Kavli Affiliate: Michael McDonald
| First 5 Authors: Michael Reefe, Michael McDonald, Marios Chatzikos, Jerome Seebeck, Richard Mushotzky
| Summary:
We present integral field unit observations of the Phoenix Cluster with the
JWST Mid-infrared Instrument’s Medium Resolution Spectrometer (MIRI/MRS). We
focus this study on the molecular gas, dust, and star formation in the
brightest cluster galaxy (BCG). We use precise spectral modeling to produce
maps of the silicate dust, molecular gas, and polycyclic aromatic hydrocarbons
(PAHs) in the inner $sim$50 kpc of the cluster. We have developed a novel
method for measuring the optical depth from silicates by comparing the observed
H$_2$ line ratios to those predicted by excitation models. We provide updated
measurements of the total molecular gas mass of $2.2^{+0.4}_{-0.1} times
10^{10}$ ${rm M}_odot$, which agrees with CO-based estimates, providing an
estimate of the CO-to-H$_2$ conversion factor of $alpha_{rm CO} = 0.9 pm
0.2,{rm M}_{odot},{rm pc}^{-2},({rm K},{rm km},{rm s}^{-1})^{-1}$;
an updated stellar mass of $M_* = 2.6 pm 0.5 times 10^{10}$ ${rm M}_odot$;
and star formation rates averaged over 10 and 100 Myr of $langle{rm
SFR}rangle_{rm 10} = 1340 pm 100$ ${rm M}_odot,{rm yr}^{-1}$ and
$langle{rm SFR}rangle_{rm 100} = 740 pm 80$ ${rm M}_odot,{rm
yr}^{-1}$, respectively. The H$_2$ emission seems to be powered predominantly
by star formation within the central $sim 20$ kpc, with no need for an extra
particle heating component as is seen in other BCGs. Additionally, we find
nearly an order of magnitude drop in the star formation rates estimated by PAH
fluxes in cool core BCGs compared to field galaxies, suggesting that hot
particles from the intracluster medium are destroying PAH grains even in the
centralmost 10s of kpc.
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