episodic activity in radio galaxies -...

Episodic activity in radio galaxies

D.J. Saikia

National Centre for Radio Astrophysics, TIFR, India

Collaborators

Chiranjib Konar, NCRA, TIFR, IndiaMarek Jamrozy, Uniwersytet Jagiellonski, Poland

Jerzy Machalski, Uniwersytet Jagiellonski, PolandNeeraj Gupta, NCRA, TIFR, India

L. Stawarz, Uniwersytet Jagiellonski, PolandK.-H. Mack, Istituto di Radioastronomia, Italy

A. Siemiginowska, Harvard-Smithsonian Center for Astrophysics, USA

1

Introduction

Duration of their active galactic nuclei (AGN)phase?

Are such periods of activity episodic?

Radio loud and radio quiet dichotomy?

For radio loud objects history may be probedvia structural and spectral information on thelobes of radio emission.

Double-double radio galaxies (DDRGs): a strik-ing example of episodic jet activity.

Some results on episodic activity in radio galax-ies using the Giant Metrewave Radio Tele-scope (GMRT) and the Very Large Array (VLA).

2

Figure 1: A view of three of the Central Square antennas of GMRT.

• Thirty antennas each of 45 metre diameter, spread over ∼25km

• Frequencies of operation: ∼150 MHz to 1400 MHz

• Angular resolution:∼20 arcsec (150 MHz) to 2 arcsec (1400 MHz)

• rms sensitivities:

1.5 mJy beam−1 (150 MHz), 0.6 mJy beam−1 (235 MHz),0.3 mJy beam−1 (325 MHz), 0.02 mJy beam−1 (610 MHz),0.03 mJy beam−1 (1400 MHz)

3

J0041+3224: a new double-double radio galaxy discovered withthe GMRT

J0041+3224 NVSS 1400 MHz

Cont peak flux = 4.0129E-01 JY/BEAM Levs = 1.000E-03 * (-1, 1, 2, 4, 8, 16, 32, 64,128, 256, 512, 1024, 2048, 4096)

DECL

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RIGHT ASCENSION (J2000)00 42 00 41 55 50 45 40 35 30

32 27 30

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26 30

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Figure 2: The NVSS image of J0041+3224 with an angular resolution of 45 arcsec (upperpanel) and the GMRT image at 1287 MHz with an angular resolution of ∼2.7 arcsec(Saikia, Konar & Kulkarni 2006).

• Outer size: 969 kpc; inner size: 171 kpc(estimated redshift = 0.45)

• Outer and inner luminosity: ∼3.3×1026 W Hz−1 at 1400 MHz

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Spectra of the different components of J0041+3224

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Figure 3: The spectra of the western and eastern components of the outer double (upperpanel) and the inner double (lower panel). The integrated spectrum is shown in boththe panels.

• Spectral index of entire source: −1.01±0.02 (S∝ να)

• Spectral index of outer double: −1.15±0.01 (western) and−1.35±0.01 (eastern)

• Spectral index of inner double: −0.85±0.03 (western) and

−0.73±0.02 (eastern)

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Multifrequency study of the DDRG J1453+3308

Figure 4: GMRT image of the double-double radio galaxy J1453+3308 at 334 MHz witha resolution of ∼9 arcsec (Konar, Saikia, Jamrozy & Machalski 2006).

• Outer size: 1297 kpc; inner size: 159 kpc

(redshift = 0.249)

• Outer luminosity: ∼7.9×1025 W Hz−1 at 1400 MHz;

inner luminosity: ∼5.9×1024 W Hz−1 at 1400 MHz

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J1453+3308 GMRT 605 MHz

Cont peak flux = 4.0E-02 Jy/b Levs = 4.4E-04 * (-1, 1, 2, 4, 8, 16, 32,64) Jy/b

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RIGHT ASCENSION (J2000)14 53 08 06 04 02 0052 58 56

33 11

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J1453+3308 outer double

a)

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J1453+3308 inner double

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Figure 5: The GMRT image of the DDRG J1453+3308 at 605 MHz with an angularresolution of ∼5.4 arcsec. Spectra of the outer and inner doubles fitted with the modelsof radiative losses. Upper panel: the outer double fitted with the Jaffe-Perola model;lower panel: the inner double fitted with the continuous-injection model. (Konar, Saikia,Jamrozy & Machalski 2006).

• Outer double: injection spectrum ∼0.57;break frequency ∼6700 MHz

• inner double: injection spectrum ∼0.57;

break frequency ∼8.6×105 MHz

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Spec

tral a

ge (M

yr)

Distance from the core (kpc)

N lobeS lobe

Figure 6: Radiative age of the relativistic particles in the outer lobes of J1453+3308plotted against the distance from the radio core using the revised (filled circles) andclassical (open circles) equipartition magnetic fields.

• Maximum ages for the outer double: ∼47 Myr (northern)

and ∼58 Myr (southern)

• Mean separation velocity of lobe head: ∼0.036c;

maximum age: ∼ 134 Myr

• Spectral age of inner double: ∼2 Myr;apparent advance speed: ∼0.1c

• Variable core

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Symmetry parameters of DDRGs

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Armlength ratio: outer

Armlength ratio: inner

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Flux density ratio: inner

Figure 7: The armlength (upper panel) and flux density (lower panel) ratios of the innerdoubles are plotted against the corresponding values for the outer doubles for the sampleof DDRGs.

• Inner double more asymmetric in its armlength ratio

• Inner double more asymmetric in its flux density ratio

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Symmetry parameters of DDRGs

0 5 10 15 20

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Misalignment angle: inner

Figure 8: The misalignment angle of the outer double in degrees is plotted against thecorresponding value for the inner double.

• Inner doubles tend to be more aligned than the outer dou-bles.

• Large-scale density gradients?

• Motion of the parent galaxy?

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Inermittent jet activity in the radio galaxy 4C29.30?

4C 29.30 a)DE

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RIGHT ASCENSION (J2000)08 40 15 10 05 00 39 55 50 45

29 54

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4C 29.30 b)

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Figure 9: 1400-MHz VLA images of 4C 29.30. a) D-array contour map of the entire sourceoverlayed on the optical field from the Digital Sky Survey (DSS). b) B-array contourmap of the central part of the source from FIRST (Jamrozy, Konar, Saikia, Stawarz,Mack and Siemiginowska).

• Outer size: 637 kpc; inner size: 36 kpc(redshift = 0.06471)

• Outer luminosity: ∼1.9×1024 W Hz−1 at 1400 MHz;inner luminosity: ∼5.5×1024 W Hz−1 at 1400 MHz

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4C29.30 GMRT 240 MHz

Cont peak flux = 7.7811E-01 JY/BEAM Levs = 5.200E-03 * (-2, -1, 1, 2, 4, 8, 16, 32,64, 128, 256, 512, 1024, 2048)

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4C29.30 GMRT 333 MHz

Cont peak flux = 5.2700E-01 JY/BEAM Levs = 2.400E-03 * (-2, -1, 1, 2, 4, 8, 16, 32,64, 128, 256, 512, 1024, 2048)

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29 50 00

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Figure 10: The GMRT images of 4C29.30. Left panel: Image at 240 MHz with an angularan angular resolution of 13.8×11.1 arcsec2 along PA 64◦; right panel: the 334-MHz imagewith an angular resolution of 10.6×8.5 arcsec2 along PA 68◦.

• Spectrum of inner double determined over a large frequency

range from low-frequency GMRT and higher frequency VLAobservations

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Figure 11: Upper panel: Spectrum of the 4C29.30 using flux densities from the literature.The linear least-squares fit has been made using only measurements between 325 and4850 MHz. Lower panel: Spectrum of the inner double using our GMRT and VLAimages between 235 and 8460 MHz. The contributions of the core component withina region of ∼4 arcsec (4.9 kpc) have been subtracted. The spectrum also shows thelow-frequency measurement at 74 MHz from VLSS. The linear least squares fit has beenmade using only measurements between 235 and 8460 MHz and has been extrapolatedto lower frequencies.

• Flux densities from literature with different resolutions and

sensitivities

• Total spectrum dominated by the inner double

• Spectrum of inner double determined from GMRT and VLA

observations consistent with VLSS flux density

• Inner double is consistent with a straight spectrum

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J0840+2949 alias 4C29.30 inner-core

Table:template.syndatPoint 5

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J0840+2949 alias 4C29.30

Table:template.syndatPoint 4

Figure 12: The radio spectrum of the inner double and a fit to it using the continuousinjection model (upper panel); the radio spectrum of the diffuse emission and a fit usingthe Jaffe-Perola model (lower panel).

• Inner double is consistent with a straight spectrumEstimated age is less than about 0.1 Myr

• Break frequency of outer emission: ∼4 to 8 GHzEstimated age is ∼34 to 47 Myr

• Variable core

14

Hi gas and rejuvenation of radio galaxies

J1247+6723 NVSS 1400 MHz

Cont peak flux = 2.3663E-01 JY/BEAM Levs = 1.500E-03 * (-1, 1, 2, 4, 8, 16, 32, 64,128, 256, 512, 1024)

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Figure 13: The NVSS image of J1247+6723 with an angular resolution of 45 arcsec (upperpanel) and the radio spectrum of the central component.

• Outer size: 1195 kpc; inner size: 0.014 kpc

(redshift = 0.1073)

• Central component: mini double with a GPS spectrum

• Outer luminosity: ∼3.5×1024 W Hz−1 at 1400 MHz;

inner luminosity: ∼7.4×1024 W Hz−1 at 1400 MHz

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Hi gas and rejuvenation of radio galaxies

Figure 14: The Hi absorption spectrum (histogram) towards the compact inner double ofthe radio galaxy J1247+6723. The spectrum has been smoothed using a 3-pixel wideboxcar filter. The Gaussian components fitted to the absorption profile and the sum ofthese components i.e. the fit are plotted as dotted and dashed lines respectively. Thesystemic velocity (32157 km s−1) has been marked by an arrow (Saikia, Gupta and Konar2006).

• Absorption profile consists of four components

• Total Hi column density is N(Hi)=6.73×1020(Ts/100)(fc/1.0)−1

cm−2

• Close relationship between Hi absorption and evidence of

renewed activity

• Other cases: 3C236, 3C293, 3C258

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episodic activity in radio galaxies -...

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