Kavli Affiliate: Luis C. Ho
| First 5 Authors: Xuchen Lin, Jing Wang, Lister Staveley-Smith, Suoqing Ji, Dong Yang
| Summary:
With a new joint-deconvolution pipeline, we combine the single-dish and
interferometric atomic hydrogen (HI) data of M51 observed by the FAST (FEASTS
program) and VLA (THINGS). The product data cube has a typical line width of
$13,text{km},text{s}^{-1}$ and a $2sigma$ line-of-sight (LOS) sensitivity
of HI column density $N_text{HI}sim3.2times10^{18},text{cm}^{-2}$ at a
spatial resolution of ${sim}18”$ (${sim}0.7,text{kpc}$). Among the
HI-detected LOSs extending to ${sim}50,text{kpc}$, ${sim}89%$ consist of
diffuse HI only, which is missed by previous VLA observations. The distribution
of dense HI is reproduced by previous hydrodynamical simulations of this
system, but the diffuse component is not, likely due to unresolved physics
related to the interaction between the circumgalactic and interstellar media.
With simple models, we find that these low-$N_text{HI}$ structures could
survive the background ultraviolet photoionization, but are susceptible to the
thermal evaporation. We find a positive correlation between LOS velocity
dispersion ($sigma_v$) and $N_text{HI}$ with a logarithmic index of
${sim}0.5$. Based on existing turbulent mixing layer (TML) theories and
simulations, we propose a scenario of hot gas cooling and accreting onto the
disk through a TML, which could reproduce the observed power index of
${sim}0.5$. We estimate the related cooling and accretion rates to be roughly
$1/3$ to $2/3$ of the star-formation rate. A typical column density of diffuse
HI (${sim}10^{19},text{cm}^{-2}$) can be accreted within $300,text{Myr}$,
the interaction time scale previously estimated for the system. Such a gas
accretion channel has been overlooked before, and may be important for gas-rich
interacting systems and for high redshift galaxy evolution.
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