Related papers: Age of High Redshift Objects - a Litmus Test for t…

We present the discovery of three z>5 quasars in the AGN and Galaxy Evolution Survey (AGES) spectroscopic observations of the NOAO Deep Wide-Field Survey (NDWFS) Bootes Field. These quasars were selected as part of a larger Spitzer…

Quasars at high redshift provide direct information on the mass growth of supermassive black holes and, in turn, yield important clues about how the Universe evolved since the first (Pop III) stars started forming. Yet even basic questions…

If the current energy density of the universe is indeed dominated by a cosmological constant, then high-redshift sources will remain visible to us only until they reach some finite age in their rest-frame. The radiation emitted beyond that…

In this invited talk I show how the reddest and rarest galaxies at high redshift ($z \simeq 1.5$) can be used to set the stellar evolution clock. I argue that one can confidently compute the collapse redshift of these objects. This yields…

We present low-resolution near-infrared stacked spectra from the 3D-HST survey up to $z=2.0$ and fit them with commonly used stellar population synthesis models: BC03 (Bruzual & Charlot, 2003), FSPS10 (Flexible Stellar Population Synthesis,…

Using the low limit of cosmic ages from globular cluster and the white dwarfs: $t_0 > 12$Gyr, together with recent new high redshift supernova observations from the HST/GOODS program and previous supernova data, we give a considerable…

The quest for high-redshift quasars has led to a series of record-breaking sources, with the current record holder at $z=7.642$. Here, we show how future detections of $z>8$ quasars impact the constraints on the parameters for black hole…

The APM multicolor survey for bright z > 4 objects, covering 2500 deg^2 of sky to m(R)~19, resulted in the discovery of thirty-one quasars with z > 4. High signal-to-noise optical spectrophotometry at 5A resolution has been obtained for the…

Most of the successful physical theories rely on the constancy of few fundamental quantities (such as the speed of light, $c$, the fine-structure constant, \alpha, the proton to electron mass ratio, \mu, etc), and constraining the possible…

A new age-redshift test is proposed in order to constrain $H_0$ with basis on the existence of old high redshift galaxies (OHRG). As should be expected, the estimates of $H_0$ based on the OHRG are heavily dependent on the cosmological…

WMAP precision data enables accurate testing of cosmological models. We find that the emerging standard model of cosmology, a flat Lambda-dominated universe seeded by nearly scale-invariant adiabatic Gaussian fluctuations, fits the WMAP…

High-redshift blazars are valuable tools to study the early Universe. So far only a handful of $\gamma$-ray blazars have been found at redshifts above 3. $\gamma$-ray signals are detected in the direction of PMN J2219-2719 ($z=3.63$) and…

Enhanced ionizing radiation in close proximity to redshift $z\gtrsim 6$ quasars creates short windows of intergalactic Ly$\alpha$ transmission blueward of the quasar Ly$\alpha$ emission lines. The majority of these Ly$\alpha$ near-zones are…

Results of a careful analysis of the absorption systems with zabs = zem seen toward the bright, z_em ~ 3.91, gravitationally lensed quasar APM 08279+5255 are presented. Two of the narrow-line systems, at z_abs = 3.8931 and z_abs = 3.9135,…

The concordance (LambdaCDM) model reproduces the main current cosmological observations assuming the validity of general relativity at all scales and epochs, the presence of cold dark matter, and of a cosmological constant, equivalent to a…

We report a new changing-look quasar, WISE~J105203.55+151929.5 at $z=0.303$, found by identifying highly mid-IR variable quasars in the WISE/NEOWISE data stream. Compared to multi-epoch mid-IR photometry of a large sample of SDSS-confirmed…

We have obtained complete redshift information for a sample of 442 radio-loud quasars with flux densities S(11cm) >= 0.25Jy. These come from a completely-identified sample of 878 flat-spectrum radio sources, so there is no optical magnitude…

We use the parallax measurements of RE J 0317-853 to determine its mass, radius, and cooling age and thereby constrain its evolutionary origins. We observed RE J 0317-853 with the the Hubble Space Telescope's Fine Guidance System to measure…

We report the discovery of five quasars with redshifts of 4.67 - 5.27 and z'-band magnitudes of 19.5-20.7 M_B ~ -27. All were originally selected as distant quasar candidates in optical/near-infrared photometry from the Sloan Digital Sky…

The discovery of quasars few hundred megayears after the Big Bang represents a major challenge to our understanding of black holes and galaxy formation and evolution. Their luminosity is produced by extreme gas accretion onto black holes,…