269 research outputs found
The WiggleZ Dark Energy Survey: high-resolution kinematics of luminous star-forming galaxies
We report evidence of ordered orbital motion in luminous star-forming galaxies at z~ 1.3. We present integral field spectroscopy (IFS) observations, performed with the OH Suppressing InfraRed Imaging Spectrograph (OSIRIS) system, assisted by laser guide star adaptive optics on the Keck telescope, of 13 star-forming galaxies selected from the WiggleZ Dark Energy Survey. Selected via ultraviolet and [O ii] emission, the large volume of the WiggleZ survey allows the selection of sources which have comparable intrinsic luminosity and stellar mass to IFS samples at z > 2. Multiple 1–2 kpc size subcomponents of emission, or ‘clumps’, are detected within the Hα spatial emission which extends over 6–10 kpc in four galaxies, resolved compact emission (r 100 km s^(−1)) in the most compact sources. This unique data set reveals that the most luminous star-forming galaxies at z > 1 are gaseous unstable discs indicating that a different mode of star formation could be feeding gas to galaxies at z > 1, and lending support to theories of cold dense gas flows from the intergalactic medium
Size-scaling of clump instabilities in turbulent, feedback regulated disks
We explore the scaling between the size of star-forming clumps and rotational
support in massively star-forming galactic disks. The analysis relies on
simulations of a clumpy galaxy at and the observed DYNAMO sample of rare
clumpy analogs at to test a predictive clump size scaling
proposed by \citet{Fisher2017ApJ...839L...5F} in the context of the Violent
Disk Instability (VDI) theory. We here determine the clump sizes using a
recently presented 2-point estimator, which is robust against resolution/noise
effects, hierarchical clump substructure, clump-clump overlap and other
galactic substructure. After verifying Fisher's clump scaling relation for the
DYNAMO observations, we explore whether this relation remains characteristic of
the VDI theory, even if realistic physical processes, such as local asymetries
and stellar feedback, are included in the model. To this end, we rely on
hydrodynamic zoom-simulations of a Milky Way-mass galaxy with four different
feedback prescriptions. We find that, during its marginally stable epoch at
, this mock galaxy falls on the clump scaling relation, although its
position on this relation depends on the feedback model. This finding implies
that Toomre-like stability considerations approximately apply to large
() instabilities in marginally stable turbulent disks,
irrespective of the feedback model, but also emphasizes that the global clump
distribution of a turbulent disk depends strongly on feedback.Comment: Accepted by ApJ, no changes made. 11 pages, 4 figure
The connection between the peaks in velocity dispersion and star-forming clumps of turbulent galaxies
We present Keck/OSIRIS adaptive optics observations with 150-400 pc spatial
sampling of 7 turbulent, clumpy disc galaxies from the DYNAMO sample
(). DYNAMO galaxies have previously been shown to be well matched
in properties to main sequence galaxies at . Integral field
spectroscopy observations using adaptive optics are subject to a number of
systematics including a variable PSF and spatial sampling, which we account for
in our analysis. We present gas velocity dispersion maps corrected for these
effects, and confirm that DYNAMO galaxies do have high gas velocity dispersion
(\kms), even at high spatial sampling. We find statistically
significant structure in 6 out of 7 galaxies. The most common distance between
the peaks in velocity dispersion and emission line peaks is ~kpc, we
note this is very similar to the average size of a clump measured with HST
H maps. This could suggest that the peaks in velocity dispersion in
clumpy galaxies likely arise due to some interaction between the clump and the
surrounding ISM of the galaxy, though our observations cannot distinguish
between outflows, inflows or velocity shear. Observations covering a wider area
of the galaxies will be needed to confirm this result.Comment: Accepted for publication in MNRA
Spatially resolved dust properties and quasar-galaxy decomposition of HyLIRG at redshift 4.4
We report spatially resolved dust properties of the quasar host galaxy BRI
1335-0417 at redshift constrained by the ALMA observations. The dust
temperature map, derived from a greybody fit to rest-frame 90 and 161 m
continuum images, shows a steep increase towards the centre, reaching K. Image decomposition analysis reveals the presence of a point source in
both dust continuum images at the same position as the highest temperature peak
and the optical quasar position, which we attribute to warm dust heated by an
active galactic nucleus (AGN). We show that a model including this warm
component along with cooler dust heated by star formation describes the global
SED better than a single component model, with dust temperatures of
87.1 K (warm component) and 52.6 K (cold
component). The star formation rate (SFR) estimated from the cold dust
component is yr, a factor of three smaller
than previous estimates due to a large AGN contribution (%).
The unresolved warm dust component also explains the steep temperature
gradient, as the temperature profile derived after the point source subtraction
is flat. We further show that AGN-host galaxy decomposition is critical for
estimating SFR distribution, as point source subtraction reduces the estimated
central SFR surface density by over a factor of three.
With this correction, spatially resolved measurements of
and the surface gas mass density
form a roughly linear sequence in the Kennicutt-Schmidt
diagram with a constant gas depletion time of 50-200 Myr.Comment: 25pages, 25figures, 4tables, Submitted to MNRAS, Comments are warmly
welcome
Extreme gas fractions in clumpy, turbulent disk galaxies at z~0.1
In this letter we report the discovery of CO fluxes, suggesting very high gas
fractions in three disk galaxies seen in the nearby Universe (z ~ 0.1). These
galaxies were investigated as part of the DYnamics of Newly Assembled Massive
Objects (DYNAMO) survey. High-resolution Hubble Space Telescope imaging of
these objects reveals the presence of large star forming clumps in the bodies
of the galaxies, while spatially resolved spectroscopy of redshifted Halpha
reveals the presence of high dispersion rotating disks. The internal dynamical
state of these galaxies resembles that of disk systems seen at much higher
redshifts (1 < z < 3). Using CO(1-0) observations made with the Plateau de Bure
Interferometer, we find gas fractions of 20-30% and depletion times of tdep ~
0.5 Gyr (assuming a Milky Way-like CO conversion factor). These properties are
unlike those expected for low- redshift galaxies of comparable specific star
formation rate, but they are normal for their high-z counterparts. DYNAMO
galaxies break the degeneracy between gas fraction and redshift, and we show
that the depletion time per specific star formation rate for galaxies is
closely tied to gas fraction, independent of redshift. We also show that the
gas dynamics of two of our local targets corresponds to those expected from
unstable disks, again resembling the dynamics of high-z disks. These results
provide evidence that DYNAMO galaxies are local analogues to the clumpy,
turbulent disks, which are often found at high redshift.Comment: Accepted to ApJ Letter
The physical drivers of gas turbulence in simulated disc galaxies
We use the EAGLE cosmological simulations to study the evolution of the
vertical velocity dispersion of cold gas, , in central disc
galaxies and its connection to stellar feedback, gravitational instabilities,
cosmological gas accretion and galaxy mergers. To isolate the impact of
feedback, we analyse runs that turn off stellar and (or) AGN feedback in
addition to a run that includes both. The evolution of and its
dependence on stellar mass and star formation rate in EAGLE are in good
agreement with observations. Galaxies hosted by haloes of similar virial mass,
, have similar values even in runs where feedback is
absent. The prevalence of local instabilities in discs is uncorrelated with
at low redshift and becomes only weakly correlated at high redshifts
and in galaxies hosted by massive haloes. correlates most strongly
with the specific gas accretion rate onto the disc as well as with the degree
of misalignment between the inflowing gas and the disc's rotation axis. These
correlations are significant across all redshifts and halo masses, with
misaligned accretion being the primary driver of high gas turbulence at
redshifts and for halo masses . Galaxy mergers increase , but because they are rare in
our sample, they play only a minor role in its evolution. Our results suggest
that the turbulence of cold gas in EAGLE discs results from a complex interplay
of different physical processes whose relative importance depends on halo mass
and redshift.Comment: 22 pages, 12 figures. Accepted for publication in MNRA
Connecting Clump Sizes in Turbulent Disk Galaxies to Instability Theory
In this letter we study the mean sizes of Halpha clumps in turbulent disk
galaxies relative to kinematics, gas fractions, and Toomre Q. We use 100~pc
resolution HST images, IFU kinematics, and gas fractions of a sample of rare,
nearby turbulent disks with properties closely matched to z~1.5-2 main-sequence
galaxies (the DYNAMO sample). We find linear correlations of normalized mean
clump sizes with both the gas fraction and the velocity dispersion-to-rotation
velocity ratio of the host galaxy. We show that these correlations are
consistent with predictions derived from a model of instabilities in a
self-gravitating disk (the so-called "violent disk instability model"). We also
observe, using a two-fluid model for Q, a correlation between the size of
clumps and self-gravity driven unstable regions. These results are most
consistent with the hypothesis that massive star forming clumps in turbulent
disks are the result of instabilities in self-gravitating gas-rich disks, and
therefore provide a direct connection between resolved clump sizes and this in
situ mechanism.Comment: Accepted to Apj Letter
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