1,301 research outputs found
The Line Emission Region in III Zw 2: Kinematics and Variability
We have studied the Ly-al, Hbeta, Halpha and Mg II2798 line profiles of the
Seyfert 1 galaxy III Zw 2. The shapes of these broad emission lines show
evidence of a multicomponent origin and also features which may be identified
as the peaks due to a rotating disk. We have proposed a two-component Broad
Line Region (BLR) model consisting of an inner Keplerian relativistic disk and
an outer structure surrounding the disk. The results of the fitting of the four
Broad Emission Lines (BELs) here considered, are highly consistent in both the
inner and outer component parameters. Adopting a mass of approx. 2 E8 sollar
masses for the central object we found that the outer radius of the disk is
approximately equal for the four considered lines (approx 0.01 pc). However,
the inner radius of the disk is not the same: 0.0018 pc for Ly-alpha, 0.0027 pc
for Mg II, and 0.0038 pc for the Balmer lines. This as well as the relatively
broad component present in the blue wings of the narrow [OIII] lines indicate
stratification in the emission-line region. Using long-term Hbeta observations
(1972-1990, 1998) we found a flux variation of the BEL with respect to the
[OIII] lines.Comment: ApJ, accepted, 22 pages, 10 figure
Galaxies Probing Galaxies at High Resolution: Co-Rotating Gas Associated with a Milky Way Analog at z=0.4
We present results on gas flows in the halo of a Milky Way-like galaxy at
z=0.413 based on high-resolution spectroscopy of a background galaxy. This is
the first study of circumgalactic gas at high spectral resolution towards an
extended background source (i.e., a galaxy rather than a quasar). Using
longslit spectroscopy of the foreground galaxy, we observe spatially extended H
alpha emission with circular rotation velocity v=270 km/s. Using echelle
spectroscopy of the background galaxy, we detect Mg II and Fe II absorption
lines at impact parameter rho=27 kpc that are blueshifted from systemic in the
sense of the foreground galaxy's rotation. The strongest absorber EW(2796) =
0.90 A has an estimated column density (N_H>10^19 cm-2) and line-of-sight
velocity dispersion (sigma=17 km/s) that are consistent with the observed
properties of extended H I disks in the local universe. Our analysis of the
rotation curve also suggests that this r=30 kpc gaseous disk is warped with
respect to the stellar disk. In addition, we detect two weak Mg II absorbers in
the halo with small velocity dispersions (sigma<10 km/s). While the exact
geometry is unclear, one component is consistent with an extraplanar gas cloud
near the disk-halo interface that is co-rotating with the disk, and the other
is consistent with a tidal feature similar to the Magellanic Stream. We can
place lower limits on the cloud sizes (l>0.4 kpc) for these absorbers given the
extended nature of the background source. We discuss the implications of these
results for models of the geometry and kinematics of gas in the circumgalactic
medium.Comment: 14 pages, 6 figures, submitted to ApJ, comments welcom
High-Velocity Outflows Without Agn Feedback: Eddington-Limited Star Formation in Compact Massive Galaxies
We present the discovery of compact, obscured star formation in galaxies at z ~ 0.6 that exhibit 1000 km s–1 outflows. Using optical morphologies from the Hubble Space Telescope and infrared photometry from the Wide-field Infrared Survey Explorer, we estimate star formation rate (SFR) surface densities that approach ΣSFR ≈ 3000 M ☉ yr–1 kpc–2, comparable to the Eddington limit from radiation pressure on dust grains. We argue that feedback associated with a compact starburst in the form of radiation pressure from massive stars and ram pressure from supernovae and stellar winds is sufficient to produce the high-velocity outflows we observe, without the need to invoke feedback from an active galactic nucleus
The OPTX Project IV: How Reliable is [OIII] as a Measure of AGN Activity?
We compare optical and hard X-ray identifications of AGNs using a uniformly
selected (above a flux limit of f_2-8 keV = 3.5e-15 erg/cm2/s) and highly
optically spectroscopically complete ( > 80% for f_2-8 keV > 1e-14 erg/cm2/s
and > 60% below) 2-8 keV sample observed in three Chandra fields (CLANS,
CLASXS, and the CDF-N). We find that empirical emission-line ratio diagnostic
diagrams misidentify 20-50% of the X-ray selected AGNs that can be put on these
diagrams as star formers, depending on which division is used. We confirm that
there is a large (2 orders in magnitude) dispersion in the log ratio of the
[OIII]5007A to hard X-ray luminosities for the non-broad line AGNs, even after
applying reddening corrections to the [OIII] luminosities. We find that the
dispersion is similar for the broad-line AGNs, where there is not expected to
be much X-ray absorption from an obscuring torus around the AGN nor much
obscuration from the galaxy along the line-of-sight if the AGN is aligned with
the galaxy. We postulate that the X-ray selected AGNs that are misidentified by
the diagnostic diagrams have low [OIII] luminosities due to the complexity of
the structure of the narrow-line region, which causes many ionizing photons
from the AGN not to be absorbed. This would mean that the [OIII] luminosity can
only be used to predict the X-ray luminosity to within a factor of ~3 (one
sigma). Despite selection effects, we show that the shapes and normalizations
of the [OIII] and transformed hard X-ray luminosity functions show reasonable
agreement, suggesting that the [OIII] samples are not finding substantially
more AGNs at low redshifts than hard X-ray samples.Comment: Accepted for publication in the Astrophysical Journal. 11 pages, 10
figure
Violent quenching : Molecular Gas Blown to 1000 km s -1 during a Major Merger
Accepted for publication in ApJ LettersWe present Atacama Large Millimeter/submillimeter Array observations of a massive () compact ( pc) merger remnant at z = 0.66 that is driving a 1000 km s -1 outflow of cool gas, with no observational trace of an active galactic nucleus (AGN). We resolve molecular gas on scales of approximately 1-2 kpc, and our main finding is the discovery of a wing of blueshifted CO J(2 → 1) emission out to-1000 km s -1 relative to the stars. We argue that this is the molecular component of a multiphase outflow, expelled from the central starburst within the past 5 Myr through stellar feedback, although we cannot rule out previous AGN activity as a launching mechanism. If the latter is true, then this is an example of a relic multiphase AGN outflow. We estimate a molecular mass outflow rate of approximately 300 M o yr -1, or about one third of the 10 Myr-Averaged star formation rate. This system epitomizes the multiphase "blowout" episode following a dissipational major merger-a process that has violently quenched central star formation and supermassive black hole growth.Peer reviewedFinal Accepted Versio
Stellar feedback as the origin of an extended molecular outflow in a starburst galaxy
Recent observations have revealed that starburst galaxies can drive molecular gas outflows through stellar radiation pressure. Molecular gas is the phase of the interstellar medium from which stars form, so these outflows curtail stellar mass growth in galaxies. Previously known outflows, however, involve small fractions of the total molecular gas content and have typical scales of less than a kiloparsec. In at least some cases, input from active galactic nuclei is dynamically important, so pure stellar feedback (the momentum return into the interstellar medium) has been considered incapable of rapidly terminating star formation on galactic scales. Molecular gas has been detected outside the galactic plane of the archetypal starburst galaxy M82 (refs 4 and 5), but so far there has been no evidence that starbursts can propel substantial quantities of cold molecular gas to the same galactocentric radius (about 10 kiloparsecs) as the warmer gas that has been traced by metal ion absorbers in the circumgalactic medium. Here we report observations of molecular gas in a compact (effective radius 100 parsecs) massive starburst galaxy at redshift 0.7, which is known to drive a fast outflow of ionized gas. We find that 35 per cent of the total molecular gas extends approximately 10 kiloparsecs, and one-third of this extended gas has a velocity of up to 1,000 kilometres per second. The kinetic energy associated with this high-velocity component is consistent with the momentum flux available from stellar radiation pressure. This demonstrates that nuclear bursts of star formation are capable of ejecting large amounts of cold gas from the central regions of galaxies, thereby strongly affecting their evolution by truncating star formation and redistributing matter.Peer reviewedFinal Accepted Versio
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