J/A+A/569/A95 SDSS optically selected BL Lac candidates (Kuegler+, 2014)
Properties of optically selected BL Lacertae candidates from the SDSS.
Kuegler S.D., Nilsson K., Heidt J., Esser J., Schultz T.
<Astron. Astrophys., 569, A95-95 (2014)>
=2014A&A...569A..95K 2014A&A...569A..95K
ADC_Keywords: Active gal. nuclei ; BL Lac objects ; Polarization
Keywords: galaxies: active - BL Lacertae objects: general - polarization
Abstract:
Deep optical surveys open the avenue for finding large numbers of BL
Lac objects that are hard to identify because they lack the unique
properties classifying them as such. While radio or X-ray surveys
typically reveal dozens of sources, recent compilations based on
optical criteria alone have increased the number of BL Lac candidates
considerably. However, these compilations are subject to biases and
may contain a substantial number of contaminating sources. In this
paper we extend our analysis of 182 optically selected BL Lac object
candidates from the SDSS with respect to an earlier study. The main
goal is to determine the number of bona fide BL Lac objects in this
sample. We examine their variability characteristics, determine their
broad-band radio-UV spectral energy distributions (SEDs), and search
for the presence of a host galaxy. In addition we present new optical
spectra for 27 targets with improved signal-to-noise ratio with
respect to the SDSS spectra. At least 59% of our targets have shown
variability between SDSS DR2 and our observations by more than
0.1-0.27mag depending on the telescope used. A host galaxy was
detected in 36% of our targets. The host galaxy type and luminosities
are consistent with earlier studies of BL Lac host galaxies. Simple
fits to broad-band SEDs for 104 targets of our sample derived
synchrotron peak frequencies between 13.5≤log10(νpeak)≤16
with a peak at log10∼14.5. Our new optical spectra do not reveal any
new redshift for any of our objects. Thus the sample contains a large
number of bona fide BL Lac objects and seems to contain a substantial
fraction of intermediate-frequency peaked BL Lacs.
Description:
The data that we use for variability and host galaxy analysis were
presented in Paper I (Heidt & Nilsson, 2011A&A...529A.162H 2011A&A...529A.162H, Cat.
J/A+A/529/A162).
Alltogether, 123 targets were observed at the ESO New Technology
Telescope (NTT) on La Silla, Chile during Oct. 2-6, 2008 and Mar.
28-Apr. 1, 2009. The observations were made with the EFOSC2
instrument through a Gunn-r filter (#786).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 93 66 Host galaxy results for the bulge model
tablea2.dat 90 195 Main properties objects discussed in Heidt & Nilsson
(2011, J/A+A/529/A162) and the present work
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See also:
J/AJ/129/2542 : BL Lac from SDSS (Collinge+, 2005)
J/A+A/529/A162 : Optically selected BL Lac cand. polarimetry (Heidt+, 2011)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- SDSS Target SDSS designation (HHMMSS.ss+DDMMSS.s)
20- 22 A3 --- Tel Telescope used: CA=Calar Alto 2.2m,
NOT=Nordic Optical Telescope, NTT at ESO
24- 29 F6.4 --- z [0.04/0.71]?=- Redshift, listed only when
the redshift determination is secure
31- 35 F5.2 mag rmag.c ?=- SDSS r' magnitude of the core mc
37- 40 F4.2 mag e_rmag.c ? rms uncertainty in rmag.c
42- 46 F5.2 mag rmag.g r' magnitude of the host galaxy mg
48- 51 F4.2 mag e_rmag.g rms uncertainty in rmag.g
53- 55 F3.1 arcsec re [0.5/8.4] Effective radius re
57- 59 F3.1 arcsec e_re rms uncertainty on re
61- 64 F4.2 --- ell.g [0/1] Ellipticity of host galaxy εg
66- 68 I3 deg pa.g Position angle of the host galaxy θg
70 A1 --- T.g [BU] Host galaxy type: B=bulge, U=undefined
72- 75 F4.2 --- fc [0/1] Fraction of the core flux in total flux
77- 80 F4.2 --- e_fc rms uncertainty on fc
81 A1 --- u_fc [)] Uncertainty flag on fc
83- 88 F6.2 mag rMAG ?=- Absolute r' magnitude Mr'
90- 93 F4.1 kpc Re ?=- Effective radius in kpc
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- SDSS Target SDSS designation (HHMMSS.ss+DDMMSS.s)
20 A1 --- l_z Limit flag on z
21- 26 F6.4 --- z [0.04/5.1]?=- SDSS spectroscopic redshift
28 A1 --- u_z [u] SDSS z flag (u for uncertain)
30 A1 --- l_aox Limit flag on aox
31- 35 F5.2 --- aox Spectral index Optical/X-ray αox (1)
37 A1 --- l_aro Limit flag on aro
38- 41 F4.2 --- aro ?=- Spectral index Radio/Optical αro (1)
43 A1 --- l_Pol Limit flag on Pol
44- 48 F5.2 % Pol ?=- Polarisation
50- 53 F4.2 % e_Pol ?=- rms uncertainty on Pol
55- 59 F5.3 mag VL [0.03/0.15] Variability limit
61 A1 --- f_Vamp [-] Variability amplitude is negative?
62- 66 F5.3 mag Vamp Variability amplitude
68 A1 --- l_fc Limit flag on fc
69- 72 F4.2 --- fc Core (AGN) fraction over the total flux
fraction as derived from the host galaxy fits
74- 77 F4.2 --- e_fc ?=- rms uncertainty on fc
79- 83 F5.2 [Hz] lognuP ?=- Peak frequency determined from SED fits
85- 90 A6 --- f_lognuP Flag for uncertain lognuP with respect to
the SED fits (2)
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Note (1): All these properties are from Collinge et al. (2005AJ....129.2542C 2005AJ....129.2542C,
Cat. J/AJ/129/2542).
Note (2): The flags indicate whether the peak estimate is uncertain due to the
shallowness of the radio data:
radio = if only one or no radio point available
galaxy = due to the presence of a strong host galaxy if the host galaxy
fraction of the total flux exceeds 0.5
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History:
From electronic version of the journal
References:
Heidt & Nilsson, Paper I 2011A&A...529A.162H 2011A&A...529A.162H, Cat. J/A+A/529/A162
(End) Patricia Vannier [CDS] 17-Nov-2014