245 research outputs found
Characterizing Extragalactic Anomalous Microwave Emission in NGC 6946 with CARMA
Using 1 cm and 3 mm CARMA and 2 mm GISMO observations, we follow up the first
extragalactic detection of anomalous microwave emission (AME) reported by
Murphy et al. 2010 in an extranuclear region (Enuc. 4) of the nearby face-on
spiral galaxy NGC 6946. We find the spectral shape and peak frequency of AME in
this region to be consistent with models of spinning dust emission. However,
the strength of the emission far exceeds the Galactic AME emissivity given the
abundance of polycyclic aromatic hydrocarbons (PAHs) in that region. Using our
galaxy-wide 1 cm map (21" resolution), we identify a total of eight 21"x21"
regions in NGC 6946 that harbour AME at >95% significance at levels comparable
to that observed in Enuc. 4. The remainder of the galaxy has 1 cm emission
consistent with or below the observed Galactic AME emissivity per PAH surface
density. We probe relationships between the detected AME and dust surface
density, PAH emission, and radiation field, though no environmental property
emerges to delineate regions with strong versus weak or non-existent AME. On
the basis of these data and other AME observations in the literature, we
determine that the AME emissivity per unit dust mass is highly variable. We
argue that the spinning dust hypothesis, which predicts the AME power to be
approximately proportional to the PAH mass, is therefore incomplete.Comment: 12 pages, submitted to MNRAS, comments welcom
Dust formation, evolution, and obscuration effects in the very high-redshift universe
The evolution of dust at redshifts z>9, and consequently the dust properties,
differs greatly from that in the local universe. In contrast to the local
universe, core collapse supernovae (CCSNe) are the only source of
thermally-condensed dust. Because of the low initial dust-to-gas mass ratio,
grain destruction rates are low, so that CCSNe are net producers of
interstellar dust. Galaxies with large initial gas mass or high mass infall
rate will therefore have a more rapid net rate of dust production comported to
galaxies with lower gas mass, even at the same star formation rate. The dust
composition is dominated by silicates, which exhibit a strong rise in the UV
opacity near the Lyman break. This "silicate-UV break" may be confused with the
Lyman break, resulting in a misidentification of a galaxies' photometric
redshift. In this paper we demonstrate these effects by analyzing the spectral
energy distribution (SED) of MACS1149-JD, a lensed galaxy at z=9.6. A potential
2mm counterpart of MACS1149-JD has been identified with GISMO. While additional
observations are required to corroborate this identification, we use this
possible association to illustrate the physical processes and the observational
effects of dust in the very high redshift universe.Comment: Accepted for publication in ApJ Letter
New constraints on dust emission and UV attenuation of z=6.5-7.5 galaxies from millimeter observations
We have targeted two recently discovered Lyman break galaxies (LBGs) to
search for dust continuum and [CII] 158 micron line emission. The strongly
lensed z~6.8 LBG A1703-zD1 behind the galaxy cluster Abell 1703, and the
spectroscopically confirmed z=7.508 LBG z8-GND-5296 in the GOODS-N field have
been observed with the Plateau de Bure interferometer (PdBI) at 1.2mm. These
observations have been combined with those of three z>6.5 Lya emitters (named
HCM6A, Himiko, and IOK-1), for which deep measurements were recently obtained
with the PdBI and ALMA. [CII] is undetected in both galaxies, providing a deep
upper limit for Abell1703-zD1, comparable to recent ALMA non-detections. Dust
continuum emission from Abell1703-zD1 and z8-GND-5296 is not detected with an
rms of 0.12 and 0.16 mJy/beam. From these non-detections we derive upper limits
on their IR luminosity and star formation rate, dust mass, and UV attenuation.
Thanks to strong gravitational lensing the limit for Abell1703-zD1 is probing
the sub-LIRG regime ( Lsun) and very low dust
masses ( Msun). We find that all five galaxies are
compatible with the Calzetti IRX- relation, their UV attenuation is
compatible with several indirect estimates from other methods (the UV slope,
extrapolation of the attenuation measured from the IR/UV ratio at lower
redshift, and SED fits), and the dust-to-stellar mass ratio is not incompatible
with that of galaxies from z=0 to 3. For their stellar mass the high-z galaxies
studied here have an attenuation below the one expected from the mean relation
of low redshift (z<1.5) galaxies. More and deeper (sub)-mm data are clearly
needed to directly determine the UV attenuation and dust content of the
dominant population of high-z star-forming galaxies and to establish more
firmly their dependence on stellar mass, redshift, and other properties.Comment: 10 pages, 7 figures. Minor revisions. Accepted for publication in A&
An Analysis of ALMA Deep Fields and the Perceived Dearth of High-z Galaxies
Deep, pencil-beam surveys from ALMA at 1.1-1.3mm have uncovered an apparent
absence of high-redshift dusty galaxies, with existing redshift distributions
peaking around . This has led to a perceived dearth of dusty
systems at , and the conclusion, according to some models, that the early
Universe was relatively dust-poor. In this paper, we extend the backward
evolution galaxy model described by Casey et al. (2018) to the ALMA regime (in
depth and area) and determine that the measured number counts and redshift
distributions from ALMA deep field surveys are fully consistent with
constraints of the infrared luminosity function (IRLF) at determined by
single-dish submillimeter and millimeter surveys conducted on much larger
angular scales (deg). We find that measured 1.1-1.3mm number
counts are most constraining for the measurement of the faint-end slope of the
IRLF at . Recent
studies have suggested that UV-selected galaxies at may be particularly
dust-poor, but we find their millimeter-wave emission cannot rule out
consistency with the Calzetti dust attenuation law even by assuming relatively
typical, cold-dust (K) SEDs. Our models suggest that
the design of ALMA deep fields requires substantial revision to constrain the
prevalence of early Universe obscured starbursts. The most promising
avenue for detection and characterization of such early dusty galaxies will
come from future ALMA 2mm blank field surveys covering a few hundred
arcmin and the combination of existing and future dual-purpose 3mm
datasets.Comment: 21 pages, 12 figures, accepted for publication in Ap
The Galactic centre mini-spiral in the mm-regime
The mini-spiral is a feature of the interstellar medium in the central ~2 pc
of the Galactic center. It is composed of several streamers of dust and ionised
and atomic gas with temperatures between a few 100 K to 10^4 K. There is
evidence that these streamers are related to the so-called circumnuclear disk
of molecular gas and are ionized by photons from massive, hot stars in the
central parsec. We attempt to constrain the emission mechanisms and physical
properties of the ionized gas and dust of the mini-spiral region with the help
of our multiwavelength data sets. Our observations were carried out at 1.3 mm
and 3 mm with the mm interferometric array CARMA in California in March and
April 2009, with the MIR instrument VISIR at ESO's VLT in June 2006, and the
NIR Br-gamma with VLT NACO in August 2009. We present high resolution maps of
the mini-spiral, and obtain a spectral index of 0.5 for Sgr A*, indicating an
inverted synchrotron spectrum. We find electron densities within the range
0.8-1.5x10^4 cm-3 for the mini-spiral from the radio continuum maps, along with
a dust mass contribution of ~0.25 solar masses from the MIR dust continuum, and
extinctions ranging from 1.8-3 at 2.16 micron in the Br-gamma line. We observe
a mixture of negative and positive spectral indices in our 1.3 mm and 3 mm
observations of the extended emission of the mini-spiral, which we interpret as
evidence that there are a range of contributions to the thermal free-free
emission by the ionized gas emission and by dust at 1.3 mm.Comment: 9 pages, 11 figures, accepted to A&
CO(1-0) in z ≳ 4 Quasar Host Galaxies: No Evidence for Extended Molecular Gas Reservoirs
We present ^(12)CO(J = 1 → 0) observations of the high-redshift quasi-stellar objects (QSOs) BR 1202-0725 (z = 4.69), PSS J2322+1944 (z = 4.12), and APM 08279+5255 (z = 3.91) using the NRAO Green Bank Telescope (GBT) and the MPIfR Effelsberg 100 m telescope. We detect, for the first time, the CO ground-level transition in BR 1202-0725. For PSS J2322+1944 and APM 08279+5255, our observations result in line fluxes that are consistent with previous NRAO Very Large Array (VLA) observations, but they reveal the full line profiles. We report a typical lensing-corrected velocity-integrated intrinsic ^(12)CO(J = 1 → 0) line luminosity of L'_(CO) = 5 × 10^(10) K km s^(-1) pc^2 and a typical total H_2 mass of M(H_2) = 4 × 10^(10) M_☉ for the sources in our sample. The CO/FIR luminosity ratios of these high-z sources follow the same trend as seen for low-z galaxies, leading to a combined solution of log L_(FIR) = (1.39 ± 0.05) log L_(CO) - 1.76. It has previously been suggested that the molecular gas reservoirs in some quasar host galaxies may exhibit luminous, extended ^(12)CO(J = 1 → 0) components that are not observed in the higher J CO transitions. Using the line profiles and the total intensities of our observations and large velocity gradient (LVG) models based on previous results for higher J CO transitions, we derive that emission from all CO transitions is described well by a single gas component in which all molecular gas is concentrated in a compact nuclear region. Thus, our observations and models show no indication of a luminous extended, low surface brightness molecular gas component in any of the high-redshift QSOs in our sample. If such extended components exist, their contribution to the overall luminosity is limited to at most 30%
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