 1043 erg s-1. The total kinetic energy of the outflow is Ekin,OF is of the same order of the total energy of the molecular disk, Edisk. Remarkably, our analysis of the X-ray data reveals a nuclear ultra-fast outflow (UFO) with velocity −20 000 km s-1, \hbox{$\rm \dot {\it M}$} M ˙ UFO = 0.3−2.1 M⊙ yr-1, and momentum load \hbox{$\rm \dot {\it P}$} P ˙ UFO/ \hbox{$\dot {\it P}$} P ˙ rad = 0.2−1.6. We find Ėkin,UFO ~ Ėkin,OF as predicted for outflows undergoing an energy conserving expansion. This suggests that most of the UFO kinetic energy is transferred to mechanical energy of the kpc-scale outflow, strongly supporting that the energy released during accretion of matter onto super-massive black holes is the ultimate driver of giant massive outflows. The momentum flux \hbox{$\rm \dot {\it P}$} P ˙ OF derived for the large scale outflows in Mrk 231 enables us to estimate a momentum boost \hbox{$\rm \dot {\it P}$} P ˙ OF/ \hbox{$\dot {\it P}$} P ˙ UFO ≈ 30−60. The ratios Ėkin,UFO/Lbol,AGN = 1−5 % and Ėkin,OF/Lbol,AGN = 1−3 % agree with the requirements of the most popular models of AGN feedback.
The study of the space density of bright active galactic nuclei (AGNs) at z > 4 has been subject to extensive effort given its importance in the estimation of cosmological ionizing emissivity and ...growth of supermassive black holes. In this context we have recently derived high space densities of AGNs at z ∼ 4 and −25 < M1450 < −23 in the Cosmic Evolution Survey (COSMOS) field from a spectroscopically complete sample. In the present paper we attempt to extend the knowledge of the AGN space density at fainter magnitudes (−22.5 < M1450 < −18.5) in the 4 < z < 6.1 redshift interval by means of a multiwavelength sample of galaxies in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) GOODS-South, GOODS-North, and EGS fields. We use an updated criterion to extract faint AGNs from a population of near-IR (rest-frame UV) selected galaxies at photometric z > 4 showing X-ray detection in deep Chandra images available for the three CANDELS fields. We have collected a photometric sample of 32 AGN candidates in the selected redshift interval, six of which having spectroscopic redshifts. Including our COSMOS sample as well as other bright QSO samples allows a first guess on the shape of the UV luminosity function (LF) at z ∼ 4.5. The resulting emissivity and photoionization rate appear consistent with that derived from the photoionization level of the intergalactic medium at z ∼ 4.5. An extrapolation to z ∼ 5.6 suggests an important AGN contribution to the ionization of intergalactic medium if there are no significant changes in the shape of the UV LF.
ABSTRACT The COSMOS-Legacy survey is a 4.6 Ms Chandra program that has imaged 2.2 deg2 of the COSMOS field with an effective exposure of ks over the central 1.5 deg2 and of ks in the remaining area. ...The survey is the combination of 56 new observations obtained as an X-ray Visionary Project with the previous C-COSMOS survey. We describe the reduction and analysis of the new observations and the properties of 2273 point sources detected above a spurious probability of 2 × 10−5. We also present the updated properties of the C-COSMOS sources detected in the new data. The whole survey includes 4016 point sources (3814, 2920 and 2440 in the full, soft, and hard band). The limiting depths are 2.2 × 10−16, 1.5 × 10−15, and 8.9 × 10−16 in the 0.5-2, 2-10, and 0.5-10 keV bands, respectively. The observed fraction of obscured active galactic nuclei with a column density >1022 cm−2 from the hardness ratio (HR) is ∼50 %. Given the large sample we compute source number counts in the hard and soft bands, significantly reducing the uncertainties of 5%-10%. For the first time we compute number counts for obscured (HR > −0.2) and unobscured (HR < −0.2) sources and find significant differences between the two populations in the soft band. Due to the unprecedent large exposure, COSMOS-Legacy area is three times larger than surveys at similar depths and its depth is three times fainter than surveys covering similar areas. The area-flux region occupied by COSMOS-Legacy is likely to remain unsurpassed for years to come.
We compute the non-thermal emissions produced by relativistic particles accelerated by the shocks driven by the active galactic nucleus (AGN) in NGC 1068, and we compare the model predictions with ...the observed γ-ray and radio spectra. The former is produced by pion decay, inverse Compton scattering, and bremsstrahlung, while the latter is produced by synchrotron radiation. We derive the γ-ray and radio emissions by assuming the standard acceleration theory, and we discuss how our results compare with those corresponding to other commonly assumed sources of γ-ray and radio emissions, like supernova remnants (SNR) or AGN jets. We find that the AGN-driven shocks observed in the circumnuclear molecular disk of NGC 1068 provide a contribution to the γ-ray emission comparable to that provided by the starburst activity when standard particle acceleration efficiencies are assumed, while the shocks can yield the whole γ-ray emission only when the parameters describing the acceleration efficiency and the proton coupling with the molecular gas are tuned to values larger than those assumed in standard, SNR-driven shocks. We discuss the range of acceleration efficiencies (for protons and electrons) and of proton calorimetric fractions required to account for the observed γ-ray emission in the AGN outflow model. We further compare the neutrino flux expected in our model with constraints from current experiments, and we provide predictions for the detections by the upcoming KM3NeT neutrino telescope. This analysis strongly motivates observations of NGC 1068 at ≳TeV energies with current and future Cherenkov telescopes in order to gain insight into the nature of the γ-rays source.
ABSTRACT
We present the results of the latest NuSTAR monitoring campaign of the Compton-thick Seyfert 2 galaxy NGC 1068, composed of four ∼50 ks observations performed between 2017 July and 2018 ...February to search for flux and spectral variability on time-scales from 1 to 6 months. We detect one unveiling and one eclipsing event with time-scales less than 27 and 91 d, respectively, ascribed to Compton-thick material with NH = (1.8 ± 0.8) × 1024 and ≥ (2.4 ± 0.5) × 1024 cm−2 moving across our line of sight. This gas is likely located in the innermost part of the torus or even further inward, thus providing further evidence of the clumpy structure of the circumnuclear matter in this source. Taking advantage of simultaneous Swift–XRT observations, we also detected a new flaring ULX, at a distance d ∼ 30 arcsec (i.e. ∼2 kpc) from the nuclear region of NGC 1068, with a peak X-ray intrinsic luminosity of (3.0 ± 0.4) × 1040 erg s−1 in the 2–10 keV band.
ABSTRACT We present the 3-8 keV and 8-24 keV number counts of active galactic nuclei (AGNs) identified in the Nuclear Spectroscopic Telescope Array (NuSTAR) extragalactic surveys. NuSTAR has now ...resolved 33%-39% of the X-ray background in the 8-24 keV band, directly identifying AGNs with obscuring columns up to . In the softer 3-8 keV band the number counts are in general agreement with those measured by XMM-Newton and Chandra over the flux range S(3-8 keV)/ probed by NuSTAR. In the hard 8-24 keV band NuSTAR probes fluxes over the range S(8-24 keV)/ , a factor ∼100 fainter than previous measurements. The 8-24 keV number counts match predictions from AGN population synthesis models, directly confirming the existence of a population of obscured and/or hard X-ray sources inferred from the shape of the integrated cosmic X-ray background. The measured NuSTAR counts lie significantly above simple extrapolation with a Euclidian slope to low flux of the Swift/BAT 15-55 keV number counts measured at higher fluxes (S(15-55 keV) 10−11 ), reflecting the evolution of the AGN population between the Swift/BAT local ( ) sample and NuSTAR's sample. CXB synthesis models, which account for AGN evolution, lie above the Swift/BAT measurements, suggesting that they do not fully capture the evolution of obscured AGNs at low redshifts.
We compute the effect of galactic absorption on active galactic nucleus (AGN) emission in a cosmological context by including a physical model for AGN feeding and feedback in a semianalytic model of ...galaxy formation. This is based on galaxy interactions as triggers for AGN accretion and on expanding blast waves as a mechanism to propagate outwards the AGN energy injected into the interstellar medium at the center of galaxies. We first test our model against the observed number density of AGNs with different intrinsic luminosities as a function of redshift. The model yields a 'downsizing' behavior in close agreement with the observed one for image. At higher redshifts, the model predicts an overall abundance of AGNs (including Compton-thick sources) larger than the observed Compton-thin sources by a factor of sim2 for image and image erg s super(-1). Thus, we expect that at such luminosities and redshifts, Compton-thick sources contribute to about 1/2 of the total AGN population. We then investigate the dependence of the absorbing column density image associated with cold galactic gas (and responsible for the Compton-thin component of the overall obscuration) on AGN luminosity and redshift. We find that the absorbed fraction of AGNs with image cm super(-2) decreases with luminosity for image. In addition, the total (integrated over luminosity) absorbed fraction increases with redshift up to image, and saturates to the value sim0.8 at higher redshifts. Finally, we predict that the luminosity dependence of the absorbed fraction of AGNs with image erg s super(-1) will weaken with increasing redshift. We compare our results with recent observations and discuss their implications in the context of cosmological models of galaxy formation.
We present a NuSTAR and XMM–Newton monitoring campaign in 2014/2015 of the Compton-thick Seyfert 2 galaxy, NGC 1068. During the 2014 August observation, we detect with NuSTAR a flux excess above ...20 keV (32 ± 6 per cent) with respect to the 2012 December observation and to a later observation performed in 2015 February. We do not detect any spectral variation below 10 keV in the XMM–Newton data. The transient excess can be explained by a temporary decrease of the column density of the obscuring material along the line of sight (from N
H ≃ 1025 cm−2 to N
H = 6.7 ± 1.0 × 1024 cm−2), which allows us for the first time to unveil the direct nuclear radiation of the buried active galactic nucleus in NGC 1068 and to infer an intrinsic 2–10 keV luminosity L
$_{\rm X}=7^{+7}_{-4} \times 10^{43}$
erg s−1.
ABSTRACT We present new Nuclear Spectroscopic Telescope Array (NuSTAR ) and Chandra observations of NGC 3393, a galaxy reported to host the smallest separation dual active galactic nuclei (AGN) ...resolved in the X-rays. While past results suggested a 150 pc separation dual AGN, three times deeper Chandra imaging, combined with adaptive optics and radio imaging suggest a single, heavily obscured, radio-bright AGN. Using Very Large Array and Very Long Baseline Array data, we find an AGN with a two-sided jet rather than a dual AGN and that the hard X-ray, UV, optical, near-infrared, and radio emission are all from a single point source with a radius <0 2. We find that the previously reported dual AGN is most likely a spurious detection resulting from the low number of X-ray counts (<160) at 6-7 keV and Gaussian smoothing of the data on scales much smaller than the point-spread function (PSF) (0 25 versus 0 80 FWHM). We show that statistical noise in a single Chandra PSF generates spurious dual peaks of the same separation (0 55 0 07 versus 0 6) and flux ratio (39% 9% versus 32% counts) as the purported dual AGN. With NuSTAR, we measure a Compton-thick source ( ) with a large torus half-opening angle, which we postulate results from feedback from strong radio jets. This AGN shows a 2-10 keV intrinsic-to-observed flux ratio of ( versus ). Using simulations, we find that even the deepest Chandra observations would severely underestimate the intrinsic luminosity of NGC 3393 above , but would detect an unobscured AGN of this luminosity out to high redshift ( ).
ABSTRACT We construct the rest-frame 2-10 keV intrinsic X-ray luminosity function (XLF) of active galactic nuclei (AGNs) from a combination of X-ray surveys from the all-sky Swift BAT survey to the ...Chandra Deep Field South. We use ∼3200 AGNs in our analysis, which covers six orders of magnitude in flux. The inclusion of XMM and Chandra COSMOS data has allowed us to investigate the detailed behavior of the XLF and evolution. In deriving our XLF, we take into account realistic AGN spectrum templates, absorption corrections, and probability density distributions in photometric redshift. We present an analytical expression for the overall behavior of the XLF in terms of the luminosity-dependent density evolution, smoothed two-power-law expressions in 11 redshift shells, three-segment power-law expression of the number density evolution in four luminosity classes, and binned XLF. We observe a sudden flattening of the low luminosity end slope of the XLF slope at z 0.6. Detailed structures of the AGN downsizing have also been revealed, where the number density curves have two clear breaks at all luminosity classes above . The two-break structure is suggestive of two-phase AGN evolution, consisting of major merger triggering and secular processes.
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