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
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
Ness Mayker Chen
Adam K. Leroy
Laura A. Lopez
Samantha Benincasa
Mélanie Chevance
Simon C. O. Glover
Annie Hughes
Kathryn Kreckel
Sumit Sarbadhicary
Jiayi Sun
Todd A. Thompson
Dyas Utomo
Frank Bigiel
Guillermo A. Blanc
Daniel A. Dale
Kathryn Grasha
J. M. Diederik Kruijssen
Hsi-An Pan
Miguel Querejeta
Eva Schinnerer
Abstract： We measure the molecular gas environment near recent ($< 100$ yr old) supernovae (SNe) using $\sim1''$ or $\leq 150$pc resolution CO (2-1) maps from the PHANGS-ALMA survey of nearby star-forming galaxies. This is arguably the first such study to approach the scales of individual massive molecular clouds ($M_{\rm mol} \gtrsim 10^{5.3}$ M$_{\odot}$). Using the Open Supernova Catalog (OSC), we identify 63 SNe within the PHANGS-ALMA footprint. We detect CO (2-1) emission near $\sim60\%$ of the sample at 150pc resolution, compared to $\sim35\%$ of map pixels with CO (2-1) emission, and up to $\sim95\%$ of the SNe at 1kpc resolution compared to $\sim80\%$ of map pixels with CO (2-1) emission. We expect the $\sim60\%$ of SNe within the same 150pc beam as a GMC will likely interact with these clouds in the future, consistent with the observation of widespread SN-molecular gas interaction in the Milky Way, while the other $\sim40\%$ of SNe without strong CO (2-1) detections will deposit their energy in the diffuse interstellar medium (ISM), perhaps helping drive large-scale turbulence or galactic outflows. Broken down by type, we detect CO (2-1) emission at the sites of $\sim85\%$ of our 9 stripped-envelope SNe (SESNe), $\sim40\%$ of our 34 Type II SNe, and $\sim35\%$ of our 13 Type Ia SNe, indicating that SESNe are most closely associated with the brightest CO (2-1) emitting regions in our sample. Our results confirm that SN explosions are not restricted to only the densest gas, and instead exert feedback across a wide range of molecular gas densities.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Elizabeth J. Watkins
Ashley Barnes
Kiana F. Henny
Hwihyun Kim
Kathryn Kreckel
Sharon E. Meidt
Ralf S. Klessen
Simon C. O. Glover
Thomas G. Williams
B. W. Keller
Adam K. Leroy
Erik W. Rosolowsky
Mederic Boquien
Gagandeep S. Anand
Francesco Belfiore
Frank Bigiel
Guillermo Blanc
Yixian Cao
Rupali Chandar
Ness Mayker Chen
Abstract： The first JWST observations of nearby galaxies have unveiled a rich population of bubbles that trace the stellar feedback mechanisms responsible for their creation. Studying these bubbles therefore allows us to chart the interaction between stellar feedback and the interstellar medium, and the larger galactic flows needed to regulate star formation processes globally. We present the first catalog of bubbles in NGC628, visually identified using MIRI F770W PHANGS-JWST observations, and use them to statistically evaluate bubble characteristics. We classify 1694 structures as bubbles with radii between 6-552 pc. Of these, 31% contain at least one smaller bubble at their edge, indicating that previous generations of star formation have a local impact on where new stars form. On large scales, most bubbles lie near a spiral arm, and their radii increase downstream compared to upstream. Furthermore, bubbles are elongated in a similar direction to the spiral arm ridge-line. These azimuthal trends demonstrate that star formation is intimately connected to the spiral arm passage. Finally, the bubble size distribution follows a power-law of index $p=-2.2\pm0.1$, which is slightly shallower than the theoretical value by 1-3.5$\sigma$ that did not include bubble mergers. The fraction of bubbles identified within the shells of larger bubbles suggests that bubble merging is a common process. Our analysis therefore allows us to quantify the number of star-forming regions that are influenced by an earlier generation, and the role feedback processes have in setting the global star formation rate. With the full PHANGS-JWST sample, we can do this for more galaxies.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Enrico Congiu
Guillermo A. Blanc
Francesco Belfiore
Francesco Santoro
Fabian Scheuermann
Kathryn Kreckel
Eric Emsellem
Brent Groves
Hsi-An Pan
Frank Bigiel
Daniel A. Dale
Simon C. O. Glover
Kathryn Grasha
Oleg V. Egorov
Adam Leroy
Eva Schinnerer
Elizabeth J. Watkins
Thomas G. Williams
Abstract： In this work, we present a new catalogue of >40000 ionised nebulae distributed across the 19 galaxies observed by the PHANGS-MUSE survey. The nebulae have been classified using a new model-comparison-based algorithm that exploits the odds ratio principle to assign a probabilistic classification to each nebula in the sample. The resulting catalogue is the largest catalogue containing complete spectral and spatial information for a variety of ionised nebulae available so far in the literature. We developed this new algorithm to address some of the limitations of the traditional classification criteria, such as their binarity, the sharpness of the involved limits, and the limited amount of data they rely on for the classification. The analysis of the catalogue shows that the algorithm performs well when selecting H II regions. We can recover their luminosity function, and its properties are in line with what is available in the literature. We also identify a rather significant population of shock-ionised regions (mostly composed of supernova remnants), an order of magnitude larger than any other homogeneous catalogue of supernova remnants currently available in the literature. The number of supernova remnants we identify per galaxy is in line with results in our Galaxy and other very nearby sources. However, limitations in the source detection algorithm result in an incomplete sample of planetary nebulae, even though their classification seems robust. Finally, we demonstrate how applying a correction for the contribution of the diffuse ionised gas to the nebulae's spectra is essential to obtain a robust classification of the objects and how a correct measurement of the extinction using DIG-corrected line fluxes prompts the use of a higher theoretical Ha/Hb ratio (3.03) than what is commonly used when recovering the E(B-V) via the Balmer decrement technique in massive star-forming galaxies.
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
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
Eva Schinnerer
Eric Emsellem
Jonathan D. Henshaw
Daizhong Liu
Sharon E. Meidt
Miguel Querejeta
Florent Renaud
Mattia C. Sormani
Jiayi Sun
Oleg V. Egorov
Kirsten L. Larson
Adam K. Leroy
Erik Rosolowsky
Karin M. Sandstrom
T. G. Williams
Ashley T. Barnes
F. Bigiel
Melanie Chevance
Yixian Cao
Rupali Chandar
Abstract： Large-scale bars can fuel galaxy centers with molecular gas, often leading to
the development of dense ring-like structures where intense star formation
occurs, forming a very different environment compared to galactic disks. We
pair ~0.3" (30pc) resolution new JWST/MIRI imaging with archival ALMA CO(2-1)
mapping of the central ~5kpc of the nearby barred spiral galaxy NGC1365, 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 ~ 475pc)
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
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
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
Jaeyeon Kim
Mélanie Chevance
J. M. Diederik Kruijssen
Ashley. T. Barnes
Frank Bigiel
Guillermo A. Blanc
Médéric Boquien
Yixian Cao
Enrico Congiu
Daniel A. Dale
Oleg V. Egorov
Christopher M. Faesi
Simon C. O. Glover
Kathryn Grasha
Brent Groves
Hamid Hassani
Annie Hughes
Ralf S. Klessen
Kathryn Kreckel
Kirsten L. Larson
Abstract： The earliest stages of star formation, when young stars are still deeply embedded in their natal clouds, represent a critical phase in the matter cycle between gas clouds and young stellar regions. Until now, the high-resolution infrared observations required for characterizing this heavily obscured phase (during which massive stars have formed, but optical emission is not detected) could only be obtained for a handful of the most nearby galaxies. One of the main hurdles has been the limited angular resolution of the Spitzer Space Telescope. With the revolutionary capabilities of the JWST, it is now possible to investigate the matter cycle during the earliest phases of star formation as a function of the galactic environment. In this Letter, we demonstrate this by measuring the duration of the embedded phase of star formation and the implied time over which molecular clouds remain inert in the galaxy NGC628 at a distance of 9.8Mpc, demonstrating that the cosmic volume where this measurement can be made has increased by a factor of $>100$ compared to Spitzer. We show that young massive stars remain embedded for $5.1_{-1.4}^{+2.7}$Myr ($2.3_{-1.4}^{+2.7}$Myr of which being heavily obscured), representing $\sim20\%$ of the total cloud lifetime. These values are in broad agreement with previous measurements in five nearby ($D < 3.5$Mpc) galaxies and constitute a proof of concept for the systematic characterization of the early phase of star formation across the nearby galaxy population with the PHANGS-JWST survey.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Nils Hoyer
Francesca Pinna
Albrecht W. H. Kamlah
Francisco Nogueras-Lara
Anja Feldmeier-Krause
Nadine Neumayer
Mattia C. Sormani
Médéric Boquien
Eric Emsellem
Anil C. Seth
Ralf S. Klessen
Thomas G. Williams
Eva Schinnerer
Ashley T. Barnes
Adam K. Leroy
Silvia Bonoli
J. M. Diederik Kruijssen
Justus Neumann
Patricia Sánchez-Blázquez
Daniel A. Dale
Abstract： We combine archival HST and new JWST 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 x 400 pc cavity, lacking both dust and gas. We find roughly constant values for the effective radius (r_eff ~ 5 pc) and ellipticity ({\epsilon} ~ 0.05), while the S\'ersic index (n) and position angle (PA) drop from n ~ 3 to ~ 2 and PA ~ 130{\deg} to 90{\deg}, respectively. In the mid-infrared, r_eff ~ 12pc, {\epsilon} ~ 0.4, and n ~ 1-1.5, with the same PA ~ 90{\deg}. The NSC has a stellar mass of log10 (M_nsc / M_Sun) = 7.06 +- 0.31, as derived through B-V, confirmed when using multi-wavelength data, and in agreement with the literature value. Fitting the spectral energy distribution, excluding the mid-infrared data, yields a main stellar population's 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 Gyr. 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.
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
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
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
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
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
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
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
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