45 research outputs found
The global dust SED: Tracing the nature and evolution of dust with DustEM
The Planck and Herschel missions are currently measuring the farIR-mm
emission of dust, which combined with existing IR data, will for the first time
provide the full SED of the galactic ISM dust emission with an unprecedented
sensitivity and angular resolution. It will allow a systematic study of the
dust evolution processes that affect the SED. Here we present a versatile
numerical tool, DustEM, that predicts the emission and extinction of dust given
their size distribution and their optical and thermal properties. In order to
model dust evolution, DustEM has been designed to deal with a variety of grain
types, structures and size distributions and to be able to easily include new
dust physics. We use DustEM to model the dust SED and extinction in the diffuse
interstellar medium at high-galactic latitude (DHGL), a natural reference SED.
We present a coherent set of observations for the DHGL SED. The dust components
in our DHGL model are (i) PAHs, (ii) amorphous carbon and (iii) amorphous
silicates. We use amorphous carbon dust, rather than graphite, because it
better explains the observed high abundances of gas-phase carbon in shocked
regions of the interstellar medium. Using the DustEM model, we illustrate how,
in the optically thin limit, the IRAS/Planck HFI (and likewise Spitzer/Herschel
for smaller spatial scales) photometric band ratios of the dust SED can
disentangle the influence of the exciting radiation field intensity and
constrain the abundance of small grains relative to the larger grains. We also
discuss the contributions of the different grain populations to the IRAS,
Planck and Herschel channels. Such information is required to enable a study of
the evolution of dust as well as to systematically extract the dust thermal
emission from CMB data and to analyze the emission in the Planck polarized
channels. The DustEM code described in this paper is publically available.Comment: accepted for publication in A&
Determination of the gas-to-dust ratio in nearby dense clouds using X-ray absorption measurements
We present a comparison of the gas and dust properties of the dense
interstellar matter in six nearby star-forming regions (d<500 pc): rho Oph, Cha
I, R CrA, IC 348, NGC 1333, and Orion. We measure from Chandra and XMM-Newton
observations the X-ray absorption toward pre-main sequence stars (PMS) without
accretion disks (i.e., Class III sources) to obtain the total hydrogen column
density N_{H,X}. For these sources we take from the literature the
corresponding dust extinction in the near-infrared, A_J, or when unavailable we
derive it from SED fitting using the available DENIS, 2MASS, ISOCAM and other
data. We then compare N_{H,X} and A_J for each object, up to unprecedently high
extinction. For the rho Oph dark cloud with a relatively large sample of 20
bona-fide Class III sources, we probe the extinction up to A_J <~ 14 (A_V <~
45), and find a best-fit linear relation N_{H,X}/A_J = 5.6 (+/- 0.4)x10^{21}
cm^{-2} mag^{-1}, adopting standard ISM abundances. The other regions reveal a
large dispersion in the N_{H,X}/A_J ratio for each source but for lack of
adequate IR data these studies remain limited to moderate extinctions (A_J <~
1.5 or A_V ~2
sigma) than the galactic value, derived using the standard extinction curve
(R_V = 3.1). This result is consistent with the recent downwards revision of
the metallicity of the Sun and stars in the solar vicinity. We find that the
rho Oph dense cloud has the same metallicity than the local ISM when assuming
that the galactic gas-to-dust ratio remains unchanged. The difference between
galactic and local values of the gas-to-dust ratio can thus be attributed
entirely to a difference in metallicity.Comment: 21 Pages including 12 figures. Accepted for publication in Astronomy
and Astrophysic
PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar
(Abridged) We investigate the impact of radiative feedback from massive stars
on their natal cloud and focus on the transition from the HII region to the
atomic PDR (crossing the ionisation front (IF)), and the subsequent transition
to the molecular PDR (crossing the dissociation front (DF)). We use
high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST
to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science
Program. The NIRSpec data reveal a forest of lines including, but not limited
to, HeI, HI, and CI recombination lines, ionic lines, OI and NI fluorescence
lines, Aromatic Infrared Bands (AIBs including aromatic CH, aliphatic CH, and
their CD counterparts), CO2 ice, pure rotational and ro-vibrational lines from
H2, and ro-vibrational lines HD, CO, and CH+, most of them detected for the
first time towards a PDR. Their spatial distribution resolves the H and He
ionisation structure in the Huygens region, gives insight into the geometry of
the Bar, and confirms the large-scale stratification of PDRs. We observe
numerous smaller scale structures whose typical size decreases with distance
from Ori C and IR lines from CI, if solely arising from radiative recombination
and cascade, reveal very high gas temperatures consistent with the hot
irradiated surface of small-scale dense clumps deep inside the PDR. The H2
lines reveal multiple, prominent filaments which exhibit different
characteristics. This leaves the impression of a "terraced" transition from the
predominantly atomic surface region to the CO-rich molecular zone deeper in.
This study showcases the discovery space created by JWST to further our
understanding of the impact radiation from young stars has on their natal
molecular cloud and proto-planetary disk, which touches on star- and planet
formation as well as galaxy evolution.Comment: 52 pages, 30 figures, submitted to A&
PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar
(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are
dominated by strong emission features called aromatic infrared bands (AIBs).
The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 m. The
most sensitive, highest-resolution infrared spectral imaging data ever taken of
the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an
inventory of the AIBs found in the Orion Bar, along with mid-IR template
spectra from five distinct regions in the Bar: the molecular PDR, the atomic
PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of
the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288).
We extract five template spectra to represent the morphology and environment of
the Orion Bar PDR. The superb sensitivity and the spectral and spatial
resolution of these JWST observations reveal many details of the AIB emission
and enable an improved characterization of their detailed profile shapes and
sub-components. While the spectra are dominated by the well-known AIBs at 3.3,
6.2, 7.7, 8.6, 11.2, and 12.7 m, a wealth of weaker features and
sub-components are present. We report trends in the widths and relative
strengths of AIBs across the five template spectra. These trends yield valuable
insight into the photochemical evolution of PAHs, such as the evolution
responsible for the shift of 11.2 m AIB emission from class B in
the molecular PDR to class A in the PDR surface layers. This
photochemical evolution is driven by the increased importance of FUV processing
in the PDR surface layers, resulting in a "weeding out" of the weakest links of
the PAH family in these layers. For now, these JWST observations are consistent
with a model in which the underlying PAH family is composed of a few species:
the so-called 'grandPAHs'.Comment: 25 pages, 10 figures, to appear in A&
PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula
The JWST has captured the most detailed and sharpest infrared images ever
taken of the inner region of the Orion Nebula, the nearest massive star
formation region, and a prototypical highly irradiated dense photo-dissociation
region (PDR). We investigate the fundamental interaction of far-ultraviolet
photons with molecular clouds. The transitions across the ionization front
(IF), dissociation front (DF), and the molecular cloud are studied at
high-angular resolution. These transitions are relevant to understanding the
effects of radiative feedback from massive stars and the dominant physical and
chemical processes that lead to the IR emission that JWST will detect in many
Galactic and extragalactic environments. Due to the proximity of the Orion
Nebula and the unprecedented angular resolution of JWST, these data reveal that
the molecular cloud borders are hyper structured at small angular scales of
0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are
observed such as ridges, waves, globules and photoevaporated protoplanetary
disks. At the PDR atomic to molecular transition, several bright features are
detected that are associated with the highly irradiated surroundings of the
dense molecular condensations and embedded young star. Toward the Orion Bar
PDR, a highly sculpted interface is detected with sharp edges and density
increases near the IF and DF. This was predicted by previous modeling studies,
but the fronts were unresolved in most tracers. A complex, structured, and
folded DF surface was traced by the H2 lines. This dataset was used to revisit
the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a
complete view of the PDR, all the way from the PDR edge to the substructured
dense region, and this allowed us to determine, in detail, where the emission
of the atomic and molecular lines, aromatic bands, and dust originate
Breastfeeding offers protection against obesity in children of recently immigrated Latina women.
Recommended from our members
Telemedicine for Pediatric Inflammatory Bowel Disease in the Era of COVID-19.
Bisphenol a increases risk for presumed non-alcoholic fatty liver disease in Hispanic adolescents in NHANES 2003–2010
Abstract Background Bisphenol-A (BPA) is a ubiquitous chemical and recognized endocrine disruptor associated with obesity and related disorders. We explored the association between BPA levels and suspected non-alcoholic fatty liver disease (NAFLD). Methods Unweighted analyses were used to study the relationship between urinary BPA levels and suspected NAFLD (alanine aminotransferase (ALT). > 30 U/L, body mass index (BMI) Z-score > 1.064 and evidence of insulin resistance) using National Health and Nutrition Examination Survey (NHANES) data (2003–2010) on 12–19 year olds. Unweighted and weighted analyses were used to evaluate the risk with only elevated ALT. Results We included 944 adolescents with urinary BPA and fasting laboratory tests from a total of 7168 adolescents. Risk of suspected NAFLD was increased in the second quartile of BPA levels (1.4–2.7 ng/mL) when compared to the first (< 1.4 ng/mL) (Odds Ratio (OR) 4.23, 95% Confidence Interval (CI) 1.44–12.41). The ORs for the third and second quartiles were positive but did not reach statistical significance. The association was stronger in Hispanics (n = 344) with BPA levels in the second (OR 6.12, 95% C.I. 1.62–23.15) quartile and when limiting the analyses to overweight/obese adolescents (n = 332), in the second (OR 5.56, 95% C.I. 1.28–24.06) and fourth BPA quartiles (OR 6.85, 95% C.I. 1.02–46.22) compared to the first quartile. BPA levels were not associated with ALT elevation. Conclusions The risk of suspected NAFLD is increased in participants in higher quartiles of BPA exposure, particularly in those of Hispanic ethnicity. Further studies are required to fully understand the potential role of BPA in non-alcoholic fatty liver disease
Recommended from our members
Depression Predicts Prolonged Length of Hospital Stay in Pediatric Inflammatory Bowel Disease.
OBJECTIVE:Few studies report the impact of depression on inflammatory bowel disease (IBD)-related hospitalizations. We evaluated the association between depression and pediatric IBD-related hospitalizations. Our primary aim was to test the hypothesis that depression is associated with hospital length of stay (LOS); our secondary goal was to evaluate if patients with depression are at higher risk for undergoing additional imaging and procedures. METHODS:Data were extracted from the 2012 Kids Inpatient Database (KID), the largest nationally representative publicly available all-payer pediatric inpatient cross-sectional database in the United States. Hospitalizations for patients less than 21 years with a primary diagnosis Crohn disease (CD) or ulcerative colitis (UC) by ICD-9 code were included. Multivariable logistic regression was used to predict long LOS controlling for patient- and hospital-level variables and for potential disease confounders. RESULTS:For primary IBD-related hospitalizations (N = 8222), depression was associated with prolonged LOS (odds ratio [OR] 1.50; 95% confidence interval [CI] 1.19-1.90) and total parenteral nutrition use (OR 1.54; 95% CI 1.04-2.27). Depression was not associated with increased likelihood of surgery (OR 0.97; 95% CI 0.72-1.30), endoscopy (OR 0.91; 95% CI 0.74-1.14), blood transfusion (OR 0.85; 95% CI 0.58-1.23), or abdominal imaging (OR 1.15; 95% CI 0.53-2.53). CONCLUSIONS:Depression is associated with prolonged LOS in pediatric patients with IBD, even when controlling for gastrointestinal disease severity. Future research evaluating the efficacy of standardized depression screening and early intervention may be beneficial to improving inpatient outcomes in this population