NASA Technical Reports Server (NTRS) 19930017636: High chemical abundances in stripped Virgo spiral galaxies

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by  NASA Technical Reports Server (NTRS)

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HIGH CHEMICAL ABUNDANCES IN STRIPPED VIRGO SPIRAL GALAXIES
E. D. Skillman (U. Minnesota)
R. C. Kennicutt (U. Arizona)
G. A. Shields (U. Texas)
Based on a comparison of the oxygen abundances in H II regions in field and
Virgo cluster late type spiral galaxies, Shields, Skillman, & Kennicutt (1991) sug-
gested that the highly stripped spiral galaxies in the Virgo cluster have systemati-
cally higher abundances than comparable field galaxies.
In April 1991 and May 1992 we used the blue channel spectrograph on the MMT
to obtain new observations of 30 H II regions in Virgo spiral galaxies. These spectra
cover the wavelength range from [O II] A3727 to [S II] A6731. We now have observed
at least 4 H II regions in 9 spiral galaxies in the Virgo cluster. Combining [O II]
and [O III] line strengths, we calculate the H II region oxygen abundances based on
the empirical calibration of Edmunds & Pagel (1984). Figure 1 shows a mosaic of
empirical oxygen abundances versus galactic radius (normalized to effective radius)'
for the 9 Virgo spirals. Figure 2 compares the (HI diameter/optical diameter) ratios
for the galaxies in Warmels (1986) field sample to those of our observed Virgo
spirals as a function of RC3 morphological T-type. These observations show: 1)
The stripped, low luminosity Virgo spirals (N4689, N4571) truly have abundances
characteristic of much more luminous field spirals; 2) Virgo spirals which show no
evidence of stripping (N4651, N4713) have abundances comparable to field galax-
ies; and 3) Evidence for transition galaxies (e.g., N4254, N4321), with marginally
stripped disks and marginal abundance enhancements.
The new observations presented here confirm the validity of the oxygen over-
abundances in the stripped Virgo spirals. Shields et al. (1991) discussed two different
mechanisms for producing the higher abundances in the disks of stripped galaxies
in Virgo. The first is the suppression of infall of near-primordial material, the
second is the suppression of radial inflow of metal-poor gas. Distinguishing between
the two cases will require more observations of the Virgo cluster spirals and a
better understanding of which parameters determine the variation of abundance
with radius in field spirals (cf., Garnett & Shields 1987).
References
Edmunds, M.G., & Pagel, B.E.J. 1984, MNRAS, 211, 507.
Garnett, D.R., & Shields, G.A. 1987, ApJ, 317, 82.
Shields, Skillman, & Kennicutt 1991, ApJ, 371, 82.
Warmels, R.H. 1986, Ph.D. thesis, Groningen University.
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Rgure 1: Radial Oxygen Abundance Gradients for 9 Virgo Spirals
1 1 1 1 | 1 1 T T | 1 1 1 1 | 1 1 1 1 | 1 1 1 1 I T I 1 ] 1 1 1 T'l'f I'l I [ 1 ri'T-["T T 1 1 .' ' ' ' i ' ' ' ' i ' • • • i ' • • • i ' ' • '.
1 N4254 _ L N4303 - '- N4321 J
9.5 0 9.5 9.5
g- • • * * •; £- 1 •§ • I '* *• •
§ Q *AA O • £
0, 9 0. 97 + ~ 0, 9 ~ -
•
CM CM '- * ^ - CM
as - 8.5 • *- 8.5 -
', , , , | , , , , | , , , , | , . . ,-
( S 1 1.5 2 25 ) .5 1 R/RE15 2 25 ) 5 1 1.5 2 2.
R/RE R/RE
i i i i | i . i i | . i i i | i i i i | i i i i i i i i | .. i i | i i i i | i i i i | i i i i
1 N4501 J L N4571 J : N4651 :
9.5 • • • 95 9.5 -
^^ .. • • %• .5 . 0
§ •- - ^Og, 9- . - Og) 9 -
• • - * -
CM CM CM
as - 85 - 8.5 * , -
', , , , i , , , , i , , , . i , , , , i , , , ," •,,,,!,,,,! , , , | , . , ,'
( S 1 1.5 2 25 .5 1 15 2 25 .5 1 1.5 2 2.
R/RE R/RE R/RE
1 1 1 1 1 . 1 1 1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 , 1 1 1 1 1 1 1 1 . 1 . 1 1 1 1 . . 1 1 1 1 1 1 1
N4654 : L N4689 - L N4713 -I
9.5 i 9.5 9.5_
? • A A
0 £• 5
O O 0
g, 9 • : g, 9 - ~ S '~ —
CM • • - OJ . OJ
as • j 63 _ _ 8.5 •• '
~, , , , 1 , , , , 1 , , , , 1 , , , , 1 , , , ," l l i i 1 l l l l 1 i i i i 1 i- 1 i i 1 i i i i-
0 £ 1 1.5 2 2£ 0 .5 1 1.5 2 2.5 0 .5 1 1.5 2 2.5
R/R. R/R, R'R
Figure 2: Virgo Galaxies vs. Warmels Field Sample
1 r 1 r i \ r
2.5
N4713
O
I 1.5 N4654
X, N4254
Q
• N4571
1 N4501-L
• N4689
Sa Sab Sb Sbc Sc Scd Sd Sdm Sm
j L I I I I l I I I I I I I 1 1 1 1
4 6 8 10
RC3 T-type
245