H α morphologies of star clusters: a LEGUS study of H ii region evolution time-scales and stochasticity in low-mass clusters

Hannon, Stephen; Lee, Janice; Whitmore, Bradley C.; Chandar, Rupali; Adamo, Angela; Mobasher, Bahram; Aloisi, Alessandra; Calzetti, Daniela; Cignoni, M.; Cook, D.; Dale, Daniel A.; Deger, Sinan; Bruna, Lorenza Della; Elmegreen, D. M.; Gouliermis, Dimitrios A.; Grasha, Kathryn; Grebel, Eva K.; Herrero, A.; Hunter, Deidre A.; Johnson, K. E.; Kennicutt, Robert C.; Kim, Hwi; Sacchi, Elena; Smith, Lindsey F.; Thilker, David A.; Turner, Jordan A.; Walterbos, R. A. M.; Wofford, Aida

doi:10.1093/mnras/stz2820

Cited by 54 publications

(92 citation statements)

References 37 publications

(71 reference statements)

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“…If cloud disruption occurs soon after the onset of star formation within a cloud, then the resulting efficiency of the conversion of gas into stars will be low. This idea is supported by recent observations showing that young stellar clusters and H II regions with ages in the range 1-10 Myr have already dispersed their parent cloud (Kawamura et al 2009;Whitmore et al 2014;Hollyhead et al 2015;Corbelli et al 2017;Grasha et al 2019;Hannon et al 2019;Kruijssen et al 2019b;Chevance et al 2020). The various feedback mechanisms that may be responsible for the rapid dispersal of the natal cloud are discussed in Sect.…”

Section: Fast and Inefficient Star Formationsupporting

confidence: 64%

“…the ages of young stellar clusters and their association to nearby GMCs to estimate how quickly the feedback from the young stellar population drives GMC dispersal. For instance, Hollyhead et al (2015) and Hannon et al (2019) found that clusters in four nearby galaxies are no longer embedded once they reach ages of ∼ 4-5 Myr. For clusters in M51, Grasha et al (2019) find a GMC dispersal timescale of ∼ 6 Myr, consistent with the measurement for the same galaxy by Chevance et al (2020), who find 4.8 +2.1 −1.1 Myr.…”

Section: Feedback Timescalesmentioning

confidence: 99%

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The Molecular Cloud Lifecycle

et al. 2020

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Giant molecular clouds (GMCs) and their stellar offspring are the building blocks of galaxies. The physical characteristics of GMCs and their evolution are tightly connected to galaxy evolution. The macroscopic properties of the interstellar medium propagate into the properties of GMCs condensing out of it, with correlations between e.g. the galactic and GMC scale gas pressures, surface densities and volume densities. That way, the galactic environment sets the initial conditions for star formation within GMCs. After the onset of massive star formation, stellar feedback from e.g. photoionisation, stellar winds, and supernovae eventually contributes to dispersing the parent cloud, depositing energy, momentum and metals into the surrounding medium, thereby changing the properties of galaxies. This cycling of matter between gas and stars, governed by star formation and feedback, is therefore a major driver of galaxy evolution. Much of the recent debate has focused on the durations of the various evolutionary phases that constitute this cycle in galaxies, and what these can teach us about the physical mechanisms driving the cycle. We review results from observational, theoretical, and numerical work to build a dynamical picture of the evolutionary lifecycle of GMC evolution, star formation, and feedback in galaxies.

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Section: Fast and Inefficient Star Formationsupporting

confidence: 64%

Section: Feedback Timescalesmentioning

confidence: 99%

The Molecular Cloud Lifecycle

et al. 2020

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“…Alvensleben 2003;Groves et al 2008;Boquien et al 2010;Reines et al 2010;Pellegrini et al 2020). PHANGS-HST observations, however, benefit from the combination of HST's angular resolution and relative proximity of PHANGS galaxies, such that star clusters and surrounding H II regions can often be spatially disentangled, except for (1) crowded regions where it is still often unclear which star clusters are responsible for ionizing a given patch of H α emission and (2) clusters with compact H α morphologies (Hannon et al 2019). The YGGDRASIL tracks with zero covering fraction (i.e.…”

Section: Single-aged Stellar Population Models and Nebular Emissionmentioning

confidence: 99%

“…The stellar population will also be fainter than a higher mass population which fully populates the IMF. This effect is called sampling stochasticity and it results in a broad range of possible luminosities and colours for these low-mass clusters (Barbaro & Bertelli 1977;Girardi & Bica 1993;Lançon & Mouhcine 2000;Bruzual 2002;Cerviño & Luridiana 2006;Deveikis et al 2008;Fouesneau et al 2012;Hannon et al 2019). In colour-colour space, clusters, which may be stochastically sampling the IMF, can be found in the region bluer in V−I than the SSP tracks at 1-5 Myr.…”

Section: Stochasticity In Sampling the Imfmentioning

confidence: 99%

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PHANGS–HST: star cluster spectral energy distribution fitting with cigale

Turner

Dale

Lee

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The sensitivity and angular resolution of photometric surveys executed by the Hubble Space Telescope (HST) enable studies of individual star clusters in galaxies out to a few tens of megaparsecs. The fitting of spectral energy distributions (SEDs) of star clusters is essential for measuring their physical properties and studying their evolution. We report on the use of the publicly available Code Investigating GALaxy Emission (cigale) SED fitting package to derive ages, stellar masses, and reddenings for star clusters identified in the Physics at High Angular resolution in Nearby GalaxieS–HST (PHANGS–HST) survey. Using samples of star clusters in the galaxy NGC 3351, we present results of benchmark analyses performed to validate the code and a comparison to SED fitting results from the Legacy Extragalactic Ultraviolet Survey. We consider procedures for the PHANGS–HST SED fitting pipeline, e.g. the choice of single stellar population models, the treatment of nebular emission and dust, and the use of fluxes versus magnitudes for the SED fitting. We report on the properties of clusters in NGC 3351 and find, on average, the clusters residing in the inner star-forming ring of NGC 3351 are young (<10 Myr) and massive (105 M⊙) while clusters in the stellar bulge are significantly older. Cluster mass function fits yield β values around −2, consistent with prior results with a tendency to be shallower at the youngest ages. Finally, we explore a Bayesian analysis with additional physically motivated priors for the distribution of ages and masses and analyse the resulting cluster distributions.

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Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE

Bruna

Adamo

Boquien

et al. 2021

A&A

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Context. Feedback from massive stars affects the interstellar medium (ISM) from the immediate surroundings of the stars (parsec scales) to galactic (kiloparsec) scales. High-spatial resolution studies of H II regions are critical to investigate how this mechanism operates. Aims. We study the ionised ISM in NGC 7793 with the MUSE instrument at ESO Very Large Telescope (VLT), over a field of view (FoV) of ∼2 kpc2 and at a spatial resolution of ∼10 pc. The aim is to link the physical conditions of the ionised gas (reddening, ionisation status, abundance measurements) within the spatially resolved H II regions to the properties of the stellar populations producing Lyman continuum photons. Methods. The analysis of the MUSE dataset, which provides a map of the ionised gas and a census of Wolf Rayet stars, is complemented with a sample of young star clusters (YSCs) and O star candidates observed with the Hubble Space Telescope (HST) and of giant molecular clouds traced in CO(2–1) emission with the Atacama Large Millimeter/submillimeter Array (ALMA). We estimated the oxygen abundance using a temperature-independent strong-line method. We determined the observed total amount of ionising photons (Q(H0)) from the extinction corrected Hα luminosity. This estimate was then compared to the expected Q(H0) obtained by summing the contributions of YSCs and massive stars. The ratio of the two values gives an estimate for the escape fraction (fesc) of photons in the region of interest. We used the [S II]/[O III] ratio as a proxy for the optical depth of the gas and classified H II regions into ionisation bounded, or as featuring channels of optically thin gas. We compared the resulting ionisation structure with the computed fesc. We also investigated the dependence of fesc on the age spanned by the stellar population in each region. Results. We find a median oxygen abundance of 12 + log(O/H) ∼ 8.37, with a scatter of 0.25 dex, which is in agreement with previous estimates for our target. We furthermore observe that the abundance map of H II regions is rich in substructures, surrounding clusters and massive stars, although clear degeneracies with photoionisation are also observed. From the population synthesis analysis, we find that YSCs located in H II regions have a higher probability of being younger and less massive as well as of emitting a higher number of ionising photons than clusters in the rest of the field. Overall, we find fesc,HII = 0.67−0.12+0.08 for the population of H II regions. We also conclude that the sources of ionisation observed within the FoV are more than sufficient to explain the amount of diffuse ionised gas (DIG) observed in this region of the galaxy. We do not observe a systematic trend between the visual appearance of H II regions and fesc, pointing to the effect of 3D geometry in the small sample probed.

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H α morphologies of star clusters: a LEGUS study of H ii region evolution time-scales and stochasticity in low-mass clusters

Cited by 54 publications

References 37 publications

The Molecular Cloud Lifecycle

The Molecular Cloud Lifecycle

PHANGS–HST: star cluster spectral energy distribution fitting with cigale

Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE

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