R. Pello', etc al. have detected what may be the highest redshift object (a galaxy) as of to date. They used the Very Large Telescope's (VLT) ISAAC detector to obtain ultra-deep JHK band images in the core of a gravitational lensing cluster named Abell 1835. The redshift of the galaxy is based on a very faint emission line in the J band. If the emission line is Lyman Alpha then the redshift of the object is z=10.0, in excellent agreement with photometric redshift determinations. Astronomers usually detect high redshift objects (galaxies and quasars) by applying what is known as the "traditional Lyman drop-out technique" to deep optical images. Due to the Gunn- Peterson trough, i.e. the nearly complete absorption of the flux shortward of Lyman Alpha (1216 Angstroms) as a result of the large neutral hydrogen column density in the Intergalactic Medium (IGM), the an observed spectral discontinuity at redshifts greater than about 6. In practice Astronomers search for objects which are not detectable in optical (VRI) bands. If there is a detection of the object in J, H, and K bands, a fairly red J-H due to the appearance of the Gunn-Peterson trough in the J band, and a blue H-K bands color corresponding to an intrinsically blue UV restframe spectrum (such as is expected for UV bright starbursts), then it is highly probable that the object being observed has a very high redshift, somewhere between 7-10. This method is based on simulations of galaxy synthesis models for different metallicities.
Spectra were obtained of the candidate high redshift galaxy #1916 in the J band using the ISAAC detector on the VLT under very good seeing conditions ranging between 0.4 and 0.5 arcsec. At a resolution of about 5400, the spectra shows what appears to be the Lyman Alpha emission line redshifted from its rest UV (1216 Angstrom) wavelength to an observed wavelength in the IR of about 1.33745 microns. This places the galaxy #1916 at a redshift of z=10.00175 assuming the emission line identified is Lyman Alpha.
The two-dimensional spectrum shows the detected emission line of galaxy #1916 and the nearby field galaxy. The [OIII] (5007 Angstrom) line of a galaxy at a redshift of z=1.68 is also present in the spectrum.
Assuming a universe model with the following parameters: Redshift of galaxy = 10.0 Hubble constant = 70 km/s/Mpc Constant dark energy equation of state parameter = -1.0 Present matter density (relative to critical density) = 0.3 Present dark energy mass density = 0.7 The cosmological parameters associated with the z=10 Protogalaxy are: An accelerating universe at present epoch (q0=-0.549) Age of universe at present epoch (at z=0) = 13.469 Gyr Age of universe at z=10.0 = 0.466 Gyr (460 Myr after big bang) Light travel time from z=10.0 to z=0.0 = 13.003 Gyr Comoving radial distance to z=10.0 = 9446.784 Mpc Angular size distance to z=10.0 = 858.798 Mpc Luminosity distance to z=10.0 = 103914.634 Mpc 1 kpc at redshift z=10.0 will subtend about 0.240 arcsec Comoving volume to z=10.0 per steradian = 281.015 Gpc3
Because high-redshift quasars are receeding at relativistic velocities the Lyman alpha emission line is shifted from the ultraviolet into the red region of the electromagnetic spectrum. The Next Generation Space Telescope (NGST) will be optimized in the infrared in order to detect very distant objects at redshifts greater than z=5.
The properties of the intergalactic medium can be studied back to the time of galaxy formation using distant quasars. The number density of absorption lines as a function of epoch will provide an important cosmological test. Observations of correlated absorption, both in redshift and in nearby quasars on the plane of the sky, are leading to important information on the evolution of the large-scale distribution of galaxies in space. The Lyman alpha clouds offer the opportunity to investigate the evolution of the intergalactic medium and the meta-galactic ionizing radiation flux and to provide information on primordial abundances of the elements
Because the recessional velocities are a significant fraction of the speed of light, the relativistic Doppler equation is used to estimate the redshift of a quasar. Comoving coordinates of these objects are estimated using the luminosity distance since they are located at large cosmological distances.
The angular size of a source (galaxy, etc.) of size D at redshift z is
Both autocorrelation and cross-correlation analysis provide a statistical measure of the velocity structure of the intervening gas clouds along the line of sight and across adjacent sight lines, respectively. This allows the Astronomer to study the three-dimensional topology of the large scale structure of the Universe.
Assuming cosmological models with a negligible cosmological constant, the comoving coordinate for a source with redshift z can be estimated from the expressions
A correlation function in redshift based on the separation s0=S0(z2)-S0(z1) can now be defined. Using this separation the probability of intercepting two Lyman alpha clouds separated by s0 is
where phi0 is the number density of clouds per comoving volume and sigma is the cross section (assumed constant) of a cloud.
Recent observations of quasar absorption spectra reveal a random, uncorrelated (Poissonian) distribution for the Lyman alpha clouds. It is thought that the Lyman alpha systems are due to primoridal neutral hydrogen gas.
The actual distance between the Lyman alpha clouds were they to survive to the present epoch fixed in cosmological coordinates is the splitting in the S0 coordinate. Thus one has, in units of the present Hubble radius,
The velocity splitting due to the Hubble flow between two such clouds, measured at the present epoch and as seen by an observer near the clouds is the velocity splitting due to the Hubble flow (measured in Hubble radii)
The velocity splitting observed at the cosmic time when the photons were passing through the clouds due to the Hubble flow as seen by an observer near the clouds is
When using the two-point correlation function for analyzing Lyman alpha clouds, one must allow for the fact that a finite span of data necessarily permits more small separations than do large ones. Therefore, the number of separations s0 must be divided by a response function
With this correlation, a Poissonian distribution of cloud separations will then appear flat (see correlation plot for QSO2206-199N), with an average of
line pairs in a bin. If one finds m(s0) line pairs in a bin, then the correlation function is approximately m(s0)/mb -1
In summary, for most observations to date, the observed two-point correlation function for the Lyman alpha absorption lines is flat on all scales from 300 km/s to 30,000 km/s
Quasar absorption systems showing a damped Ly-alpha line are though to arise in high-redshift progenitors of present-day disk galaxies. Abundance studies in the local ISM have identified Zn as a highly convenient species for surveying the overall level of metallicity of the damped systems, while a quantitative indication of the dust content can be obtained by measuring the Zn II/Cr II ratio since, unlike Zn, Cr is readily bound to interstellar grains. The absence of significant amounts of dust in high redshift galaxies is of relevance to several problems, including the measurement of abundance ratios as a function of metallicity for a wide range of elements and the visibility of quasars at very high redshifts.
Assuming this system is not a gravitational lens and that the two quasars are gravitationally bound, their projected separation and velocity difference can be used to place a lower limit to the total mass of the system. Equating the kinetic and potential energies, and using the shape of the orbit, one obtains the equation for the total mass of the binary quasar system
where R is the three dimensional separation of the quasars and v is their three dimensional mutual velocity.
Example Case in QSO Absorption Spectroscopy
Results from the Hubble Deep Fields
Results from the Hubble Ultra Deep Field
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