H-alpha Star Formation Rates of the SHIELD Dwarf Galaxies

Abstract

The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) galaxy sample is an HI-selected catalog of galaxies that occupy the extreme low-mass end of the HI mass function. Our team is carrying out a comprehensive multi-wavelength observational program targeting these gas-rich, star-forming dwarf galaxies. The current paper presents H-alpha narrowband observations of the full SHIELD sample. We detect 55 of the 82 galaxies (67%) with nebular H-alpha emission, and infer sensitive upper limits to the H-alpha fluxes for the 27 non-detections. We derive H-alpha luminosities and star formation rates (SFRs), or upper limits, for all 82 SHIELD galaxies. We also present, for the first time, deep broadband and continuum-subtracted H-alpha images plus a summary of the properties for the entire sample. Our analysis of the H-alpha data re-affirms previous results which show that at low levels of star formation (log(SFR_{H-alpha}) < -2.5), H-alpha becomes an increasingly poor tracer of the recent average SFR as measured by far-UV (FUV) luminosities. However, we show that this effect is not strictly correlated with the mass of the galaxy. Some very low-mass SHIELD galaxies with higher H-alpha-based SFRs show good agreement with SFR_{FUV}. The SHIELD galaxies show no correlation between H-alpha SFR and gas mass fraction, but reveal a modest correlation between H-alpha specific SFR and gas mass fraction. Overall, the star formation efficiency exhibited by the SHIELD dwarfs is rather low, despite the gas-rich nature of the sample (68% have M_{gas} > M_{stellar}).

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BibTeX RIS

BibTeX

@misc{shepley2026halpha,
  title = {{H-alpha Star Formation Rates of the SHIELD Dwarf Galaxies}},
  author = {Madeline Shepley and David G. Gormanous and John J. Salzer and Nathalie Haurberg and Steven Janowiecki and John M. Cannon and Elizabeth A. K. Adams and Martha P. Haynes and Alec S. Hirschauer and Kristen B. W. McQuinn and Katherine L. Rhode and Evan D. Skillman},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.32159},
  eprint = {2609.32159},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.32159},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - H-alpha Star Formation Rates of the SHIELD Dwarf Galaxies
AU  - Madeline Shepley
AU  - David G. Gormanous
AU  - John J. Salzer
AU  - Nathalie Haurberg
AU  - Steven Janowiecki
AU  - John M. Cannon
AU  - Elizabeth A. K. Adams
AU  - Martha P. Haynes
AU  - Alec S. Hirschauer
AU  - Kristen B. W. McQuinn
AU  - Katherine L. Rhode
AU  - Evan D. Skillman
PY  - 2026
DA  - 2026/09/26
PB  - arXiv
DO  - 10.48550/arxiv.2609.32159
UR  - https://arxiv.org/abs/2609.32159
AB  - The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) galaxy sample is an HI-selected catalog of galaxies that occupy the extreme low-mass end of the HI mass function. Our team is carrying out a comprehensive multi-wavelength observational program targeting these gas-rich, star-forming dwarf galaxies. The current paper presents H-alpha narrowband observations of the full SHIELD sample. We detect 55 of the 82 galaxies (67%) with nebular H-alpha emission, and infer sensitive upper limits to the H-alpha fluxes for the 27 non-detections. We derive H-alpha luminosities and star formation rates (SFRs), or upper limits, for all 82 SHIELD galaxies. We also present, for the first time, deep broadband and continuum-subtracted H-alpha images plus a summary of the properties for the entire sample. Our analysis of the H-alpha data re-affirms previous results which show that at low levels of star formation (log(SFR_{H-alpha}) < -2.5), H-alpha becomes an increasingly poor tracer of the recent average SFR as measured by far-UV (FUV) luminosities. However, we show that this effect is not strictly correlated with the mass of the galaxy. Some very low-mass SHIELD galaxies with higher H-alpha-based SFRs show good agreement with SFR_{FUV}. The SHIELD galaxies show no correlation between H-alpha SFR and gas mass fraction, but reveal a modest correlation between H-alpha specific SFR and gas mass fraction. Overall, the star formation efficiency exhibited by the SHIELD dwarfs is rather low, despite the gas-rich nature of the sample (68% have M_{gas} > M_{stellar}).
ER  -

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