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Register a new userThe Hot and Cold Outflows of NGC 3079
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N. Shafi
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Very deep neutral hydrogen (HI) observations of the edge-on spiral galaxy NGC 3079 with the Westerbork Synthesis Radio Telescope (WSRT) are presented. The galaxy has been studied extensively in different wavelengths and known for its several unique and complex features. However, the new data still revealed several new features and show that the galaxy is even more complicated and interesting than previously thought. In the new data a large stream of gas, encircling the entire galaxy, was discovered, while the data also show, for the first time, that not only hot gas is blown into space by the starburst/AGN, but also large amounts of cold gas, despite the high energies involved in the outflow.
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We present new observations at three frequencies (326 MHz, 615 MHz, and 1281 MHz) of the radio lobe spiral galaxy, NGC 3079, using the Giant Metrewave Radio Telescope. These observations are consistent with previous data obtained at other telescopes and reveal the structure of the nuclear radio lobes in exquisite detail. In addition, new features are observed, some with HI counterparts, showing broad scale radio continuum emission and extensions. The galaxy is surrounded by a radio halo that is at least 4.8 kpc in height. Two giant radio extensions/loops are seen on either side of the galaxy out to $sim$ 11 kpc from the major axis, only slightly offset from the direction of the smaller nuclear radio lobes. If these are associated with the nuclear outflow, then the galaxy has experienced episodic nuclear activity. Emission along the southern major axis suggests motion through a local IGM (not yet detected) and it may be that NGC 3079 is itself creating this local intergalactic gas via outflows. We also present maps of the minimum energy parameters for this galaxy, including cosmic ray energy density, electron diffusion length, magnetic field strength, particle lifetime, and power.
Using the BeppoSAX observatory, we have observed a nearby LINER/Seyfert 2 galaxy, NGC 3079, which is known as an outflow galaxy and a bright H_2O-maser source. Using the PDS detector, we have revealed that the NGC 3079 nucleus suffers from a Compton-thick absorption, with a hydrogen column density sim 10^{25} cm^{-2}. After corrected the absorption, the 2--10 keV luminosity becomes 10^{42-43} erg s^{-1} at a distance of 16 Mpc. It is 2-3 orders of magnitude higher than that observed in the MECS band (below 10 kev). We also detected a strong Fe-K line at 6.4^{+0.3}_{-0.2} keV with an equivalent width of 2.4^{+2.9}_{-1.5} keV, which is consistent with the heavy absorption.
Images in the J, H and K bands and in the the v=1-0 S(1) line of H2 of the central region of the almost edge-on galaxy NGC 3079 reveal contributions from direct and scattered starlight, emission from hot dust and molecular gas, and extinction gradients. The central 100 pc suffers an extinction of 6 mag. Extremely red near-infrared colours require the presence of hot dust at about 1000 K. Less reddened parts of the bulge require either a 20% J-band contribution from young stars in a stellar bar, or a 20-30% contribution from scattered stellar light. The nucleus is surrounded by a dense molecular disk of radius 300 pc. Emission from H2 and hot dust traces a cavity of radius 120 pc. In the central few hundred pc, HI spin temperatures must be less than 275 K and the CO-to_H2 conversion factor is at most 5% of the standard Galactic value. This is consistent with theoretical predictions for environments subjected to dissociative shocks, where reformation of H2 is impeded by high dust grain temperatures. The overall molecular gas content of NGC 3079 is normal for a late-type galaxy.
The nearby radio galaxy 3C293 is one of a small group of objects where extreme outflows of neutral hydrogen have been detected. However, due to the limited spatial resolution of previous observations, the exact location of the outflow was not able to be determined. In this letter, we present new higher resolution VLA observations of the central regions of this radio source and detect a fast outflow of HI with a FWZI velocity of Delta v~1200 km/s associated with the inner radio jet, approximately 0.5 kpc west of the central core. We investigate possible mechanisms which could produce the observed HI outflow and conclude that it is driven by the radio-jet. However, this outflow of neutral hydrogen is located on the opposite side of the nucleus to the outflow of ionised gas previously detected in this object. We calculate a mass outflow rate in the range of 8-50 solar masses/yr corresponding to a kinetic energy power injected back into the ISM of 1.38x10^{42} - 1.00x10^{43} erg/s or 0.01 - 0.08 percent of the Eddington luminosity. This places it just outside the range required by some galaxy evolution simulations for negative feedback from the AGN to be effective in halting star-formation within the galaxy.
It is shown that there are at least 21 QSOs within 1 degree of the nearby active spiral galaxy NGC3079. Many of them are bright (mag<18) so that the surface density of those closer than 15 arc minutes to the galaxy centre is close to 100 times the average in the field. The probability that this is an accidental configuration is shown to be less or equal to one in a million. Discovery selection effects and microlensing fail by a large factor to explain the phenomenon, suggesting that the QSOs may lie in the same physical space as NGC3079. However, two of them make up the apparently lensed pair 0957+561A, B whose lensing galaxy lies at z=0.355. This problem is discussed in the concluding section.
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