Stellar populations in a complete sample of local radio galaxies

Raimann, Daniel Iunes; Storchi‐Bergmann, Thaisa; Quintana, H.; Hunstead, R. W.; Wisotzki, L.

doi:10.1111/j.1365-2966.2005.09665.x

Cited by 32 publications

(53 citation statements)

References 22 publications

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“…There is increasing evidence that the host galaxies of various types of AGN are bluer than inactive ellipticals (Govoni et al 2000;Schade et al 2000;Örndahl et al 2003;Sanchez et al 2004;Jahnke et al 2004;Kotilainen & Falomo 2004;Hyvönen et al 2007a) and that they do not follow the color-magnitude relation of inactive Article published by EDP Sciences ellipticals (Peletier et al 1990) indicating a recent star formation episode. This scenario is also supported by optical spectroscopic studies of nearby radio galaxies (RG) (Raimann et al 2005;Holt et al 2007). The observed blue colors are not affected by the dust content of the galaxy, because in the presence of dust reddening the intrinsic color of the galaxy would be even bluer.…”

Section: Introductionmentioning

confidence: 65%

“…These studies have only recently been followed by systematic studies by e.g. Nolan et al (2001), Jahnke (2002), Raimann et al (2005) and Silva et al (2008). According to the unified model of radio-loud AGN, RGs are seen edge-on so that the bright central region is obscured, making spectroscopy of the inner part of the host galaxy much easier.…”

Section: Introductionmentioning

confidence: 99%

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The stellar content of low redshift radio galaxies from near-infrared spectroscopy

Hyvönen¹,

Kotilainen²,

Reunanen³

et al. 2009

A&A

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Context. We present medium spectral resolution near-infrared (NIR) HK-band spectra for eight low redshift (z < 0.06) radio galaxies to study the NIR stellar properties of their host galaxies. The sample was selected from a radio galaxy sample imaged previously in the B-and R-band. They were found to be bluer than inactive elliptical galaxies, possibly indicating a recent star formation episode. As a homogeneous comparison sample, we used nine inactive elliptical galaxies that were observed with the same telescope and detector with similar resolution and wavelength range. Aims. The aim of the study is, by using the advantage of NIR absorption features, to compare the NIR spectral properties of radio galaxies to those of inactive early-type galaxies and, furthermore, produce the first NIR HK-band spectra for low redshift radio galaxies. Methods. For the radio galaxy and inactive elliptical samples, spectral indices of several diagnostic absorption features, namely SiI(1.589 μm), CO(1.619 μm) in the H-band and NaI(2.207 μm), CaI(2.263 μm), CO(>2.29 μm) in the K-band, were measured. The strength of absorption lines depends on the luminosity and/or temperature of stars and, therefore, spectral indices can be used to trace the stellar population of galaxies. To characterize the age of the populations, the measured EWs of the absorption features were fitted with the corresponding theoretical evolutionary curves of the EWs calculated by the stellar synthesis model. Results. On average, EW(CO 2.29) of radio galaxies is somewhat greater than that of inactive ellipticals. Most likely, EW(CO 2.29) is not significantly affected by dilution, thus indicating that elliptical galaxies containing AGN are in a different stage in their evolution than inactive ellipticals. This is also supported by comparing other NIR absorption line features, such as CaI and NaI, with each other. Based on the theoretical evolutionary curves of EWs, absorption features are consistent with the intermediate age stellar population, suggesting that host galaxies contain both old and intermediate age components. An intermediate age population is also consistent with previous optical spectroscopy studies, which have shown evidence of an intermediate age (∼2 Gyr) stellar population in radio galaxies, and also in some of the early-type galaxies.Conclusions. An intermediate stellar population component indicates that radio galaxies have experienced a star formation epoch relatively recently. The existence of an intermediate stellar population is a link between the star formation episode, possibly induced by an interaction or merging event, and triggering of nuclear activity.

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Section: Introductionmentioning

confidence: 65%

Section: Introductionmentioning

confidence: 99%

The stellar content of low redshift radio galaxies from near-infrared spectroscopy

Hyvönen¹,

Kotilainen²,

Reunanen³

et al. 2009

A&A

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“…A set of 3CR and 6C sources at redshift ≈1 has been investigated with great detail in the nineties (Best et al 1997(Best et al , 1998(Best et al , 1999 to understand this effect (see also Inskip et al 2006a, and references therein). More recently the UV-excess has been found in local samples of radio galaxies as well (Aretxaga et al 2001;Raimann et al 2005).…”

Section: A Comparison Sample Of Large Size Radio Galaxiesmentioning

confidence: 97%

“…The presence of young stellar populations in these objects has been revealed several times (Holt 2009;Labiano et al 2008;deVries et al 2007;Tadhunter et al 2002). Their origin is attributed to the shocks generated by the young radio source expanding into the interstellar medium (Rees 1989;Mellema et al 2002;Bicknell et al 2000), and/or as the result of a galaxy merger process which, at some later epoch, also triggered the onset of the radio source (Raimann et al 2005;Holt 2009). …”

Section: Introductionmentioning

confidence: 94%

The B3-VLA CSS sample

Fanti

Zanichelli

et al. 2011

A&A

120

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Context. Compact steep-spectrum radio sources and giga-hertz peaked spectrum radio sources (CSS/GPS) are generally considered to be mostly young radio sources. In recent years we studied at many wavelengths a sample of these objects selected from the B3-VLA catalog: the B3-VLA CSS sample. Only ≈60% of the sources were optically identified. Aims. We aim to increase the number of optical identifications and study the properties of the host galaxies of young radio sources. Methods. We cross-correlated the CSS B3-VLA sample with the Sloan Digital Sky Survey (SDSS), DR7, and complemented the SDSS photometry with available GALEX (DR 4/5 and 6) and near-IR data from UKIRT and 2MASS. Results. We obtained new identifications and photometric redshifts for eight faint galaxies and for one quasar and two quasar candidates. Overall we have 27 galaxies with SDSS photometry in five bands, for which we derived the ultraviolet-optical spectral energy distribution (UV-O-SED). We extended our investigation to additional CSS/GPS selected from the literature. Most of the galaxies show an excess of ultra-violet (UV) radiation compared with the UV-O-SED of local radio-quiet ellipticals. We found a strong dependence of the UV excess on redshift and analyzed it assuming that it is generated either from the nucleus (hidden quasar) or from a young stellar population (YSP). We also compare the UV-O-SEDs of our CSS/GPS sources with those of a selection of large size (LSO) powerful radio sources from the literature. Conclusions. If the major process of the UV excess is caused by a YSP, our conclusion is that it is the result of the merger process that also triggered the onset of the radio source with some time delay. We do not see evidence for a major contribution from a YSP triggered by the radio sources itself.

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“…This is supported by existence of the dust lane in the optical counterpart (Ekers et al, 1978;Kotanyi & Ekers, 1979) in addition to a tenuous HI bridge reaching 400 kpc from the disk of NGC 612 towards its nearest neighbour, NGC 619 (Emonts et al, 2008). Furthermore, Tadhunter et al (1993) argue that recent star-formation has taken place, as suggested by the observation of strong and narrow absorption features in the optical spectrum, with weak [OII] and [OIII] emission and both Raimann et al (2005) and Holt et al (2007) observe a young stellar population throughout the stellar disk.…”

Section: Introductionmentioning

confidence: 88%

Revealing the Faraday depth structure of radio galaxy NGC 612 with broad-band radio polarimetric observations

Kaczmarek

Purcell

Gaensler

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present full-polarisation, broadband observations of the radio galaxy NGC 612 (PKS B0131-637) from 1.3 to 3.1 GHz using the Australia Telescope Compact Array. The relatively large angular scale of the radio galaxy makes it a good candidate with which to investigate the polarisation mechanisms responsible for the observed Faraday depth structure. By fitting complex polarisation models to the polarised spectrum of each pixel, we find that a single polarisation component can adequately describe the observed signal for the majority of the radio galaxy. While we cannot definitively rule out internal Faraday rotation, we argue that the bulk of the Faraday rotation is taking place in a thin skin that girts the polarised emission. Using minimum energy estimates, we find an implied total magnetic field strength of 4.2 µG.

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Stellar populations in a complete sample of local radio galaxies

Cited by 32 publications

References 22 publications

The stellar content of low redshift radio galaxies from near-infrared spectroscopy

The stellar content of low redshift radio galaxies from near-infrared spectroscopy

The B3-VLA CSS sample

Revealing the Faraday depth structure of radio galaxy NGC 612 with broad-band radio polarimetric observations

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