1,152 research outputs found
Kinematic Evidence for Superbubbles in I Zw 18: Constraints on the Star Formation History and Chemical Evolution
We have combined measurements of the kinematics, morphology, and oxygen
abundance of the ionized gas in \IZw18, one of the most metal-poor galaxies
known, to examine the star formation history and chemical mixing processes.Comment: 31 pages including 6 figures. Accepted for publication in the
Astrophysical Journa
Resolving Gas Flows in the Ultraluminous Starburst IRAS23365+3604 with Keck LGSAO/OSIRIS
Keck OSIRIS/LGSAO observations of the ultraluminous galaxy IRAS~23365+3604
resolve a circumnuclear bar (or irregular disk) of semimajor axis 0.42" (520
pc) in Paschen-alpha emission. The line-of-sight velocity of the ionized gas
increases from the northeast toward the southwest; this gradient is
perpendicular to the photometric major axis of the infrared emission. Two pairs
of bends in the zero-velocity line are detected. The inner bend provides
evidence for gas inflow onto the circumnuclear disk/bar structure. We interpret
the gas kinematics on kiloparsec scales in relation to the molecular gas disk
and multiphase outflow discovered previously. In particular, the fast component
of the outflow (detected previously in line wings) is not detected, adding
support to the conjecture that the fast wind originates well beyond the
nucleus. These data directly show the dynamics of gas inflow and outflow in the
central kiloparsec of a late-stage, gas-rich merger and demonstrate the
potential of integral field spectroscopy to improve our understanding of the
role of gas flows during the growth phase of bulges and supermassive black
holes.Comment: 14 pages with 7 figures accepted to the astrophysical journa
Resolving 3D Disk Orientation using High-Resolution Images: New Constraints on Circumgalactic Gas Inflows
We constrain gas inflow speeds in star-forming galaxies with color gradients
consistent with inside-out disk growth. Our method combines new measurements of
disk orientation with previously described circumgalactic absorption in
background quasar spectra. Two quantities, a position angle and an axis ratio,
describe the projected shape of each galactic disk on the sky, leaving an
ambiguity about which side of the minor axis is tipped toward the observer.
This degeneracy regarding the 3D orientation of disks has compromised previous
efforts to measure gas inflow speeds. We present HST and Keck/LGSAO imaging
that resolves the spiral structure in five galaxies at redshift .
We determine the sign of the disk inclination for four galaxies, under the
assumption that spiral arms trail the rotation. We project models for both
radial infall in the disk plane and circular orbits onto each quasar sightline.
We compare the resulting line-of-sight velocities to the observed velocity
range of Mg II absorption in spectra of background quasars, which intersect the
disk plane at radii between 69 and 115 kpc. For two sightlines, we constrain
the maximum radial inflow speeds as 30-40 km s. We also rule out a
velocity component from radial inflow in one sightline, suggesting that the
structures feeding gas to these growing disks do not have unity covering
factor. We recommend appropriate selection criteria for building larger samples
of galaxy--quasar pairs that produce orientations sensitive to constraining
inflow properties.Comment: 15 pages with 8 figures and 2 tables; accepted for publication in Ap
The ring around SN1987A
Stars in the 9-40 solar mass range play a prominent role in the hydrodynamical and chemical evolution of galaxies. Their stellar winds and supernova explosions are believed to create the hot component of the interstellar medium (ISM). In some galactic disks, the kiloparsec sized super bubbles formed around clusters of massive stars may blow out of the disk plane and release hot, metal enriched gas into the galaxy's halo. Additionally, the expanding shock front of a super bubble in the disk may trigger additional star formation. Furthermore, similar processes probably drive the galactic winds associated with star burst nuclei that enrich the intracluster and intergalactic mediums. Nonetheless, the explosion of a blue super giant in the Large Magellanic Cloud (LMC), SN1987A, illuminated the incompleteness of our understanding of massive stars. Evolutionary models of massive stars do not synthesize the observed super giant populations in either the Milky Way or LMC. Our modeling of the formation of SN1987A's ring will improve our knowledge of both the post-main-sequence evolution of massive stars and their coupling to the ISM in galaxies
Temperature-based metallicity measurements at z=0.8: direct calibration of strong-line diagnostics at intermediate redshift
We present the first direct calibration of strong-line metallicity
diagnostics at significant cosmological distances using a sample at z=0.8 drawn
from the DEEP2 Galaxy Redshift Survey. Oxygen and neon abundances are derived
from measurements of electron temperature and density. We directly compare
various commonly used relations between gas-phase metallicity and strong line
ratios of O, Ne, and H at z=0.8 and z=0. There is no evolution with redshift at
high precision (, ). O, Ne, and H line ratios follow the same
locus at z=0.8 as at z=0 with 0.02 dex evolution and low scatter
(0.04 dex). This suggests little or no evolution in physical
conditions of HII regions at fixed oxygen abundance, in contrast to models
which invoke more extreme properties at high redshifts. We speculate that
offsets observed in the [N II]/H versus [O III]/H diagram at
high redshift are therefore due to [NII] emission, likely as a result of
relatively high N/O abundance. If this is indeed the case, then nitrogen-based
metallicity diagnostics suffer from systematic errors at high redshift. Our
findings indicate that locally calibrated abundance diagnostics based on
alpha-capture elements can be reliably applied at z1 and possibly at
much higher redshifts. This constitutes the first firm basis for the widespread
use of empirical calibrations in high redshift metallicity studies.Comment: 14 pages, 10 figures, accepted to Ap
Spatially Resolved Gas Kinematics within a Ly Nebula: Evidence for Large-scale Rotation
We use spatially extended measurements of Ly as well as less
optically thick emission lines from an 80 kpc Ly nebula at
to assess the role of resonant scattering and to disentangle
kinematic signatures from Ly radiative transfer effects. We find that
the Ly, CIV, HeII, and CIII] emission lines all tell a similar story in
this system, and that the kinematics are broadly consistent with large-scale
rotation. First, the observed surface brightness profiles are similar in extent
in all four lines, strongly favoring a picture in which the Ly photons
are produced in situ instead of being resonantly scattered from a central
source. Second, we see low kinematic offsets between Ly and the less
optically thick HeII line (100-200 km s), providing further
support for the argument that the Ly and other emission lines are all
being produced within the spatially extended gas. Finally, the full velocity
field of the system shows coherent velocity shear in all emission lines:
500 km s over the central 50 kpc of the nebula. The
kinematic profiles are broadly consistent with large-scale rotation in a gas
disk that is at least partially stable against collapse. These observations
suggest that the Ly nebula represents accreting material that is
illuminated by an offset, hidden AGN or distributed star formation, and that is
undergoing rotation in a clumpy and turbulent gas disk. With an implied mass of
M(<R=20 kpc) , this system may represent the
early formation of a large Milky Way mass galaxy or galaxy group.Comment: Accepted to ApJ; 25 pages in emulateapj format; 15 figures, 4 table
Ly emission from Green Peas: the role of circumgalactic gas density, covering, and kinematics
We report Hubble Space Telescope/Cosmic Origins Spectrograph observations of
the Ly emission and interstellar absorption lines in a sample of ten
star-forming galaxies at . Selected on the basis of high equivalent
width optical emission lines, the sample, dubbed "Green Peas," make some of the
best analogs for young galaxies in an early Universe. We detect Ly
emission in all ten galaxies, and 9/10 show double-peaked line profiles
suggestive of low HI column density. We measure Ly/H flux
ratios of 0.5-5.6, implying that 5% to 60% of Ly photons escape the
galaxies. These data confirm previous findings that low-ionization metal
absorption (LIS) lines are weaker when Ly escape fraction and
equivalent width are higher. However, contrary to previously favored
interpretations of this trend, increased Ly output cannot be the result
of varying HI covering: the Lyman absorption lines (Ly and higher) show
a covering fraction near unity for gas with cm.
Moreover, we detect no correlation between Ly escape and the outflow
velocity of the LIS lines, suggesting that kinematic effects do not explain the
range of Ly/H flux ratios in these galaxies. In contrast, we
detect a strong anti-correlation between the Ly escape fraction and the
velocity separation of the Ly emission peaks, driven primarily by the
velocity of the blue peak. As this velocity separation is sensitive to HI
column density, we conclude that Ly escape in these Green Peas is
likely regulated by the HI column density rather than outflow velocity or HI
covering fraction.Comment: 27 pages, 26 figures; Accepted for publication in the Astrophysical
Journa
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