6 research outputs found
JWST reveals widespread CO ice and gas absorption in the Galactic Center cloud G0.253+0.016
We report JWST NIRCam observations of G0.253+0.016, the molecular cloud in
the Central Molecular Zone known as The Brick, with the F182M, F187N, F212N,
F410M, F405N, and F466N filters. We catalog 56,146 stars detected in all 6
filters using the crowdsource package. Stars within and behind The Brick
exhibit prodigious absorption in the F466N filter that is produced by a
combination of CO ice and gas. In support of this conclusion, and as a general
resource, we present models of CO gas and ice and CO ice in the F466N,
F470N, and F410M filters. Both CO gas and ice may contribute to the observed
stellar colors. We show, however, that CO gas does not absorb the Pf and
Hu lines in F466N, but that these lines show excess absorption,
indicating that CO ice is also present and contributes to observed F466N
absorption. The most strongly absorbed stars in F466N are extincted by 2
magnitudes, corresponding to 80\% flux loss. This high observed absorption
requires very high column densities of CO, requiring total CO column that is in
tension with standard CO abundance and/or gas-to-dust ratios. There is
therefore likely to be a greater CO/H ratio (X) and more
dust per H molecule () in the Galactic Center than the Galactic
disk. Ice and/or gas absorption is observed even in the cloud outskirts,
implying that additional caution is needed when interpreting stellar photometry
in filters that overlap with ice bands throughout our Galactic Center. The
widespread CO absorption in our Galactic Center hints that significant ice
absorption is likely present in other galactic centers.Comment: Submitted to ApJ. Revised after second referee report. 16 pages, 11
figure
Pure point diffraction implies zero entropy for Delone sets with uniform cluster frequencies
Delone sets of finite local complexity in Euclidean space are investigated.
We show that such a set has patch counting and topological entropy 0 if it has
uniform cluster frequencies and is pure point diffractive. We also note that
the patch counting entropy is 0 whenever the repetitivity function satisfies a
certain growth restriction.Comment: 16 pages; revised and slightly expanded versio
Delayed Stellar Mass Assembly in the Low Surface Brightness Dwarf Galaxy KDG215
We present HI spectral line and optical broadband images of the nearby low
surface brightness dwarf galaxy KDG215. The HI images, acquired with the Karl
G. Jansky Very Large Array (VLA), reveal a dispersion dominated ISM with only
weak signatures of coherent rotation. The HI gas reaches a peak mass surface
density of 6 M pc at the location of the peak surface
brightness in the optical and the UV. Although KDG215 is gas-rich, the
H non-detection implies a very low current massive star formation rate.
In order to investigate the recent evolution of this system, we have derived
the recent and lifetime star formation histories from archival Hubble Space
Telescope images. The recent star formation history shows a peak star formation
rate 1 Gyr ago, followed by a decreasing star formation rate to the
present day quiescent state. The cumulative star formation history indicates
that a significant fraction of the stellar mass assembly in KDG215 has occurred
within the last 1.25 Gyr. KDG215 is one of only a few known galaxies which
demonstrates such a delayed star formation history. While the ancient stellar
population (predominantly red giants) is prominent, the look-back time by which
50% of the mass of all stars ever formed had been created is among the youngest
of any known galaxy.Comment: Accepted for publication in the Astrophysical Journal Letter
A wind-blown bubble in the Central Molecular Zone cloud G0.253+0.016
G0.253+0.016, commonly referred to as "the Brick" and located within the Central Molecular Zone, is one of the densest ( cm) molecular clouds in the Galaxy to lack signatures of widespread star formation. We set out to constrain the origins of an arc-shaped molecular line emission feature located within the cloud. We determine that the arc, centred on , has a radius of pc and kinematics indicative of the presence of a shell expanding at km s. Extended radio continuum emission fills the arc cavity and recombination line emission peaks at a similar velocity to the arc, implying that the molecular and ionised gas are physically related. The inferred Lyman continuum photon rate is photons s, consistent with a star of spectral type B1-O8.5, corresponding to a mass of M. We explore two scenarios for the origin of the arc: i) a partial shell swept up by the wind of an interloper high-mass star; ii) a partial shell swept up by stellar feedback resulting from in-situ star formation. We favour the latter scenario, finding reasonable (factor of a few) agreement between its morphology, dynamics, and energetics and those predicted for an expanding bubble driven by the wind from a high-mass star. The immediate implication is that G0.253+0.016 may not be as quiescent as is commonly accepted. We speculate that the cloud may have produced a M star cluster Myr ago, and demonstrate that the high-extinction and stellar crowding observed towards G0.253+0.016 may help to obscure such a star cluster from detection
JWST Reveals Widespread CO Ice and Gas Absorption in the Galactic Center Cloud G0.253+0.016
We report JWST NIRCam observations of G0.253+0.016, the molecular cloud in the Central Molecular Zone known as “The Brick,” with the F182M, F187N, F212N, F410M, F405N, and F466N filters. We catalog 56,146 stars detected in all six filters using the crowdsource package. Stars within and behind The Brick exhibit prodigious absorption in the F466N filter that is produced by a combination of CO ice and gas. In support of this conclusion, and as a general resource, we present models of CO gas and ice and CO _2 ice in the F466N, F470N, and F410M filters. Both CO gas and ice contribute to the observed stellar colors. We show, however, that CO gas does not absorb the Pf β and Hu ϵ lines in F466N, but that these lines show excess absorption, indicating that CO ice is present and contributes to observed F466N absorption. The most strongly absorbed stars in F466N are extincted by ∼2 mag, corresponding to >80% flux loss. This high observed absorption requires very high column densities of CO, and thus a total CO column that is in tension with standard CO abundance and/or gas-to-dust ratios. This result suggests the CO/H _2 ratio and dust-to-gas ratio are greater in the Galactic Center than in the Galactic disk. Ice and/or gas absorption is observed even in the cloud outskirts, implying that additional caution is needed when interpreting stellar photometry in filters that overlap with ice bands throughout galactic centers
A wind-blown bubble in the Central Molecular Zone cloud G0.253+0.016
G0.253+0.016, commonly referred to as "the Brick" and located within the
Central Molecular Zone, is one of the densest ( cm)
molecular clouds in the Galaxy to lack signatures of widespread star formation.
We set out to constrain the origins of an arc-shaped molecular line emission
feature located within the cloud. We determine that the arc, centred on
, has a radius of pc and
kinematics indicative of the presence of a shell expanding at
km s. Extended radio continuum emission fills the
arc cavity and recombination line emission peaks at a similar velocity to the
arc, implying that the molecular and ionised gas are physically related. The
inferred Lyman continuum photon rate is
photons s, consistent with a star of spectral type B1-O8.5,
corresponding to a mass of M. We explore two scenarios
for the origin of the arc: i) a partial shell swept up by the wind of an
interloper high-mass star; ii) a partial shell swept up by stellar feedback
resulting from in-situ star formation. We favour the latter scenario, finding
reasonable (factor of a few) agreement between its morphology, dynamics, and
energetics and those predicted for an expanding bubble driven by the wind from
a high-mass star. The immediate implication is that G0.253+0.016 may not be as
quiescent as is commonly accepted. We speculate that the cloud may have
produced a M star cluster Myr ago, and
demonstrate that the high-extinction and stellar crowding observed towards
G0.253+0.016 may help to obscure such a star cluster from detection.Comment: 17 pages, 7 figures. Accepted for publication in MNRAS (October 15,
2021