Kavli Affiliate: Wendy L. Freedman
| First 5 Authors: Abigail J. Lee, Wendy L. Freedman, In Sung Jang, Barry F. Madore, Kayla A. Owens
| Summary:
The J-region Asymptotic Giant Branch (JAGB) method is a standard candle that
leverages the constant luminosities of color-selected, carbon-rich AGB stars,
measured in the near infrared at 1.2 microns. The Chicago-Carnegie Hubble
Program (CCHP) has obtained JWST imaging of the SN Ia host galaxies NGC 7250,
NGC 4536, and NGC 3972. With these observations, the JAGB method can be studied
for the first time using JWST. Lee et al. 2022 [arXiv:2205.11323] demonstrated
the JAGB magnitude is optimally measured in the outer disks of galaxies,
because in the inner regions the JAGB magnitude can vary significantly due to a
confluence of reddening, blending, and crowding effects. However, determining
where the ‘outer disk’ lies can be subjective. Therefore, we introduce a novel
method for systematically selecting the outer disk. In a given galaxy, the JAGB
magnitude is first separately measured in concentric regions, and the ‘outer
disk’ is then defined as the first radial bin where the JAGB magnitude
stabilizes to a few hundredths of a magnitude. After successfully employing
this method in our JWST galaxy sample, we find the JAGB stars are
well-segregated from other stellar populations in color-magnitude space, and
have observed dispersions about their individual F115W modes of
$sigma_{N7250}=0.32$ mag, $sigma_{N4536}=0.34$ mag, and $sigma_{N3972}=0.35$
mag. These measured dispersions are similar to the scatter measured for the
JAGB stars in the LMC using 2MASS data ($sigma=0.33$ mag, Weinberg & Nikolaev
2001 [arXiv:astro-ph/0003204 ). In conclusion, the JAGB stars as observed with
JWST clearly demonstrate their considerable power both as high-precision
extragalactic distance indicators and as SN Ia supernova calibrators.
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