Do spiral arms enhance star formation efficiency?

Miguel Querejeta; Adam K. Leroy; Sharon E. Meidt; Eva Schinnerer; Francesco Belfiore; Eric Emsellem; Ralf S. Klessen; Jiayi Sun; Mattia Sormani; Ivana Bešlic; Yixian Cao; Mélanie Chevance; Dario Colombo; Daniel A. Dale; Santiago García-Burillo; Simon C. O. Glover; Kathryn Grasha; Brent Groves; Eric W. Koch; Lukas Neumann; Hsi-An Pan; Ismael Pessa; Jérôme Pety; Francesca Pinna; Lise Ramambason; Alessandro Razza; Andrea Romanelli; Erik Rosolowsky; Marina Ruiz-García; Patricia Sánchez-Blázquez; Rowan Smith; Sophia Stuber; Leonardo Ubeda; Antonio Usero; Thomas G. Williams

doi:10.1051/0004-6361/202449733

Do spiral arms enhance star formation efficiency?

Miguel Querejeta, Adam K. Leroy, Sharon E. Meidt, Eva Schinnerer, Francesco Belfiore, Eric Emsellem, Ralf S. Klessen, Jiayi Sun, Mattia Sormani, Ivana Bešlic, Yixian Cao, Mélanie Chevance, Dario Colombo, Daniel A. Dale, Santiago García-Burillo, Simon C. O. Glover, Kathryn Grasha, Brent Groves, Eric W. Koch, Lukas NeumannHsi-An Pan, Ismael Pessa, Jérôme Pety, Francesca Pinna, Lise Ramambason, Alessandro Razza, Andrea Romanelli, Erik Rosolowsky, Marina Ruiz-García, Patricia Sánchez-Blázquez, Rowan Smith, Sophia Stuber, Leonardo Ubeda, Antonio Usero, Thomas G. Williams

School of Physics and Astronomy

Research output: Contribution to journal › Article › peer-review

Abstract

Spiral arms, as those of our own Milky Way, are some of the most spectacular features in disc galaxies. It has been argued that star formation should proceed more efficiently in spiral arms as a result of gas compression. Yet, observational studies have so far yielded contradictory results. Here, we examine arm/interarm surface density contrasts at ∼100 pc resolution in 28 spiral galaxies from the PHANGS survey. We find that the arm/interarm contrast in stellar mass surface density (Σ_⋆) is very modest, typically a few tens of percent. This is much smaller than the contrasts measured for molecular gas (Σ_mol) or star formation rate (Σ_SFR) surface density, which typically reach a factor of ∼2 − 3. However, Σ_mol and Σ_SFR contrasts show a significant correlation with the enhancement in Σ_⋆, suggesting that the small stellar contrast largely dictates the stronger accumulation of gas and star formation. All these contrasts increase for grand-design spirals compared to multi-armed and flocculent systems (and for galaxies with high stellar mass). The median star formation efficiency (SFE) of the molecular gas is 16% higher in spiral arms than in interarm regions, with a large scatter, and the contrast increases significantly (median SFE contrast 2.34) for regions of particularly enhanced stellar contrast (Σ_⋆ contrast > 1.97). The molecular-to-atomic gas ratio (Σ_mol/Σ_atom) is higher in spiral arms, pointing to a transformation of atomic to molecular gas. As a consequence, the total gas contrast (Σ_mol + Σ_atom) slightly drops compared to Σ_mol (median 4% lower, working at ∼kpc resolution), while the SFE contrast increases when we include atomic gas (median 8% higher than for Σ_mol). The contrasts show important fluctuations with galactocentric radius. We confirm that our results are robust against a number of effects, such as spiral mask width, tracers, resolution, and binning. In conclusion, the boost in the SFE of molecular gas in spiral arms is generally modest or absent, except for locations with exceptionally large stellar contrasts.

Original language	English
Article number	A293
Number of pages	26
Journal	Astronomy & Astrophysics
Volume	687
Early online date	23 Jul 2024
DOIs	https://doi.org/10.1051/0004-6361/202449733
Publication status	Published - Jul 2024

Keywords

Galaxies: spiral
Galaxies: star formation
Galaxies: structure

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Copyright © The Authors 2024. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article is published in open access under the Subscribe to Open model.
Final published version, 7.05 MBLicence: CC BY

https://arxiv.org/abs/2405.05364Licence: CC BY

Cite this

Querejeta, M., Leroy, A. K., Meidt, S. E., Schinnerer, E., Belfiore, F., Emsellem, E., Klessen, R. S., Sun, J., Sormani, M., Bešlic, I., Cao, Y., Chevance, M., Colombo, D., Dale, D. A., García-Burillo, S., Glover, S. C. O., Grasha, K., Groves, B., Koch, E. W., ... Williams, T. G. (2024). Do spiral arms enhance star formation efficiency? Astronomy & Astrophysics, 687, Article A293. https://doi.org/10.1051/0004-6361/202449733

@article{a2e74aae52b54454afd0b3c28095bd47,

title = "Do spiral arms enhance star formation efficiency?",

abstract = "Spiral arms, as those of our own Milky Way, are some of the most spectacular features in disc galaxies. It has been argued that star formation should proceed more efficiently in spiral arms as a result of gas compression. Yet, observational studies have so far yielded contradictory results. Here, we examine arm/interarm surface density contrasts at ∼100 pc resolution in 28 spiral galaxies from the PHANGS survey. We find that the arm/interarm contrast in stellar mass surface density (Σ⋆) is very modest, typically a few tens of percent. This is much smaller than the contrasts measured for molecular gas (Σmol) or star formation rate (ΣSFR) surface density, which typically reach a factor of ∼2 − 3. However, Σmol and ΣSFR contrasts show a significant correlation with the enhancement in Σ⋆, suggesting that the small stellar contrast largely dictates the stronger accumulation of gas and star formation. All these contrasts increase for grand-design spirals compared to multi-armed and flocculent systems (and for galaxies with high stellar mass). The median star formation efficiency (SFE) of the molecular gas is 16% higher in spiral arms than in interarm regions, with a large scatter, and the contrast increases significantly (median SFE contrast 2.34) for regions of particularly enhanced stellar contrast (Σ⋆ contrast > 1.97). The molecular-to-atomic gas ratio (Σmol/Σatom) is higher in spiral arms, pointing to a transformation of atomic to molecular gas. As a consequence, the total gas contrast (Σmol + Σatom) slightly drops compared to Σmol (median 4% lower, working at ∼kpc resolution), while the SFE contrast increases when we include atomic gas (median 8% higher than for Σmol). The contrasts show important fluctuations with galactocentric radius. We confirm that our results are robust against a number of effects, such as spiral mask width, tracers, resolution, and binning. In conclusion, the boost in the SFE of molecular gas in spiral arms is generally modest or absent, except for locations with exceptionally large stellar contrasts.",

keywords = "Galaxies: spiral, Galaxies: star formation, Galaxies: structure",

author = "Miguel Querejeta and Leroy, {Adam K.} and Meidt, {Sharon E.} and Eva Schinnerer and Francesco Belfiore and Eric Emsellem and Klessen, {Ralf S.} and Jiayi Sun and Mattia Sormani and Ivana Be{\v s}lic and Yixian Cao and M{\'e}lanie Chevance and Dario Colombo and Dale, {Daniel A.} and Santiago Garc{\'i}a-Burillo and Glover, {Simon C. O.} and Kathryn Grasha and Brent Groves and Koch, {Eric W.} and Lukas Neumann and Hsi-An Pan and Ismael Pessa and J{\'e}r{\^o}me Pety and Francesca Pinna and Lise Ramambason and Alessandro Razza and Andrea Romanelli and Erik Rosolowsky and Marina Ruiz-Garc{\'i}a and Patricia S{\'a}nchez-Bl{\'a}zquez and Rowan Smith and Sophia Stuber and Leonardo Ubeda and Antonio Usero and Williams, {Thomas G.}",

note = "Funding: MQ, SGB, MRG, and AU acknowledge support from the Spanish grant PID2022-138560NB-I00, funded by MCIN/AEI/10.13039/501100011033/FEDER, EU. JS acknowledges support by the National Aeronautics and Space Administration (NASA) through the NASA Hubble Fellowship grant HST-HF2-51544 awarded by the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under contract NAS 5-26555. MCS acknowledges financial support from the European Research Council under the ERC Starting Grant {\textquoteleft}GalFlow{\textquoteright} (grant 101116226) and from the Royal Society (URF\R1\221118). MC gratefully acknowledges funding from the DFG through an Emmy Noether Research Group (grant number CH2137/1-1).",

year = "2024",

month = jul,

doi = "10.1051/0004-6361/202449733",

language = "English",

volume = "687",

journal = "Astronomy & Astrophysics",

issn = "0004-6361",

publisher = "EDP SCIENCES S A",

}

Querejeta, M, Leroy, AK, Meidt, SE, Schinnerer, E, Belfiore, F, Emsellem, E, Klessen, RS, Sun, J, Sormani, M, Bešlic, I, Cao, Y, Chevance, M, Colombo, D, Dale, DA, García-Burillo, S, Glover, SCO, Grasha, K, Groves, B, Koch, EW, Neumann, L, Pan, H-A, Pessa, I, Pety, J, Pinna, F, Ramambason, L, Razza, A, Romanelli, A, Rosolowsky, E, Ruiz-García, M, Sánchez-Blázquez, P, Smith, R, Stuber, S, Ubeda, L, Usero, A & Williams, TG 2024, 'Do spiral arms enhance star formation efficiency?', Astronomy & Astrophysics, vol. 687, A293. https://doi.org/10.1051/0004-6361/202449733