One of the next decade's most exciting prospects is to explore the cosmic "dark ages," during which the first stars in the Universe formed, with the 21 cm line of neutral hydrogen. At z>6, this light ...redshifts into the low-frequency radio regime and can be observed with new generations of wide-field arrays. These experiments have the potential to observe enormous volumes and to improve both cosmological and astrophysical constraints dramatically. In this white paper, we describe how the next decade will see the first steps toward unlocking this potential, allowing us to answer two key questions about the fundamental physics of our Universe and the intergalactic medium: Does the standard cosmological model describe the Universe during the "dark ages?" How did the intergalactic medium evolve during this important time, ending with the reionization of hydrogen?
The cosmic dark ages and the epoch of reionization, during which the first generations of stars and galaxies formed, are among the most compelling frontiers of extragalactic astrophysics and ...cosmology. Here we describe an exciting new probe of these eras: the 21 cm line of neutral hydrogen, which will allow us to map the neutral intergalactic medium throughout the era of first galaxy formation. In this white paper, we describe how these studies can answer two key questions about galaxy formation: What were the properties of high-redshift galaxies? How did they affect the Universe around them?
Mon.Not.Roy.Astron.Soc. 344 (2003) 169 We have observed 23 sources from the MAMBO 1200 micron survey with SCUBA at
850 microns, detecting 19 of the sources. The sources generally have low values
for ...the ratio of 850 micron to 1200 micron flux. Two possible explanations for
the low values are either that the sources are at very high redshift or that
the global properties of the dust in the MAMBO sources are different from the
global properties of dust in low-redshift galaxies. If the former explanation
is correct, we estimate that 15 of the MAMBO sources lie at z > 3.
We present here the sensitive HCN(1-0) observations made with the VLA of two submillimeter galaxies and two QSOs at high-redshift. HCN emission is the signature of dense molecular gas found in GMC ...cores, the actual sites of massive star formation. We have made the first detection of HCN in a submillimeter galaxy, SMM J16359+6612. The HCN emission is seen with a signal to noise ratio of 4\(\sigma\) and appears to be resolved as a double-source of \(\approxlt 2''\) separation. Our new HCN observations, combined with previous HCN detections and upper limits, show that the FIR/HCN ratios in these high redshift sources lie systematically above the FIR/HCN correlation established for nearby galaxies by about a factor of 2. Even considering the scatter in the data and the presence of upper limits, this is an indication that the FIR/HCN ratios for the early Universe molecular emission line galaxies (EMGs) deviate from the correlation that fits Galactic giant molecular cloud cores, normal spirals, LIRGs, and ULIRGs. This indicates that the star formation rate per solar mass of dense molecular gas is higher in the high-\(z\) objects than in local galaxies including normal spirals LIRGs and ULIRGs. The limited HCN detections at high-redshift show that the HCN/CO ratios for the high-\(z\) objects are high and are comparable to those of the local ULIRGs rather than those of normal spirals. This indicates that EMGs have a high fraction of dense molecular gas compared to total molecular gas traced by CO emission.
We present sensitive near-infrared spectroscopic observations for a sample of five z ~ 6 quasars. These are amongst the most distant, currently known quasars in the universe. The spectra have been ...obtained using ISAAC at the VLT and include the CIV, MgII and FeII lines. We measure the FeII/MgII line ratio, as an observational proxy for the Fe/alpha element ratio. We derive a ratio of 2.7+/-0.8 for our sample, which is similar to that found for lower redshift quasars, i.e., we provide additional evidence for the lack of evolution in the FeII/MgII line ratio of quasars up to the highest redshifts. This result demonstrates that the sample quasars must have undergone a major episode of iron enrichment in less than one Gyr and star formation must have commenced at z > 8. The linewidths of the MgII and CIV lines give two estimates for the black hole masses. A third estimate is given by assuming that the quasars emit at their Eddington luminosity. The derived masses using these three methods agree well, implying that the quasars are not likely to be strongly lensed. We derive central black hole masses of 0.3-5.2 10^9 solar masses. We use the difference between the redshift of MgII (a proxy for the systemic redshift of the quasar) and the onset of the Gunn Peterson trough to derive the extent of the ionized Stromgren spheres around our target quasars. The derived physical radii are about five Mpc. Using a simple ionization model, the emission of the central quasars would need of order 10^6-10^8 year to create these cavities in a surrounding intergalactic medium with a neutral fraction between 0.1 and 1.0. As the e-folding time scale for the central accreting black hole is on the order of a few times 10^7 year, it can grow by one e-folding or less within this time span.
The ultraluminous broad absorption line quasar APM08279+5255 is one of the most luminous systems known. Here, we present an analysis of its nuclear CO(1-0) emission. Its extended distribution ...suggests that the gravitational lens in this system is highly elliptical, probably a highly inclined disk. The quasar core, however, lies in the vicinity of naked cusp, indicating that APM08279+5255 is truly the only odd-image gravitational lens. This source is the second system for which the gravitational lens can be used to study structure on sub-kpc scales in the molecular gas associated with the AGN host galaxy. The observations and lens model require CO distributed on a scale of \(\sim 400\) pc. Using this scale, we find that the molecular gas mass makes a significant, and perhaps dominant, contribution to the total mass within a couple hundred parsecs of the nucleus of APM08279+5255.
Radio AGN Surveys De Breuck, Carlos; Wil van Breugel; Rottgering, Huub ...
arXiv.org,
11/2001
Paper
Open access
We present a short overview of radio surveys for AGN, including the `complete' flux limited surveys and `filtered' surveys. We also describe our ultra-steep spectrum search for the highest redshift ...radio galaxies, and our follow-up VLA and ATCA observations of the most distant (z=5.19) and the most luminous z<2 radio galaxy known.
Molecular hydrogen is an important component of galaxies because it fuels star formation and accretion onto AGN, the two processes that generate the large infrared luminosities of gas-rich galaxies. ...Observations of spectral-line emission from the tracer molecule CO are used to probe the properties of this gas. But the lines that have been studied in the local Universe, mostly the lower rotational transitions of J = 1-0 and J = 2-1, have hitherto been unobservable in high-redshift galaxies. Instead, higher transitions have been used, although the densities and temperatures required to excite these higher transitions may not be reached by much of the gas. As a result, past observations may have underestimated the total amount of molecular gas by a substantial amount. Here we report the discovery of large amounts of low-excitation molecular gas around the infrared-luminous quasar, APM 08279+5255 at z = 3.91, using the two lowest excitation lines of 12CO (J = 1-0 and J = 2-1). The maps confirm the presence of hot and dense gas near the nucleus, and reveal an extended reservoir of molecular gas with low excitation that is 10 to 100 times more massive than the gas traced by higher-excitation observations. This raises the possibility that significant amounts of low-excitation molecular gas may lurk in the environments of high-redshift (z > 3) galaxies.
In this paper we use ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field in band. 3 and band. 6, to place blind constraints on the CO luminosity function and the evolution of the ...cosmic molecular gas density as a function of redshift up to z similar to 4.5. This study is based on galaxies that have been selected solely through their CO emission and not through any other property. In all of the redshift bins the ASPECS measurements reach the predicted "knee" of the CO luminosity function (around 5 x 10(9) K km s(-1) pc(2)). We find clear evidence of an evolution in the CO luminosity function with respect to z similar to 0, with more CO-luminous galaxies present at z similar to 2. The observed galaxies at z similar to 2 also appear more gas-rich than predicted by recent semi-analytical models. The comoving cosmic molecular gas density within galaxies as a function of redshift shows a drop by a factor of 3-10 from z similar to 2 to z similar to 0 (with significant error bars), and possibly a decline at z > 3. This trend is similar to the observed evolution of the cosmic star formation rate density. The latter therefore appears to be at least partly driven by the increased availability of molecular gas reservoirs at the peak of cosmic star formation (z similar to 2).
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