C. Goudis

The distribution of the ISM in the Milky Way - A three-dimensional large-scale model

We use the COBE/DIRBE (1.2, 2.2, 60, 100, 140, and 240 µm) maps and the COBE/FIRAS spectra (for the wavelength range 100−1000 µm) to constrain a model for the spatial distribution of the dust, the stars, and the gas in the Milky Way. By assuming exponential axisymmetric distributions for the dust and the stars and by performing the corresponding radiative transfer calculations we closely (given the simple geometry of the model) reproduce the FIR and NIR maps of the Milky Way. Similar distributions for the atomic and molecular hydrogen in the disk are used (with an inner cut-off radius for the atomic hydrogen) to fit the gas data. The star formation rate as a function of the Galactic radius is derived from the FIR emission and is well in agreement with existing estimates from various star formation tracers. The gas surface density is plotted against the star formation rate density and an “intrinsic” Galactic Schmidt law is derived with excellent agreement with the “external” Schmidt law found for spiral galaxies. The Milky Way is found to consume ∼1% and ∼10% of its gas in the outer and inner regions respectively (for a period of 0.1 Gyr) to make stars. The dust-induced B − V color excess observed in various directions and distances (up to ∼6.5 kpc) with well-studied Cepheid stars is compared with the model predictions showing a good agreement. The simple assumption of exponential distributions of stars and dust in the Galaxy is found to be quite instructive and adequate in modeling all the available data sets from 0.45 µ m( B-band) to 1000 µm.

The Orion Complex: A Case Study of Interstellar Matter

1: Large Scale View of the Orion Region.- 1.1. General Morphology of Barnards Loop and the Neighbouring Region.- 1.2. Nature of Barnards Loop and the Associated Filamentary Structure.- 1.3. Origin of the I Orion OB Association.- Tables.- Figures.- 2: The H II Regions M42 and M43.- 2.1. Optical and Radio Structure.- 2.2. Physical Parameters Derived from Radio and Optical Observations.- 2.3. Ionized Stellar-Size Condensations (ISC) and Ionized Knots (IK) Associated with the Core of M42.- 2.4. Dust in the Orion Nebula (M42).- Tables.- Figures.- 3: The Orion Complex (M42/OMC1, M43/OMC2).- 3.1. Infrared Structure.- 3.2. Physical Parameters Derived from Infrared Observations.- 3.3. Structure and Physical Parameters of the Molecular Complex (OMC 1, OMC 2).- 3.4. Maser Sources.- 3.5. Magnetic Field in the Orion Complex.- Tables.- Figures.- 4: Empirical Models of the Orion Complex.- 4.1 Empirical Models.- Tables.- Figures.- 5: NGC2024 and the Associated Molecular Complex.- 5.1. Optical and Radio Structure of NGC2024.- 5.2. Infrared and Molecular Structure of the NGC2024/Molecular Complex.- 5.3. Excitation of NGC2024.- Tables.- Figures.- Appendices.- Appendix I: Radiative Transfer.- I. 1. The Various Forms of the Equation of Radiative Transfer.- Figure.- Appendix II: Physical Parameters of an H II Region.- II. 1. Physical Parameters Derived from Observations of the Radio Continuum Emission.- II. 2. Determination of Density from Optical Methods.- II. 3. Determination of Temperature from Optical and Radio Methods.- II. 4. Chemical Composition.- II. 5. Determination of Radial Velocity and Turbulence.- Tables.- Figures.- Appendix III: Physical Parameters of the Dust Associated With an H II Region.- III. 1. Visual Extinction Derived from the Comparison of Optical with Radio Data.- III. 2. Physical Parameters Derived from Observations of the Infrared Continuum.- Figures.- Appendix IV: Physical Parameters of a Molecular Cloud.- IV. 1. Physical Parameters Derived from Observations of Molecular Lines.- References.

Local and Large-Scale Environment of Seyfert Galaxies

We present a three-dimensional study of the local (≤100 h-1 kpc) and the large-scale (≤1 h-1 Mpc) environment of the two main types of Seyfert AGN galaxies. For this purpose we use 48 Seyfert 1 galaxies (with redshifts in the range 0.007 ≤ z ≤ 0.036) and 56 Seyfert 2 galaxies (with 0.004 ≤ z ≤ 0.020), located at high galactic latitudes, as well as two control samples of nonactive galaxies having the same morphological, redshift, and diameter size distributions as the corresponding Seyfert samples. Using the Center for Astrophysics (CfA2) and Southern Sky Redshift Survey (SSRS) galaxy catalogs (mB ~ 15.5) and our own spectroscopic observations (mB ~ 18.5), we find that within a projected distance of 100 h-1 kpc and a radial velocity separation of δv 600 km s-1 around each of our AGNs, the fraction of Seyfert 2 galaxies with a close neighbor is significantly higher than that of their control (especially within 75 h-1 kpc) and Seyfert 1 galaxy samples, confirming a previous two-dimensional analysis of Dultzin-Hacyan et al. We also find that the large-scale environment around the two types of Seyfert galaxies does not vary with respect to their control sample galaxies. However, the Seyfert 2 and control galaxy samples do differ significantly when compared to the corresponding Seyfert 1 samples. Since the main difference between these samples is their morphological type distribution, we argue that the large-scale environmental difference cannot be attributed to differences in nuclear activity but rather to their different type of host galaxies.We present a three-dimensional study of the local (<100 h^-1} kpc) and the large scale (<1 h^{-1} Mpc) environment of the two main types of Seyfert AGN galaxies. For this purpose we use 48 Sy1 galaxies (with redshifts in the range 0.007<z<0.036) and 56 Sy2 galaxies (with 0.004<z<0.020), located at high galactic latitudes, as well as two control samples of non-active galaxies having the same morphological, redshift, and diameter size distributions as the corresponding Seyfert samples. Using the Center for Astrophysics (CfA2) and Southern Sky Redshift Survey (SSRS) galaxy catalogues (m_B~15.5) and our own spectroscopic observations (m_B~18.5), we find that within a projected distance of 100 h^-1 kpc and a radial velocity separation of dv<600 km/sec around each of our AGNs, the fraction of Seyfert 2 galaxies with a close neighbor is significantly higher than that of their control (especially within 75 h^{-1} kpc) and Seyfert 1 galaxy samples, confirming a previous two-dimensional analysis of Dultzin-Hacyan et al. We also find that the large-scale environment around the two types of Seyfert galaxies does not vary with respect to their control sample galaxies. However, in the Seyfert 2 and control galaxy samples do differ significantly when compared to the corresponding Seyfert 1 samples. Since the main difference between these samples is their morphological type distribution, we argue that the large-scale environmental difference cannot be attributed to differences in nuclear activity but rather to their different type of host galaxies.

Evidence for an outflow from the Seyfert galaxy NGC

New observations using narrow band imaging, long-slit spectroscopy and MERLIN observations of the nuclear region of the Seyfert galaxy NGC 4051 have been made. An edge brightened, triangular region of ionized gas extending 420 pc from the centre of the galaxy has been detected. Long-slit spectra of this ionised gas, taken at 1.5 ′′ from the core, show the [O iii] 5007-u emission line to consist of two velocity components, both blue-shifted from the systemic radial velocity, with velocity widths of 140 kms −1 and separated by 120 kms −1 . This region is co-spatial with weak extended radio emission and is suggestive of a centrally driven outflow. The [O iii] 5007-u line spectrum and image of this region have been modelled as an outflowing conical structure at 50 ◦ to the line of sight with a half opening angle of 23 ◦ . In addition to the extended structure, high resolution MERLIN observations of the 18-cm nuclear radio emission reveal a compact (1 ′′ ) radio triple source in PA 73 ◦ . This source is coincident with the HST-imaged emission line structure. These high resolution observations are consistent with a more compact origin of activity (i.e. a Seyfert nucleus) than a starburst region.

W28-A possible association of supernova remnants and Hii regions

The nature of various components of the W28 complex region is investigated. The radio spectra of W28-A1 (G 6.4-0.2), M20 (G 7.0-0.2), W28-A2 (G 5.9-0.4), W28-A4 (G 5.3-1.1), KE59 (G 6.6-0.3) and G 6.4-0.5 are established over a wide range of frequencies. The W28-A1 (G 6.4-0.2) source is a SNR (sp. index −0.41), the M20, W28-A2 and KE59 seem to be thermal sources (sp. indexes −0.06, −0.15 and −0.04 respectively) whereas the W28-A4 and G 6.4-0.5 are possibly mixed sources containing thermal and non-thermal features. Certain physical parameters of the thermal components are derived by adopting a model. The physical properties of the W28-A1 SNR are investigated. The possibility of a SNR-Hii regions association in the W28 region is also discussed.

Abundant dust found in intergalactic space

Galactic dust constitutes approximately half of the elements more massive than helium produced in stellar nucleosynthesis. Notwithstanding the formation of dust grains in the dense, cool atmospheres of late-type stars, there still remain huge uncertainties concerning the origin and fate of galactic stardust. In this Letter, we identify the intergalactic medium (i.e., the region between gravitationally bound galaxies) as a major sink for galactic dust. We discover a systematic shift in the color of background galaxies viewed through the intergalactic medium of the nearby M81 group. This reddening coincides with atomic, neutral gas previously detected between the group members. The dust-to-H I mass ratio is high (1/20) compared to that of the solar neighborhood (1/120), suggesting that the dust originates from the center of one or more of the galaxies in the group. Indeed, M82, which is known to be ejecting dust and gas in a starburst-driven superwind, is cited as the probable main source.

Deep optical observations of the interaction of the SS 433 microquasar jet with the W50 radio continuum shell

Four mosaics of deep, continuum-subtracted, CCD images have been obtained over the extensive Galactic radio continuum shell, W50, which surrounds the remarkable stellar system SS 433. Two of these mosaics in the Hα + [N II] and [O III] 5007 A emission lines, respectively, cover a field of ∼2. ◦ 3 × 2. 5 which contains all of W50 but at a low angular resolution of 5 arcsec. The third and fourth mosaics cover the eastern (in [O III] 5007 A) and western (in Hα + [N II] 6548, 6584 A) filamentary nebulosity, respectively, but at an angular resolution of 1 arcsec. These observations are supplemented by new low-dispersion spectra and longslit, spatially resolved echelle spectra. The [O III] 5007 A images show for the first time the distribution of this emission in both the eastern and western filaments while new Hα + [N II] emission features are also found in both of these regions. Approaching flows of faintly emitting material from the bright eastern filaments of up 100 km s −1 in radial velocity are detected. The present observations also suggest that the heliocentric systemic radial velocity of the whole system is 56 ± 2k m s −1 . Furthermore, very deep imagery and high-resolution spectroscopy of a small part of the northern radio ridge of W50 has revealed for the first time the very faint optical nebulosity associated with this edge. It is suggested that patchy foreground dust along the ≈5 kpc sightline is inhibiting the detection of all of the optical nebulosity associated with W50. The interaction of the microquasar jets of SS 433 with the W50 shell is discussed.

Radio observations of the Chandra Deep Field South : Exploring the possible link between radio emission and star formation in X-ray selected AGN

We explore the nature of the radio emission of X-ray selected AGN by combining deep radio (1.4 GHz; 60µJy) and X-ray data with multiwavelength (optical, mid-infrared) observations in the Extend ed Chandra Deep Field South (E-CDFS). The fraction of radio detected X-ray sources increases from 9% in the E-CDFS to 14% in the central region of this field, which has deeper X-ray coverage from the 1 Ms CDFS. We find evidence that the radio emission of up to 60% of the hard X-ray/radio matched AGN is likely associated with star-formation in the host galaxy. Firstly, the mid-IR (24 µm) properties of these sources are consistent with the infra red/radio correlation of starbursts. Secondly, most of them are found in galaxies with blue rest-frame optical colours ( U− V), suggesting a young stellar population. On the contrary, X-ray/radio matched AGN which are not detected in the mid-infrared have red U− V colours suggesting their radio emission is associated with AGN activity. We also find no evidence for a population of heavily obscured r adio-selected AGN that are not detected in X-rays. Finally, we do no confirm previous claims for a correlation between radio emission and X-ray obscuration. Assuming that the radio continuum measures star-formation, this finding is against models where the dust and gas clouds as sociated with circumnuclear starbursts are spherically bl ocking our view to the central engine.

Discovery of optical emission from the supernova remnant G 32.8 0.1 (Kes 78)

Deep optical CCD images of the supernova remnant G 32.8−0.1 were obtained where filamentary and diffuse emission was discovered. The images were acquired in the emission lines of Hα + [N ii ]a nd [Sii]. Filamentary and diffuse structures are detected in most areas of the remnant, while no significant [O iii] emission is present. The flux-calibrated images suggest that the optical emission originates from shock-heated gas since the [S ii]/Hα ratio is greater than 1.2. The Spitzer images at 8 μm and 24 μm show a few filamentary structures to be correlated with the optical filaments, while the radio emission at 1.4 GHz in the same area is found to be very well correlated with the brightest optical filaments. The results from deep long-slit spectra also support the origin of the emission being from shock-heated gas ([S ii]/H α> 1.5). The absence of [O iii] emission indicates slow shock velocities into the interstellar “clouds” (≤100 km s −1 ), while the [S ii]λλ 6716/6731 ratio indicates electron densities up to ∼200 cm −3 .T he Hα emission is measured to lie between 1.8 to 4.6 × 10 −17 erg s −1 cm −2 arcsec −2 , while from VGPS Hi images the distance to the SNR is estimated to be between 6 to 8.5 kpc.

Normal galaxies in the XMM-Newton fields: x-rays as a star formation indicator

Context. We use the first XMM serendipitous source catalogue (1XMM) to compile a sample of normal X-ray galaxies. Aims. We seek to expand the database of X-ray selected normal galaxies at intermediate redshifts and examine the relation between X-ray emission and star formation for late-type systems. Methods. The candidates are selected based on their X-ray (soft spectra), X-ray to optical (log(f x /f o ) < -2) and optical (extended sources) properties. 44 candidates are found and 35 are spectroscopically observed with the Australian National Universitys 2.3 m telescope to examine their nature. Results. Of the 35 sources observed, 2 are AGN, 11 emission line galaxies, 12 absorption line galaxies, 6 have featureless spectra while 4 are associated with Galactic stars. We combine our emission line sample with earlier works forming the most comprehensive X-ray selected galaxy sample for the study of the X-ray luminosity to the Hα luminosity - a well-calibrated star-formation indicator - relation. Conclusions. We find that the X-ray luminosity strongly correlates with the Hα luminosity, suggesting that the X-rays efficiently trace the star-formation.