Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.sao.ru/precise/Laboratory/Publications/2000/UM-reobs/node3.html
Дата изменения: Mon Feb 7 17:12:03 2000
Дата индексирования: Sat Sep 11 20:53:25 2010
Кодировка:
Поисковые слова: п п п п п п п п п п п п п п п п

Results and conclusions

The results of chemical abundance determination for the studied galaxies are presented in Table 2. The comparison of the respective data for UM 133 and UM 382 with the abundance ratios from Izotov & Thuan ([1999]) shows that they well agree with the derived average values for the sample of low metallicity BCGs.

UM 133 The galaxy is elongated and resembles on morphology a comet-like object. It looks like an edge-on disk, bent on NE edge. Our long-slit spectrum in the H$\alpha$-region with the dispersion of 1.2 Å/pixel allows to derive the radial velocity curve along the ``disk'' (see Fig. 1a). A velocity gradient is well seen over the whole body and there is no sign of a flattening on both NE and SW edges. The full range of the velocity curve is about 100 km s^-1. This is slightly lower than W_0.2=122$\pm$11 km s^-1 - the full width for the 21 cm line of the integrated H I emission at the level 0.2 of peak (Thuan et al. [1999]).

  

Table 2: Abundances in studied galaxies

Value	UM 133	UM 382	UM 283
$T_{\rm e}$(OIII)(K)	16,125$\pm$744	16,292$\pm$1122	16,100$^{\bf a}$
$T_{\rm e}$(OII)(K)	14,270$\pm$627	14,343$\pm$940	14,070
$N_{\rm e}$(SII)(cm-3)	<10	<10	100$^{\bf a}$
O+/H+($\times$105)	1.101$\pm$0.134	0.634$\pm$0.122	2.99
O++/H+($\times$105)	3.378$\pm$0.390	5.178$\pm$0.888	6.09
O/H($\times$105)	4.479$\pm$0.412	5.811$\pm$0.896	9.08
12+log(O/H)	7.65$\pm$0.04	7.76$\pm$0.07	7.95
log(N/O)	-1.63$\pm$0.10	--	--
log(Ne/O)	-0.75$\pm$0.08	-0.74$\pm$0.13	--
log(S/O)	-1.49$\pm$0.05	--	--
$^{\bf a}$ data from Gallego et al. ([1997]).

With these data in hands it is difficult to go further into global kinematics of UM 133. Apparent rather strong deviations from a regular rotation curve, amounting up to 15-20 km s^-1 (seemingly due to outflows in the regions of current and recent intensive SF) prevent us to derive the form of the galaxy rotation curve. From the B-band image of UM 133 (Fig 1c) it is reasonable to suggest that its dynamical centre is situated near the second, less luminous, quasi-central H II region, roughly corresponding to the position along the slit at R =-18. Respective systemic radial velocity of 1630$\pm$5 km s^-1 is well consistent with that derived from the integrated H I profile (Thuan et al. [1999]).

The continuous H$\alpha$-emission and a smooth velocity distribution along the galaxy body favour its interpretation as a single object in opposite to the NED data, where UM 133 is shown as two galaxies with the difference of radial velocities of $\approx$500 km s^-1.

We notice the detection of characteristic WR-galaxy broad feature, in which Si III 4565 Å, N III 4640 Å and He II 4640 Å can be identified. Thus UM 133 is one of a few very metal-poor galaxies, where WR-features are detected.

The measured total B = 1571$\pm$005, and corresponding absolute magnitude, corrected for Galaxy extinction (A_B=007) M_B⁰ = -1604. For UM 133 SBP in Fig. 1b we performed an exponential "disc" fitting, resulted in the central surface brightness $\mu_{E,0}^B$ = 22.83$\pm$0.01 mag arcsec^-2 and the scale length $\alpha^B_E$ = 812$\pm$018 (or 0.88 kpc). Then, based on the measured total B-magnitude we derive the apparent magnitude of the SF burst component in SW knot and that of the underlying galaxy as 1706 and 1606, respectively. From the H$\alpha$ brightness profile in Fig. 1a one can see that the current SF activity besides of SW bright knot ``a'' is well traced almost over the whole galaxy body. Therefore the emission sampled in our B-band SBP, is probably heavily contaminated by current and recent SF and should rather be considered as a "plateau" component (Papaderos et al. [1996]), than real underlying disc of old stellar population.

UM 382 Our oxygen abundance for UM 382 (12+log(O/H) = 7.76$\pm$0.07) is significantly higher than those presented by Masegosa et al. ([1994]) (7.45$\pm$0.04) and derived on the same data by Telles ([1995]) (7.52$\pm$0.07). Since those results were obtained from a Reticon spectrum with a lower S/N ratio we consider the new data as a more reliable. Therefore UM 382 is not an extremely metal-poor H  II galaxy. We derive for this galaxy heliocentric velocity V_hel = 3510$\pm$54 km s^-1 in comparison to the value 3598 km s^-1 from Terlevich et al. ([1991]).

UM 283 This galaxy have appeared with 12+log(O/H)=7.59 in Gallego et al. ([1997]) as UCM 0049+0017. We have paid attention that the relative line intensities for this object reproduced in our Table 1 from Table 4 of Gallego et al ([1996]), according to the standard method by Pagel et al. ([1992]) lead, with T_e=16,100 (Gallego et al. [1997]) to the value 7.95, but not 7.59. Therefore, we suggest that UM 283 appeared as a very metal-poor object just as a result of a misprint.

Summarising the new data presented above we conclude: 1) UM 133 is confirmed as a BCG with very low metallicity (Z $\approx$ 1/20 Z$_\odot$) and its SW bright H  II region, in which we detected WR blue bump, is confirmed as the part of the larger galaxy; 2) UM 382 is significantly more metal-rich (Z $\sim$ 1/15 Z$_\odot$) than it was claimed based on an early Reticon spectrum; 3) UM 283 is significantly more metal-rich than claimed in the literature (Z$\sim$ 1/10 Z$_\odot$).