University Of Tasmania
Article_Lovell_2013_Micro_Scintil_Induced_MASIV.pdf (1011.44 kB)
Download file

The micro-arcsecond scintillation-induced variability (MASIV) survey. III. optical identifications and new redshifts

Download (1011.44 kB)
journal contribution
posted on 2023-05-17, 18:24 authored by Pursimo, T, Ojha, R, Jauncey, DL, Rickett, BJ, Dutka, MS, Koay, JY, James LovellJames Lovell, Bignall, HE, Kedziora-Chudczer, L, MacQuart, J-P
Intraday variability (IDV) of the radio emission from active galactic nuclei is now known to be predominantly due to interstellar scintillation (ISS). The MASIV (The Micro-Arcsecond Scintillation-Induced Variability) survey of 443 flat spectrum sources revealed that the IDV is related to the radio flux density and redshift. A study of the physical properties of these sources has been severely handicapped by the absence of reliable redshift measurements for many of these objects. This paper presents 79 new redshifts and a critical evaluation of 233 redshifts obtained from the literature. We classify spectroscopic identifications based on emission line properties, finding that 78% of the sources have broad emission lines and are mainly FSRQs. About 16% are weak lined objects, chiefly BL Lacs, and the remaining 6% are narrow line objects. The gross properties (redshift, spectroscopic class) of the MASIV sample are similar to those of other blazar surveys. However, the extreme compactness implied by ISS favors FSRQs and BL Lacs in the MASIV sample as these are the most compact object classes. We confirm that the level of IDV depends on the 5 GHz flux density for all optical spectral types. We find that BL Lac objects tend to be more variable than broad line quasars. The level of ISS decreases substantially above a redshift of about two. The decrease is found to be generally consistent with ISS expected for beamed emission from a jet that is limited to a fixed maximum brightness temperature in the source rest frame.


Publication title

Astrophysical Journal



Article number









School of Natural Sciences


Univ Chicago Press

Place of publication

1427 E 60th St, Chicago, USA, Il, 60637-2954

Rights statement

Copyright 2013 The American Astronomical Society

Repository Status

  • Open

Socio-economic Objectives

Expanding knowledge in the physical sciences