Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Second APM UKST Colour Survey for z>4 Quasars
108
0
0.0
(
0
)
Added by
Lisa Storrie-Lombardi
Publication date
2000
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We present the spectra, positions, and finding charts for 31 bright (R<19.3) colour-selected quasars covering the redshift range z=3.85-4.78, with 4 having redshifts z>4.5. The majority are in the southern sky (dec<-25 deg). The quasar candidates were selected for their red (B-R > 2.5) colours from UK or POSSII Schmidt Plates scanned at the Automated Plate Measuring facility in Cambridge. Low resolution (~> 10A) spectra were obtained to identify the quasars, primarily at the Las Campanas Observatory. The highest redshift quasar in our survey is at z ~ 4.8 (R = 18.7) and its spectrum shows a damped Lyman-alpha absorption system at z = 4.46. This is currently the highest redshift damped Lyman-alpha absorber detected. Five of these quasars exhibit intrinsic broad absorption line features. Combined with the previously published results from the first part of the APM UKST survey we have now surveyed a total of ~8000 squ deg of sky i.e. 40% of the high galactic latitude (|b|>30 deg) sky, resulting in 59 optically selected quasars in the redshift range 3.85 to 4.78; 49 of which have z>=4.00.
rate research
Read More
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 twenty-eight quasars easily accessible from the northern hemisphere. These spectra have been surveyed to create new samples of high redshift Lyman-limit systems, damped Lyman-alpha absorbers, and metal absorption systems (e.g. CIV and MgII). In this paper we present the spectra, together with line lists of the detected absorption systems. The QSOs display a wide variety of emission and absorption line characteristics, with 5 exhibiting broad absorption lines and one with extremely strong emission lines (BR2248-1242). Eleven candidate damped Ly-alpha absorption systems have been identified covering the redshift range 2.8<z<4.4 (8 with z>3.5). An analysis of the measured redshifts of the high ionization emission lines with the low ionization lines shows them to be blueshifted by 430+/-60 km/s. In a previous paper (Storrie-Lombardi et. al. 1994) we discussed the redshift evolution of the Lyman limit systems catalogued here. In subsequent papers we will discuss the properties of the Ly-alpha forest absorbers and the redshift and column density evolution of the damped Ly-alpha absorbers.
Eleven candidate damped Lya absorption systems were identified in 27 spectra of the quasars from the APM z>4 survey covering the redshift range 2.8<z(abs)<4.4 (8 with z(abs)>3.5). High resolution echelle spectra (0.8A FWHM) have been obtained for three quasars, including 2 of the highest redshift objects in the survey. Two damped systems have confirmed HI column densities of N(HI) >= 10^20.3 atoms cm^-2, with a third falling just below this threshold. We have discovered the highest redshift damped Lya absorber known at z=4.383 in QSO BR1202-0725. The APM QSOs provide a substantial increase in the redshift path available for damped surveys for z>3. We combine this high redshift sample with other quasar samples covering the redshift range 0.008 < z < 4.7 to study the redshift evolution and the column density distribution function for absorbers with log N(HI)>=17.2. In the HI column density distribution f(N)=kN^-beta we find evidence for breaks in the power law, flattening for 17.2< log N(HI)<21 and steepening for log N(HI)>21.2. The column density distribution function for the data with log N(HI)>=20.3 is better fit with the form f(N)=(f*/N*)(N/N*)^-beta exp(-N/N*). Significant redshift evolution in the number density per unit redshift is evident in the higher column density systems with an apparent decline in N(z) for z>3.5.
The UK Schmidt Telescope (UKST) of the Anglo-Australian Observatory completed a narrow-band H-alpha plus [NII] 6548, 6584A survey of the Southern Galactic Plane and Magellanic Clouds in late 2003. The survey, which was the last UKST wide-field photographic survey, and the only one undertaken in a narrow band, is now an on-line digital data product of the Wide-Field Astronomy Unit of the Royal Observatory Edinburgh (ROE). The survey utilised a high specification, monolithic H-alpha interference band-pass filter of exceptional quality. In conjunction with the fine grained Tech-Pan film as a detector it has produced a survey with a powerful combination of area coverage (4000 square degrees), resolution (~1 arcsecond) and sensitivity (<=5 Rayleighs), reaching a depth for continuum point sources of R~20.5. The main survey consists of 233 individual fields on a grid of centres separated by 4 degrees at declinations below +2 degrees and covers a swathe approximately 20 degrees wide about the Southern Galactic Plane. The original survey films were scanned by the SuperCOSMOS measuring machine at the Royal Observatory, Edinburgh to provide the on-line digital atlas called the SuperCOSMOS H-alpha Survey (SHS). We present the background to the survey, the key survey characteristics, details and examples of the data product, calibration process, comparison with other surveys and a brief description of its potential for scientific exploitation.
We calculate synthetic UBVRIJHKLM images, integrated spectra and colours for the disk galaxy formation models of Samland & Gerhard (2002), from redshift z=4 to z=0. Two models are considered, an accretion model based on LambdaCDM structure formation simulations, and a classical collapse model in a dark matter halo. Both models provide the star formation history and dynamics of the baryonic component within a three-dimensional chemo-dynamical description. To convert to spectra and colours, we use the latest, metallicity-calibrated spectral library of Westera et al. (2002), including internal absorption. As a first application, we compare the derived colours with Hubble Deep Field North bulge colours and find good agreement. With our model, we disentangle metallicity effects and absorption effects on the integrated colours, and find that absorption effects are dominant for redshift z < 1.5. Furthermore, we confirm the quality of m_K as a mass tracer, and find indications for a correlation between (J-K) and metallicity gradients.
We present high signal-to-noise, 5 A resolution (FWHM) spectra of 66 z ga 4 bright quasars obtained with the 4 m Cerro Tololo Inter-American Observatory and 4.2 m William Hershel telescopes. The primary goal of these observations was to undertake a new survey for intervening absorption systems detected in the spectra of background quasars. We look for both Lyman-limit systems (column densities N(HI) > 1.6 * 10^{17} atoms cm-2) and damped Ly-alpha systems (column densities N(HI) > 2 * 10^{20} atoms cm-2). This work resulted in the discovery of 49 Lyman-limit systems, 15 of which are within 3000 km s-1 of the quasar emission and thus might be associated with the quasar itself, 26 new damped Ly-alpha absorption candidates, 15 of which have z>3.5 and numerous metal absorption systems. In addition ten of the quasars presented here exhibit intrinsic broad absorption lines.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
