Aims. We calculate the contribution to the neutrino background from the non-jetted active galactic nuclei (AGN) population following the recent IceCube association of TeV neutrinos with NGC 1068. ...Methods. We exploited our robust knowledge of the AGN X-ray luminosity function and evolution and converted it to the neutrino band by using NGC 1068 as a benchmark, together with a theoretically motivated neutrino spectrum. Results. The resulting neutrino background up to redshift 5 does not violate either the IceCube diffuse flux or the upper bounds for non-jetted AGN, although barely so. This is consistent with a scenario in which the latter class makes a substantial contribution mostly below 1 PeV, while jetted AGN, that is, blazars, dominate above this energy, in intriguing agreement with the dip in the neutrino data at ∼300 TeV. More and better IceCube data on Seyfert galaxies will allow us to constrain the fraction of neutrino emitters among non-jetted AGN.
We exploit the 7 Ms Chandra observations in the Chandra Deep Field-South (CDF-S), the deepest X-ray survey to date, coupled with CANDELS/GOODS-S data, to measure the total X-ray emission arising from ...2076 galaxies at 3.5 ≤ z < 6.5. This aim is achieved by stacking the Chandra data at the positions of optically selected galaxies, reaching effective exposure times of ≥109s. We detect significant (>3.7σ) X-ray emission from massive galaxies at z ≈ 4. We also report the detection of massive galaxies at z ≈ 5 at a 99.7 per cent confidence level (2.7σ), the highest significance ever obtained for X-ray emission from galaxies at such high redshifts. No significant signal is detected from galaxies at even higher redshifts. The stacking results place constraints on the BHAD associated with the known high-redshift galaxy samples, as well as on the SFRD at high redshift, assuming a range of prescriptions for X-ray emission due to X- ray binaries. We find that the X-ray emission from our sample is likely dominated by processes related to star formation. Our results show that low-rate mass accretion on to SMBHs in individually X-ray-undetected galaxies is negligible, compared with the BHAD measured for samples of X-ray detected AGN, for cosmic SMBH mass assembly at high redshift. We also place, for the first time, constraints on the faint-end of the AGN X-ray luminosity function (logLX ∼ 42) at z > 4, with evidence for fairly flat slopes. The implications of all of these findings are discussed in the context of the evolution of the AGN population at high redshift.
Abstract
We study the spectrophotometric properties of a highly magnified (
) pair of stellar systems identified at
z
= 3.2222 behind the Hubble Frontier Field galaxy cluster MACS J0416. Five ...multiple images (out of six) have been spectroscopically confirmed by means of VLT/MUSE and VLT/X-Shooter observations. Each image includes two faint (
), young (
Myr), low-mass (
), low-metallicity (12 + Log(O/H) ≃ 7.7, or 1/10 solar), and compact (30 pc effective radius) stellar systems separated by
pc after correcting for lensing amplification. We measured several rest-frame ultraviolet and optical narrow (
km s
−1
) high-ionization lines. These features may be the signature of very hot (
K) stars within dense stellar clusters, whose dynamical mass is likely dominated by the stellar component. Remarkably, the ultraviolet metal lines are not accompanied by Ly
α
emission (e.g., C
iv
/Ly
α
), despite the fact that the Ly
α
line flux is expected to be 150 times brighter (inferred from the H
β
flux). A spatially offset, strongly magnified (
) Ly
α
emission with a spatial extent
kpc
2
is instead identified 2 kpc away from the system. The origin of such a faint emission could be the result of fluorescent Ly
α
induced by a transverse leakage of ionizing radiation emerging from the stellar systems and/or may be associated with an underlying and barely detected object (with
de-lensed). This is the first confirmed metal-line emitter at such low-luminosity and redshift without Ly
α
emission—suggesting that, at least in some cases, a non-uniform covering factor of the neutral gas might hamper the Ly
α
detection.
Context.
Obscured active galactic nuclei (AGN) represent a significant fraction of the entire AGN population, especially at high redshift (∼70% at
z
= 3 − 5). They are often characterized by the ...presence of large gas and dust reservoirs that are thought to sustain and possibly obscure vigorous star formation processes that make these objects shine at FIR and submillimeter wavelengths. Studying the physical properties of obscured AGN and their host galaxies is crucial to shedding light on the early stages of a massive system lifetime.
Aims.
We aim to investigate the contribution of the interstellar medium (ISM) to the obscuration of quasars in a sample of distant highly star forming galaxies and to unveil their morphological and kinematics properties.
Methods.
We exploit Atacama Large Millimeter/submillimeter Array Cycle 4 observations of the continuum (∼2.1 mm) and high-
J
CO emission of a sample of six X-ray selected, FIR detected galaxies hosting an obscured AGN at
z
spec
> 2.5 in the 7 Ms
Chandra
Deep Field-South. We measured the masses and sizes of the dust and molecular gas by fitting the images, visibilities, and spectra, and we derived the gas density and column density on the basis of a uniform sphere geometry. Finally, we compared the measured column densities with those derived from the
Chandra
X-ray spectra.
Results.
We detected both the continuum and line emission for three sources for which we measured both the flux density and size. For the undetected sources, we derived an upper limit on the flux density from the root mean square of the images. We found that the detected galaxies are rich in gas and dust (molecular gas mass in the range < 0.5–2.7 × 10
10
M
⊙
for
α
CO
= 0.8 and up to ∼2 × 10
11
M
⊙
for
α
CO
= 6.5, and dust mass < 0.9–4.9 × 10
8
M
⊙
) and generally compact (gas major axis 2.1–3.0 kpc, dust major axis 1.4–2.7 kpc). The column densities associated with the ISM are on the order of 10
23 − 24
cm
−2
, which is comparable with those derived from the X-ray spectra. For the detected sources we also derived dynamical masses in the range 0.8–3.7 × 10
10
M
⊙
.
Conclusions.
We conclude that the ISM of high redshift galaxies can substantially contribute to nuclear obscuration up to the Compton-thick (> 10
24
cm
−2
) regime. In addition, we found that all the detected sources show a velocity gradient reminding one rotating system, even though two of them show peculiar features in their morphology that can be associated with a chaotic, possibly merging, structure.
Based on ALMA Band 3 observations of the CO(2→1) line transition, we report the discovery of three new gas-rich (
M
H
2
∼ 1.5 − 4.8 × 10
10
M
⊙
) galaxies in an overdense region at
z
= 1.7 that ...already contains eight spectroscopically confirmed members. This leads to a total of 11 confirmed overdensity members within a projected distance of ∼1.15 Mpc and in a redshift range of Δ
z
= 0.012. Under simple assumptions, we estimate that the system has a total mass of ≥3 − 6 × 10
13
M
⊙
, and show that it will likely evolve into a ≳10
14
M
⊙
cluster at
z
= 0. The overdensity includes a powerful Compton-thick Fanaroff-Riley type II (FRII) radio galaxy, around which we discovered a large molecular gas reservoir (
M
H
2
∼ 2 × 10
11
M
⊙
). We fit the FRII resolved CO emission with a 2D Gaussian model with a major (minor) axis of ∼27 (∼17) kpc, which is a factor of ∼3 larger than the optical rest-frame emission. Under the assumption of a simple edge-on disk morphology, we find that the galaxy interstellar medium produces a column density toward the nucleus of ∼5.5 × 10
23
cm
−2
. A dense interstellar medium like this may then contribute significantly to the total nuclear obscuration measured in the X-rays (
N
H, X
∼ 1.5 × 10
24
cm
−2
) in addition to a small, paresec-scale absorber around the central engine. The velocity map of this source unveils a rotational motion of the gas that is perpendicular to the radio jets. All ALMA sources have a dust-reddened counterpart in deep
Hubble
Space Telescope images (bands
i
,
z
,
H
), while we do not detect any molecular gas reservoir around the known UV-bright, star-forming members discovered by MUSE. This highlights the capability of ALMA of tracing gas-rich members of the overdensity. For the MUSE sources, we derive 3
σ
upper limits to the molecular gas mass of
M
H
2
≤ 2.8 − 4.8 × 10
10
M
⊙
. We derive star formation rates in the range ∼5 − 100
M
⊙
yr
−1
for the three new ALMA sources. The FRII is located at the center of the projected spatial distribution of the structure members, and its velocity offset from the peak of the redshift distribution is well within the velocity dispersion of the structure. All this, coupled with the large amount of gas around the FRII, its stellar mass of ∼3 × 10
11
M
⊙
, star formation rate of ∼200 − 600
M
⊙
yr
−1
, and powerful radio-to-X-ray emission, suggests that this source is the likely progenitor of the future brightest cluster galaxy.
ABSTRACT We present X-ray source catalogs for the 7 Ms exposure of the Chandra Deep Field-South (CDF-S), which covers a total area of 484.2 arcmin2. Utilizing wavdetect for initial source detection ...and ACIS Extract for photometric extraction and significance assessment, we create a main source catalog containing 1008 sources that are detected in up to three X-ray bands: 0.5-7.0 keV, 0.5-2.0 keV, and 2-7 keV. A supplementary source catalog is also provided, including 47 lower-significance sources that have bright ( ) near-infrared counterparts. We identify multiwavelength counterparts for 992 (98.4%) of the main-catalog sources, and we collect redshifts for 986 of these sources, including 653 spectroscopic redshifts and 333 photometric redshifts. Based on the X-ray and multiwavelength properties, we identify 711 active galactic nuclei (AGNs) from the main-catalog sources. Compared to the previous 4 Ms CDF-S catalogs, 291 of the main-catalog sources are new detections. We have achieved unprecedented X-ray sensitivity with average flux limits over the central 1 arcmin2 region of 1.9 × 10−17, 6.4 × 10−18, and 2.7 × 10−17 erg cm−2 s−1 in the three X-ray bands, respectively. We provide cumulative number-count measurements observing, for the first time, that normal galaxies start to dominate the X-ray source population at the faintest 0.5-2.0 keV flux levels. The highest X-ray source density reaches 50,500 deg−2, and 47% 4% of these sources are AGNs ( 23,900 deg−2).
We present a series of new, publicly available mock catalogs of X-ray selected active galactic nuclei (AGNs), nonactive galaxies, and clusters of galaxies. These mocks are based on up-to-date ...observational results on the demographic of extragalactic X-ray sources and their extrapolations. They reach fluxes below 10-20 erg cm-2 s-1 in the 0.5–2 keV band, that is, more than an order of magnitude below the predicted limits of future deep fields, and they therefore represent an important tool for simulating extragalactic X-ray surveys with both current and future telescopes. We used our mocks to perform a set of end-to-end simulations of X-ray surveys with the forthcoming ATHENA mission and with the AXIS probe, a subarcsecond resolution X-ray mission concept proposed to the Astro 2020 Decadal Survey. We find that these proposed, next generation surveys may transform our knowledge of the deep X-ray Universe. As an example, in a total observing time of 15 Ms, AXIS would detect ~225 000 AGNs and ~50 000 nonactive galaxies, reaching a flux limit of f0:5-2 ~ 5 x 10-19 erg cm-2 s-1 in the 0.5–2 keV band, with an improvement of over an order of magnitude with respect to surveys with current X-ray facilities. Consequently, 90% of these sources would be detected for the first time in the X-rays. Furthermore, we show that deep and wide X-ray surveys with instruments such as AXIS and ATHENA are expected to detect ~20 000 z > 3 AGNs and ~250 sources at redshift z > 6, thus opening a new window of knowledge on the evolution of AGNs over cosmic time and putting strong constraints on the predictions of theoretical models of black hole seed accretion in the early universe.
Context. The coeval active galactic nuclei (AGN) and galaxy evolution, and the observed local relations between super massive black holes (SMBHs) and galaxy properties suggest some sort of connection ...or feedback between SMBH growth (i.e., AGN activity) and galaxy build-up (i.e., star formation history). Aims. We looked for correlations between average properties of X-ray detected AGN and their far-IR (FIR) detected, star forming host galaxies in order to find quantitative evidence for this connection, which has been highly debated in recent years. Methods. We exploited the rich multiwavelength data set (from X-ray to FIR) available in the COSMOS field for a large sample (692 sources) of AGN and their hosts in the redshift range 0.1 <z< 4. We use X-ray data to select AGN and determine their properties, such as X-ray intrinsic luminosity and nuclear obscuration, and broadband (from UV to FIR) SED fitting results to derive host galaxy properties, such as stellar mass (M∗) and star formation rate (SFR). Results. We find that the AGN 2–10 keV luminosity (LX) and the host 8−1000 μm star formation luminosity (LIRSF) are significantly correlated, even after removing the dependency of both quantities with redshift. However, the average host LIRSF has a flat distribution in bins of AGN LX, while the average AGN LX increases in bins of host LIRSF with logarithmic slope of ~0.7 in the redshift range 0.4 <z< 1.2. We also discuss the comparison between the full distribution of these two quantities and the predictions from hydrodynamical simulations. No other significant correlations between AGN LX and host properties is found. On the other hand, we find that the average column density (NH) shows a clear positive correlation with the host M∗ at all redshifts, but not with the SFR (or LIRSF). This translates into a negative correlation with specific SFR at all redshifts. The same is true if the obscured fraction is computed. Conclusions. Our results are in agreement with the idea, introduced in recent galaxy evolutionary models, that SMBH accretion and SFRs are correlated, but occur with different variability time scales. Finally, the presence of a positive correlation between NH and host M∗ suggests that the column density that we observe in the X-rays is not entirely due to the circumnuclear obscuring torus, but may also include a significant contribution from the host galaxy.
We present the results from a ~ 500 ks Chandra observation of the z = 6.31 QSO SDSS J1030 + 0524. This is the deepest X-ray observation to date of a z ~ 6 QSO. The QSO is detected with a total of 125 ...net counts in the full (0.500A0–7 keV) band and its spectrum can be modeled by a single power-law model with photon index of Γ = 1.81 ± 0.18 and full band flux of f = 3.95 × 10−15 erg s−1 cm−2. When compared with the data obtained by XMM-Newton in 2003, our Chandra observation in 2017 shows a harder (ΔΓ ≈ −0.6) spectrum and a 2.5 times fainter flux. Such a variation, in a timespan of ~ 2 yr rest-frame, is unexpected for such a luminous QSO powered by a > 109M⨀ black hole. The observed source hardening and weakening could be related to an intrinsic variation in the accretion rate. However, the limited photon statistics does not allow us to discriminate between an intrinsic luminosity and spectral change, and an absorption event produced by an intervening gas cloud along the line of sight. We also report the discovery of diffuse X-ray emission that extends for 30″ × 20″ southward of the QSO with a signal-to-noise ratio (S/N) of approximately six, hardness ratio of HR = 0.03+0.20−0.25 HR = 0.03 - 0.25 + 0.20 $\text{HR} = {0.03}_{-0.25}^{+0.20}$ , and soft band flux of f0.5– keV = 1.1+0.3−0.3 × 10−15 erg s−1 cm−2 f 0.5 - 2 keV = 1.1 - 0.3 + 0.3 × 10 - 15 erg s - 1 cm - 2 $ f_{0.5-2\,\text{keV}}={1.1}_{-0.3}^{+0.3}\enspace \times \enspace 1{0}^{-15\enspace }\mathrm{erg}\enspace {\mathrm{s}}^{-1}\;\rm{cm}^{-2}$ , that is not associated to a group or cluster of galaxies. We discuss two possible explanations for the extended emission, which may be either associated with the radio lobe of a nearby, foreground radio galaxy (at z ≈ 1 – 2), or ascribed to the feedback from the QSO itself acting on its surrounding environment, as proposed by simulations of early black hole formation.
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