We have used the Arecibo Telescope to carry out one of the deepest-ever integrations in radio astronomy, targeting the redshifted conjugate satellite OH 18 cm lines at z≈0.247 towards PKS 1413+135. ...The satellite OH 1720 and 1612 MHz lines are, respectively, in emission and absorption, with exactly the same line shapes due to population inversion in the OH ground state levels. Since the 1720 and 1612 MHz line rest frequencies have different dependences on the fine structure constant α and the proton-electron mass ratio μ, a comparison between their measured redshifts allows one to probe changes in α and μ with cosmological time. In the case of conjugate satellite OH 18 cm lines, the predicted perfect cancellation of the sum of the line optical depths provides a strong test for the presence of systematic effects that might limit their use in probing fundamental constant evolution. A nonparametric analysis of our new Arecibo data yields ΔX/X=(+0.97±1.52)×10^{-6}, where X≡μα^{2}. Combining this with our earlier results from the Arecibo Telescope and the Westerbork Synthesis Radio Telescope, we obtain ΔX/X=(-1.0±1.3)×10^{-6}, consistent with no changes in the quantity μα^{2} over the last 2.9 Gyr. This is the most stringent present constraint on fractional changes in μα^{2} from astronomical spectroscopy, and with no evidence for systematic effects.
The radio-loud fraction of quasars at z > 6 Keller, Pascal M; Thyagarajan, Nithyanandan; Kumar, Ajay ...
Monthly notices of the Royal Astronomical Society,
02/2024, Volume:
528, Issue:
4
Journal Article
Peer reviewed
Open access
ABSTRACT
Quasars at redshifts z > 6 are an excellent probe of the formation and evolution of supermassive black holes in the early Universe. The population of radio-luminous quasars is of particular ...interest, as such quasars could potentially be used to study the neutral intergalactic medium during cosmic reionization via H i 21 cm absorption studies. However, the lack of deep radio observations of z > 6 quasars leaves the population poorly constrained, and suitable candidates for an H i 21 cm absorption study have yet to be found. In this work, we present Jansky Very Large Array (VLA) 1–2 GHz radio continuum observations of 138 quasars at redshifts 6.0 ≤ z < 7.6. We detect the radio continuum emission of the z = 6.1 quasar J1034−1425, with a 1.6 GHz flux density of $170\pm 36\, \mu$Jy. This quasar is radio-quiet with radio-loudness, R ≡ f5 GHz/fν, 4400 Å = 2.4 ± 0.5. In addition, we detect seven other quasars at z > 6, which have previously been characterized in the literature at these frequencies. Using the full sample, we estimate the radio-loud fraction to be $3.8^{+6.2}_{-2.4}\ \hbox{per cent}$, where the uncertainties are 95 per cent confidence intervals. This is lower than recent estimates of the radio-loud fraction in the literature, but is still marginally consistent with no redshift evolution of the radio-loud fraction. We explore the undetected quasar population by stacking their continuum images at their optical positions and obtain a median stacked flux density of 13.8 ± 3.9 µJy and luminosity of log L5 GHz/(W Hz−1) = 24.2 ± 0.1.
We report high-spectral-resolution Australia Telescope Compact Array (ATCA) H i 21-cm observations resulting in the detection of the warm neutral medium (WNM) of the Galaxy in absorption against two ...extragalactic radio sources, PKS 1814−637 and PKS 0407−658. The two lines of sight were selected on the basis of the simplicity of their absorption profiles and the strength of the background sources; the high velocity resolution of the spectra then enabled us to estimate the kinetic temperatures of the absorbing gas by fitting multiple Gaussians to the absorption profiles. Four separate WNM components were detected towards the two sources, with peak optical depths τmax = (1.0 ± 0.08) × 10−2, (1.4 ± 0.2) × 10−3, (2.2 ± 0.5) × 10−3 and (3.4 ± 0.5) × 10−3 and kinetic temperatures Tk = 3127 ± 300, 3694 ± 1595, 3500 ± 1354 and 2165 ± 608 K, respectively. All four components were thus found to have temperatures in the thermally unstable range 500 < Tk < 5000 K; this suggests that thermal equilibrium has not been reached throughout the WNM.
We present results from a survey designed to probe the star formation properties of 32 damped Lyman α systems (DLAs) at z ~ 2.7. By using the 'double-DLA' technique that eliminates the glare of the ...bright background quasars, we directly measure the rest-frame far-ultraviolet flux from DLAs and their neighbouring galaxies. At the position of the absorbing gas, we place stringent constraints on the unobscured star formation rates (SFRs) of DLAs to 2... limits of ..., corresponding to SFR surface densities ... The implications of these limits for the star formation law, metal enrichment, and cooling rates of DLAs are examined. By studying the distribution of impact parameters as a function of SFRs for all the galaxies detected around these DLAs, we place new direct constraints on the bright end of the UV luminosity function of DLA hosts. We find that ≤13 per cent of the hosts have ... at impact parameters ..., differently from current samples of confirmed DLA galaxies. Our observations also disfavour a scenario in which the majority of DLAs arise from bright Lyman-break galaxies at distances 20 = ... < 100 kpc. These new findings corroborate a picture in which DLAs do not originate from highly star-forming systems that are coincident with the absorbers, and instead suggest that DLAs are associated with faint, possibly isolated, star-forming galaxies. Potential shortcomings of this scenario and future strategies for further investigation are discussed. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
The neutral atomic hydrogen (H
i
) mass function (H
i
MF) describes the distribution of the H
i
content of galaxies at any epoch; its evolution provides an important probe of models of ...galaxy formation and evolution. Here, we report Giant Metrewave Radio Telescope H
i
21 cm spectroscopy of blue star-forming galaxies at
z
≈ 0.20–0.42 in the Extended Groth Strip, which has allowed us to determine the scaling relation between the average H
i
mass (
M
H
i
) and the absolute
B
-band magnitude (
M
B
) of such galaxies at
z
≈ 0.35, by stacking the H
i
21 cm emission signals of galaxy subsamples in different
M
B
ranges. We combine this
M
H
i
−
M
B
scaling relation (with a scatter assumed to be equal to that in the local universe) with the known
B
-band luminosity function of star-forming galaxies at these redshifts to determine the H
i
MF at
z
≈ 0.35. We show that the use of the correct scatter in the
M
H
i
−
M
B
scaling relation is critical for an accurate estimate of the H
i
MF. We find that the H
i
MF has evolved significantly from
z
≈ 0.35 to
z
≈ 0, i.e., over the last 4 Gyr, especially at the high-mass end. High-mass galaxies, with
M
H
i
≳ 10
10
M
⊙
, are a factor of ≈3.4 less prevalent at
z
≈ 0.35 than at
z
≈ 0. Conversely, there are more low-mass galaxies, with
M
H
i
≈ 10
9
M
⊙
, at
z
≈ 0.35 than in the local universe. While our results may be affected by cosmic variance, we find that massive star-forming galaxies have acquired a significant amount of H
i
through merger events or accretion from the circumgalactic medium over the past 4 Gyr.
Gas surrounding high-redshift galaxies has been studied through observations of absorption line systems toward background quasars for decades. However, it has proven difficult to identify and ...characterize the galaxies associated with these absorbers due to the intrinsic faintness of the galaxies compared with the quasars at optical wavelengths. Using the Atacama Large Millimeter/Submillimeter Array, we report on detections of C ii 158-μm line and dust-continuum emission from two galaxies associated with two such absorbers at a redshift of z ~ 4. Our results indicate that the hosts of these high-metallicity absorbers have physical properties similar to massive star-forming galaxies and are embedded in enriched neutral hydrogen gas reservoirs that extend well beyond the star-forming interstellar medium of these galaxies.
We have used the Green Bank Telescope to carry out a deep search for redshifted CO J = 2?1 line emission from an extended (> 17 kpc) Ly alpha blob (LAB), "Himiko," at z ~ 6.595. Our non-detection of ...CO J = 2-1 emission places the strong 3sigma upper limit of L' sub(CO) < 1.8 x 10 super(10) x ( Delta V/250) super(1/2) K km s super(-1) pc super(2) on the CO line luminosity. This is comparable to the best current limits on the CO line luminosity in LABs at z ~ 3 and lower-luminosity Ly alpha emitters at z > ~ 6.5. High-z LABs appear to have lower CO line luminosities than the host galaxies of luminous quasars and submillimeter galaxies at similar redshifts, despite their high stellar mass. Although the CO-to-H sub(2) conversion factor is uncertain for galaxies in the early universe, we assume X sub(CO) = 0.8 M sub(middot in circle) (K km s super(-1) pc super(2)) super(-1) to obtain the limit M(H sub(2)) <1.4 x 10 super(10) M sub(middot in circle) on Himiko's molecular gas mass; this is a factor of > ~2.5 lower than the stellar mass in the z ~ 6.595 LAB.
ABSTRACT This is the second paper directed toward finding new highly redshifted atomic and molecular absorption lines at radio frequencies. To this end, we selected a sample of 80 candidates for ...obscured radio-loud active galactic nuclei (AGNs) and presented their basic optical/near-infrared (NIR) properties in Paper I. In this paper, we present both high-resolution radio continuum images for all of these sources and H i 21 cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz Very Large Array continuum observations find that 52 sources are compact or have substantial compact components with size <0 5 and flux densities >0.1 Jy at 4.9 GHz. The 36 most compact sources were then observed with the Very Long Baseline Array at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, which is a detection rate of CSOs ∼three times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty-seven sources were observed for H i 21 cm absorption at their photometric or spectroscopic redshifts with only six detections (five definite and one tentative). However, five of these were from a small subset of six CSOs with pure galaxy optical/NIR spectra (i.e., any AGN emission is obscured) and for which accurate spectroscopic redshifts place the redshifted 21 cm line in a radio frequency intereference (RFI)-free spectral "window" (i.e., the percentage of H i 21 cm absorption-line detections could be as high as ∼90% in this sample). It is likely that the presence of ubiquitous RFI and the absence of accurate spectroscopic redshifts preclude H i detections in similar sources (only 1 detection out of the remaining 22 sources observed, 13 of which have only photometric redshifts); that is, H i absorption may well be present but is masked by the RFI. Future searches for highly redshifted H i and molecular absorption can easily find more distant CSOs among bright, "blank field" radio sources, but will be severely hampered by an inability to determine accurate spectroscopic redshifts due to their lack of rest-frame UV continuum.
PDF
![[C ii] 158-μm emission from...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0036-8075/small "[C ii] 158-μm emission from the host galaxies of damped Lyman-alpha systems")
