A survey of the ISM in early-type galaxies. I. The ionized gas

Abstract

Abstract. -We present results of a CCD optical imaging survey of the ionized gas in 73 luminous elliptical and lenticular galaxies, selected from the RC3 catalog to represent a broad variety of X-ray, radio, infrared and kinematical properties. For each galaxy we have used broad-band R images and narrow-band images centered at the Hα and [NII] emission lines to derive the luminosity and distribution of the ionized gas. We found that a large fraction of E (72%) and SO (85%) galaxies in our sample contain ionized gas. The gas morphology appears to be rather smooth for most galaxies; however ~ 12% of the sample galaxies show a very extended filamentary structure. According to the morphology and size of the gas distribution, the galaxies have been classified into three broad groups, named small disk (SD), regular extended (RE) and filamentary structure (F). The mean diameter of the emitting region ranges between 1 and 10 kpc; the derived mass of the ionized gas ranges between 103 and 105 solar masses. A sig nificant correlation between Hα +[NII] and X-ray luminosities is found for those galaxies (27% of the sample) for which we have detected ionized gas and are also listed as X-ray sources. However, there are relatively strong X-ray emitting galaxies for which we have not detected Ha+[NII] emission and objects which show emission-lines but are not listed either in the EINSTEIN or in the ROSAT databases. The distribution of datapoint and upper limits in this diagram suggests that galaxies with warm gas are also X-ray emitters, while there are X-ray emitters without measur able Hα+[NII] emission. Similar characteristics are present in the correlation between the infrared luminosity in the 12 p m band and Lhα+ [nii]; correlations with other infrared wavelengths are weaker. A strong correlation was also found between the Ha+[NIIj luminosity and the luminosity in the B band inside the region occupied by the lineemitting gas. We use these correlations to discuss the possible mechanisms responsible for the gas ionization and excitation, analyzing in particular the role of the post-AGB stars and the thermal conduction from the X-ray halo in providing the necessary source of ionization.

Leo II Group: decoupled cores of NGC 3607 and NGC3608

“…1f of Shields (1991) -it is P A ≈ 325 • , very close to our measurements of the [NII] emission-line brightness distribution elongation at R > 3 ′′ . The gray-scaled emission brightness map provided by Macchetto et al (1996)) confirms also the turn of the innermost emission isophotes toward larger P As. The concordance of the photometric major axis provided by the HST data and the kinematical major axis of the ionized gas near P A ≈ 325 • −330 • at R ≈ 1 ′′ −2 ′′ implies axisymmetry.…”

“…An X-ray atlas of Mulchaey et al (2002) demonstrates two maxima of the hot gas concentration -one at NGC 3607 and another at NGC 3608 -which fact forces authors to suggest a recent assembly of the Leo II group. Also NGC 3607, though of early type, is known to have a rather extended ionized-gas disk (Shields 1991;Macchetto et al 1996) with a radius of ∼ 15 ′′ (∼ 1.5 kpc) containing a broad dust ring between R = 8. ′′ 4 and R = 13.…”

HST/ACS observations of shell galaxies: inner shells, shell colours and dust

“…Second, we consider a possible bias due to the presence of ionized gas. It is well known that dust is almost always accompanied with ionized gas in early type galaxies (Macchetto et al 1996;Sarzi et al 2006). Due to selection effects in the detection of visible dust, the converse is not true, although the probability to detect dust in early type galaxies with ionized gas is still quite high (Tran et al 2001).…”

Nearby early-type galaxies with ionized gas

“…The derived masses of the warm ISM range from ∼10 3 to ∼10 6 M (Phillips et al 1986;Trinchieri & di Serego Alighieri 1991;Macchetto et al 1996;Goudfrooij et al 1994aGoudfrooij et al , 1994bGoudfrooij et al , 1994cGoudfrooij & de Jong 1995), orders of magnitude below the Xray emitting hot ISM and the stellar mass. Ionized gas is detected in 40-80% of early-type galaxies from their optical emission lines (Caldwell 1984;Phillips et al 1986;Macchetto et al 1996;Sarzi et al 2006Sarzi et al , 2009Yan et al 2006;Serra et al 2008). A&A 519, A40 (2010) The ionized gas is also usually morphologically associated with dust (Kim 1989;Goudfrooij et al 1994c).…”