On how leakage can affect the star formation rate estimation using Hα luminosity

Relaño, M.; Kennicutt, Robert C.; Eldridge, J. J.; Lee, Janice; Verley, S.

doi:10.1111/j.1365-2966.2012.21107.x

Cited by 46 publications

(41 citation statements)

References 66 publications

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“…Modelling effects of IMF variation using Hα or Hβ to UV flux ratios have strong dependence on the assumed SFH and dust extinction of the galaxies and is only sensitive to the upper end of the high mass IMF. Apart from IMF variation (Boselli et al 2009;Meurer et al 2009;Pflamm-Altenburg et al 2009), stochasticity in SFH (Boselli et al 2009;Fumagalli et al 2011;Guo et al 2016), non-constant SFHs (Weisz et al 2012), and Lyman leakage (Relaño et al 2012) can provide viable explanations to describe offsets between expected Balmer line to UV flux ratios and observed values. Kauffmann (2014) used SFRs derived via multiple nebular emission line analysis with the 4000Å break and Hδ A absorption to probe the recent SFHs of SDSS galaxies with log 10 (M * /M ) < 10 and infer possibilities for IMF variation.…”

Section: Investigating the Imf With Hα Emissionmentioning

confidence: 99%

ZFIRE: using Hα equivalent widths to investigate the in situ initial mass function at z ∼ 2

Nanayakkara

Glazebrook

Kacprzak

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We use the ZFIRE a survey to investigate the high mass slope of the initial mass function (IMF) for a mass-complete (log 10 (M * /M ) ∼ 9.3) sample of 102 star-forming galaxies at z ∼ 2 using their Hα equivalent widths (Hα-EW) and rest frame optical colours. We compare dust-corrected Hα-EW distributions with predictions of star-formation histories (SFH) from PEGASE.2 and Starburst99 synthetic stellar population models. We find an excess of high Hα-EW galaxies that are up to 0.3-0.5 dex above the model-predicted Salpeter IMF locus and the Hα-EW distribution is much broader (10-500Å) than can easily be explained by a simple monotonic SFH with a standard Salpeter-slope IMF. Though this discrepancy is somewhat alleviated when it is assumed that there is no relative attenuation difference between stars and nebular lines, the result is robust against observational biases, and no single IMF (i.e. non-Salpeter slope) can reproduce the data. We show using both spectral stacking and Monte Carlo simulations that starbursts cannot explain the EW distribution. We investigate other physical mechanisms including models with variations in stellar rotation, binary star evolution, metallicity, and the IMF upper-mass cutoff. IMF variations and/or highly rotating extreme metal poor stars (Z∼ 0.1Z ) with binary interactions are the most plausible explanations for our data. If the IMF varies, then the highest Hα-EWs would require very shallow slopes (Γ > −1.0) with no one slope able to reproduce the data. Thus, the IMF would have to vary stochastically. We conclude that the stellar populations at z 2 show distinct differences from local populations and there is no simple physical model to explain the large variation in Hα-EWs at z ∼ 2.

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Section: Investigating the Imf With Hα Emissionmentioning

confidence: 99%

ZFIRE: using Hα equivalent widths to investigate the in situ initial mass function at z ∼ 2

Nanayakkara

Glazebrook

Kacprzak

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Leakage of ionising photons from galaxies is likely negligible, at the level of a few percent or less (e.g., Heckman et al 2011), although the jury is still out in the case of low-mass, low-density galaxies (Hunter et al 2010;Pellegrini et al 2012). Starforming regions within galaxies tend, on the other hand, to be leaky, and lose about 25%-40% of their ionising photons (see recent work by Pellegrini et al 2012;Relaño et al 2012;Crocker et al 2012). Thus, the use of ionising photon tracers for local SFRs may be biased downwards by about 1/3 of their true value because of this effect.…”

Section: Indicators Based On Ionised Gas Emissionmentioning

confidence: 99%

Star formation rate indicators

Calzetti¹

2013

Secular Evolution of Galaxies

199

191

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If we are to develop a comprehensive and predictive theory of galaxy formation and evolution, it is essential that we obtain an accurate assessment of how and when galaxies assemble their stellar populations, and how this assembly varies with environment. There is strong observational support for the hierarchical assembly of galaxies, but by definition the dwarf galaxies we see today are not the same as the dwarf galaxies and proto-galaxies that were disrupted during the assembly. Our only insight into those disrupted building blocks comes from sifting through the resolved field populations of the surviving giant galaxies to reconstruct the star formation history, chemical evolution, and kinematics of their various structures. To obtain the detailed distribution of stellar ages and metallicities over the entire life of a galaxy, one needs multi-band photometry reaching solar-luminosity main sequence stars. The Hubble Space Telescope can obtain such data in the outskirts of Local Group galaxies. To perform these essential studies for a fair sample of the Local Universe will require observational capabilities that allow us to extend the study of resolved stellar populations to much larger galaxy samples that span the full range of galaxy morphologies, while also enabling the study of the more crowded regions of relatively nearby galaxies. With such capabilities in hand, we will reveal the detailed history of star formation and chemical evolution in the universe.

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“…However, the absorption of the hard radiation from the hot stars and subsequent re-emission as either recombination lines or dust continuum occurs far -at distances >100 pc, in the case of NGC 346-from the actual location of these stars. See also Relaño et al (2012) and Li et al (2013) for excellent discussions on how radiation escaping the local environment affects H α and dust emission as SFR tracers on small spatial scales. As a consequence, these indirect tracers which depend on absorption and re-emission, cannot be used for our present purpose, which is to relate the stellar densities with the ISM on smaller scales within the star forming complex.…”

Section: Star Formation Rate Surface Densitiesmentioning

confidence: 99%

Star formation rates from young-star counts and the structure of the ISM across the NGC 346/N66 complex in the SMC★

Hony¹,

Gouliermis²,

Galliano³

et al. 2015

Monthly Notices of the Royal Astronomical Society

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The rate at which interstellar gas is converted into stars, and its dependence on environment, is one of the pillars on which our understanding of the visible Universe is build. We present a comparison of the surface density of young stars (Σ ) and dust surface density (Σ dust ) across NGC 346 (N66) in 115 independent pixels of 6×6 pc 2 . We find a correlation between Σ and Σ dust with a considerable scatter. A power law fit to the data yields a steep relation with an exponent of 2.6±0.2. We convert Σ dust to gas surface density (Σ gas ) and Σ to star formation rate (SFR) surface densities (Σ SFR ), using simple assumptions for the gas-to-dust mass ratio and the duration of star formation. The derived total SFR (4±1·10 −3 M yr −1 ) is consistent with SFR estimated from the H α emission integrated over the H α nebula. On small scales the Σ SFR derived using H α systematically underestimates the count-based Σ SFR , by up to a factor of 10. This is due to ionizing photons escaping the area, where the stars are counted. We find that individual 36 pc 2 pixels fall systematically above integrated disc-galaxies in the Schmidt-Kennicutt diagram by on average a factor of ∼7. The NGC 346 average SFR over a larger area (90 pc radius) lies closer to the relation but remains high by a factor of ∼3. The fraction of the total mass (gas plus young stars) locked in young stars is systematically high (∼10 per cent) within the central 15 pc and systematically lower outside (2 per cent), which we interpret as variations in star formation efficiency. The inner 15 pc is dominated by young stars belonging to a centrally condensed cluster, while the outer parts are dominated by a dispersed population. Therefore, the observed trend could reflect a change of star formation efficiency between clustered and non-clustered star-formation.

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On how leakage can affect the star formation rate estimation using Hα luminosity

Cited by 46 publications

References 66 publications

ZFIRE: using Hα equivalent widths to investigate the in situ initial mass function at z ∼ 2

ZFIRE: using Hα equivalent widths to investigate the in situ initial mass function at z ∼ 2

Star formation rate indicators

Star formation rates from young-star counts and the structure of the ISM across the NGC 346/N66 complex in the SMC★

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