Measuring star formation with resolved observations: the test case of M 33

Boquien, M.; Calzetti, Daniela; Aalto, S.; Boselli, A.; Braine, J.; Buat, V.; Combes, F.; Israel, F. P.; Krämer, C.; Lord, S. D.; Relaño, M.; Rosolowsky, Erik; Stacey, G. J.; Tabatabaei, F. S.; Tak, F. F. S. van der; Werf, P. van der; Verley, S.; Xilouris, E. M.

doi:10.1051/0004-6361/201423518

Cited by 47 publications

(70 citation statements)

References 89 publications

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“…In the recent study Boquien et al (2015) came to the same conclusions based on more data in different wavelengths including FUV as well. Analysing the spatial distribution of CO/Hα peaks in M 33 Schruba et al (2010) established that the scaling relation between gas and star formation rate surface density observed at large scales does not have its direct origin in an instantaneous cloud-scale relation.…”

Section: Introductionsupporting

confidence: 56%

A Kennicutt–Schmidt relation at molecular cloud scales and beyond

Khoperskov

Vasiliev

2017

Monthly Notices of the Royal Astronomical Society

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Using N -body/gasdynamic simulations of a Milky Way-like galaxy we analyse a Kennicutt-Schmidt relation, Σ SFR ∝ Σ gas N , at different spatial scales. We simulate synthetic observations in CO lines and UV band. We adopt the star formation rate (SFR) defined in two ways: based on free fall collapse of a molecular cloud -Σ SFR, cl , and calculated by using a UV flux calibration -Σ SFR, UV . We study a KS relation for spatially smoothed maps with effective spatial resolution from molecular cloud scales to several hundred parsecs. We find that for spatially and kinematically resolved molecular clouds the Σ SFR, cl ∝ Σ gas N relation follows the power-law with index N ≈ 1.4. Using UV flux as SFR calibrator we confirm a systematic offset between the Σ SFR, UV and Σ gas distributions on scales compared to molecular cloud sizes. Degrading resolution of our simulated maps for surface densities of gas and star formation rates we establish that there is no relation Σ SFR, UV − Σ gas below the resolution ∼ 50 pc. We find a transition range around scales ∼ 50 − 120 pc, where the power-law index N increases from 0 to 1 − 1.8 and saturates for scales larger ∼ 120 pc. A value of the index saturated depends on a surface gas density threshold and it becomes steeper for higher Σ gas threshold. Averaging over scales with size of > ∼ 150 pc the power-law index N equals 1.3 − 1.4 for surface gas density threshold ∼ 5 M ⊙ pc −2 . At scales > ∼ 120 pc surface SFR densities determined by using CO data and UV flux, Σ SFR, UV /Σ SFR, cl , demonstrate a discrepancy about a factor of 3. We argue that this may be originated from overestimating (constant) values of conversion factor, star formation efficiency or UV calibration used in our analysis.

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Section: Introductionsupporting

confidence: 56%

A Kennicutt–Schmidt relation at molecular cloud scales and beyond

Khoperskov

Vasiliev

2017

Monthly Notices of the Royal Astronomical Society

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“…In early-type galaxies, this quantity drops to less than 15% Calzetti (2001). In M33, Boquien et al (2015) found 75% of star formation in a H , with only 25% in the infrared. In Figure 9, we combine our synthetic FUV flux maps to examine the fraction of obscured star formation within the PHAT footprint and compare them with corresponding observed data from GALEX and Spitzer.…”

Section: Obscured Flux and Star Formationmentioning

confidence: 94%

“…A number of studies have examined how interpreting the observed galaxy flux is affected by some of these assumptions (e.g., Lee et al 2009;Chomiuk & Povich 2011;Weisz et al 2012;Wilkins et al 2012;Johnson et al 2013;Boquien et al 2014;Simones et al 2014, among many others). In a recent paper, Boquien et al (2015) analyzed the scale dependence of SFR tracers. They found broad agreement between tracers on ∼1 kpc scales, presumably because variations between regions of active star formation and diffuse emission (i.e., from older stellar populations) have averaged out.…”

Section: Introductionmentioning

confidence: 99%

The Panchromatic Hubble Andromeda Treasury. Xvii. Examining Obscured Star Formation With Synthetic Ultraviolet Flux Maps in M31*

Lewis

Simones

Johnson

et al. 2017

ApJ

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We present synthetic far-and near-ultraviolet (FUV and NUV) maps of M31, both with and without dust reddening. These maps were constructed from spatially resolved star formation histories (SFHs) derived from optical Hubble Space Telescope imaging of resolved stars, taken as part of the Panchromatic Hubble Andromeda Treasury program. We use stellar population synthesis modeling to generate synthetic UV maps with a spatial resolution of ∼100 pc (∼24 arcsec), projected. When reddening is included, these maps reproduce all of the main morphological features in the GALEX imaging, including rings and large star-forming complexes. The predicted UV flux also agrees well with the observed flux, with median ratios between the modeled and observed flux of in the FUV and NUV, respectively. This agreement is particularly impressive given that we used only optical photometry to construct these UV maps. Having verified the synthetic reddened maps, we use the dust-free maps to examine properties of obscured flux and star formation. We compare our dust-free and reddened maps of FUV flux with the observed GALEX FUV flux and FUV + 24 μm flux to examine the fraction of obscured flux. We find that the maps of synthetic flux require that ∼90% of the FUV flux in M31 is obscured by dust, while the GALEX -based methods suggest that ∼70% of the FUV flux is absorbed by dust. This 30% increase in the estimate of the obscured flux is driven by significant differences between the dust-free synthetic FUV flux and that derived when correcting the observed FUV flux for dust absorption with 24 μm emission observations. The difference is further illustrated when we compare the SFRs derived from the FUV + 24 μm flux with the 100 Myr average SFR from the CMD-based SFHs. We find that the 24 μm corrected FUV flux underestimates the SFR by a factor of 2.3-2.5, depending on the chosen calibration. This discrepancy could be reduced by allowing for variability in the weight applied to the 24 μm data, as has been recently suggested in the literature.

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“…deg. The PACS 70 µm image was obtained as a follow-up open time cycle 2 programme, on 25 June 2012 in two orthogonal directions and five repetitions to achieve better sensitivity (Boquien et al 2015). The PACS reduction was performed using the mapmaking software Scanamorphos (Roussel 2013) as described in Boquien et al (2011).…”

Section: Herschelmentioning

confidence: 99%

Millimeter and submillimeter excess emission in M 33 revealed byPlanckand LABOCA

Hermelo

Relaño

Lisenfeld

et al. 2016

A&A

Self Cite

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Context. Previous studies have shown the existence of an excess of emission at submillimeter (submm) and millimeter (mm) wavelengths in the spectral energy distribution (SED) of many low-metallicity galaxies. The so-called "submm excess", whose origin remains unknown, challenges our understanding of the dust properties in low-metallicity environments. Aims. The goal of the present study is to model separately the emission from the star forming (SF) component and the emission from the diffuse interstellar medium (ISM) in the nearby spiral galaxy M 33 in order to determine whether both components can be well fitted using radiation transfer models or whether there is an excess of submm emission associated with one or both of them. Methods. We decomposed the observed SED of M 33 into its SF and diffuse components. Mid-infrared (MIR) and far-infrared (FIR) fluxes were extracted from Spitzer and Herschel data. At submm and mm wavelengths, we used ground-based observations from APEX to measure the emission from the SF component and data from the Planck space telescope to estimate the diffuse emission. Both components were separately fitted using radiation transfer models based on standard dust properties (i.e., emissivity index β = 2) and a realistic geometry. The large number of previous studies helped us to estimate the thermal radio emission and to constrain an important part of the input parameters of the models. Both modeled SEDs were combined to build the global SED of M 33. In addition, the radiation field necessary to power the dust emission in our modeling was compared with observations from GALEX, Sloan, and Spitzer. Results. Our modeling is able to reproduce the observations at MIR and FIR wavelengths, but we found a strong excess of emission at submm and mm wavelengths where the model expectations severely underestimate the LABOCA and Planck fluxes. We also found that the ultraviolet (UV) radiation escaping the galaxy is 70% higher than the model predictions. From the total mass of dust derived from our modeling and the mass of atomic and molecular gas measured with the VLA and the IRAM 30 m telescope, we determined a gas-to-dust mass ratio G dust ∼ 100, significantly lower than the value expected from the subsolar metallicity of M 33. Conclusions. We discussed different hypotheses to explain the discrepancies found in our study (i.e., excess of emission at submm and mm wavelengths, deficit of UV attenuation, and abnormally low value of G dust ), concluding that different dust properties in M 33 is the most plausible explanation.

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Measuring star formation with resolved observations: the test case of M 33

Cited by 47 publications

References 89 publications

A Kennicutt–Schmidt relation at molecular cloud scales and beyond

A Kennicutt–Schmidt relation at molecular cloud scales and beyond

The Panchromatic Hubble Andromeda Treasury. Xvii. Examining Obscured Star Formation With Synthetic Ultraviolet Flux Maps in M31*

Millimeter and submillimeter excess emission in M 33 revealed byPlanckand LABOCA

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