A Giant Metrewave Radio Telescope survey for associated H i 21 cm absorption in the Caltech–Jodrell flat-spectrum sample

Aditya, J. N. H. S.; Kanekar, Nissim

doi:10.1093/mnras/sty2184

Cited by 34 publications

(48 citation statements)

References 94 publications

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“…with detection rates of ∼10-40% in Vermeulen et al 2003;Gupta et al 2006;Chandola et al 2011;Glowacki et al 2017a) and slightly higher than for compact flat spectrum sources (e.g. detection rate of 17% in the Caltech-Jodrell flat-spectrum sample; Aditya & Kanekar 2018). Our detections made towards the GPS sources also support the findings of Maccagni et al (2017), who find a higher Hi detection rate towards compact radio galaxies (32% versus 16% for the extended sources within their sample).…”

Section: Hi Detections In Gps Sourcessupporting

confidence: 87%

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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Section: Hi Detections In Gps Sourcessupporting

confidence: 87%

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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“…In particular, there is a factor of ∼ 6 discrepancy between the detection rates in nearby objects and those at higher redshifts (e.g. Curran et al 2008;Curran & Whiting 2010Aditya et al 2016;Aditya & Kanekar 2018;Curran et al 2019;Grasha et al 2019). The lower detection rates of intrinsic absorbers in highredshift objects are thought to be due to selection bias -from either UV-luminous quasars that ionize the gas or excitation of the gas by 21-cm photons from the radio source -and possibly also intrinsic redshift evolution in the host galaxy population.…”

Section: Intrinsic 21-cm Absorbersmentioning

confidence: 99%

“…The sample of Maccagni et al (2017) spanned comparatively lower luminosities between L 1.4 = 3.2 × 10 22 and 1.6 × 10 26 W Hz −1 , indicating that there could be a bias. However, Aditya & Kanekar (2018) 1.2) compact flat-spectrum radio sources with max-imum radio luminosity max(L 1.4 ) = 5.0 × 10 27 W Hz −1 . Furthermore, in their targeted survey of 145 compact radio sources, spanning luminosities in the range L 1.4 = 1.6 × 10 25 and 4.5 × 10 28 W Hz −1 , Grasha et al (2019) found no evidence for a statistical correlation between their detection rate and radio luminosity.…”

Section: Intrinsic 21-cm Absorbersmentioning

confidence: 99%

FLASH early science – discovery of an intervening H i 21-cm absorber from an ASKAP survey of the GAMA 23 field

Allison

Sadler

Bellstedt

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present early science results from the First Large Absorption Survey in H I (FLASH), a spectroscopically blind survey for 21-cm absorption lines in cold hydrogen (H I) gas at cosmological distances using the Australian Square Kilometre Array Pathfinder (ASKAP). We have searched for H I absorption towards 1253 radio sources in the GAMA 23 field, covering redshifts between z = 0.34 and 0.79 over a sky area of approximately 50 deg 2 . In a purely blind search we did not obtain any detections of 21-cm absorbers above our reliability threshold. Assuming a fiducial value for the H I spin temperature of T spin = 100 K and source covering fraction c f = 1, the total comoving absorption path length sensitive to all Damped Lyman α Absorbers (DLAs; N HI ≥ 2 × 10 20 cm −2 ) is ∆X = 6.6 ± 0.3 (∆z = 3.7 ± 0.2) and super-DLAs (N HI ≥ 2 × 10 21 cm −2 ) is ∆X = 111 ± 6 (∆z = 63 ± 3). We estimate upper limits on the H I column density frequency distribution function that are consistent with measurements from prior surveys for redshifted optical DLAs, and nearby 21-cm emission and absorption. By cross-matching our sample of radio sources with optical spectroscopic identifications of galaxies in the GAMA 23 field, we were able to detect 21-cm absorption at z = 0.3562 towards NVSS J224500−343030, with a column density of N HI = (1.2±0.1)×10 20 (T spin /100 K) cm −2 . The absorber is associated with GAMA J22450.05−343031.7, a massive early-type galaxy at an impact parameter of 17 kpc with respect to the radio source and which may contain a massive (M HI 3 × 10 9 M ) gas disc. Such gas-rich early types are rare, but have been detected in the nearby Universe.

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“…Overall, at present over 650 systems have been searched for associated Hi 21-cm absorption (e.g., Vermeulen et al 2003;Gupta et al 2006;Curran et al 2013;Aditya et al 2016;Maccagni et al 2017;Aditya & Kanekar 2018b), with more than 120 detections reported in the literature. A majority ( 550) of the searches have been limited to redshifts z < 0.6, that consist of samples of both compact, flat-to-inverted spectrum sources and extended, steepspectrum radio sources.…”

Section: Introductionmentioning

confidence: 99%

“…At redshifts z > 1.0, however, compact, flat-spectrum radio sources dominate the samples that have been searched for associated Hi 21-cm absorption. Approximately 90 sources have been searched at z > 1.0 (e.g., Curran et al 2013;Aditya et al 2016;Aditya & Kanekar 2018b) with the detection rate being consistently low at 10% (compared to ∼ 30% at low-z -cf. Geréb et al 2015 ).…”

Section: Introductionmentioning

confidence: 99%

uGMRT detections of H i 21-cm absorption associated with intermediate redshift galaxies

Aditya

2018

Monthly Notices of the Royal Astronomical Society

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I report detections of four new Hi 21-cm absorbers associated with sources at intermediate redshifts, 0.7 < z < 1.0. The sources are part of a sample of 11 radio-loud galaxies, all at 0.7 < z < 1.0, that were searched for associated Hi 21-cm absorption using uGMRT. Previously, just four such absorbers were known in the literature at these redshifts; the current observations have increased the total to eight. The results indicate that the detection fraction at intermediate redshifts could be as high as that at lower redshifts, ≈ 30%, on contrary to a much lower detection fraction observed in samples at z > 1. Three detections show strong blueshifted features, indicating cold gas outflows. These three sources also tentatively show excess [O ii] line luminosity compared to a bulk of the remaining sample, possibly suggesting that the hosts of these AGNs harbour different environments, either due to interaction with the radio jets or due to excess star formation in the host galaxy. Further, a cold Hi mass outflow rate of ≈ 78 M ⊙ yr −1 , assuming T s = 1000 K, is estimated for the detection towards SDSS J014652.79-015721.2, at z = 0.95904, which is the highest till date in comparison to similar estimates available in the literature.

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A Giant Metrewave Radio Telescope survey for associated H i 21 cm absorption in the Caltech–Jodrell flat-spectrum sample

Cited by 34 publications

References 94 publications

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

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

FLASH early science – discovery of an intervening H i 21-cm absorber from an ASKAP survey of the GAMA 23 field

uGMRT detections of H i 21-cm absorption associated with intermediate redshift galaxies

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