172 research outputs found
CO-Dark Star Formation and Black Hole Activity in 3C 368 at z = 1.131: Coeval Growth of Stellar and Supermassive Black Hole Masses
We present the detection of four far-infrared fine-structure oxygen lines, as
well as strong upper limits for the CO(2-1) and [N II] 205 um lines, in 3C 368,
a well-studied radio-loud galaxy at z = 1.131. These new oxygen lines, taken in
conjunction with previously observed neon and carbon fine-structure lines,
suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and
extended star formation. A starburst dominated by O8 stars, with an age of ~6.5
Myr, provides a good fit to the fine-structure line data. This estimated age of
the starburst makes it nearly concurrent with the latest episode of AGN
activity, suggesting a link between the growth of the supermassive black hole
and stellar population in this source. We do not detect the CO(2-1) line, down
to a level twelve times lower than the expected value for star forming
galaxies. This lack of CO line emission is consistent with recent star
formation activity if the star-forming molecular gas has low metallicity, is
highly fractionated (such that CO is photodissociated through much of the
clouds), or is chemically very young (such that CO has not yet had time to
form). It is also possible, though we argue unlikely, that the ensemble of fine
structure lines are emitted from the region heated by the AGN.Comment: 10 pages, 4 figures, 2 tables, accepted for publication in the
Astrophysical Journa
Resolving Star Formation on Sub-Kiloparsec Scales in the High-Redshift Galaxy SDP.11 Using Gravitational Lensing
We investigate the properties of the interstellar medium, star formation, and
the current-day stellar population in the strongly-lensed star-forming galaxy
H-ATLAS J091043.1-000321 (SDP.11), at z = 1.7830, using new Herschel and ALMA
observations of far-infrared fine-structure lines of carbon, oxygen and
nitrogen. We report detections of the [O III] 52 um, [N III] 57 um, and [O I]
63 um lines from Herschel/PACS, and present high-resolution imaging of the [C
II] 158 um line, and underlying continuum, using ALMA. We resolve the [C II]
line emission into two spatially-offset Einstein rings, tracing the red- and
blue-velocity components of the line, in the ALMA/Band-9 observations at 0.2"
resolution. The values seen in the [C II]/FIR ratio map, as low as ~ 0.02% at
the peak of the dust continuum, are similar to those of local ULIRGs,
suggesting an intense starburst in this source. This is consistent with the
high intrinsic FIR luminosity (~ 3 x 10^12 Lo), ~ 16 Myr gas depletion
timescale, and < 8 Myr timescale since the last starburst episode, estimated
from the hardness of the UV radiation field. By applying gravitational lensing
models to the visibilities in the uv-plane, we find that the lensing
magnification factor varies by a factor of two across SDP.11, affecting the
observed line profiles. After correcting for the effects of differential
lensing, a symmetric line profile is recovered, suggesting that the starburst
present here may not be the result of a major merger, as is the case for local
ULIRGs, but instead could be powered by star-formation activity spread across a
3-5 kpc rotating disk.Comment: 17 pages, 8 figures, 3 tables, accepted for publication in the
Astrophysical Journa
CASSIS: The Cornell Atlas of Spitzer/Infrared Spectrograph Sources. II. High-resolution observations
The Infrared Spectrograph (IRS) on board the Spitzer Space Telescope observed about 15,000 objects during the cryogenic mission lifetime. Observations provided low-resolution (R~60-127) spectra over ~5-38um and high-resolution (R~600) spectra over ~10-37um. The Cornell Atlas of Spitzer/IRS Sources (CASSIS) was created to provide publishable quality spectra to the community. Low-resolution spectra have been available in CASSIS since 2011, and we present here the addition of the high-resolution spectra. The high-resolution observations represent approximately one third of all staring observations performed with the IRS instrument. While low-resolution observations are adapted to faint objects and/or broad spectral features (e.g., dust continuum, molecular bands), high-resolution observations allow more accurate measurements of narrow features (e.g., ionic emission lines) as well as a better sampling of the spectral profile of various features. Given the narrow aperture of the two high-resolution modules, cosmic ray hits and spurious features usually plague the spectra. Our pipeline is designed to minimize these effects through various improvements. A super sampled point-spread function was created in order to enable the optimal extraction in addition to the full aperture extraction. The pipeline selects the best extraction method based on the spatial extent of the object. For unresolved sources, the optimal extraction provides a significant improvement in signal-to-noise ratio over a full aperture extraction. We have developed several techniques for optimal extraction, including a differential method that eliminates low-level rogue pixels (even when no dedicated background observation was performed). The updated CASSIS repository now includes all the spectra ever taken by the IRS, with the exception of mapping observations
Mid-J CO Emission From NGC 891: Microturbulent Molecular Shocks in Normal Star Forming Galaxies
We have detected the CO(6-5), CO(7-6), and [CI] 370 micron lines from the
nuclear region of NGC 891 with our submillimeter grating spectrometer ZEUS on
the CSO. These lines provide constraints on photodissociation region (PDR) and
shock models that have been invoked to explain the H_2 S(0), S(1), and S(2)
lines observed with Spitzer. We analyze our data together with the H_2 lines,
CO(3-2), and IR continuum from the literature using a combined PDR/shock model.
We find that the mid-J CO originates almost entirely from shock-excited warm
molecular gas; contributions from PDRs are negligible. Also, almost all the H_2
S(2) and half of the S(1) line is predicted to emerge from shocks. Shocks with
a pre-shock density of 2x10^4 cm^-3 and velocities of 10 km/s and 20 km/s for
C-shocks and J-shocks, respectively, provide the best fit. In contrast, the
[CI] line emission arises exclusively from the PDR component, which is best
parameterized by a density of 3.2x10^3 cm^-3 and a FUV field of G_o = 100 for
both PDR/shock-type combinations. Our mid-J CO observations show that
turbulence is a very important heating source in molecular clouds, even in
normal quiescent galaxies. The most likely energy sources for the shocks are
supernovae or outflows from YSOs. The energetics of these shock sources favor
C-shock excitation of the lines.Comment: 18 pages, 2 figures, 6 tables, accepted by Ap
PCAdmix: Principal Components-Based Assignment of Ancestry along Each Chromosome in Individuals with Admixed Ancestry from Two or More Populations
Identifying ancestry along each chromosome in admixed individuals provides a wealth of information for understanding the population genetic history of admixture events and is valuable for admixture mapping and identifying recent targets of selection. We present PCAdmix (available at https://sites.google.com/site/pcadmix/home), a Principal Componentsbased algorithm for determining ancestry along each chromosome from a high-density, genome-wide set of phased single-nucleotide polymorphism (SNP) genotypes of admixed individuals. We compare our method to HAPMIX on simulated data from two ancestral populations, and we find high concordance between the methods. Our method also has better accuracy than LAMP when applied to three-population admixture, a situation as yet unaddressed by HAPMIX. Finally, we apply our method to a data set of four Latino populations with European, African, and Native American ancestry. We find evidence of assortative mating in each of the four populations, and we identify regions of shared ancestry that may be recent targets of selection and could serve as candidate regions for admixture-based association mapping
Panchromatic spectral energy distributions of Herschel sources
(abridged) Far-infrared Herschel photometry from the PEP and HerMES programs
is combined with ancillary datasets in the GOODS-N, GOODS-S, and COSMOS fields.
Based on this rich dataset, we reproduce the restframe UV to FIR ten-colors
distribution of galaxies using a superposition of multi-variate Gaussian modes.
The median SED of each mode is then fitted with a modified version of the
MAGPHYS code that combines stellar light, emission from dust heated by stars
and a possible warm dust contribution heated by an AGN. The defined Gaussian
grouping is also used to identify rare sources. The zoology of outliers
includes Herschel-detected ellipticals, very blue z~1 Ly-break galaxies,
quiescent spirals, and torus-dominated AGN with star formation. Out of these
groups and outliers, a new template library is assembled, consisting of 32 SEDs
describing the intrinsic scatter in the restframe UV-to-submm colors of
infrared galaxies. This library is tested against L(IR) estimates with and
without Herschel data included, and compared to eight other popular methods
often adopted in the literature. When implementing Herschel photometry, these
approaches produce L(IR) values consistent with each other within a median
absolute deviation of 10-20%, the scatter being dominated more by fine tuning
of the codes, rather than by the choice of SED templates. Finally, the library
is used to classify 24 micron detected sources in PEP GOODS fields. AGN appear
to be distributed in the stellar mass (M*) vs. star formation rate (SFR) space
along with all other galaxies, regardless of the amount of infrared luminosity
they are powering, with the tendency to lie on the high SFR side of the "main
sequence". The incidence of warmer star-forming sources grows for objects with
higher specific star formation rates (sSFR), and they tend to populate the
"off-sequence" region of the M*-SFR-z space.Comment: Accepted for publication in A&A. Some figures are presented in low
resolution. The new galaxy templates are available for download at the
address http://www.mpe.mpg.de/ir/Research/PEP/uvfir_temp
Molecular line mapping of the giant molecular cloud associated with RCW 106 - II. Column density and dynamical state of the clumps
We present a fully sampled C^{18}O (1-0) map towards the southern giant
molecular cloud (GMC) associated with the HII region RCW 106, and use it in
combination with previous ^{13}CO (1-0) mapping to estimate the gas column
density as a function of position and velocity. We find localized regions of
significant ^{13}CO optical depth in the northern part of the cloud, with
several of the high-opacity clouds in this region likely associated with a
limb-brightened shell around the HII region G333.6-0.2. Optical depth
corrections broaden the distribution of column densities in the cloud, yielding
a log-normal distribution as predicted by simulations of turbulence.
Decomposing the ^{13}CO and C^{18}O data cubes into clumps, we find relatively
weak correlations between size and linewidth, and a more sensitive dependence
of luminosity on size than would be predicted by a constant average column
density. The clump mass spectrum has a slope near -1.7, consistent with
previous studies. The most massive clumps appear to have gravitational binding
energies well in excess of virial equilibrium; we discuss possible
explanations, which include magnetic support and neglect of time-varying
surface terms in the virial theorem. Unlike molecular clouds as a whole, the
clumps within the RCW 106 GMC, while elongated, appear to show random
orientations with respect to the Galactic plane.Comment: 17 pages, to appear in MNRA
The dust content of high-z submillimeter galaxies revealed by Herschel
We use deep observations taken with the Photodetector Array Camera and
Spectrometer (PACS), on board the Herschel satellite as part of the PACS
evolutionary probe (PEP) guaranteed project along with submm ground-based
observations to measure the dust mass of a sample of high-z submillimeter
galaxies (SMGs). We investigate their dust content relative to their stellar
and gas masses, and compare them with local star-forming galaxies. High-z SMGs
are dust rich, i.e. they have higher dust-to-stellar mass ratios compared to
local spiral galaxies (by a factor of 30) and also compared to local
ultraluminous infrared galaxies (ULIRGs, by a factor of 6). This indicates that
the large masses of gas typically hosted in SMGs have already been highly
enriched with metals and dust. Indeed, for those SMGs whose gas mass is
measured, we infer dust-to-gas ratios similar or higher than local spirals and
ULIRGs. However, similarly to other strongly star-forming galaxies in the local
Universe and at high-z, SMGs are characterized by gas metalicities lower (by a
factor of a few) than local spirals, as inferred from their optical nebular
lines, which are generally ascribed to infall of metal-poor gas. This is in
contrast with the large dust content inferred from the far-IR and submm data.
In short, the metalicity inferred from the dust mass is much higher (by more
than an order of magnitude) than that inferred from the optical nebular lines.
We discuss the possible explanations of this discrepancy and the possible
implications for the investigation of the metalicity evolution at high-z.Comment: Accepted for publication in Astronomy & Astrophysics Letters. One
reference update
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