Atomic and molecular absorption in redshifted radio sources

Curran, S. J.; Whiting, M. T.; Allison, J. R.; Tanna, A.; Sadler, E. M.; Athreya, R.

doi:10.1093/mnras/stx408

Cited by 16 publications

(27 citation statements)

References 104 publications

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“…Thus, H i absorption studies allow us to study the impact of the radio nuclear activity on the ISM in a variety of radio sources (e.g. Vermeulen et al 2003;Pihlström et al 2003;Gupta et al 2006;Emonts et al 2010;Allison et al 2012;Chandola et al 2013;Allison et al 2014;Geréb et al 2014Geréb et al , 2015Chandola & Saikia 2017;Glowacki et al 2017;Curran et al 2017). Among several results, these studies show that in compact steep spectrum sources and gigahertz peaked sources, (i.e.…”

Section: Introductionmentioning

confidence: 98%

Kinematics and physical conditions of H i in nearby radio sources

Maccagni

Morganti

Oosterloo

et al. 2017

A&A

221

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We present an analysis of the properties of neutral hydrogen (H i) in 248 nearby (0.02 < z < 0.25) radio galaxies with S 1.4 GHz > 30 mJy and for which optical spectroscopy is available. The observations were carried out with the Westerbork Synthesis Radio Telescope as the last large project before the upgrade of the telescope with phased array feed receivers (Apertif). The sample covers almost four orders of magnitude in radio power from log P 1.4 GHz = 22.5 W Hz −1 and 26.2 W Hz −1 . We detect H i in absorption in 27% ± 5.5% of the objects. The detections are found over the full range of radio power. However, the distribution and kinematics of the absorbing H i gas appear to depend on radio power, the properties of the radio continuum emission, and the dust content of the sources. Among the sources where H i is detected, gas with kinematics deviating from regular rotation is more likely found as the radio power increases. In the great majority of these cases, the H i profile is asymmetric with a significant blue-shifted component. This is particularly common for sources with log P 1.4 GHz > 24 W Hz −1 , where the radio emission is small, possibly because these radio sources are young. The same is found for sources that are bright in the mid-infrared, i.e. sources rich in heated dust. In these sources, the H i is outflowing likely under the effect of the interaction with the radio emission. Conversely, in dust-poor galaxies, and in sources with extended radio emission, at all radio powers we only detect H i distributed in a rotating disk. Stacking experiments show that in sources for which we do not detect H i in absorption directly, the H i has a column density that is lower than 3.5 × 10 17 (T spin /c f ) cm −2 . We use our results to predict the number and type of H i absorption lines that will be detected by the upcoming surveys of the Square Kilometre Array precursors and pathfinders (Apertif, MeerKAT, and ASKAP).

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Section: Introductionmentioning

confidence: 98%

Kinematics and physical conditions of H i in nearby radio sources

Maccagni

Morganti

Oosterloo

et al. 2017

A&A

221

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“…Since our previous analysis of the relationship between the absorption strength and V − K colour (Curran et al 2011b), there has only been one new detection of OH (Gupta et al 2018a), although a plethora of non-detections (Curran et al 2016(Curran et al , 2017Gupta et al 2018aGupta et al , 2021bGrasha et al 2019Grasha et al , 2020Dutta et al 2020;Zheng et al 2020). As stated above, all OH absorbers were previously detected in H I 21-cm absorption and so we consider only these (Table 1).…”

Section: Resultsmentioning

confidence: 99%

“…This suggests that the selection of optically bright sources introduces a bias against dustier, and more molecular rich, sight-lines. Since then there have been many more searches for OH absorption (Curran et al 2007(Curran et al , 2008(Curran et al , 2011b(Curran et al , 2016Allison et al 2017;Curran et al 2017;Grasha et al 2019Grasha et al , 2020Dutta et al 2020;Zheng et al 2020;Gupta et al 2021b), resulting in only one new detection (at z abs = 0.05, Gupta et al 2018a).…”

Section: Introductionmentioning

confidence: 99%

On the scarcity of redshifted OH and millimetre-band molecular absorption

Curran

2021

Preprint

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Despite much searching, redshifted decimetre and millimetre-band absorption by molecular gas remains very rare, limited to just six systems at z abs > ∼ 0.05. Detection of these transitions can yield precise diagnostics of the conditions of the star forming gas in the earlier Universe, the hydroxyl (OH) radical being of particular interest as in the λ = 18 cm ground state there are four different transitions located close to H I 21-cm and thus detectable with the Square Kilometre Array and its pathfinders. The four transitions of OH have very different dependences on the fundamental constants, thus having much potential in testing for any evolution in these over large look-back times. By collating the photometry in a uniform manner, we confirm our previous hypothesis that the normalised OH absorption strength is correlated with the optical-near-infrared red colour of the sight-line. Applying this to the published searches, we find that all, but one (J0414+054), have simply not been searched sufficiently deeply. We suggest that this is due to the standard selection of sources with reliable optical redshifts introducing a bias against those with enough dust with which to shield the molecular gas. For the single source searched to sufficient depth, we have reason to suspect that the high degree of reddening arises from another system along the sight-line, thus not being inconsistent with our hypothesis. We also show that the same optical redshift bias can account for the scarcity of millimetre-band absorption.

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“…large DLA catalogues, blind surveys with the SKA are expected to yield a large number of redshifted absorption systems which are dust reddened (Webster et al 1995;Carilli et al 1998;Curran et al 2017) and thus missed by those pre-selected based upon their optical/UV spectrum. The lack of an optical spectrum does, of course, prevent the nature of the absorber being determinedwhether it arises in a quiescent galaxy, intervening a more distant continuum source (as per the DLAs), or is associated with the host of the background continuum source itself.…”

Section: Prospects With the Skamentioning

confidence: 99%

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

Curran

2018

Publ. Astron. Soc. Aust.

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It has recently been shown that the abundance of cold neutral gas may follow a similar evolution as the star formation history. This is physically motivated, since stars form out of this component of the neutral gas and if the case, would resolve the longstanding issue that there is a clear disparity between the total abundance of neutral gas and star forming activity over the history of the Universe. Radio-band 21-cm absorption traces the cold gas and comparison with the Lyman-α absorption, which traces all of the gas, provides a measure of the cold gas fraction, or the spin temperature, Tspin. The recent study has shown that the spin temperature (degenerate with the ratio of the absorber/emitter extent) appears to be anti-correlated with the star formation density, ψ * , with 1/Tspin undergoing a similar steep evolution as ψ * over redshifts of 0 < ∼ z < ∼ 3, whereas the total neutral hydrogen exhibits little evolution. Above z ∼ 3, where ψ * shows a steep decline with redshift, there is insufficient 21-cm data to determine whether 1/Tspin continues to follow ψ * . Knowing this is paramount in ascertaining whether the cold neutral gas does trace the star formation over the Universe's history. We explore the feasibility of resolving this with 21-cm observations of the largest contemporary sample of reliable damped Lyman-α absorption systems and conclude that, while today's largest radio interferometers can reach the required sensitivity at z < ∼ 3.5, the Square Kilometre Array is required to probe to higher redshifts.

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Atomic and molecular absorption in redshifted radio sources

Cited by 16 publications

References 104 publications

Kinematics and physical conditions of H i in nearby radio sources

Kinematics and physical conditions of H i in nearby radio sources

On the scarcity of redshifted OH and millimetre-band molecular absorption

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

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