M. Blietz

The Nature of the dense obscuring material in the nucleus of NGC 1068

High spatial and spectral resolution observations of the distribution, physical parameters, and kinematics of the molecular interstellar medium toward the nucleus of the Seyfert 2 galaxy NGC 1068 are reported. The data consist of 2.4 by 3.4 arcseconds resolution interferometry of the 88.6 GHz HCN J = 1 towards 0 line at 17 km/s spectral resolution, single dish observations of several mm/submm isotopic lines of CO and HCN, and 0.85 arcseconds imaging spectroscopy of the 2.12 micron H2 S(1) line at a velocity resolution of 110 km/s. The central few hundred parsecs of NGC 1068 contain a system of dense (N(H2) approximately 10(exp 5) cm(exp -3)), warm (T greater than or equal to 70 K) molecular cloud cores. The low density molecular envelopes have probably been stripped by the nuclear wind and radiation. The molecular gas layer is located in the plane of NGC 1068s large scale disk (inclination approximately 35 deg) and orbits in elliptical streamlines in response to the central stellar bar. The spatial distribution of the 2 micron H2 emission suggests that gas is shocked at the leading edge of the bar, probably resulting in gas influx into the central 100 pc at a rate of a few solar mass per year. In addition to large scale streaming (with a solid body rotation curve), the HCN velocity field requires the presence of random motions of order 100 km/s. We interpret these large random motions as implying the nuclear gas disk to be very thick (scale height/radius approximately 1), probably as the result of the impact of nuclear radiation and wind on orbiting molecular clouds. Geometry and column density of the molecular cloud layer between approximately 30 pc to 300 pc from the nucleus can plausibly account for the nuclear obscuration and anisotropy of the radiation field in the visible and UV.

Near-infrared line imaging of NGC 6240 : collision shock and nuclear starburst

Images of the merging luminous IR galaxy NGC 6240 in the H 2 v=1→0 S(1) 2.12 μm line and the [Fe II] 1.64 μm line are presented, together with velocity-resolved slit spectra of these lines. The images have an angular resolution of ≤1″, and for the H 2 line, images in three adjacent 320 km s −1 wide velocity intervals are presented. The H 2 emission does not follow the stellar light and shows no trace of the two nuclei of the galaxy. Instead, it peaks between these nuclei. The H 2 emission extends over ∼5 kpc and shows a complex morphology and velocity structure in its outer parts

High-resolution imaging of forbidden Fe II 1.64 microns, Brackett-gamma, and H2 1-0 S(1) emission in the starburst galaxy NGC 253

We present 1″ resolution imaging of the nuclear region of the starburst galaxy NGC 253 in the near-infrared lines of [Fe II] 1.64 μm, Brackett-γ, and H 2 1-0 S(1), together with the adjacent continuum. The data reveal an emission region extended some 10″ northeast of the nucleus, with several embedded compact peaks or hot spots. The continuum and the three spectral lines have the same general distribution but differ in detail. The line emission from H 2 and Brγ are closely matched in the circumnuclear region. However, the H 2 emission reveals wispy structures which are more prominent to the northwest of the nucleus

High Resolution Images and Spectroscopy of the Galactic Center

We present deep H and K images of the central pc of our galaxy at 0.15″ resolution. Most of the identified compact sources (340) K≤14 are K or M giants. About 15 of the bright blue stars emit broad (FWHM up to 1000 km/s) HeI and/or Brγ lines, indicating a very strong stellar wind. We confirm the presence of a blue NIR object (K13) at the position of the compact radio source SgrA*. The spatial centroid of the source number distribution is consistent with the position of SgrA*. The stellar density in the central 10″ is very well fitted by an isothermal cluster model yielding a stellar core density of a few 107 M⊙pc-3. Stellar collisions seem to be important at this density. We present 2.22 µm [FeIII] and 2.17 µm Brγ narrow-band imaging of the “mini-cavity” region. The derived fractional abundances of Fe/H, Fe++/Fe+ together with other parameters suggest a wind driven scenario. A fast wind (1000 km/s) interacts with the streamer gas and creates an expanding bubble. Possible origins of the wind are the HeI stars or a jet from SgrA*.

The Galactic Center [FE III] Bubble

We present spectroscopy and 1″ narrow-band imaging of near-infrared line emission from the ‘mini-cavity’ region south-west of the radio source SgrA*. The bright 2.217µm line emission is now unambiguously identified as [FeIII]. The fractional abundances of Fe++ and Fe+, together with the observed spatial distributions and line profiles suggest the following model: A fast wind blows into the partially neutral gas streamers orbiting the dynamic center and creates an expanding gas bubble. Fast shocks triggered by this interaction destroy dust grains and release iron into the gas phase. The iron-rich shocked streamer gas cools rapidly and is now excited by the central UV field. Morphology and bubble dynamics can be explained either by models invoking He I emission line stars as a local wind source or, perhaps more likely, by models in which a jet from SgrA* acts as an external wind source.

Excitation of the inner pc of the Galactic Center: Results from near-infrared spectroscopy

We present near-infrared spectroscopy and line imaging of the central 0.5 pc of the Galaxy. The “mini-cavity” region south-west of SgrA∗ is a source of bright 2.217 μm emission now identified as due to [Fe III]. We infer that iron is released from grains in shocks triggered by fast wind blowing into the Galactic Center gas streamers. After cooling the shocked streamer gas is maintained at about 7000 K by the central UV field. Morphology and dynamics can be explained either by models invoking HeI emission line stars as a local wind source or by models in which a jet from SgrA∗ acts as an external wind source. Velocity-resolved spectroscopy of the brightest HeI emission line star in the Galactic Center has been used to constrain atmospheric models. The star is found to be similar to evolved massive stars of type Ofpe/WN9, undergoing heavy mass loss. Helium is overabundant in the atmosphere. Extrapolating from this star it is likely that the Galactic Center HeI stars contribute a large fraction of the total luminosity and a significant fraction of the Lyman continuum luminosity of the central parsec. Hotter stars are needed to provide the HeI ionizing flux.