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Up: Colour distributions in E-S0

Subsections

1 Introduction

1.1 Background of this contribution

The colour distributions in S0-galaxies have not been much studied, although they are expected to be more complex than happens for pure spheroidal objects. Indeed Sandage (1961) introduced the three subclasses S01, S02, and S03, to represent three degrees in the visibility of dust, from none seen to obvious. It may be also expected that the two main components of any S0, i.e. the bulge and the disk (and perhaps also the envelope), will present different stellar populations, assuming some analogy with galaxies of later types. Pursuing the analogy, we might predict bluer populations, but perhaps also more dust in the disk, leading to rather complex colour distributions. A study of NGC 3115 by Silva et al. (1989) points to a disk much bluer than the bulge. Bothun & Gregg (1990) studied a significant sample of S0's by B-H and H-K photometry, and found "evidence for star formation 5 gigayears ago" in a number of disks. Some papers dealing with both S0's and disk galaxies of later types are obviously relevant. Balcells & Peletier (1994) (BP94) studied the colour profiles in bulges. The same authors (Peletier & Balcells 1996), compared bulge and disk colours from UBRJK photometry for a large sample of S0-Sbc objects. They find some tendency for the disks to be bluer, but with a large scatter: this is not surprising in view of the mixed Hubble types in the sample, and of the necessarily coarse definition of bulge and disk colours respectively. A follow-up of this work is the survey by Peletier & Balcells (1997).

Some years ago a program was started to obtain some data on the colour distributions in S0's, using good resolution frames from the Pic du Midi, plus a few from the CFHT. This program was not favoured with good weather and usable data are available only for a dozen objects of high inclination to the line of sight. In some cases the high resolution frames could be supplemented with frames from the Observatoire de Haute-Provence, of much lesser resolution, but larger field and often better S/N. The OHP observations were previously used in morphological studies of E-S0 galaxies, including the present sample, by Michard & Marchal (1993) (or MM93) and (1994) (or MM94).

This paper presents the data from this small sample. Section 2 reviews the observations, Sect. 3 the data analysis: as in previous papers of this series, it has been tried to reduce the errors due to "differential seeing", that is the different PSF of the two frames needed for measuring a colour. Section 4 collects the data mostly in tabular form, with colour maps and graphs of radial colour profiles assembled in the Appendix. Section 5 gives some tentative conclusions.

1.2 Notations and abbreviations

It may be useful to collect here the notations and abbreviations currently used below.


 
Table 1: Literature data for sample galaxies. Types are from the RSA. The velocities $V_{\rm op}$ and galactic B absorption $A_{\rm g}$ are from the RC3. The total magnitudes $V_{\rm T}$, the radius log$r_{\rm e}$ in arcsec, the estimated luminosity $M_{\rm T}$ in B are from MM94. Env. gives our classification of the outer envelopes (the notations are explained above in I.2)
NGC Type $V_{\rm opt}$ $A_{\rm g}$ $V_{\rm T}$ log$r_{\rm e}$ $-M_{\rm T}$ Env.  
2549 S01(7) 1070 0.13 11.20 1.05 19.12 exD  
3098 S01(9) 1401 0.11 12.06 0.90 18.43 spH  
3115 S01(7) 670 0.10 9.00 1.61 19.91 spH  
3245 S01(5) 1348 0.05 10.90 1.32 19.05 thD  
4026 S01(9) 930 0.04 10.53 1.21 19.44 thD  
4036 S03(8) 1397 0.03 10.69 1.30 19.33 exD  
4111 S01(9) 815 0.00 10.63 1.02 19.01 thD  
4350 S01(8) 1234 0.03 11.00 1.16 19.11 spH  
5308 S01(8) 2041 0.01 11.47 1.10 18.96 thD  
5422 S03(8) 1782 0.03 11.92 1.12 19.05 thD  
7332 S02(8) 1202 0.12 11.00 1.13 18.62 thD  
7457 S01(5) 824 0.22 11.14 1.52 18.86 exD  



 
Table 2: First list of frames used in this work. OBS = Telescope, coded as CFH, TBL for the 2 m Bernard Lyot telescope at the Pic du Midi, OHP for the 120 cm telescope at Observatoire de Haute-Provence. F = filter. Exposure times are in seconds. For the CFHT, dates are for the begining of the night in HST; for the TBL or OHP they are for the begining of the night in UT. W0 = FWHM in arcsec of the original PSF. $W_{\rm i}$ = same for the "improved" PSF (see Sect. 3). When the file code contains an m, it was obtained by merging two frames
NGC OBS F File Date Exp. W0 $W_{\rm i}$
2549 CFH B h042 04/04/92 900 0.59 -
id id R h042 id 60 0.62 -
id OHP B 2b33 18/01/91 1080 2.66 1.98
id id V 2b30 id 180 2.26 2.00
id id R 2b31 id 120 2.10 1.94
id id I 2b32 id 120 2.39 1.82
id id U 6a17 13/01/94 3000 2.92 2.00
id id V 6a16 id 150 2.52 1.85
3098 CFH B h032 03/04/92 900 0.54 -
id id R h033 id 60 0.61 -

id

 OHP B 2b48 18/01/91 1200 2.96 2.60
id id V 2b45 id 360 2.54 -
id id R 2b46 id 300 2.91 2.60
id id I 2b47 id 300 2.88 2.47
id id U 6a61 14/01/94 3600 4.93 3.75
id id U 6a62 id 3600 4.90 3.75
id id V 6a60 id 120 4.29 3.75
3115 CFH B h06m 06/12/89 90 0.73 -
id id R h064 id 60 0.55 -
id OHP U 3c33 18/03/91 2700 3.85 3.00
id id B 3c34 id 600 3.06 2.75
id id V 3b28 16/03/91 180 3.00 2.51
id id R 3c32 18/03/91 180 2.70 -
id id I 3c35 id 300 2.50 -

3245

 CFH B h042 04/04/92 900 0.67 -
id id R h041 id 60 0.53 -
id OHP U 2c57 20/01/91 4200 3.25 -
id id B 2c54 id 1000 2.90 2.18
id id V 2c53 id 120 2.06 1.95
id id R 2c55 id 120 2.49 2.07
id id I 2c56 id 150 2.28 2.12
id id U 6b20 15/01/94 3600 3.68 2.94

             



 
Table 3: Second list of frames used in this work. See previous Table for explanations
NGC OBS F File Date Exp. W0 $W_{\rm i}$  
4026 TBL B t116 07/03/94 1453 1.15 0.75  
id id V t113 id 332 1.06 0.85  
id id R t114 id 360 0.91 0.76  
id id I t115 id 360 1.27 1.10  
id OHP B 6b56 17/01/94 480 3.36 2.21  
id id R 6b57 id 60 2.64 2.20  
id id I 6b58 id 60 2.87 2.15  
id id V 6c29 18/01/94 120 2.20 1.99  
id id U 6c30 id 3600 2.86 2.11  
4036 TBL B t120 07/03/94 1500 1.35 0.95  
id id V t117 id 360 0.99 -  
id id R t118 id 360 1.05 -  
id id I t119 id 360 1.35 -  
id OHP U 6c32 18/01/94 3000 2.86 2.35  
id id B 1c14 13/12/90 780 2.58 2.03  
id id V 2a59 18/01/91 180 2.35 2.04  
id id V 6c31 18/01/94 120 2.08 -  
id id R 1c12 13/12/90 180 2.66 1.93  
id id I 1c13 id 180 2.39 2.18  
4111 TBL B t311 10/03/94 1500 1.22 0.94  
id id V t308 id 342 1.18 0.94  
id id R t309 id 410 1.13 0.96  
id OHP U 6c34 18/01/94 3600 2.81 2.01  
id id B 2b53 18/01/91 1080 2.50 1.91  
id id B 2b54 id 360 2.54 1.92  
id id V 2b52 id 180 2.07 1.95  
id id V 6c33 18/01/94 180 2.07 1.95  
id id R 2b56 id 180 2.60 1.92  
id id I 2b57 id 180 2.42 1.99  
4350 TBL B t316 10/03/94 1500 0.98 -  
id id V t313 id 360 1.29 -  
id id R t314 id 360 1.30 -  
id id I t315 id 360 1.96 -  
id OHP U 3a3s 15/3/91 4800 2.85 2.30  
id id B 2b65 19/1/91 1200 2.63 1.88  
id id V 2b64 id 180 2.34 1.87  
id id V 3a32 15/3/91 180 2.27 -  
id id R 2b66 19/1/91 180 2.54 1.87  



 
Table 4: Third list of frames used in this work. See previous Table for explanations
NGC OBS F File Date Exp. W0 $W_{\rm i}$  
5308 TBL B t124 07/03/94 1500 1.07 -  
id id V t121 id 360 0.94 -  
id id R t122 id 360 1.00 -  
id id I t123 id 360 1.45 -  
id OHP B 3a39 15/03/91 900 1.96 1.84  
id id V 3a37 id 120 2.06 -  
id id V 3a40 id 300 2.05 -  
id id R 3a41 id 300 2.10 1.87  
id id I 3a42 id 300 1.68 -  
5422 TBL V t125 07/03/94 360 0.85 -  
id id R t126 id 360 0.81 -  
id id I t127 id 360 1.32 -  
id OHP B 3c52 18/03/91 720 3.11 2.08  
id id V 3c53 id 300 3.02 1.94  
id id R 3c54 id 300 2.89 1.95  
id id I 3c55 id 300 2.62 2.01  
7332 TBL B td74 16/08/93 1200 1.65 -  
id id R td72 id 600 2.41 1.60  
id OHP B 1c31 13/12/90 720 3.02 2.15  
id id V 1c30 id 240 3.03 2.16  
7457 CFH B h04 22/10/90 240 0.77 -  
id id R h02 id 60 0.56 -  
id OHP B 1a3 10/12/90 900 3.23 -  
id id V 1a4 id 450 3.01 -  


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