Journal Article

Interactions, star formation and extended nebulae in SDSS type 2 quasars at 0.3 ≤ <i>z</i> ≤ 0.6*

M. Villar-Martín, C. Tadhunter, A. Humphrey, R. Fraga Encina, R. González Delgado, M. Pérez Torres and A. Martínez-Sansigre

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 1, pages 262-278
Published in print September 2011 | ISSN: 0035-8711
Published online August 2011 | e-ISSN: 1365-2966 | DOI:
Interactions, star formation and extended nebulae in SDSS type 2 quasars at 0.3 ≤ z ≤ 0.6*

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We present long-slit spectroscopy and imaging data obtained with the Focal Reducer and Low Dispersion Spectrograph (FORS2) on the Very Large Telescope of 13 optically selected type 2 quasars at z ∼ 0.3–0.6 from the original sample of Zakamska et al. (2003). The sample is likely to be affected by different selection biases. We investigate the evidence for (i) mergers/interactions (ii) star formation activity in the neighbourhood of the quasars and (iii) extended emission-line regions (EELRs) and their nature. Evidence for mergers/interactions is found in 5/13 objects. This is a lower limit for our sample, given the shallowness of most of our continuum images. Although active galactic nucleus (AGN) photoionization cannot be totally discarded, line ratios consistent with stellar photoionization are found in general in companion galaxies/knots/nuclei near these same objects. On the contrary, the gas in the neighbourhood of the quasar nucleus shows line ratios inconsistent with H ii galaxies and typical of AGN photoionized nebulae. A natural scenario to explain the observations is that star formation is ongoing in companion galaxies/knots/nuclei, possibly triggered by the interactions. These systems are, therefore, composite in their emission-line properties showing a combination of AGN and star formation features.

EELRs have been found in 7/13 objects, although this fraction might be higher if a complete spatial coverage around the quasars was performed. The sizes vary between a few and up to 64 kpc. In general, the EELR apparently consists of an extended nebula associated with the quasar. In at least one case, the EELR is associated with ionized tidal features.

Keywords: galaxies: active; quasars: emission lines; quasars: general

Journal Article.  11858 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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