The relations between dust properties and galaxy global / integrated quantities in the nearby Universe

TL;DR

The paper develops a grid-based, single-temperature modified blackbody method to derive dust temperature $T_d$ and emissivity index $\beta_d$ for 24 nearby KINGFISH/SINGS galaxies using independently derived dust masses, avoiding full SED fits. It confirms a persistent $T_d$-$\beta_d$ anti-correlation and explores how $T_d$ and $\beta_d$ relate to metallicity, dust surface density, and star-formation indicators, finding $T_d$ largely unconstrained by $\mathrm{SFR}$ measures and $\Sigma_d$ most strongly tied to $M_*$. The study also compares dust spatial extents with optical stellar discs, showing dust discs are typically slightly smaller but broadly scale with the stellar discs, and discusses systematic uncertainties and limitations of a single-temperature approach. The results provide scalable relations for interpreting dust evolution and ISM/ SF processes in low-to-mid redshift galaxies and offer a practical framework for extending to larger surveys.

Abstract

Results of a case study of a sample of low-redshift galaxies are presented, to determine dust temperatures and emissivity indices through a less time-consuming method, and to connect both global and integrated galaxy properties with those of dust, ISM and star-formation. Dust temperatures ($T_{d}$) are determined based on the corresponding galaxy dust masses, independently calculated in our previous work, through a self-consistent method, without the need to actually perform a complete spectral energy distribution (SED) fit of the cold dust emission fluxes. The range and average dust temperatures are found to be consistent within errors with values from other studies. Simultaneously, the dust emissivity indices ($β_{d}$) are determined, and their evolution with temperature quantified, with the $T_{d}$ anti-correlation still being present. It is investigated whether $β_{d}$ can be predicted from other relation or if it scales with other integrated dust / ISM or galaxy property, which could be used as a proxy. In this respect, new and established relations between $T_{d}$, $β_{d}$, the dust surface density and global / integrated galaxy and star-formation related quantities are presented and analysed. We find that SFR, sSFR or $Σ_{SFR}$ are inconclusive traces of the dust temperature. We also find that the extent of dust emission distribution is slightly lower on average, but comparable with the optical stellar continuum emission one. The results and conclusions can be relevant for larger scales studies of low to mid-redshift galaxies from the latest surveys.

Figures (5)

• Figure 1: The dust temperature ($T_{d}$) - dust emissivity index evolution ($\beta_{d}$). The observed $T_{d}$ are shown with black triangles, while the corrected ones are represented with red stars. The black (red) dotted curves are polynomial regression fits of second order to the observed (corrected) values. The error bars represent the standard deviations. The average standard deviation of $T_{d}$ is overplotted in the lower left corner.
• Figure 2: A comparison of the relations between the dust temperature ($T_{d}$) and some of the relevant dust/ISM and star-formation related quantities, when $\beta_{d}$ is either free or fixed to a value of $2.0$. Upper row: Dust temperature vs. metallicity (Z[O/H], taken from Mous10), dust surface density ($\Sigma_{d}$), sSFR and SFR, when $\beta_{d}$ is left free; Lower row: the same plots for a fixed $\beta_{d}=2$ value. The red dotted line is a linear regression fit of the corrected values, while the two red solid ones delimit the $\pm1\sigma$ uncertainty range for the best-fit relation. The error bars represent the standard deviations. The average standard deviations of the abscisa quantities are overplotted on the figures.
• Figure 3: The relation between the dust emissivity index, $\beta_{d}$, and other ISM/SFR quantities: metallicity (12+[O/H]), stellar mass ($M_{\odot}$), SFR and sSFR. The black dotted line is a linear regression fit of the observed values. The two red solid lines delimit the $\pm1\sigma$ uncertainty range for the best-fit relation of the corrected values. The rest of symbols, colors and lines have the same meaning as those in Fig. \ref{['fig:Tdust_compare_plots_beta_free_vs_fixed']}.
• Figure 4: The relation between the dust surface density, $\Sigma_{d}$ and other dust/ISM/SFR quantities: $\beta_{d}$, stellar mass ($M_{\odot}$), SFR and sSFR. The black dotted line is a linear regression fit of the observed values, while the two black solid lines delimit the $\pm1\sigma$ uncertainty range for the best-fit relation of the observed values. The rest of symbols, colors and lines have the same meaning as those in Fig. \ref{['fig:Tdust_compare_plots_beta_free_vs_fixed']}.
• Figure 5: Upper panel The ratio between the observed (black triangles) / intrinsic (red stars) scale-lengths of the dust discs and the ones of the stellar emission discs (seen in optical B band), as a function of the stellar mass. Lower panel The same scale-lengths, plotted agains each other. The black and red dotted line show a linear-regression best-fit of the observed and corrected values. The rest of symbols, colors and lines have the same meaning as those in Fig. \ref{['fig:Tdust_compare_plots_beta_free_vs_fixed']}.