Evidence for the absorption of crystalline silicates at 11.1 $\mu$m in the spectra of the nucleus of the Circinus galaxy

Several mid-infrared spectra of the Circinus galaxy nucleus taken with T-ReCS on Gemini South and MIDI on VLTI have consistently shown an inflection centred around 11 $\mu$m. We ascribe this feature to the absorption of crystalline silicate, based on their similarity in profile shape and improvement in fitting quality using a partially crystalline silicate model, compared to entirely amorphous models. Spectral fits reveal a fraction of 0.6–2.0 per cent of crystalline forsterite in the nucleus of the Circinus galaxy, which is similar to the values obtained for the interstellar medium (ISM) of the Milky Way. This is probably the first detection of crystalline silicate absorption in the nucleus of this Seyfert 2 galaxy. In addition, the presence of large grain-size amorphous silicates, together with the similarity in profile shape of the optical depth of Circinus with those of young stellar objects in the Milky Way, implies that most of the contribution to the spectra of Circinus comes from dust in the star formation regions near the centre of the nucleus or along the line of sight to the Earth, rather than in the ISM of Circinus. We also compare our optical depths of Circinus with those in previous studies.

Supermassive black holes (SMBH) at work: M87, a case study of the effects of SMBH outbursts

Supermassive black holes (SMBHs) play key roles in galaxy and cluster evolution. This is most clearly seen in the “fossil record” that is imprinted in the gas rich atmospheres of early type galaxies, groups, and clusters by powerful SMBH outbursts. From a detailed X-ray study of M87, we present the properties of a typical SMBH outburst, its evolution, and the energy partition between shocks and the enthalpy of the gas cavities inflated by the SMBH. About 12 Myr ago, the SMBH in M87 inflated a cavity of relativistic plasma which is still centered near the galaxy nucleus. This outburst drove a shock into the surrounding gas. For M87, we show that the outburst duration is a few Myr and that about 50% of the total energy (5 × 1057 ergs) resides in the bubble inflated by the jet from the SMBH, that 25% of the outburst energy is deposited directly into the ambient atmosphere by the shock, and that 25% of the outburst energy is lost from the radiatively bright core as the weak shock moves to large radii. We conclude by describing a future X-ray mission, SMART-X, with < 1” angular resolution that would allow us to study the evolution of SMBHs and the hot, X-ray emitting atmospheres from high redshifts to the present for M87-like systems.

The Milky Way's nuclear star cluster and massive black hole

Because of its nearness to Earth, the centre of the Milky Way is the only galaxy nucleus in which we can study the characteristics, distribution, kinematics, and dynamics of the stars on milli-parsec scales. We have accurate and precise measurements of the Galactic centre's central black hole, Sagittarius A*, and can study its interaction with the surrounding nuclear star cluster in detail. This contribution aims at providing a concise overview of our current knowledge about the Milky Way's central black hole and nuclear star cluster, at highlighting the observational challenges and limitations, and at discussing some of the current key areas of investigation.

Properties of Dust in Giant Elliptical Galaxies: The rôle of the Environment

The properties of dust in giant elliptical galaxies are reviewed, with particular emphasis on the influence of the environment.After normalizing by the optical luminosities, a strong anticorrelation between the masses of dust and hot gas in X-ray bright ellipticals is found. Furthermore, large-scale, regularly-shaped dust lanes (which are symmetric with respect to the galaxy nucleus) are only found to be present in ellipticals with the lowest ratios of the mass of hot gas to the blue luminosity (Mhot/LB ≲ 0.04 in solar units). This can be explained by the short time scale for the destruction of dust grains within the hot, X-ray- emitting gas compared to the formation timescale of such dust lanes in early-type galaxies.Dust within ellipticals in “loose” environments (i.e. in the field or in loose groups) is typically characterized by small values of RV ≡ AV/EB−V (i-e. small characteristic grain sizes), and distributed in dust lanes with a smooth, relaxed morphology. On the other hand, dust in ellipticals that are in or near the center of dense groups or clusters is typically much more irregularly distributed, and characterized by RV values that are close to the Galactic one.I predict that ellipticals containing “relaxed” dust lanes with typical dust masses of 106 − 107M⊙ do not contain hot, X-ray-emitting gas.

INTERMITTENT LASER EMISSION OF A SEYFERT GALAXY NUCLEUS

Intermittent emission of the Seyfert galaxy NGC 4151 nucleus is described by a new type of statistical distribution — multifractal Bernoulli distribution, that allows to identified this emission with intermittent emission of an optically pumped NH3 ring laser.

1.2. The bulge stellar population in M31

We obtained WFPC2 high spatial resolution images, in filters F555W and F814W, of a few fields in the bulge of M31. Two are located SW along the major axis of M31, respectively at 6.1 and 3.2 arcmin of the galaxy nucleus; another is located NE along the major axis at 3.7 arcmin. Adopting 1 arcmin = 250 pc from Rich & Mighell (1995), these separations correspond to projected distances of about 1.55, 0.80, and 0.92 kpc, respectively. We present here some of our results after analysis of the I; V – I colour magnitude diagrams of the bulge stellar population, which are part of an extensive work to be published elsewhere (Jablonka et al. 1997).

The NGC 1275 Galaxy Nucleus Emission Spectrum Variability at Various Stages of Activity

Emission lines variability of Seyfert galaxy NGC 1275 nucleus in the scales of years and months has been observed since 1971 (I. Pronik, 1980). The photoelectric observations of I. Pronik and N. Merkulova (1987) show, that the variability in Hβ and 4959+ 5007 A [OIII] lines occurs also in the time scale of several days. Hereinafter the analysis of Hβ and [OIII] variable emission lines within months is presented according to photographic observations carried out from 1971 till 1982 by I. Pronik (1980), V. Doroshenko and V. Terebizh (1983) and K. Chuvaev (1985).

Photoelectric Observations of Continuous and Emission Lines Variability in Spectra of Seyfert Galaxy NGC 1275 Nucleus

The spectral observations of NGC 1275 nucleus in the range of 3700-7000 AA being carried out since 1971 to 1978 showed the existance of hydrogen and forbidden emission lines variability with the time scale of 5–6 and 1–2 years (Pronik, 1980). Observations on 6-m telescope during 4 nights in January, 1977 permit to reveal the scale variability of these lines 2–3 days, too (Merkulova, Pronik, 1985). These results evidenced the necessary of close photoelectric series of spectral observations of the galaxy nucleus with the filling factor of several days and hours.