1998AJ....116..707R


Query : 1998AJ....116..707R

1998AJ....116..707R - Astron. J., 116, 707-722 (1998/August-0)

Isolating red giant stars in M31's elusive outer spheroid.

REITZEL D.B., GUHATHAKURTA P. and GOULD A.

Abstract (from CDS):

Deep UBRI images of a 15'x15' field in the outer spheroid of the galaxy M31 obtained using the Kitt Peak National Observatory's 4 m telescope and I-band images obtained with the Keck 10 m telescope and Low Resolution Imaging Spectrograph are used to isolate a sample of candidate red giant branch stars located at a projected radial distance of 19 kpc along the minor axis. These stars are distinguished from the more numerous distant field galaxies on the basis of broadband U - B, B - R, and R - I colors and image morphology; we isolate objects whose colors are consistent with the long, but relatively narrow, locus occupied by red giants in UBRI color space (as observed in Galactic globular cluster giants and predicted by models spanning a wide range of metallicities and ages), and those whose angular sizes are consistent with the stellar point-spread function, FWHM = 0".6-0".9 (Keck) and FWHM = 0".9-1".5 (Kitt Peak). We carry out the same analysis of data on a comparison field with a Galactic latitude similar to the M31 halo field. The color-magnitude diagram of objects in the comparison field is well described by a superposition of foreground Galactic dwarf stars (in keeping with a standard empirical model of the Galaxy) against a backdrop of contaminating faint blue field galaxies (I ≳ 21, B - I ∼ 1-2.5), while the M31 halo field contains a clear excess of faint red objects (I ∼ 20-23, B - I ∼ 2-3.5) in addition to these two components. The location of this population of faint red objects in the color-magnitude diagram is as would be expected for red giant stars at the distance of M31. The surface density of RGB candidates in the R = 19 kpc M31 halo field is consistent with the findings of two recent Hubble Space Telescope (HST) studies. The data indicate that M31's halo is much denser and/or larger than that of the Galaxy: ρRGBM31RGBMWΛM1.5–ν ∼ 10 , where Λ is the ratio of the radial scale lengths of M31 and the Galaxy and ν = -3.8 is the assumed power-law index of the density profile; in fact, M31's profile may be steeper than this (ν < -3.8). The color and slope of the red giant branch in M31's outer halo are suggestive of a relatively metal-rich population, [Fe/H] ≳ -1, in agreement with the HST measurements.

Abstract Copyright:

Journal keyword(s): galaxies: individual (M31) - galaxies: individual (NGC 224) - galaxies: individual (UGC 454) - galaxies: individual (CGCG 535-017) - Galaxies: Formation - Stars: General

Simbad objects: 13

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Number of rows : 13
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 NGC 104 GlC 00 24 05.359 -72 04 53.20   5.78 4.09     ~ 3730 0
2 NAME Mayall II GlC 00 32 46.5323801712 +39 34 40.504803060   14.564 13.807 13.208 12.684 ~ 385 1
3 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 11841 1
4 NAME Mayall IV GlC 00 43 17.8552869120 +39 49 13.076914764 15.900 15.710 15.219 14.639 14.122 ~ 83 0
5 Bol 240 GlC 00 45 25.0383161496 +41 06 22.112717688 16.030 15.930 15.210 14.730 14.210 ~ 76 0
6 Bol 379 GlC 00 45 58.8308321424 +40 42 31.402542528 17.460 17.032 16.183 15.560 14.936 ~ 74 0
7 M 79 GlC 05 24 10.59 -24 31 27.3   9.21 8.16     ~ 763 0
8 M 5 GlC 15 18 33.22 +02 04 51.7   7.34 5.95     ~ 1875 0
9 GCl 114 GlC 19 45 14.40 -08 00 26.0     7.54     ~ 129 0
10 NGC 6934 GlC 20 34 11.37 +07 24 16.1   10.48 9.75     ~ 389 0
11 NGC 7006 GlC 21 01 29.465 +16 11 16.49     10.46     ~ 502 0
12 M 15 GlC 21 29 58.33 +12 10 01.2   3       ~ 3026 0
13 M 2 GlC 21 33 27.02 -00 49 23.7     6.25     ~ 965 1

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2022.07.05-09:10:01

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