Interaction in the NGC 3079 group Nebiha Shafi University of Witwatersrand and HartRAO Supervisors: Prof. Roy Booth (HartRAO) Dr. Raffaella Morganti Dr. Tom Oosterloo (ASTRON) Bursary and Fellowship Conference 2009

Outline  Introduction to the primary source  Observation & Data reduction  Results  Interaction in the NGC 3079 group  Summary & Future work N. Shafi Bursary and Fellowship Conference 2009

The primary Source HST image NGC 3079 Type:SB(s)c RA: DEC: Inclination: ~ 84 o Velocity: ~ 1116 km s -1 Distance: ~ 16 Mpc  Host to a nuclear starburst and an AGN.  Classified as Seyfert2.  Displays 2 extended radio lobes.  Rapid ionized gas outflow up to 1000 km s -1. N. Shafi Bursary and Fellowship Conference 2009

Observation & Data reduction Telescope: WSRT Bandwidth: 20 MHz Frequency : 1.42 GHz Integration time: 5 x 12 hrs Velocity resolution: 16 km s -1 Data reduction: MIRIAD  Standard reduction  Non-Standard reduction “Peeling” Observations: N. Shafi Bursary and Fellowship Conference 2009 Beam size: 47″.5 x 44″.7 Rms noise: 0.18 mJy beam -1 ‏ The data cube

α and δ(J2000) Name (NED)Vsys (km s −1 ) NGC NGC MCG J J N J N J N J N N – new redshift information N. Shafi Bursary and Fellowship Conference 2009 MCG NGC 3073 Total HI contours overlaid on DSS2 image Interaction in the NGC 3079 group: The NGC 3079 Group

Ram pressure  The ram pressure required to strip off gas from a galaxy as it moves in the intergalactic medium (IGM) : ρv 2 ≥ 2πGΣ ∗ Σ HI (Gunn & Gott 1972) Force due to IGM Gravitational restoring force Interaction Scenarios Where ρ - the density of the IGM G - gravitational constant v - the velocity dispersion of the group Σ ∗ and Σ HI are the stellar and gas surface mass densities N. Shafi Bursary and Fellowship Conference 2009

Interaction Scenarios  Disruption happens at radius r > r J (r - size of the companion) Where r J - radius in which material remain bound to one galaxy m- mass of the companion M - mass of the primary galaxy R sep - the separation between the two galaxies ( Binney & Tremaine 1987 ) r J = R sep ( m /3M ) 1/3 Tidal interaction  The strength of the tidal force on a galaxy can be inferred from the tidal radius (Jacobi limit): N. Shafi Bursary and Fellowship Conference 2009

MCG : Tidal or Ram pressure stripped? contours in steps of 3σ Total HI overlaid on DSS2 red image contours of 0.2, 1, 5,10, 20, x cm -2 HI bridge A third tail? MCG N. Shafi Bursary and Fellowship Conference 2009

Problems with tidal scenario  The HI gas is still be bound to the galaxy. 1. At the projected distance of 30 kpc between the two galaxies, NGC 3079 and MCG the tidal radius is: r J ∼ 8 kpc And the size of MGC is: r ∼ 5 kpc 2. The lack of any disturbance sign in the optical disk of the galaxy N. Shafi Bursary and Fellowship Conference cm -2 6x10 20 cm -2

IS MCG being ram pressure stripped?  Ruled out based on the morphology of the streaming gas.  Since such gas would be blown away from the galaxy. Assuming Σ HI /Σ ∗ = constant, the minimum ram pressure required to strip off gas from MCG (for N H at half-maximum) is: ρv 2 ≥ 6.9x dyn cm Ram pressure due to the super-wind from NGC 3079: N. Shafi Bursary and Fellowship Conference 2009  Ram pressure due to the super-wind or the hot X-ray halo of NGC 3079?

 L x ∼ 6 × erg/s and extends kpc (Cecil et al. 2002). Assuming T= 3.5 × 10 6 K gives an electron density of : n e = 7 × 10 − 4 cm −3 This yields a ram pressure: ρv 2 =2.4 × 10 − 11 dyn cm −2 This is ~ 72% higher than the gravitational restoring force of MCG  The hot X-ray halo of NGC 3079 seems to be responsible for stripping off gas from this galaxy. N. Shafi Bursary and Fellowship Conference Ram pressure due to the hot X-ray halo of NGC 3079: (Breitschwerdt et al. 2002)

The case of NGC 3073:  What is the origin of the ‘Cometary’ appearance? Tidal or ram pressure? N. Shafi Bursary and Fellowship Conference 2009

Problems with tidal scenario  The HI gas is still bound to the galaxy. 1. At the projected distance of 50 kpc between the two galaxies, NGC 3079 and NGC 3073 the tidal radius is: r J ∼ 10 kpc And the size of NGC 3073is: r ∼ 7.5 kpc 2. The lack of any disturbance sign in the optical disk of the galaxy. N. Shafi Bursary and Fellowship Conference x10 20 cm cm -2

Ram pressure due to the super-wind or X-ray halo of NGC 3079?  The minimum ram pressure required to strip off gas from NGC 3073 (for N H half-maximum) is: ρv 2 ≥ 9x dyn cm Ram pressure due to the hot X-ray halo of NGC 3079: Rejected based on the morphology.  Since such gas would be trailing behind NGC N. Shafi Bursary and Fellowship Conference 2009

2. Ram pressure due to the super-wind of NGC 3079:  Considering density decline as a function of distance gives a ram pressure of: ρv 2 ~ 3.6 × 10 − 8 dyn cm −2  Adopting the lower limit for the electron density and the velocity of the super-wind from Cecil et al. (2001): n e = 1.35 × 10 2 cm −3, and V ~1000 km s −1 This value is much higher than the required ram pressure to produce the tail. The outflowing gas from NGC 3079 seems to be responsible. N. Shafi Dec 2009N. Shafi Bursary and Fellowship Conference 2009

 Five new galaxies associated with NGC 3079 group were revealed.  Two of the companion galaxies, MCG and NGC 3073 seem to be ram pressure stripped due to the hot X-ray halo and super-wind of NGC 3079 respectively.  Investigate the effect of the interaction on the individual companion galaxies.  Study the role of the companions in the nuclear activity of NGC N. Shafi Bursary and Fellowship Conference 2009

Thank you!

Results N. Shafi Dec 2009 HI emission  Much extended HI emission than previous observations.  Five new companion galaxies were revealed.  Asymmetric HI disk.  Extraplanar HI.  Interaction with three companions. HI Absorption  Broad and strong central absorption with a hint of blue shifted absorption detected.

 Broad and strong central absorption with a hint of blueshifted component τ peak = 0.18 blue-shifted? > 600 km s -1 V sys Hi absorption

Model Model data cube Cloud of points Tilted-ring parameters Thin disk Thick disk slow rotating halo TiRiFiC (Jozsa et al. 2007)  Free parameters: SBR VROT PA INCL  Constant parameters: Z0 XPOS YPOS VSYS DISP N. Shafi Oct 2009

 Data  Thin disk  Thick disk The results of the models N. Shafi Oct 2009

NGC 3079 Oosterloo et al NGC 891

 Standard reduction The result of the standard reduction ← Need different calibration for different direction -- “peeling”  Non-Standard reduction N. Shafi Oct 2009 After “Peeling”