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A radio continuum study of dwarf galaxies: 6 cm imaging of LITTLE THINGS

A radio continuum study of dwarf galaxies: 6 cm imaging of LITTLE THINGS
A radio continuum study of dwarf galaxies: 6 cm imaging of LITTLE THINGS

In this paper, we examine to what extent the radio continuum can be used as an extinction-free probe of star formation in dwarf galaxies. To that aim, we observe 40 nearby dwarf galaxies with the Very Large Array at 6 cm (4-8 GHz) in C-configuration. We obtained images with 3″-8″ resolution and noise levels of 3-15 μJy beam-1. We detected emission associated with 22 of the 40 dwarf galaxies, eight of which are new detections. The general picture is that of an interstellar medium largely devoid of radio continuum emission, interspersed by isolated pockets of emission associated with star formation. We find an average thermal fraction of ∼50%-70% and an average magnetic field strength of ∼5-8 μG, only slightly lower than that found in larger, spiral galaxies. At 100 pc scales, we find surprisingly high values for the average magnetic field strength of up to 50 μG. We find that dwarf galaxies follow the theoretical predictions of the radio continuum-star formation rate relation within regions of significant radio continuum emission but that the nonthermal radio continuum is suppressed relative to the star formation rate when considering the entire optical disk. We examine the far-infrared-star formation rate relation for our sample and find that the far-infrared is suppressed compared to the expected star formation rate. We discuss explanations for these observed relations and the impact of our findings on the radio continuum-far-infrared relation. We conclude that radio continuum emission at centimeter wavelengths has the promise of being a largely extinction-free star formation rate indicator. We find that star formation rates of gas-rich, low-mass galaxies can be estimated with an uncertainty of ± 0.2 dex between the values of 2 × 10-4 and 0.1 M o yr-1.

galaxies: dwarf, galaxies: magnetic fields, galaxies: star formation, radio continuum: galaxies, radio continuum: ISM
0067-0049
Hindson, Luke
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Kitchener, Ged
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Brinks, Elias
095e592f-8325-418c-b00c-d9e783fd5703
Heesen, Volker
b8b21826-1b25-493c-9f2a-9b0428dd1713
Westcott, Jonathan
27e046c8-5f59-4880-8dd5-db67cb3c46a2
Hunter, Deidre
2acbf3d0-4bba-4771-99ca-043f3acc2ba4
Zhang, Hong Xin
bcb089e1-b7be-4da0-9c1e-1675d2a902d9
Rupen, Michael
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Rau, Urvashi
21677f1a-a06f-46eb-94aa-c4bb8dc44a1b
Hindson, Luke
df61d68d-f05f-42a4-ad6b-dda1c5c67f27
Kitchener, Ged
2c7b3d39-d3b2-4356-a389-8624333fbb79
Brinks, Elias
095e592f-8325-418c-b00c-d9e783fd5703
Heesen, Volker
b8b21826-1b25-493c-9f2a-9b0428dd1713
Westcott, Jonathan
27e046c8-5f59-4880-8dd5-db67cb3c46a2
Hunter, Deidre
2acbf3d0-4bba-4771-99ca-043f3acc2ba4
Zhang, Hong Xin
bcb089e1-b7be-4da0-9c1e-1675d2a902d9
Rupen, Michael
06b774d4-6205-4f11-975d-6659d5378f59
Rau, Urvashi
21677f1a-a06f-46eb-94aa-c4bb8dc44a1b

Hindson, Luke, Kitchener, Ged, Brinks, Elias, Heesen, Volker, Westcott, Jonathan, Hunter, Deidre, Zhang, Hong Xin, Rupen, Michael and Rau, Urvashi (2018) A radio continuum study of dwarf galaxies: 6 cm imaging of LITTLE THINGS. The Astrophysical Journal Supplement Series, 234 (2), [29]. (doi:10.3847/1538-4365/aaa42c).

Record type: Article

Abstract

In this paper, we examine to what extent the radio continuum can be used as an extinction-free probe of star formation in dwarf galaxies. To that aim, we observe 40 nearby dwarf galaxies with the Very Large Array at 6 cm (4-8 GHz) in C-configuration. We obtained images with 3″-8″ resolution and noise levels of 3-15 μJy beam-1. We detected emission associated with 22 of the 40 dwarf galaxies, eight of which are new detections. The general picture is that of an interstellar medium largely devoid of radio continuum emission, interspersed by isolated pockets of emission associated with star formation. We find an average thermal fraction of ∼50%-70% and an average magnetic field strength of ∼5-8 μG, only slightly lower than that found in larger, spiral galaxies. At 100 pc scales, we find surprisingly high values for the average magnetic field strength of up to 50 μG. We find that dwarf galaxies follow the theoretical predictions of the radio continuum-star formation rate relation within regions of significant radio continuum emission but that the nonthermal radio continuum is suppressed relative to the star formation rate when considering the entire optical disk. We examine the far-infrared-star formation rate relation for our sample and find that the far-infrared is suppressed compared to the expected star formation rate. We discuss explanations for these observed relations and the impact of our findings on the radio continuum-far-infrared relation. We conclude that radio continuum emission at centimeter wavelengths has the promise of being a largely extinction-free star formation rate indicator. We find that star formation rates of gas-rich, low-mass galaxies can be estimated with an uncertainty of ± 0.2 dex between the values of 2 × 10-4 and 0.1 M o yr-1.

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Hindson 2018 Ap J S 234 29 - Version of Record
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Accepted/In Press date: 25 December 2017
e-pub ahead of print date: 1 February 2018
Published date: 1 February 2018
Keywords: galaxies: dwarf, galaxies: magnetic fields, galaxies: star formation, radio continuum: galaxies, radio continuum: ISM

Identifiers

Local EPrints ID: 418623
URI: http://eprints.soton.ac.uk/id/eprint/418623
ISSN: 0067-0049
PURE UUID: bad22e49-e495-47cd-b272-44435a091093

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Date deposited: 13 Mar 2018 17:30
Last modified: 16 Dec 2019 18:22

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