A search for damped Lyman-alpha systems towards radio-loud quasars I: The optical survey

Abstract

We present the results from the optical component of a survey for damped Lyman-alpha systems (DLAs) towards radio-loud quasars. Our quasar sample is drawn from the Texas radio survey with the following primary selection criteria: z_em > 2.4, optical magnitudes B < 22 and 365 MHz flux density S_365 > 400 mJy. We obtained spectra for a sample of 45 QSOs with the William Herschel Telescope, Very Large Telescope and Gemini-North, resulting in a survey redshift path Delta z = 38.79. We detect nine DLAs and one sub-DLA with a mean absorption redshift <z> = 2.44. The DLA number density is n(z) = 0.23^{+0.11}_{-0.07}, in good agreement with the value derived for DLAs detected in the Sloan Digital Sky Survey at this redshift. The DLA number density of our sample is also in good agreement with optically-complete radio-selected samples, supporting previous claims that n(z) is not significantly affected by dust obscuration bias. We present N(HI) column density determinations and metal line equivalent width measurements for all our DLAs. The low frequency flux density selection criterion used for the quasar sample implies that all absorbers will be suitable for follow-up absorption spectroscopy in the redshifted HI 21 cm line. A following paper (Kanekar et al.) will present HI 21 cm absorption studies of, and spin temperature determinations for, our DLA sample.

Accepted for publication in the MNRAS

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Cited by in corpus (6)

• Damped Lyman Alpha Systems in Galaxy Formation Simulations
• Inspiraling Halo Accretion Mapped in Lyman-$\alpha$ Emission around a $z\sim 3$ Quasar
• Giant Metrewave Radio Telescope detection of two new HI 21cm absorbers at $z\approx 2$
• Evolution of cold gas at 2<z<5: a blind search for HI and OH absorption lines towards mid-infrared color selected radio-loud AGNs
• MALS SALT-NOT survey of MIR-selected powerful radio-bright AGN at 0<z<3.5
• A search for H$\alpha$ emission in high-metallicity damped Lyman-$\alpha$ systems at $z\sim 2.4$