12 research outputs found
Evolution of the Mass-Metallicity Relation from Redshift to the Local Universe
A tight positive correlation between the stellar mass and the gas-phase
metallicity of galaxies has been observed at low redshifts. The redshift
evolution of this correlation can strongly constrain theories of galaxy
evolution. The advent of JWST allows probing the mass-metallicity relation at
redshifts far beyond what was previously accessible. Here we report the
discovery of two emission-line galaxies at redshifts 8.15 and 8.16 in JWST
NIRCam imaging and NIRSpec spectroscopy of targets gravitationally lensed by
the cluster RXJ2129.40005. We measure their metallicities and stellar masses
along with nine additional galaxies at to report the
first quantitative statistical inference of the mass-metallicity relation at
. We measure dex evolution in the normalization of the
mass-metallicity relation from to the local Universe; at fixed
stellar mass, galaxies are 8 times less metal enriched at
compared to the present day. Our inferred normalization is in agreement with
the predictions of the FIRE simulations. Our inferred slope of the
mass-metallicity relation is similar to or slightly shallower than that
predicted by FIRE or observed at lower redshifts. We compare the
galaxies to extremely low metallicity analog candidates in the local Universe,
finding that they are generally distinct from extreme emission-line galaxies or
"green peas" but are similar in strong emission-line ratios and metallicities
to "blueberry galaxies". Despite this similarity, at fixed stellar mass, the galaxies have systematically lower metallicities compared to
blueberry galaxies.Comment: Published in Ap
Spectroscopy from Lyman alpha to [O III] 5007 of a Triply Imaged Magnified Galaxy at Redshift z = 9.5
Given their extremely faint apparent brightness, the nature of the first
galaxies and how they reionized the Universe's gas are not yet understood. Here
we report the discovery, in James Webb Space Telescope (JWST) imaging, of a
highly magnified, low-mass (log(M_*/M_sol)=7.70^{+0.11}_{-0.09}) galaxy visible
when the Universe was only 510 Myr old, and follow-up prism spectroscopy of the
galaxy extending from Lyman alpha to [O III] 5007 in its rest frame. Our JWST
spectrum provides [O III] 5007 and H beta detections with a respective
signal-to-noise ratio (S/N) of 40 and 13, as well as six additional lines with
S/N > 3. These emission lines yield a redshift of z=9.51 and star-formation
rate of 2.12 +- 0.53 solar masses per year. The galaxy's large inferred value
of [O III]/[O II] = 16 +- 6 suggests that this galaxy has an escape fraction of
ionizing radiation larger than 10%, indicating that a population of similar
objects could contribute substantially to the reionization budget. Using
multiple techniques, we infer a gas oxygen abundance of 12 + log(O/H) = 7.48 +-
0.05 dex, consistent within 2 sigma of the mass-metallicity relation observed
for dwarf galaxies in the local Universe
QUIJOTE scientific results -- XIII. Intensity and polarization study of supernova remnants in the QUIJOTE-MFI wide survey: CTB 80, Cygnus Loop, HB 21, CTA 1, Tycho and HB 9
We use the new QUIJOTE-MFI wide survey (11, 13, 17 and 19 GHz) to produce
spectral energy distributions (SEDs), on an angular scale of 1 deg, of the
supernova remnants (SNRs) CTB 80, Cygnus Loop, HB 21, CTA 1, Tycho and HB 9. We
provide new measurements of the polarized synchrotron radiation in the
microwave range. For each SNR, the intensity and polarization SEDs are obtained
and modelled by combining QUIJOTE-MFI maps with ancillary data. In intensity,
we confirm the curved power law spectra of CTB 80 and HB 21 with a break
frequency at 2.0 GHz and 5.0 GHz
respectively; and spectral indices respectively below and above the spectral
break of and for CTB 80, and and
for HB 21. In addition, we provide upper limits on the Anomalous
Microwave Emission (AME), suggesting that the AME contribution is negligible
towards these remnants. From a simultaneous intensity and polarization fit, we
recover synchrotron spectral indices as flat as , and the whole sample
has a mean and scatter of . The polarization fractions have a
mean and scatter of \%. When combining our results with the
measurements from other QUIJOTE studies of SNRs, we find that radio spectral
indices are flatter for mature SNRs, and particularly flatter for CTB 80
() and HB 21 (). In addition, the
evolution of the spectral indices against the SNRs age is modelled with a
power-law function, providing an exponent and amplitude
(normalised at 10 kyr), which are conservative with respect to
previous studies of our Galaxy and the Large Magellanic Cloud.Comment: 33 pages, 15 figure, 15 tables. Submitted to MNRAS. QUIJOTE data maps
available at https://research.iac.es/proyecto/quijot
Detailed magnetic field morphology of the Vela C molecular cloud from the BLASTPol 2012 flight
In order to understand the role of magnetic fields in the process of star formation, we require detailed observations of field morphology on scales ranging from clouds to cores. However, ground based millimetre/submillimetre polarimetry is usually limited to small maps of relatively dense regions. BLASTPol, the Balloon-borne Large Aperture Sub-mm Telescope for Polarimetry, maps linear polarization at 250, 350 and 500 microns with arcminute resolution. Its high sensitivity and resolving power allow BLASTPol to bridge the gap in spatial scales between the polarization capabilities of Planck and ALMA.I will present early results from the second flight of BLASTPol, focusing on our observations of the Vela C molecular cloud, an early stage intermediate mass star forming region (d~700 pc). With thousands of independent measurements of magnetic field direction, this is the most detailed sub-mm polarization map of a GMC to date. The field we observe in this elongated cloud exhibits a coherent, large-scale ~ 90 degree bend between its high latitude and low latitude edges. I will discuss what we can learn about star formation in Vela C from the combination of BLASTPol polarization maps and velocity information from molecular line observations, and what the variation of polarization strength across the cloud can tell us about dust grain alignment in GMCs
Mapping magnetic fields in star forming regions with BLASTPol
A key outstanding question in our understanding of star formation is whether magnetic fields provide support against the gravitational collapse of their parent molecular clouds and cores. Direct measurement of magnetic field strength is observationally challenging, however observations of polarized thermal emission from dust grains aligned with respect to the local cloud magnetic field can be used to map out the magnetic field orientation in molecular clouds. Statistical comparisons between these submillimeter polarization maps and three-dimensional numerical simulations of magnetized star-forming clouds provide a promising method for constraining magnetic field strength. We present early results from a BLASTPol study of the nearby giant molecular cloud (GMC) Vela C, using data collected during a 2012 Antarctic flight. This sensitive balloon-borne polarimeter observed Vela C for 57 hours, yielding the most detailed submillimeter polarization map ever made of a GMC forming high mass stars. We find that most of the structure in p can be modeled by a power-law dependence on two quantities: the hydrogen column density and the local dispersion in magnetic field orientation. Our power-law model for p(N,S) provides new constraints for models of magnetized star-forming clouds and an important first step in the interpretation of the BLASTPol 2012 data set
Comparing polarized submm emission and near-infrared extinction polarization in the Vela C giant molecular cloud
We present one of largest studies to date of combined near-infrared and submillimeter linear polarization data for a giant molecular cloud. The dust polarized emission data (at 250, 350 and 500 μm) were obtained using the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) during its 2012 Antarctic flight. The near-infrared polarization, which is produced by dichroic extinction of background starlight, was measured in the I band (0.8 μm) using the Pico dos Dias Observatory in Brazil. The study targets the Vela C cloud, a conspicuous star-forming environment at a distance of approximately 700 pc, hosting HII regions, protostars, and dense filamentary structures. By studying the relationship between polarized emission and polarized absorption, we can investigate how this relates to the physical properties of dust grains. The area of overlap of the two data sets corresponds to a large fraction of the molecular cloud (approximately 1.5° × 2.0°), with hundreds of combined polarization pseudo-vectors distributed mainly along the borders of the cloud. For most sight-lines, the inferred magnetic field orientations match within 20°. Visual extinction values (AV) for near-infrared pseudo-vectors are estimated from 2MASS photometry. Based on these extinction values, we determine and correct for a small foreground contribution (~0.4%) in the near-infrared sample. We calculate the polarization efficiency ratio, defined as the polarization fraction at 500 μm divided by the polarization efficiency in the near-infrared (defined as P/AV). Models of aligned dust grains are helpful for producing predicted polarization maps from numerical simulations of turbulent molecular clouds, and the polarization efficiency ratio provides a constraint for such dust alignment models. Preliminary results show that the measured polarization efficiency ratio appears to be roughly consistent with the predictions of the Draine and Fraisse (2009) models