Cold dust but warm gas in the unusual elliptical galaxy NGC 4125
  Data from the Herschel Space Observatory have revealed an unusual elliptical
galaxy, NGC 4125, which has strong and extended submillimeter emission from
cold dust but only very strict upper limits to its CO and HI emission.
Depending on the dust emissivity, the total dust mass is 2-5x10^6 Msun. While
the neutral gas-to-dust mass ratio is extremely low (< 12-30), including the
ionized gas traced by [CII] emission raises this limit to < 39-100. The dust
emission follows a similar r^{1/4} profile to the stellar light and the dust to
stellar mass ratio is towards the high end of what is found in nearby
elliptical galaxies. We suggest that NGC 4125 is currently in an unusual phase
where evolved stars produced in a merger-triggered burst of star formation are
pumping large amounts of gas and dust into the interstellar medium. In this
scenario, the low neutral gas-to-dust mass ratio is explained by the gas being
heated to temperatures >= 10^4 K faster than the dust is evaporated. If
galaxies like NGC 4125, where the far-infrared emission does not trace neutral
gas in the usual manner, are common at higher redshift, this could have
significant implications for our understanding of high redshift galaxies and
galaxy evolution.
