HST/ACS color-magnitude diagrams of candidate intermediate-age M 31 globular clusters

Perina, S.; Galleti, S.; Pecci, F. Fusi; Bellazzini, M.; Federici, L.; Buzzoni, A.

doi:10.1051/0004-6361/201117028

Cited by 23 publications

(37 citation statements)

References 76 publications

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“…At least some of the programs which targeted M31 GCs with HST (e.g. Ajhar et al 1996;Meylan et al 2001;Brown et al 2004;Barmby et al 2007;Perina et al 2011;Tanvir et al 2012) favored massive clusters but, to our knowledge, none of them used the presence of an LMXB as a selection criterion. 4 In this work we did not search the HST archive for additional non-LMXB clusters, and the LMXB and non-LMXB cluster samples do differ in both galactocentric position and metallicity (see Figure 2).…”

Section: Cluster Sample and Archival Datamentioning

confidence: 99%

M31 Globular Cluster Structures and the Presence of X-Ray Binaries

Agar¹,

Barmby²

2013

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The Andromeda galaxy, M31, has several times the number of globular clusters found in the Milky Way. It contains a correspondingly larger number of low mass X-ray binaries (LMXBs) associated with globular clusters, and as such can be used to investigate the cluster properties which lead to X-ray binary formation. The best tracer of the spatial structure of M31 globulars is the high-resolution imaging available from the Hubble Space Telescope (HST), and we have used HST data to derive structural parameters for 29 LMXB-hosting M31 globular clusters. These measurements are combined with structural parameters from the literature for a total of 41 (of 50 known) LMXB clusters and a comparison sample of 65 non-LMXB clusters. Structural parameters measured in blue bandpasses are found to be slightly different (smaller core radii and higher concentrations) than those measured in red bandpasses; this difference is enhanced in LMXB clusters and could be related to stellar population differences. Clusters with LMXBs show higher collision rates for their mass compared to clusters without LMXBs and collision rates estimated at the core radius show larger offsets than rates estimated at the half-light radius. These results are consistent with the dynamical formation scenario for LMXBs. A logistic regression analysis finds that, as expected, the probability of a cluster hosting an LMXB increases with increasing collision rate and proximity to the galaxy center. The same analysis finds that probability of a cluster hosting an LMXB decreases with increasing cluster mass at a fixed collision rate, although we caution that this could be due to sample selection effects. Metallicity is found to be a less important predictor of LMXB probability than collision rate, mass, or distance, even though LMXB clusters have a higher metallicity on average. This may be due to the interaction of location and metallicity: a sample of M31 LMXBs with a greater range in galactocentric distance would likely contain more metal-poor clusters and make it possible to disentangle the two effects.

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Section: Cluster Sample and Archival Datamentioning

confidence: 99%

M31 Globular Cluster Structures and the Presence of X-Ray Binaries

Agar¹,

Barmby²

2013

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“…Those clusters whose HB morphology was classified as red or blue based on CMD studies are employed in this work for a comparison with spectroscopy. Eleven GCs with blue HB stars and 6 GCs with red HB stars are taken from the combined list of GC CMDs by Rich et al (2005) and Perina et al (2009Perina et al ( , 2011.…”

Section: The M31 Globular Cluster Samplementioning

confidence: 99%

Nonlinear Color-Metallicity Relations of Globular Clusters. V. Nonlinear Absorption-Line Index Versus Metallicity Relations and Bimodal Index Distributions of M31 Globular Clusters

Kim

Yoon

Chung

et al. 2013

ApJ

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Recent spectroscopy on the globular cluster (GC) system of M31 with unprecedented precision witnessed a clear bimodality in absorption-line index distributions of old GCs. Such division of extragalactic GCs, so far asserted mainly by photometric color bimodality, has been viewed as the presence of merely two distinct metallicity subgroups within individual galaxies and forms a critical backbone of various galaxy formation theories. Given that spectroscopy is a more detailed probe into stellar population than photometry, the discovery of index bimodality may point to the very existence of dual GC populations. However, here we show that the observed spectroscopic dichotomy of M31 GCs emerges due to the nonlinear nature of metallicity-to-index conversion and thus one does not necessarily have to invoke two separate GC subsystems. We take this as a close analogy to the recent view that metallicity-color nonlinearity is primarily responsible for observed GC color bimodality. We also demonstrate that the metallicity-sensitive magnesium line displays non-negligible metallicity-index nonlinearity and Balmer lines show rather strong nonlinearity. This gives rise to bimodal index distributions, which are routinely interpreted as bimodal metallicity distributions, not considering metallicityindex nonlinearity. Our findings give a new insight into the constitution of M31's GC system, which could change much of the current thought on the formation of GC systems and their host galaxies.

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“…Lee et al 2000; Schiavon et al 2004; Koleva et al 2008; Ocvirk 2010; Percival & Salaris 2011; Xin et al 2011). Examples for such ‘age bias’ are the metal‐poor Galactic GCs NGC 3201 and 5024 featuring BHBs, whose spectroscopically derived age (from Hβ versus Mg2) is ∼8 Gyr (Perina et al 2011), while their ages from deep HST colour–magnitude diagram (CMD) fitting is ≳12 Gyr (Dotter et al 2010). Furthermore, nearly all massive ( mag) Galactic GCs have hot HBs (e.g.…”

Section: Vik′ Colour Age and Metallicity Distributions Of Globularmentioning

confidence: 99%

New insights into the star formation histories of candidate intermediate-age early-type galaxies from K′-band imaging of globular clusters

Georgiev¹,

Goudfrooij²,

Puzia³

2012

Monthly Notices of the Royal Astronomical Society

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We investigate the age and metallicity distributions of bright globular clusters (GCs) in the candidate intermediate‐age early‐type galaxies NGC 3610, 584 and 3377 using a combination of new Gemini’s Near InfraRed Imager and Spectrometer K′‐band imaging and existing optical VI photometry from Hubble Space Telescope data. The V−I versus I−K′ colour–colour diagram is found to break the age–metallicity degeneracy present in optical colours and spectroscopy, as I−K′ primarily measures a population’s metallicity. In addition, it is relatively insensitive to the effect of hot horizontal branch (HB) stars that are known to be present in massive old GCs. By interpolation between simple stellar population model tracks, we derive photometric cluster ages, metallicities and masses. In general, we find that ‘metal‐poor’ GCs with [Z/H] ≲−0.7 dex are older than more metal rich GCs. For the most massive GCs () in NGC 3610 with available spectroscopic data, the photometric ages are older by ∼2 Gyr, and this difference is more pronounced for the metal‐poor GCs. However, the photometric and spectroscopic metallicities are in good agreement. We suggest that this indicates the presence of a hot HB in these massive clusters, which renders spectroscopic ages from Balmer line strengths to be underestimated. To support this suggestion, we show that all Galactic GCs with feature hot HBs, except 47 Tuc. Using a recent observational relation between the luminosity of the most massive GC and the galaxies’ star formation rate (SFR) at a given age, we find that the galaxies’ peak SFR was attained at the epoch of the formation of the oldest (metal‐poor) GCs. The age and [Z/H] distributions of the metal‐rich GCs are broad, indicating prolonged galaxy star formation histories. The peak ages of the metal‐rich GCs in the sample galaxies NGC 3610, 584 and 3377 are 3.7, 5.9 and 8.9 Gyr, respectively. The peak value of the age and metallicity distributions of the GCs is correlated with the host galaxies’ luminosity‐weighted age and metallicity, respectively, indicating that the GCs can indeed be used as relevant proxies of the star formation histories of galaxies.

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HST/ACS color-magnitude diagrams of candidate intermediate-age M 31 globular clusters

Cited by 23 publications

References 76 publications

M31 Globular Cluster Structures and the Presence of X-Ray Binaries

M31 Globular Cluster Structures and the Presence of X-Ray Binaries

Nonlinear Color-Metallicity Relations of Globular Clusters. V. Nonlinear Absorption-Line Index Versus Metallicity Relations and Bimodal Index Distributions of M31 Globular Clusters

New insights into the star formation histories of candidate intermediate-age early-type galaxies from K′-band imaging of globular clusters

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