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Register a new userHighly-Ionized High-Velocity Gas in the Vicinity of the Galaxy
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We report the results of an extensive FUSE study of high velocity OVI absorption along 102 complete sight lines through the Galactic halo. The high velocity OVI traces a variety of phenomena, including tidal interactions with the Magellanic Clouds, accretion of gas, outflow from the Galactic disk, warm/hot gas interactions in a highly extended Galactic corona, and intergalactic gas in the Local Group. We identify 85 high velocity OVI features at velocities of -500 < v(LSR) < +500 km/s along 59 of the 102 sight lines. Approximately 60% of the sky (and perhaps as much as 85%) is covered by high velocity H+ associated with the high velocity OVI. Some of the OVI is associated with known high velocity HI structures (e.g., the Magellanic Stream, Complexes A and C), while some OVI features have no counterpart in HI 21cm emission. The smaller dispersion in the OVI velocities in the GSR and LGSR reference frames compared to the LSR is necessary (but not conclusive) evidence that some of the clouds are extragalactic. Most of the OVI cannot be produced by photoionization, even if the gas is irradiated by extragalactic background radiation. Collisions in hot gas are the primary OVI ionization mechanism. We favor production of some of the OVI at the boundaries between warm clouds and a highly extended [R > 70 kpc], hot [T > 10^6 K], low-density [n < 10^-4 cm^-3] Galactic corona or Local Group medium. A hot Galactic corona or Local Group medium and the prevalence of high velocity OVI are consistent with predictions of galaxy formation scenarios. Distinguishing between the various phenomena producing high velocity OVI will require continuing studies of the distances, kinematics, elemental abundances, and physical states of the different types of high velocity OVI features found in this study. (abbreviated)
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We present results of Hubble Space Telescope observations of the radio galaxy 3C 244.1. The broadband F702W (R) and F555W (V) images (WFPC2/PC) show an elliptical galaxy and gaseous filaments and blobs surrounding it. In the narrow-band ramp filter, dominated by [OIII]lambda5007, these filaments are bright and have the same morphology as the broad band images. To the south, the filaments have a cone-shaped structure and the radio jet is located at the center of this cone. To the north of the galaxy, the structure is found near the nucleus of the galaxy within its elliptical profile. From the photometry, the two brighter structures seem to be extended narrow line emission regions (ENLRs). The comparison with diagnostic line ratios shows that the observed emission is consistent with interactions between the expanding radio-jet and the local denser medium.
We have used the VIMOS IFU to map the properties of the Seyfert 1.9 galaxy LEDA 135736. These maps reveal a number of interesting features including: an Extended Narrow Line Region detectable out to 9 kpc, an area of intense star formation located at a projected distance of 12 kpc from the centre, an elliptical companion galaxy, and kinematic features, aligned along the long-axis of the ENLR, that are consistent with radio jet-driven mass outflow. We propose that the ENLR results from extra-planar gas ionized by the AGN, and that the AGN in turn might be triggered by interaction with the companion galaxy, which can also explain the burst of star formation and morphological features. Only about two percent of the ENLRs kinetic energy is in the mass outflow. We infer from this that the bulk of mechanical energy imparted by the jet is used to heat this gas.
We report the results from observations of H30$alpha$ line emission in Sgr A West with the Submillimeter Array at a resolution of 2arcsec and a field of view of about 40arcsec. The H30$alpha$ line is sensitive to the high-density ionized gas in the minispiral structure. We compare the velocity field obtained from H30$alpha$ line emission to a Keplerian model, and our results suggest that the supermassive black hole at Sgr A* dominates the dynamics of the ionized gas. However, we also detect significant deviations from the Keplerian motion, which show that the impact of strong stellar winds from the massive stars along the ionized flows and the interaction between Northern and Eastern arms play significant roles in the local gas dynamics.
We report a study of the H30$alpha$ line emission at 1.3 mm from the region around Sgr A* made with the Submillimeter Array at a resolution of 2arcsec over a field of 60arcsec (2 parsec) and a velocity range of -360 to +345 kms. This field encompasses most of the Galactic centers minispiral. With an isothermal homogeneous HII model, we determined the physical conditions of the ionized gas at specific locations in the Northern and Eastern Arms from the H30$alpha$ line data along with Very Large Array data from the H92$alpha$ line at 3.6 cm and from the radio continuum emission at 1.3 cm. The typical electron density and kinetic temperature in the minispiral arms are 3-21$times10^4$ cm$^{-3}$ and 5,000-13,000 K, respectively. The H30$alpha$ and H92$alpha$ line profiles are broadened due to the large velocity shear within and along the beam produced by dynamical motions in the strong gravitational field near Sgr A*. We constructed a 3D model of the minispiral using the orbital parameters derived under the assumptions that the gas flows are in Keplerian motion. The gas in the Eastern Arm appears to collide with the Northern Arm flow in the Bar region, which is located 0.1-0.2 parsec south of and behind Sgr A*. Finally, a total Lyman continuum flux of $3times10^{50}$ photons s$^{-1}$ is inferred from the assumption that the gas is photoionized and the ionizing photons for the high-density gas in the minispiral arms are from external sources, which is equivalent to $sim250$ O9-type zero-age-main-sequence stars.
Previous HST and FUSE observations have revealed highly ionized high-velocity clouds (HVCs) or more generally low HI column HVCs along extragalactic sightlines over 70-90% of the sky. The distances of these HVCs have remained largely unknown hampering to distinguish a Galactic origin (e.g., outflow, inflow) from a Local Group origin (e.g., warm-hot intergalactic medium). We present the first detection of highly ionized HVCs in the Cosmic Origins Spectrograph (COS) spectrum of the early-type star HS1914+7134 (l = 103, b=+24) located in the outer region of the Galaxy at 14.9 kpc. Two HVCs are detected in absorption at v_LSR = -118 and -180 km/s in several species, including CIV, SiIV, SiIII, CII, SiII, OI, but HI 21-cm emission is only seen at -118 km. Within 17 degrees of HS1914+7134, we found HVC absorption of low and high ions at similar velocities toward 5 extragalactic sight lines, suggesting that these HVCs are related. The component at -118 km/s is likely associated with the Outer Arm of the Milky Way. The highly ionized HVC at -180 km/s is an HVC plunging at high speed onto the thick disk of the Milky Way. This is the second detection of highly ionized HVCs toward Galactic stars, supporting a Galactic origin for at least some of these clouds.
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