773 research outputs found
The far-infrared/radio correlation and radio spectral index of galaxies in the SFR-M* plane up to z 2
[Abridged] We study the evolution of the radio spectral index and
far-infrared/radio correlation (FRC) across the star-formation rate-stellar
masse (i.e. SFR-M*) plane up to z 2. We start from a M*-selected sample of
galaxies with reliable SFR and redshift estimates. We then grid the SFR-M*
plane in several redshift ranges and measure the infrared luminosity, radio
luminosity, radio spectral index, and ultimately the FRC index (i.e. qFIR) of
each SFR-M*-z bin. The infrared luminosities of our SFR-M*-z bins are estimated
using their stacked far-infrared flux densities inferred from observations
obtained with Herschel. Their radio luminosities and radio spectral indices
(i.e. alpha, where Snu nu^-alpha) are estimated using their stacked 1.4GHz and
610MHz flux densities from the VLA and GMRT, respectively. Our far-infrared and
radio observations include the most widely studied blank extragalactic fields
-GOODS-N/S, ECDFS, and COSMOS- covering a sky area of 2deg^2. Using this
methodology, we constrain the radio spectral index and FRC index of
star-forming galaxies with M*>10^10Msun and 0<z<2.3. We find that
alpha^1.4GHz_610MHz does not evolve significantly with redshift or with the
distance of a galaxy with respect to the main sequence (MS) of the SFR-M* plane
(i.e. Delta_log(SSFR)_MS=log[SSFR(galaxy)/SSFR_MS(M*,z)]). Instead,
star-forming galaxies have a radio spectral index consistent with a canonical
value of 0.8, which suggests that their radio spectra are dominated by
non-thermal optically thin synchrotron emission. We find that qFIR displays a
moderate but statistically significant redshift evolution as
qFIR(z)=(2.35+/-0.08)*(1+z)^(-0.12+/-0.04), consistent with some previous
literature. Finally, we find no significant correlation between qFIR and
Delta_log(SSFR)_MS, though a weak positive trend, as observed in one of our
redshift bins, cannot be firmly ruled out using our dataset.Comment: Accepted for publication in A&A; 18 pages, 10 figure
Optimizing transcranial magnetic stimulation for spaceflight applications
As space agencies aim to reach and build installations on Mars, the crews will face longer exposure to extreme environments that may compromise their health and performance. Transcranial magnetic stimulation (TMS) is a painless non-invasive brain stimulation technique that could support space exploration in multiple ways. However, changes in brain morphology previously observed after long-term space missions may impact the efficacy of this intervention. We investigated how to optimize TMS for spaceflight-associated brain changes. Magnetic resonance imaging T1-weighted scans were collected from 15 Roscosmos cosmonauts and 14 non-flyer participants before, after 6 months on the International Space Station, and at a 7-month follow-up. Using biophysical modeling, we show that TMS generates different modeled responses in specific brain regions after spaceflight in cosmonauts compared to the control group. Differences are related to spaceflight-induced structural brain changes, such as those impacting cerebrospinal fluid volume and distribution. We suggest solutions to individualize TMS to enhance its efficacy and precision for potential applications in long-duration space missions. © 2023, The Author(s)
Cobalt toxicity in humans-A review of the potential sources and systemic health effects
Cobalt (Co) and its compounds are widely distributed in nature and are part of numerous anthropogenic activities. Although cobalt has a biologically necessary role as metal constituent of vitamin B12, excessive exposure has been shown to induce various adverse health effects. This review provides an extended overview of the possible Co sources and related intake routes, the detection and quantification methods for Co intake and the interpretation thereof, and the reported health effects. The Co sources were allocated to four exposure settings: occupational, environmental, dietary and medical exposure. Oral intake of Co supplements and internal exposure through metal-on-metal (MoM) hip implants deliver the highest systemic Co concentrations. The systemic health effects are characterized by a complex clinical syndrome, mainly including neurological (e.g. hearing and visual impairment), cardiovascular and endocrine deficits. Recently, a biokinetic model has been proposed to characterize the dose-response relationship and effects of chronic exposure. According to the model, health effects are unlikely to occur at blood Co concentrations under 300 ÎŒg/l (100 ÎŒg/l respecting a safety factor of 3) in healthy individuals, hematological and endocrine dysfunctions are the primary health endpoints, and chronic exposure to acceptable doses is not expected to pose considerable health hazards. However, toxic reactions at lower doses have been described in several cases of malfunctioning MoM hip implants, which may be explained by certain underlying pathologies that increase the individual susceptibility for Co-induced systemic toxicity. This may be associated with a decrease in Co bound to serum proteins and an increase in free ionic Co2+. As the latter is believed to be the primary toxic form, monitoring of the free fraction of Co2+ might be advisable for future risk assessment. Furthermore, future research should focus on longitudinal studies in the clinical setting of MoM hip implant patients to further elucidate the dose-response discrepancies
Dust temperature and CO-to-H2 conversion factor variations in the SFR-M* plane
Deep Herschel imaging and 12CO(2-1) line luminosities from the IRAM PdBI are
combined for a sample of 17 galaxies at z>1 from the GOODS-N field. The sample
includes galaxies both on and above the main sequence (MS) traced by
star-forming galaxies in the SFR-M* plane. The far-infrared data are used to
derive dust masses, Mdust. Combined with an empirical prescription for the
dependence of the gas-to-dust ratio on metallicity (GDR), the CO luminosities
and Mdust values are used to derive for each galaxy the CO-to-H2 conversion
factor, alpha_co. Like in the local Universe, the value of alpha_co is a factor
of ~5 smaller in starbursts compared to normal star-forming galaxies (SFGs). We
also uncover a relation between alpha_co and dust temperature (Tdust; alpha_co
decreasing with increasing Tdust) as obtained from modified blackbody fits to
the far-infrared data. While the absolute normalization of the alpha_co(Tdust)
relation is uncertain, the global trend is robust against possible systematic
biases in the determination of Mdust, GDR or metallicity. Although we cannot
formally distinguish between a step and a smooth evolution of alpha_co with the
dust temperature, we can conclude that in galaxies of near-solar metallicity, a
critical value of Tdust=30K can be used to determine whether the appropriate
alpha_co is closer to the starburst value (1.0 Msun(K kms pc^2)^-1, if
Tdust>30K) or closer to the Galactic value (4.35 Msun (K kms pc^2)^-1, if
Tdust<30K). This indicator has the great advantage of being less subjective
than visual morphological classifications of mergers/SFGs, which can be
difficult at high z because of the clumpy nature of SFGs. In the absence of
far-infrared data, the offset of a galaxy from the main sequence (i.e.,
log[SSFR(galaxy)/SSFR_MS(M*,z)]) can be used to identify galaxies requiring the
use of an alpha_co conversion factor lower than the Galactic value.Comment: Accepted for publication in Astronomy and Astrophysics (A&A); 15
pages, 6 figures; V2: updated reference lis
A Substantial Population of Red Galaxies at z > 2: Modeling of the Spectral Energy Distributions of an Extended Sample
We investigate the nature of the substantial population of high-z galaxies
with Js-Ks>2.3 discovered as part of our FIRES survey. This colour cut
efficiently isolates z>2 galaxies with red rest-frame optical colors ("Distant
Red Galaxies" or DRGs). We select objects in the 2.5'x2.5' HDF-South (HDF-S)
and 5'x5' field around the MS1054-03 cluster; the surface densities at Ks<21
are 1.6+-0.6 and 1.0+-0.2 arcmin^-2. We discuss the 34 DRGs at 2<z<3.5: 11 at
Ks<22.5 in HDF-S and 23 at Ks<21.7 in the MS1054-03 field. We analyze the SEDs
constructed from our deep near-infrared (NIR) and optical imaging from the ESO
VLT and HST. We develop diagnostics involving I-Js, Js-H, and H-Ks to argue
that the red NIR colors of DRGs cannot be attributed solely to extinction and
require for many an evolved stellar population with prominent Balmer/4000A
break. In the rest-frame, the optical colours of DRGs fall within the envelope
of normal nearby galaxies and the UV colours suggest a wide range in star
formation activity and/or extinction. This contrasts with the much bluer and
more uniform SEDs of Lyman break galaxies (LBGs). From evolutionary synthesis
models with constant star formation, solar metallicity, Salpeter IMF, and
Calzetti et al. extinction law, we derive for the HDF-S (MS1054-03 field) DRGs
median ages of 1.7(2.0) Gyr, A_V = 2.7(2.4) mag, stellar masses 0.8(1.6)x10^11
Msun, M/L_V = 1.2(2.3) Msun/LVsun, and SFR = 120(170) Msun/yr. Models assuming
declining SFRs with e-folding timescales of 10Myr-1Gyr generally imply younger
ages, lower A_V's and SFRs, but similar stellar masses within a factor of two.
Compared to LBGs at similar redshifts and rest-frame L_V's, DRGs are older,
more massive, and more obscured for any given star formation history.
[ABRIDGED]Comment: Accepted for publication in the Astrophysical Journal. 27 pages, 14
b/w figure
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
DOCK6 Mutations Are Responsible for a Distinct Autosomal-Recessive Variant of Adams-Oliver Syndrome Associated with Brain and Eye Anomalies
Author contacted for file
Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
We combine molecular gas masses inferred from CO emission in 500 star forming
galaxies (SFGs) between z=0 and 3, from the IRAM-COLDGASS, PHIBSS1/2 and other
surveys, with gas masses derived from Herschel far-IR dust measurements in 512
galaxy stacks over the same stellar mass/redshift range. We constrain the
scaling relations of molecular gas depletion time scale (tdepl) and gas to
stellar mass ratio (Mmolgas/M*) of SFGs near the star formation main-sequence
with redshift, specific star formation rate (sSFR) and stellar mass (M*). The
CO- and dust-based scaling relations agree remarkably well. This suggests that
the CO-H2 mass conversion factor varies little within 0.6dex of the main
sequence (sSFR(ms,z,M*)), and less than 0.3dex throughout this redshift range.
This study builds on and strengthens the results of earlier work. We find that
tdepl scales as (1+z)^-0.3 *(sSFR/sSFR(ms,z,M*))^-0.5, with little dependence
on M*. The resulting steep redshift dependence of Mmolgas/M* ~(1+z)^3 mirrors
that of the sSFR and probably reflects the gas supply rate. The decreasing gas
fractions at high M* are driven by the flattening of the SFR-M* relation.
Throughout the redshift range probed a larger sSFR at constant M* is due to a
combination of an increasing gas fraction and a decreasing depletion time
scale. As a result galaxy integrated samples of the Mmolgas-SFR rate relation
exhibit a super-linear slope, which increases with the range of sSFR. With
these new relations it is now possible to determine Mmolgas with an accuracy of
0.1dex in relative terms, and 0.2dex including systematic uncertainties.Comment: ApJ accepte
PHIBSS: molecular gas content and scaling relations in z~1-3 normal star forming galaxies
We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2
survey of the molecular gas properties in normal star forming galaxies (SFGs)
near the cosmic star formation peak. PHIBSS provides 52 CO detections in two
redshift slices at z~1.2 and 2.2, with log(M*(M_solar))>10.4 and
log(SFR(M_solar/yr))>1.5. Including a correction for the incomplete coverage of
the M*-SFR plane, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at
z~2.2. Gas fractions drop with stellar mass, in agreement with cosmological
simulations including strong star formation feedback. Most of the z~1-3 SFGs
are rotationally supported turbulent disks. The sizes of CO and UV/optical
emission are comparable. The molecular gas - star formation relation for the
z=1-3 SFGs is near-linear, with a ~0.7 Gyrs gas depletion timescale; changes in
depletion time are only a secondary effect. Since this timescale is much less
than the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied
with a fairly high duty cycle over several billion years. At given z and M*,
gas fractions correlate strongly with the specific star formation rate. The
variation of specific star formation rate between z~0 and 3 is mainly
controlled by the fraction of baryonic mass that resides in cold gas.Comment: Submitted to the Astrophysical Journal; 14 figure
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