•The majority of the children walk to school, with only 12% accompanied by an adult.•More than half (53%) of self-reported pedestrian collisions involved a bicycle.•Older boys (10–15 years) were most ...likely to report a severe pedestrian collision.•Children who walk accompanied reported more severe pedestrian collisions.•Children who spend more time walking engage in safer Sight Behaviour.
Pedestrian injuries are a leading cause of death among South African children, and young children residing in low-income communities are more at risk, due to various factors such as inadequate road infrastructure, exposure to traffic due to reliance on walking as a means of transport, and lack of supervision. This study used a cross-sectional, non-randomized self-report survey to assess pedestrian safety knowledge, road-crossing behaviour and pedestrian injuries of primary school children in selected low-income settings in Cape Town. The survey focused on three primary schools that had joined the Safe Kids Worldwide Model School Zone Project and was administered to 536 children aged 6–15 years, in their home language of isiXhosa. Descriptive and bivariate analyses as well as multivariate regression analyses were conducted to investigate potential predictor variables for pedestrian collision severity and unsafe road-crossing behaviour. Walking was the sole form of travel for 81% of the children, with a large proportion regularly walking unsupervised. Children who walk to or from school alone were younger and reported riskier road-crossing behaviour, although children who walk accompanied tended to have higher pedestrian collision severity. “Negligent Behaviour” related to road-crossing was significantly associated with higher pedestrian collision severity, with predictors of “Negligent Behaviour” including the lack of pedestrian safety knowledge and greater exposure to traffic in terms of time spent walking. More than half of the reported pedestrian collisions involved a bicycle, and older boys (10–15 years) were most at risk of experiencing a severe pedestrian injury. The findings substantiate emerging evidence that children in low-income settings are at greater risk for child pedestrian injury, and emphasise the need for evidence-based safety promotion and injury prevention interventions in these settings.
We present an Atacama Large Millimeter/submillimeter Array (ALMA) survey of dust continuum emission in a sample of 70 galaxies in the redshift range z = 2-5 selected from the CANDELS GOODS-S field. ...Multi-epoch abundance matching (MEAM) is used to define potential progenitors of a z = 0 galaxy of stellar mass 1.5 × 1011 M . Gas masses are derived from the 850 m luminosity. Ancillary data from the CANDELS GOODS-S survey are used to derive the gas mass fractions. The results at z 3 are mostly in accord with expectations: The detection rates are 75% for the z = 2 redshift bin, 50% for the z = 3 bin, and 0% for z 4. The average gas mass fraction for the detected z = 2 galaxies is fgas = 0.55 0.12 and fgas = 0.62 0.15 for the z = 3 sample. This agrees with expectations for galaxies on the star-forming main sequence, and shows that gas fractions have decreased at a roughly constant rate from z = 3 to z = 0. Stacked images of the galaxies not detected with ALMA give upper limits to fgas of <0.08 and <0.15, for the z = 2 and z = 3 redshift bins. None of our galaxies in the z = 4 and z = 5 sample are detected, and the upper limit from stacked images, corrected for low metallicity, is fgas < 0.66. We do not think that lower gas-phase metallicities can entirely explain the lower dust luminosities. We briefly consider the possibility of accretion of very low-metallicity gas to explain the absence of detectable dust emission in our galaxies at z 4.
The Opacity of Galactic Disks at z ~ 0.7 Sargent, M. T; Carollo, C. M; Kampczyk, P ...
Astrophysical journal. Letters,
05/2010, Letnik:
714, Številka:
1
Journal Article
Abstract
We analyze a sample of
z
-dropout galaxies in the CANDELS GOODS South and UDS fields that have been targeted by a dedicated spectroscopic campaign aimed at detecting their Ly
α
line. Deep ...IRAC observations at 3.6 and 4.5
μ
m are used to determine the strength of optical emission lines affecting these bands at
z
∼ 6.5–6.9 in order to (1) investigate possible physical differences between Ly
α
emitting and non-emitting sources; (2) constrain the escape fraction of ionizing photons; and (3) provide an estimate of the specific star formation rate at high redshifts. We find evidence of strong O
iii
+H
β
emission in the average (stacked) SEDs of galaxies both with and without Ly
α
emission. The blue IRAC 3.6–4.5 color of the stack with detected Ly
α
line can be converted into a rest-frame equivalent width EW(O
iii
+H
β
) =
Å assuming a flat intrinsic stellar continuum. This strong optical line emission enables a first estimate of
on the escape fraction of ionizing photons from Ly
α
detected objects. The objects with no Ly
α
line show less extreme EW(O
iii
+H
β
) =
Å, suggesting different physical conditions of the H
ii
regions with respect to Ly
α
-emitting ones, or a larger
. The latter case is consistent with a combined evolution of
and the neutral hydrogen fraction as an explanation of the lack of bright Ly
α
emission at
z
> 6. A lower limit on the specific star formation rate, SSFR > 9.1 Gyr
−1
for
galaxies at these redshifts can be derived from the spectroscopically confirmed sample.
ABSTRACT
Hubble Space Telescope observations show that low-mass ($M_*=10^9\!-\!10^{10}\, \mathrm{M}_{\odot }$) galaxies at high redshift (z = 1.0–2.5) tend to be elongated (prolate) rather than disky ...(oblate) or spheroidal. This is explained in zoom-in cosmological hydrodynamical simulations by the fact that these galaxies are forming in cosmic web filaments where accretion happens preferentially along the direction of elongation. We ask whether the elongated morphology of these galaxies allows them to be used as effective tracers of cosmic web filaments at high redshift via their intrinsic alignments. Using mock light cones and spectroscopically confirmed galaxy pairs from the Cosmic Assembly Near-infared Deep Extragalactic Legacy Survey (CANDELS), we test two types of alignments: (1) between the galaxy major axis and the direction to nearby galaxies of any mass and (2) between the major axes of nearby pairs of low-mass, likely prolate, galaxies. The mock light cones predict strong signals in 3D real space, 3D redshift space, and 2D projected redshift space for both types of alignments (assuming prolate galaxy orientations are the same as those of their host prolate haloes), but we do not detect significant alignment signals in CANDELS observations. However, we show that spectroscopic redshifts have been obtained for only a small fraction of highly elongated galaxies, and accounting for spectroscopic incompleteness and redshift errors significantly degrades the 2D mock signal. This may partly explain the alignment discrepancy and highlights one of several avenues for future work.
We investigate the star formation main sequence (MS; SFR– M _⋆ ) down to 10 ^8−9 M _⊙ using a sample of 34,061 newly discovered ultrafaint (27 mag ≲ i ≲ 30 mag) galaxies at 1 < z < 3 detected in the ...GOODS-N field. Virtually none of these galaxies are contained in previous public catalogs, effectively doubling the number of known sources in the field. The sample was constructed by stacking the optical broadband observations taken by the HST/GOODS-CANDELS surveys, as well as the 25 ultradeep medium-band images gathered by the GTC/SHARDS project. Our sources are faint (average observed magnitudes 〈 i 〉 ∼ 28.2 and 〈 H 〉 ∼ 27.9 mag), blue (UV slope 〈 β 〉 ∼ −1.9), star-forming (rest-frame colors 〈 U − V 〉 ∼ 0.10 and 〈 V − J 〉 ∼ 0.17 mag) galaxies. These observational characteristics are identified with young (mass-weighted age 〈 t _M _− _w 〉 ∼ 0.014 Gyr) stellar populations subject to low attenuations (〈 A ( V )〉 ∼ 0.30 mag). Our sample allows us to probe the MS down to 10 ^8.0 M _⊙ at z = 1 and 10 ^8.5 M _⊙ at z = 3, around 0.6 dex deeper than previous analyses. In the low-mass galaxy regime, we find an average value for the slope of 0.97 at 1 < z < 2 and 1.12 at 2 < z < 3. Nearly 60% of our sample presents stellar masses in the range 10 ^6-8 M _⊙ at 1 < z <G 3. If the slope of the MS remained constant in this regime, the sources populating the low-mass tail of our sample would qualify as starburst galaxies.
Abstract
We present the data release and data reduction process for the Epoch 1 NIRCam observations for the Cosmic Evolution Early Release Science Survey (CEERS). These data consist of NIRCam imaging ...in six broadband filters (F115W, F150W, F200W, F277W, F356W and F444W) and one medium-band filter (F410M) over four pointings, obtained in parallel with primary CEERS MIRI observations. We reduced the NIRCam imaging with the JWST Calibration Pipeline, with custom modifications and reduction steps designed to address additional features and challenges with the data. Here we provide a detailed description of each step in our reduction and a discussion of future expected improvements. Our reduction process includes corrections for known prelaunch issues such as 1/
f
noise, as well as in-flight issues including snowballs, wisps, and astrometric alignment. Many of our custom reduction processes were first developed with prelaunch simulated NIRCam imaging over the full 10 CEERS NIRCam pointings. We present a description of the creation and reduction of this simulated data set in the Appendix. We provide mosaics of the real images in a public release, as well as our reduction scripts with detailed explanations to allow users to reproduce our final data products. These represent one of the first official public data sets released from the Directors Discretionary Early Release Science (DD-ERS) program.
The relation between the galaxy stellar mass M-star and the dark matter halo mass M-h gives important information on the efficiency in forming stars and assembling stellar mass in galaxies. We ...present measurements of the ratio of stellar mass to halo mass (SMHR) at redshifts 2 \textless z \textless 5, obtained from the VIMOS Ultra Deep Survey. We use halo occupation distribution (HOD) modelling of clustering measurements on similar to 3000 galaxies with spectroscopic redshifts to derive the dark matter halo mass M-h, and spectral energy density fitting over a large set of multi-wavelength data to derive the stellar mass M-star and compute the SMHR = M-star/M-h. We find that the SMHR ranges from 1% to 2.5% for galaxies with M-star = 1.3 x 10(9) M-star to M-star = 7.4 x 10(9) M-circle dot in DM halos with M-h = 1.3 x 10(11) M-circle dot to M-h = 3 x 10(11) M-circle dot. We derive the integrated star formation efficiency (ISFE) of these galaxies and find that the star formation efficiency is a moderate 6-9% for lower mass galaxies, while it is relatively high at 16% for galaxies with the median stellar mass of the sample similar to 7 x 10(9) M-circle dot. The lower ISFE at lower masses may indicate that some efficient means of suppressing star formation is at work (like SNe feedback), while the high ISFE for the average galaxy at z similar to 3 indicates that these galaxies efficiently build up their stellar mass at a key epoch in the mass assembly process. Based on our results, we propose a possible scenario in which the average massive galaxy at z similar to 3 begins to experience truncation of its star formation within a few million years.
The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.5 deg2 of the COSMOS field (centered at 10 h, +02 o ) with an effective exposure of ~160 ks, and ...an outer 0.4 deg2 area with an effective exposure of ~80 ks. The limiting source detection depths are 1.9 X 10-16 erg cm-2 s-1 in the soft (0.5-2 keV) band, 7.3 X 10-16 erg cm-2 s-1 in the hard (2-10 keV) band, and 5.7 X 10-16 erg cm-2 s-1 in the full (0.5-10 keV) band. Here we describe the strategy, design, and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2 X 10-5 (1655 in the full, 1340 in the soft, and 1017 in the hard bands). By using a grid of 36 heavily (~50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform (+/-12%) exposure across the inner 0.5 deg2 field was obtained, leading to a sharply defined lower flux limit. The widely different point-spread functions obtained in each exposure at each point in the field required a novel source detection method, because of the overlapping tiling strategy, which is described in a companion paper. This method produced reliable sources down to a 7-12 counts, as verified by the resulting logN-logS curve, with subarcsecond positions, enabling optical and infrared identifications of virtually all sources, as reported in a second companion paper. The full catalog is described here in detail and is available online.
Abstract
We present the mid-infrared (MIR) morphologies for 64 star-forming galaxies (SFGs) at 0.2 <
z
< 2.5 with stellar mass
M
*
> 10
9
M
⊙
using James Webb Space Telescope (JWST) Mid-Infrared ...Instrument (MIRI) observations from the Cosmic Evolution Early Release Science survey. The MIRI bands span the MIR (7.7–21
μ
m), enabling us to measure the effective radii (
R
eff
) and Sérsic indexes of these SFGs at rest-frame 6.2 and 7.7
μ
m, which contains strong emission from Polycyclic aromatic hydrocarbon (PAH) features, a well-established tracer of star formation in galaxies. We define a “PAH band” as the MIRI bandpass that contains these features at the redshift of the galaxy. We then compare the galaxy morphologies in the PAH bands to those in the rest-frame near-ultraviolet (NUV) using Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/F435W or ACS/F606W and optical/near-IR using HST WFC3/F160W imaging from UVCANDELS and CANDELS. The
R
eff
of galaxies in the PAH band are slightly smaller (∼10%) than those in F160W for galaxies with
M
*
≳ 10
9.5
M
⊙
at
z
≤ 1.2, but the PAH band and F160W have similar fractions of light within 1 kpc. In contrast, the
R
eff
of galaxies in the NUV band are larger, with lower fractions of light within 1 kpc compared to F160W for galaxies at
z
≤ 1.2. Using the MIRI data to estimate the SFR
IR
surface density, we find that the correlation between the SFR
IR
surface density and stellar mass has a steeper slope than that of the SFR
UV
surface density and stellar mass, suggesting more massive galaxies having increasing amounts of obscured fraction of star formation in their inner regions. This paper demonstrates how the high-angular resolution data from JWST/MIRI can reveal new information about the morphology of obscured star formation.
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