561 research outputs found
ALMA observations of atomic carbon in z~4 dusty star-forming galaxies
We present ALMA [CI]() (rest frequency 492 GHz) observations for a
sample of 13 strongly-lensed dusty star-forming galaxies originally discovered
at 1.4mm in a blank-field survey by the South Pole Telescope. We compare these
new data with available [CI] observations from the literature, allowing a study
of the ISM properties of extreme dusty star-forming galaxies spanning
a redshift range . Using the [CI] line as a tracer of the molecular
ISM, we find a mean molecular gas mass for SPT-DSFGs of
M. This is in tension with gas masses derived via low- CO
and dust masses; bringing the estimates into accordance requires either (a) an
elevated CO-to-H conversion factor for our sample of and a gas-to-dust ratio , or (b) an high carbon abundance . Using observations of a range of additional atomic
and molecular lines (including [CI], [CII], and multiple transitions of CO), we
use a modern Photodissociation Region code (3D-PDR) to assess the physical
conditions (including the density, UV radiation field strength, and gas
temperature) within the ISM of the DSFGs in our sample. We find that the ISM
within our DSFGs is characterised by dense gas permeated by strong UV fields.
We note that previous efforts to characterise PDR regions in DSFGs may have
significantly underestimated the density of the ISM. Combined, our analysis
suggests that the ISM of extreme dusty starbursts at high redshift consists of
dense, carbon-rich gas not directly comparable to the ISM of starbursts in the
local Universe.Comment: 21 pages, 12 figures. Accepted for publication in MNRA
Editorials
Trauma - today and tomorrowNeutron therapy - clinical considerationsDon Craib's legacyHealth informatic
Sub-kiloparsec Imaging of Cool Molecular Gas in Two Strongly Lensed Dusty, Star-Forming Galaxies
We present spatially-resolved imaging obtained with the Australia Telescope
Compact Array (ATCA) of three CO lines in two high-redshift gravitationally
lensed dusty star-forming galaxies, discovered by the South Pole Telescope.
Strong lensing allows us to probe the structure and dynamics of the molecular
gas in these two objects, at z=2.78 and z=5.66, with effective source-plane
resolution of less than 1kpc. We model the lensed emission from multiple CO
transitions and the dust continuum in a consistent manner, finding that the
cold molecular gas as traced by low-J CO always has a larger half-light radius
than the 870um dust continuum emission. This size difference leads to up to 50%
differences in the magnification factor for the cold gas compared to dust. In
the z=2.78 galaxy, these CO observations confirm that the background source is
undergoing a major merger, while the velocity field of the other source is more
complex. We use the ATCA CO observations and comparable resolution Atacama
Large Millimeter/submillimeter Array dust continuum imaging of the same objects
to constrain the CO-H_2 conversion factor with three different procedures,
finding good agreement between the methods and values consistent with those
found for rapidly star-forming systems. We discuss these galaxies in the
context of the star formation - gas mass surface density relation, noting that
the change in emitting area with observed CO transition must be accounted for
when comparing high-redshift galaxies to their lower redshift counterparts.Comment: 14 pages, 7 figures; accepted for publication in Ap
SPT 0538-50: Physical conditions in the ISM of a strongly lensed dusty star-forming galaxy at z=2.8
We present observations of SPT-S J053816-5030.8, a gravitationally-lensed
dusty star forming galaxy (DSFG) at z = 2.7817, first discovered at millimeter
wavelengths by the South Pole Telescope. SPT 0538-50 is typical of the
brightest sources found by wide-field millimeter-wavelength surveys, being
lensed by an intervening galaxy at moderate redshift (in this instance, at z =
0.441). We present a wide array of multi-wavelength spectroscopic and
photometric data on SPT 0538-50, including data from ALMA, Herschel PACS and
SPIRE, Hubble, Spitzer, VLT, ATCA, APEX, and the SMA. We use high resolution
imaging from HST to de-blend SPT 0538-50, separating DSFG emission from that of
the foreground lens. Combined with a source model derived from ALMA imaging
(which suggests a magnification factor of 21 +/- 4), we derive the intrinsic
properties of SPT 0538-50, including the stellar mass, far-IR luminosity, star
formation rate, molecular gas mass, and - using molecular line fluxes - the
excitation conditions within the ISM. The derived physical properties argue
that we are witnessing compact, merger-driven star formation in SPT 0538-50,
similar to local starburst galaxies, and unlike that seen in some other DSFGs
at this epoch.Comment: 16 pages, 11 figures. Accepted for publication in Ap
Extragalactic millimeter-wave point source catalog, number counts and statistics from 771 square degrees of the SPT-SZ Survey
We present a point source catalog from 771 square degrees of the South Pole
Telescope Sunyaev Zel'dovich (SPT-SZ) survey at 95, 150, and 220 GHz. We detect
1545 sources above 4.5 sigma significance in at least one band. Based on their
relative brightness between survey bands, we classify the sources into two
populations, one dominated by synchrotron emission from active galactic nuclei,
and one dominated by thermal emission from dust-enshrouded star-forming
galaxies. We find 1238 synchrotron and 307 dusty sources. We cross-match all
sources against external catalogs and find 189 unidentified synchrotron sources
and 189 unidentified dusty sources. The dusty sources without counterparts are
good candidates for high-redshift, strongly lensed submillimeter galaxies. We
derive number counts for each population from 1 Jy down to roughly 9, 5, and 11
mJy at 95, 150, and 220 GHz. We compare these counts with galaxy population
models and find that none of the models we consider for either population
provide a good fit to the measured counts in all three bands. The disparities
imply that these measurements will be an important input to the next generation
of millimeter-wave extragalactic source population models.Comment: 23 pages, 8 figures, submitted to Ap
The Rest-Frame Submillimeter Spectrum of High-Redshift, Dusty, Star-Forming Galaxies
We present the average rest-frame spectrum of high-redshift dusty,
star-forming galaxies from 250-770GHz. This spectrum was constructed by
stacking ALMA 3mm spectra of 22 such sources discovered by the South Pole
Telescope and spanning z=2.0-5.7. In addition to multiple bright spectral
features of 12CO, [CI], and H2O, we also detect several faint transitions of
13CO, HCN, HNC, HCO+, and CN, and use the observed line strengths to
characterize the typical properties of the interstellar medium of these
high-redshift starburst galaxies. We find that the 13CO brightness in these
objects is comparable to that of the only other z>2 star-forming galaxy in
which 13CO has been observed. We show that the emission from the high-critical
density molecules HCN, HNC, HCO+, and CN is consistent with a warm, dense
medium with T_kin ~ 55K and n_H2 >~ 10^5.5 cm^-3. High molecular hydrogen
densities are required to reproduce the observed line ratios, and we
demonstrate that alternatives to purely collisional excitation are unlikely to
be significant for the bulk of these systems. We quantify the average emission
from several species with no individually detected transitions, and find
emission from the hydride CH and the linear molecule CCH for the first time at
high redshift, indicating that these molecules may be powerful probes of
interstellar chemistry in high-redshift systems. These observations represent
the first constraints on many molecular species with rest-frame transitions
from 0.4-1.2mm in star-forming systems at high redshift, and will be invaluable
in making effective use of ALMA in full science operations.Comment: 19 pages, 10 figures (2 in appendices); accepted for publication in
Ap
The Spatial Extent of (U)LIRGs in the mid-Infrared I: The Continuum Emission
We present an analysis of the extended mid-infrared (MIR) emission of the
Great Observatories All-Sky LIRG Survey (GOALS) sample based on 5-15um low
resolution spectra obtained with the IRS on Spitzer. We calculate the fraction
of extended emission as a function of wavelength for the galaxies in the
sample, FEE_lambda. We can identify 3 general types of FEE_lambda: one where it
is constant, one where features due to emission lines and PAHs appear more
extended than the continuum, and a third which is characteristic of sources
with deep silicate absorption at 9.7um. More than 30% of the galaxies have a
median FEE_lambda larger than 0.5 implying that at least half of their MIR
emission is extended. Luminous Infrared Galaxies (LIRGs) display a wide range
of FEE in their warm dust continuum (0<=FEE_13.2um<=0.85). The large values of
FEE_13.2um that we find in many LIRGs suggest that their extended MIR continuum
emission originates in scales up to 10kpc. The mean size of the LIRG cores at
13.2um is 2.6kpc. However, once the LIR of the systems reaches the threshold of
~10^11.8Lsun, all sources become clearly more compact, with FEE_13.2um<=0.2,
and their cores are unresolved. Our estimated upper limit for the core size of
ULIRGs is less than 1.5kpc. The analysis indicates that the compactness of
systems with LIR>~10^11.25Lsun strongly increases in those classified as
mergers in their final stage of interaction. The FEE_13.2um is also related to
the contribution of an active galactic nucleus (AGN) to the MIR. Galaxies which
are more AGN-dominated are less extended, independently of their LIR. We
finally find that the extent of the MIR continuum emission is correlated with
the far-IR IRAS log(f_60um/f_100um) color. This enables us to place a lower
limit to the area in a galaxy from where the cold dust emission may originate,
a prediction which can be tested soon with the Herschel Space Telescope.Comment: 18 pages, 8 figures, accepted for publication in Ap
- …