TY - JOUR
T1 - Uncovering blue diffuse dwarf galaxies
AU - James, Bethan L.
AU - Koposov, Sergey
AU - Stark, Daniel P.
AU - Belokurov, Vasily
AU - Pettini, Max
AU - Olszewski, Edward W.
N1 - Funding Information:
Observations reported here were obtained at the MMT Observatory, a joint facility of theUniversity of Arizona and the SmithsonianInstitution.We are grateful to the University of Arizona Observatory time assignment committee who awarded time to this programme, and thank the MMT telescope operators and staff for technical support. We are indebted to Alis Deason for providing the first-look spectroscopic observations of a subset of our sample that were used to support our initial MMT proposal. It is a pleasure to acknowledge Rob Kennicutt for useful discussions concerning dwarf galaxy populations, Matt Auger who helped with various aspects of the data analysis, and Evan Skillman for insightful comments on an early version of this work. We sincerely thank the reviewer of the paper, Jorge Sanchez Almeida, whose helpful comments and suggestions greatly improved the paper. EWO is partially supported by NSF grant AST1313006. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No. 308024. SK acknowledges financial support from the ERC. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Publisher Copyright:
© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2015/4/11
Y1 - 2015/4/11
N2 - Extremely metal poor (XMP) galaxies are known to be very rare, despite the large numbers of low-mass galaxies predicted by the local galaxy luminosity function. This paper presents a subsample of galaxies that were selected via a morphology-based search on Sloan Digital Sky Survey images with the aim of finding these elusive XMP galaxies. By using the recently discovered XMP galaxy, Leo P, as a guide, we obtained a collection of faint, blue systems, each with isolated H II regions embedded in a diffuse continuum, that have remained optically undetected until now. Here we show the first results from optical spectroscopic follow-up observations of 12 of ~100 of these blue diffuse dwarf (BDD) galaxies yielded by our search algorithm. Oxygen abundances were obtained via the direct method for eight galaxies, and found to be in the range 7.45 < 12 + log (O/H) < 8.0, with two galaxies being classified as XMPs. All BDDs were found to currently have a young star-forming population (< 10 Myr) and relatively high ionization parameters of their H II regions. Despite their low luminosities (-11 ≲ MB ≲ -18) and low surface brightnesses (~23-25 mag arcsec-2), the galaxies were found to be actively star forming, with current star formation rates between 0.0003 and 0.078Modot; yr-1. From our current subsample, BDD galaxies appear to be a population of nonquiescent dwarf irregular galaxies, or the diffuse counterparts to blue compact galaxies and as such may bridge the gap between these two populations. Our search algorithm demonstrates that morphology-based searches are successful in uncovering more diffuse metal-poor starforming galaxies, which traditional emission-line-based searches overlook.
AB - Extremely metal poor (XMP) galaxies are known to be very rare, despite the large numbers of low-mass galaxies predicted by the local galaxy luminosity function. This paper presents a subsample of galaxies that were selected via a morphology-based search on Sloan Digital Sky Survey images with the aim of finding these elusive XMP galaxies. By using the recently discovered XMP galaxy, Leo P, as a guide, we obtained a collection of faint, blue systems, each with isolated H II regions embedded in a diffuse continuum, that have remained optically undetected until now. Here we show the first results from optical spectroscopic follow-up observations of 12 of ~100 of these blue diffuse dwarf (BDD) galaxies yielded by our search algorithm. Oxygen abundances were obtained via the direct method for eight galaxies, and found to be in the range 7.45 < 12 + log (O/H) < 8.0, with two galaxies being classified as XMPs. All BDDs were found to currently have a young star-forming population (< 10 Myr) and relatively high ionization parameters of their H II regions. Despite their low luminosities (-11 ≲ MB ≲ -18) and low surface brightnesses (~23-25 mag arcsec-2), the galaxies were found to be actively star forming, with current star formation rates between 0.0003 and 0.078Modot; yr-1. From our current subsample, BDD galaxies appear to be a population of nonquiescent dwarf irregular galaxies, or the diffuse counterparts to blue compact galaxies and as such may bridge the gap between these two populations. Our search algorithm demonstrates that morphology-based searches are successful in uncovering more diffuse metal-poor starforming galaxies, which traditional emission-line-based searches overlook.
KW - Galaxies: abundances
KW - Galaxies: dwarf
KW - Galaxies: evolution
KW - Galaxies: irregular
KW - Galaxies: star formation
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U2 - 10.1093/mnras/stv175
DO - 10.1093/mnras/stv175
M3 - Article
AN - SCOPUS:85015704388
SN - 0035-8711
VL - 448
SP - 2687
EP - 2703
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 3
ER -