Three newly discovered globular clusters in NGC 6822

Huxor, Avon; Ferguson, Annette M. N.; Veljanoski, J.; Mackey, A. D.; Tanvir, N. R.

doi:10.1093/mnras/sts387

Cited by 29 publications

(38 citation statements)

References 46 publications

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“…alignment of the GCs in the Local Group dSph NGC 6822 (Hwang et al 2011;Huxor et al 2013). It remains to be shown spectroscopically whether the IKN GCs have disk kinematics or the apparent distribution is a chance alignment.…”

Section: Discussionmentioning

confidence: 96%

Optical-near-IR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history

Tudorica

Georgiev

Chies-Santos

2015

A&A

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Context. Age, metallicity, and spatial distribution of globular clusters (GCs) provide a powerful tool for reconstructing major starformation episodes in galaxies. IKN is a faint dwarf spheroidal (dSph) in the M 81 group of galaxies. It contains five old GCs, which makes it the galaxy with the highest known specific frequency (S N = 126). Aims. We estimate the photometric age, metallicity, and spatial distribution of the poorly studied IKN GCs. We search SDSS for GC candidates beyond the HST/ACS field of view, which covers half of IKN. Methods. To break the age-metallicity degeneracy in the V −I colour, we used WHT/LIRIS K S -band photometry and derived photometric ages and metallicities by comparison with SSP models in the V, I, K s colour space. Results. IKN GCs' V IK s colours are consistent with old ages (≥8 Gyr) and a metallicity distribution with a higher mean than is typical for such a dSph ([Fe/H] −1.4 +0.6 −0.2 dex). Their photometric mass range (0.5 < M GC < 4 × 10 5 M ) implies an unusually high mass ratio between GCs and field stars, of 10.6%. Mixture model analysis of the RGB field stars' metallicity suggests that 72% of the stars may have formed together with the GCs. Using the most massive GC−SFR relation, we calculated a star formation rate (SFR) of ∼10 M /yr during its formation epoch. We note that the more massive GCs are closer to the galaxy photometric centre. IKN GCs also appear spatially aligned along a line close to the major axis of the IKN and nearly orthogonal to the plane of spatial distribution of galaxies in the M 81 group. We identify one new IKN GC candidate based on colour and the PSF analysis of the SDSS data. Conclusions. The evidence of i) broad and high metallicity distribution of the field IKN RGB stars and its GCs, ii) high fraction, and iii) spatial alignment of IKN GCs supports a scenario for tidally triggered, complex IKN's star formation history in the context of interactions with galaxies in the M 81 group.

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Section: Discussionmentioning

confidence: 96%

Optical-near-IR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history

Tudorica

Georgiev

Chies-Santos

2015

A&A

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“…This led Demers et al (2006) to label the system as a "polar ring galaxy." A population of remote star clusters aligned with the elongated old stellar halo have been discovered (Hwang et al 2011;Huxor et al 2013). In summary, the extended structures of NGC 6822 suggest some form of recent interaction.…”

Section: Introductionmentioning

confidence: 92%

Red Supergiant Stars as Cosmic Abundance Probes: Kmos Observations in NGC 6822

Patrick

Evans

Davies

et al. 2015

ApJ

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We present near-IR spectroscopy of red supergiant (RSG) stars in NGC 6822, obtained with the new K-band Multi-Object Spectrograph Very Large Telescope, Chile. From comparisons with model spectra in the J-band we determine the metallicity of 11 RSGs, finding a mean value of [Z] = −0.52 ± 0.21, which agrees well with previous abundance studies of young stars and H II regions. We also find an indication for a low-significance abundance gradient within the central 1 kpc. We compare our results with those derived from older stellar populations and investigate the difference using a simple chemical evolution model. By comparing the physical properties determined for RSGs in NGC 6822 with those derived using the same technique in the Galaxy and the Magellanic Clouds, we show that there appears to be no significant temperature variation of RSGs with respect to metallicity, in contrast to recent evolutionary models.

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“…14 Notable exceptions to this trend are the brightest four of the seven new clusters discovered in NGC6822 by Hwang et al (2011) and Huxor et al (2013); NGC6822-SC1 is of similar age, half-light radius, and luminosity to DDO 216-A1, although it is significantly more metal-poor (Veljanoski et al 2015).…”

Section: Ddo 216-a1 In Contextmentioning

confidence: 99%

DDO 216-A1: A Central Globular Cluster in a Low-luminosity Transition-type Galaxy^∗

Cole¹,

Weisz²,

Skillman³

et al. 2017

ApJ

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We confirm that the object DDO 216-A1 is a substantial globular cluster at the center of Local Group galaxy DDO 216 (the Pegasus dwarf irregular), using Hubble Space Telescope ACS imaging. By fitting isochrones, we find the cluster metallicity [M/H]=−1.6±0.2, for reddening E(B-V )=0.16±0.02; the best-fit age is 12.3±0.8 Gyr.There are »30 RRLyrae variables in the cluster; the magnitude of the fundamental mode pulsators gives a distance modulus of 24.77±0.08-identical to the host galaxy. The ratio of overtone to fundamental mode variables and their mean periods make DDO 216-A1 an Oosterhoff Type I cluster. We find a central surface brightness of 20.85±0.17 F814W magarcsec −2 , a half-light radius of  3. 1 (13.4 pc), and an absolute magnitude M814=−7.90±0.16 (). King models fit to the cluster give the core radius and concentration index, r c =  2. 1±  0. 9 and c=1.24±0.39. The cluster is an "extended" cluster somewhat typical of some dwarf galaxies and the outer halo of the Milky Way. The cluster is projected 30 pc south of the center of DDO 216, unusually central compared to most dwarf galaxy globular clusters. Analytical models of dynamical friction and tidal destruction suggest that it probably formed at a larger distance, up to ∼1 kpc, and migrated inward. DDO 216 has an unexceptional specific cluster frequency, S N =10. DDO 216 is the lowest-luminosity Local Group galaxy to host a 10 5   M globular cluster and the only transition-type (dSph/dIrr) galaxy in the Local Group with a globular cluster.

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Three newly discovered globular clusters in NGC 6822

Cited by 29 publications

References 46 publications

Optical-near-IR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history

Optical-near-IR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history

Red Supergiant Stars as Cosmic Abundance Probes: Kmos Observations in NGC 6822

DDO 216-A1: A Central Globular Cluster in a Low-luminosity Transition-type Galaxy^∗

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Three newly discovered globular clusters in NGC 6822

Cited by 29 publications

References 46 publications

Optical-near-IR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history

Optical-near-IR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history

Red Supergiant Stars as Cosmic Abundance Probes: Kmos Observations in NGC 6822

DDO 216-A1: A Central Globular Cluster in a Low-luminosity Transition-type Galaxy∗

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DDO 216-A1: A Central Globular Cluster in a Low-luminosity Transition-type Galaxy^∗