The High A(V) Quasar Survey

The NOT/NTT High A(V) QSO (HAQ) Survey is a spectroscopic follow-up of candidate quasars selected using photometry from the Sloan Digital Sky Survey (SDSS) and the UKIRT Infrared Deep Sky Survey (UKIDSS). The survey is carried out with the Nordic Optical Telescope (NOT) on La Palma, Canarias, Spain and the New Technology Telescope (NTT) on ESOs La Silla Observatory in Chile. The primary goal of the survey is to look for missing quasars reddened by dusty, foreground galaxies. These would be missed by the optical color criteria utilized by SDSS-I/II to identify quasars and hence introduce a possible bias in the samples of quasar absorbers, specifically here damped Lyman-α absorbers.

HAQ: Technical Description

The candidates are selected from the photometry in the overlapping parts of the SDSS and UKIDSS surveys. We combine the optical and infrared photometry in order to select unidentified point sources that are consistent with QSOs being reddened by dust. After the first sample was chosen (data and selection are presented by Fynbo et al. 2013) we revised the color selection to effectively exclude contaminating objects, e.g., red galaxies or cold stars. Below are the color criteria used in the revised sample all on the AB magnitude system:

    J−K > 0 ;   H−K > 0 ;   J−H < 0.4 ;   0.5 < g−r < 1.0 ;   0.1 < r−i < 0.7
Out of roughly 570 targets selected this way we have observed 159 targets (see Data page).
All 159 targets were observed at the NOT during 2012, 2013, and 2014 with the Andalucia Faint Object Spectrograph and Camera (ALFOSC) using a setup providing low resolution (R≈350) spectroscopy in the wavelength range 3800−9000Å.



eHAQ: The Extended High A(V) Quasar Survey

Building on the experience of the HAQ survey, we have expanded the survey to specifically search for high-redshift candidates using mid-infrared photometry from WISE. Below are the color criteria used in the revised sample photometry from SDSS and UKIDSS is on the AB magnitude system, WISE photometry is on the Vega system:

    g−r > 0.5 ;   r−i > 0.4   ;   J−K > −0.05 ;
    W1−W2 > 0.6 ;   2.0 < W2−W3 < 4.0 ;

    for W2−W3 < 2.85 : W1−W2 < 1.0 ;
    for W2−W3 ≥ 2.85 : W1−W2 < 1.2 x (W2−W3) − 2.42;
The details of the target selection and the subsequent spectroscopic observations are presented in the work by Krogager et al. (2016). In total, 108 candidates were observed out of 1073 targets.


Publications

    "Optical/Near-infrared Selection of Red Quasi-stellar Objects:
    Evidence for Steep Extinction Curves toward Galactic Centers?    "
    Fynbo, Krogager, Venemans, et al. (2013), ApJS, 204, 6
    "The High A(V) Quasar Survey: Reddened quasi-stellar objects selected from optical/near-infrared photometry - II"
    Krogager, Geier, Fynbo, et al. (2015), ApJS, 217, 5
    "Extinction curve template for intrinsically reddened quasars "
    Zafar, Møller, Watson, et al. (2015), A&A, 584, 100
    "A quasar reddened by a sub-parsec-sized, metal-rich and dusty cloud in a damped Lymanα absorber at z = 2.13 "
    Krogager, Fynbo, Noterdaeme, et al. (2016), MNRAS, 455, 2698
    "Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths"
    Heintz, Fynbo, Møller, et al. (2016), A&A, 595, 13
    "The Extended High A(V) Quasar Survey: Searching for Dusty Absorbers toward Mid-infrared-selected Quasars"
    Krogager, Fynbo, Heintz, et al. (2016), ApJ, 832, 49
    "The High A(V) Quasar Survey: A z = 2.027 metal-rich damped Lyman-α absorber towards a red quasar at z = 3.21 "
    Fynbo, Krogager, Heintz, et al. (2017), A&A, 606, 13
    "A quasar hiding behind two dusty absorbers. Quantifying the selection bias of metal-rich, damped Lyα absorption systems"
    Heintz, Fynbo, Ledoux, et al. (2018), A&A, 615, 43
    "The effect of dust bias on the census of neutral gas and metals in the high-redshift Universe due to SDSS-II quasar colour selection"
    Krogager, Fynbo, Møller, et al. (2019), MNRAS, 486, 4377
    "Gaia-assisted selection of a quasar reddened by dust in an extremely strong damped Lyman-α absorber at z = 2.226 "
    Geier, Heintz, Fynbo, et al. (2019), A&A, 625, 9

Created by Jens-Kristian Krogager
Dark Cosmology Centre, Copenhagen University & ESO, Santiago, Chile

Oct 14, 2020