Deep Near‐Infrared Imaging of a Field in the Outer Disk of M82 with the Altair Adaptive Optics System on Gemini‐North

Davidge, T. J.; Stoesz, J.; Rigaut, François; Véran, Jean-Pierre; Herriot, Glen

doi:10.1086/380850

Cited by 3 publications

(6 citation statements)

References 52 publications

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“…3), which evolve at a faster pace than first-ascent giants, and so have a lower space density. The dotted line shows the power law computed from the RGB LF, but with the y-intercept shifted to account for a population of objects with a space density that is one-fifth that of RGB stars in each distance interval; such a difference in space density more or less matches AGB number counts in old systems and is roughly consistent with stellar evolution models (e.g., Davidge et al 2004;Davidge 2006). It should be emphasized that the dotted line is shown simply as a point of reference, and that the ratio of AGB to RGB stars will depend on the star-forming history of a system.…”

Section: The Number Density Of Red Giantssupporting

confidence: 64%

NGC 5253 and ESO 269-G058: Dwarf Galaxies with a Past

Davidge¹

2007

Astron J

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Deep r' and i' images obtained with GMOS on Gemini South are used to probe the bright stellar content in the outer regions of NGC 5253 and ESO269-G058. Red giant branch (RGB) stars are traced out to a distance of 8 kpc along the major axis of NGC 5253, and 6 kpc in ESO269-G058. The outer regions of both galaxies are metal-poor; RGB stars located between projected major axis distances of 2 and 4 kpc in NGC 5253 have [Fe/H] ~ -1, whereas RGB stars in the corresponding portion of ESO269-G058 have [Fe/H] ~ -1.8. Stars with metallicities that differ from the mean by more than a few tenths of a dex make only a modest contribution to the stellar content in the outer regions of both galaxies. A population of bright asymptotic giant branch (AGB) stars is seen in both galaxies. Roughly 1 - 10% of the stellar mass of NGC 5253 may have formed during the past few hundred million years, and it is suggested that the progenitors of the two recent SN Ia in this galaxy may have formed at this time. It is argued that the current episodes of star formation in NGC 5253 and ESO269-G058 may have been triggered up to ~ 1 Gyr in the past. Finally, a distance modulus is computed for each galaxy based on the brightness of the RGB-tip, and the results are 27.48 +/- 0.14 for NGC 5253, and 27.93 +/- 0.18 for ESO269-G058.Comment: 36 pages, including 11 postscript pages. Astronomical Journal in pres

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Section: The Number Density Of Red Giantssupporting

confidence: 64%

NGC 5253 and ESO 269-G058: Dwarf Galaxies with a Past

Davidge¹

2007

Astron J

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“…The dotted line shows the power-law computed from the RGB LF, but with the y-intercept shifted to account for a population of objects with a space density that is one fifth that of RGB stars in each distance interval; such a difference in space density more-or-less matches AGB number counts in old systems, and is roughly consistent with stellar evolution models (e.g. Davidge et al 2004;Davidge 2006). It should be emphasized that the dotted line is shown simply as a point of reference, and that the ratio of AGB to RGB stars will depend on the star-forming history of a system.…”

Section: The Number Density Of Red Giantssupporting

confidence: 58%

“…The integrated brightnesses of the M31 dEs range between M K = −17.3 (NGC 147) and M K = −18.9 (NGC 205), and so overlap with the range of plausible faded brightnesses of NGC 5253 and ESO269-G058. Davidge (2004) points out that the globular cluster content of amorphous star-forming dwarf galaxies may provide clues into their past histories, and a search for classical globular clusters near NGC 5253 and ESO269-G058 is one means of testing the hypothesis that these galaxies are dEs. The dE companions of M31 have globular cluster specific frequencies S N ∼ 2 − 6, whereas late-type disk systems tend to have S N < 1 (e.g.…”

Section: Ngc 5253 and Eso269-g058 As Dwarf Ellipticalsmentioning

confidence: 99%

NGC 5253 and ESO 269-G058: Dwarf Galaxies with a Past

Davidge

2007

Preprint

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Deep r ′ and i ′ images obtained with GMOS on Gemini South are used to probe the bright stellar content in the outer regions of the Centaurus Group dwarf galaxies NGC 5253 and ESO269-G058. Red giant branch (RGB) stars are traced out to a distance of 8 kpc along the major axis of NGC 5253, and 6 kpc in ESO269-G058. The outer regions of both galaxies are metal-poor; RGB stars located between projected major axis distances of 2 and 4 kpc in NGC 5253 have [Fe/H] ∼ −1, whereas RGB stars in the corresponding portion of ESO269-G058 have [Fe/H] ∼ −1.8. Stars with metallicities that differ from the mean by more than a few tenths of a dex make only a modest contribution to the stellar content in the outer regions of both galaxies. A population of bright asymptotic giant branch (AGB) stars is seen in both galaxies. In the particular case of NGC 5253, roughly 1 -10% of the stellar mass may have formed during the past few hundred million years, and it is suggested that the progenitors of the two recent SN Ia in this galaxy may have formed at this time. That NGC 5253 has experienced either episodic or continuing elevated levels of star formation during the past few hundred million years is reminiscent of what is seen in other dwarf starburst galaxies, such as NGC 3077, and it is argued that the current episodes of star formation in NGC 5253 and ESO269-G058 may have been triggered up to ∼ 1

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“…While the interstellar medium (ISM) and young stars in M82 have metallicities approaching (e.g., Martin 1997; Gallagher & Smith 1999) and even exceeding (Origlia et al 2004) solar, the metallicities of stars that formed during intermediate epochs are almost certainly lower than those of younger stars. Parmentier et al (2003) estimated metallicities for clusters in M82, and these data indicate that clusters with ages log(t) = 8.0 have slightly subsolar metallicities, while clusters with log(t) = 8.5 have Z = 0.008 (e.g., Table 1 of Davidge et al 2004). The Z = 0.008 models are adopted as the baseline for subsequent discussion and comparison, although the reader is reminded that the AGB age estimates depend on the adopted metallicity.…”

Section: Comparisons With Isochronesmentioning

confidence: 99%

“…A number of luminous candidate asymptotic giant branch (AGB) stars were also identified, hinting at star-forming activity during intermediate epochs. Davidge et al (2004) used H and K images recorded with the near-infrared images (NIRI) + ALTAIR on Gemini North to investigate the stellar content at a projected distance of ∼1 kpc south of the M82 disk plane. The relative numbers of AGB and RGB stars were found to be consistent with stellar evolution models, while the peak brightness of the AGB is consistent with that of an intermediate-age population.…”

Section: Introductionmentioning

confidence: 99%

And the Rest: The Stellar Archeological Record of M82 Outside the Central Starburst

Davidge

2008

The Astronomical Journal

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Deep images obtained with MegaCam and WIRCam on the Canada-France-Hawaii Telescope are used to probe the stellar content outside of the central star-forming regions of M82. Stars evolving on the asymptotic giant branch (AGB) are traced along the major axis out to projected distances of 12 kpc, which corresponds to 13 disk scale lengths. The numbers of red supergiants (RSGs) and AGB stars normalized to local surface brightness (the "specific frequency" or SF) is constant when R GC > 4 kpc, indicating that RSGs and AGB stars are well mixed throughout the disk. Moreover, the SF of bright AGB stars in the outer disks of M82 and the Sc galaxy NGC 2403 are identical, suggesting that the specific star-formation rates (SFRs) in these galaxies during intermediate epochs were similar. This similarity in stellar content, coupled with the presence of an extended stellar disk, is consistent with M82 having been a late-type disk galaxy prior to interacting with M81. Still, there is a paucity of RSGs in the outer disk of M82 when compared with NGC 2403, indicating that the SFR in the outer regions of M82 during the past ∼0.1 Gyr has declined dramatically with respect to that in isolated late-type galaxies. The stellar content of the M82 disk plane is also investigated. A mixture of bright main-sequence stars, RSGs, and AGB stars is detected out to minor-axis distances of 7 kpc. These stars, which span a range of ages, are concentrated along the outflow. The brightest extraplanar AGB stars define a system with an exponential scale height of 1.8 ± 0.2 kpc, as measured along the minor axis. It is suggested that the young-and intermediate-aged stars in the extraplanar regions formed in structures similar to M82 South, and that these were subsequently disrupted by the tidal action of M82.

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Deep Near‐Infrared Imaging of a Field in the Outer Disk of M82 with the Altair Adaptive Optics System on Gemini‐North

Cited by 3 publications

References 52 publications

NGC 5253 and ESO 269-G058: Dwarf Galaxies with a Past

NGC 5253 and ESO 269-G058: Dwarf Galaxies with a Past

NGC 5253 and ESO 269-G058: Dwarf Galaxies with a Past

And the Rest: The Stellar Archeological Record of M82 Outside the Central Starburst

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