2015A&A...574A.101M


Query : 2015A&A...574A.101M

2015A&A...574A.101M - Astronomy and Astrophysics, volume 574A, 101-101 (2015/2-1)

The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343.

MURIEL H., DONZELLI C., ROVERO A.C. and PICHEL A.

Abstract (from CDS):

The BL-Lac blazar PKS 0447-439 is one of the brightest HE gamma-ray sources that were first detected by Fermi-LAT. It was also detected by H.E.S.S. at VHE gamma-rays, which allowed constraining the redshift of PKS 0447-439 by considering the attenuation caused by gamma-ray interactions with ambient photons in the extragalactic background light (EBL). This constraint agreed with color-magnitude and spectroscopic redshift constraints (0.179<z<0.56). Recently, however, a much higher redshift was proposed for this blazar (z>1.2). This value was debated because if true, it would imply either that the relevant absorption processes of gamma-rays are not well understood or that the EBL is dramatically different from what is believed today. This high redshift was not confirmed by three independent new spectroscopic observations at high signal-to-noise ratios. The scenario is clear evidence of the difficulties in estimating the redshift of BL-Lac objects, whose optical spectra are typically featureless. Neither of the estimated redshifts for PKS 0447-439 are confirmed as yet. Given that BL-Lac are typically hosted by elliptical galaxies, which in turn are associated with groups, we aim to find the host group of galaxies of PKS 0447-439. The ultimate goal is to estimate a redshift for this blazar. Spectra of twenty-one objects in the field of view of PKS 0447-439 were obtained with the Gemini Multi-Object Spectrograph. Based on the redshifts and coordinates of these galaxies, we searched for groups of galaxies. Using a deep catalog of groups, we studied the probability of finding by chance a group of galaxies in the line of sight of PKS 0447-439. We identified a group of galaxies that was not previously cataloged at z=0.343 with seven members, a virial radius of 0.42Mpc, and a velocity dispersion of 622km/s. We found that the probability of the host galaxy of PKS 0447-439 to be a member of the new group is>97%. Therefore, we propose to adopt z=0.343±0.002 as the most likely redshift for PKS 0447-439.

Abstract Copyright:

Journal keyword(s): BL Lacertae objects: individual: PKS 0447-439 - galaxies: distances and redshifts - galaxies: groups: general

Nomenclature: Table 1: [MDR2015] NN (Nos 1-22).

Simbad objects: 26

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Number of rows : 26
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 QSO B0218+357 QSO 02 21 05.4920852208 +35 56 13.848581904   20.0 20.0 19.60   ~ 530 3
2 [MDR2015] 1 G 04 49 12.445 -43 48 26.81           ~ 1 0
3 [MDR2015] 3 G 04 49 14.687 -43 50 09.11           ~ 1 0
4 [MDR2015] 2 * 04 49 15.279 -43 48 18.28           ~ 1 0
5 [MDR2015] 10 G 04 49 19.931 -43 50 33.49           ~ 1 0
6 [MDR2015] 7 G 04 49 20.393 -43 49 08.37           ~ 1 0
7 [MDR2015] 6 G 04 49 21.540 -43 50 32.75           ~ 1 0
8 [MDR2015] 5 G 04 49 22.458 -43 49 36.00           ~ 1 0
9 [MDR2015] 8 G 04 49 23.399 -43 50 28.13           ~ 1 0
10 [MDR2015] 9 G 04 49 23.929 -43 49 15.51           ~ 1 0
11 [MDR2015] 4 ? 04 49 24.655 -43 50 10.06           ~ 1 0
12 6dFGS gJ044924.7-435009 BLL 04 49 24.6981911928 -43 50 08.960970948 14.95 17.52 15.24 16.27   ~ 145 1
13 [MDR2015] 18 G 04 49 26.109 -43 50 45.69           ~ 1 0
14 [MDR2015] 19 G 04 49 27.256 -43 49 17.23           ~ 1 0
15 [MDR2015] 15 G 04 49 27.931 -43 52 26.44           ~ 1 0
16 [MDR2015] 14 G 04 49 28.429 -43 52 22.24           ~ 1 0
17 [MDR2015] 17 G 04 49 29.962 -43 49 59.50           ~ 1 0
18 [MDR2015] 11 * 04 49 30.571 -43 51 44.91           ~ 1 0
19 [MDR2015] 12 G 04 49 31.161 -43 50 18.97           ~ 1 0
20 [MDR2015] 13 G 04 49 32.1695746296 -43 47 58.652443716           ~ 1 0
21 [MDR2015] 16 ? 04 49 33.070 -43 49 27.06           ~ 1 0
22 [MDR2015] 20 G 04 49 34.382 -43 52 33.67           ~ 1 0
23 [MDR2015] 21 G 04 49 35.463 -43 47 52.18           ~ 1 0
24 [MDR2015] 22 * 04 49 36.763 -43 49 36.69           ~ 1 0
25 NAME COSMOS Field reg 10 00 28.60 +02 12 21.0           ~ 2591 0
26 NGC 7793 GiG 23 57 49.7540045856 -32 35 27.701550744 10.26 9.74 9.28 9.06 9.7 ~ 1035 2

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2022.10.02-03:02:21

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