We investigate the dependence of black hole accretion rate (BHAR) on host-galaxy star formation rate (SFR) and stellar mass (M*) in the CANDELS/GOODS-South field in the redshift range of . Our sample ...consists of galaxies, allowing us to probe galaxies with and/or . We use sample-mean BHAR to approximate long-term average BHAR. Our sample-mean BHARs are derived from the Chandra Deep Field-South 7 Ms observations, while the SFRs and M* have been estimated by the CANDELS team through spectral energy distribution fitting. The average BHAR is correlated positively with both SFR and M*, and the BHAR-SFR and BHAR-M* relations can both be described acceptably by linear models with a slope of unity. However, BHAR appears to be correlated more strongly with M* than SFR. This result indicates that M* is the primary host-galaxy property related to supermassive black hole (SMBH) growth, and the apparent BHAR-SFR relation is largely a secondary effect due to the star-forming main sequence. Among our sources, massive galaxies ( ) have significantly higher BHAR/SFR ratios than less massive galaxies, indicating that the former have higher SMBH fueling efficiency and/or higher SMBH occupation fraction than the latter. Our results can naturally explain the observed proportionality between and M* for local giant ellipticals and suggest that their is higher than that of local star-forming galaxies. Among local star-forming galaxies, massive systems might have higher compared to dwarfs.
In this paper we present the results of the radio light curve and X-ray observations of broad-lined Type Ic (Ic-BL) SN 2007bg. The light curve shows three distinct phases of spectral and temporal ...evolution, implying that the supernova (SN) shock likely encountered at least three different circumstellar medium regimes. We interpret this as the progenitor of SN 2007bg having at least two distinct mass-loss episodes (i.e. phases 1 and 3) during its final stages of evolution, yielding a highly stratified circumstellar medium. Modelling the phase 1 light curve as a freely expanding, synchrotron-emitting shell, self-absorbed by its own radiating electrons, requires a progenitor mass-loss rate of
M yr−1 for the last t ∼ 20(v
w/1000 km s−1) yr before explosion and a total energy of the radio-emitting ejecta of E 1 × 1048 erg 10 d after explosion. This places SN 2007bg among the most energetic Type Ib/c events. We interpret the second phase as a sparser 'gap' region between the two winds stages. Phase 3 shows a second absorption turn-on before rising to a peak luminosity 2.6 times higher than in phase 1. Assuming this luminosity jump is due to a circumstellar medium density enhancement from a faster previous mass-loss episode, we estimate that the phase 3 mass-loss rate could be as high as
M yr−1. The phase 3 wind would have transitioned directly into the phase 1 wind for a wind speed difference of 2. In summary, the radio light curve provides robust evidence for dramatic global changes in at least some Ic-BL progenitors just prior (∼10-1000 yr) to explosion. The observed luminosity of this SN is the highest observed for a non-gamma-ray-burst Ic-BL SN, reaching L
8.46 GHz 1 × 1029 erg Hz−1 s−1, ∼567 d after explosion.
Context.
The discovery of hundreds of quasi-stellar objects (QSOs) in the first gigayear of the Universe powered by already grown supermassive black holes (SMBHs) challenges our knowledge of SMBH ...formation. In particular, investigations of
z
> 6 QSOs that present notable properties can provide unique information on the physics of fast SMBH growth in the early Universe.
Aims.
We present the results of follow-up observations of the
z
= 6.515 radio-quiet QSO PSO167–13, which is interacting with a close companion galaxy. The PSO167–13 system has recently been proposed to host the first heavily obscured X-ray source at high redshift. The goals of these new observations are to confirm the existence of the X-ray source and to investigate the rest-frame UV properties of the QSO.
Methods.
We observed the PSO167–13 system with
Chandra
/ACIS-S (177 ks) and obtained new spectroscopic observations (7.2 h) with
Magellan
/FIRE.
Results.
No significant X-ray emission is detected from the PSO167–13 system, suggesting that the obscured X-ray source previously tentatively detected was either due to a strong background fluctuation or is highly variable. The upper limit (90% confidence level) on the X-ray emission of PSO167–13 (
L
2−10 keV
< 8.3 × 10
43
erg s
−1
) is the lowest available for a
z
> 6 QSO. The ratio between the X-ray and UV luminosity of
α
ox
< −1.95 makes PSO167–13 a strong outlier from the
α
ox
−
L
UV
and
L
X
−
L
bol
relations. In particular, its X-ray emission is more than six times weaker than the expectation based on its UV luminosity. The new
Magellan
/FIRE spectrum of PSO167–13 is strongly affected by unfavorable sky conditions, but the tentatively detected C IV and Mg II emission lines appear strongly blueshifted.
Conclusions.
The most plausible explanations for the X-ray weakness of PSO167–13 are intrinsic weakness or small-scale absorption by Compton-thick material. The possible strong blueshift of its emission lines hints at the presence of nuclear winds, which could be related to its X-ray weakness.
Deep SCUBA surveys have uncovered a large population of massive submillimeter-emitting galaxies (SMGs; f sub(850km) 4 mJy) at z 1. Although it is generally believed that these galaxies host intense ...star formation activity, there is growing evidence that a substantial fraction also harbor an active galactic nucleus (AGN; i.e., an accreting super-massive black hole SMBH). We present here possibly the strongest evidence for this viewpoint to date: the combination of ultradeep X-ray observations (the 2 Ms Chandra Deep Field-North) and deep Keck spectroscopic data of SMGs with radio counterparts. We find that the majority (-75%) of these radio-selected spectroscopically identified SMGs host AGN activity; the other -25% have X-ray properties consistent with star formation (X-ray-derived star formation rates of -1300-2700 M sub( )yr super(-1)). The AGNs have properties generally consistent with those of nearby luminous AGNs ( - 1.8 c 0.5, N sub(H) - 10 super(20)-10 super(24) cm super(-2), and L sub(X) - 10 super(43)-10 super(44.5) ergs s super(-1)), and the majority (-80%) are heavily obscured (N sub(H) 10 super(23) cm super(-2)). We construct composite rest-frame 2-20 keV spectra for three different obscuration classes N sub(H) < 10 super(23) cm super(-2), N sub(H) = (1-5) x 10 super(23) cm super(-2), and N sub(H) > 5 x 10 super(23) cm super(-2), which reveal features not seen in the individual X-ray spectra. An -1 keV equivalent width Fe Ka emission line is seen in the composite X-ray spectrum of the most heavily obscured AGNs, suggesting Compton-thick or near Compton-thick absorption. Even taking into account the effects of absorption, we find that the average X-ray to far-IR luminosity ratio of the AGN-classified SMGs (L sub(X)/L sub(FIR) = 0.004) is approximately 1 order of magnitude below that found for typical quasars. This result suggests that intense star formation activity (of order -1000 M sub( )yr super(-1)) dominates the bolometric output of these SMGs. However, we also explore the possibility that the X-ray to far-IR luminosity ratio of the AGN components is intrinsically less than that found for typical quasars and postulate that some SMGs may be AGN dominated. We investigate the implications of our results for the growth of massive black holes, discuss the prospects for deeper X-ray observations, and explore the scientific potential offered by the next generation of X-ray observatories.
The Circinus galaxy is one of the closest obscured active galactic nuclei (AGNs), making it an ideal target for detailed study. Combining archival Chandra and XMM-Newton data with new NuSTAR ...observations, we model the 2-79 keV spectrum to constrain the primary AGN continuum and to derive physical parameters for the obscuring material. Chandra's high angular resolution allows a separation of nuclear and off-nuclear galactic emission. In the off-nuclear diffuse emission, we find signatures of strong cold reflection, including high equivalent-width neutral Fe lines. This Compton-scattered off-nuclear emission amounts to 18% of the nuclear flux in the Fe line region, but becomes comparable to the nuclear emission above 30 keV. The new analysis no longer supports a prominent transmitted AGN component in the observed band. We find that the nuclear spectrum is consistent with Compton scattering by an optically thick torus, where the intrinsic spectrum is a power law of photon index Gamma = 2.2-2.4, the torus has an equatorial column density of N sub(H) = (6-10) x 10 super(24) cm super(-2), and the intrinsic AGN 2-10 keV luminosity is (2.3-5.1) x 10 super(42) erg s super(-1). These values place Circinus along the same relations as unobscured AGNs in accretion rate versus Gamma and L sub(x) versus L sub(TR) phase space. NuSTAR's high sensitivity and low background allow us to study the short timescale variability of Circinus at X-ray energies above 10 keV for the first time. The lack of detected variability favors a Compton-thick absorber, in line with the spectral fitting results.
We present NuSTAR observations of the bright Seyfert 2 galaxy NGC 2110 obtained in 2012, when the source was at the highest flux level ever observed, and in 2013, when the source was at a more ...typical flux level. We include archival observations from other X-ray satellites, namely XMM–Newton, Suzaku, BeppoSAX, Chandra and Swift. Simultaneous NuSTAR and Swift broad-band spectra (in the 3–80 keV range) indicate a cutoff energy E
c > 210 keV, with no detectable contribution from Compton reflection. NGC 2110 is one of the very few sources where no evidence for distant Compton-thick scattering is found and, by using temporal information collected over more than a decade, we investigate variations of the iron Kα line on time-scales of years. The Fe Kα line is likely the sum of two components: one constant (originating from distant Compton-thick material) and the other one variable and linearly correlated with the source flux (possibly arising from Compton-thin material much closer to the black hole).
ABSTRACT
The merger of two or more galaxies can enhance the inflow of material from galactic scales into the close environments of active galactic nuclei (AGNs), obscuring and feeding the ...supermassive black hole (SMBH). Both recent simulations and observations of AGN in mergers have confirmed that mergers are related to strong nuclear obscuration. However, it is still unclear how AGN obscuration evolves in the last phases of the merger process. We study a sample of 60 luminous and ultra-luminous IR galaxies (U/LIRGs) from the GOALS sample observed by NuSTAR. We find that the fraction of AGNs that are Compton thick (CT; $N_{\rm H}\ge 10^{24}\rm \, cm^{-2}$) peaks at $74_{-19}^{+14}{{\ \rm per\ cent}}$ at a late merger stage, prior to coalescence, when the nuclei have projected separations (dsep) of 0.4–6 kpc. A similar peak is also observed in the median NH $(1.6\pm 0.5)\times 10^{24}\rm \, cm^{-2}$. The vast majority ($85^{+7}_{-9}{{\ \rm per\ cent}}$) of the AGNs in the final merger stages (dsep ≲ 10 kpc) are heavily obscured ($N_{\rm H}\ge 10^{23}\rm \, cm^{-2}$), and the median NH of the accreting SMBHs in our sample is systematically higher than that of local hard X-ray-selected AGN, regardless of the merger stage. This implies that these objects have very obscured nuclear environments, with the $N_{\rm H}\ge 10^{23}\rm \, cm^{-2}$ gas almost completely covering the AGN in late mergers. CT AGNs tend to have systematically higher absorption-corrected X-ray luminosities than less obscured sources. This could either be due to an evolutionary effect, with more obscured sources accreting more rapidly because they have more gas available in their surroundings, or to a selection bias. The latter scenario would imply that we are still missing a large fraction of heavily obscured, lower luminosity ($L_{2-10}\lesssim 10^{43}\rm \, erg\, s^{-1}$) AGNs in U/LIRGs.
We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift ...range (median ). The spectral analysis is performed over the broad 0.5-24 keV energy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical and physically motivated models. This constitutes the largest sample of AGN selected at to be homogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters such as photon index, column density ( ), reflection parameter ( ), and 10-40 keV luminosity ( ). Heavily obscured ( ) and Compton-thick (CT; ) AGN constitute ∼25% (15-17 sources) and ∼2-3% (1-2 sources) of the sample, respectively. The observed distribution agrees fairly well with predictions of cosmic X-ray background population-synthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of , accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CT AGN relative to AGN is poorly constrained, formally in the range 2-56% (90% upper limit of 66%). We derived a fraction (fabs) of obscured AGN ( ) as a function of in agreement with CXBPSM and previous X-ray determinations. Furthermore, fabs at and agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anti-correlation of R with (confirmed by our companion paper on stacked spectra) with considerable scatter around the median R values.
We present the infrared (IR) and X-ray properties of a sample of 33 mid-IR luminous quasars (νL
6 μm ≥ 6 × 1044 erg s−1) at redshift z ≈ 1–3, identified through detailed spectral energy distribution ...analyses of distant star-forming galaxies, using the deepest IR data from Spitzer and Herschel in the GOODS–Herschel fields. The aim is to constrain the fraction of obscured, and Compton-thick (CT, N
H > 1.5 × 1024 cm−2) quasars at the peak era of nuclear and star formation activities. Despite being very bright in the mid-IR band, ≈30 per cent of these quasars are not detected in the extremely deep 2 and 4 Ms Chandra X-ray data available in these fields. X-ray spectral analysis of the detected sources reveals that the majority (≈67 per cent) are obscured by column densities N
H > 1022 cm−2; this fraction reaches ≈80 per cent when including the X-ray-undetected sources (9 out of 33), which are likely to be the most heavily obscured, CT quasars. We constrain the fraction of CT quasars in our sample to be ≈24–48 per cent, and their space density to be Φ = (6.7 ± 2.2) × 10−6 Mpc−3. From the investigation of the quasar host galaxies in terms of star formation rates (SFRs) and morphological distortions, as a sign of galaxy mergers/interactions, we do not find any direct relation between SFRs and quasar luminosity or X-ray obscuration. On the other hand, there is tentative evidence that the most heavily obscured quasars have, on average, more disturbed morphologies than the unobscured/moderately obscured quasar hosts, which preferentially live in undisturbed systems. However, the fraction of quasars with disturbed morphology amongst the whole sample is ≈40 per cent, suggesting that galaxy mergers are not the main fuelling mechanism of quasars at z ≈ 2.
SN 2005kd is among the most luminous supernovae (SNe) to be discovered at X-ray wavelengths. We have re-analysed all good angular resolution (better than 20 arcsec full width at half-maximum point ...spread function) archival X-ray data for SN 2005kd. The data reveal an X-ray light curve that decreases as t
−1.62±0.06. Our modelling of the data suggests that the early evolution is dominated by emission from the forward shock in a high-density medium. Emission from the radiative reverse shock is absorbed by the cold dense shell formed behind the reverse shock. Our results suggest a progenitor with a mass-loss rate towards the end of its evolution of ≥4.3 × 10
$^{-4} \,{{\rm M}_{{\odot }}}\,{\rm \,yr}^{-1}$
, for a wind velocity of 10 km s−1, at 4.0 × 1016 cm. This mass-loss rate is too high for most known stars, except perhaps hypergiant stars. A higher wind velocity would lead to a correspondingly higher mass-loss rate. A luminous blue variable star undergoing a giant eruption could potentially fulfill this requirement, but would need a high mass-loss rate lasting for several hundred years, and need to explain the plateau observed in the optical light curve. The latter could perhaps be due to the ejecta expanding in the dense circum-stellar material at relatively small radii. These observations are consistent with the fact that Type IIn SNe appear to expand into high-density and high mass-loss rate environments, and also suggest rapid variability in the wind mass-loss parameters within at least the last 5000 yr of stellar evolution prior to core-collapse.
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