Local Volume HI Survey: the far-infrared radio correlation

Kavli Affiliate: Luis Ho

| First 5 Authors: Li Shao, Baerbel Koribalski, Jing Wang, Luis Ho, Lister Staveley-Smith

| Summary:

In this paper we measure the far-infrared (FIR) and radio flux densities of a
sample of 82 local gas-rich galaxies, including 70 "dwarf" galaxies ($M_* <
10^9 M_odot$), from the Local Volume HI Survey (LVHIS), which is close to
volume limited. It is found that LVHIS galaxies hold a tight linear FIR-radio
correlation (FRC) over four orders of magnitude ($F_{1.4GHz} propto
F_{FIR}^{1.00pm0.08}$). However, for detected galaxies only, a trend of larger
FIR-to-radio ratio with decreasing flux density is observed. We estimate the
star formation rate by combining UV and mid-IR data using empirical
calibration. It is confirmed that both FIR and radio emission are strongly
connected with star formation but with significant non-linearity. Dwarf
galaxies are found radiation deficient in both bands, when normalized by star
formation rate. It urges a "conspiracy" to keep the FIR-to-radio ratio
generally constant for dwarf galaxies. By using partial correlation coefficient
in Pearson definition, we identify the key galaxy properties associated with
the FIR and radio deficiency. Some major factors, such as stellar mass surface
density, will cancel out when taking the ratio between FIR and radio fluxes.
The remaining factors, such as HI-to-stellar mass ratio and galaxy size, are
expected to cancel each other due to the distribution of galaxies in the
parameter space. Such cancellation is probably responsible for the "conspiracy"
to keep the FRC alive.

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