Radial distribution of gas and dust in the two spiral galaxies M99 and M100

TL;DR

This study maps the distribution of gas and dust in the spiral galaxies M99 and M100 using Herschel-SPIRE data combined with archival observations, revealing dust extent, temperature gradients, and gas-to-dust ratio variations.

Contribution

First detailed measurement of cool dust distribution in M99 and M100 beyond optical radii using Herschel-SPIRE data.

Findings

Dust extends to at least the optical radius of the galaxies.

Radial decrease in dust temperature indicated by color indices.

Gas-to-dust ratio increases with radius in outer regions.

Abstract

By combining Herschel-SPIRE data with archival Spitzer, HI, and CO maps, we investigate the spatial distribution of gas and dust in the two famous grand-design spirals M99 and M100 in the Virgo cluster. Thanks to the unique resolution and sensitivity of the Herschel-SPIRE photometer, we are for the first time able to measure the distribution and extent of cool, submillimetre (submm)-emitting dust inside and beyond the optical radius. We compare this with the radial variation in both the gas mass and the metallicity. Although we adopt a model-independent, phenomenological approach, our analysis provides important insights. We find the dust extending to at least the optical radius of the galaxy and showing breaks in its radial profiles at similar positions as the stellar distribution. The colour indices f350/f500 and f250/f350 decrease radially consistent with the temperature decreasing with radius. We also find evidence of an increasing gas to dust ratio with radius in the outer regions of both galaxies.