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Query : 2001AJ....122.3017S |
2001AJ....122.3017S - Astron. J., 122, 3017-3045 (2001/December-0)
High-mass, OB star formation in M51: Hubble Space Telescope Hα and Paα imaging.
SCOVILLE N.Z., POLLETTA M., EWALD S., STOLOVY S.R., THOMPSON R. and RIEKE M.
Abstract (from CDS):
To analyze the variations of H II region properties vis-à-vis the galactic structure, the spiral arm areas were defined independently from millimeter-CO and optical continuum imaging. Although the arms constitute only 25% of the disk surface area, the arms contain 45% of the cataloged H II regions. The luminosity function is somewhat flatter in spiral arm regions than in the interarm areas (-0.72 to -0.95); however, this is very likely the result of increased blending of individual H II regions in the arms that have higher surface density. No significant difference is seen in the sizes and electron densities of the H II regions in spiral arm and interarm regions. For 209 regions that had ≥5 σ detections in both Paα and Hα, the observed line ratios indicate visual extinctions in the range A_V_=0-6 mag. The mean extinction was AV=3.1 mag (weighting each region equally), 2.4 mag (weighting each by the observed Hα luminosity), and 3.0 mag (weighting by the extinction-corrected luminosity). On average, the observed Hα luminosities should be increased by a factor of ∼10, implying comparable increases in global OB star cluster luminosities and star formation rates. The full range of extinction-corrected Hα luminosities is between 1037 and 2x1040 ergs.s–1.
The most luminous regions have sizes ≥100 pc, so it is very likely that they are blends of multiple regions. This is clear based on their sizes, which are much larger than the maximum diameter (≤50 pc) to which an H II region might conceivably expand within the ∼3x106 yr lifetime of the OB stars. It is also consistent with the observed correlation (L∝D2) between the measured luminosities and sizes of the H II regions. We therefore generated a subsample of 1101 regions with sizes ≤50 pc, which is made up of those regions that might conceivably be ionized by a single cluster. Their extinction-corrected luminosities range between 2x1037 and 1039 ergs.s–1, or between two-thirds of M42 (the Orion Nebula) and W49 (the most luminous Galactic radio H II region). The upper limit for individual clusters is therefore conservatively ≤1039 ergs.s–1, implying QLyc,up≃7x1050.s–1 (with no corrections for dust absorption of the Lyman continuum or UV that escapes to the diffuse medium). This corresponds to cluster masses ≤5000 M☉ (between 1 and 120 M☉).
The total star formation rate in M51 is estimated from the extinction-corrected Hα luminosities to be ∼4.2 M☉.yr–1 (assuming a Salpeter initial mass function between 1 and 120 M☉), and the cycling time from the neutral interstellar medium into these stars is 1.2x109 yr.
We develop a simple model for the UV output from OB star clusters as a function of the cluster mass and age in order to interpret constraints provided by the observed luminosity functions. The power-law index at the high-luminosity end of the luminosity function (α=-1.01) implies N(Mcl)/dMcl∝M–2.01cl. This implies that high-mass star formation, cloud disruption due to OB stars, and UV production are contributed to by a large range of cluster masses with equal effects per logarithmic interval of cluster mass. The high-mass clusters (∼1000 M☉) have a mass such that the initial mass function is well sampled up to ∼120 M☉, but this cluster mass is ≤1% of that available in a typical giant molecular cloud. We suggest that OB star formation in a cloud core region is terminated at the point that radiation pressure on the surrounding dust exceeds the self-gravity of the core star cluster and that this is what limits the maximum mass of standard OB star clusters. This occurs at a stellar luminosity-to-mass ratio of ∼500-1000 (L/M)☉, which happens for clusters ≥750 M☉. We have modeled the core collapse hydrodynamically and have found that a second wave of star formation may propagate outward in a radiatively compressed shell surrounding the core star cluster–this triggered, secondary star formation may be the mechanism for formation of the super-star clusters seen in starburst galaxies.
Abstract Copyright: ∼
Journal keyword(s): Galaxies: ISM - Galaxies: Spiral - ISM: H II Regions - Stars: Early-Type
Simbad objects: 21
Number of rows : 21 |
N | Identifier | Otype |
ICRS (J2000) RA |
ICRS (J2000) DEC |
Mag U | Mag B | Mag V | Mag R | Mag I | Sp type |
#ref
1850 - 2024 |
#notes |
---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | IC 1795 | HII | 02 25 43.5 | +62 06 13 | ~ | 238 | 0 | |||||
2 | W 3 | MoC | 02 27 04.10 | +61 52 27.1 | ~ | 1032 | 3 | |||||
3 | NAME LMC | G | 05 23 34.6 | -69 45 22 | 0.4 | ~ | 17438 | 0 | ||||
4 | NAME OMC-1 | MoC | 05 35 14 | -05 22.4 | ~ | 1170 | 2 | |||||
5 | NAME Ori Trapezium | OpC | 05 35 16.5 | -05 23 14 | ~ | 1619 | 1 | |||||
6 | M 42 | HII | 05 35 17 | -05 23.4 | ~ | 4077 | 0 | |||||
7 | M 43 | HII | 05 35 31 | -05 16.2 | ~ | 187 | 0 | |||||
8 | NAME Ori I | As* | 05 38 | -02.8 | ~ | 615 | 0 | |||||
9 | NAME Ori A | MoC | 05 38 | -07.1 | ~ | 3012 | 0 | |||||
10 | NGC 2070 | Cl* | 05 38 42 | -69 06.0 | 7.25 | ~ | 378 | 1 | ||||
11 | NGC 2024 | Cl* | 05 41 43 | -01 50.5 | ~ | 1154 | 1 | |||||
12 | NAME Orion Molecular Cloud | MoC | 05 56 | -01.8 | ~ | 1098 | 1 | |||||
13 | NGC 2264 | OpC | 06 40 52.1 | +09 52 37 | ~ | 1793 | 0 | |||||
14 | M 82 | AGN | 09 55 52.430 | +69 40 46.93 | 9.61 | 9.30 | 8.41 | ~ | 5861 | 6 | ||
15 | NGC 4038 | EmG | 12 01 53.002 | -18 52 03.32 | 10.91 | 9.74 | 11.0 | ~ | 1333 | 1 | ||
16 | NAME Antennae | IG | 12 01 53.170 | -18 52 37.92 | ~ | 1692 | 0 | |||||
17 | NGC 4039 | GiP | 12 01 53.51 | -18 53 10.3 | 11.08 | 9.77 | ~ | 1161 | 1 | |||
18 | M 51 | Sy2 | 13 29 52.698 | +47 11 42.93 | 9.26 | 8.36 | 8.40 | ~ | 4330 | 4 | ||
19 | M 101 | GiP | 14 03 12.583 | +54 20 55.50 | 8.46 | 7.86 | 7.76 | ~ | 2916 | 2 | ||
20 | W 49 | SFR | 19 10 20 | +09 07.7 | ~ | 575 | 1 | |||||
21 | W 51 | SNR | 19 23 50 | +14 06.0 | ~ | 1278 | 1 |
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