Query : 2009A&A...493...71C

2009A&A...493...71C - Astronomy and Astrophysics, volume 493, 71-78 (2009/1-1)

Searching for spiral features in the outer Galactic disk. The field towards WR38 and WR38a.


Abstract (from CDS):

The detailed spiral structure of the outer Galactic disk remains poorly constrained, and for several line of sights in the Galaxy we depend on model extrapolations. One of these regions is the fourth Galactic quadrant, between Vela and Carina (270°≤l≤300°), where, apart from the conspicuous Carina branch of the Carina Sagittarius arm, no spiral arms have been detected so far in the optical beyond l∼270°. By means of deep UBVI photometry, we search for spiral features in known low absorption windows. Although observationally demanding, U photometry constitutes a powerful tool for detecting and characterizing distant aggregates of young stars, and allows firmer distance estimates to be derived. We study a direction close to the tangent (l∼290°) of the Carina arm, in an attempt to detect optical spiral tracers far beyond the Carina branch, where radio observations and model predictions appear to indicate the presence of an extension of the Perseus and Norma-Cygnus spiral arms in the fourth quadrant. Along this line of sight, we detect three distinct groups of young stars. Two of them, at distances of ∼2.5 and ∼6.0kpc, belong to the Carina spiral arm, which is traversed twice in this particular direction. Interestingly, the latter is detected for the first time. The third group, at a distance of ∼12.7kpc, is probably related to the Perseus arm which lies beyond the Carina arm, and constitutes the first optical detection of this arm in the fourth Galactic quadrant. The position of this feature is consistent with both HI observations and model predictions. We also present evidence that this extremely distant group, formerly assumed to be a star cluster (Shorlin 1), is a diffuse, young population, typically found in spiral galaxies. In addition, our data-set does not support, as claimed in the literature, the possible presence of the Monoceros Ring in this direction This study highlights how multicolor optical studies can be effective in probing the spiral structure of the outer Galactic disk. More fields need to be studied in this region of the Galaxy to constrain the spiral structure in the fourth Galactic quadrant more accurately, in particular, the shape and extent of the Perseus arm, and, possibly, to detect the even more distant Norma-Cygnus arm.

Abstract Copyright:

Journal keyword(s): Galaxy: general - Galaxy: structure - Galaxy: stellar content

VizieR on-line data: <Available at CDS (J/A+A/493/71): cluster.dat>

Nomenclature: Catalog: [CC2009] NNNN (Nos 1-7425).

Status at CDS : All or part of tables of objects could be ingested in SIMBAD with priority 2.

Simbad objects: 13

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Number of rows : 13
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 NAME Per Arm PoG 03 30 +45.0           ~ 1405 0
2 NAME Gal Anticenter reg 05 46 +28.9           ~ 826 0
3 SA 98- reg 06 52 04.1 -00 23 58           ~ 171 0
4 NAME Car Arm PoG 10 00 -60.0           ~ 415 1
5 NAME Shorlin 1 OpC 11 05 46 -61 13.9           ~ 16 0
6 [MS70] 8 WR* 11 05 46.42920 -61 13 48.7524     14.66 14.713   WC4 38 0
7 WR 38a WR* 11 05 48.9639107880 -61 13 41.352428748 16.33 16.27 15.12     WN5o 14 0
8 NAME Car-Sgr Arm PoG 15 00 -40.0           ~ 469 1
9 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 13179 0
10 NAME Vela Field reg ~ ~           ~ 163 0
11 NAME Carina Region reg ~ ~           ~ 177 0
12 NAME Norma-Cygnus Arm reg ~ ~           ~ 76 0
13 NAME Monoceros Stream St* ~ ~           ~ 338 0

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