Comparison of Hα and UV Star Formation Rates in the Local Volume: Systematic Discrepancies for Dwarf Galaxies. Lee, J. C., Gil de Paz, A., Tremonti, C., Kennicutt, Salim, S., Bothwell, M., Calzetti, D., Dalcanton, J., Dale, D., Engelbracht, C., Funes, S. J. J. G., Johnson, B., Sakai, S., Skillman, E., van Zee, L., Walter, F., & Weisz, D. The Astrophysical Journal, 706:599–613, November, 2009. ![Comparison of Hα and UV Star Formation Rates in the Local Volume: Systematic Discrepancies for Dwarf Galaxies [link]](https://bibbase.org/img/filetypes/link.svg "link")
Paper doi abstract bibtex Using a complete sample of \textasciitilde300 star-forming galaxies within 11 Mpc of the Milky Way, we evaluate the consistency between star formation rates (SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum and Hα nebular emission, assuming standard conversion recipes in which the SFR scales linearly with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders of magnitude, down to ultra-low activities on the order of \textasciitilde10-4 M sun yr-1. The data are drawn from the 11 Mpc Hα and Ultraviolet Galaxy Survey (11HUGS), which has obtained Hα fluxes from ground-based narrowband imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies (SFR \textasciitilde 1 M sun yr-1), our results are consistent with previous work which has shown that FUV SFRs tend to be lower than Hα SFRs before accounting for internal dust attenuation, but that there is relative consistency between the two tracers after proper corrections are applied. However, a puzzle is encountered at the faint end of the luminosity function. As lower luminosity dwarf galaxies, roughly less active than the Small Magellanic Cloud, are examined, Hα tends to increasingly underpredict the total SFR relative to the FUV. The trend is evident prior to corrections for dust attenuation, which affects the FUV more than the nebular Hα emission, so this general conclusion is robust to the effects of dust. Although past studies have suggested similar trends, this is the first time this effect is probed with a statistical sample for galaxies with SFR \textless\textasciitilde 0.1 M sun yr-1. By SFR \textasciitilde 0.003 M sun yr-1, the average Hα-to-FUV flux ratio is lower than expected by a factor of two, and at the lowest SFRs probed, the ratio exhibits an order of magnitude discrepancy for the handful of galaxies that remain in the sample. A range of standard explanations does not appear to be able to fully account for the magnitude of the systematic. Some recent work has argued for a stellar initial mass function which is deficient in high-mass stars in dwarf and low surface brightness galaxies, and we also consider this scenario. Under the assumption that the FUV traces the SFR in dwarf galaxies more robustly, the prescription relating Hα luminosity to SFR is re-calibrated for use in the low SFR regime when FUV data are not available.
@article{lee_comparison_2009,
title = {Comparison of {Hα} and {UV} {Star} {Formation} {Rates} in the {Local} {Volume}: {Systematic} {Discrepancies} for {Dwarf} {Galaxies}},
volume = {706},
issn = {0004-637X},
shorttitle = {Comparison of {Hα} and {UV} {Star} {Formation} {Rates} in the {Local} {Volume}},
url = {http://adsabs.harvard.edu/abs/2009ApJ...706..599L},
doi = {10.1088/0004-637X/706/1/599},
abstract = {Using a complete sample of {\textasciitilde}300 star-forming galaxies within 11 Mpc of
the Milky Way, we evaluate the consistency between star formation rates
(SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum
and Hα nebular emission, assuming standard conversion recipes in
which the SFR scales linearly with luminosity at a given wavelength. Our
analysis probes SFRs over 5 orders of magnitude, down to ultra-low
activities on the order of {\textasciitilde}10-4 M sun
yr-1. The data are drawn from the 11 Mpc Hα and
Ultraviolet Galaxy Survey (11HUGS), which has obtained Hα fluxes
from ground-based narrowband imaging, and UV fluxes from imaging with
GALEX. For normal spiral galaxies (SFR {\textasciitilde} 1 M sun
yr-1), our results are consistent with previous work which
has shown that FUV SFRs tend to be lower than Hα SFRs before
accounting for internal dust attenuation, but that there is relative
consistency between the two tracers after proper corrections are
applied. However, a puzzle is encountered at the faint end of the
luminosity function. As lower luminosity dwarf galaxies, roughly less
active than the Small Magellanic Cloud, are examined, Hα tends to
increasingly underpredict the total SFR relative to the FUV. The trend
is evident prior to corrections for dust attenuation, which affects the
FUV more than the nebular Hα emission, so this general conclusion
is robust to the effects of dust. Although past studies have suggested
similar trends, this is the first time this effect is probed with a
statistical sample for galaxies with SFR {\textless}{\textasciitilde} 0.1 M sun
yr-1. By SFR {\textasciitilde} 0.003 M sun yr-1, the
average Hα-to-FUV flux ratio is lower than expected by a factor of
two, and at the lowest SFRs probed, the ratio exhibits an order of
magnitude discrepancy for the handful of galaxies that remain in the
sample. A range of standard explanations does not appear to be able to
fully account for the magnitude of the systematic. Some recent work has
argued for a stellar initial mass function which is deficient in
high-mass stars in dwarf and low surface brightness galaxies, and we
also consider this scenario. Under the assumption that the FUV traces
the SFR in dwarf galaxies more robustly, the prescription relating
Hα luminosity to SFR is re-calibrated for use in the low SFR
regime when FUV data are not available.},
urldate = {2019-05-12},
journal = {The Astrophysical Journal},
author = {Lee, Janice C. and Gil de Paz, Armando and Tremonti, Christy and Kennicutt, Jr., Robert C. and Salim, Samir and Bothwell, Matthew and Calzetti, Daniela and Dalcanton, Julianne and Dale, Daniel and Engelbracht, Chad and Funes, S. J. José G. and Johnson, Benjamin and Sakai, Shoko and Skillman, Evan and van Zee, Liese and Walter, Fabian and Weisz, Daniel},
month = nov,
year = {2009},
keywords = {galaxies: dwarf, galaxies: evolution, galaxies: photometry, stars: formation, surveys, ultraviolet: galaxies},
pages = {599--613},
}
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G.","Johnson, B.","Sakai, S.","Skillman, E.","van Zee, L.","Walter, F.","Weisz, D."],"bibdata":{"bibtype":"article","type":"article","title":"Comparison of Hα and UV Star Formation Rates in the Local Volume: Systematic Discrepancies for Dwarf Galaxies","volume":"706","issn":"0004-637X","shorttitle":"Comparison of Hα and UV Star Formation Rates in the Local Volume","url":"http://adsabs.harvard.edu/abs/2009ApJ...706..599L","doi":"10.1088/0004-637X/706/1/599","abstract":"Using a complete sample of \\textasciitilde300 star-forming galaxies within 11 Mpc of the Milky Way, we evaluate the consistency between star formation rates (SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum and Hα nebular emission, assuming standard conversion recipes in which the SFR scales linearly with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders of magnitude, down to ultra-low activities on the order of \\textasciitilde10-4 M sun yr-1. The data are drawn from the 11 Mpc Hα and Ultraviolet Galaxy Survey (11HUGS), which has obtained Hα fluxes from ground-based narrowband imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies (SFR \\textasciitilde 1 M sun yr-1), our results are consistent with previous work which has shown that FUV SFRs tend to be lower than Hα SFRs before accounting for internal dust attenuation, but that there is relative consistency between the two tracers after proper corrections are applied. However, a puzzle is encountered at the faint end of the luminosity function. As lower luminosity dwarf galaxies, roughly less active than the Small Magellanic Cloud, are examined, Hα tends to increasingly underpredict the total SFR relative to the FUV. The trend is evident prior to corrections for dust attenuation, which affects the FUV more than the nebular Hα emission, so this general conclusion is robust to the effects of dust. Although past studies have suggested similar trends, this is the first time this effect is probed with a statistical sample for galaxies with SFR \\textless\\textasciitilde 0.1 M sun yr-1. By SFR \\textasciitilde 0.003 M sun yr-1, the average Hα-to-FUV flux ratio is lower than expected by a factor of two, and at the lowest SFRs probed, the ratio exhibits an order of magnitude discrepancy for the handful of galaxies that remain in the sample. A range of standard explanations does not appear to be able to fully account for the magnitude of the systematic. Some recent work has argued for a stellar initial mass function which is deficient in high-mass stars in dwarf and low surface brightness galaxies, and we also consider this scenario. Under the assumption that the FUV traces the SFR in dwarf galaxies more robustly, the prescription relating Hα luminosity to SFR is re-calibrated for use in the low SFR regime when FUV data are not available.","urldate":"2019-05-12","journal":"The Astrophysical Journal","author":[{"propositions":[],"lastnames":["Lee"],"firstnames":["Janice","C."],"suffixes":[]},{"propositions":["Gil","de"],"lastnames":["Paz"],"firstnames":["Armando"],"suffixes":[]},{"propositions":[],"lastnames":["Tremonti"],"firstnames":["Christy"],"suffixes":[]},{"firstnames":[],"propositions":[],"lastnames":["Kennicutt"],"suffixes":["Jr.",",","Robert","C."]},{"propositions":[],"lastnames":["Salim"],"firstnames":["Samir"],"suffixes":[]},{"propositions":[],"lastnames":["Bothwell"],"firstnames":["Matthew"],"suffixes":[]},{"propositions":[],"lastnames":["Calzetti"],"firstnames":["Daniela"],"suffixes":[]},{"propositions":[],"lastnames":["Dalcanton"],"firstnames":["Julianne"],"suffixes":[]},{"propositions":[],"lastnames":["Dale"],"firstnames":["Daniel"],"suffixes":[]},{"propositions":[],"lastnames":["Engelbracht"],"firstnames":["Chad"],"suffixes":[]},{"propositions":[],"lastnames":["Funes"],"firstnames":["S.","J.","José","G."],"suffixes":[]},{"propositions":[],"lastnames":["Johnson"],"firstnames":["Benjamin"],"suffixes":[]},{"propositions":[],"lastnames":["Sakai"],"firstnames":["Shoko"],"suffixes":[]},{"propositions":[],"lastnames":["Skillman"],"firstnames":["Evan"],"suffixes":[]},{"propositions":["van"],"lastnames":["Zee"],"firstnames":["Liese"],"suffixes":[]},{"propositions":[],"lastnames":["Walter"],"firstnames":["Fabian"],"suffixes":[]},{"propositions":[],"lastnames":["Weisz"],"firstnames":["Daniel"],"suffixes":[]}],"month":"November","year":"2009","keywords":"galaxies: dwarf, galaxies: evolution, galaxies: photometry, stars: formation, surveys, ultraviolet: galaxies","pages":"599–613","bibtex":"@article{lee_comparison_2009,\n\ttitle = {Comparison of {Hα} and {UV} {Star} {Formation} {Rates} in the {Local} {Volume}: {Systematic} {Discrepancies} for {Dwarf} {Galaxies}},\n\tvolume = {706},\n\tissn = {0004-637X},\n\tshorttitle = {Comparison of {Hα} and {UV} {Star} {Formation} {Rates} in the {Local} {Volume}},\n\turl = {http://adsabs.harvard.edu/abs/2009ApJ...706..599L},\n\tdoi = {10.1088/0004-637X/706/1/599},\n\tabstract = {Using a complete sample of {\\textasciitilde}300 star-forming galaxies within 11 Mpc of \nthe Milky Way, we evaluate the consistency between star formation rates\n(SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum\nand Hα nebular emission, assuming standard conversion recipes in\nwhich the SFR scales linearly with luminosity at a given wavelength. Our\nanalysis probes SFRs over 5 orders of magnitude, down to ultra-low\nactivities on the order of {\\textasciitilde}10-4 M sun\nyr-1. The data are drawn from the 11 Mpc Hα and\nUltraviolet Galaxy Survey (11HUGS), which has obtained Hα fluxes\nfrom ground-based narrowband imaging, and UV fluxes from imaging with\nGALEX. For normal spiral galaxies (SFR {\\textasciitilde} 1 M sun\nyr-1), our results are consistent with previous work which\nhas shown that FUV SFRs tend to be lower than Hα SFRs before\naccounting for internal dust attenuation, but that there is relative\nconsistency between the two tracers after proper corrections are\napplied. However, a puzzle is encountered at the faint end of the\nluminosity function. As lower luminosity dwarf galaxies, roughly less\nactive than the Small Magellanic Cloud, are examined, Hα tends to\nincreasingly underpredict the total SFR relative to the FUV. The trend\nis evident prior to corrections for dust attenuation, which affects the\nFUV more than the nebular Hα emission, so this general conclusion\nis robust to the effects of dust. Although past studies have suggested\nsimilar trends, this is the first time this effect is probed with a\nstatistical sample for galaxies with SFR {\\textless}{\\textasciitilde} 0.1 M sun\nyr-1. By SFR {\\textasciitilde} 0.003 M sun yr-1, the\naverage Hα-to-FUV flux ratio is lower than expected by a factor of\ntwo, and at the lowest SFRs probed, the ratio exhibits an order of\nmagnitude discrepancy for the handful of galaxies that remain in the\nsample. A range of standard explanations does not appear to be able to\nfully account for the magnitude of the systematic. Some recent work has\nargued for a stellar initial mass function which is deficient in\nhigh-mass stars in dwarf and low surface brightness galaxies, and we\nalso consider this scenario. Under the assumption that the FUV traces\nthe SFR in dwarf galaxies more robustly, the prescription relating\nHα luminosity to SFR is re-calibrated for use in the low SFR\nregime when FUV data are not available.},\n\turldate = {2019-05-12},\n\tjournal = {The Astrophysical Journal},\n\tauthor = {Lee, Janice C. and Gil de Paz, Armando and Tremonti, Christy and Kennicutt, Jr., Robert C. and Salim, Samir and Bothwell, Matthew and Calzetti, Daniela and Dalcanton, Julianne and Dale, Daniel and Engelbracht, Chad and Funes, S. J. José G. and Johnson, Benjamin and Sakai, Shoko and Skillman, Evan and van Zee, Liese and Walter, Fabian and Weisz, Daniel},\n\tmonth = nov,\n\tyear = {2009},\n\tkeywords = {galaxies: dwarf, galaxies: evolution, galaxies: photometry, stars: formation, surveys, ultraviolet: galaxies},\n\tpages = {599--613},\n}\n\n","author_short":["Lee, J. 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