HI absorption in nearby compact radio galaxies

5.6 MB·

by  M. Glowacki

MNRAS000,1–22(2002) Preprint26January2017 CompiledusingMNRASLATEXstylefilev3.0
i
H absorption in nearby compact radio galaxies
M. Glowacki1,2,3(cid:63), J. R. Allison2,3, E. M. Sadler1,2, V. A. Moss1,2, S. J. Curran4,
A. Musaeva1, C. Deng1, R. Parry1, M. C. Sligo1
1Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006, Australia
2ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), Australia
3CSIRO Astronomy & Space Science, PO Box 76, Epping NSW 1710, Australia
4School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6140, New Zealand
7
1
26January2017
0
2

n ABSTRACT
a HiabsorptionstudiesyieldinformationonbothAGNfeedingandfeedbackprocesses.
J
This AGN activity interacts with the neutral gas in compact radio sources, which
4
are believed to represent the young or recently re-triggered AGN population. We
2 present the results of a survey for Hi absorption in a sample of 66 compact ra-

dio sources at 0.040 < z < 0.096 with the Australia Telescope Compact Array. In
]
A total, we obtained seven detections, five of which are new, with a large range of
peak optical depths (3% to 87%). Of the detections, 71% exhibit asymmetric, broad
G
(∆v >100kms−1)features,indicativeofdisturbedgaskinematics.Suchbroad,
FWHM
.
h shallow and offset features are also found within low-excitation radio galaxies which
p is attributed to disturbed circumnuclear gas, consistent with early-type galaxies typ-
- ically devoid of a gas-rich disk. Comparing mid-infrared colours of our galaxies with
o Hi detections indicates that narrow and deep absorption features are preferentially
r
t foundinlate-typeandhigh-excitationradiogalaxiesinoursample.Thesefeaturesare
s
attributed to gas in galactic disks. By combining XMM-Newton archival data with
a
[ 21-cm data, we find support that absorbed X-ray sources may be good tracers of HI
content within the host galaxy. This sample extends previous Hi surveys in compact
1
radiogalaxiestolowerradioluminositiesandprovidesabasisforfutureworkexploring
v
the higher redshift universe.
6
3 Key words: galaxies:active–galaxies:ISM–galaxies:nuclei–radiolines:galaxies.
0
7
0
.
1
1 INTRODUCTION sion beyond redshifts of z > 0.2 (e.g. Verheijen et al. 2007;
0
7 Catinella et al. 2008; Freudling et al. 2011).
Compact radio galaxies are thought to represent the
1
youngest or most recently triggered active galactic nuclei There is no such redshift limit for detecting the tran-
:
v (AGN Fanti et al. 1995; Readhead et al. 1996; Owsianik & sition in absorption, as the line strength only depends on
i Conway1998).Studiesareongoingonthesignificanteffects the brightness of the background source, and the spin tem-
X
AGNfeedbackhaveonthehostgalaxy,suchaswhetherthis perature and column density of Hi along the line of sight.
r activity triggers or suppresses star-formation, and what its Therefore, Hi can be detected towards sufficiently strong
a
role is in galaxy evolution (see review by Heckman & Best continuumradiosourcesregardlessofgasredshift(e.g.Mor-
2014).Thiscanbeexaminedviathekinematicsofcircumnu- ganti et al. 2005). Absorption from Hi gas located in front
clearneutralgas,sometimesexhibitingfast(>1000kms−1) of an AGN is a good tracer for the kinematics of gas, and
andmassive(upto50M(cid:74) yr−1)outflows createdbyinter- hence Hi associated absorption surveys allow us to investi-
actions from radio-loud AGN (e.g. Morganti et al. 2005). gate how AGN feedback directly interacts with the clumpy
The21-cmlineofatomichydrogen(HI)isausefultool medium in the host galaxy in compact radio sources (e.g.
for tracing the neutral gas within galaxies in emission to Wagner et al. 2012).
study the diffuse neutral gas in galaxies (see Giovanelli &
It was suggested that intrinsically compact sources -
Haynes 2016, and references therein). However, due to flux primarily, gigahertz peaked spectrum (GPS) ((cid:54) 1 kpc in
limitations, it is currently difficult to detect Hi in emis-
size) and compact steep-spectrum (CSS) radio sources (∼1
- 10 kpc) - have higher detection rates of Hi than extended
sources(e.g.withdetectionratesof∼20-40%inVermeulen
(cid:63) E-mail:[email protected] et al. 2003; Gupta et al. 2006; Chandola et al. 2011). Fur-
(cid:13)c 2002TheAuthors
2
thermore,Curranetal.(2016c)showsthattheHidetection 2 SAMPLE SELECTION, OBSERVATIONS
rate is proportional to the turnover frequency, which is in- AND DATA REDUCTION
versely proportional to source size. Morganti et al. (2001)
searched for Hi in 23 nearby (z < 0.22) radio galaxies and 2.1 Observations
foundadetectionrateofHiof23%inthecompactsources, 2.1.1 Sample Selection
higherthanthatofasubsetofextendedFanaroff-Rileytype
IandII(FR-I,FR-II)sources(10%).Pihlstro¨m,Conway,& To study the Hi content of the inner circumnuclear regions
Vermeulen (2003) also suggest an anti-correlation between ofgalaxies,wechoseradiogalaxiesknowntohaveabright,
theHicolumndensityandsourcesize.Curranetal.(2013a) compact core. Targets were selected at 20 GHz from the
attributed this to a source size anti-correlation with optical AT20G survey catalogue (Murphy et al. 2010), which were
depth,proposingthisisduetoaneffectofgeometrywitha cross-matched with the 6dF Galaxy Survey (Jones et al.
larger covering factor for smaller source sizes. 2009) to obtain redshift information (Sadler et al. 2014).
These studies reveal evidence for disturbed neutral gas In order to select compact sources, those with extended ra-
kinematicsnearyoungAGN.Ger´ebetal.(2015)foundthat dioemissiononscalesgreaterthan15arcsecondsat20GHz
asymmetric,broadabsorptionfeaturesappearmoreoftenin wereremoved.Followingthis,thesamplewasrestrictedto45
compactsources,suggestingagreaterinterplaybetweenthe sourcessouthofdeclinationδ = −20◦,withintheredshift
AGN feedback of the host galaxy and the neutral gas envi- range of 0.04 < z < 0.08. This range was chosen to search
ronment. Such interplay, where the ultra-violet luminosity for the 21-cm Hi line within a convenient and available fre-
of the active nucleus has a direct impact on the neutral gas quencyrangeoftheATCA,andtoavoidcontaminatingthe
in the host, has been suggested by Curran et al. (2008), spectrawithHiemissionlinesbyprobingsufficientlynearby
who first noted a decrease in the detection of associated Hi galaxies.Theinstrumentsalsoimposedaminimumfluxden-
absorption with redshift. They attributed this to the flux sitylimitof50mJyat1.4GHz(asabsorptionlinestrength
limitations of optical surveys, biasing towards increasingly depends on the brightness of the background source).
UV luminous sources (further demonstrated by Curran & The results from observations of 29 sources were re-
Whiting 2010). The detection rate reaches zero at ionising ported by Allison et al. (2012a). Two sources within our
photonratesofQHi ∼3×1056sec−1(LUV ∼1023WHz−1at sample (J062706–352916 and J164416–771548) were previ-
λ=912˚A),atwhichpointalloftheneutralgasinthehost ously observed by Morganti et al. (2001) to optical depths
galaxy is believed to be ionised (Curran & Whiting 2012). upper limits of τ < 4.7%, and so were not re-observed by
This critical UV luminosity limit has been observed several us. These observations have since been extended by three
timessince,throughthenon-detectionofHiabovethisvalue separateobservationrunsmadewiththeATCAinorderto
(Curranetal.2011a,2013b,c;Curranetal.2016a;Grasha& expand to the sample:
Darling2011;Allisonetal.2012a;Ger´ebetal.2015;Aditya
• 14 targets in February 2013 with the same selection
et al. 2016).
criteria as that by Allison et al. (2012a). Of these targets,
Here we present the results of the search of Hi ab-
the source J091856–243829 was included for an intervening
sorption complementrary to Allison et al. (2012a), who
Hi search, but while we give its spectrum, it is not part of
searched for Hi in 29 targets as part of a sample of 66
our sample.
nearby (0.04 < z < 0.08) compact sources selected from
• 9 targets in June 2013, in a higher redshift range
the Australia Telescope 20 GHz survey (AT20G; Murphy
(0.080 < z < 0.096). This redshift range was within the
et al. 2010), with the Australian Telescope Compact Array
receiverlimitsandavoidedspecificradiofrequencyinterfer-
(ATCA) on the Broadband Backend (CABB). A total of
ence (RFI).
three detections were made by Allison et al. (2012a), two
• 14targetsinSeptember2014.Thesewerepartofasep-
ofwhichwerepreviouslyunknown.Thesampleexploresthe
arate sample of 68 compact GPS sources imaged with the
Hicontentwithinnearbycompactradiogalaxieswithyoung
Very Long Baseline Array (VLBA). They had also been se-
ornewlytriggeredAGN.Wealsopresentouranalysismade
lectedfromtheAT20Gsurveywithredshiftsidentifiedinthe
through consideration of infrared and X-ray properties.
6dFGalaxySurvey.Thesetargetshadadditionalconstraints
This work also involved the development of a data
of declinations of δ > -40◦, redshifts of 0.04 < z < 0.08, a
reduction pipeline for wide-band data, and an automated
minimumfluxdensityof50mJyat1.4GHz,andanangular
spectral-line finding method based on Bayesian inference.
size of 0.2 arcseconds or less at 20 GHz.
These tools are part of preparation for the First Large Ab-
sorption Survey in Hi (FLASH) with the Australian SKA SeveraloftheVLBA-imagedsourceshadbeendetected
Pathfinder (ASKAP; Deboer et al. 2009; Johnston et al. in the continuum with the Australian Long Baseline Array
2009; Schinckel et al. 2012), and has been successfully em- (LBA) by Hancock et al. (2009) at 4.8 GHz, where all tar-
ployed in the ongoing ASKAP-FLASH commissioning sur- gets were observed but unresolved on scales of ∼100 mas,
vey (e.g. Allison et al. 2015). FLASH’s redshift regime of implyinglinearsizesoflessthan100pc.TheVLBAimaging
0.4 < z < 1.0 will explore both associated and intervening spatialresolutionis0.5mas,andhencewillallowforacom-
(withinanothergalaxyalongthelineofsight)Hiabsorption, prehensive study of the radio source morphology on parsec
andallowustoextensivelyexaminehowtheHicontenthas scales.
evolved with redshift in a largely unexplored epoch. Intotaloursampleconsistedof66targetswhicharede-
In this paper the standard cosmological model is tailedinTable2.Ashortdescriptionofeachofthecolumns
used, with parameters ΩM = 0.27, ΩΛ = 0.73 and follows.
H = 71kms−1Mpc−1. All uncertainties refer to the
0
68.3percent confidence interval, unless otherwise stated. Column (1): The AT20G source name.
MNRAS000,1–22(2002)
Hi absorption in nearby compact radio galaxies 3
Table 1.Summaryofobservations,includingthosemadebyAllisonetal.(2012a).Inorderofcolumn,welisttheobservinggroupID
(obs.ID),observingdates,theATCAarrayconfiguration,centralfrequencyofthezoomchannel,averageintegrationtimepersourcein
hours,thenumberofobservedsources,theaverage1-σ noiseinthechannels,andnotes.
Obs.ID Dates Arrayconfig ν tint n σchan Notes
MHz hr mJy/beam
A 2011Feb03-06 6A 1342 3.5 14 4.0 PublishedbyAllisonetal.(2012a).
B 2011Apr23-26 6A 1342 3.5 15 4.0 PublishedbyAllisonetal.(2012a).
C 2013Feb13-16 6A 1342 4.0 14 6.3 Carriedoutin3contiguous24hourperiods.
D 2013June08-10 6C 1310 1.5 9 7.4 Madeacrossthreeseparateperiodsof6–10hours.
E 2014Sept25-28 6A 1340 4.0 14 3.4 Carriedoutin3contiguous24hourperiods.
Columns (2) & (3): The right ascension and declination of
the source at J2000.
Column(4):TheAT20G20GHzfluxdensity(Murphyetal.
2010).
Column(5):S istheNVSS1.4GHzfluxdensity(Condon
1.4
et al. 1998).
Column (6): S is the SUMSS 843MHz flux density
0.843
(Mauch et al. 2003).
Columns (7) & (8): The corresponding spectral indices be-
tween the two lower-frequencies and 20GHz are given by
α20 and α20 respectively.
1.4 0.843
Column(9):ObservationID.RefertoTable1forthedetails
of each run.
Column (10): z is the optical spectroscopic redshift.
opt
Column (11): SC is the optical spectroscopic classification
as defined by Mahony et al. (2011). Aa means only absorp-
tion lines were detected, Ae corresponds to only emission Figure1.Spectralindicesforthe49sourcesinoursampleswith
lines, AeB broad emission lines, and Aae means both were measurements at 20 GHz, 8.4 GHz and 4.8 GHz. All but nine
observed. fall in a flat-spectrum regime in either axis (spectral indices of
Column (12): M is the Two Micron All Sky Survey -0.5 < α < 0.5), with 26 flat in both indices. The majority are
K
foundtohaveeitheradecreasingspectralenergydistributionwith
(2MASS) K-band absolute magnitude (Skrutskie et al.
frequency(steep/falling)orwithaspectralpeakbetween4.8and
2006).
20GHz(GPS).
Column (13): The 20 GHz compactness, 6km , defined as
vis
theratioofthemeasuredvisibilityamplitudeonthelongest
ATCA baselines to that on the shortest baselines (Chhetri either a decreasing spectral energy distribution with fre-
et al. 2013). They find a lower limit of 0.86 for unresolved quency (steep/falling) or with a spectral peak between 4.8
sources. and 20 GHz (GPS).
Column(14):FRistheFanaroff-Rileytypeatlowfrequency
(1.4 GHz) (Fanaroff & Riley 1974; Baldi & Capetti 2009;
Ghisellini 2011). 2.1.3 ATCA Observations
AllobservationsweremadeusingtheCABBsystem(Ferris
& Wilson 2002), with a 64 MHz zoom-band across 2048
2.1.2 Spectral indices of radio sources channels. This band was centred at either 1310, 1340 or
1342 MHz to allow a simultaneous search for associated Hi
Instead of selecting by spectral index, our survey targeted
absorptionovertherespectiveredshiftrangesforeachsetof
compact radio galaxies selected at 20 GHz, including both
targetswithinasinglezoom-band.TheATCAobservations
steepandflat-spectrumsources,andsooursourceselection
are detailed in Table 2.
differed from similar surveys, such as Gupta et al. (2006)
Like the survey of Allison et al. (2012a), sources were
and Chandola et al. (2011), which targeted GPS and CSS
observedin20or30minutescansandinterleavedwith1.5or
radio sources. Of the full sample, 38 (58%) are classified as
2minuteobservationsofanearbybrightcalibratorforgain
flat-spectrum sources (-0.5 < α < 0.5 between 1.4/0.843 andphasecalibration.PKS1934–638(Reynolds1994)1 was
GHz and 20 GHz; Table 2).
observedregularlyastheprimarybandpassandfluxcalibra-
We examined additional flux density measurements to
tor, and for some nearby targets as a secondary calibrator.
confirm how many of our compact core-selected sources are
All2048zoomchannelswereusedcorrespondingtoaband-
classifiedas flat-spectrum. Fig.1 shows thespectralindices
width of 64 MHz, although channels affected by RFI were
from the AT20G survey (Murphy et al. 2010) for 49 of our
removed during data reduction.
sources with flux measurements at 20 GHz, 8.4 GHz and
4.8GHz.Consideringonlythesefluxmeasurements,thema-
jority have flat spectral indices. Most were found to have 1 http://www.narrabri.atnf.csiro.au/calibrators/
MNRAS000,1–22(2002)
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MNRAS000,1–22(2002)
Hi absorption in nearby compact radio galaxies 5
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20AT20GnameRADec.SSSα201.40.8431.4(J2000)(J2000)(mJy)(mJy)(mJy)(1)(2)(3)(4)(5)(6)(7) J131124–442240(cid:63)131124.04-442240.544···208.3···J132920–264022(cid:63)132920.70-264022.2101102.4···-0.01J135036–163449*135036.14-163449.5186109.2···0.20J135607–172433*135607.02-172433.1239180.1···0.11J140912–231550*140911.97-231549.5137599.4···-0.55J151741–242220*‡151741.76-242220.234492041.9···0.20J164416–771548*†164416.03-771548.5399···1165.9···J165710–735544*165710.08-735544.542···99.3···J171522–652018(cid:63)171522.19-652018.653···190.5···J180957–455241(cid:63)180957.79-455241.21087···1530.0···J181857–550815*181857.99-550815.075···185.6···J181934–634548(cid:63)†181934.99-634548.21704···19886.0···J191457–255202*191457.79-255202.8147367.6···-0.34J192043–383107(cid:63)192043.13-383107.163239.7247.8-0.5J204552–510627*204552.29-510627.754···620.9···J205306–162007*205306.00-162007.456116.5···-0.27J205401–424238(cid:63)205401.79-424238.786···160.2···J205754–662919*205754.01-662919.649···282.7···J205837–575636(cid:63)205837.39-575636.597···846.2···J210602–712218(cid:63)210602.92-712217.9246···1206.0···J212222–560014*212222.81-560014.658···100.9···J214824–571351*214824.27-571351.548···292.5···J220253–563543(cid:63)220253.31-563543.069···58.4···J220538–053531*220538.59-053531.967187.2···-0.39J221220–251829*221220.77-251829.071304.4···-0.55J223931–360912(cid:63)223931.26-360912.564661.0842.5-0.88J231905–420648(cid:63)231905.92-420648.9150···911.6···J233355–234340(cid:63)233355.28-234340.8957782.1···0.08J234129–291915(cid:63)234129.72-291915.3120239.6···-0.26J234205–160840*234205.82-160840.443151.9···-0.47 *Sourceobservedinour2013/2014ATCAprogrammes(thispaper)(cid:63)SourcesearchedinAllisonetal.(2012a)i(cid:62)SourcesearchedforHabsorptionbyLedlowetal.(2001)i†SourcesearchedforHabsorptionbyMorgantietal.(2001)i‡SourcesearchedforHabsorptionbyvanGorkometal.(1989)i•SourcesearchedforHabsorptionbutnotpartofthissurveysample(seeSectioabcSpectroscopicredshiftreference:Jonesetal.(2009),Vettolanietal.(1989),JfghiDrinkwateretal.(2001),Petersonetal.(1979),Simpsonetal.(1993),MorlmMahonyetal.(2011),Cavaetal.(2009)
MNRAS000,1–22(2002)
6
2.2 Data Reduction detection rate of ∼10% within both the flat-spectrum and
steep-spectrum sources (indicated in Table 2).
All flagging, calibration and imaging of the data were
Table 4 gives the optical depth and Hi column density
performed using tasks from the miriad2 package (Sault,
for each of the sources observed in 2013-2014. The 21-cm
Teuben,&Wright1995)andimplementedusingapurpose-
optical depth is given by
built Hi data reduction pipeline written in Python (Allison
(cid:18) (cid:19)
etal.2012a).Channelsthatareknowntocontainsignificant τ(ν)=−ln 1− ∆Sline(ν) , (1)
RFI (e.g. birdies, CABB-generated self-interference due to fSC(ν)
clockharmonics)wereflaggedoutontheflybythecorrela-
where S is the continuum flux density at the optical spec-
torandappliedwhendatawasloadedusingatlod.pgflag C
troscopic redshift, ∆S is the spectral-line depth (detec-
andblflagwereusedbothbeforeandaftercalibrationfor line
tion)or3-σrmsnoise(non-detection),andf isthecovering
eachtargetandcalibratortoidentifyandflagoutremaining
factorofthebackgroundsource.Intheopticallythinregime
RFI.Carewastakentoavoidexcessiveflaggingofdataand (∆S /S (cid:46) 0.3), the above expression reduces to:
line C
hence the removal of any putative spectral lines, and com-
parisons were made between flagged and unflagged data. τ(ν)≈ ∆Sline(ν) ≈ τobs(ν), (2)
Typically less than 0.1% of data was flagged by the corre- fSC f
lator, and less than 2% in total, although the spectra for where τ (v) ≡ ∆Sline is the observed optical depth as a
theJune2013observationswerefarmorecorruptedbyRFI obs SC
function of velocity. The Hi column density (in cm−2) is
(upward of 10% removed in a few cases).
related to the integrated optical depth (km s−1) as follows
The absolute flux scale and spectral index corrections
(e.g. Wolfe & Burbidge 1975):
based on the flux model of PKS 1934-638 (Reynolds 1994)
(cid:90)
were applied to each of the secondary calibrators. We then N = 1.823×1018T τ(v)dv
calculated the time-varying bandpass and gain corrections HI spin
for the amplitude and phase for each of these, and applied T (cid:90)
≈ 1.823×1018 spin τ (v)dv, (3)
their calibration solutions to their paired target sources. f obs
We repeated the remaining methods and process described
where T is the harmonic mean spin temperature of the
by Allison et al. (2012a) for obtaining the source spectra. spin
gas (in K).
Fig. 1 displays the extracted spectrum for each of the tar-
gets sources, where the arrow below the spectra indicates
the expected position for any associated 21-cm Hi absorp- 3.2 Notes on detections
tion lines, calculated using the known optical spectroscopic
OurfournewHidetectionshavealargerangeofpeakopti-
redshift of the target.
caldepths(fromashighasτ ∼87%toatentativedetec-
We analysed the spectra through a Bayesian linefinder obs
tionatτ ∼3%).Ournon-detectionsshowasimilarrange
and parameterisation pipeline (Allison et al. 2012b). Im- obs
ofupperlimitsonthepeakopticaldepths(Table4),anex-
provements made to the pipeline made since Allison et al.
pectedresultgiventherangeoffluxdensitiesandsensitivity
(2012b)haveallowedforhigher-orderpolynomialmodelfits
of our survey (Fig. 3). Some sources had higher upper lim-
to be made for the continuum, to account for any spectral
its found for their line strengths due to shorter integration
artefacts that could not be successfully removed, e.g. band-
times in the June 2013 observation run (Table 2).
passcalibratorripples.Asaresult,therearenowfewerfalse
J031552-190644 (z = 0.0671)-Apreviouslyknown
positive detections.
strongHiabsorptionfeature(Ledlowetal.2001)isdetected
against the compact flat spectrum core of this well-studied
FR-I radio source. The AGN is hosted by a disc-dominated
3 RESULTS spiralgalaxy(Ledlowetal.1998).Thehostgalaxyislocated
close to the centre of the galaxy cluster A428.
3.1 Detections of HI
Ledlow et al. (2001) found that the very narrow peak
We obtained four detections of Hi absorption (three pre- absorption in the host galaxy gave a large apparent optical
viously unknown) in addition to those obtained by Allison depthof0.98±0.06thatisonlyseenagainsttheradiocore
et al. (2012a). Fig. 4 shows the optical SuperCosmos Sky andnot against eitherofthe twoobserved radiojets,hence
Survey(Hamblyetal.2001)andourobservedradiocontin- ruling out a large, diffuse Hi halo. They measure a column
uum images for the targets with Hi absorption, and results density of NHI (cid:39) 1.82 × 1018TfSτ∆νFWHM cm−2, with a
ofspectralmodelfitting.Table3summarisestheproperties FWHM velocity width of ∆νFWHM = 34 km s−1 giving a
of the individual Gaussian components which were fitted value of NHI (cid:39) 6.19 × 1019TfSτ cm−2. Ledlow et al. (2001)
using Bayesian model comparisons of the new detections. suggests that, given this high optical depth, the absorbing
Thesefourdetectionsaddtothepreviousthree(Allison gas is either of a high density, or the sightline goes through
et al. 2012a), giving a total of 7/66 detections, or a detec- thediscinsuchawaytomaximisetheamountofabsorbing
tion rate of 11%. Of these seven detections, four have been gas (e.g. through a spiral arm or very dense cloud, possibly
categorised as a flat-spectrum source (-0.5 < α < 0.5 be- originatingintheISMofthehostgalaxyduetothenarrow
tween1.4/0.843GHzand20GHz;Table2;alsoseeninFig. linewidth they observe).
1for5to8GHzand8to20GHz).WehaveaHiabsorption Ourmeasurementofthepeakopticaldepthissimilarto
that of Ledlow et al. (2001); we find the Hi column density
to be N = 5.62 (± 0.27) × 1019TS cm−2 (Table 4). The
HI f
2 www.atnf.csiro.au/computing/software/miriad/ absorptionlinefeatureinourspectrumisbestfittedbytwo
MNRAS000,1–22(2002)
Hi absorption in nearby compact radio galaxies 7
AT20GJ005734-012328 AT20GJ011132-730209
AT20GJ025955-123635 AT20GJ031357-395403
AT20GJ031552-190644 AT20GJ033114-524148
AT20GJ033913-173600 AT20GJ034630-342246
AT20GJ035145-274311 AT20GJ035257-683117
AT20GJ035410-265013 AT20GJ043022-613201
AT20GJ060555-392905 AT20GJ065359-415144
AT20GJ084452-100059 AT20GJ090802-095937
Figure2.CABB21-cmspectrafornewlyobservedsourcesinoursample(seeTable2),withtheamplitudeinflux(mJy)plottedagainst
the Doppler corrected barycentric velocity (cz, in 103 km s−1). The arrow indicates the optical redshift of the host galaxy, where any
associatedHiabsorptionfeaturewouldbeexpected.The1σ redshifterrorisindicatedbythehorizontallineonthearrow.
MNRAS000,1–22(2002)
8
AT20GJ091856-243829 AT20GJ114539-105350
AT20GJ123148-321314 AT20GJ125615-114635
AT20GJ125711-172434 AT20GJ135036-163449
AT20GJ135607-172433 AT20GJ140912-231550
AT20GJ151741-242220 AT20GJ165710-735544
AT20GJ181857-550815 AT20GJ191457-255202
AT20GJ204552-510627 AT20GJ205306-162007
AT20GJ205754-662919 AT20GJ212222-560014
Figure 2.Continued.
MNRAS000,1–22(2002)
Hi absorption in nearby compact radio galaxies 9
AT20GJ214824-571351 AT20GJ220538-053531
AT20GJ221220-251829 AT20GJ234205-160840
Figure 2.Continued.
tive new detection of a weak broad line against this steep-
spectrum source (spectral index of α = −0.7). As with
J060555-392905,itwasspectroscopicallyidentifiedasanAa
galaxy in Mahony et al. (2011). It is classified as a FR-I
type galaxy due to its extended low-frequency emission in
NVSS.Beyondthatthereisalackofinformationregarding
the morphology of the galaxy within the literature. Its in-
frared colours are similar to those of elliptical galaxies, and
its optical image suggests this morphology as well (Fig. 2).
The feature is best modelled by a wide, weak absorp-
tion line centred slightly blueward of the source galaxy’s
optical redshift (shifted by ∼ 180 km s−1). This detection
has low significance compared to the other detections (Ta-
ble3).However,thelogarithmicoddsratioofR=13.9±0.3
means the spectral line model is favoured over the contin-
Figure3.The21-cmlinestrengthversusthemeasuredfluxden- uum fit (where there is a higher probability for a model to
sity of the source. Blue points give our detections, and red the betruerelativetoanotherifithasa(log)Bayesoddsratio
upperlimitsofournon-detections.Afewsourceshadshorterin- R > 1).
tegrationtimesandsolieabovetherangeforourdetections(see
Itisararebroadfeaturewithoutanassociatednarrow,
Table2).
deeper line. Like the previously reported Hi detection in
J205401-424238 (Allison et al. 2012a), this line is apparent
throughout the observation in both polarization feeds, and
narrow Gaussians, both located around the spectroscopic
does not appear in spectra that are extracted from spatial
optical redshift, and matches the narrow, deep feature that
positionssignificantlyoffthesource.Ifreal,thisisthesecond
Ledlow et al. (2001) observed.
such feature within our sample (Fig. 4, and Allison et al.
J060555-392905 (z = 0.0452) - This is a flat-
spectrumradiosourcewithanewHidetection.Itwasspec- 2013) that may have been dismissed by visual inspection if
notforourspectrallinedetectiontechnique.Tofullyverify
troscopically classified as an AGN source with only absorp-
thisdetectionhowever,werequirefurthermoresensitive21-
tion features (Aa) within its optical spectrum by Mahony
cm observations.
etal.(2011).Thepresenceofaforegroundstaraffectsboth
thespectrumandthevisualclassificationofthemorphology As the WISE mid-infrared colours indicate this galaxy
of the host galaxy (Fig. 4). has a low star formation rate, the absorbing gas we ob-
A one-component, narrow Gaussian fit slightly serve may only lie close to the AGN rather than being dis-
blueshifted (∼ 68 ± 4 km s−1) from the spectroscopic op- tributed throughout the galaxy, possibly fuelling the radio
tical redshift was the most statistically likely in modelling AGN (Maccagni et al. 2014, 2016). It may also represent
(Table 3). Given the narrow absorption line and its slightly an outflow of gas created by the AGN feedback, given the
blueshifted location, the cold Hi gas we observe could be blueward offset of the line peak.
located close to the host galaxy’s AGN, and perhaps be J125711-172434(z=0.0475)-Wefindanewdetec-
an outflow of a clump of gas. However, the galaxy’s mid- tion against this flat spectrum radio source, which is clas-
infrared colours suggest at a star-forming host galaxy with sified as a cD4 elliptical galaxy with a very faint yet sig-
alowAGNaccretionrate(Section5.1.1),andhencetheab- nificantly extended corona (de Vaucouleurs et al. 1991). It
sorptioncouldbeduetoagas-richgalacticdisc.Moreinfor- is also the brightest source in the cluster A1644 (Hoessel
mationaboutthemorphologyofthishostgalaxyisrequired etal.1980;Postman&Lauer1995).Thisclusteristhehost
to aid this interpretation. of a few X-ray sources, including 3XMM J125712.0-172431
J084452-100059 (z = 0.0423) - We find a tenta- whichhasaX-rayfluxof1.39×10−13ergscm−2s−1(Rosen
MNRAS000,1–22(2002)
10
Table 3. The inferred values for parameters from fitting a multiple Gaussian spectral-line model for the new sources we detect Hi
absorption. See Allison et al. (2012a) for parameters on the other Hi detections. zcentre is the redshift of the centre of the absorption
component;∆vFWHM,i istheFWHM;∆Si isthedepthandRisthenaturallogarithmoftheratioofprobabilityforthismodelversus
thenospectral-linemodel(theBayesoddsratio).
AT20G name z ∆v 1σ error ∆S 1σ error R
centre FWHM,i i
(kms−1) (kms−1) (mJy) (mJy)
J031552-190644 0.0671 29 +4 26 +2 284.6±0.3
−6 −5
0.0672 19 +22 12 +3
− 5 −2
J060555-392905 0.0448 50 +1 51 +1 471.4±0.3
−1 −1
J084452-100059 0.0423 450 +40 4 +1 13.8±0.3
−80 −1
J125711-172434 0.0474 100 +110 8 +1 91.1±0.4
− 30 −2
0.0477 210 + 10 5 +2
−120 −1
Table 4. A summary of derived Hi absorption properties from model fitting for our 2013 and 2014 observing runs. See Allison et al.
(2012a) for information on the other observations. σchan is the estimated uncertainty per channel; SC is the spectral flux density of
the continuum model at either the position of peak absorption or the optical redshift estimate; 1σ error is the continuum model’s flux
(cid:82)
density error, ∆S is the peak spectral-line depth; τ is the observed peak optical depth and τ dv is the observed velocity
line obs,peak obs
integratedopticaldepth.UpperlimitsassumedasingleGaussianspectrallineofFWHM=30kms−1,andpeakdepth=3σ .
chan
AT20G name σ S 1σ error ∆S τ (cid:82) τ dv log (cid:16)NHIf(cid:17)
chan C line obs,peak obs 10 Tspin
(mJy) (mJy) (mJy) (mJy) (kms−1) cm−2 K−1
J005734-012328 3.70 677.2 +0.5 <11.1 <0.02 <0.52 <18.0
−0.5
J011132-730209 2.96 66.5 +0.1 <8.9 <0.13 <4.26 <18.9
−0.1
J025955-123635 4.93 452.1 +0.2 <14.8 <0.03 <1.04 <18.3
−0.2
J031357-395403 7.79 521.4 +0.2 <23.4 <0.04 <1.43 <18.4
−0.2
J031552-190644 2.00 44.5 +0.1 25.9+1.5 0.87+0.09 31.16+1.73 19.75+0.02
−0.1 −1.6 −0.08 −1.76 −0.02
J033114-524148 2.66 29.4 +0.1 <8.0 <0.27 <8.66 <19.2
−0.1
J033913-173600 2.40 123.4 +0.1 <7.2 <0.06 <1.86 <18.5
−0.1
J034630-342246 2.99 57.1 +0.1 <9.0 <0.16 <5.01 <19.0
−0.1
J035145-274311 2.84 12.0 +0.1 <8.5 <0.71 <22.76 <19.6
−0.2
J035257-683117 4.33 149.0 +0.2 <13.0 <0.09 <2.78 <18.7
−0.2
J035410-265013 3.26 70.5 +0.1 <9.8 <0.14 <4.43 <18.9
−0.1
J043022-613201 3.29 181.0 +0.1 <9.9 <0.05 <1.74 <18.5
−0.1
J060555-392905 2.96 106.4 +0.1 34.8+1.4 0.40+0.02 31.86+1.41 19.76+0.02
−0.1 −1.5 −0.02 −1.44 −0.02
J065359-415144 7.49 159.4 +0.3 <22.5 <0.14 <4.50 <18.9
−0.3
J084452-100059 2.65 134.3 +0.2 4.1+0.6 0.03+0.01 14.20+2.64 19.41+0.08
−0.2 −0.7 −0.01 −2.71 −0.08
J090802-095937 2.57 137.0 +0.1 <7.7 <0.06 <1.80 <18.5
−0.1
J091856-243829 2.04 53.1 +0.1 <6.1 <0.12 <3.68 <18.8
−0.1
J114539-105350 3.75 46.7 +0.1 <11.2 <0.24 <7.69 <19.1
−0.1
J123148-321314 8.71 146.9 +0.3 <26.1 <0.18 <5.68 <19.0
−0.3
J125615-114635 2.82 89.5 +0.1 <8.5 <0.09 <3.02 <18.7
−0.1
J125711-172434 2.83 111.9 +0.1 10.8+1.2 0.10+0.01 18.46+1.76 19.53+0.04
−0.1 −1.3 −0.01 −1.65 −0.04
J135036-163449 8.44 35.6 +0.3 <25.3 <0.71 <22.72 <19.6
−0.3
J135607-172433 2.70 185.2 +0.1 <8.1 <0.04 <1.40 <18.4
−0.1
J140912-231550 11.40 583.4 +0.4 <34.2 <0.06 <1.87 <18.5
−0.4
J151741-242220 3.22 2336.3 +0.2 <9.7 <0.01 <0.13 <17.4
−0.2
J165710-735544 2.48 58.4 +0.1 <7.4 <0.13 <4.07 <18.9
−0.1
J181857-550815 2.37 35.8 +0.1 <7.1 <0.20 <6.33 <19.1
−0.1
J191457-255202 2.99 189.4 +0.1 <9.0 <0.05 <1.51 <18.4
−0.1
J204552-510627 3.52 64.7 +0.1 <10.6 <0.16 <5.21 <19.0
−0.1
J205306-162007 2.41 69.2 +0.1 <7.2 <0.10 <3.34 <18.8
−0.1
J205754-662919 2.29 46.0 +0.1 <6.9 <0.15 <4.77 <18.9
−0.1
J212222-560014 2.43 19.2 +0.1 <7.3 <0.38 <12.15 <19.3
−0.1
J214824-571351 8.84 90.1 +0.3 <26.5 <0.29 <9.40 <19.2
−0.3
J220538-053531 2.94 157.1 +0.1 <8.8 <0.06 <1.79 <18.5
−0.1
J221220-251829 4.57 145.6 +0.1 <13.7 <0.09 <3.01 <18.7
−0.1
J234205-160840 2.78 52.2 +0.1 <8.3 <0.16 <5.10 <19.0
−0.1
MNRAS000,1–22(2002)