The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

Grasha, Kathryn; Calzetti, Daniela; Adamo, Angela; Kim, Hwi; Elmegreen, Bruce G.; Gouliermis, D. A.; Dale, Daniel A.; Fumagalli, Michele; Grebel, Eva K.; Johnson, K. E.; Kahre, L.; Kennicutt, Robert C.; Messa, Matteo; Pellerin, Anne; Ryon, J. E.; Smith, L. J.; Shabani, F.; Thilker, David A.; Úbeda, Leonardo

doi:10.3847/1538-4357/aa6f15

Cited by 78 publications

(100 citation statements)

References 66 publications

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“…clustered young star clusters and associations) considering the comparable size as observed for local galaxies (e.g. Grasha et al 2017). While the non-ionizing UV photons can escape from most of the star-forming regions, the ionizing photons can only escape from the ones with low H I column density "cavities" in the surrounding ISM.…”

Section: Physical Mechanisms Of the Escaping Lyc Of Ion1mentioning

confidence: 93%

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

Giavalisco

Vanzella³

et al. 2020

ApJ

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We report on the HST detection of the Lyman-continuum (LyC) radiation emitted by a galaxy at redshift z = 3.794, dubbed Ion1 (Vanzella et al. 2012). The LyC from Ion1 is detected at restframe wavelength λλ 820∼890Å with HST WFC3/UVIS in the F410M band (m 410 = 27.60 ± 0.36 m AB , peak SNR = 4.17 in a circular aperture with radius r = 0.12") and at λλ 700∼830Å with the VLT/VIMOS in the U-band (m U = 27.84 ± 0.19 m AB , peak SNR = 6.7 with a r = 0.6" aperture). A 20-hr VLT/VIMOS spectrum shows low-and high-ionization interstellar metal absorption lines, the P-Cygni profile of C IV and Lyα in absorption. The latter spectral feature differs from what observed in known LyC emitters, which show strong Lyα emission. An HST far-UV color map reveals that the LyC emission escapes from a region of the galaxy that is bluer than the rest, presumably because of lower dust obscuration. The F410M image shows that the centroid of the LyC emission is offset from the centroid of the non-ionizing UV emission by 0.12"±0.03", corresponding to 0.85±0.21 kpc (physical), and that its morphology is likely moderately resolved. These morphological characteristics favor a scenario where the LyC photons produced by massive stars escape from low H I columndensity "cavities" in the ISM, possibly carved by stellar wind and/or supernova. We also collect the VIMOS U-band images of a sample of 107 Lyman-break galaxies with spectroscopic redshifts at 3.40 < z < 3.95, i.e. sampling the LyC, and stack them with inverse-variance weights. No LyC emission is detected in the stacked image, resulting in a 32.5 m AB flux limit (1σ) and an upper limit of absolute LyC escape fraction f abs esc ≤ 0.63%. LyC emitters like Ion1 are very likely at the bright-end of the LyC luminosity function.

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Section: Physical Mechanisms Of the Escaping Lyc Of Ion1mentioning

confidence: 93%

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

Giavalisco

Vanzella³

et al. 2020

ApJ

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“…Star formation proceeds in cold (T < 15, 000K), dense (n th > 10.3cm −3 ) gas and is implemented as described in Stinson et al (2006). In Buck et al (2019c) it was shown that in these kind of simulations only a high value of n th > 10cm −3 (see also Dutton et al 2019, for an extended parameter study) is able to reproduce the clustering of young star clusters observed in the Legacy Extragalactic UV Survey (LEGUS) (Calzetti et al 2015;Grasha et al 2017).…”

Section: Cosmological Zoom-in Simulationsmentioning

confidence: 99%

On the origin of the chemical bimodality of disc stars: a tale of merger and migration

Buck

2019

Monthly Notices of the Royal Astronomical Society

149

132

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The Milky Way's stellar disk exhibits a bimodality in the [Fe/H] vs. [α/Fe] plane, showing a distinct high-α and low-α sequence whose origin is still under debate. We examine the [Fe/H]-[α/Fe] abundance plane in cosmological hydrodynamical simulations of Milky Way like galaxies from the NIHAO-UHD project and show that the bimodal α-sequence is a generic consequence of a gas-rich merger at some time in the Galaxy's evolution. The high-α sequence evolves first in the early galaxies, extending to high metallicities, while it is the low-α sequence that is formed after the gas-rich merger. The merger brings in fresh metal-poor gas diluting the interstellar medium's metallicity while keeping the [α/Fe] abundance almost unchanged. The kinematic, structural and spatial properties of the bimodal α-sequence in our simulations reproduces that of observations. In all simulations, the high-α disk is old, radially concentrated towards the galaxy's center and shows large scale heights. In contrast, the low-α disk is younger, more radially extended and concentrated to the disk mid-plane. Our results show that the abundance plane is well described by these two populations that have been distributed radially across the disk by migration: at present-day in the solar neighbourhood, low-α stars originate from both the inner and outer disk while high-α stars have all migrated from the inner disk. We show that age dating the stars in the [Fe/H]-[α/Fe] plane can constrain the time of the low-α sequence forming merger and conclude that α-bimodality is likely a not uncommon feature of disk galaxies.

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“…The visual inspection step, either by humans or by a trained algorithm, is the only way to reliably remove non-cluster interlopers The black outline shows the UVIS footprint. Cluster classifications are based off of morphology and our morphological cluster classification is a good approximation to also a dynamical classification (Adamo et al 2017;Grasha et al 2017a;Ryon et al 2017). The typical ages of class 1 clusters are older and show median ages of 90 Myr than the median age of 20 Myr for the class 2 clusters.…”

Section: Visual Inspection and Star Cluster Classificationmentioning

confidence: 99%

“…Thus, M 51 is an excellent benchmark to investigate the clustering nature of star clusters as a function of galactocentric distance in a grand-design spiral, in addition to the connection of the young stellar clusters with maps of molecular clouds, both investigated in this paper. The former has been the main topic of two previous papers (Grasha et al 2015(Grasha et al , 2017a, but not yet performed in such a cluster-rich galaxy to explore trends at sub-galactic scales.…”

Section: Introductionmentioning

confidence: 99%

The spatial relation between young star clusters and molecular clouds in M51 with LEGUS

Grasha

Calzetti

Adamo

et al. 2018

Monthly Notices of the Royal Astronomical Society

Self Cite

108

105

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We present a study correlating the spatial locations of young star clusters with those of molecular clouds in NGC 5194, in order to investigate the timescale over which clusters separate from their birth clouds. The star cluster catalogues are from the Legacy ExtraGalactic UV Survey (LEGUS) and the molecular clouds from the Plateau de Bure Interefrometer Arcsecond Whirpool Survey (PAWS). We find that younger star clusters are spatially closer to molecular clouds than older star clusters. The median ages for clusters associated with clouds is 4 Myr whereas it is 50 Myr for clusters that are sufficiently separated from a molecular cloud to be considered unassociated. After ∼6 Myr, the majority of the star clusters lose association with their molecular gas. Younger star clusters are also preferentially located in stellar spiral arms where they are hierarchically distributed in kpc-size regions for 50-100 Myr before dispersing. The youngest star clusters are more strongly clustered, yielding a two-point correlation function with α = −0.28 ± 0.04, than the GMCs (α = −0.09 ± 0.03) within the same PAWS field. However, the clustering strength of the most massive GMCs, supposedly the progenitors of the young clusters for a star formation efficiency of a few percent, is comparable (α = −0.35 ± 0.05) to that of the clusters. We find a galactocentric-dependence for the coherence of star formation, in which clusters located in the inner region of the galaxy reside in smaller star-forming complexes and display more homogeneous distributions than clusters further from the centre. This result suggests a correlation between the survival of a cluster complex and its environment.

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The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

Cited by 78 publications

References 66 publications

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

On the origin of the chemical bimodality of disc stars: a tale of merger and migration

The spatial relation between young star clusters and molecular clouds in M51 with LEGUS

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