Reply to comments by J. S. M. Willis

Rees, Judith; Rees, Ray

doi:10.1080/09595237300185191

Cited by 134 publications

(168 citation statements)

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“…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: 99%

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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Section: Introductionmentioning

confidence: 99%

The B3-VLA CSS sample

Fanti

Zanichelli

et al. 2011

A&A

120

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“…Theoretical scenarios for a "starburst-AGN connection" vary from those in which starbursts are a key piece of the AGN machinery, either through symbiotic or evolutionary processes (e.g., Perry & Dyson 1985;Sanders et al 1988; Norman & Scoville 1988;Rees 1989;Daly 1990; Terlevich et al 1992;Williams, Baker & Perry 1999), to those in which these are fundamentally decoupled phenomena, but which are likely to coexist merely because both are triggered by and live on gas fueling (e.g., Byrd et al 1986 Mihos & Hernquist 1996). Given the enormous breadth of possibilities in between these extremes, it is likely that progress in understanding this connection will be driven more by input from observations than from theoretical considerations.…”

Section: Introductionmentioning

confidence: 99%

Empirical Diagnostics of the Starburst‐AGN Connection

Fernandes

Heckman

Schmitt

et al. 2001

ApJ

190

201

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We examine a representative sample of 35 Seyfert 2 nuclei. Previous work has shown that nearly half (15) of these nuclei show the direct (but difficult-to-detect) spectroscopic signature at optical/near-UV wavelengths of the hot massive stars that power circum-nuclear starbursts. In the present paper we examine a variety of more-easily-measured quantities for this sample, such as the equivalent widths of strong absorption features, continuum colors, emission-line equivalent widths, emission line ratios and profiles, far-IR luminosities, and near-UV surface brightness. We compare the composite starburst + Seyfert 2 nuclei to "pure" Seyfert 2 nuclei, Starburst galaxies and normal galactic nuclei. Our goals are to verify whether the easily-measured properties of the composite nuclei are consistent with the expected impact of a starburst, and to investigate alternative less-demanding methods to infer the presence of starbursts in Seyfert 2 nuclei, applicable to larger or more distant samples. We show that starbursts do indeed leave clear and easily quantifiable imprints on the near-UV to optical continuum and emission line properties of Seyfert 2's. Composite starburst + Seyfert 2 systems can be recognized by: (1) a strong "Featureless Continuum" (FC), which dilutes the CaII K line from old stars in the host's bulge to an equivalent width W K < 10Å; (2) emission lines whose equivalent widths are intermediate between Starburst galaxies and "pure" Seyfert 2's; (3) relatively low excitation line-ratios, which indicate that part of the gas ionization in these Seyfert 2's (typically ∼ 50% of Hβ) is due to photoionization by OB stars; (4) large far IR luminosities ( 10 10 L ); (5) High near-UV surface brightness (∼ 10 3 L pc −2 ). These characteristics are all consistent with the expected impact of circum-nuclear starbursts on the observed properties of Seyfert 2's. Furtheremore, they offer alternative empirical diagnostics of the presence of circum-nuclear starbursts from a few easily measured quantities.

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“…A recourse has to be taken to indirect methods. A regular pattern of variability of optical emission lines (Halpern & Fillippenko 1988), the precessional behavior of radio jets, (Rees 1984) and the changing precessional period due to orbital motion of the binary (Roos 1988;Roos, Kaastra & Hummel 1993) are expected.…”

Section: Results and Conclusionmentioning

confidence: 99%

Analytical binary black hole model of Sgr A* and its implications

Chatterjee

2006

Proc. IAU

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Abstract. Surrounding the Galactic center is a molecular cloud with a central black hole. This raises the question as to how the hole was formed. While clouds containing HCN are circulating around the Galactic center, they do not all move at the same speed and so collide mutually and should make a more uniform motion and distribution after a period of some 100 kyrs (e.g., Ekers, van Gorkom, Schwartz et al. 1983). Hence some very energetic phenomena must have occurred within that period.

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Reply to comments by J. S. M. Willis

Cited by 134 publications

References 0 publications

The B3-VLA CSS sample

The B3-VLA CSS sample

Empirical Diagnostics of the Starburst‐AGN Connection

Analytical binary black hole model of Sgr A* and its implications

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