Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Adam K. Leroy
Karin Sandstrom
Erik Rosolowsky
Francesco Belfiore
Alberto D. Bolatto
Yixian Cao
Eric W. Koch
Eva Schinnerer
Ashley. T. Barnes
Ivana Bešlić
F. Bigiel
Guillermo A. Blanc
Jérémy Chastenet
Ness Mayker Chen
Mélanie Chevance
Ryan Chown
Enrico Congiu
Daniel A. Dale
Oleg V. Egorov
Eric Emsellem
Abstract： We compare mid-infrared (mid-IR), extinction-corrected H$\alpha$, and CO (2-1) emission at 70--160 pc resolution in the first four PHANGS-JWST targets. We report correlation strengths, intensity ratios, and power law fits relating emission in JWST's F770W, F1000W, F1130W, and F2100W bands to CO and H$\alpha$. At these scales, CO and H$\alpha$ each correlate strongly with mid-IR emission, and these correlations are each stronger than the one relating CO to H$\alpha$ emission. This reflects that mid-IR emission simultaneously acts as a dust column density tracer, leading to the good match with the molecular gas-tracing CO, and as a heating tracer, leading to the good match with the H$\alpha$. By combining mid-IR, CO, and H$\alpha$ at scales where the overall correlation between cold gas and star formation begins to break down, we are able to separate these two effects. We model the mid-IR above $I_\nu = 0.5$~MJy sr$^{-1}$ at F770W, a cut designed to select regions where the molecular gas dominates the interstellar medium (ISM) mass. This bright emission can be described to first order by a model that combines a CO-tracing component and an H$\alpha$-tracing component. The best-fitting models imply that $\sim 50\%$ of the mid-IR flux arises from molecular gas heated by the diffuse interstellar radiation field, with the remaining $\sim 50\%$ associated with bright, dusty star forming regions. We discuss differences between the F770W, F1000W, F1130W bands and the continuum dominated F2100W band and suggest next steps for using the mid-IR as an ISM tracer.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Kirsten L. Larson
Janice C. Lee
David A. Thilker
Bradley C. Whitmore
Sinan Deger
James Lilly
Rupali Chandar
Daniel A. Dale
Frank Bigiel
Kathryn Grasha
Brent Groves
Ralf S. Klessen
Kathryn Kreckel
J. M. Diederik Kruijssen
Adam K. Leroy
Hsi-An Pan
Erik Rosolowsky
Eva Schinnerer
Andreas Schruba
Elizabeth J. Watkins
Abstract： We develop a method to identify and determine the physical properties of stellar associations using Hubble Space Telescope (HST) NUV-U-B-V-I imaging of nearby galaxies from the PHANGS-HST survey. We apply a watershed algorithm to density maps constructed from point source catalogues Gaussian smoothed to multiple physical scales from 8 to 64 pc. We develop our method on two galaxies that span the distance range in the PHANGS-HST sample: NGC 3351 (10 Mpc), NGC 1566 (18 Mpc). We test our algorithm with different parameters such as the choice of detection band for the point source catalogue (NUV or V), source density image filtering methods, and absolute magnitude limits. We characterise the properties of the resulting multi-scale associations, including sizes, number of tracer stars, number of associations, photometry, as well as ages, masses, and reddening from Spectral Energy Distribution fitting. Our method successfully identifies structures that occupy loci in the UBVI colour-colour diagram consistent with previously published catalogues of clusters and associations. The median ages of the associations increases from log(age/yr) = 6.6 to log(age/yr) = 6.9 as the spatial scale increases from 8 pc to 64 pc for both galaxies. We find that the youngest stellar associations, with ages < 3 Myr, indeed closely trace H ii regions in H$\alpha$ imaging, and that older associations are increasingly anti-correlated with the H$\alpha$ emission. Owing to our new method, the PHANGS-HST multi-scale associations provide a far more complete census of recent star formation activity than found with previous cluster and compact association catalogues. The method presented here will be applied to the full sample of 38 PHANGS-HST galaxies.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Karin Sandstrom
Jérémy Chastenet
Jessica Sutter
Adam K. Leroy
Oleg V. Egorov
Thomas G. Williams
Alberto D. Bolatto
Médéric Boquien
Yixian Cao
Daniel A. Dale
Janice C. Lee
Erik Rosolowsky
Eva Schinnerer
Ashley. T. Barnes
Francesco Belfiore
F. Bigiel
Mélanie Chevance
Kathryn Grasha
Brent Groves
Hamid Hassani
Abstract： We present maps of the 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission feature in NGC 628, NGC 1365, and NGC 7496 as observed with the Near-Infrared Camera (NIRCam) imager on JWST from the PHANGS-JWST Cycle 1 Treasury project. We create maps that isolate the 3.3 micron PAH feature in the F335M filter (F335M$_{\rm PAH}$) 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 micron. We modify the empirical prescription from Lai et al. (2020) 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$_{\rm PAH}$ emission, we find that between 5-65% of the F335M intensity comes from the 3.3 micron 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 micron emission is well correlated with the 11.3 micron PAH feature traced with the MIRI F1130W filter, as is expected, since both features arise from C-H vibrational modes. The average F335M$_{\rm PAH}$/F1130W ratio agrees with the predictions of recent models by Draine et al. (2021) for PAHs with size and charge distributions shifted towards larger grains with normal or higher ionization.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jiayi Sun
Adam K. Leroy
Eve C. Ostriker
Sharon Meidt
Erik Rosolowsky
Eva Schinnerer
Christine D. Wilson
Dyas Utomo
Francesco Belfiore
Guillermo A. Blanc
Eric Emsellem
Christopher Faesi
Brent Groves
Annie Hughes
Eric W. Koch
Kathryn Kreckel
Daizhong Liu
Hsi-An Pan
Jerome Pety
Miguel Querejeta
Abstract： We measure empirical relationships between the local star formation rate (SFR) and properties of the star-forming molecular gas on 1.5 kpc scales across 80 nearby galaxies. These relationships, commonly referred to as "star formation laws," aim at predicting the local SFR surface density from various combinations of molecular gas surface density, galactic orbital time, molecular cloud free-fall time, and the interstellar medium dynamical equilibrium pressure. Leveraging a multiwavelength database built for the PHANGS survey, we measure these quantities consistently across all galaxies and quantify systematic uncertainties stemming from choices of SFR calibrations and the CO-to-H$_2$ conversion factors. The star formation laws we examine show 0.3-0.4 dex of intrinsic scatter, among which the molecular Kennicutt-Schmidt relation shows a $\sim$10% larger scatter than the other three. The slope of this relation ranges $\beta\approx0.9{-}1.2$, implying that the molecular gas depletion time remains roughly constant across the environments probed in our sample. The other relations have shallower slopes ($\beta\approx0.6{-}1.0$), suggesting that the star formation efficiency (SFE) per orbital time, the SFE per free-fall time, and the pressure-to-SFR surface density ratio (i.e., the feedback yield) may vary systematically with local molecular gas and SFR surface densities. Last but not least, the shapes of the star formation laws depend sensitively on methodological choices. Different choices of SFR calibrations can introduce systematic uncertainties of at least 10-15% in the star formation law slopes and 0.15-0.25 dex in their normalization, while the CO-to-H$_2$ conversion factors can additionally produce uncertainties of 20-25% for the slope and 0.10-0.20 dex for the normalization.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Ness Mayker Chen
Michael A. Tucker
Nils Hoyer
Saurabh W. Jha
Lindsey Kwok
Adam K. Leroy
Erik Rosolowsky
Chris Ashall
Gagandeep Anand
Frank Bigiel
Médéric Boquien
Chris Burns
Daniel Dale
James M. DerKacy
Oleg V. Egorov
L. Galbany
Kathryn Grasha
Hamid Hassani
Peter Hoeflich
Eric Hsiao
Abstract： We present new 0.3-21 micron photometry of SN 2021aefx in the spiral galaxy NGC 1566 at +357 days after B-band maximum, including the first detection of any SN Ia at >15 micron. These observations follow earlier JWST observations of SN 2021aefx at +255 days after the time of maximum brightness, allowing us to probe the temporal evolution of the emission properties. We measure the fraction of flux emerging at different wavelengths and its temporal evolution. Additionally, the integrated 0.3-14 micron decay rate of $\Delta m_{0.3-14} = 1.35 \pm 0.05$ mag/100 days is higher than the decline rate from the radioactive decay of $^{56}$Co of $\sim 1.2$mag/100 days. The most plausible explanation for this discrepancy is that flux is shifting to >14 micron, and future JWST observations of SNe Ia will be able to directly test this hypothesis. However, models predicting non-radiative energy loss cannot be excluded with the present data.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Sharon E. Meidt
Erik Rosolowsky
Jiayi Sun
Eric W. Koch
Ralf S. Klessen
Adam K. Leroy
Eva Schinnerer
Ashley. T. Barnes
Simon C. O. Glover
Janice C. Lee
Arjen van der Wel
Elizabeth J. Watkins
Thomas G. Williams
Frank Bigiel
Médéric Boquien
Guillermo A. Blanc
Yixian Cao
Mélanie Chevance
Daniel A. Dale
Oleg V. Egorov
Abstract： JWST/MIRI imaging of the nearby galaxies IC 5332, NGC 628, NGC 1365 and NGC 7496 from PHANGS reveals a richness of gas structures that in each case form a quasi-regular network of interconnected filaments, shells and voids. We examine whether this multi-scale network of structure is consistent with the fragmentation of the gas disk through gravitational instability. We use FilFinder to detect the web of filamentary features in each galaxy and determine their characteristic radial and azimuthal spacings. These spacings are then compared to estimates of the most Toomre-unstable length (a few kpc), the turbulent Jeans length (a few hundred pc) and the disk scale height (tens of pc) reconstructed using PHANGS-ALMA observations of the molecular gas as a dynamical tracer. Our analysis of the four galaxies targeted in this work indicates that Jeans-scale structure is pervasive. Future work will be essential for determining how the structure observed in gas disks impacts not only the rate and location of star formation but also how stellar feedback interacts positively or negatively with the surrounding multi-phase gas reservoir.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Bradley C. Whitmore
Rupali Chandar
M. Jimena Rodríguez
Janice C. Lee
Eric Emsellem
Matthew Floyd
Hwihyun Kim
J. M. Diederik Kruijssen
Angus Mok
Mattia C. Sormani
Médéric Bodquien
Daniel A. Dale
Christopher M. Faesi
Kiana F. Henny
Stephen Hannon
David A. Thilker
Richad L. White
Ashley T. Barnes
F. Bigiel
Mélanie Chevance
Abstract： A primary new capability of JWST is the ability to penetrate the dust in star forming galaxies to identify and study the properties of young star clusters that remain embedded in dust and gas. In this paper we combine new infrared images taken with JWST with our optical HST images of the star-bursting barred (Seyfert2) spiral galaxy NGC 1365. We find that this galaxy has the richest population of massive young clusters of any known galaxy within 30 Mpc, with $\sim$ 30 star clusters that are more massive than 10$^6$ Msolar and younger than 10 Myr. Sixteen of these clusters are newly discovered from our JWST observations. An examination of the optical images reveals that 4 of 30 ($\sim$13$\%$) are so deeply embedded that they cannot be seen in the I band (AV $\gt$ 10 mag), and that 11 of 30 ($\sim$37$\%$) are missing in the HST B band, so age and mass estimates from optical measurements alone are challenging. These numbers suggest that massive clusters in NGC 1365 remain obscured in the visible for $\sim$ 1.3 $\pm$ 0.7 Myr, and are either completely or partially obscured for $\sim$ 3.7 $\pm$ 1.1 Myr. We also use the JWST observations to gain new insights into the triggering of star cluster formation by the collision of gas and dust streamers with gas and dust in the bar. The JWST images reveal previously unknown structures (e.g., bridges and overshoot regions from stars that form in the bar) that help us better understand the orbital dynamics of barred galaxies and associated star-forming rings. Finally, we note that the excellent spatial resolution of the NIRCAM F200W filter provides a better way to separate barely resolved compact clusters from individual stars based on their sizes.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Ashley T. Barnes
Elizabeth J. Watkins
Sharon E. Meidt
Kathryn Kreckel
Mattia C. Sormani
Robin G. Tress
Simon C. O. Glover
Frank Bigiel
Rupali Chandar
Eric Emsellem
Janice C. Lee
Adam K. Leroy
Karin M. Sandstrom
Eva Schinnerer
Erik W. Rosolowsky
Francesco Belfiore
Guillermo Blanc
Mederic Boquien
Jakob S. den Brok
Yixian Cao
Abstract： We present a high-resolution view of bubbles within The Phantom Galaxy (NGC 628); a nearby (~10Mpc), star-forming (~2Msun/yr), face-on (i~9deg) grand-design spiral galaxy. With new data obtained as part of the 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 1kpc 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 Halpha observations from the Hubble Space Telescope (HST), we see that the ionized gas is brightest in the shells of both bubbles, and is coincident with the youngest (~1Myr) and most massive (~100,000Msun) stellar associations. We also find an older generation (~20Myr) of stellar associations is present within the bubble of The Phantom Void. From our kinematic analysis of the HI, H2 (CO) and HII gas across The Phantom Void, we infer a high expansion speed of around 15 to 50km/s. 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 SNe 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.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Adam K. Leroy
Alberto D. Bolatto
Karin Sandstrom
Erik Rosolowsky
Ashley. T. Barnes
F. Bigiel
Médéric Boquien
Jakob S. den Brok
Yixian Cao
Jérémy Chastenet
Mélanie Chevance
I-Da Chiang
Ryan Chown
Dario Colombo
Sara L. Ellison
Eric Emsellem
Kathryn Grasha
Jonathan D. Henshaw
Annie Hughes
Ralf S. Klessen
Abstract： We explore the relationship between mid-infrared (mid-IR) and CO rotational line emission from massive star-forming galaxies, which is one of the tightest scalings in the local universe. We assemble a large set of unresolved and moderately ($\sim 1$ kpc) spatially resolved measurements of CO (1-0) and CO (2-1) intensity, $I_{\rm CO}$, and mid-IR intensity, $I_{\rm MIR}$, at 8, 12, 22, and 24$\mu$m. The $I_{\rm CO}$ vs. $I_{\rm MIR}$ relationship is reasonably described by a power law with slopes $0.7{-}1.2$ and normalization $I_{\rm CO} \sim 1$ K km s$^{-1}$ at $I_{\rm MIR} \sim 1$ MJy sr$^{-1}$. Both the slopes and intercepts vary systematically with choice of line and band. The comparison between the relations measured for CO~(1-0) and CO (2-1) allow us to infer that $R_{21} \propto I_{\rm MIR}^{0.2}$, in good agreement with other work. The $8\mu$m and $12\mu$m bands, with strong PAH features, show steeper CO vs. mid-IR slopes than the $22\mu$m and $24\mu$m, consistent with PAH emission arising not just from CO-bright gas but also from atomic or CO-dark gas. The CO-to-mid-IR ratio correlates with global galaxy stellar mass ($M_\star$) and anti-correlates with SFR/$M_\star$. At $\sim 1$ kpc resolution, the first four PHANGS-JWST targets show CO to mid-IR relationships that are quantitatively similar to our larger literature sample, including showing the steep CO-to-mid-IR slopes for the JWST PAH-tracing bands, although we caution that these initial data have a small sample size and span a limited range of intensities.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Karin M. Sandstrom
Eric W. Koch
Adam K. Leroy
Erik Rosolowsky
Eric Emsellem
Rowan J. Smith
Oleg V. Egorov
Thomas G. Williams
Kirsten L. Larson
Janice C. Lee
Eva Schinnerer
David A. Thilker
Ashley. T. Barnes
Francesco Belfiore
F. Bigiel
Guillermo A. Blanc
Alberto D. Bolatto
Médéric Boquien
Yixian Cao
Jérémy Chastenet
Abstract： JWST observations of polycyclic aromatic hydrocarbon (PAH) emission provide some of the deepest and highest resolution views of the cold interstellar medium (ISM) in nearby galaxies. If PAHs are well mixed with the atomic and molecular gas and illuminated by the average diffuse interstellar radiation field, PAH emission may provide an approximately linear, high resolution, high sensitivity tracer of diffuse gas surface density. We present a pilot study that explores using PAH emission in this way based on MIRI observations of IC 5332, NGC 628, NGC 1365, and NGC 7496 from the PHANGS-JWST Treasury. Using scaling relationships calibrated in Leroy et al. (2022), scaled F1130W provides 10--40 pc resolution and 3$\sigma$ sensitivity of $\Sigma_{\rm gas} \sim 2$ M$_\odot$ pc$^{-2}$. We characterize the surface densities of structures seen at $< 7$ M$_\odot$ pc$^{-2}$ in our targets, where we expect the gas to be HI-dominated. We highlight the existence of filaments, inter-arm emission, and holes in the diffuse ISM at these low surface densities. Below $\sim 10$ M$_\odot$ pc$^{-2}$ for NGC 628, NGC 1365, and NGC 7496 the gas distribution shows a ``Swiss cheese''-like topology due to holes and bubbles pervading the relatively smooth distribution of diffuse ISM. Comparing to recent galaxy simulations, we observe similar topology for the low surface density gas, though with notable variations between simulations with different setups and resolution. Such a comparison of high resolution, low surface density gas with simulations is not possible with existing atomic and molecular gas maps, highlighting the unique power of JWST maps of PAH emission.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Daniel A. Dale
Médéric Boquien
Ashley T. Barnes
Francesco Belfiore
F. Bigiel
Yixian Cao
Rupali Chandar
Jérémy Chastenet
Mélanie Chevance
Sinan Deger
Oleg V. Egorov
Kathryn Grasha
Brent Groves
Hamid Hassani
Kiana F. Henny
Ralf S. Klessen
Kathryn Kreckel
J. M. Diederik Kruijssen
Kirsten L. Larson
Janice C. Lee
Abstract： We present a comparison of theoretical predictions of dust continuum and polycyclic aromatic hydrocarbon (PAH) emission with new JWST observations in three nearby galaxies: NGC 628, NGC 1365, and NGC 7496. Our analysis focuses on a total of 1063 compact stellar clusters and 2654 stellar associations previously characterized by HST in the three galaxies. We find that the distributions and trends in the observed PAH-focused infrared colors generally agree with theoretical expectations, and that the bulk of the observations is more aligned with models of larger, ionized PAHs. These JWST data usher in a new era of probing interstellar dust and studying how the intense radiation fields near stellar clusters and associations play a role in shaping the physical properties of PAHs.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jérémy Chastenet
Jessica Sutter
Karin Sandstrom
Francesco Belfiore
Oleg V. Egorov
Kirsten L. Larson
Adam K. Leroy
Daizhong Liu
Erik Rosolowsky
David A. Thilker
Elizabeth J. Watkins
Thomas G. Williams
Ashley T. Barnes
Frank Bigiel
Médéric Boquien
Mélanie Chevance
I-Da Chiang
Daniel A. Dale
J. M. Diederik Kruijssen
Eric Emsellem
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 ($7.7~\mu$m) and F1130W ($11.3~\mu$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 average $R{\rm_{PAH} = (F770W+F1130W)/F2100W}$ 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$\alpha$ 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$\alpha$ to trace the interstellar gas phase and find that the PAH fraction decreases above a value of I$_{H\alpha}/\Sigma_{H~I+H_2}$ $\sim~10^{37.5}$ erg s$^{-1}$ kpc$^{-2}$ (M$_\odot$ 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.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
David A. Thilker
Janice C. Lee
Sinan Deger
Ashley T. Barnes
Frank Bigiel
Médéric Boquien
Yixian Cao
Mélanie Chevance
Daniel A. Dale
Oleg V. Egorov
Simon C. O. Glover
Kathryn Grasha
Jonathan D. Henshaw
Ralf S. Klessen
Eric Koch
J. M. Diederik Kruijssen
Adam K. Leroy
Ryan A. Lessing
Sharon E. Meidt
Francesca Pinna
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 25-400 pc in NGC 628. MIRI images at 7.7, 10, 11.3 and 21$\mu$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 HII regions, young star clusters and associations within the DFN. We examine the dependence of these quantities with 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 co-spatial 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 HII regions and 60% of star clusters younger than 5 Myr are contained within the DFN. However, the DFN at this scale is anti-correlated with looser associations of stars younger than 5 Myr identified using PHANGS-HST near-UV imaging. We discuss the impact of these findings for studies of star formation and the ISM, and the broad range of new investigations enabled with multi-scale maps of the DFN.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Thomas G. Williams
Jiayi Sun
Ashley T. Barnes
Eva Schinnerer
Jonathan D. Henshaw
Sharon E. Meidt
Miguel Querejeta
Elizabeth J. Watkins
Frank Bigiel
Guillermo A. Blanc
Médéric Boquien
Yixian Cao
Mélanie Chevance
Oleg V. Egorov
Eric Emsellem
Simon C. O. Glover
Kathryn Grasha
Hamid Hassani
Sarah Jeffreson
María J. Jiménez-Donaire
Abstract： We combine JWST observations with ALMA CO and VLT-MUSE H$\alpha$ data to examine off-spiral arm star formation in the face-on, grand-design spiral galaxy NGC 628. We focus on the northern spiral arm, around a galactocentric radius of 3-4 kpc, and study two spurs. These form an interesting contrast, as one is CO-rich and one CO-poor, and they have a maximum azimuthal offset in MIRI 21$\mu$m and MUSE H$\alpha$ of around 40$^\circ$ (CO-rich) and 55$^\circ$ (CO-poor) from the spiral arm. The star formation rate is higher in the regions of the spurs near to spiral arms, but the star formation efficiency appears relatively constant. Given the spiral pattern speed and rotation curve of this galaxy and assuming material exiting the arms undergoes purely circular motion, these offsets would be reached in 100-150 Myr, significantly longer than the 21$\mu$m and H$\alpha$ star formation timescales (both <10 Myr). The invariance of the star formation efficiency in the spurs versus the spiral arms indicates massive star formation is not only triggered in spiral arms, and cannot simply occur in the arms and then drift away from the wave pattern. These early JWST results show that in-situ star formation likely occurs in the spurs, and that the observed young stars are not simply the `leftovers' of stellar birth in the spiral arms. The excellent physical resolution and sensitivity that JWST can attain in nearby galaxies will well resolve individual star-forming regions and help us to better understand the earliest phases of star formation.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Oleg V. Egorov
Kathryn Kreckel
Karin M. Sandstrom
Adam K. Leroy
Simon C. O. Glover
Brent Groves
J. M. Diederik Kruijssen
Ashley. T. Barnes
Francesco Belfiore
F. Bigiel
Guillermo A. Blanc
Médéric Boquien
Yixian Cao
Jérémy Chastenet
Mélanie Chevance
Enrico Congiu
Daniel A. Dale
Eric Emsellem
Kathryn Grasha
Ralf S. Klessen
Abstract： Polycyclic aromatic hydrocarbons (PAHs) play a critical role in the reprocessing of stellar radiation and in balancing the heating and cooling processes in the interstellar medium (ISM), but appear to be destroyed in HII 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 HII regions across four nearby star-forming galaxies (NGC 628, NGC 1365, NGC 7496, IC 5332). We find a strong anti-correlation between the PAH fraction and the ionization parameter (the ratio between the ionizing photon flux and the hydrogen density) of HII regions. This relation becomes steeper for more luminous HII regions. The metallicity of HII regions has only a minor impact on these results in our galaxy sample. We find that the PAH fraction decreases with the H$\alpha$ equivalent width - a proxy for the age of the HII 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.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jérémy Chastenet
Jessica Sutter
Karin Sandstrom
Francesco Belfiore
Oleg V. Egorov
Kirsten L. Larson
Adam K. Leroy
Daizhong Liu
Erik Rosolowsky
David A. Thilker
Elizabeth J. Watkins
Thomas G. Williams
Ashley T. Barnes
Frank Bigiel
Médéric Boquien
Mélanie Chevance
Daniel A. Dale
J. M. Diederik Kruijssen
Eric Emsellem
Kathryn Grasha
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 $\mu$m features, we infer changes to the average PAH size and ionization state across the different galaxy environments. High values of F335M$_{\rm PAH}$/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$\alpha$ intensity.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jiayi Sun
Adam K. Leroy
Erik Rosolowsky
Annie Hughes
Eva Schinnerer
Andreas Schruba
Eric W. Koch
Guillermo A. Blanc
I-Da Chiang
Brent Groves
Daizhong Liu
Sharon Meidt
Hsi-An Pan
Jerome Pety
Miguel Querejeta
Toshiki Saito
Karin Sandstrom
Amy Sardone
Antonio Usero
Dyas Utomo
Abstract： We present a rich, multiwavelength, multiscale database built around the PHANGS-ALMA CO$\,$(2-1) survey and ancillary data. We use this database to present the distributions of molecular cloud populations and sub-galactic environments in 80 PHANGS galaxies, to characterize the relationship between population-averaged cloud properties and host galaxy properties, and to assess key timescales relevant to molecular cloud evolution and star formation. We show that PHANGS probes a wide range of kpc-scale gas, stellar, and star formation rate (SFR) surface densities, as well as orbital velocities and shear. The population-averaged cloud properties in each aperture correlate strongly with both local environmental properties and host galaxy global properties. Leveraging a variable selection analysis, we find that the kpc-scale surface densities of molecular gas and SFR tend to possess the most predictive power for the population-averaged cloud properties. Once their variations are controlled for, galaxy global properties contain little additional information, which implies that the apparent galaxy-to-galaxy variations in cloud populations are likely mediated by kpc-scale environmental conditions. We further estimate a suite of important timescales from our multiwavelength measurements. The cloud-scale free-fall time and turbulence crossing time are ${\sim}5{-}20$ Myr, comparable to previous cloud lifetime estimates. The timescales for orbital motion, shearing, and cloud-cloud collisions are longer, ${\sim}100$ Myr. The molecular gas depletion time is $1{-}3$ Gyr and shows weak to no correlations with the other timescales in our data. We publish our measurements online and expect them to have broad utility to future studies of molecular clouds and star formation.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Hamid Hassani
Erik Rosolowsky
Adam K. Leroy
Mederic Boquien
Janice C. Lee
Ashley. T. Barnes
Francesco Belfiore
Frank Bigiel
Yixian Cao
Melanie Chevance
Daniel A. Dale
Oleg V. Egorov
Eric Emsellem
Christopher M. Faesi
Kathryn Grasha
Jaeyeon Kim
Ralf S. Klessen
Kathryn Kreckel
J. M. Diederik Kruijssen
Kirsten L. Larson
Abstract： We use PHANGS-JWST data to identify and classify 1271 compact 21 $\mu$m sources in four nearby galaxies using MIRI F2100W data. We identify sources using a dendrogram-based algorithm, and we measure the background-subtracted flux densities for JWST bands from 2 $\mu$m to 21 $\mu$m. Using the SED in JWST as well as HST bands, plus ALMA and MUSE/VLT observations, we classify the sources by eye. Then we use this classification to define regions in color-color space, and so establish a quantitative framework for classifying sources. We identify 1085 sources as belonging to the ISM of the target galaxies with the remainder being dusty stars or background galaxies. These 21 $\mu$m sources are strongly spatially associated with HII regions ($>92\%$ of sources), while 74$\%$ of sources are coincident with a stellar association defined in the HST data. Using SED fitting, we find that the stellar masses of the 21 $\mu$m sources span a range of 10$^{2}$ to 10$^{4}~M_\odot$ with mass-weighted ages down to 2 Myr. There is a tight correlation between attenuation-corrected H$\alpha$ and 21 $\mu$m luminosity for $L_{\nu,\mathrm{F2100W}}>10^{19}~\mathrm{W~Hz}^{-1}$. Young embedded source candidates selected at 21 $\mu$m are found below this threshold and have $M_\star < 10^{3}~M_\odot$.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Janice C. Lee
Karin M. Sandstrom
Adam K. Leroy
David A. Thilker
Eva Schinnerer
Erik Rosolowsky
Kirsten L. Larson
Oleg V. Egorov
Thomas G. Williams
Judy Schmidt
Eric Emsellem
Gagandeep S. Anand
Ashley T. Barnes
Francesco Belfiore
Ivana Beslic
Frank Bigiel
Guillermo A. Blanc
Alberto D. Bolatto
Mederic Boquien
Jakob den Brok
Abstract： The PHANGS collaboration has been building a reference dataset for the multi-scale, multi-phase study of star formation and the interstellar medium in nearby galaxies. With the successful launch and commissioning of JWST, we can now obtain high-resolution infrared imaging to probe the youngest stellar populations and dust emission on the scales of star clusters and molecular clouds ($\sim$5-50 pc). In Cycle 1, PHANGS is conducting an 8-band imaging survey from 2-21$\mu$m of 19 nearby spiral galaxies. CO(2-1) mapping, optical integral field spectroscopy, and UV-optical imaging for all 19 galaxies have been obtained through large programs with ALMA, VLT/MUSE, and Hubble. PHANGS-JWST enables a full inventory of star formation, accurate measurement of the mass and age of star clusters, identification of the youngest embedded stellar populations, and characterization of the physical state of small dust grains. When combined with Hubble catalogs of $\sim$10,000 star clusters, MUSE spectroscopic mapping of $\sim$20,000 HII regions, and $\sim$12,000 ALMA-identified molecular clouds, it becomes possible to measure the timescales and efficiencies of the earliest phases of star formation and feedback, build an empirical model of the dependence of small dust grain properties on local ISM conditions, and test our understanding of how dust-reprocessed starlight traces star formation activity, all across a diversity of galactic environments. Here we describe the PHANGS-JWST Treasury survey, present the remarkable imaging obtained in the first few months of science operations, and provide context for the initial results presented in the first series of PHANGS-JWST publications.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Daizhong Liu
Eva Schinnerer
Yixian Cao
Adam Leroy
Antonio Usero
Erik Rosolowsky
Eric Emsellem
J. M. Diederik Kruijssen
Mélanie Chevance
Simon C. O. Glover
Mattia C. Sormani
Alberto D. Bolatto
Jiayi Sun
Sophia K. Stuber
Yu-Hsuan Teng
Frank Bigiel
Ivana Bešlić
Kathryn Grasha
Jonathan D. Henshaw
Ashley. T. Barnes
Abstract： We compare embedded young massive star clusters (YMCs) to (sub-)millimeter line observations tracing the excitation and dissociation of molecular gas in the starburst ring of NGC 1365. This galaxy hosts one of the strongest nuclear starbursts and richest populations of YMCs within 20 Mpc. Here we combine near-/mid-IR PHANGS-JWST imaging with new ALMA multi-J CO (1-0, 2-1 and 4-3) and [CI](1-0) mapping, which we use to trace CO excitation via R42 = I_CO(4-3)/I_CO(2-1) and R21 = I_CO(2-1)/I_CO(1-0) and dissociation via RCICO = I_[CI](1-0)/I_CO(2-1) at 330 pc resolution. We find that the gas flowing into the starburst ring from northeast to southwest appears strongly affected by stellar feedback, showing decreased excitation (lower R42) and increased signatures of dissociation (higher RCICO) in the downstream regions. There, radiative transfer modeling suggests that the molecular gas density decreases and temperature and [CI/CO] abundance ratio increase. We compare R42 and RCICO with local conditions across the regions and find that both correlate with near-IR 2 um emission tracing the YMCs and with both PAH (11.3 um) and dust continuum (21 um) emission. In general, RCICO exhibits ~ 0.1 dex tighter correlations than R42, suggesting CI to be a more sensitive tracer of changing physical conditions in the NGC 1365 starburst than CO (4-3). Our results are consistent with a scenario where gas flows into the two arm regions along the bar, becomes condensed/shocked, forms YMCs, and then these YMCs heat and dissociate the gas.
Peer Review Status:Awaiting Review
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