Evolution of the cold gas fraction and the star formation history: Prospects with current and future radio facilities

Curran, S. J.

doi:10.1017/pasa.2018.28

Cited by 5 publications

(1 citation statement)

References 72 publications

(85 reference statements)

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“…The availability of cold neutral gas in galaxies is clearly important for the formation of self-gravitating clouds of dense molecular gas. Understanding the content and distribution of neutral hydrogen in galaxies located before the SFR peak epoch is crucial for understanding the mechanisms driving the evolution of SFR density over the cosmic time (Curran 2018). It is known that in the sample of compact GPS and compact steep spectrum (CSS) radio sources, the detected fraction of AGN-associated HI 21-cm absorption is relatively higher, 30%, in comparison to sources with extended radio morphology (e.g.…”

Section: Discussionmentioning

confidence: 99%

A compact symmetric radio source born at one-tenth the current age of the Universe

An,

Wang,

Zhang

et al. 2021

Preprint

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Studies of high redshift radio galaxies can shed light on the activity of active galactic nuclei (AGN) in massive elliptical galaxies, and on the assembly and evolution of galaxy clusters in the Universe. The vast majority of observed high redshift (𝑧 > 4.5) AGN are quasars, with very few galaxies. J1606+3124 is a radio galaxy at a redshift of 4.56, at an era of one-tenth of the current age of the Universe. Very long baseline interferometry (VLBI) images reveal a two-sided jet structure with edge-brightened terminal hotspots separated by about 68 parsecs. No evidence for the presence of extended emission (relic of past activity) is found, suggesting that it might be a nascent radio source. We study the radio properties of J1606+3124 including radio spectrum, variability, core brightness temperature, jet proper motion. All observations consistently indicate that it is a GHz Peaked Spectrum (GPS) source, making it the highest redshift GPS galaxy known to date. The expansion velocity of the hotspots and the turnover in the radio spectrum suggest that J1606+3124 is a young (kinematic age of ∼3000 years) and developing radio source. Its ultra-high jet power gives it a good chance to grow into a large-scale double-lobe radio galaxy. Infrared observations reveal a gas-and dust-rich host galaxy environment, which may hinder the jet growth.

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Section: Discussionmentioning

confidence: 99%

A compact symmetric radio source born at one-tenth the current age of the Universe

An,

Wang,

Zhang

et al. 2021

Preprint

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The evolution of cold neutral gas and the star formation history

Curran

2019

Monthly Notices of the Royal Astronomical Society

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There is a well known disparity between the evolution the star formation rate density, ψ * , and the abundance of neutral hydrogen (H I), the raw material for star formation. Recently, however, we have shown that ψ * may be correlated with the fraction of cool atomic gas, as traced through the 21-cm absorption of H I. This is expected since star formation requires cold (T ∼ 10 K) gas and so this could address the issue of why the star formation rate density does not trace the bulk atomic gas. The data are, however, limited to redshifts of z < ∼ 2, where both ψ * and the cold gas fraction exhibit a similar steep climb from the present day (z = 0), and so it is unknown whether the cold gas fraction follows the same decline as ψ * at higher redshift. In order to address this, we have used unpublished archival observations of 21-cm absorption in high redshift damped Lyman-α absorption systems to increase the sample at z > ∼ 2. The data suggest that the cold gas fraction does exhibit a decrease, although this is significantly steeper than ψ * at z ∼ 3. This is, however, degenerate with the extents of the absorbing galaxy and the background continuum emission and upon removing these, via canonical evolution models, we find the mean spin temperature of the gas to be T spin ≈ 3000 K, compared to the ≈ 2000 K expected from the ψ * T spin ≈ 100 M ⊙ yr −1 Mpc −3 K fit at z < ∼ 2. These temperatures are consistent with the observed high neutral hydrogen column densities, which require T < ∼ 4000 K in order for the gas not to be highly ionised.

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An ASKAP survey for H i absorption towards dust-obscured quasars

Glowacki

Allison

Moss

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Obscuration of quasars by accreted gas and dust, or dusty intervening galaxies, can cause active galactic nuclei (AGN) to be missed in optically-selected surveys. Radio observations can overcome this dust bias. In particular, radio surveys searching for Hi absorption inform us on how the AGN can impact on the cold neutral gas medium within the host galaxy, or the population of intervening galaxies through the observed line of sight gas kinematics. We present the results of a Hi absorption line survey at 0.4 < z < 1 towards 34 obscured quasars with the Australian SKA Pathfinder (ASKAP) commissioning array. We detect three Hi absorption lines, with one of these systems previously unknown. Through optical follow-up for two sources, we find that in all detections the Hi gas is associated with the AGN, and hence that these AGN are obscured by material within their host galaxies. Most of our sample are compact, and in addition, are either gigahertz peaked spectrum (GPS), or steep spectrum (CSS) sources, both thought to represent young or recently re-triggered radio AGN. The radio spectral energy distribution classifications for our sample agree with galaxy evolution models in which the obscured AGN has only recently become active. Our associated Hi detection rate for GPS and compact SS sources matches those of other surveys towards such sources. We also find shallow and asymmetric Hi absorption features, which agrees with previous findings that the cold neutral medium in compact radio galaxies is typically kinematically disturbed by the AGN.

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Evolution of the cold gas fraction and the star formation history: Prospects with current and future radio facilities

Cited by 5 publications

References 72 publications

A compact symmetric radio source born at one-tenth the current age of the Universe

A compact symmetric radio source born at one-tenth the current age of the Universe

The evolution of cold neutral gas and the star formation history

An ASKAP survey for H i absorption towards dust-obscured quasars

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