The Herschel Virgo Cluster Survey - XIII. Dust in early-type galaxies
  Aims. We study the dust content of a large optical input sample of 910
early-type galaxies (ETG) in the Virgo cluster, extending also to the dwarf
ETG, and examine the results in relation with those on the other cold ISM
components. Methods. We searched for far-infrared emission in all galaxies of
the input sample using the 250 micron image of the Herschel Virgo Cluster
Survey (HeViCS). This image covers a large fraction of the cluster. For the
detected ETG we measured fluxes in 5 bands from 100 to 500 micron, and
estimated the dust mass and temperature with modified black-body fits. Results.
Dust is detected above the completeness limit of 25.4 mJy at 250 micron in 46
ETG, 43 of which are in the optically complete part of the input sample. In
addition dust is present at fainter levels in another 6 ETG. We detect dust in
the 4 ETG with synchrotron emission, including M 87. Dust appears to be much
more concentrated than stars and more luminous ETG have higher dust
temperatures. Dust detection rates down to the 25.4 mJy limit are 17% for
ellipticals, about 40% for lenticulars (S0 + S0a) and around 3% for dwarf ETG.
Dust mass does not correlate clearly with stellar mass and is often much more
than that expected for a passive galaxy in a closed-box model. The
dust-to-stars mass ratio anticorrelates with galaxy luminosity, and for some
dwarf ETG reaches values as high as for dusty late-type galaxies. In the Virgo
cluster slow rotators appear more likely to contain dust than fast ones.
Comparing the dust results with those on HI from ALFALFA, there are only 8 ETG
detected both in dust and in HI in the HeViCS area; 39 have dust but only an
upper limit on HI, and 8 have HI but only an upper limit on dust. The locations
of these galaxies in the cluster are different, with the dusty ETG concentrated
in the densest regions, while the HI rich ETG are at the periphery.
