Study of Dust and Ionized gas in Early-type Galaxies
  We present results of optical broad-band and narrow-band Halpha observations
of a sample of forty nearby early-type galaxies. The majority of sample
galaxies are known to have dust in various forms viz. dust lanes, nuclear dust
and patchy/filamentary dust. A detailed study of dust was performed for 12
galaxies with prominent dust features. The extinction curves for these galaxies
run parallel to the Galactic extinction curve, implying that the properties of
dust in these galaxies are similar to those of the Milky-Way. The ratio of
total to selective extinction (Rv) varies between 2.1 and 3.8, with an average
of 2.9 +/- 0.2, fairly close to its canonical value of 3.1 for our Galaxy. The
average relative grain size <a>/a_Gal of dust particles in these galaxies turns
out to be 1.01 +/- 0.2, while dust mass estimated using optical extinction lies
in the range 10^2 to 10^4 M(sun) . The Halpha emission was detected in 23 out
of 29 galaxies imaged through narrow- band filters with the Halpha luminosities
in the range 10^38 - 10^41 erg s^-1. The mass of the ionized gas is in the
range 10^3-10^5 M(sun). The morphology and extent of ionized gas is found
similar to those of dust, indicating possible coexistence of dust and ionized
gas in these galaxies. The absence of any apparent correlation between blue
luminosity and normalized IRAS dust mass is suggestive of merger related origin
of dust and gas in these galaxies.
