We previously identified LH146, a diffuse X-ray source in the Lockman Hole, as a galaxy cluster at redshift 1.753. The redshift was based on one spectroscopic value, buttressed by seven additional photometric redshifts. We here confirm the previous spectroscopic redshift and present concordant spectroscopic redshifts for an additional eight galaxies. The average of these nine redshifts is 1.714 +/- 0.012 (error on mean). Scrutiny of the galaxy distribution in redshift and the plane of the sky shows that there are two concentrations of galaxies near the X-ray source. In addition there are three diffuse X-ray sources spread along the axis connecting the galaxy concentrations. LH146 is one of these three and lies approximately at the center of the two galaxy concentrations and the outer two diffuse X-ray sources. We thus conclude that LH146 is at the redshift initially reported but it is not a single virialized galaxy cluster as previously assumed. Rather it appears to mark the approximate center of a larger region containing more objects. For brevity we term all these objects and their alignments as large scale structure. The exact nature of LH146 itself remains unclear.
We aim to study the nature of the faint, polarised radio source population whose source composition and redshift dependence contain information about the strength, morphology, and evolution of magnetic fields over cosmic timescales. We use a 15 pointing radio continuum L-band mosaic of the Lockman Hole, observed in full polarisation, generated from archival data of the WSRT. The data were analysed using the RM-Synthesis technique. We achieved a noise of 7 μJy/beam in polarised intensity, with a resolution of 15''. Using infrared and optical images and source catalogues, we were able to cross-i…
Optical and infrared properties of active galactic nuclei in the Lockman Hole
本文介绍了洛克曼洞中X射线选择活动星系核的光学、近红外和中红外特性。使用光学，近红外或中红外目录的似然比方法，我们分配对应的401的XMM牛顿目录的409个X射线源。收集了从U到24 μ m的所有源的准确光度。我们使用X射线和光学标准，以消除任何正常的星系，银河系恒星，或X射线团之间，并研究了剩余的377 AGN的多波长特性。我们使用了中红外颜色的选择，以了解活动星系核的光学和红外辐射的贡献。利用这种选择，我们确定了不同的行为的活动星系核为主的和主机为主的来源，在X射线光学红外彩色图。更具体地说，活动星系核主导的源在f_x/f_R vs. R-K和f_24um/f_R vs. R-K图上表现出明显的趋势，而宿主则遵循非X射线探测星系的行为。在光学-近红外色星等图中，我们看到已知的红色物体在X射线中更加模糊的趋势在活动星系核主导的系统中比在主机主导的系统中更强。这是一个迹象表明，这种趋势更多地与活动星系核污染了整体的颜色有关，而不是任何进化的影响。最后，我们发现，一个显着的分数（~30%）的最红的活动星系核是不模糊的X射线。
Studying the spatial distribution of extragalactic source populations is vital in understanding the matter distribution in the Universe. It also enables understanding the cosmological evolution of dark matter density fields and the relationship between dark matter and luminous matter. Clustering studies are also required for EoR foreground studies since it affects the relevant angular scales. This paper investigates the angular and spatial clustering properties and the bias parameter of radio-selected sources in the Lockman Hole field at 325 MHz. The data probes sources with fluxes $\gtrsim$0.…
Identification of a Complete 160 micron Flux-Limited Sample of Infrared Galaxies in the ISO Lockman Hole 1-Deg^2 Deep Fields: Source Properties and Evidence for Strong Evolution in the FIR Luminosity Function for ULIRGs
We present a study of the 1173 sources brighter than $S_{1.4\,\rm GHz}= 120\,μ$Jy detected over an area of $\simeq 1.4\,\hbox{deg}^{2}$ in the Lockman Hole field. Exploiting the multi-band information available in this field for $\sim$79% of the sample, sources have been classified into radio loud (RL) active galactic nuclei (AGNs), star forming galaxies (SFGs) and radio quiet (RQ) AGNs, using a variety of diagnostics available in the literature. Exploiting the observed tight anti-correlations between IRAC band 1 or band 2 and the source redshift we could assign a redshift to 177 sources missi…
One of the key science goals for the most sensitive telescopes, both current and upcoming, is the detection of the redshifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization. The success of detection relies on accurate foreground modeling for their removal from data sets. This paper presents the characterization of astrophysical sources in the Lockman Hole region. Using 325 MHz data obtained from the GMRT, a $6^\circ \times 6^\circ$ mosaiced map is produced with an RMS reaching 50 $μ$Jy $\mathrm{beam}^{-1}$. A source catalog containing 6186 sources is created, and the Euclidean nor…
The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterising the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper we present new 150-MHz observations carried out with the LOw Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6$\times$14.7 arcsec and rea…
A complete, flux density limited sample of 96 faint ($> 0.5$ mJy) radio sources is selected from the 10C survey at 15.7 GHz in the Lockman Hole. We have matched this sample to a range of multi-wavelength catalogues, including SERVS, SWIRE, UKIDSS and optical data; multi-wavelength counterparts are found for 80 of the 96 sources and spectroscopic redshifts are available for 24 sources. Photometric reshifts are estimated for the sources with multi-wavelength data available; the median redshift of the sample is 0.91 with an interquartile range of 0.84. Radio-to-optical ratios show that at least 9…
We find that the Fe III$λλ$2039-2113 spectral feature in quasars appears systematically redshifted by amounts accountable under the hypothesis of gravitational redshift induced by the central supermassive black hole. Our analysis of 27 composite spectra from the BOSS survey indicates that the redshift and the broadening of the lines in the Fe III$λλ$2039-2113 blend roughly follow the expected correlation in the weak limit of Schwarzschild geometry for virialized kinematics. Assuming that the Fe III UV redshift provides a measure of $M_{BH}\over R$ (${Δλ\over λ}\simeq{3\over2}{G\over c^2} {M_{B…
We show that the gravitational wave signals from primordial black hole (PBH) binaries at high redshift can be detected. The detectability of PBH binaries is enhanced by redshift bias and more PBH binaries at high redshift. The initial clustering of PBHs is also included and enhances the effectively detectable mass ranges of PBHs at high redshift. Future observations on the gravitational wave at high redshift by space-based detectors such as LISA and SKA can constrain the fraction of PBHs in dark matter and PBHs initial distribution.
We suggest that the redshift of photons traveling from past to future null infinity through a collapsing object could provide an observational signature capable of differentiating between the formation of a globally naked singularity and the formation of an event horizon. Supporting evidence for this idea is drawn from the analysis of photons with zero angular momentum through the center of a collapsing spherical dust cloud. We show that the frequency shift as a function of proper time with respect to stationary observers has distinct features depending on whether the object collapses to a bla…
Application of the most robust method of measuring black hole masses, spatially resolved kinematics of gas and stars, is presently limited to nearby galaxies. The Atacama Large Millimeter/sub-millimeter Array (ALMA) and thirty meter class telescopes (the Thirty Meter Telescope, the Giant Magellan Telescope, and the European Extremely Large Telescope) with milli-arcsecond resolution are expected to extend such measurements to larger distances. Here, we study the possibility of exploiting the angular magnification provided by strong gravitational lensing to measure black hole masses at high reds…
In this paper, we explore the possibility of accreting primordial black holes as the source of heating for the collapsing gas in the context of the direct collapse black hole scenario for the formation of super-massive black holes (SMBHs) at high redshifts, $z\sim 6-7$. One of the essential requirements for the direct collapse model to work is to maintain the temperature of the in falling gas at $\approx 10^4$ K. We show that even under the existing abundance limits, the primordial black holes of masses $\gtrsim 10^{-2} \ {\rm M}_\odot$, can heat the collapsing gas to an extent that the ${\rm …
We present ALMA observations of two moderate luminosity quasars at redshift 6. These quasars from the Canada-France High-z Quasar Survey (CFHQS) have black hole masses of ~10^8 M_solar. Both quasars are detected in the [CII] line and dust continuum. Combining these data with our previous study of two similar CFHQS quasars we investigate the population properties. We show that z>6 quasars have a significantly lower far-infrared luminosity than bolometric-luminosity-matched samples at lower redshift, inferring a lower star formation rate, possibly correlated with the lower black hole masses at z…
An upper limit on the mass of a black hole set by the pair-instability supernovae (PISN) process can be useful in inferring the redshift of the gravitational wave (GW) sources by lifting the degeneracy between mass and redshift. However, for this technique to work, it is essential that the PISN mass-scale is redshift independent or at least has a predictable redshift dependence. We show that the observed PISN mass-scale can get smeared and the position of the PISN mass-scale is likely to exhibit a strong redshift dependence due to a combined effect from the non-zero value of the delay time bet…
We study the prospects of using the low-redshift and high-redshift black hole shadows as new cosmological standard rulers for measuring cosmological parameters. We show that, using the low-redshift observation of the black hole shadow of M87$^\star$, the Hubble constant can be independently determined with a precision of about $13\%$ as $H_0=70\pm 9$ km s$^{-1}$ Mpc$^{-1}$. The high-redshift observations of super-massive black hole shadows may accurately determine a combination of parameters $H_0$ and ${Ω_{\rm m}}$, and we show by a simple simulation that combining them with the type Ia supern…
The possible existence of primordial black holes in the stellar mass window has received considerable attention because their mergers may contribute to current and future gravitational-wave detections. Primordial black hole mergers, together with mergers of black holes originating from Population~III stars, are expected to dominate at high redshifts ($z\gtrsim 10$). However the primordial black hole merger rate density is expected to rise monotonically with redshift, while Population~III mergers can only occur after the birth of the first stars. Next-generation gravitational-wave detectors suc…
The observation of quasars at high redshifts presents a mystery in the theory of black hole formation. In order to source such objects, one often relies on the presence of heavy seeds ($M \approx 10^{4-6} \, M_{\odot}$) in place at early times. Unfortunately, the formation of these heavy seeds are difficult to realize within the standard astrophysical context. Here, we investigate whether superconducting cosmic string loops can source sufficiently strong overdensities in the early universe to address this mystery. We review a set of direct collapse conditions under which a primordial gas cloud…
