Detections of 21 cm absorption with a blind FAST survey at <i>z</i> ≤ 0.09

Hu, Wenkai; Wang, Yougang; Li, Yichao; Xu, Yuehang; Yang, Wenxiu; Lagache, G.

doi:10.1051/0004-6361/202245549

Cited by 6 publications

(4 citation statements)

References 93 publications

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“…The H I 21 cm absorption line profile in DLA systems against background radio sources shows complex spectral structures with multiple asymmetric components, reflecting the presence of unsettled gas in the ISM. This includes gas outflows from radio jets or tidal streams, as well as infalling H I gas toward central black holes in host galaxies Roy et al 2013Geréb et al 2015;Morganti & Oosterloo 2018;Hu et al 2023), and the minor wing components are needed for precise fits, yet they are omitted from the z measurement when the S/N is sufficiently high (Carilli et al 1992;Darling 2012). The DLA system facing PKS1315+145 features two Gaussian components within its absorption line at z = 0.24670374, according to the analysis (Darling 2012).…”

Section: Resultsmentioning

confidence: 99%

“…By using a combination of blind searches and targeted observations at a redshift of z 0.35, it is expected to identify approximately 70 DLA systems by scanning the celestial equator for one month. Extending the observing time to one year will yield around 800 DLA systems, five years could result in 1900, and a decade-long search can obtain the detections of 2600 DLAs (Jiao et al 2020;Hu et al 2023).…”

Section: Introductionmentioning

confidence: 99%

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Toward a Direct Measurement of the Cosmic Acceleration: The Pilot Observation of HI 21 cm Absorption Line at FAST

Kang,

Lu,

Zhang

et al. 2024

Res. Astron. Astrophys.

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In this study, we present findings on the detection of neutral atomic hydrogen (HI) 21cm absorption in the spectrum of PKS1413+135 at redshift $z=0.24670041$. The observations were conducted by FAST, with a spectral resolution of 10 Hz, using 10 minutes of observing time.The global spectral profile is examined by modeling the absorption line using a single Gaussian function with a resolution of 10kHz within a 2MHz bandwidth. The goal is to determine the rate of the latest cosmic acceleration by directly measuring the evolution of the redshift of HI 21cm absorption line with Hubble flow towards a common background Quasar over a decade or longer time span. This will serve as a detectable signal generated by the accelerated expansion of the Universe at redshift $z < 1$, specifically redshift drift $\dot{z}$ or the SL effect.The measured HI gas column density in this DLA system is approximately equivalent to the initial observation value, considering uncertainties in the spin temperature of a spiral host galaxy. The high signal-to-noise ratio of 57, obtained at a 10kHz resolution, strongly supports the feasibility of using the HI 21cm absorption line in DLA systems to accurately measure the redshift rate at a precision level of around $10^{-10}$ per decade.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Toward a Direct Measurement of the Cosmic Acceleration: The Pilot Observation of HI 21 cm Absorption Line at FAST

Kang,

Lu,

Zhang

et al. 2024

Res. Astron. Astrophys.

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“…Constructed as the most sensitive single-dish radio telescope, the Five-hundred-meter Aperture Spherical radio Telescope (FAST; Nan 2006;Nan et al 2011;Jiang et al 2020) has made significant progress in probing the faintest H I gas in our Milky Way (Hong et al 2022) and the nearby universe (Zhu et al 2021;Xu et al 2022). FAST has also successfully carried out a blind search and targeted observations of H I 21 cm absorption lines (Zhang et al 2021;Hu et al 2023;Jing et al 2023). Recently, Yu et al (2022) discovered a new H I absorber in an interacting galaxy pair observed by FAST.…”

Section: Introductionmentioning

confidence: 99%

H i Absorption in Low-power Radio AGNs Detected by FAST

Yu¹,

Fang²,

Wang³

et al. 2023

ApJ

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We report the discovery of three H i absorbers toward low-power radio active galactic nuclei (AGNs) in a pilot H i absorption survey with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Compared to past studies, FAST observations have explored lower radio powers by ∼0.4 dex and detected these weakest absorbers at given redshifts. By comparing the gas properties and kinematics of sources along radio powers, we aim to explore the interplay between AGN and the surrounding interstellar medium (ISM). Compared to brighter sources at similar redshifts, our observations suggest a slightly lower detection rate of H i absorption lines (∼11.5%) in low-power radio AGNs with log ( P 1.4 GHz / W Hz − 1 ) = 21.8 – 23.7 . The low-power sources with log ( P 1.4 GHz / W Hz − 1 ) < 23 have a lower detection rate of ∼6.7%. Due to the incompleteness of the sample, these detection rates may represent the lower limits. The selection of more extended sources and dilution by H i emission at lower redshifts may contribute to the lower detection rate of H i absorption lines. These detected absorbers present relatively narrow line widths and comparable column densities consistent with previous observations. One absorber has a symmetric profile with a large velocity offset, while the other two show asymmetric profiles that can be decomposed into multiple components, suggesting various possibilities of gas origins and kinematics. These H i absorbers may have connections with rotating disks, gas outflows, galactic gas clouds, gas fueling of the AGN, and jet–ISM interactions, which will be further investigated with the upcoming systematic survey and spatially resolved observations.

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“…The advent of the Five-hundred-meter Aperture Spherical radio Telescope (FAST; Nan et al 2011Nan et al , 2016Li et al 2018;Jiang et al 2019Jiang et al , 2020 gives us an ideal tool to explore such shallow H I outflows by utilizing its large collecting area. Recent observations have demonstrated FAST's capability in detecting H I absorption lines (Zhang et al 2021;Hu et al 2023).…”

Section: Introductionmentioning

confidence: 99%

FAST Discovery of a Fast Neutral Hydrogen Outflow

Su,

Gu,

Curran

et al. 2023

ApJL

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In this letter, we report the discovery of a fast neutral hydrogen outflow in SDSS J145239.38+062738.0, a merging radio galaxy containing an optical type I active galactic nucleus (AGN). This discovery was made through observations conducted by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) using redshifted 21 cm absorption. The outflow exhibits a blueshifted velocity likely up to ∼−1000 km s−1 with respect to the systemic velocity of the host galaxy with an absorption strength of ∼−0.6 mJy beam−1 corresponding to an optical depth of 0.002 at v = −500 km s−1. The mass outflow rate ranges between 2.8 × 10−2 and 3.6 M ⊙ yr−1, implying an energy outflow rate ranging between 4.2 × 1039 and 9.7 × 1040 erg s−1, assuming 100 K < T s < 1000 K. Plausible drivers of the outflow include the starbursts, AGN radiation, and radio jet, the last of which is considered the most likely culprit according to the kinematics. By analyzing the properties of the outflow, AGN, and jet, we find that if the H i outflow is driven by the AGN radiation, the AGN radiation does not seem powerful enough to provide negative feedback, whereas the radio jet shows the potential to provide negative feedback. Our observations contribute another example of a fast outflow detected in neutral hydrogen and demonstrate the capability of FAST in detecting such outflows.

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Detections of 21 cm absorption with a blind FAST survey at z ≤ 0.09

Cited by 6 publications

References 93 publications

Toward a Direct Measurement of the Cosmic Acceleration: The Pilot Observation of HI 21 cm Absorption Line at FAST

Toward a Direct Measurement of the Cosmic Acceleration: The Pilot Observation of HI 21 cm Absorption Line at FAST

H i Absorption in Low-power Radio AGNs Detected by FAST

FAST Discovery of a Fast Neutral Hydrogen Outflow

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