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Register a new userBeppoSAX Observation of the NGC 3079 Nucleus
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Authors
Naoko Iyomoto
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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.
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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.
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.
This paper presents a BeppoSAX observation of NGC 7582 made during 1998 November and an optical spectrum taken in 1998 October. The new X-ray data reveal a previously unknown hard X-ray component in NGC 7582, peaking close to 20 keV. Rapid variability is observed with correlated changes in the 5-10 and 13-60 keV bands indicating that a single continuum component, produced by the active nucleus, provides the dominant flux across both bands. Changes in the nuclear X-ray flux appear unrelated to the gradual decline in optical flux noted since the high-state in 1998 July. The X-ray continuum is attenuated by a thick absorber of N_H ~ 1.6 x 10E24 cm^-2 covering ~60% of the nucleus, plus a screen with N_H ~ 1.4 x 10E23 cm^-2 covering the entire nucleus. Comparison of the BeppoSAX and ASCA spectra shows an increase in the full screen by N_H ~7 x 10E22 cm^-2 since 1994, confirming the absorption variability found by Xue et al. The increase in soft X-ray flux between 1994 and 1998 is consistent with the appearance of holes in the full screen producing some clear lines-of-sight to the broad-line-region.
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.
The Seyfert 2 galaxy NGC 2110 has been observed with BeppoSAX between 0.5 and 150 keV. The high energy instrument onboard, PDS, has succeeded in measuring for the first time the spectrum of this source in the 13-150 keV range. The PDS spectrum, having a photon index Gamma~1.86 is fully compatible with that expected from a Seyfert 1 nucleus. In the framework of unified models, the harder (Gamma~1.67) 2-10 keV spectrum is well explained assuming the presence of a complex partial + total absorber (Nh~30x10^22 cm^-2 x25% + Nh~4x10^22 cm^-2 x100%). The high column density of this complex absorber is consistent both with the FeK_alpha line strength and with the detection of an absorption edge at E~7.1 keV in the power-law spectrum.
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