Evolved Supergiants in PHANGS I: Red Supergiants in 19 Galaxies between 5-20 Mpc with HST and JWST

TL;DR

The paper addresses the challenge of cataloging red supergiants in external galaxies beyond the Local Group by exploiting the resolving power of HST and JWST. It constructs a 97,057-star RSG catalog in 19 PHANGS galaxies (5–20 Mpc) using PSF photometry in F814W and F200W and isochrone-based CMD regions from PARSEC. The results show RSGs concentrate in active star-forming regions and exhibit strong correlations with local SFR surface densities, yielding a production rate of roughly one RSG per about $6\times10^{3}$ M$_{\odot}$ of stars formed over 6–30 Myr. This catalog provides a valuable resource for studying SN progenitors, young stellar populations, and feedback processes within the PHANGS framework, and sets the stage for future refinements in completeness, bolometric properties, and dust effects.

Abstract

Red supergiants (RSGs) are important for our understanding of supernova progenitors, stellar populations, stellar evolution, mass loss and dust production. Extragalactic surveys of RSGs have a long history in the Local Group, but few studies exist beyond that due to the limited resolution and sensitivity of ground-based and previous space-based infrared observatories. Here we demonstrate the combined power of HST and JWST to push systematic searches of RSGs out to $\sim$20 Mpc. We introduce a catalog of 97057 RSGs -- the largest single-survey release of RSGs -- with masses $\gtrsim$10 M$_{\odot}$ in 19 galaxies from the PHANGS HST+JWST Treasury program. We use HST F814W and JWST F200W photometry to select stars as RSGs based on predicted colors and magnitudes from PARSEC isochrones. The spatial distribution of our recovered RSGs follow the familiar pattern of mostly being concentrated in active star-forming regions such as spiral arms and central starburst rings. The RSG number density on kpc-scales is strongly correlated ($r_s$$\sim$0.82) with local star-formation rate density ($Σ_{SFR}$) traced by extinction-corrected far-ultraviolet (FUV) from GALEX+WISE, and weakly correlated ($r_s$$\sim$0.57) with the total stellar mass density ($Σ_*$), traced by near-infrared emission from WISE+Spitzer. The number of RSGs per mass of stellar populations with ages 6-30 Myr (the likely age range of RSGs $>$10 M$_{\odot}$) is $\sim$1 per 10$^{3.77\pm0.27}$ M$_{\odot}$, assuming constant star-formation rates from FUV+W4. Our sample will be a useful resource for tracking progenitors and feedback sites of future supernovae in PHANGS, age-dating stellar populations, and more.

Figures (7)

• Figure 1: The selection process of RSGs from theoretical CMDs based on PARSEC isochrones. Left+Middle: F814W$-$F200W CMDs predicted by PARSEC for two metallicities $[M/H]=0$ and $[M/H]=-0.5$. Colored tracks are for zero-age main-sequence ages $<40$ Myr (or initial mass $>8$ M$_{\odot}$), which are expected to evolve into RSGs ($\leq4000$ K). Gray tracks are for lower-mass ($<8$ M$_{\odot}$) stars that may produce luminous AGBs. RSGs are selected in the region defined by the red (bold) dashed polygon, and giants with temperatures $<$4000 K in the isochrones appear as larger circles. A thinner red dashed polygon captures younger RSGs ($>$14 M$_{\odot}$). The reddening vector for $A_V$=1 mag is shown with arrow, which is a typical value observed for our galaxies Right: Comparison of the selection box with an example F814W$-$F200W from IC5332. The protrusion of the RSG branch on top of the C-rich AGBs are clearly visible. The black contour represents 68% of the sample, and within this the data are plotted as 2D histograms. The black dashed line represents the 5$\sigma$ completeness cut in our DOLPHOT photometry.
• Figure 2: F814W$-$F200W CMDs of all 19 galaxies, sorted by distance. Grey points show stars with magnitudes above the 5$\sigma$DOLPHOT completeness limit (dashed black line) for F814W and F200W, as well as passing the crowding and sharpness cuts in Section \ref{['sec:dolphot']}. We also show the colored polygons from Figure \ref{['fig:rsgselection']}, showing the selection region for all RSGs in this paper (thick dashed) and younger RSGs (thin dashed).
• Figure 3: Zoom-in of a $\sim0.89\times0.47$ kpc$^2$ star-forming region in NGC 1566 at a distance of 17.7 Mpc showing the distribution of RSGs (white circles). Top and middle zoom-in panels show an rgb HST image with $r$: F814W, $g$: F555W and $b$: F438W filters, and the bottom zoom-in panel is a JWST NIRCam rgb image with $r$: F360M, $g$: F300M and $b$: F200W. The zoom-in region in the middle panel is shown in red in the top panel. Because RSGs typically peak around 1 $\mu$m , they appear as reddish point sources in the HST image (i.e. bright in F814W) and bluish in the NIRCam image (i.e. bright in F200W). Even at 17.7 Mpc, near the distance limit of our sample, these RSGs are clearly resolved in the HST and NIRCam images.
• Figure 4: Spatial distribution of all RSGs (light-red), with the young RSGs from Figure \ref{['fig:rsgselection']} highlighted in darker red, shown alongside RGB HST images, with B: F438W/F435W, G: F555W, and R: F814W. Yellow/black dashed regions denote the NIRCam footprint, while gray dashed denote the HST footprints.
• Figure 5: Same as Figure \ref{['fig:rsgspatial1']}, for the remaining galaxies in our sample.