The Extended High A(v) Quasar Survey: Searching for Dusty Absorbers Toward Mid-Infrared-Selected Quasars

Møller

et al. 2020

A&A

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We report on the discovery of a peculiar Broad Absorption Line (BAL) quasar identified in our Gaia-assisted survey of red quasars. The systemic redshift of this quasar was difficult to establish due to the absence of conspicuous emission lines. Based on deep and broad BAL troughs (at least Si iv, C iv, and Al iii), a redshift of z = 2.41 was established under the assumption that the systemic redshift can be inferred from the red edge of the BAL troughs. However, we observe a weak and spatially-extended emission line at 4450 Å most likely due to Lyman-α emission, which implies a systemic redshift of z = 2.66 if correctly identified. There is also evidence for the onset of Lyman-α forest absorption bluewards of 4450 Å and evidence for Hα emission in the K-band consistent with a systemic redshift of z = 2.66. If this redshift is correct, the quasar is an extreme example of a detached low-ionisation BAL quasar. The BAL lines must originate from material moving with very large velocities ranging from 22 000 to 40 000 km s −1 . To our knowledge, this is the first case of a systemic-redshift measurement based on extended Lyman-α emission for a BAL quasar, a method that should also be useful in cases of sufficiently distant BL Lac quasars without systemic-redshift information.

Section: The Not Spectrummentioning

confidence: 55%

Gaia-assisted discovery of a detached low-ionisation BAL quasar with very large ejection velocities

Møller

et al. 2020

A&A

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“…At red g−r colours (g − r > 1), the zero-proper-motion sources have optical colours consistent with M or G dwarf stars. While some of these are likely to be stellar contaminations, removing these candidates will also exclude dust-reddened quasars and broad absorption line (BAL) quasars from the sample, which are found to have very red optical colours and to be systematically missing in most existing quasar samples (Fynbo et al 2013;Krogager et al 2015Krogager et al , 2016Ross et al 2015;Krawczyk et al 2015).…”

Section: Selection Efficiency and Completenessmentioning

confidence: 99%

Unidentified quasars among stationary objects from Gaia DR2

Høg

et al. 2018

A&A

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Here we apply a technique selecting quasar candidates purely as sources with zero proper motions in the Gaia data release 2 (DR2). We demonstrate that this approach is highly efficient toward high Galactic latitudes with 25% contamination from stellar sources. Such a selection technique offers very pure sample completeness, since all cosmological point sources are selected regardless of their intrinsic spectral properties within the limiting magnitude of Gaia. We carry out a pilot-study, defining a sample compiled by including all Gaia-DR2 sources within one degree of the north Galactic pole (NGP) selected to have proper motions consistent with zero within 2σ uncertainty. By cross-matching the sample to the optical Sloan Digital Sky Survey (SDSS) and the mid-infrared (MIR) AllWISE photometric catalogues, we investigate the colours of each of our sources. We determine the efficiency of our selection by comparison with previously spectroscopically confirmed quasars. The majority of the zero-proper-motion sources selected here have optical to MIR colours consistent with known quasars. The remaining population may be contaminating stellar sources, but some may also be quasars with colours similar to stars. Spectroscopic follow-up of the zero-proper-motion sources is needed to unveil such a hitherto hidden quasar population. This approach has the potential to allow substantial progress on many important questions concerning quasars, such as determining the fraction of dust-obscured quasars, the fraction of broad absorption line (BAL) quasars, and the metallicity distribution of damped Lyman-α absorbers. The technique could also potentially reveal new types of quasars or even new classes of cosmological point sources.

“…Motivated by the object studied in Fynbo et al (2011) the High A V Quasar Survey (HAQ; Fynbo et al 2013;Krogager et al 2015Krogager et al , 2016a for reddened quasars was initiated in 2011 with the objective of measuring the frequency of sources that are reddened out of the quasar selection criteria typically adopted in surveys such as SDSS (e.g. Schneider et al 2010).…”

Section: Introductionmentioning

confidence: 99%

The HighA_VQuasar Survey: Az = 2.027 metal-rich damped Lyman-αabsorber towards a red quasar atz = 3.21

Krogager

et al. 2017

A&A

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It is important to understand the selection effects behind the quasar samples to fully exploit the potential of quasars as probes of cosmic chemical evolution and the internal gas dynamics of galaxies; in particular, it is vital to understand whether the selection criteria exclude foreground galaxies with certain properties, most importantly a high dust content. Here we present spectroscopic follow-up from the 10.4 m GTC telescope of a dust-reddened quasar, eHAQ0111+0641, from the extended High A V Quasar (HAQ) survey. We find that the z = 3.21 quasar has a foreground damped Lyman-α absorber (DLA) at z = 2.027 along the line of sight. The DLA has very strong metal lines due to a moderately high metallicity with an inferred lower limit of 25% of the solar metallicity, but a very large gas column density along the line of sight in its host galaxy. This discovery is further evidence that there is a dust bias affecting the census of metals, caused by the combined effect of dust obscuration and reddening, in existing samples of z > 2 DLAs. The case of eHAQ0111+0641 illustrates that dust bias is not only caused by dust obscuration, but also dust reddening.