相关论文: Dust-free quasars in the early Universe
Interstellar dust plays a crucial role in the evolution of the Universe by assisting the formation of molecules, by triggering the formation of the first low-mass stars, and by absorbing stellar ultraviolet-optical light and subsequently…
Observations suggest that high-redshift galaxies are either very dusty or essentially dust free. The evolution from one regime to the other must also be very fast, since evolved and dusty galaxies show up at redshifts corresponding to a…
Although dust emission at cosmological distances has only been detected a little more than a decade ago, remarkable progress has been achieved since then in characterizing the far-infrared emission of high-redshift systems. The mere fact…
Understanding how super-massive black holes form and grow in the early Universe has become a major challenge since the discovery of luminous quasars only 700 million years after the Big Bang. Simulations indicate an evolutionary sequence of…
This paper reviews the dust content of the high redshift (z > 2) universe. Studies of the various "species" in the high-z "zoo" show that almost all have strong evidence for containing dust. The one exception, where the evidence is not yet…
We test emission models of circum-nuclear dust torii around quasars, at low and high redshifts, by using a large collection of photometric data for an unbiased sample of 120 optically-selected objects with millimetric and sub-millimetric…
The detection of powerful near-infrared emission in high redshift (z>5) quasars demonstrates that very hot dust is present close to the active nucleus also in the very early universe. A number of high-redshift objects even show significant…
Quasars are among the most luminous objects in the universe, and they can be studied in detail up to the highest known redshift. Assuming that the gas associated with quasars is closely related to the interstellar medium of the host galaxy,…
It is currently unknown whether the Universe was reionized by quasars or stars at z>5. We point out that quasars can be best distinguished from stellar systems by their X-ray emission. Based on a simple hierarchical CDM model, we predict…
We identify and characterize a population of luminous dust poor quasars at 0<z<5, similar in photometric properties to the objects found at z>6 previously. This class of active galactic nuclei has been known to show little IR emission from…
Luminous distant quasars are unique probes of the high redshift intergalactic medium (IGM) and of the growth of massive galaxies and black holes in the early universe. Absorption due to neutral Hydrogen in the IGM makes quasars beyond a…
High-redshift quasars are currently the only probes of the growth of supermassive black holes and potential tracers of structure evolution at early cosmic time. Here we present our candidate selection criteria from the Panoramic Survey…
High redshift quasars mark the locations where massive galaxies are rapidly being assembled and forming stars. There is growing evidence that quasar environments are metal-rich out to redshifts of at least five. The gas-phase metallicities…
Quasars at z>4 provide direct information on the first massive structures to form in the Universe. Recent ground-based optical surveys (e.g., the Sloan Digital Sky Survey) have discovered large numbers of high-redshift quasars, increasing…
We present a sample of 120 dust-reddened quasars identified by matching radio sources detected at 1.4 GHz in the FIRST survey with the near-infrared 2MASS catalog and color-selecting red sources. Optical and/or near-infrared spectroscopy…
Dust-obscured star formation has dominated the cosmic history of star formation since z = 4. However, the recent finding of significant amount of dust in galaxies out to z = 8 has opened the new frontier of investigating the origin of dust…
We investigate the dust properties and star-formation signature of galaxies in the early universe by stacking 111227 objects in the recently released COSMOS catalogue on maps at wavelengths bracketing the peak of warmed dust emission. We…
In order to derive information on the star formation history in the early universe we observed 6 high-redshift (z=3.4) quasars in the near-infrared to measure the relative iron and \mgii emission strengths. A detailed comparison of the…
Quasars are galaxies hosting accreting supermassive black holes; due to their brightness, they are unique probes of the early universe. To date, only few quasars have been reported at $z > 6.5$ ($<$800 Myr after the Big Bang). In this work,…
Since the beginning of the new millennium, more than 100 $z\sim 6$ quasars have been discovered through several surveys and followed-up with multi-wavelength observations. These data provided a large amount of information on the growth of…