We report on the second round of Chandra observations of the 3C snapshot survey developed to observe the complete sample of 3C radio sources with z<0.3 for 8 ksec each. In the first paper, we ...illustrated the basic data reduction and analysis procedures performed for the 30 sources of the 3C sample observed during the Chandra Cycle 9, while here, we present the data for the remaining 27 sources observed during Cycle 12. We measured the X-ray intensity of the nuclei and of any radio hotspots and jet features with associated X-ray emission. X-ray fluxes in three energy bands: soft, medium and hard for all the sources analyzed are also reported. For the stronger nuclei, we also applied the standard spectral analysis which provides the best fit values of X-ray spectral index and absorbing column density. In addition, a detailed analysis of bright X-ray nuclei that could be affected by pileup has been performed. X-ray emission was detected for all the nuclei of the radio sources in our sample except for 3C 319. Amongst the current sample, there are two compact steep spectrum radio sources; two broad line radio galaxies; and one wide angle tail radio galaxy, 3C 89, hosted in a cluster of galaxies clearly visible in our Chandra snapshot observation. In addition, we also detected soft X-ray emission arising from the galaxy cluster surrounding 3C 196.1. Finally, X-ray emission from hotspots have been found in three FR II radio sources and, in the case of 3C 459, we also report the detection of X-ray emission associated with the eastern radio lobe and as well as that cospatial with radio jets in 3C 29 and 3C 402.
Astrophys.J.651:728-734,2006 We derive the spectral energy distribution (SED) of the nucleus of the
Seyfert galaxy NGC4565. Despite its classification as a Seyfert2, the nuclear
source is ...substantially unabsorbed. The absorption we find from Chandra data
(N_H=2.5 X 10^21 cm^-2) is consistent with that produced by material in the
galactic disk of the host galaxy. HST images show a nuclear unresolved source
in all of the available observations, from the near-IR H band to the optical U
band. The SED is completely different from that of Seyfert galaxies and QSO, as
it appears basically ``flat'' in the IR-optical region, with a small drop-off
in the U-band. The location of the object in diagnostic planes for low
luminosity AGNs excludes a jet origin for the optical nucleus, and its
extremely low Eddington ratio L_o/L_Edd indicates that the radiation we observe
is most likely produced in a radiatively inefficient accretion flow (RIAF).
This would make NGC4565 the first AGN in which an ADAF-like process is
identified in the optical. We find that the relatively high OIII flux
observed from the ground cannot be all produced in the nucleus. Therefore, an
extended NLR must exist in this object. This may be interpreted in the
framework of two different scenarios: i) the radiation from ADAFs is sufficient
to give rise to high ionization emission-line regions through photoionization,
or ii) the nuclear source has recently ``turned-off'', switching from a
high-efficiency accretion regime to the present low-efficiency state.
A microcalorimetric method was used for the direct study of the interaction of methotrexate, its metabolites, and new antifolates N10-propargyl-5,8-dideazafolate (CB 3717) and 2-methyl,2-desamino ...N10-propargyl-5,8-dideazafolate (CB 3819), with thymidylate synthase. We show that 7-hydroxymethotrexate and dideazafolates require the prior binding of dUMP or its fluorinated derivative FdUMP to bind to thymidylate synthase, as does methotrexate. Conversely, we show that methotrexate-G2 can interact directly with the enzyme alone. On the other hand, both dUMP and FdUMP exhibited a large cooperative effect on the affinity for thymidylate synthase of the inhibitors, and surprisingly, no significant difference was shown at this level between the natural substrate dUMP and its fluorinated derivative. It was demonstrated that this cooperative effect had an enthalpic origin. In the presence of FdUMP or dUMP, all the studied compounds except 7-hydroxymethotrexate exhibited a large negative enthalpy variation when binding to thymidylate synthase (from -44 to -91 kJ/mol). CB 3717 and methotrexate-G2 are competitors for the same protein binding site. Polyglutamation of methotrexate lead to compounds with higher affinity (association constants were 6.6 x 10(3) M-1 and 2.3 x 10(6) M-1 for methotrexate and methotrexate-G2 respectively) while hydroxylation has an unfavourable effect (association constant of 7-hydroxymethotrexate inferior to 500 M-1). Evidence for the influence of polyglutamation was also provided by the relatively low affinity of dideazofolates for thymidylate synthase (association constant equal to 1.4 and 1.7 x 10(7) M-1 for CB 3717 and CB 3819, respectively), whereas these compounds are known to be strong inhibitors of the enzyme in cells in their polyglutamated forms.
Abridged We investigate the physical properties of a Lyman continuum emitter candidate at \(z=3.212\) with photometric coverage from \(U\) to MIPS 24\(\mu\)m band and VIMOS/VLT and MOSFIRE/Keck ...spectroscopy. Investigation of the UV spectrum confirms a direct spectroscopic detection of the Lyman continuum emission with \(S/N>5\). Non-zero Ly\(\alpha\) flux at the systemic redshift and high Lyman-\(\alpha\) escape fraction suggest a low HI column density. The weak C and Si low-ionization absorption lines are also consistent with a low covering fraction along the line of sight. The OIII\(\lambda\lambda4959,5007+\mathrm{H}\beta\) equivalent width is one of the largest reported for a galaxy at \(z>3\) (\(\mathrm{EW}(\mathrm{OIII}\lambda\lambda4959,5007+\mathrm{H}\beta) \simeq 1600\AA\), rest-frame) and the NIR spectrum shows that this is mainly due to an extremely strong OIII emission. The large observed OIII/OII ratio (\(>10\)) and high ionization parameter are consistent with prediction from photoionization models in case of a density-bounded nebula scenario. Furthermore, the \(\mathrm{EW}(\mathrm{OIII}\lambda\lambda4959,5007+\mathrm{H}\beta)\) is comparable to recent measurements reported at \(z\sim7-9\), in the reionization epoch. We also investigate the possibility of an AGN contribution to explain the ionizing emission but most of the AGN identification diagnostics suggest that stellar emission dominates instead. This source is currently the first high-\(z\) example of a Lyman continuum emitter exhibiting indirect and direct evidences of a Lyman continuum leakage and having physical properties consistent with theoretical expectation from Lyman continuum emission from a density-bounded nebula.
We will briefly discuss the importance of sensitive X-ray observations above 10 keV for a better understanding of the physical mechanisms associated to the Supermassive Black Hole primary emission ...and to the cosmological evolution of the most obscured Active Galactic Nuclei.
We present results from a spectral analysis of a sample of high-redshift (z>3) X-ray selected AGN in the 4 Ms Chandra Deep Field South (CDF-S), the deepest X-ray survey to date. The sample is ...selected using the most recent spectroscopic and photometric information available in this field. It consists of 34 sources with median redshift z=3.7, 80 median net counts in the 0.5-7 keV band and median rest-frame absorption-corrected luminosity \(L_{2-10 \rmn{keV}}\approx1.5\times10^{44}\rmn{erg} \rmn{s^{-1}}\). Spectral analysis for the full sample is presented and the intrinsic column density distribution, corrected for observational biases using spectral simulations, is compared with the expectations of X-ray background (XRB) synthesis models. We find that \(\approx57\) per cent of the sources are highly obscured (\(N_H>10^{23}\rmn{cm^{-2}}\)). Source number counts in the \(0.5-2\rmn{keV}\) band down to flux \(F_{0.5-2 \rmn{keV}}\approx4\times10^{-17}\rmn{erg} \rmn{s^{-1}cm^{-2}}\) are also presented. Our results are consistent with a decline of the AGN space density at z>3 and suggest that, at those redshifts, the AGN obscured fraction is in agreement with the expectations of XRB synthesis models.
We present here a new spectral energy distribution (SED) fitting approach that we adopt to select radio-excess sources amongst distant star-forming galaxies in the GOODS-Herschel (North) field and to ...reveal the presence of hidden, highly obscured AGN. Through extensive SED analysis of 458 galaxies with radio 1.4 GHz and mid-IR 24 um detections using some of the deepest Chandra X-ray, Spitzer and Herschel infrared, and VLA radio data available to date, we have robustly identified a sample of 51 radio-excess AGN (~1300 deg^-2) out to redshift z~3. These radio-excess AGN have a significantly lower far-IR/radio ratio (q<1.68) than the typical relation observed for star-forming galaxies (q~2.2). We find that ~45% of these radio-excess sources have a dominant AGN component in the mid-IR band, while for the remainders the excess radio emission is the only indicator of AGN activity. The fraction of radio-excess AGN increases with X-ray luminosity reaching ~60% at Lx~10^44-10^45 erg/s, making these sources an important part of the total AGN population. However, almost half (24/51) of these radio-excess AGN are not detected in the deep Chandra X-ray data, suggesting that some of these sources might be heavily obscured. We also find that the specific star formation rates (sSFRs) of the radio-excess AGN are on average lower that those observed for X-ray selected AGN hosts, indicating that our sources are forming stars more slowly than typical AGN hosts, and possibly their star formation is progressively quenching.
Using the 4 Ms Chandra Deep Field-South (CDF-S) survey, we have identified a sample of 6845 X-ray undetected galaxies that dominates the unresolved ~ 20-25% of the 6-8 keV cosmic X-ray background ...(XRB). This sample was constructed by applying mass and color cuts to sources from a parent catalog based on GOODS-South HST z-band imaging of the central 6'-radius area of the 4 Ms CDF-S. The stacked 6-8 keV detection is significant at the 3.9 sigma level, but the stacked emission was not detected in the 4-6 keV band which indicates the existence of an underlying population of highly obscured active galactic nuclei (AGNs). Further examinations of these 6845 galaxies indicate that the galaxies on the top of the blue cloud and with redshifts of 1 < z < 3, magnitudes of 25 < z_850 < 28, and stellar masses of 2E8 < M_star/M_sun < 2E9 make the majority contributions to the unresolved 6-8 keV XRB. Such a population is seemingly surprising given that the majority of the X-ray detected AGNs reside in massive (> ~1E10 M_sun) galaxies. We discuss constraints upon this underlying AGN population, supporting evidence for relatively low-mass galaxies hosting highly obscured AGNs, and prospects for further boosting the stacked signal.
We investigated the presence of galaxy overdensities around four \(z\sim6\) QSOs, namely SDSS J1030+0524 (z = 6.28), SDSS J1148+5251 (z = 6.41), SDSS J1048+4637 (z = 6.20) and SDSS J1411+1217 (z = ...5.95), through deep \(r\)-, \(i\)- and \(z\)- band imaging obtained with the wide-field (\(\sim23'\times25'\)) Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT). We adopted color-color selections within the \(i-z\) vs \(r-z\) plane to identify samples of \(i\)-band dropouts at the QSO redshift and measure their relative abundance and spatial distribution in the four LBC fields, each covering \(\sim8\times8\) physical Mpc at \(z\sim6\). The same selection criteria were then applied to \(z\)-band selected sources in the \(\sim\)1 deg\(^2\) Subaru-XMM Newton Deep Survey to derive the expected number of dropouts over a blank LBC-sized field (\(\sim\)0.14 deg\(^2\)). The four observed QSO fields host a number of candidates larger than what is expected in a blank field. By defining as \(i\)-band dropouts objects with \(z_{AB}<25\), \(i-z>1.4\) and undetected in the \(r\)-band, we found 16, 10, 9, 12 dropouts in SDSS J1030+0524, SDSS J1148+5251, SDSS J1048+4637, and SDSS J1411+1217, respectively, whereas only 4.3 such objects are expected over a 0.14 deg\(^2\) blank field. This corresponds to overdensity significances of 3.3, 1.9, 1.7, 2.5\(\sigma\), respectively. By considering the total number of dropouts in the four LBC fields and comparing it with what is expected in four blank fields of 0.14 deg\(^2\) each, we find that high-z QSOs reside in overdense environments at the \(3.7\sigma\) level. This is the first direct and unambiguous measurement of the large scale structures around \(z\sim6\) QSOs. shortened
Recent observational results obtained with SCUBA, COBE and ISO have greatly
improved our knowledge of the infrared and sub-mm background radiation. These
limits become constraining given the ...realization that most AGNs are heavily
obscured and must reradiate strongly in the IR/sub-mm. Here we predict the
contribution of AGNs to the IR/sub-mm background, starting from measurements of
the hard X-ray background. We show that an application of what we know of AGN
Spectral Energy Distributions (SEDs) and the IR background requires that a
significant fraction of the 10-150 micron background comes from AGNs. This
conclusion can only be avoided if obscured AGNs are intrinsically brighter in
the X-rays (with respect to the optical-UV) than unobscured AGNs, contrary to
``unified schemes'' for AGNs, or have a dust to gas ratio much lower (< 0.1)
than Galactic. We show that these results are rather robust and not strongly
dependent on the details of the modeling.
