Absorption by neutral hydrogen and ionized magnesium in quasi-stellar objects and BL Lacertae objects

ABSTRACT Under the assumption that galaxies and quasi-stellar objects (QSOs) dominate the metagalactic ultraviolet (UV) background, it is shown that at high redshifts, fluctuations in the UV background are dominated by QSO shot noise and have an autocorrelation length of a few to several comoving Mpcs, depending on the bright end of the QSO luminosity function. The correlations create long-range spatial coherence in the neutral hydrogen fraction. Using a semi-analytic model, it is demonstrated that the coherence may account for the broad distribution in effective optical depths measured in the Lyα forest spectra of background QSOs, for line-of-sight segments of comoving length $50\, h^{-1}$ Mpc at redshifts 5 < z < 6. Capturing the fluctuations in a numerical simulation requires a comoving box size of ∼1 Gpc, although a box half this size may be adequate if sufficient random realizations of the QSO population are performed.

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The properties of the dusty inner regions of nearby QSOs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320002665 ◽

2019 ◽

Vol 15 (S356) ◽

pp. 95-95

Author(s):

Itziar Aretxaga

Keyword(s):

Star Formation ◽

Polycyclic Aromatic Hydrocarbon ◽

Aromatic Hydrocarbon ◽

Stellar Objects ◽

X Ray ◽

Mir Spectroscopy ◽

Polycyclic Aromatic ◽

Quasi Stellar Objects

AbstractWe present MIR spectroscopy and photometry obtained with CanariCam on the 10.4 m Gran Telescopio CANARIAS for a sample of 20 nearby, MIR bright and X-ray luminous quasi-stellar objects (QSOs). We find that for the majority of QSOs the MIR emission is unresolved at angular scales ∼0.3 arcsec. We derive the properties of the dusti tori that surround the nucleus based on these observations and find significant differences in the parameters compared with a sample of Seyfert 1 and 2 nuclei. We also find evidence for polycyclic aromatic hydrocarbon (PAH) features in the spectra, indicative of star formation, more centrally peaked (on scales of a few hundred pc) than previously believed.

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Classification of Compact Objects: QSS, QSOs, N-Type and Compact Galaxies, Seyfert and Galactic Nuclei

Symposium - International Astronomical Union ◽

10.1017/s0074180900005386 ◽

1972 ◽

Vol 44 ◽

pp. 97-103

Author(s):

W. W. Morgan

Keyword(s):

Galactic Nuclei ◽

Seyfert Galaxy ◽

Classification Criteria ◽

Compact Objects ◽

Stellar Objects ◽

Quasi Stellar Objects ◽

Compact Galaxies

Some methods currently in use for the classification of the optical forms of the ‘compact’ galaxies and quasi-stellar objects are reviewed. It is shown that the category ‘Seyfert Galaxy’ is basically a spectroscopic (rather than a form) classification.An optical form-classification is described which is, in principle, identical with published classification criteria for QSO, N-type, and compact objects. The importance of maintaining rigid form-standards is emphasized.

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