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Dust lane galaxies

 

We present in this section images of the dust lane galaxies in the radio sample along with various parameters related to the dust lanes. The parameters we provide include the angle of (mis)alignment between the dust lane and the major axis of the galaxy and between the dust lane and the radio axis. The latter is sometimes ambiguous owing to the poor quality of the radio maps.

We estimate the color excess in the dust lane by comparing the color in it with that of the surroundings. For this purpose we used a square aperture with side tex2html_wrap_inline5989 (3 pixels) on the tex2html_wrap_inline3807 images separately to extract magnitudes along the lane and in a neighboring region free of dust. The mean of the color excesses, E(B-R), obtained in this manner is then used for further calculations. We use the standard relation from Savage and Mathis (1979) to calculate the optical depths in tex2html_wrap_inline3807 :

eqnarray2853

Here, tex2html_wrap_inline3831 denotes wavelength and tex2html_wrap_inline5999 and tex2html_wrap_inline6001 respectively denote the extinction and optical depth at tex2html_wrap_inline3831 . We have assumed here that the dust lane obscures all stars.

Following Burstein and Heiles (1978), the column density of neutral hydrogen and the total neutral hydrogen content in the dust disk can be obtained from

eqnarray2855

where, D is the distance to the galaxy. We assume that the dust-to-gas ratio in these galaxies is similar to the ratio in our Galaxy, tex2html_wrap_inline6007 , to obtain the dust mass. This is a lower limit, since not all stars are actually obscured and the actual amount is at least 1/f larger where f;SPMlt;1 is the fraction of stars obscured.

We describe below dust related features found in the dust lane galaxies.

0354-263

This is one of the two galaxies in the radio sample for which we do not have an accurate redshift. The redshift is estimated to be 0.3 (McCarthy, private communication). The radio source is of the FR II type and the host galaxy is well fit by de Vaucouleurs' law ( tex2html_wrap_inline6013 with a disk having tex2html_wrap_inline6015 ). The dust lane extent is tex2html_wrap_inline6017 with tex2html_wrap_inline6019 and tex2html_wrap_inline6021 . The dust lane makes an angle of tex2html_wrap_inline6023 with the major axis of the galaxy and tex2html_wrap_inline6023 with the radio axis as well. There is a small galaxy to the south-east (see Figure gif) with which 0354-263 could be associated. A possible tidal feature is seen. Owing to the uncertainty in redshift, this object has been excluded from subsequent calculations in this chapter.

0420-263

This galaxy is well fit by de Vaucouleurs' law in the R filter but provides a marginal fit in the B filter ( tex2html_wrap_inline6031 ). The size of the dust lane is tex2html_wrap_inline6033 with tex2html_wrap_inline6035 and tex2html_wrap_inline6037 . The dust lane makes an angle of tex2html_wrap_inline6039 with the major axis of the galaxy. We do not have a radio map for this object.

1254-268

This galaxy too provides a good de Vaucouleurs' law fit in the R filter but a poor fit in B filter ( tex2html_wrap_inline6045 is large). The dust lane extent is tex2html_wrap_inline6047 and is rather diffuse. It has tex2html_wrap_inline6049 and tex2html_wrap_inline6051 . In this galaxy the radio axis is approximately along the major axis of the galaxy and the dust lane makes an angle of tex2html_wrap_inline6053 with both.

1257-253

This galaxy is fit well by de Vaucouleurs' law in the B filter but not in the R filter. The radio source has FR I structure. The dust lane extent is tex2html_wrap_inline6059 with a tex2html_wrap_inline6049 and tex2html_wrap_inline6063 . In the case of this galaxy the major axis is approximately perpendicular to the radio axis. The dust lane makes an angle of tex2html_wrap_inline6053 with the radio axis and tex2html_wrap_inline6067 with the major axis of the galaxy.

1323-271

This is an FR II radio source, well fit by de Vaucouleurs' law in tex2html_wrap_inline3807 filters. There is a companion galaxy, which was masked during the fitting. Lack of distortion in the outer isophotes of both galaxies suggests that it is only a chance superposition rather than an interacting pair. The dust lane extent is tex2html_wrap_inline6071 with a tex2html_wrap_inline6049 and tex2html_wrap_inline6075 . In this case the dust lane in the galaxy is approximately along the galaxy major axis while the radio axis makes an angle of tex2html_wrap_inline6053 with both.

1344-241

This is most likely an S0 galaxy, well fit by de Vaucouleurs' law in B but not in R. It has a large dust lane ( tex2html_wrap_inline6071 ) with tex2html_wrap_inline6085 and tex2html_wrap_inline6087 . The dust lane is curved and along the major axis of the galaxy. The radio structure is not very well determined.


[Properties of the radio galaxies with dust lanes] Properties of the dust lane radio galaxies from our sample. The dust mass is calculated as described in Section gif. The dust lanes are, in general, not perpendicular to the radio axis.  
Object z size E(B-R) tex2html_wrap_inline6091 tex2html_wrap_inline6093 tex2html_wrap_inline4521 tex2html_wrap_inline6097 tex2html_wrap_inline6099
tex2html_wrap_inline4243 magnitude tex2html_wrap_inline6103 max tex2html_wrap_inline6105 tex2html_wrap_inline6105
0354-263 0.30+ tex2html_wrap_inline6109 0.20 0.42 tex2html_wrap_inline6111 -0.010 45 45
0420-263 0.130 tex2html_wrap_inline6113 0.15 0.32 tex2html_wrap_inline6115 -0.010 NA 10
1254-268 0.135 tex2html_wrap_inline6117 0.10 0.21 tex2html_wrap_inline6115 -0.003 30 30
1257-253 0.045 tex2html_wrap_inline6121 0.10 0.21 tex2html_wrap_inline6123 -0.005 30 60
1323-271 0.044 tex2html_wrap_inline6125 0.10 0.21 tex2html_wrap_inline6123 -0.003 30 00
1344-241 0.019 tex2html_wrap_inline6125 0.07 0.21 tex2html_wrap_inline6131 -0.005 00 00


next up previous contents
Next: Discussion and conclusions Up: Dusty galaxies Previous: Detection techniques