On the nature of the brightest globular cluster in M81

Mayya, Y. D.; Rosa-González, D.; Santiago-Cortés, M.; Rodríguez-Merino, L. H.; Vega, O.; Torres‐Papaqui, J. P.; Bressan, A.; Carrasco, L.

doi:10.1093/mnras/stt1784

Cited by 18 publications

(48 citation statements)

References 85 publications

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“…These clusters may be analogous to the metal-rich Galactic globular cluster NGC 6441, which has both red-HB stars and a tail of much hotter HB stars resulting in its relatively bright FUV emission. We note that similarly FUV bright metal-rich clusters are also observed in the Milky Way (NGC 6388 and NGC 6441), M 87 (Sohn et al 2006;Peacock et al 2017) and M 81 (GC1; Mayya et al 2013). Metal-poor globular clusters tend to host blue HB populations for standard helium abundances.…”

Section: Second Populations In M 31's Globular Clusterssupporting

confidence: 64%

Hubble Space Telescope FUV observations of M31’s globular clusters suggest a spatially homogeneous helium-enriched subpopulation

Peacock

Zepf

Maccarone

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present high spatial resolution, far ultraviolet (FUV) F140LP observations of 12 massive globular clusters in M 31 obtained using the ACS/SBC on the Hubble Space Telescope (HST). These observations resolve the cluster profiles to scales similar to their core radii and enable the study of the spatial distribution of blue and extreme horizontal branch (HB) stars, which dominate the emission in the F140LP images. We confirm that some of these clusters have excess FUV emission, suggesting additional hot populations beyond those expected by canonical single stellar populations models. We find no evidence that the hot populations are spatially distinct from the majority populations in these clusters, as would be expected if the excess FUV emission is a result of a dynamically enhanced population of extreme-HB stars. We conclude that a second population of stars with significantly enhanced helium abundance is a viable explanation for the observed FUV emission which is both bright and distributed similarly to the rest of the cluster light. Our results support the use of FUV observations as a path to characterising helium enhanced sub populations in extragalactic clusters. These M31 clusters also show a correlation such that more massive and denser clusters are relatively FUV bright. Similar to extant Milky Way results, this may indicate the degree of helium enrichment, or second population fraction increases with cluster mass.

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Section: Second Populations In M 31's Globular Clusterssupporting

confidence: 64%

Hubble Space Telescope FUV observations of M31’s globular clusters suggest a spatially homogeneous helium-enriched subpopulation

Peacock

Zepf

Maccarone

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…Following Peacock et al (2011), we limit the sample to old confirmed clusters (class 1 in Peacock et al 2010) with low extinction (with E(B − V) < 0.16) and deredden using the reddening values presented by Fan et al (2008). For optical photometry we use the catalog of Peacock et al (2010) Mayya et al (2013). We take the distance modulus of M 81, (m − M) 0 = 27.8 (Freedman et al 1994).…”

Section: Galex Observations Of Local Galaxiesmentioning

confidence: 99%

Globular clusters in the far-ultraviolet: evidence for He-enriched second populations in extragalactic globular clusters?

Peacock

Zepf

Kundu

et al. 2016

Mon. Not. R. Astron. Soc.

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We investigate the integrated far-ultraviolet (FUV) emission from globular clusters. We present new FUV photometry of M 87's clusters based on archival HST WFPC2 F170W observations. We use these data to test the reliability of published photometry based on HST STIS FUV-MAMA observations, which are now known to suffer from significant red-leak. We generally confirm these previous FUV detections, but suggest they may be somewhat fainter. We compare the FUV emission from bright (M V < −9.0) clusters in the Milky Way, M 31, M 81 and M 87 to each other and to the predictions from stellar populations models. Metal-rich globular clusters show a large spread in FUV − V, with some clusters in M 31, M 81 and M 87 being much bluer than standard predictions. This requires that some metal-rich clusters host a significant population of blue/extreme horizontal branch (HB) stars. These hot HB stars are not traditionally expected in metal-rich environments, but are a natural consequence of multiple populations in clusters -since the enriched population is observed to be He-enhanced and will therefore produce bluer HB stars, even at high metallicity. We conclude that the observed FUV emission from metal-rich clusters in M 31, M 81 and M 87 provides evidence that He-enhanced second populations, similar to those observed directly in the Milky Way, may be a ubiquitous feature of globular clusters in the local universe. Future HST FUV photometry is required to both confirm our interpretation of these archival data and provide constraints on He-enriched second populations of stars in extra-galactic globular clusters.

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“…The slit positions were selected to pass through some of the brightest stellar compact clusters in the catalogue of Santiago-Cortés, Mayya & Rosa-González (2010) for M81. These observations are part of a large-scale program dedicated to study the star formation in this galaxy (Mayya et al 2013). Here we use them to study the chemical abundances and the abundance gradient provided by H ii regions in M81.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

The oxygen abundance gradient in M81 and the robustness of abundance determinations in H ii regions

Arellano-Córdova

Rodríguez

Mayya

et al. 2015

Mon. Not. R. Astron. Soc.

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We study the sensitivity of the methods available for abundance determinations in H ii regions to potential observational problems. We compare the dispersions they introduce around the oxygen and nitrogen abundance gradients when applied to five different sets of spectra of H ii regions in the galaxy M81. Our sample contains 116 H ii regions with galactocentric distances of 3 to 33 kpc, including 48 regions observed by us with the OSIRIS long-slit spectrograph at the 10.4-m Gran Telescopio Canarias telescope. The direct method can be applied to 31 regions, where we can get estimates of the electron temperature. The different methods imply oxygen abundance gradients with slopes of −0.010 to −0.002 dex kpc −1 , and dispersions in the range 0.06-0.25 dex. The direct method produces the shallowest slope and the largest dispersion, illustrating the difficulty of obtaining good estimates of the electron temperature. Three of the strong-line methods, C, ONS, and N2, are remarkably robust, with dispersions of ∼ 0.06 dex, and slopes in the range −0.008 to −0.006 dex kpc −1 . The robustness of each method can be directly related to its sensitivity to the line intensity ratios that are more difficult to measure properly. Since the results of the N2 method depend strongly on the N/O abundance ratio and on the ionization parameter, we recommend the use of the C and ONS methods when no temperature estimates are available or when they have poor quality, although the behaviour of these methods when confronted with regions that have different properties and different values of N/O should be explored.

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On the nature of the brightest globular cluster in M81

Cited by 18 publications

References 85 publications

Hubble Space Telescope FUV observations of M31’s globular clusters suggest a spatially homogeneous helium-enriched subpopulation

Hubble Space Telescope FUV observations of M31’s globular clusters suggest a spatially homogeneous helium-enriched subpopulation

Globular clusters in the far-ultraviolet: evidence for He-enriched second populations in extragalactic globular clusters?

The oxygen abundance gradient in M81 and the robustness of abundance determinations in H ii regions

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