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Поисковые слова: dust disk

NGC 253 is a nearby edge-on galaxy and the brightest member of the Sculptor group. Its nuclear region is particularly active, revealing numerous compact radio sources (Antonucci & Ulvestad 1988), as well as bright optical and infrared emission lines. The strong and extended radio emission makes it especially suitable for HI absorption measurements (see e.g., Combes, Gottesman & Weliachew 1977; Dickey, Brinks & Puche 1992; Koribalski, Whiteoak & Houghton 1995). Gardner & Whiteoak (1974) also measured broad H₂CO and OH absorption lines. NGC 253 reveals a bar which has been detected in the near-infrared (Scoville et al. 1985; Forbes & DePoy 1992), optical (Pence 1980), and -- on a much smaller scale -- in the CO emission (Canzian, Mundy & Scoville 1988; see also Mauersberger et al. 1996).

Table: Some basic parameters of the selected galaxies

Name	$\alpha$(2000)	$\delta$(2000)	Type	i	v21
	[$^{\rm h~m~s}$]	[$^{\circ}$  ]		[$^{\circ}$]	[kms-1]
NGC 253	00 47 33.1	-25 17 18	.SXS5..	78	251
NGC 660	01 43 01.4	+13 38 37	.SBS1P.	65	853
NGC 1068	02 42 40.2	-00 00 48	RSAT3..	40	1137
NGC 1365	03 33 36.6	-36 08 17	.SBS3..	60	1662
NGC 1808	05 07 42.8	-37 30 51	RSXS1..	57	1005
NGC 3034	09 55 54.0	+69 40 57	.I.0../	82	203
NGC 3079	10 01 58.2	+55 40 43	.SBS5./	85	1125
NGC 3628	11 20 16.3	+13 35 22	.S..3P/	82	847
NGC 4945	13 05 26.2	-49 28 15	.SBS6*/	78	560
Circinus	14 13 10.2	-65 20 20	.SAS3*.	60	438
NGC 6221	16 52 46.7	-59 12 59	.SBS5..	43	1482
NGC 7552	23 16 10.9	-42 35 01	PSBS2..	28	1585
NGC 7582	23 18 23.3	-42 22 11	PSBS2..	64	1575

Column (1): Galaxy name. Columns (2) & (3): Galaxy position. Column (4): Galaxy type. Column (5): Approximate galaxy inclination. Column (6): Mean heliocentric radial velocity derived from HI observations. References: All parameters except the inclination are taken from the Third Reference Catalog (RC3) by de Vaucouleurs et al. (1991). The galaxy inclination has either been taken from the HI catalog by Huchtmeier & Richter (1989) or references mentioned in the summary of the individual galaxies.

Various authors have also indicated the possibility of large-scale outflow of ionized gas into the halo (see Schulz & Wegner 1992, and references therein). Extended X-ray emission has been observed by Fabbiano & Trinchieri (1984) and Pietsch & Trümper (1993) using the Einstein- and ROSAT satellites, respectively.

Figures 2 and 3 show the HI gas distribution and velocity field of NGC 253, respectively. The emission is distributed rather similar to the optical light and shows a rather regularly rotating spiral galaxy (Koribalski, Whiteoak & Houghton 1995). The HI absorption against the central continuum sources causes the prominent `hole' in the centre of the distribution. The major-axis position-velocity diagram of NGC 253 is rather similar to that of NGC 1808 (Fig. 1), with one major difference: here the absorption spectrum is not quite as broad as the emission spectrum and it is asymmetric with respect to the systemic velocity (see Table 1). Whereas the large width of the absorption is most likely caused by a fast-rotating nuclear ring, the asymmetry of the line has been interpreted as due to gas outflow from the nuclear region. A detailed analysis of the HI data is in progress.

Table: Far-infrared flux, luminosity and derived star-formation rate

	D	F$_{\rm FIR}$	L$_{\rm FIR}$	SFR
	[Mpc]	[10-11 Wm-2]	[109 L$_{\odot}$]	[M$_{\odot}$yr-1]
NGC 253	3.4	5.59 (a)	20	5.2
NGC 660	11.2	0.35 (a)	14	3.6
NGC 1068	15.2	0.97 (b)	71	18.4
NGC 1365	20.5	0.51 (a)	68	17.6
NGC 1808	10.9	0.57 (c)	21	5.5
NGC 3034	3.25	5.84 (a)	19	4.9
NGC 3079	15.6	0.25 (b)	19	4.9
NGC 3628	10.2	0.31 (a)	10	2.6
NGC 4945	6.7	3.70 (a)	52	13.5
Circinus	3.6	1.21 (d)	5	1.3
NGC 6221	17.7	0.22 (d)	22	5.6
NGC 7552	20.9	0.36 (d)	50	12.9
NGC 7582	20.7	0.25 (d)	34	8.8

Column (1): Galaxy name. Column (2): Adopted distance, assuming H₀ = 75kms^-1 Mpc^-1. Column (3): Far-infrared flux as calculated from the IRAS 60$\mu$m and 100$\mu$m fluxes. References: (a) Rice et al. 1988, (b) Young et al. 1989, (c) Danks, Perez & Altner 1990, (d) IRAS Point Source Catalog 1985. Column (4): Far-infrared luminosity ($\propto D^2$). Column (5): Star-formation rate: SFR( $M \ge 0.1~{\rm M}_{\odot}$) = 0.26 $\ast$ column(4), see Hunter et al. (1986).

Figure 2: (top) HI distribution of the starburst galaxy NGC 253.

Figure 3: (bottom) HI mean velocity field of NGC 253 (for a full description see Koribalski, Whiteoak & Houghton 1995). The data were taken with three different arrays of the ATCA (12 h each).