6 research outputs found
A JWST/MIRI and NIRCam Analysis of the Young Stellar Object Population in the Spitzer I region of NGC 6822
We present an imaging survey of the Spitzer~I star-forming region in NGC 6822
conducted with the NIRCam and MIRI instruments onboard JWST. Located at a
distance of 490 kpc, NGC 6822 is the nearest non-interacting low-metallicity
(0.2 ) dwarf galaxy. It hosts some of the brightest known HII
regions in the local universe, including recently discovered sites of
highly-embedded active star formation. Of these, Spitzer I is the youngest and
most active, and houses 90 color-selected candidate young stellar objects
(YSOs) identified from Spitzer Space Telescope observations. We revisit the YSO
population of Spitzer~I with these new JWST observations. By analyzing
color-magnitude diagrams (CMDs) constructed with NIRCam and MIRI data, we
establish color selection criteria and construct spectral energy distributions
(SEDs) to identify candidate YSOs and characterize the full population of young
stars, from the most embedded phase to the more evolved stages. In this way, we
have identified 129 YSOs in Spitzer I. Comparing to previous Spitzer studies of
the NGC 6822 YSO population, we find that the YSOs we identify are fainter and
less massive, indicating that the improved resolution of JWST allows us to
resolve previously blended sources into individual stars.Comment: 17 pages, 9 figures, 2 tables, to be submitted to ApJ, comments
welcom
JWST MIRI and NIRCam Unveil Previously Unseen Infrared Stellar Populations in NGC 6822
NGC 6822 is a nearby (\sim490 kpc) non-interacting low-metallicity (0.2
Z_\odot) dwarf galaxy which hosts several prominent Hii regions, including
sites of highly embedded active star formation. In this work, we present an
imaging survey of NGC 6822 conducted with the NIRCam and MIRI instruments
onboard JWST. We provide a description of the data reduction, source
extraction, and stellar population identifications from combined near- and
mid-infrared (IR) photometry. Our NIRCam observations reach seven magnitudes
deeper than previous JHKs surveys of this galaxy, which were sensitive to just
below the tip of the red giant branch (TRGB). These JWST observations thus
reveal for the first time in the near-IR the red clump stellar population and
extend nearly three magnitudes deeper. In the mid-IR, we observe roughly two
magnitudes below the TRGB with the MIRI F770W and F1000W filters. With these
improvements in sensitivity, we produce a catalogue of \sim900,000 point
sources over an area of \sim 6.0 x 4.3 arcmin2. We present several NIRCam and
MIRI colour-magnitude diagrams and discuss which colour combinations provide
useful separations of various stellar populations to aid in future JWST
observation planning. Finally, we find populations of carbon- and oxygen-rich
asymptotic giant branch stars which will assist in improving our understanding
of dust production in low-metallicity, early Universe analogue galaxies
DUVET: Spatially Resolved Observations of Star Formation Regulation via Galactic Outflows in a Starbursting Disk Galaxy
We compare 500~pc scale, resolved observations of ionised and molecular gas
for the starbursting disk galaxy IRAS08339+6517, using measurements
from KCWI and NOEMA. We explore the relationship of the star formation driven
ionised gas outflows with colocated galaxy properties. We find a roughly linear
relationship between the outflow mass flux () and star
formation rate surface density (), , and a strong correlation between
and the gas depletion time, such that
. Moreover, we find these
outflows are so-called ``breakout" outflows, according to the relationship
between the gas fraction and disk kinematics. Assuming that ionised outflow
mass scales with total outflow mass, our observations suggest that the regions
of highest in IRAS08 are removing more gas via the outflow
than through the conversion of gas into stars. Our results are consistent with
a picture in which the outflow limits the ability for a region of a disk to
maintain short depletion times. Our results underline the need for resolved
observations of outflows in more galaxies.Comment: 16 pages, 7 figures, Submitted to Ap
CO Excitation in High-z Main-sequence Analogues: Resolved CO(4−3)/CO(3−2) Line Ratios in DYNAMO Galaxies
The spectral line energy distribution of carbon monoxide contains information about the physical conditions of the star-forming molecular hydrogen gas; however, the relation to local radiation field properties is poorly constrained. Using ∼1–2 kpc scale Atacama Large Millimeter Array observations of CO(3−2) and CO(4−3), we characterize the CO(4−3)/CO(3−2) line ratios of local analogues of main-sequence galaxies at z ∼ 1–2, drawn from the DYnamics of Newly Assembled Massive Objects (DYNAMO) sample. We measure CO(4−3)/CO(3−2) across the disk of each galaxy and find a median line ratio of R _43 = 0.54 for the sample. This is higher than literature estimates of local star-forming galaxies and is consistent with multiple lines of evidence that indicate DYNAMO galaxies, despite residing in the local universe, resemble main-sequence galaxies at z ∼ 1–2. Comparing with existing lower-resolution CO(1−0) observations, we find R _41 and R _31 values in the range ∼0.2–0.3 and ∼0.4–0.8, respectively. We combine our kiloparsec-scale resolved line ratio measurements with Hubble Space Telescope observations of H α to investigate the relation to the star formation rate surface density and compare this relation to expectations from models. We find increasing CO(4−3)/CO(3−2) with increasing star formation rate surface density; however, models overpredict the line ratios across the range of star formation rate surface densities we probe, in particular at the lower range. Finally, Stratospheric Observatory for Infrared Astronomy observations with the High-resolution Airborne Wideband Camera Plus and Field-Imaging Far-Infrared Line Spectrometer reveal low dust temperatures and no deficit of [C ii ] emission with respect to the total infrared luminosity