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Register a new userThe properties of the extended warm ionised gas around low-redshift QSOs and the lack of extended high-velocity outflows
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(Abridged) We present a detailed analysis of a large sample of 31 low-redshift, mostly radio-quiet type 1 QSOs observed with integral field spectroscopy to study their extended emission-line regions (EELRs). We focus on the ionisation state of the gas, size and luminosity of extended narrow line regions (ENLRs), which corresponds to those parts of the EELR dominated by ionisation from the QSO, as well as the kinematics of the ionised gas. We detect EELRs around 19 of our 31 QSOs (61%) after deblending the unresolved QSO emission and the extended host galaxy light in the integral field data. We identify 13 EELRs to be entirely ionised by the QSO radiation, 3 EELRs are composed of HII regions and 3 EELRs display signatures of both ionisation mechanisms at different locations. The typical size of the ENLR is 10kpc at a median nuclear [OIII] luminosity of log(L([OIII])/[erg/s])=42.7+-0.15. We show that the ENLR sizes are least a factor of 2 larger than determined with HST, but are consistent with those of recently reported type 2 QSOs at matching [OIII] luminosities. The ENLR of type 1 and type 2 QSOs appear to follow the same size-luminosity relation. Furthermore, we show for the first time that the ENLR size is much better correlated with the QSO continuum luminosity than with the total/nuclear [OIII] luminosity. We show that ENLR luminosity and radio luminosity are correlated, and argue that radio jets even in radio-quiet QSOs are important for shaping the properties of the ENLR. Strikingly, the kinematics of the ionised gas is quiescent and likely gravitationally driven in the majority of cases and we find only 3 objects with radial gas velocities exceeding 400km/s in specific regions of the EELR that can be associate with radio jets. In general, these are significantly lower outflow velocities and detection rates compared to starburst galaxies or radio-loud QSOs.
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We present new HST ACS medium- and narrow-band images and long-slit, optical (4000 - 7200A) spectra obtained using the Isaac Newton Telescope (INT) on La Palma, of the merging system Mrk273. The HST observations sample the [OIII]4959,5007 emission from the galaxy and the nearby continuum. The images show that the morphologies of the extended continuum and the ionised gas emission from the galaxy are decoupled, extending almost perpendicular to each other. In particular, we detect for the first time a spectacular structure of ionised gas in the form of filaments extending ~23 kpc to the east of the nuclear region. The quiescent ionised gas kinematics at these locations suggests that these filaments are tidal debris left over from a secondary merger event that are illuminated by an AGN in the nuclear regions. The images also reveal a complex morphology in the nuclear region of the galaxy for both the continuum and the [OIII] emission. Kinematic disturbance, in the form of broad (FWHM > 500 km s-1) and/or strongly shifted (abs(DeltaV) >150 km s-1) emission line components, is found at almost all locations within a radius of ~4 kpc to the east and west of the northern nucleus. We fit the profiles of all the emission lines of different ionisation with a kinematic model using up to 3 Gaussian components. From these fits we derive diagnostic line ratios that are used to investigate the ionisation mechanisms at the different locations in the galaxy. We show that, in general, the line ratios are consistent with photoionization by an AGN as the main ionisation mechanism. Finally, the highest surface brightness [OIII] emission is found in a compact region that is coincident with the so-called SE nuclear component. The compactness, kinematics and emission line ratios of this component suggest that it is a separate nucleus with its own AGN.
Recent stacked ALMA observations have revealed that normal, star-forming galaxies at $zapprox 6$ are surrounded by extended ($approx 10,mathrm{kpc}$) [CII] emitting halos which are not predicted by the most advanced, zoom-in simulations. We present a model in which these halos are the result of supernova-driven cooling outflows. Our model contains two free parameters, the outflow mass loading factor, $eta$, and the parent galaxy dark matter halo circular velocity, $v_c$. The outflow model successfully matches the observed [CII] surface brightness profile if $eta = 3.20 pm 0.10$ and $v_c = 170 pm 10{,rm km,s^{-1}}$, corresponding to a dynamical mass of $approx 10^{11}, mathrm{M}_odot$. The predicted outflow rate and velocity range are $128 pm 5 ,mathrm{M}_odot {rm yr}^{-1}$ and $300-500 {,rm km,s^{-1}}$, respectively. We conclude that: (a) extended halos can be produced by cooling outflows; (b) the large $eta$ value is marginally consistent with starburst-driven outflows, but it might indicate additional energy input from AGN; (c) the presence of [CII] halos requires an ionizing photon escape fraction from galaxies $f_{rm esc} ll 1$. The model can be readily applied also to individual high-$z$ galaxies, as those observed, e.g., by the ALMA ALPINE survey now becoming available.
We investigate galactic-scale outflowing winds in 72 star-forming galaxies at z~1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering SiII, CIV, FeII, MgII, and MgI lines in the rest-frame ultraviolet. Using GALEX, HST, and Spitzer imaging, we examine galaxies on a per-object basis in order to understand both the prevalence of galactic winds at z~1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from the centroids of FeII interstellar absorption lines, span the interval [-217, +155] km/s. We find that ~40% (10%) of the sample exhibits blueshifted FeII lines at the 1-sigma (3-sigma) level. We also measure maximal outflow velocities using the profiles of the FeII and MgII lines, and show that MgII frequently traces higher velocity gas than FeII. Quantitative morphological parameters derived from the HST imaging suggest that mergers are not a prerequisite for driving outflows. More face-on galaxies also show stronger winds than highly-inclined systems, consistent with the canonical picture of winds emanating perpendicular to galactic disks. Using star-formation rates calculated from GALEX data, and areas estimated from HST imaging, we detect a ~3-sigma correlation between outflow velocity and star-formation rate surface density, but only a weak (~1-sigma) trend between outflow velocity and star-formation rate. Higher resolution data are needed in order to test the scaling relations between outflow velocity and both star-formation rate and star-formation rate surface density predicted by theory.
Feedback from active galactic nuclei (AGN) on their host galaxies, in the form of gas outflows capable of quenching star formation, is considered a major player in galaxy evolution. However, clear observational evidence of such major impact is still missing; uncertainties in measuring outflow properties might be partly responsible because of their critical role in comparisons with models and in constraining the impact of outflows on galaxies. Here we briefly review the challenges in measuring outflow physical properties and present an overview of outflow studies from high to low redshift. Finally, we present highlights from our MAGNUM survey of nearby AGN with VLT/MUSE, where the high intrinsic spatial resolution (down to $sim$10 pc) allows us to accurately measure the physical and kinematic properties of ionised gas outflows.
We report on the observed properties of the plasma revealed through high signal-to-noise (S/N) observations of 54 intervening O VI absorption systems containing 85 O VI and 133 H I components in a blind survey of 14 QSOs observed at ~18 km s-1 resolution with the Cosmic Origins Spectrograph (COS) over a redshift path of 3.52 at z < 0.5. Simple systems with one or two H I components and one O VI component comprise 50% of the systems. For a sample of 45 well-aligned absorption components where the temperature can be estimated, we find evidence for cool photoionized gas in 31 (69%) and warm gas (6 > log T > 5) in 14 (31%) of the components. The total hydrogen content of the 14 warm components can be estimated from the temperature and the measured value of log N(H I). The very large implied values of log N(H) range from 18.38 to 20.38 with a median of 19.35. The metallicity, [O/H], in the 6 warm components with log T > 5.45 ranges from -1.93 to 0.03 with a median value of -1.0 dex. Ground-based galaxy redshift studies reveal that most of the absorbers we detect sample gas in the IGM extending 200 to 600 kpc beyond the closest associated galaxy. We estimate the warm aligned O VI absorbers contain (4.1+/-1.1)% of the baryons at low z. The warm plasma traced by the aligned O VI and H I absorption contains nearly as many baryons as are found in galaxies.
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