Abstract
We conduct one of the largest systematic investigations of bright X-ray binaries (XRBs) in both young star clusters and ancient globular clusters (GCs) using a sample of six nearby ...star-forming galaxies. Combining complete CXO X-ray source catalogs with optical Physics at High Angular Resolution in Nearby Galaxies-Hubble Space Telescope cluster catalogs, we identify a population of 33 XRBs within or near their parent clusters. We find that GCs that host XRBs in spiral galaxies appear to be brighter, more compact, denser, and more massive than the general GC population. However, these XRB hosts do not appear to be preferentially redder or more metal-rich, pointing to a possible absence of the metallicity-boosted formation of low-mass X-ray binaries (LMXBs) that is observed in the GCs of older galaxies. We also find that a smaller fraction of LMXBs is found in spiral GC systems when compared with those in early-type galaxies: between 8% and 50%, or an average of 20% across galaxies in our sample. Although there is a non-negligible probability of a chance superposition between an XRB and an unrelated young cluster, we find that among clusters younger than 10 Myr, which most likely host high-mass XRBs, the fraction of clusters associated with an XRB increases at higher cluster masses and densities. The X-ray luminosity of XRBs appears to increase with the mass of the cluster host for clusters younger than ∼400 Myr, while the inverse relation is found for XRBs in GCs.
We introduce the GALEX Arecibo SDSS Survey (GASS), an on-going large programme that is gathering high quality H i-line spectra using the Arecibo radio telescope for an unbiased sample of ∼1000 ...galaxies with stellar masses greater than 1010 M⊙ and redshifts 0.025 < z < 0.05, selected from the Sloan Digital Sky Survey (SDSS) spectroscopic and Galaxy Evolution Explorer (GALEX) imaging surveys. The galaxies are observed until detected or until a low gas mass fraction limit (1.5–5 per cent) is reached. This paper presents the first Data Release, consisting of ∼20 per cent of the final GASS sample. We use this data set to explore the main scaling relations of the H i gas fraction with galaxy structure and NUV−r colour. A large fraction (∼60 per cent) of the galaxies in our sample are detected in H i. Even at stellar masses above 1011 M⊙, the detected fraction does not fall below ∼40 per cent. We find that the atomic gas fraction MH i/M★ decreases strongly with stellar mass, stellar surface mass density and NUV−r colour, but is only weakly correlated with the galaxy bulge-to-disc ratio (as measured by the concentration index of the r-band light). We also find that the fraction of galaxies with significant (more than a few per cent) H i decreases sharply above a characteristic stellar surface mass density of 108.5 M⊙ kpc−2. The fraction of gas-rich galaxies decreases much more smoothly with stellar mass. One of the key goals of GASS is to identify and quantify the incidence of galaxies that are transitioning between the blue, star-forming cloud and the red sequence of passively evolving galaxies. Likely transition candidates can be identified as outliers from the mean scaling relations between MH i/M★ and other galaxy properties. We have fitted a plane to the two-dimensional relation between the H i mass fraction, stellar surface mass density and NUV−r colour. Interesting outliers from this plane include gas-rich red sequence galaxies that may be in the process of regrowing their discs, as well as blue, but gas-poor spirals.
ABSTRACT
We present improved methods for segmenting CO emission from galaxies into individual molecular clouds, providing an update to the cprops algorithms presented by Rosolowsky & Leroy. The new ...code enables both homogenization of the noise and spatial resolution among data, which allows for rigorous comparative analysis. The code also models the completeness of the data via false source injection and includes an updated segmentation approach to better deal with blended emission. These improved algorithms are implemented in a publicly available Python package, pycprops. We apply these methods to 10 of the nearest galaxies in the PHANGS-ALMA survey, cataloguing CO emission at a common 90 pc resolution and a matched noise level. We measure the properties of 4986 individual clouds identified in these targets. We investigate the scaling relations among cloud properties and the cloud mass distributions in each galaxy. The physical properties of clouds vary among galaxies, both as a function of galactocentric radius and as a function of dynamical environment. Overall, the clouds in our target galaxies are well-described by approximate energy equipartition, although clouds in stellar bars and galaxy centres show elevated line widths and virial parameters. The mass distribution of clouds in spiral arms has a typical mass scale that is 2.5× larger than interarm clouds and spiral arms clouds show slightly lower median virial parameters compared to interarm clouds (1.2 versus 1.4).
Abstract
Polycyclic aromatic hydrocarbons (PAHs) play a critical role in the reprocessing of stellar radiation and balancing the heating and cooling processes in the interstellar medium but appear to ...be destroyed in H
ii
regions. However, the mechanisms driving their destruction are still not completely understood. Using PHANGS–JWST and PHANGS–MUSE observations, we investigate how the PAH fraction changes in about 1500 H
ii
regions across four nearby star-forming galaxies (NGC 628, NGC 1365, NGC 7496, and IC 5332). We find a strong anticorrelation between the PAH fraction and the ionization parameter (the ratio between the ionizing photon flux and the hydrogen density) of H
ii
regions. This relation becomes steeper for more luminous H
ii
regions. The metallicity of H
ii
regions has only a minor impact on these results in our galaxy sample. We find that the PAH fraction decreases with the H
α
equivalent width—a proxy for the age of the H
ii
regions—although this trend is much weaker than the one identified using the ionization parameter. Our results are consistent with a scenario where hydrogen-ionizing UV radiation is the dominant source of PAH destruction in star-forming regions.
Abstract
Ratios of polycyclic aromatic hydrocarbon (PAH) vibrational bands are a promising tool for measuring the properties of the PAH population and their effect on star formation. The photometric ...bands of the MIRI and NIRCam instruments on JWST provide the opportunity to measure PAH emission features across entire galaxy disks at unprecedented resolution and sensitivity. Here we present the first results of this analysis in a sample of three nearby galaxies: NGC 628, NGC 1365, and NGC 7496. Based on the variations observed in the 3.3, 7.7, and 11.3
μ
m features, we infer changes to the average PAH size and ionization state across the different galaxy environments. High values of F335M
PAH
/F1130W and low values of F1130W/F770W are measured in H
ii
regions in all three galaxies. This suggests that these regions are populated by hotter PAHs, and/or that the PAH ionization fraction is larger. We see additional evidence of heating and/or changes in PAH size in regions with higher molecular gas content as well as increased ionization in regions with higher H
α
intensity.
Abstract
We present maps tracing the fraction of dust in the form of polycyclic aromatic hydrocarbons (PAHs) in IC 5332, NGC 628, NGC 1365, and NGC 7496 from JWST/MIRI observations. We trace the PAH ...fraction by combining the F770W (7.7
μ
m) and F1130W (11.3
μ
m) filters to track ionized and neutral PAH emission, respectively, and comparing the PAH emission to F2100W, which traces small, hot dust grains. We find the average
R
PAH
= (F770W + F1130W)/F2100W values of 3.3, 4.7, 5.1, and 3.6 in IC 5332, NGC 628, NGC 1365, and NGC 7496, respectively. We find that H
ii
regions traced by MUSE H
α
show a systematically low PAH fraction. The PAH fraction remains relatively constant across other galactic environments, with slight variations. We use CO+H
i
+H
α
to trace the interstellar gas phase and find that the PAH fraction decreases above a value of
I
H
α
/
Σ
H
I
+
H
2
∼
10
37.5
erg
s
−
1
kpc
−
2
(
M
⊙
pc
−
2
)
−
1
in all four galaxies. Radial profiles also show a decreasing PAH fraction with increasing radius, correlated with lower metallicity, in line with previous results showing a strong metallicity dependence to the PAH fraction. Our results suggest that the process of PAH destruction in ionized gas operates similarly across the four targets.
Abstract
The PHANGS program is building the first data set to enable the multiphase, multiscale study of star formation across the nearby spiral galaxy population. This effort is enabled by large ...survey programs with the Atacama Large Millimeter/submillimeter Array (ALMA), MUSE on the Very Large Telescope, and the Hubble Space Telescope (HST), with which we have obtained CO(2–1) imaging, optical spectroscopic mapping, and high-resolution UV–optical imaging, respectively. Here, we present PHANGS-HST, which has obtained NUV–
U
–
B
–
V
–
I
imaging of the disks of 38 spiral galaxies at distances of 4–23 Mpc, and parallel
V
- and
I
-band imaging of their halos, to provide a census of tens of thousands of compact star clusters and multiscale stellar associations. The combination of HST, ALMA, and VLT/MUSE observations will yield an unprecedented joint catalog of the observed and physical properties of ∼100,000 star clusters, associations, H
ii
regions, and molecular clouds. With these basic units of star formation, PHANGS will systematically chart the evolutionary cycling between gas and stars across a diversity of galactic environments found in nearby galaxies. We discuss the design of the PHANGS-HST survey and provide an overview of the HST data processing pipeline and first results. We highlight new methods for selecting star cluster candidates, morphological classification of candidates with convolutional neural networks, and identification of stellar associations over a range of physical scales with a watershed algorithm. We describe the cross-observatory imaging, catalogs, and software products to be released. The PHANGS high-level science products will seed a broad range of investigations, in particular, the study of embedded stellar populations and dust with the James Webb Space Telescope, for which a PHANGS Cycle 1 Treasury program to obtain eight-band 2–21
μ
m imaging has been approved.
We have initiated a search for extended ultraviolet disk (XUV-disk) galaxies in the local universe. Here we compare GALEX UV and visible-NIR images of 189 nearby (D < 40 Mpc) S0-Sm galaxies Included ...in the GALEX Atlas of Nearby Galaxies and present the first catalog of XUV-disk galaxies. We find that XUV-disk galaxies are surprisingly common but have varied relative (UV/optical) extent and morphology. Type 1 objects ( unk 20% incidence) have structured, UV-bright/optically faint emission features in the outer disk, beyond the traditional star formation threshold. Type 2 XUV-disk galaxies ( similar to 10% incidence) exhibit an exceptionally large, UV-bright/optically low surface brightness (LSB) zone having blue UV-K sub(S) outside the effective extent of the inner, older stellar population, but not reaching extreme galactocentric distance. If the activity occurring in XUV-disks is episodic, a higher fraction of present-day spirals could be influenced by such outer disk star formation. Type 1 disks are associated with spirals of all types, whereas Type 2 XUV-disks are predominantly found In late-type spirals. Type 2 XUV-disks are forming stars quickly enough to double their (currently low) stellar mass in the next Gyr (assuming a constant star formation rate). XUV-disk galaxies of both types are systematically more gas-rich than the general galaxy population. Minor external perturbation may stimulate XUV-disk incidence, at least for Type 1 objects. XUV-disks are the most actively evolving galaxies growing via inside-out disk formation in the current epoch, and may constitute a segment of the galaxy population experiencing significant, continued gas accretion from the intergalactic medium or neighboring objects.
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.
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