Research Note

The molecular gas content of ULIRG type 2 quasars at z < 1^⋆

¹ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: mrm@iaa.es
² Centro de Astrobiología (INTA-CSIC), Carretera de Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
³ Centro de Astrofisica, Universidade do Porto, rua das Estrelas, 4150-762 Porto, Portugal
⁴ Dept. of Earth and Space Science, Onsala Space Observatory, Chalmers U. of Technology, 43992 Onsala, Sweden
⁵ Observatorio Astronómico Nacional (OAN)-Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain

Received: 7 November 2013
Accepted: 26 February 2014

Abstract

We present new results of CO(1–0) spectroscopic observations of four Sloan Digital Sky Survey (SDSS) type 2 quasars (QSO2) at z ~ 0.3, observed with the 30-m IRAM radio telescope. The QSO2 have infrared luminosities in the ultra-luminous infrared galaxies (ULIRG) regime. We confirm the CO(1–0) detection in one of our four QSO2, SDSS J1543-00, with L′_CO and M_H2 (1.2 ± 0.2) × 10¹⁰ K km s^-1  pc² and (9.4 ± 1.4) × 10⁹ M _⊙, respectively. The full width at half maximum (FWHM) of the CO(1–0) line is =575 ± 102 km s^-1. No CO(1–0) emission is detected in SDSS J0903+02, SDSS J1337-01, SDSS J1520-01 above 3 sigma, yielding upper limits on M(H₂) ~ 9.6, 4.3 and 5.1 × 10⁹ M_⊙, respectively. We expand previous studies of the molecular gas content of intermediate z QSO2 into the ULIRG regime. Taking into account nine QSO2 at z ~ 0.3–1.0 from the literature, we discuss the location of the 13 ULIRG QSO2 at z < 1 with available L′_CO measurements in the L′_CO vs. z and L′_CO vs. L_FIR diagrams, in comparison with other QSO1 and ULIRG star forming samples.