Centaurus A - NGC 5128

Israel, F.P.

doi:10.1007/s001590050011

Cited by 316 publications

(327 citation statements)

References 143 publications

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“…The latter is the closest large elliptical (e.g. Israel 1998, and references therein). These comparisons are based on the peak AGB brightness, the shape of the LF, and the number density of bright AGB stars, normalized using published surface brightness measurements.…”

Section: Comparisons With the Dvdb Field M32 And Ngc 5128mentioning

confidence: 98%

The Upper Asymptotic Giant Branch of the Elliptical Galaxy Maffei 1 and Comparisons with M32 and NGC 5128

Davidge

2002

The Astronomical Journal

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Deep near-infrared images obtained with adaptive optics (AO) systems on the Gemini North and Canada-France-Hawaii telescopes are used to investigate the bright stellar content and central regions of the nearby elliptical galaxy Maffei 1. Stars evolving on the upper asymptotic giant branch (AGB) are resolved in a field 3 arcmin from the center of the galaxy. The locus of bright giants on the (K, H − K) color-magnitude diagram is consistent with a population of stars like those in Baade's Window reddened by E(H − K) = 0.28 ± 0.05 mag. This corresponds to A V = 4.5 ± 0.8 mag, and is consistent with previous estimates of the line of sight extinction computed from the integrated properties of Maffei 1. The AGB-tip occurs at K = 20.0, which correponds to M K = −8.7; hence, the AGB-tip brightness in Maffei 1 is comparable to that in M32, NGC 5128, and the bulges of M31 and the Milky-Way. The near-infrared luminosity functions (LFs) of bright AGB stars in Maffei 1, M32, and NGC 5128 are also in excellent agreement, both in terms of overall shape and the relative density of infrared-bright stars with respect to the fainter stars that dominate the light at visible and red wavelengths. It is concluded that the brightest AGB stars in Maffei 1, NGC 5128, M32, and the bulge of M31 trace an old, 1 Visiting Astronomer, Canada-France-Hawaii Telescope, which is operated by the National Research Council of Canada, the Centre National de le Recherche Scientifique, and the University of Hawaii.2 Visiting Astronomer, Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Research Council (Canada), the National Science Foundation (United States), the Particle Physics and Astronomy Research Council (United Kingdom), the Australian Reasearch Council (Australia), CNPq (Brazil), and CONICET (Argentina).-2 -metal-rich population, rather than an intermediate age population. It is also demonstrated that Maffei 1 contains a distinct red nucleus, and this is likely the optical signature of low-level nuclear activity and/or a distinct central stellar population. Finally, there is an absence of globular clusters brighter than the peak of the globular cluster LF in the central 700 × 700 parsecs of Maffei 1.

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Section: Comparisons With the Dvdb Field M32 And Ngc 5128mentioning

confidence: 98%

The Upper Asymptotic Giant Branch of the Elliptical Galaxy Maffei 1 and Comparisons with M32 and NGC 5128

Davidge

2002

The Astronomical Journal

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“…Cen A, which lies at a distance of about 3.4 Mpc (e.g. de Vaucouleurs 1979;Soria et al 1996;Israel 1998;Evans et al 2004;Harris et al 2010), is an FR I RG.…”

Section: The Koers and Tinyakov (Kt) Modelmentioning

confidence: 99%

High-energy neutrino fluxes from AGN populations inferred from X-ray surveys

Jacobsen

et al. 2015

Mon. Not. R. Astron. Soc.

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High-energy neutrinos and photons are complementary messengers, probing violent astrophysical processes and structural evolution of the Universe. X-ray and neutrino observations jointly constrain conditions in active galactic nuclei (AGN) jets: their baryonic and leptonic contents, and particle production efficiency. Testing two standard neutrino production models for local source Cen A (Koers & Tinyakov 2008; Becker & Biermann 2009), we calculate the high-energy neutrino spectra of single AGN sources and derive the flux of high-energy neutrinos expected for the current epoch. Assuming that accretion determines both X-rays and particle creation, our parametric scaling relations predict neutrino yield in various AGN classes. We derive redshift-dependent number densities of each class, from Chandra and Swift/BAT X-ray luminosity functions (Silverman et al. 2008;Ajello et al. 2009). We integrate the neutrino spectrum expected from the cumulative history of AGN (correcting for cosmological and source effects, e.g. jet orientation and beaming). Both emission scenarios yield neutrino fluxes well above limits set by IceCube (by " 4-10 6ˆa t 1 PeV, depending on the assumed jet models for neutrino production). This implies that: (i) Cen A might not be a typical neutrino source as commonly assumed; (ii) both neutrino production models overestimate the efficiency; (iii) neutrino luminosity scales with accretion power differently among AGN classes and hence does not follow X-ray luminosity universally; (iv) some AGN are neutrino-quiet (e.g. below a power threshold for neutrino production); (v) neutrino and X-ray emission have different duty cycles (e.g. jets alternate between baryonic and leptonic flows); or (vi) some combination of the above.

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“…With a redshift of z = 0.001825 and with a distance of d = 3.8 ± 0.1 Mpc (Harris et al 2010) the object is the brightest AGN at hard X-rays with f 20−100 keV 6 × 10 10 erg cm −2 s −1 (Beckmann et al 2009). For a review on Cen A, see Israel (1998). Owing to its brightness, Cen A has been a target for all main X-ray missions throughout the years, starting from the first 3σ detection during a balloon flight in 1969 (Bowyer et al 1970).…”

Section: Introductionmentioning

confidence: 99%

The hard X-ray emission of Centaurus A

Beckmann

Jean

Lubiński

et al. 2011

A&A

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Context. The radio galaxy Cen A has been detected all the way up to the TeV energy range. This raises the question about the dominant emission mechanisms in the high-energy domain. Aims. Spectral analysis allows us to put constraints on the possible emission processes. Here we study the hard X-ray emission, in order to distinguish between a thermal and a non-thermal inverse Compton process. Methods. Using hard X-ray data provided by INTEGRAL, we determined the cut-off of the power-law spectrum in the hard X-ray domain (3−1000 keV). In addition, INTEGRAL data are used to study the spectral variability. The extended emission detected in the gamma-rays by Fermi/LAT is investigated using the data of the spectrometre SPI in the 40−1000 keV range. Results. The hard X-ray spectrum of Cen A shows a significant cut-off at energies E C = 434 +106 −73 keV with an underlying power-law of photon index Γ = 1.73 ± 0.02. A more physical model of thermal Comptonisation (compPS) gives a plasma temperature of kT e = 206 ± 62 keV within the optically thin corona with Compton parameter y = 0.42 +0.09 −0.06 . The reflection component is significant at the 1.9σ level with R = 0.12 +0.09 −0.10 , and a reflection strength R > 0.3 can be excluded on a 3σ level. Time resolved spectral studies show that the flux, absorption, and spectral slope varied in the range f 3−30 keV = 1.2−9.2 × 10 −10 erg cm −2 s −1 , N H = 7−16 × 10 22 cm −2 , and Γ = 1.75−1.87. Extending the cut-off power-law or the Comptonisation model to the gamma-ray range shows that they cannot account for the high-energy emission. On the other hand, a broken or curved power-law model can also represent the data, therefore a non-thermal origin of the X-ray to GeV emission cannot be ruled out. The analysis of the SPI data provides no sign of significant emission from the radio lobes and gives a 3σ upper limit of f 40−1000 keV < ∼ 1.1 × 10 −3 ph cm −2 s −1 . Conclusions. While gamma-rays, as detected by CGRO and Fermi, are caused by non-thermal (jet) processes, the main process in the hard X-ray emission of Cen A is still not unambiguously determined, since it is either dominated by thermal inverse Compton emission or by non-thermal emission from the base of the jet.

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Centaurus A - NGC 5128

Cited by 316 publications

References 143 publications

The Upper Asymptotic Giant Branch of the Elliptical Galaxy Maffei 1 and Comparisons with M32 and NGC 5128

The Upper Asymptotic Giant Branch of the Elliptical Galaxy Maffei 1 and Comparisons with M32 and NGC 5128

High-energy neutrino fluxes from AGN populations inferred from X-ray surveys

The hard X-ray emission of Centaurus A

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