5 Results

 

 

Table 4: The results of the observations.

									This work					Literature
VCC	ON	OFF	Tel	Year	$T_{\rm ON}$	$T_{\rm OFF}$	R(Ha)	$n_{\frac{{\rm ON}}{{\rm OFF}}}$	H $\alpha+[{\rm NII}]EW$	$F({\rm H}\alpha+[{\rm NII}])$	Phot	Morph	Notes	${\rm H}\alpha+[{\rm NII}]EW$	$F({\rm H}\alpha+[{\rm NII}])$	Ref.	Notes
(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)	(11)	(12)	(13)	(14)	(15)	(16)	(17)
24	6568	r	INT	2001	33	10	0.86	0.30	$3 \pm 1$	$-14.03\pm0.04$	C	C		-1	-	A	*
144	6610	r	NOT	2001	45	15	0.75	0.18	$161 \pm 1$	$-12.23\pm0.04$	P	C		$159 \pm22$	-12.72	A
213	6564	r	NOT	2000	40	10	0.61	0.13	$24 \pm 2$	$-12.67\pm0.05$	P	El
324	6568	R	INT	1999	75	25	0.85	0.20	$65 \pm 8$	$-12.29\pm0.06$	P	C		$56 \pm 4$	-12.20	A	*
404	6568	R	INT	1999	75	25	0.83	0.21	$8 \pm 1$	$-13.22\pm0.07$	P	D
428	6562	r	NOT	2000	60	30	0.53	0.09	$251 \pm19$	$-12.97\pm0.04$	P	C
459	6610	r	NOT	2001	45	15	0.75	0.19	$48 \pm 1$	$-12.66\pm0.04$	P	E		$56 \pm 7$	-12.53	A	*
513	6610	r	NOT	2001	45	15	0.73	0.19	$49 \pm 1$	$-12.72\pm0.04$	P	C		$53 \pm 5$	-12.66	A
655	6568	R	INT	1999	77	18	0.87	0.23	$7 \pm 1$	$-12.75\pm0.07$	P	El		$3 \pm 1$		Hi	*
787	6568	R	INT	1999	47	10	0.87	0.46	$22 \pm 1$	$-12.48\pm0.04$	P	C+E
793	6568	R	INT	1999	75	20	0.73	0.23	$- \pm 4$	-	P
802	6568	R	INT	1999	75	20	0.86	0.24	$38 \pm 4$	$-13.54\pm0.06$	P	E
810	6568	R	INT	1999	75	20	0.85	0.23	$-1 \pm 6$	-	P
815	6568	R	INT	1999	75	20	0.84	0.23	$-1 \pm 7$	-	P
846	6568	R	INT	1999	75	20	0.84	0.23	$-1 \pm 5$	-	P
848	6568	R	INT	1999	47	10	0.83	0.47	$28 \pm 5$	$-13.02\pm0.08$	P	E		14		GS
873	6568	R	INT	1999	75	20	0.88	0.23	$12 \pm 1$	$-12.09\pm0.05$	P	D		$10 \pm 2$	-12.18	II	*
1297	6568	R	INT	1999	75	5	0.85	1.00	$-1 \pm 1$	-	P
1313	6568	R	INT	1999	75	25	0.86	0.20	$351 \pm10$	$-12.84\pm0.04$	P	C
1316	6568	R	INT	1999	75	5	0.86	1.00	$2 \pm 3$	$-12.05\pm0.63$	P	FIL		$1 \pm 3$	-11.73	M	*
1369	6568	R	INT	1999	75	25	0.87	0.20	$-1 \pm 8$	-	P
1437	6568	R	INT	1999	90	23	0.87	0.20	$17 \pm 2$	$-13.16\pm0.07$	P	C
1488	6568	R	INT	1999	90	23	0.87	0.20	$-1 \pm 3$	-	P		*
1725	6568	R	INT	1999	75	7	0.87	0.25	$43 \pm 9$	$-12.66\pm0.08$	P	C+E		$38 \pm 5$	-12.62	A	*
1804	6610	6883	NOT	2001	60	45	0.73	1.47	$3 \pm 1$	$-14.37\pm0.19$	P	D
1955	6610	r	NOT	2000	20	5	0.74	0.25	$9 \pm 4$	$-13.10\pm0.17$	P	C
2007	6610	6883	NOT	2001	60	45	0.73	1.45	$10 \pm 1$	$-13.77\pm0.04$	P	E
2033	6568	R	INT	1999	75	25	0.85	0.22	$13 \pm 3$	$-13.32\pm0.10$	P	C		$5 \pm 3$	-13.68	A	*
2034	6568	R	INT	1999	75	10	0.85	0.50	$2 \pm 2$	$-14.29\pm0.44$	P	L		$2 \pm 1$	-13.81	H	*
2037	6568	R	INT	1999	75	10	0.87	0.50	$17 \pm 6$	$-13.51\pm0.16$	P	C		$16 \pm1$		Hi
2045	6568	R	INT	1999	75	10	0.87	0.50	$-1 \pm 4$	-	P		*

Notes: long slit spectra were taken by Gavazzi et al., in prep., for VCC 24 ( ${\rm H}\alpha+[{\rm NII}]EW=19$ Å), VCC 324 ( ${\rm H}\alpha+[{\rm NII}]EW=313$ Å), VCC 459 ( ${\rm H}\alpha+[{\rm NII}]EW=67$ Å), VCC 655 ( ${\rm H}\alpha+[{\rm NII}]EW=22$ Å), VCC 873 ( ${\rm H}\alpha+[{\rm NII}]EW=14$ Å), VCC 1725 ( ${\rm H}\alpha+[{\rm NII}]EW=77$ Å) and VCC 2033 ( ${\rm H}\alpha+[{\rm NII}]EW=33$ Å).

VCC 1316: our H$\alpha$ data are already discussed in Gavazzi et al. (2000b).

VCC 1488: possible vignetting.

VCC 2034: the flux might be contaminated by a nearby bright star.

VCC 2045: no redshift available; assumed at the average velocity of the cluster, ${\rm vel} =1200$ kms^-1

References:

A: Almoznino & Brosch (1998); H: Heller et al. (1999); Hi: Hippelein et al. in prep; M: Macchetto et al. (1996); II: Paper II. GS: Gavazzi et al., in preparation (spectroscopic survey drifting the telescope over the entire disc of the galaxy).

The results of the present observations are listed in Table 4, arranged as follow:

• Column 1: galaxy name;
• Column 2 and 3: ON and OFF band filters;
• Column 4: telescope used;
• Column 5: year of the observation;
• Column 6: total integration time ON band;
• Column 7: total integration time OFF band;
• Column 8: transmissivity of the filter at the given redshifted H$\alpha$ line;
• Column 9: normalization factor obtained by dividing the flux of several field stars in the ON band frame to the OFF band frame, $n_{\frac{{\rm ON}}{{\rm OFF}}}$. In photometric conditions this quantity gives the transmission difference between the ON and the OFF band filters. Under non photometric conditions $n_{\frac{{\rm ON}}{{\rm OFF}}}$ includes variations in the sky transparency. The average values $n_{\frac{{\rm ON}}{{\rm OFF}}}$ obtained in photometric conditions are $n_{\frac{6568}{R}}= 0.067 \pm 0.003$ for the INT, $n_{\frac{6610}{r}} = 0.062 \pm 0.002$ and $n_{\frac{6610}{6883}}= 1.095 \pm 0.016$ for the NOT;
• Column 10: H$\alpha$+[NII] equivalent width ( ${\rm H}\alpha+[{\rm NII}]EW$), and error, in Å;
• Column 11: log of the H$\alpha$+[NII] flux and error, in $\rm erg~cm^{-2}\,sec^{-1}$, uncorrected for underlying Balmer absorption and galactic extinction;
• Column 12: a flag indicates whether the frame was taken under photometric (P) or cirrus (C) conditions;
• Column 13: H$\alpha$+[NII] morphology of the galaxy, as in Brosch et al. (1998): C indicates a giant, central starburst region, E emission from the edge of the galaxy, El emission along a ring structure, D diffuse emission, L linear (HII regions along the disc) and FIL a filamentary structure;
• Column 14: notes to the present observations;
• Columns 15 and 16: ${\rm H}\alpha+[{\rm NII}]EW$ and $F({\rm H}\alpha+[{\rm NII}])$ flux from the literature;
• Column 17: references to the H$\alpha$ data available in the literature;
• Column 18: notes to the reference data.

The red continuum images of all the observed galaxies are shown as contours plots superposed to the H$\alpha$+[NII] net image (grey levels) in Fig. 1. In most BCD galaxies (53% of the targets) the H$\alpha$ emission is dominated by a central sturburst region, as in VCC 1313, or by giant HII regions at the edges of the disc, as in VCC 459 (24%). In few objects, such as VCC 655, the emission is along a ring-like structure, or it is diffuse and/or homogeneously distributed along the disc (VCC 2034).

Figure 2: Comparison with data in the literature: open dots are for A, filled dots for Hi, open squares for M, filled squares for H, + for I and X for G (see Table 4).

5.1 Comparison with the literature

Fluxes and equivalent widths given in this paper are in general consistent with available measurements, as shown in Fig. 2. The average value of the difference between our measurements and those in the literature is: ${\rm H}\alpha+[{\rm NII}] EW_{\rm TW}- {\rm H}\alpha+[{\rm NII}] EW_{\rm L}= 1.9 \pm 4.5$ Å and $-\log F({\rm H}\alpha+[{\rm NII}])_{\rm TW}+\log F({\rm H}\alpha+[{\rm NII}])_{\rm L} = 0.02 \pm 0.29~\rm erg~cm^{-2}\,s^{-1}$. This has been estimated excluding long-slit spectroscopic data from (Gavazzi et al. in prep.), which, in the case of BCD, could be non-representative of the whole galaxy but biased towards high surface brightness HII regions, as in the case of VCC 24, 324, 655 and 2033. The significant difference between our H$\alpha$+[NII] flux estimate and that of Heller et al. (1999) for VCC 2034 might be due to the contamination by a nearby star.