We investigate the relationship between the dust-to-metals ratio (D/M) and the local interstellar medium environment at ∼2 kpc resolution in five nearby galaxies: IC 342, M31, M33, M101, and NGC 628. ...A modified blackbody model with a broken power-law emissivity is used to model the dust emission from 100 to 500 m observed by Herschel. We utilize the metallicity gradient derived from auroral line measurements in H i regions whenever possible. Both archival and new CO rotational line and H i 21 cm maps are adopted to calculate gas surface density, including new wide-field CO and H i maps for IC 342 from IRAM and the VLA, respectively. We experiment with several prescriptions of the CO-to-H2 conversion factor and compare the resulting D/M-metallicity and D/M-density correlations, both of which are expected to be nonnegative from depletion studies. The D/M is sensitive to the choice of the conversion factor. The conversion factor prescriptions based on metallicity only yield too much molecular gas in the center of IC 342 to obtain the expected correlations. Among the prescriptions tested, the one that yields the expected correlations depends on both metallicity and surface density. The 1 range of the derived D/M spans 0.40-0.58. Compared to chemical evolution models, our measurements suggest that the dust growth timescale is much shorter than the dust destruction timescale. The measured D/M is consistent with the D/M in galaxy-integrated studies derived from infrared dust emission. Meanwhile, the measured D/M is systematically higher than the D/M derived from absorption, which likely indicates a systematic offset between the two methods.
Abstract
We examine the three-dimensional structure and dust extinction properties in a ∼200 pc × 100 pc region in the southwest bar of the Small Magellanic Cloud (SMC). We model a deep Hubble Space ...Telescope optical color–magnitude diagram (CMD) of red clump and red giant branch stars in order to infer the dust extinction and galactic structure. We model the distance distribution of the stellar component with a Gaussian and find a centroid distance of 65.2 kpc (distance modulus
μ
= 19.07 mag) with an FWHM ≈ 11.3 kpc. This large extent along the line of sight reproduces results from previous studies using variable stars and red clump stars. Additionally, we find an offset between the stellar and dust distributions, with the dust on the near side relative to the stars by 3.22
kpc, resulting in a 73% reddened fraction of stars. Modeling the dust layer with a log-normal
A
V
distribution indicates a mean extinction 〈
A
V
〉 = 0.41 ± 0.09 mag. We also calculate
A
V
/
N
H
= 3.2–4.2 × 10
−23
mag cm
2
H
−1
, which is significantly lower than the Milky Way value but is comparable to previous SMC dust-to-gas ratio measurements. Our results yield the first joint dust extinction and 3D geometry properties in a key region in the SMC. This study demonstrates that CMD modeling can be a powerful tool to simultaneously constrain dust extinction and geometry properties in nearby galaxies.
We use Hubble Space Telescope (HST) observations of red clump stars taken as part of the Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE) program to measure the average dust ...extinction curve in a ∼200 pc × 100 pc region in the southwest bar of the Small Magellanic Cloud (SMC). The rich information provided by our eight-band ultraviolet through near-infrared photometry allows us to model the color-magnitude diagram of the red clump accounting for the extinction curve shape, a log-normal distribution of AV, and the depth of the stellar distribution along the line of sight. We measure an extinction curve with . This measurement is significantly larger than the equivalent values of published Milky Way (MW) RV = 3.1 ( ) and SMC Bar RV = 2.74 ( ) extinction curves. Similar extinction curve offsets in the Large Magellanic Cloud (LMC) have been interpreted as the effect of large dust grains. We demonstrate that the line-of-sight depth of the SMC (and LMC) introduces an apparent "gray" contribution to the extinction curve inferred from the morphology of the red clump. We show that no gray dust component is needed to explain extinction curve measurements when FWHM depth of 10 2 kpc in the stellar distribution of the SMC (5 1 kpc for the LMC) is considered, which agrees with recent studies of Magellanic Cloud stellar structure. The results of our work demonstrate the power of broadband HST imaging for simultaneously constraining dust and galactic structure outside the MW.
Abstract
We present maps of the 3.3
μ
m polycyclic aromatic hydrocarbon (PAH) emission feature in NGC 628, NGC 1365, and NGC 7496 as observed with the Near-Infrared Camera imager on JWST from the ...PHANGS–JWST Cycle 1 Treasury project. We create maps that isolate the 3.3
μ
m PAH feature in the F335M filter (F335M
PAH
) using combinations of the F300M and F360M filters for removal of starlight continuum. This continuum removal is complicated by contamination of the F360M by PAH emission and variations in the stellar spectral energy distribution slopes between 3.0 and 3.6
μ
m. We modify the empirical prescription from Lai et al. to remove the starlight continuum in our highly resolved galaxies, which have a range of starlight- and PAH-dominated lines of sight. Analyzing radially binned profiles of the F335M
PAH
emission, we find that between 5% and 65% of the F335M intensity comes from the 3.3
μ
m feature within the inner 0.5
r
25
of our targets. This percentage systematically varies from galaxy to galaxy and shows radial trends within the galaxies related to each galaxy’s distribution of stellar mass, interstellar medium, and star formation. The 3.3
μ
m emission is well correlated with the 11.3
μ
m PAH feature traced with the MIRI F1130W filter, as is expected, since both features arise from C–H vibrational modes. The average F335M
PAH
/F1130W ratio agrees with the predictions of recent models by Draine et al. for PAHs with size and charge distributions shifted toward larger grains with normal or higher ionization.
Abstract
We present a high-resolution view of bubbles within the Phantom Galaxy (NGC 628), a nearby (∼10 Mpc), star-forming (∼2
M
⊙
yr
−1
), face-on (
i
∼ 9°) grand-design spiral galaxy. With new ...data obtained as part of the Physics at High Angular resolution in Nearby GalaxieS (PHANGS)-JWST treasury program, we perform a detailed case study of two regions of interest, one of which contains the largest and most prominent bubble in the galaxy (the Phantom Void, over 1 kpc in diameter), and the other being a smaller region that may be the precursor to such a large bubble (the Precursor Phantom Void). When comparing to matched-resolution H
α
observations from the Hubble Space Telescope, we see that the ionized gas is brightest in the shells of both bubbles, and is coincident with the youngest (∼1 Myr) and most massive (∼10
5
M
⊙
) stellar associations. We also find an older generation (∼20 Myr) of stellar associations is present within the bubble of the Phantom Void. From our kinematic analysis of the H
I
, H
2
(CO), and H
ii
gas across the Phantom Void, we infer a high expansion speed of around 15 to 50 km s
−1
. The large size and high expansion speed of the Phantom Void suggest that the driving mechanism is sustained stellar feedback due to multiple mechanisms, where early feedback first cleared a bubble (as we observe now in the Precursor Phantom Void), and since then supernovae have been exploding within the cavity and have accelerated the shell. Finally, comparison to simulations shows a striking resemblance to our JWST observations, and suggests that such large-scale, stellar-feedback-driven bubbles should be common within other galaxies.
Abstract
PHANGS–JWST mid-infrared (MIR) imaging of nearby spiral galaxies has revealed ubiquitous filaments of dust emission in intricate detail. We present a pilot study to systematically map the ...dust filament network (DFN) at multiple scales between 25 and 400 pc in NGC 628. MIRI images at 7.7, 10, 11.3, and 21
μ
m of NGC 628 are used to generate maps of the filaments in emission, while PHANGS–HST
B
-band imaging yields maps of dust attenuation features. We quantify the correspondence between filaments traced by MIR thermal continuum/polycyclic aromatic hydrocarbon (PAH) emission and filaments detected via extinction/scattering of visible light; the fraction of MIR flux contained in the DFN; and the fraction of H
ii
regions, young star clusters, and associations within the DFN. We examine the dependence of these quantities on the physical scale at which the DFN is extracted. With our highest-resolution DFN maps (25 pc filament width), we find that filaments in emission and attenuation are cospatial in 40% of sight lines, often exhibiting detailed morphological agreement; that ∼30% of the MIR flux is associated with the DFN; and that 75%–80% of the star formation in H
ii
regions and 60% of the mass in star clusters younger than 5 Myr are contained within the DFN. However, the DFN at this scale is anticorrelated with looser associations of stars younger than 5 Myr identified using PHANGS–HST near-UV imaging. We discuss the impact of these findings on studies of star formation and the interstellar medium, and the broad range of new investigations enabled by multiscale maps of the DFN.
Abstract
We combine archival Hubble Space Telescope and new James Webb Space Telescope imaging data covering the ultraviolet to mid-infrared regime to morphologically analyze the nuclear star cluster ...(NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200 pc × 400 pc cavity lacking both dust and gas. We find roughly constant values for the effective radius (
r
eff
∼ 5 pc) and ellipticity (
ϵ
∼ 0.05), while the Sérsic index (
n
) and position angle (PA) drop from
n
∼ 3 to ∼2 and PA ∼ 130° to 90°, respectively. In the mid-infrared,
r
eff
∼ 12 pc,
ϵ
∼ 0.4, and
n
∼ 1–1.5, with the same PA ∼ 90°. The NSC has a stellar mass of
log
10
(
M
⋆
nsc
/
M
⊙
)
=
7.06
±
0.31
, as derived through
B
−
V
, confirmed when using multiwavelength data, and in agreement with the literature value. Fitting the spectral energy distribution (SED), excluding the mid-infrared data, yields a main stellar population age of (8 ± 3) Gyr with a metallicity of
Z
= 0.012 ± 0.006. There is no indication of any significant star formation over the last few gigayears. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.
The CO-to-H2 conversion factor (αCO) is critical to studying molecular gas and star formation in galaxies. The value of αCO has been found to vary within and between galaxies, but the specific ...environmental conditions that cause these variations are not fully understood. Previous observations on ~kiloparsec scales revealed low values of αCO in the centers of some barred spiral galaxies, including NGC 3351. We present new Atacama Large Millimeter/submillimeter Array Band 3, 6, and 7 observations of 12CO, 13CO, and C18O lines on 100 pc scales in the inner ∼2 kpc of NGC 3351. Using multiline radiative transfer modeling and a Bayesian likelihood analysis, we infer the H2 density, kinetic temperature, CO column density per line width, and CO isotopologue abundances on a pixel-by-pixel basis. Our modeling implies the existence of a dominant gas component with a density of 2–3 × 103 cm−3 in the central ∼1 kpc and a high temperature of 30–60 K near the nucleus and near the contact points that connect to the bar-driven inflows. Assuming a CO/H2 abundance of 3 × 10−4, our analysis yields αCO ∼ 0.5–2.0 M⊙ (K km s−1 pc2)−1 with a decreasing trend with galactocentric radius in the central ∼1 kpc. The inflows show a substantially lower αCO ≲ 0.1 M⊙ (K km s−1 pc2)−1, likely due to lower optical depths caused by turbulence or shear in the inflows. Over the whole region, this gives an intensity-weighted αCO of ∼1.5 M⊙ (K km s−1 pc2)−1, which is similar to previous dust-modeling-based results at kiloparsec scales. This suggests that low αCO on kiloparsec scales in the centers of some barred galaxies may be due to the contribution of low-optical-depth CO emission in bar-driven inflows.
Abstract We present NIRCam and NIRISS modules for DOLPHOT, a widely used crowded-field stellar photometry package. We describe details of the modules including pixel masking, astrometric alignment, ...star finding, photometry, catalog creation, and artificial star tests. We tested these modules using NIRCam and NIRISS images of M92 (a Milky Way globular cluster), Draco II (an ultrafaint dwarf galaxy), and Wolf–Lundmark–Mellote (a star-forming dwarf galaxy). DOLPHOT’s photometry is highly precise, and the color–magnitude diagrams are deeper and have better definition than anticipated during original program design in 2017. The primary systematic uncertainties in DOLPHOT’s photometry arise from mismatches in the model and observed point-spread functions (PSFs) and aperture corrections, each contributing ≲0.01 mag to the photometric error budget. Version 1.2 of WebbPSF models, which include charge diffusion and interpixel capacitance effects, significantly reduced PSF-related uncertainties. We also observed minor (≲0.05 mag) chip-to-chip variations in NIRCam’s zero-points, which will be addressed by the JWST flux calibration program. Globular cluster observations are crucial for photometric calibration. Temporal variations in the photometry are generally ≲0.01 mag, although rare large misalignment events can introduce errors up to 0.08 mag. We provide recommended DOLPHOT parameters, guidelines for photometric reduction, and advice for improved observing strategies. Our Early Release Science DOLPHOT data products are available on MAST, complemented by comprehensive online documentation and tutorials for using DOLPHOT with JWST imaging data.
Abstract
Large-scale bars can fuel galaxy centers with molecular gas, often leading to the development of dense ringlike structures where intense star formation occurs, forming a very different ...environment compared to galactic disks. We pair ∼0.″3 (30 pc) resolution new JWST/MIRI imaging with archival ALMA CO(2–1) mapping of the central ∼5 kpc of the nearby barred spiral galaxy NGC 1365 to investigate the physical mechanisms responsible for this extreme star formation. The molecular gas morphology is resolved into two well-known bright bar lanes that surround a smooth dynamically cold gas disk (
R
gal
∼ 475 pc) reminiscent of non-star-forming disks in early-type galaxies and likely fed by gas inflow triggered by stellar feedback in the lanes. The lanes host a large number of JWST-identified massive young star clusters. We find some evidence for temporal star formation evolution along the ring. The complex kinematics in the gas lanes reveal strong streaming motions and may be consistent with convergence of gas streamlines expected there. Indeed, the extreme line widths are found to be the result of inter-“cloud” motion between gas peaks;
ScousePy
decomposition reveals multiple components with line widths of 〈
σ
CO,scouse
〉 ≈ 19 km s
−1
and surface densities of
〈
Σ
H
2
,
scouse
〉
≈
800
M
⊙
pc
−
2
, similar to the properties observed throughout the rest of the central molecular gas structure. Tailored hydrodynamical simulations exhibit many of the observed properties and imply that the observed structures are transient and highly time-variable. From our study of NGC 1365, we conclude that it is predominantly the high gas inflow triggered by the bar that is setting the star formation in its CMZ.
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