Optical follow-up of BL Lac candidates in the 2BL sample

Nesci, R.; Sclavi, S.; Massaro, E.

doi:10.1051/0004-6361:20042391

Cited by 4 publications

(5 citation statements)

References 34 publications

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“…We are already faced with this problem when considering the sample of "optically selected" BL Lac candidates by Londish et al (2002), as a byproduct of the much wider 2QZ sample of QSOs (Croom et al 2001). Nesci et al (2005) searched for optical variability of a subsample of the 2QZ-BL sources and found that only a few of them have significant brightness changes, including all the radio-loud ones. In a recent paper, Londish et al (2007) reported a further analysis of an expanded and revised sample of potential optically identified BL Lacs and concluded that there can be no significant population of radio-quiet BL Lac objects.…”

Section: Blazar Surveysmentioning

confidence: 99%

Roma-BZCAT: a multifrequency catalogue of blazars

Massaro¹,

Giommi

Leto

et al. 2008

A&A

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454

528

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We present a new catalogue of blazars based on multifrequency surveys and on an extensive review of the literature. Blazars are classified as BL Lacertae objects, as flat spectrum radio quasars or as blazars of uncertain/transitional type. Each object is identified by a root name, coded as BZB, BZQ and BZU for these three subclasses respectively, and by its coordinates. This catalogue is being built as a tool useful for the identification of the extragalactic sources that will be detected by present and future experiments for X and gamma-ray astronomy, like Swift, AGILE, Fermi-GLAST and Simbol-X. An electronic version is available from the ASI Science Data Center web site at http://www.asdc.asi.it/bzcat.

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Section: Blazar Surveysmentioning

confidence: 99%

Roma-BZCAT: a multifrequency catalogue of blazars

Massaro¹,

Giommi

Leto

et al. 2008

A&A

Self Cite

454

528

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“…Follow-up spectroscopy and NIR-imaging has revealed that most of the sources are either stellar or extragalactic with faint, but broad emission features. Only a very few good BL Lac candidates remain (Nesci et al 2005;Londish et al 2007). On the other hand, Londish et al (2004) have found an intriguing object within their sample, which could potentially be a radioquiet BL Lac object, a class of objects not believed to exist (e.g.…”

Section: Introductionmentioning

confidence: 99%

Polarimetry of optically selected BL Lacertae candidates from the SDSS

Heidt¹,

Nilsson

2011

A&A

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We present and discuss polarimetric observations of 182 targets drawn from an optically selected sample of 240 probable BL Lac candidates out of the SDSS compiled by Collinge et al. (2005, AJ, 129, 2542. In contrast to most other BL Lac candidate samples extracted from the SDSS, its radio-and/or X-ray properties have not been taken into account for its derivation. Thus, because its selection is based on optical properties alone, it may be less prone to selection effects inherent in other samples derived at different frequencies, so it offers a unique opportunity to extract the first unbiased BL Lac luminosity function that is suitably large in size. We found 124 out of 182 targets (68%) to be polarized, 95 of the polarized targets (77%) to be highly polarized (>4%). The lowfrequency peaked BL Lac candidates in the sample are on average only slightly more polarized than the high-frequency peaked ones. Compared to earlier studies, we found a high duty cycle in high polarization (∼66 +2 −14 % to be >4% polarized) in high-frequency peaked BL Lac candidates. This may come from our polarization analysis, which minimizes the contamination by host galaxy light. No evidence of radio-quiet BL Lac objects in the sample was found. Our observations show that the probable sample of BL Lac candidates of Collinge et al. (2005) indeed contains a large number of bona fide BL Lac objects. High S /N spectroscopy and deep X-ray observations are required to construct the first luminosity function of optically selected BL Lac objects and to test more stringently for any radio-quiet BL Lac objects in the sample.

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“…They searched over ∼10 3 deg 2 and recovered 7 confident BL Lac objects. All 7 objects were additionally identified with radio and X-ray sources (post-selection), and they also showed optical flux variations in a photometric monitoring campaign over (Nesci et al 2005). An additional object (z = 0.494) is identified as a radio-quiet/weak BL Lac candidate (Londish et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Optically Selected Bl Lacertae Candidates From the Sloan Digital Sky Survey Data Release Seven

Plotkin

Anderson

Brandt

et al. 2010

The Astronomical Journal

105

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We present a sample of 723 optically selected BL Lac candidates from the SDSS DR7 spectroscopic database encompassing 8250 deg 2 of sky; our sample constitutes one of the largest uniform BL Lac samples yet derived. Each BL Lac candidate has a high-quality SDSS spectrum from which we determine spectroscopic redshifts for ∼60% of the objects. Redshift lower limits are estimated for the remaining objects utilizing the lack of host galaxy flux contamination in their optical spectra; we find that objects lacking spectroscopic redshifts are likely at systematically higher redshifts. Approximately 80% of our BL Lac candidates match to a radio source in FIRST/NVSS, and ∼40% match to a ROSAT X-ray source. The homogeneous multiwavelength coverage allows subdivision of the sample into 637 radio-loud BL Lac candidates and 86 weak-featured radio-quiet objects. The radio-loud objects broadly support the standard paradigm unifying BL Lac objects with beamed radio galaxies. We propose that the majority of the radio-quiet objects may be lower-redshift (z < 2.2) analogs to high-redshift weak line quasars (i.e., AGN with unusually anemic broad emission line regions). These would constitute the largest sample of such objects, being of similar size and complementary in redshift to the samples of high-redshift weak line quasars previously discovered by the SDSS. However, some fraction of the weak-featured radio-quiet objects may instead populate a rare and extreme radio-weak tail of the much larger radio-loud BL Lac population. Serendipitous discoveries of unusual white dwarfs, high-redshift weak line quasars, and broad absorption line quasars with extreme continuum dropoffs blueward of rest-frame 2800Å are also briefly described.12 Radio-quiet quasars are commonly defined as having radio to optical flux ratios R < 10 (e.g., see Kellermann et al. 1989;Stocke et al. 1992). Throughout this paper, we adopt the approximately similar αro < 0.2, where αro is the radio-to-optical broadband spectral index: αro = − log(Lo/Lr)/5.08, where Lo and Lr are optical and radio specific luminosities at rest-frames 5000Å and 5 GHz, respectively (Stocke et al. 1985).

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Optical follow-up of BL Lac candidates in the 2BL sample

Cited by 4 publications

References 34 publications

Roma-BZCAT: a multifrequency catalogue of blazars

Roma-BZCAT: a multifrequency catalogue of blazars

Polarimetry of optically selected BL Lacertae candidates from the SDSS

Optically Selected Bl Lacertae Candidates From the Sloan Digital Sky Survey Data Release Seven

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