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Register a new userX-Ray Detection of an Obscured Active Galactic Nucleus in a z=3.09 Radio-quiet Ly-alpha Nebula
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We present evidence for a highly obscured X-ray source in one of two giant Ly-alpha emission nebulae in the z=3.09 proto-cluster region SSA22. Neither Ly-alpha nebula is associated with significant radio emission. While one has a significant submillimeter detection and is undetected in the X-ray, the other is a factor of 2-10 times less submillimeter bright and appears to contain a hard-band X-ray source. We discuss our analysis and techniques for assessing the X-ray properties of this source and suggest that we have detected an embedded AGN source in one of these nebulae which may be at least partially responsible for exciting the Ly-alpha emission through a mechanism that is essentially decoupled from the radio, submillimeter, or optical luminosities. We also present an upper limit on the mean X-ray emission from 10 other extended Ly-alpha objects in the SSA22 region.
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We present a multiwavelength study of an atypical submillimeter galaxy in the GOODS-North field, with the aim to understand its physical properties of stellar and dust emission, as well as the central AGN activity. Although it is shown that the source is likely an extremely dusty galaxy at high redshift, its exact position of submillimeter emission is unknown. With the new NOEMA interferometric imaging, we confirm that the source is a unique dusty galaxy. It has no obvious counterpart in the optical and even NIR images observed with HST at lambda~<1.4um. Photometric-redshift analyses from both stellar and dust SED suggest it to likely be at z~>4, though a lower redshift at z~>3.1 cannot be fully ruled out (at 90% confidence interval). Explaining its unusual optical-to-NIR properties requires an old stellar population (~0.67 Gyr), coexisting with a very dusty ongoing starburst component. The latter is contributing to the FIR emission, with its rest-frame UV and optical light being largely obscured along our line of sight. If the observed fluxes at the rest-frame optical/NIR wavelengths were mainly contributed by old stars, a total stellar mass of ~3.5x10^11Msun would be obtained. An X-ray spectral analysis suggests that this galaxy harbors a heavily obscured AGN with N_H=3.3x10^23 cm^-2 and an intrinsic 2-10 keV luminosity of L_X~2.6x10^44 erg/s, which places this object among distant type 2 quasars. The radio emission of the source is extremely bright, which is an order of magnitude higher than the star-formation-powered emission, making it one of the most distant radio-luminous dusty galaxies. The combined characteristics of the galaxy suggest that the source appears to have been caught in a rare but critical transition stage in the evolution of submillimeter galaxies, where we are witnessing the birth of a young AGN and possibly the earliest stage of its jet formation and feedback.
Context. Searching for high-redshift galaxies is a field of intense activity in modern observational cosmology that will continue to grow with future ground-based and sky observatories. Over the last few years, a lot has been learned about the high-z Universe. Aims. Despite extensive Ly-alpha Blobs (LAB) surveys from low to high redshifts, giant LABs over 100 kpc have been found mostly at z~2-4. This redshift range is coincident with the transition epoch of galactic gas-circulation processes from inflows to outflows at z~2.5-3. This suggests that the formation of giant LABs may be related to a combination of gas inflows and outflows. Their extreme youth makes them interesting objects in the study of galaxy formation as they provide insight into some of the youngest known highly star forming galaxies, with only modest time investments using ground-based telescopes. Methods. Systematic narrow-band Ly-alpha nebula surveys are ongoing, but they are limited in their covered redshift range and their comoving volume. This poses a significant problem when searching for such rare sources. To address this problem, we developed a systematic searching tool, ATACAMA (A Tool for seArChing for lArge LyMan Alpha nebulae) designed to find large Ly-alpha nebulae at any redshift within deep multi-wavelength broad-band imaging. Results. We identified a Ly-alpha nebula candidate at zphot~3.3 covering an isophotal area of 29.4sq.arcsec. Its morphology shows a bright core and a faint core which coincides with the morphology of previously known Ly-alpha blobs. A first estimation of the Ly-alpha equivalent width and line flux agree with the values from the study led by several groups.
We present the discovery of a giant $gtrsim$100~kpc Ly$alpha$ nebula detected in the core of the X-ray emitting cluster CL~J1449+0856 at $z=1.99$ through Keck/LRIS narrow-band imaging. This detection extends the known relation between Ly$alpha$ nebulae and overdense regions of the Universe to the dense core of a $5-7times10^{13}$ M$_{odot}$ cluster. The most plausible candidates to power the nebula are two Chandra-detected AGN host cluster members, while cooling from the X-ray phase and cosmological cold flows are disfavored primarily because of the high Ly$alpha$ to X-ray luminosity ratio ($L_{mathrm{Lyalpha}}/L_{mathrm{X}} approx0.3$, $gtrsim10-1000times$ higher than in local cool-core clusters) and by current modeling. Given the physical conditions of the Ly$alpha$-emitting gas and the possible interplay with the X-ray phase, we argue that the Ly$alpha$ nebula would be short-lived ($lesssim10$ Myr) if not continuously replenished with cold gas at a rate of $gtrsim1000$ M$_{odot}$ yr$^{-1}$. We investigate the possibility that cluster galaxies supply the required gas through outflows and we show that their total mass outflow rate matches the replenishment necessary to sustain the nebula. This scenario directly implies the extraction of energy from galaxies and its deposition in the surrounding intracluster medium, as required to explain the thermodynamic properties of local clusters. We estimate an energy injection of the order of $thickapprox2$ keV per particle in the intracluster medium over a $2$ Gyr interval. In our baseline calculation AGN provide up to $85$% of the injected energy and 2/3 of the mass, while the rest is supplied by supernovae-driven winds.
We present new XMM-Newton observations of two luminous and high accretion-rate radio-quiet active galactic nuclei (AGNs) at z~2. Together with archival X-ray and rest-frame optical spectra of three sources with similar properties as well as 25 moderate-luminosity radio-quiet AGNs at z<0.5, we investigate, for the first time, the dependence of the hard (>~2 keV) X-ray power-law photon index on the broad H_beta emission-line width and on the accretion rate across ~3 orders of magnitude in AGN luminosity. Provided the accretion rates of the five luminous sources can be estimated by extrapolating the well-known broad-line region size-luminosity relation to high luminosities, we find that the photon indices of these sources, while consistent with those expected from their accretion rates, are significantly higher than expected from the widths of their H_beta lines. We argue that, within the limits of our sample, the hard-X-ray photon index depends primarily on the accretion rate.
We have discovered an obscured active galaxy at redshift z = 1.246 identified with the ROSAT X-ray source RX J1011.2+5545. We report on multiwavelength observations of this source and discuss its X-ray, optical and radio properties. This is the first X-ray selected, obscured active galaxy at high redshift to be shown to be radio-loud, with a radio counterpart exhibiting a classical double-lobe morphology.
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