J/ApJS/255/28 ∼420MHz uGMRT obs. of MIR selected radio-loud AGN (Gupta+, 2021)
Evolution of cold gas at 2<z<5: a blind search for HI and OH absorption lines
toward mid-infrared color-selected radio-loud AGN.
Gupta N., Srianand R., Shukla G., Krogager J-.K., Noterdaeme P., Combes F.,
Dutta R., Fynbo J.P.U., Hilton M., Momjian E., Moodley K., Petitjean P.
<Astrophys. J. Suppl. Ser., 255, 28-28 (2021)>
=2021ApJS..255...28G 2021ApJS..255...28G (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei; Redshifts; Optical; Spectroscopy;
Radio lines; Infrared sources
Keywords: Active galaxies; Galaxies; AGN host galaxies
Quasar absorption line spectroscopy; Interstellar medium
Abstract:
We present results from a spectroscopically blind search for
associated and intervening HI 21cm and OH 18cm absorption lines toward
88 active galactic nuclei (AGN) at 2<z<5 using the uGMRT. The sample
of AGN with 1.4GHz spectral luminosity in the range 1027-29.3W/Hz is
selected using mid-infrared colors and closely resembles the
distribution of the underlying quasar population. The search for
associated or proximate absorption, defined to be within 3000km/s of
the AGN redshift, led to one HI 21cm absorption detection (M1540-1453;
zabs=2.1139). This is only the fourth known absorption at z>2. The
detection rate (1.6-1.4+3.8%) suggests a low covering factor of
the cold neutral medium (CNM; T∼100K) associated with these powerful
AGN. The intervening absorption line search, with a sensitivity to
detect the CNM in damped Lyα systems (DLAs), has comoving
absorption path lengths of ΔX=130.1 and 167.7 for HI and OH,
respectively. The corresponding number of absorbers per unit comoving
path length are ≤0.014 and ≤0.011, respectively. The former is at
least 4.5 times lower than that of DLAs and consistent with the CNM
cross section estimated using H2 and CI absorbers at z>2. Our AGN
sample is optically fainter compared to the quasars used to search for
DLAs in the past. In our optical spectra obtained using SALT and NOT,
we detect five intervening (redshift path ∼9.3) and two proximate
DLAs. This is slightly excessive compared to the statistics based on
optically selected quasars. The nondetection of HI 21cm absorption
from these DLAs suggests a small CNM covering fraction around galaxies
at z>2.
Description:
In this paper, we present a spectroscopically blind search of HI 21cm
absorption at z>2 based on a sample of AGN selected using the MIR
colors from the Wide-field Infrared Survey Explorer (WISE) and having
spectroscopically confirmed redshifts using the Southern African Large
Telescope (SALT; 180hr) and the Nordic Optical Telescope (NOT; 6 nights;
Krogager+ 2018ApJS..235...10K 2018ApJS..235...10K).
These AGN are being observed as part of the MeerKAT Absorption Line
Survey (MALS), which is a large project at the MeerKAT array in South
Africa, to search HI 21cm and OH 18cm lines at z<2.
In 2018 April 21 and during six observing runs in September, we used
the recently commissioned Band 2 (120-240MHz) and Band 3 (250-500MHz)
of the upgraded Giant Metrewave Radio Telescope (uGMRT) to observe
redshifted associated and intervening HI 21cm absorption lines from
the 88 AGN selected from the SALT-NOT sample.
Additionally, five absorption candidates identified from the Band 3
survey observations were reobserved on 2019 December 10 and 2020
February 20.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 100 93 Sample of the 88 z>2 MIR-selected radio sources
observed with uGMRT
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See also:
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/ApJ/636/610 : Damped Lyα systems at z<1.65 (Rao+, 2006)
J/ApJ/675/1002 : Proximate DLA systems in SDSS-DR5 (Prochaska+, 2008)
J/ApJ/757/51 : FIRST-2MASS dust-reddened QSO spectra (Glikman+, 2012)
J/A+A/547/L1 : SDSS-III DR9 DLA catalogue (Noterdaeme+, 2012)
J/ApJ/761/184 : IR luminosities for dusty AGNs and QSOs (Weedman+, 2012)
J/MNRAS/440/696 : HI absorption in nearby radio galaxies (Allison+, 2014)
J/A+A/575/A44 : HI absorption in flux-selected radio AGNs (Gereb+, 2015)
J/A+A/585/A87 : Quasar composite made from bright QSOs (Selsing+, 2016)
J/MNRAS/465/588 : HI 21-cm absorption survey of QSO-galaxy pairs (Dutta+, 2017)
J/A+A/604/A43 : HI in nearby radio sources (Maccagni+, 2017)
J/AJ/156/18 : Binary companions of evolved stars (Price-Whelan+, 2018)
J/ApJS/245/3 : HI 21cm & OH 18cm absorption search with GBT (Grasha+, 2019)
J/MNRAS/490/243 : ELAIS N1 field uGMRT 400MHz sources (Chakraborty+, 2019)
J/A+A/648/A116 : PKS 1830-211 OH and HI spectra (Combes+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Name Source name (MHHMMSS.ss+DDMMSS.s; J2000)
based on NVSS coordinates
( in Simbad)
21 A1 --- f_Name Flag on Name
23- 28 F6.1 --- F1.4GHz [203.3/1354.9] 20cm flux density from NVSS
30- 34 F5.3 --- zem [2.006/5.064] Emission line redshift
measured from SALT-NOT survey
36- 40 A5 --- Run Observing run (1)
42 A1 --- f_Run b=only M1312-2026 was also observed at
Band 2
44- 47 F4.1 arcsec Beam1 Synthesized beam 1 (2)
48 A1 --- --- [x]
49- 52 F4.1 arcsec Beam2 Synthesized beam 2 (2)
54- 58 F5.1 deg PA [-85/90] Position angle of the beam (2)
60 A1 --- f_PA b=Corresponds to Band 2
62- 67 F6.1 mJy/beam Fp420MHz [44.2/2554.1]? Peak of the prominent
Gaussian component (2)
69- 74 F6.1 mJy F420MHz [44.1/2577] Total flux density (2)
76 A1 --- f_F420MHz b=Corresponds to Band 2
78- 81 F4.2 --- Ratio [0.64/1.11]? Ratio of Fp420MHz to F420MHz
83- 87 F5.2 --- alpha [-1.26/1.32]? Spectral index α
derived using NVSS and 420MHz flux
densities (3)
89- 93 F5.2 --- alpIn [-1.26/1.1]? In-band spectral index
95- 98 F4.1 mJy/beam delF [1.3/11.2]? Observed spectral rms at 420MHz
100 I1 --- Nc [1/4]? Number of absorption candidates
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Note (1): Details of uGMRT observations as follows:
---------------------------------------------------
Run ID Band Start date Duration (h)
---------------------------------------------------
Survey Observations
---------------------------------------------------
21APR Band 2 2018 Apr 21 7
07SEP Band 3 2018 Sep 07 11
08SEP Band 3 2018 Sep 08 10
09SEP Band 3 2018 Sep 09 11
14SEP Band 3 2018 Sep 14 10
16SEP Band 3 2018 Sep 16 21
17SEP Band 3 2018 Sep 17 20
---------------------------------------------------
Follow-up Observations
---------------------------------------------------
10DEC Band 3 2019 Dec 10 6
20FEB Band 3 2020 Feb 20 9
---------------------------------------------------
Note (2): Synthesized beam, peak of the prominent Gaussian component, and total
flux densities, respectively, from the continuum image based on a
390-450MHz range (average 420MHz).
Note (3): In a few cases, which are all sources with a single component fit,
this ratio marginally (∼5%) exceeds 1, suggesting that the radio
emission may be partially resolved.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 26-Oct-2021