We analyze the size evolution of H II regions around 27 quasars between z = 5.7 and 6.4 ('quasar near zones' or NZs). We include more sources than previous studies, and we use more accurate redshifts ...for the host galaxies, with eight CO molecular line redshifts and nine Mg II redshifts. We confirm the trend for an increase in NZ size with decreasing redshift, with the luminosity-normalized proper size evolving as R{sub NZ,corrected} = (7.4 {+-} 0.3) - (8.0 {+-} 1.1) x (z - 6) Mpc. While derivation of the absolute neutral fraction remains difficult with this technique, the evolution of the NZ sizes suggests a decrease in the neutral fraction of intergalactic hydrogen by a factor {approx}9.4 from z = 6.4 to 5.7, in its simplest interpretation. Alternatively, recent numerical simulations suggest that this rapid increase in NZ size from z = 6.4 to 5.7 is due to the rapid increase in the background photo-ionization rate at the end of the percolation or overlap phase, when the average mean-free path of ionizing photons increases dramatically. In either case, the results are consistent with the idea that z {approx} 6-7 corresponds to the tail end of cosmic reionization. The scatter in the normalized NZ sizes is larger than expected simply from measurement errors, and likely reflects intrinsic differences in the quasars or their environments. We find that the NZ sizes increase with quasar UV luminosity, as expected for photo-ionization dominated by quasar radiation.
We report the detection of CO molecular line emission in the image millimeter-detected galaxy COSMOS J100054+023436 (hereafter J1000+0234) using the IRAM Plateau de Bure interferometer (PdBI) and ...NRAO's Very Large Array (VLA). The super( 12)CO(4-3) line as observed with PdBI has a full line width of image1000 km s super(-1), an integrated line flux of 0.66 Jy km s super(-1), and a CO luminosity of 3.2 x 10 super(10) L sub(image). Comparison to the 3.3 capital sigma detection of the CO(2-1) line emission with the VLA suggests that the molecular gas is likely thermalized to the image transition level. The corresponding molecular gas mass is 2.6 x 10 super(10) M sub(image) assuming an ULIRG-like conversion factor. From the spatial offset of the red- and blueshifted line peaks and the line width a dynamical mass of 1.1 x 10 super(11) M sub(image) is estimated assuming a merging scenario. The molecular gas distribution coincides with the rest-frame optical and radio position of the object while being offset by 0.5 super(image ) from the previously detected Ly alpha emission. J1000+0234 exhibits very typical properties for lower redshift submillimeter galaxies (SMGs) and thus is very likely one of the long sought after high-redshift objects of this population. The large CO(4-3) line width taken together with its highly disturbed rest-frame UV geometry suggest an ongoing major merger about a billion years after the big bang. Given its large star formation rate (SFR) of >1000 M sub(image) yr super(-1) and molecular gas content this object could be the precursor of a "red and dead" elliptical observed at a redshift of image.
We explore the cosmic evolution of radio luminous active galactic nuclei (AGNs) with low radio powers (L 1.4 GHz 5 X 1025 W Hz-1) out to z = 1.3 using to date the largest sample of ~600 ...low-luminosity radio AGN at intermediate redshift drawn from the VLA-COSMOS survey. We derive the radio-luminosity function for these AGNs, and its evolution with cosmic time assuming two extreme cases: (1) pure luminosity and (2) pure density evolution. The former and latter yield L * (1 + z)0.8 ± 0.1, and * (1 + z)1.1 ± 0.1, respectively, both implying a fairly modest change in properties of low-radio-power AGNs since z = 1.3. We show that this is in stark contrast with the evolution of powerful (L 1.4 GHz > 5 X 1025 W Hz-1) radio AGN over the same cosmic time interval, constrained using the 3CRR, 6CE, and 7CRS radio surveys by Willot et al. We demonstrate that this can be explained through differences in black hole fueling and triggering mechanisms, and a dichotomy in host galaxy properties of weak and powerful AGNs. Our findings suggest that high- and low-radio-power AGN activities are triggered in different stages during the formation of massive red galaxies. We show that weak radio AGN occur in the most massive galaxies already at z ~ 1, and they may significantly contribute to the heating of their surrounding medium and thus inhibit gas accretion onto their host galaxies, as recently suggested for the 'radio mode' in cosmological models.
New, massively redundant low‐frequency arrays allow for a novel investigation of closure relations in interferometry. We employ commissioning data from the Hydrogen Epoch of Reionization Array to ...investigate closure quantities in this densely packed grid array of 14‐m antennas operating at 100 to 200 MHz. We investigate techniques that utilize closure phase spectra for redundant triads to estimate departures from redundancy for redundant baseline visibilities. We find a median absolute deviation from redundancy in closure phase across the observed frequency range of about 4.5°. This value translates into a nonredundancy per visibility phase of about 2.6°, using prototype electronics. The median absolute deviations from redundancy decrease with longer baselines. We show that closure phase spectra can be used to identify ill‐behaved antennas in the array, independent of calibration. We investigate the temporal behavior of closure spectra. The Allan variance increases after a 1‐min stride time, due to passage of the sky through the primary beam of the transit telescope. However, the closure spectra repeat to well within the noise per measurement at corresponding local sidereal times from day to day. In future papers in this series we will develop the technique of using closure phase spectra in the search for the H I 21‐cm signal from cosmic reionization.
Key Points
We use closure quantities to quantify departures from redundancy in massively redundant low‐frequency arrays
We can identify ill‐behaved array elements from closure quantity discrepancies
We study the time evolution of closure quantities, practical averaging times and sidereal time binning
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 giant ...molecular cloud (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 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 emissionline galaxies (EMGs) deviate from the correlation that fits Galactic GMC cores, normal spirals, and luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs, respectively). 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 observations of the molecular gas in the GN20 proto-cluster of galaxies at z = 4.05 using the Expanded Very Large Array (EVLA). This group of galaxies is the ideal laboratory for studying ...the formation of massive galaxies via luminous, gas-rich starbursts within 1.6 Gyr of the big bang. We detect three galaxies in the proto-cluster in CO 2-1 emission, with gas masses (H2) between 1010 and 1011 X ( Delta *a/0.8) M . The emission from the brightest source, GN20, is resolved with a size ~2'' and has a clear north-south velocity gradient, possibly indicating ordered rotation. The gas mass in GN20 is comparable to the stellar mass (1.3 X 1011 X ( Delta *a/0.8) M and 2.3 X 1011 M , respectively), and the sum of gas plus stellar mass is comparable to the dynamical mass of the system (~3.4 X 1011sin (i)/sin (45?)--2 M ), within a 5 kpc radius. There is also evidence for a tidal tail extending another 2'' north of the galaxy with a narrow velocity dispersion. GN20 may be a massive, gas-rich disk that is gravitationally disturbed, but not completely disrupted. There is one Lyman-break galaxy (BD29079) in the GN20 proto-cluster with an optical spectroscopic redshift within our search volume, and we set a 3 Delta *s limit to the molecular gas mass of this galaxy of 1.1 X 1010 X ( Delta *a/0.8) M .
We report the detection of the $^2\rm P_{3/2} \rightarrow {^2P_{1/2}}$ fine-structure line of $\rm C^+$ at 157.74 $\rm \mu m$ in SDSS J114816.64+525150.3 (hereafter J1148+5251), the most distant ...known quasar, at $z=6.42$, using the IRAM 30-m telescope. This is the first detection of the Cii line at high redshift, and also the first detection in a Hyperluminous Infrared Galaxy ($L_{\rm FIR} > 10^{13} \, L_\odot$). The Cii line is detected at a significance level of 8σ and has a luminosity of $ 4.4\times 10^9 \,L_\odot$. The $L_{\rm CII}/L_{\rm FIR}$ ratio is $\rm 2\times 10^{-4}$, about an order of magnitude smaller than observed in local normal galaxies and similar to the ratio observed in local Ultraluminous Infrared Galaxies. The Cii line luminosity indicates that the host galaxy of this quasar is undergoing an intense burst of star formation with an estimated rate of ≈$ 3000 \, M_\odot \, \rm yr^{-1}$. The detection of $\rm C^+$ in SDSS J1148+5251 suggests a significant enrichment of metals at $z\sim 6$ (age of the universe ~870 Myr), although the data are consistent with a reduced carbon to oxygen ratio as expected from chemical evolutionary models of the early phases of galaxy formation.
We present further analysis of the CII 158 mu m fine structure line and thermal dust continuum emission from the archetype extreme star-burst/active galactic nucleus (AGN) group of galaxies in the ...early universe, BRI 1202-0725 at z = 4.7, using the Atacama Large Millimeter Array. A short ALMA test observation reveals a rich laboratory for the study of the myriad processes involved in clustered massive galaxy formation in the early universe. In this paper, we examine in more detail the imaging results from the ALMA observations, including velocity channel images, position-velocity plots, and line moment images. We present detections of CII emission from two Ly alpha -selected galaxies in the group, demonstrating the relative ease with which ALMA can detect the CII emission from lower star formation rate galaxies at high redshift. These results provide an unprecedented view of a major merger of gas-rich galaxies driving extreme star-bursts and AGN accretion during the formation of massive galaxies and super-massive black holes within 1.3 Gyr of the big bang.
Previous observational studies of the infrared (IR)-radio relation out to high redshift employed any detectable star-forming systems at a given redshift within the restricted area of cosmological ...survey fields. Consequently, the evolution inferred relies on a comparison between the average IR/radio properties of (1) very IR-luminous high-z sources and (2) more heterogeneous low(er)-z samples that often lack the strongest IR emitters. In this Letter, we consider populations of objects with comparable luminosities over the last 10 Gyr by taking advantage of deep IR (especially Spitzer 24 {mu}m) and Very Large Array 1.4 GHz observations of the COSMOS field. Consistent with recent model predictions, both Ultra Luminous Infrared Galaxies and galaxies on the bright end of the evolving IR luminosity function do not display any change in their average IR/radio ratios out to z {approx} 2 when corrected for bias. Uncorrected data suggested {approx}0.3 dex of positive evolution.
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![First detection of [CII]158...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6361/small "First detection of [CII]158 μm at high redshift: vigorous star formation in the early universe")