2001ApJ...556..773H


C.D.S. - SIMBAD4 rel 1.7 - 2020.06.02CEST04:58:40

2001ApJ...556..773H - Astrophys. J., 556, 773-800 (2001/August-1)

Neutral hydrogen and star formation in the irregular galaxy NGC 2366.

HUNTER D.A., ELMEGREEN B.G. and VAN WOERDEN H.

Abstract (from CDS):

We present deep UBVJHK Hα images and H I maps of the irregular galaxy NGC 2366. Optically, NGC 2366 is a boxy-shaped exponential disk seen at high inclination angle. The scale length and central surface brightness of the disk are normal for late-type galaxies. Although NGC 2366 has been classified as a barred Im galaxy, we do not see any unambiguous observational signature of a bar. There is an asymmetrical extension of stars along one end of the major axis of the galaxy, and this is where the furthest star-forming regions are found, at a radius of 1.3 times the Holmberg radius. The star formation activity of the galaxy is dominated by the supergiant H II complex NGC 2363, but the global star formation rate for NGC 2366 is only moderately elevated relative to other Im galaxies. The star formation activity drops off with radius approximately as the starlight in the inner part of the galaxy but it drops faster in the outer part. There are some peculiar features of the H I distribution and kinematics. First, the integrated H I shows two ridges running parallel to the major axis that when deprojected appear as a large ring. Second, the velocity field exhibits several large-scale anomalies superposed on a rotating disk; some of these may be from a weak bar that has no inner Lindblad resonance. Third, the inclination and position angles derived from the kinematics differ from those derived from the optical and H I morphology. Fourth, there are regions in the H I of unusually high velocity dispersion, but these regions are not associated with the optical galaxy nor any obvious H I feature. Instead the velocity dispersion correlates with a deficit of H I emission in a manner suggestive of long-range, turbulent pressure equilibrium. In other respects the H I is fairly normal. The azimuthally averaged surface density of H I is comparable to that of other irregulars in the inner part of the galaxy but drops off slower and extends further in the outer parts. The H I around the star-forming complex NGC 2363 is fairly unremarkable. As in other disk galaxies, the gas in NGC 2366 is lumpy and star-forming regions are associated with these H I complexes. H II regions are found where the gas densities locally exceed 6 M.pc–2. This threshold is required to provide a cool phase of H I as a first step toward star formation. NGC 2366, like other irregulars, has low gas densities relative to the critical gas densities of gravitational instability models, so large-scale gravitational instabilities operate slowly or not at all. Considering the lack of shear in the optical part of this galaxy, the relative slowness of such instabilities may not be a problem–there is little competition to the slow gravitational contraction that follows energy dissipation. This differs from the situation in giant spiral disks where the shear time is short, comparable to the energy dissipation time, and strong self-gravity is required for a condensation to grow and dissipate its turbulent energy before it shears away. The subthreshold surface densities are also not unusual if they are viewed using the critical tidal density for gravitational self-binding of a rotating cloud, rather than the critical surface density from the usual disk instability condition. The peak densities in all regions of star formation are equal to the local tidal densities, giving an agreement between these two quantities that is much better than between the surface density and the critical value. Evidently the large-scale gas concentrations are all marginally bound against background galactic tidal forces. This condition for self-binding may be more fundamental than the instability condition because it is local, three-dimensional, and does not involve spiral arm generation as an intermediate step toward star formation.

Abstract Copyright:

Journal keyword(s): galaxies: individual (NGC 2366) - Galaxies: Irregular - Galaxies: ISM - Galaxies: Kinematics and Dynamics - Galaxies: Stellar Content

Nomenclature: Table 1, Fig.2: [HEV2001] NN (Nos 1-20).

Status at CDS:  

Simbad objects: 47

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Number of rows : 47

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 IC 10 G 00 20 23.16 +59 17 34.7   13.6 9.5     ~ 1005 0
2 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 9387 1
3 NAME Pisces I G 01 03 56.6 +21 53 41   16.18 14.3     ~ 357 0
4 IC 342 SBG 03 46 48.514 +68 05 45.98   10.5       ~ 1380 1
5 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 14750 1
6 Shapley III As* 05 31 31 -66 46.4           ~ 35 0
7 NAME 30 Dor Nebula SFR 05 38 36.0 -69 05 11           ~ 1037 2
8 [HEV2001] 1 Rad 07 24 50.0 +69 14 23           ~ 1 0
9 [HEV2001] 2 Rad 07 26 02.3 +69 17 28           ~ 1 0
10 [HEV2001] 3 Rad 07 26 17.2 +69 09 20           ~ 1 0
11 [HEV2001] 4 Rad 07 26 21.2 +68 53 04           ~ 1 0
12 [HEV2001] 5 Rad 07 27 13.3 +69 19 27           ~ 1 0
13 [HEV2001] 6 Rad 07 27 24.3 +69 23 59           ~ 1 0
14 [HEV2001] 7 Rad 07 27 47.7 +69 14 53           ~ 1 0
15 [HEV2001] 8 Rad 07 27 54.5 +68 52 53           ~ 1 0
16 [HEV2001] 9 Rad 07 28 01.3 +69 30 44           ~ 1 0
17 [HEV2001] 11 Rad 07 28 29.7 +68 50 43           ~ 1 0
18 NGC 2363 G 07 28 29.83 +69 11 32.8   15.5       ~ 250 1
19 [HEV2001] 10 Rad 07 28 29.9 +68 51 47           ~ 1 0
20 NGC 2363A HII 07 28 42.8 +69 11 21           ~ 540 3
21 NGC 2366 H2G 07 28 51.85 +69 12 31.1 12.25 11.86 11.39 11.33   ~ 698 0
22 [HEV2001] 12 Rad 07 29 50.0 +68 53 01           ~ 1 0
23 [HEV2001] 13 Rad 07 30 15.2 +69 29 07           ~ 1 0
24 NVSS J073023+690550 Rad 07 30 23.12 +69 05 50.4           ~ 2 0
25 [HEV2001] 15 Rad 07 30 42.7 +69 10 08           ~ 1 0
26 [HEV2001] 16 Rad 07 30 44.5 +69 05 04           ~ 1 0
27 [HEV2001] 18 Rad 07 31 39.1 +69 24 42           ~ 1 0
28 [HEV2001] 17 Rad 07 31 40.8 +69 19 29           ~ 1 0
29 [HEV2001] 19 Rad 07 32 29.0 +68 59 38           ~ 1 0
30 [HEV2001] 20 Rad 07 33 16.9 +69 09 07           ~ 1 0
31 NGC 2403 AGN 07 36 51.396 +65 36 09.17 9.31 8.84 8.38 8.19   ~ 1596 1
32 UGC 4305 IG 08 19 04.9878269182 +70 43 13.025604473 12.06 11.72 11.39 11.11   ~ 684 2
33 NAME M 81 Dwarf A G 08 23 55.1 +71 01 56   16.5       ~ 186 1
34 UGC 4426 G 08 28 28.560 +41 51 27.13   18       ~ 128 0
35 LSB F563-1 LSB 08 55 01.4 +19 45 06           ~ 61 0
36 LEDA 86668 LSB 09 02 53.357 +20 04 32.21   16.9       ~ 74 0
37 LEDA 86670 LSB 09 37 36.6 +21 46 15           ~ 41 0
38 NAME M 81-82 Group GrG 09 55 +69.1           ~ 630 0
39 NAME Leo Dwarf Irregular Galaxy G 09 59 26.46 +30 44 47.0 14.08 13.54 13.26 13.33   ~ 546 0
40 NAME Sex A H2G 10 11 00.5 -04 41 30 12.48 12.13 11.93 11.78   ~ 651 2
41 LEDA 86618 LSB 10 17 56.3 +21 03 41           ~ 21 0
42 UGC 6955 GiG 11 58 29.804 +38 04 34.80   15.2       ~ 70 0
43 NGC 4228 SBG 12 15 39.174 +36 19 36.80 10.63 10.30 9.93 9.74   ~ 862 1
44 NGC 4449 EmG 12 28 11.118 +44 05 36.81 10.11 9.98 9.64 9.45   ~ 1019 1
45 UGC 8091 H2G 12 58 40.1930291852 +14 13 00.737117016 15.24 15.16 14.98 14.81   ~ 437 0
46 NAME Peg Dwarf Irregular Galaxy G 23 28 35.2 +14 44 35 13.85 13.16 12.52     ~ 419 1
47 NAME NGC 2366 III HII ~ ~   13.63 13.52     ~ 7 0

    Equat.    Gal    SGal    Ecl

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2020.06.02-04:58:40

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