J/A+A/575/A44 HI absorption in flux-selected radio AGNs (Gereb+, 2015)
The HI absorption "Zoo".
Gereb K., Maccagni F.M., Morganti R., Oosterloo T.A.
<Astron. Astrophys., 575, A44-44 (2015)>
=2015A&A...575A..44G 2015A&A...575A..44G
ADC_Keywords: Active gal. nuclei ; Radio sources ; H I data
Keywords: galaxies: active - radio lines: galaxies
Abstract:
We present an analysis of the HI 21cm absorption in a sample of 101
flux-selected radio AGN (S1.4GHz>50mJy) observed with the Westerbork
Synthesis Radio Telescope (WSRT). We detect HI absorption in 32
objects (30% of the sample). In a previous paper, we performed a
spectral stacking analysis on the radio sources, while here we
characterize the absorption spectra of the individual detections using
the recently presented busy function. The HI absorption spectra show a
broad variety of widths, shapes, and kinematical properties. The full
width half maximum (FWHM) of the busy function fits of the detected HI
lines lies in the range 32km/s<FWHM<570km/s, whereas the full width at
20% of the peak absorption (FW20) lies in the range
63km/s<FW20<825km/s. The width and asymmetry of the profiles allows us
to identify three groups: narrow lines (FWHM<100km/s), intermediate
widths (100km/s<FWHM<200km/s), and broad profiles (FWHM>200km/s). We
study the kinematical and radio source properties of each group, with
the goal of identifying different morphological structures of HI.
Narrow lines mostly lie at the systemic velocity and are likely
produced by regularly rotating HI disks or gas clouds. More HI disks
can be present among galaxies with lines of intermediate widths;
however, the HI in these sources is more unsettled. We study the
asymmetry parameter and blueshift/redshift distribution of the lines
as a function of their width. We find a trend for which narrow
profiles are also symmetric, while broad lines are the most
asymmetric. Among the broadest lines, more lines appear blueshifted
than redshifted, similarly to what was found by previous studies.
Interestingly, symmetric broad lines are absent from the sample. We
argue that if a profile is broad, it is also asymmetric and shifted
relative to the systemic velocity because it is tracing unsettled HI
gas. In particular, besides three of the broadest (up to FW20=825km/s)
detections, which are associated with gas-rich mergers, we find three
new cases of profiles with blueshifted broad wings (with FW20>500km/s)
in high radio power AGN. These detections are good candidates for
being HI outflows. Together with the known cases of outflows already
included in the sample (3C 293 and 3C 305), the detection rate of HI
outflows is 5% in the total radio AGN sample. Because of the effects
of spin temperature and covering factor of the outflowing gas, this
fraction could represent a lower limit. However, if the relatively low
detection rate is confirmed by more detailed observations, it would
suggest that, if outflows are a characteristic phenomenon of all radio
AGN, they would have a short depletion timescale compared to the
lifetime of the radio source. This would be consistent with results
found for some of the outflows traced by molecular gas. Using stacking
techniques, in our previous paper we showed that compact radio sources
have higher τ, FWHM, and column density than extended sources. In
addition, here we find that blueshifted and broad/asymmetric lines are
more often present among compact sources. In good agreement with the
results of stacking, this suggests that unsettled gas is responsible
for the larger stacked FWHM detected in compact sources. Therefore in
such sources the HI is more likely to be unsettled. This may arise as
a result of jet-cloud interactions, as young radio sources clear their
way through the rich ambient gaseous medium.
Description:
The observations were carried out with the Westerbork Synthesis Radio
Telescope (WSRT). Each target was observed for 4h. In the case of
4C +52.37, we carried out 8h follow-up observations in order to
increase the HI sensitivity in the spectra.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 88 32 Characteristics of the HI detections
tableb1.dat 75 69 HI non-detections
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/32] Sequential number
5- 6 I2 h RAh Right ascension (J2000)
8- 9 I2 min RAm Right ascension (J2000)
11- 14 F4.1 s RAs Right ascension (J2000)
16 A1 --- DE- Declination sign (J2000)
17- 18 I2 deg DEd Declination (J2000)
20- 21 I2 arcmin DEm Declination (J2000)
23- 24 I2 arcsec DEs Declination (J2000)
26- 49 A24 --- OName Other name
51- 55 F5.3 --- z [0.02/0.21] SDSS redshift
57- 60 I4 mJy S1.4 [33/1670] Flux density at 1.4GHz
62- 66 F5.2 W/Hz P1.4 Radio power at 1.4GHz
68- 75 A8 --- Mph Radio morphology (1)
77 A1 --- cl compact(C)/extended(E)/merger(M) classification
79- 83 F5.3 --- tau.p [0/0.3] Peak optical depth τpeak
85- 88 F4.1 10+18cm-2/K N(HI) [0.5/87] HI density N(HI)/(Tspin/cf) (G1)
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Note (1): The radio morphology abbreviations are as follows:
CSO = compact symmetric object
CSS = compact steep spectrum source
CJ = core-jet
CX = complex morphology
U = unresolved
QSO = quasar
FSRQ = flat spectrum radio quasar
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [33/101] Sequential number
5- 6 I2 h RAh Right ascension (J2000)
8- 9 I2 min RAm Right ascension (J2000)
11- 14 F4.1 s RAs Right ascension (J2000)
16 A1 --- DE- Declination sign (J2000)
17- 18 I2 deg DEd Declination (J2000)
20- 21 I2 arcmin DEm Declination (J2000)
23- 24 I2 arcsec DEs Declination (J2000)
26- 33 F8.6 --- z [0.02/0.23] SDSS redshift
35- 49 A15 --- OName Other name
51- 54 I4 mJy S1.4 [33/1670] Flux density at 1.4GHz
56- 60 F5.2 W/Hz P1.4 Radio power at 1.4GHz
62 A1 --- cl compact(C)/extended(E) classification
64 A1 --- l_tau.p Limit flag on taupeak
65- 69 F5.3 --- tau.p Peak optical depth limit τpeak
71 A1 --- l_N(HI) Limit flag on N(HI)
72- 75 F4.1 10+18cm-2/K N(HI) [0.3/16] HI column density upper limit
N(HI)/(Tspin/cf) (G1)
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Global Notes:
Note (G1): The N(HI) column density is given in "units" of 1018(Tspin/cf)
where Tspin is the spin temperature and cf is the covering factor of
the gas. This (Tspin/cf) factor varies from 60K to ∼104K.
The upper limit is calculated from the 3σ rms,
assuming a velocity width of 100km/s.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 21-Apr-2015