H i absorption towards nearby compact radio sources

Chandola, Yogesh; Sirothia, S. K.; Saikia, D. J.

doi:10.1111/j.1365-2966.2011.19607.x

Cited by 56 publications

(81 citation statements)

References 60 publications

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“…Compact steep spectrum (CSS) and gigahertz peaked spectrum (GPS) sources have been proposed to represent young ( 10 4 yr) radio AGN, based on spectral aging analysis and lobe expansion A&A 569, A35 (2014) speed measurements (Fanti et al 1995;Readhead et al 1996;Owsianik & Conway 1998). A high detection rate of H i absorption in these sources has been reported by a number of studies Gupta et al 2006;Emonts et al 2010;Chandola et al 2011). This has been interpreted as evidence of a relation between the recent triggering of the AGN activity and the presence of H i gas.…”

Section: Introductionmentioning

confidence: 69%

Probing the gas content of radio galaxies through H I absorption stacking

Geréb

Morganti

Oosterloo

2014

A&A

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Using the Westerbork Synthesis Radio Telescope, we carried out shallow H i absorption observations of a flux-selected (S 1.4 GHz > 50 mJy) sample of 93 radio active galactic nuclei (AGN), which have available SDSS (Sloan Digital Sky Survey) redshifts between 0.02 < z < 0.23. Our main goal is to study the gas properties of radio sources down to S 1.4 GHz flux densities not systematically explored before using, for the first time, stacking of absorption spectra of extragalactic H i. Despite the shallow observations, we obtained a direct detection rate of ∼29%, comparable with deeper studies of radio galaxies. Furthermore, detections are found at every S 1.4 GHz flux level, showing that H i absorption detections are not biased toward brighter sources. The stacked profiles of detections and non-detections reveal a clear dichotomy in the presence of H i, with the 27 detections showing an average peak τ = 0.02 corresponding to N(H i) ∼ (7.4 ± 0.2) × 10 18 (T spin /c f ) cm −2 , while the 66 non-detections remain undetected upon stacking with a peak optical depth upper limit τ < 0.002 corresponding to N(H i) < (2.26 ± 0.06) × 10 17 (T spin /c f ) cm −2 (using a FWHM of 62 km s −1 , derived from the mean width of the detections). Separating the sample into compact and extended radio sources increases the detection rate, optical depth, and FWHM for the compact sample. The dichotomy for the stacked profiles of detections and non-detections still holds between these two groups of objects. We argue that orientation effects connected to a disk-like distribution of the H i can be partly responsible for the dichotomy that we see in our sample. However, orientation effects alone cannot explain all the observational results, and some of our galaxies must be genuinely depleted of cold gas. A fraction of the compact sources in the sample are confirmed by previous studies as likely young radio sources (compact steep spectrum and gigahertz peaked spectrum sources). These show an even higher detection rate of 55%. Along with their high integrated optical depth and wider profile, this reinforces the idea that young radio AGN are embedded in a medium that is rich in atomic gas. Part of our motivation is to probe for the presence of faint H i outflows at low optical depth using stacking. However, the stacked profiles do not reveal any significant blueshifted wing. We are currently collecting more data to investigate the presence of outflows. The results presented in this paper are particularly relevant for future surveys in two ways. The lack of bias toward bright sources is encouraging for the search for H i in sources with even lower radio fluxes planned by such surveys. The results also represent a reference point when searching for H i absorption at higher redshifts.

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Section: Introductionmentioning

confidence: 69%

Probing the gas content of radio galaxies through H I absorption stacking

Geréb

Morganti

Oosterloo

2014

A&A

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“…Instead of selecting by spectral index, our survey targeted compact radio galaxies selected at 20 GHz, including both steep and flat-spectrum sources, and so our source selection differed from similar surveys, such as Gupta et al (2006) and Chandola et al (2011), which targeted GPS and CSS radio sources. Of the full sample, 38 (58%) are classified as flat-spectrum sources (-0.5 < α < 0.5 between 1.4/0.843 GHz and 20 GHz; Table 2).…”

Section: Spectral Indices Of Radio Sourcesmentioning

confidence: 99%

“…with detection rates of ∼20 -40% in Vermeulen et al 2003; Gupta et al 2006;Chandola et al 2011). Fur-thermore, Curran et al (2016c) shows that the Hi detection rate is proportional to the turnover frequency, which is inversely proportional to source size.…”

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confidence: 99%

Hi absorption in nearby compact radio galaxies

Glowacki

Allison

Sadler

et al. 2017

Mon. Not. R. Astron. Soc.

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Hi absorption studies yield information on both AGN feeding and feedback processes. This AGN activity interacts with the neutral gas in compact radio sources, which are believed to represent the young or recently re-triggered AGN population. We present the results of a survey for Hi absorption in a sample of 66 compact radio sources at 0.040 < z < 0.096 with the Australia Telescope Compact Array. In 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 (∆v FWHM > 100 km s −1 ) features, indicative of disturbed gas kinematics. Such broad, shallow and offset features are also found within low-excitation radio galaxies which is attributed to disturbed circumnuclear gas, consistent with early-type galaxies typically devoid of a gas-rich disk. Comparing mid-infrared colours of our galaxies with Hi detections indicates that narrow and deep absorption features are preferentially found in late-type and high-excitation radio galaxies in our sample. These features are attributed to gas in galactic disks. By combining XMM-Newton archival data with 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 radio galaxies to lower radio luminosities and provides a basis for future work exploring the higher redshift universe.

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“…Several HI absorption surveys revealed that compact radio galaxies display a significant excess in the detection rate with respect to extended radio sources (Conway 1997;Morganti et al 2001;Pihlström et al 2003;Vermeulen et al 2003;Gupta et al 2006;Chandola et al 2011;Curran et al 2013;Geréb et al 2014).…”

Section: Absorptionmentioning

confidence: 99%

Correlation between X-Ray and Radio Absorption in Compact Radio Galaxies

Ostorero

Morganti

Diaferio

et al. 2017

ApJ

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Compact radio galaxies with a GHz-peaked spectrum (GPS) and/or compact-symmetric-object (CSO) morphology (GPS/CSOs) are increasingly detected in the X-ray domain. Their radio and X-ray emissions are affected by significant absorption. However, the locations of the X-ray and radio absorbers are still debated. We investigated the relationship between the column densities of the total (N H ) and neutral (N HI ) hydrogen to statistically constrain the picture. We compiled a sample of GPS/CSOs including both literature data and new radio data that we acquired with the Westerbork Synthesis Radio Telescope for sources whose X-ray emission was either established or under investigation. In this sample, we compared the X-ray and radio hydrogen column densities, and found that N H and N HI display a significant positive correlation, with N HI ∝N H b , where b = 0.47 and b = 0.35, depending on the subsample. The N H -N HI correlation suggests that the X-ray and radio absorbers are either co-spatial or different components of a continuous structure. The correlation displays a large intrinsic spread that we suggest to originate from fluctuations, around a mean value, of the ratio between the spin temperature and the covering factor of the radio absorber, T s /C f .

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H i absorption towards nearby compact radio sources

Cited by 56 publications

References 60 publications

Probing the gas content of radio galaxies through H I absorption stacking

Probing the gas content of radio galaxies through H I absorption stacking

Hi absorption in nearby compact radio galaxies

Correlation between X-Ray and Radio Absorption in Compact Radio Galaxies

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