All sources in the two samples satisfy the following criteria: (1) Declination: 20 – 70, to obtain the best (u,v) coverage(2) Redshift (z): 0.2 – 2.0(3) Flux density S178 MHz : 10 Jy(4) Largest angular size (arcsec): 10 – 100

A Multi-Wavelength Observational Study of FRIIs Radio Galaxies and Quasars

Ilias M. FerniniDepartment of Physics, E-mail: ifernini@uaeu.ac.ae

U. A. E. University, Al-Ain, P.O.Box: 17551, United Arab Emirates

Two statistically complete samples of 13 Fanaroff-Riley (1974) type II (FR II) radio galaxies (RGs) and 13 FR II quasars (QSRs) were observed at 3.6, 6, and 20 cm. At 6 cm, the two samples were compared in terms of the 1989 unification scheme of Barthel. Definite radio jets were detected in two RGs and candidate jets or jet components in four other RGs. These results are in strong contrast to the quasars sample, where radio jets were found in all QRSs in addition to six candidate counterjets. This jet detection is consistent with the prediction of the unification scheme. Using the 6 and 20 cm observations, the two samples were compared in terms of their depolarization properties. We found no statistically significant difference between the distribution of depolarization asymmetries in the RGs and QSRs. At 3.6 cm, the RGs and QSRs were compared in terms of the compactness and location of their hot spots on the jet and counterjet side. We have compared the largest linear size and the smallest linear size of each hot spot. The overall picture is that the QSRs hot spots are slightly more compact than the RG hot spots. In terms of location, more hot spots are edged than recessed with the jetted sources showing more recessed hot spots than the unjetted sources. We will discuss the importance of these multi-wavelength observations in terms of their implications for models of radio sources.

In terms of the ratio DPR, our statistical analysis shows that we cannot clearly discriminate between the two distributions in a statistically significant fashion. A model that was developed (but not shown here) and based upon the unification scheme viewing-angle principle, shows a difference between the RGs and the QSRs, with the RGs always having smaller DPR than the QSRs. This result may suggest that some other effects, such as the environments around these sources may play an important role in washing out the orientation effect.

Another prediction and test of the unification scheme is the asymmetric depolarization of the lobes of FR II sources that was first reported by Laing (1988) and Garrington (1988), where the lobe on the side of the brighter jet is less depolarized than the lobe on the opposite side of the compact central feature in samples dominated by QSRs. This suggests that he depolarization asymmetry could depend on orientation, if it arises from unresolved structure in a Faraday-thick magnetoionic medium that surrounds the typical FR II source. According to the unification scheme, the lobe that is fed by the brighter jet will also be closer to the observer. This lobe would be viewed along a shorter path through the magnetoionic medium and would therefore depolarize at longer wavelengths than the other lobe. If the jets in FR II QSRs are indeed oriented nearer to the line of sight than those of FR II RGs, we should expect to find greater depolarization asymmetries in the QSRs than in the RGs.

ABSTRACT

1. SAMPLES

2. VLA OBSERVATIONS at 6 cm

The observations of the 13 FR II RGs and of the 13 FR II QSRs (Bridle et al., 1994) were made to test the unification scheme of Barthel (1989). This model proposes that radio-loud quasars and classical double radio galaxies belong to the same parent population of objects. The key physical process behind the unification is relativistic beaming. Within the context of this scheme, the difference in morphologies and prominences of structures (jet, compact central feature, and hot spots) between these two types of objects are related to their orientation with respect to the line of sight. The transition from radio galaxy to quasar properties is suggested to occur around 44o to the line of sight. According to this model, in FR II QSRS the synchrotron emission of the approaching jet is beamed towards, and that of the receding counterjet beamed away from the observer. In FR II RGs, whose radio axes lie closer to the plane of the sky, the synchrotron emission of both jets is less beamed, or even suppressed, and thus more difficult to detect. The QSRs jets are therefore predicted to be more prominent relative to their lobes than those in the RGs, and Barthel’s unification predicts that the jet/counterjet ratios in RGs should be smaller than in the QSRs, both on the large and small scale.

2.1 Jet/Counterjet

3.1 Introduction

Jet/counterjet: - Definite radio jets in only two RGs out of 13 - No counterjet detection. - Definite radio jets detected in all 13 QSRs - Six candidate counterjets - Compact central features of the 13 QSRs are more prominent than those of the RGs The difference in jet detection rate is expected in the unification model if the quasar jets are closer to the line of sight, and thus more beamed towards the observer than galaxy jets. The Figure to the right shows a plot of jet/counterjet luminosity ratio versus the compact central feature for the 13 RGs and 13 QSRS. In addition to the jet prominence, the QSRs are also distinguished by the prominence of their compact central feature. The apparent luminosities of the compact central features for the RGs and the QSRs have very different distributions, with the QSRs showing more powerful radio central features. For the RGs, the radio power of the central features ranges between 1022.9 and 1024.6 W Hz-1, and for the QSRs it ranges from 1024 and 1026 W Hz-1.

2.3 Discussions

4- VLA OBSERVATIONS at 3.6 cm

Jets are abruptly stopped by their impact on the undisturbed, denser intergalactic medium, producing intense radio emission from hot spots near the end of each jet. With the availability of high resolution radio images of FR II sources, it has become clear that it is not easy to cleanly define hot spots in terms of observed parameters alone. The purpose of the observations of our two samples at 3.6 cm is to have high-quality detailed images of the hot spots in order to make a comparative study of RGs and QSRs and to better understand the properties of hot spots and their implications for models of radio sources.

3. DEPOLARIZATION TEST

We have completed the hot spots analysis for 15 sources (5 RGs and 10 QSRs). Using our definition of hot spots, we were able to identify 24 hot spots (15 of them are edged hot spots). For the 10 jetted QSRs, eight hot spots are recessed, out of which six are on the jetted side, and eight are edged, out of which four are on the jetted side. For the five unjetted RGs, seven hot spots are edged, with only one recessed. Our preliminary results show that overall these 15 objects have more edged hot spots than recessed hot spots. A trend seems to appear in which the jetted sources have more recessed hot spots than the unjetted sources. In order to quantify the amount by which the hot spots are recessed, we have computed a parameter defined as the ratio of the distance between the hot spot peak and the radio core of the source to the full extent of the lobe measured from the core along the core-hot spot axis.

Barthel, P.D. 1989, ApJ, 336, 606Bridle, A.H., Hough, D.H., Lonsdale, C.J., Burns, J.O., & Laing, R.A. 1994, AJ, 108, 766Fanaroff, B.L., & Riley, J.M. 1974, MNRAS, 167, 31PFernini, I., Burns, J.O., & Perley, R.A. 1997, AJ, 114, 2292Fernini, I. 2001, AJ, 122, 83Fernini, I. 2002, AJ, 123, 132Fernini, I. 2005, 6th UAEU Research Conf., 244.Fernini, I. 2007, AJ, 134Garrington, S.T. 1988, Ph.D Thesis, Univ. ManchesterLaing, R.A. 1988, Nature, 331, 149

REFERENCES

Basic Properties of the 13 FR II RGs

3C

Name

Redshift

z

LAS

(arcsec)

3C 20 0.174 51

3C 22 0.937 24

3C 34 0.689 48

3C 42 0.395 28

3C 55 0.7348 69

3C 244.1 0.428 51

3C 252 1.1035 57

3C 265 0.811 78

3C 324 1.2063 10

3C 325 0.86 16

3C 330 0.550 56

3C 356 1.079 75

3C 441 0.707 29

3C

Name

Redshift

z

LAS

(arcsec)

3C 9 2.012 14

3C 47 0.425 79

3C 68.1 1.238 53

3C 175 0.768 52

3C 204 1.112 37

3C 208 1.11 14

3C 215 0.411 60

3C 249.1 0.311 53

3C 263 0.646 51

3C 334 0.555 58

3C 336 0.927 28

3C 351 0.371 75

3C 432 1.805 15

2.2 Radio Images

QSR 3C175 at 6 cm (Bridle et al., 1994)

RG 3C34 at 6cm(Fernini et al., 1997)

RG 3C325 at 6 cm(Fernini et al., 1997)

RG 3C441 at 6 cm(Fernini et al., 1997)

QSR 3C263 at 6 cm(Bridle et al., 1994)

RG 3C244.1 at 6 cm(Fernini et al., 1997)

Plot of the jet/counterjetLuminosity versus the

Compact central feature.(Fernini et al. 1997)

3.2 Polarization Analysis

Basic Properties of the 13 FR II QSRs

We define the depolarization ratio, DP, as the ratio of the fractional polarization of the longer wavelength (20 cm) to that of the shorter wavelength (6cm),

DP = p(20)/p(6)where p is the fractional polarization (P/I) at 20 cm and 6 cm from each component of the radio source. It should be noted that high values of DP means less depolarization.

Statistics:Average DP: RGs: (0.71 ± 0.06) QSRs: (0.51 ± 0.07)K-S Test: 21% T-Test: 3% Plot of the depolarization ratio

(DP) vs the redshift(Fernini, 2001)

Another comparison of the two samples in terms of the depolarization was performed by computing the the ratio DPR, which is the ratio of the depolarization ratio of the side of the source with a high value of DP (DPH) to that with a low value of DP (DPL),

DPR = DPH / DPL

This ratio should be closer to 1 for the RGs than for the QSRs because of the presumed viewing angle.

Statistics:Median DPR: RGs: (1.57) - QSRs: (2.23)K-S Test: 55% T-Test:21%

Histogram of the depolarization ratio (DPR)

(Fernini, 2001)

3.3 Discussions

4.1 Hot Spots

4.3 Hot Spots Analysis

In all of our work, we have followed Bridle et al. (1994)’s definition of a hot spot. Furthermore, an edged hot spot refers to a hot spot at the extreme edges of the lobe. A recessed hot spot refers to a hot spot located near the inner edges of the lobe.

NW lobe of 3C 265 at 3.6cm(Fernini, 2007)

Western lobe of 3C 204 at 3.6cm(Fernini, 2007)

3C 249.1 at 3.6cm (Fernini, 2007)

NE lobe of 3C 351 at 3.6cm(Fernini, 2007) 3C 215 at 3.6cm (Fernini, 2007) 3C 9 at 3.6cm (Fernini, 2002)

Histogram of the -parameter.EQSR, RQSR, ERG, RRG standfor edged QSR, recessed QSR, edged RG, and recessed RG, respectively. (Fernini, 2007)

4.2 Edged – Recessed Hot Spots

0

0.2

0.4

0.6

0.8

1

1.2

0.675 0.725 0.775 0.825 0.875 0.925 0.975

Alpha Parameter

No

rmal

ized

Nu

mb

er

EQSR

RQSR

ERG

RRG

3C 336 at 3.6cm (Fernini, 2005)

RG 3C20 at 6 cm(Fernini et al., 1997) RG 3C252 at 6 cm

(Fernini et al., 1997)