Blue diffuse dwarf galaxies

A clearer picture

Bethan L. James, Sergey E. Koposov, Daniel P Stark, Vasily Belokurov, Max Pettini, Edward W Olszewski, Kristen B.W. McQuinn

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The search for chemically unevolved galaxies remains prevalent in the nearby Universe, mostly because these systems provide excellent proxies for exploring in detail the physics of highz systems. The most promising candidates are extremely metal-poor galaxies (XMPs), i.e. galaxies with <1/10 solar metallicity. However, due to the bright emission-line-based search criteria traditionally used to find XMPs, we may not be sampling the full XMP population. In 2014, we reoriented this search using only morphological properties and uncovered a population of ~150 'blue diffuse dwarf (BDD) galaxies', and published a sub-sample of 12 BDD spectra. Here, we present optical spectroscopic observations of a larger sample of 51 BDDs, along with their Sloan Digital Sky Survey (SDSS) photometric properties. With our improved statistics, we use direct-method abundances to confirm that BDDs are chemically unevolved (7.43 < 12 + log(O/H) < 8.01), with ~20 per cent of our sample classified as being XMP galaxies, and find that they are actively forming stars at rates of ~1-33 × 10-2 M yr-1 in HII regions randomly embedded in a blue, low-surface-brightness continuum. Stellar masses are calculated from population synthesis models and estimated to be in the range log(M*/M) ≃ 5-9. Unlike other low-metallicity star-forming galaxies, BDDs are in agreement with the mass-metallicity relation at low masses, suggesting that they are not accreting large amounts of pristine gas relative to their stellar mass. BDD galaxies appear to be a population of actively star-forming dwarf irregular (dIrr) galaxies which fall within the class of low-surface-brightness dIrr galaxies. Their ongoing star formation and irregular morphology make them excellent analogues for galaxies in the early Universe.

Original languageEnglish (US)
Pages (from-to)3977-4015
Number of pages39
JournalMonthly Notices of the Royal Astronomical Society
Volume465
Issue number4
DOIs
StatePublished - 2017

Fingerprint

dwarf galaxies
galaxies
metallicity
irregular galaxies
stellar mass
stars
brightness
universe
physics
star formation
metal
sampling
gas
statistics
analogs
continuums
synthesis
gases
metals

Keywords

  • Galaxies: abundances
  • Galaxies: dwarf
  • Galaxies: evolution
  • Galaxies: irregular
  • Galaxies: star formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Blue diffuse dwarf galaxies : A clearer picture. / James, Bethan L.; Koposov, Sergey E.; Stark, Daniel P; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W; McQuinn, Kristen B.W.

In: Monthly Notices of the Royal Astronomical Society, Vol. 465, No. 4, 2017, p. 3977-4015.

Research output: Contribution to journalArticle

James, BL, Koposov, SE, Stark, DP, Belokurov, V, Pettini, M, Olszewski, EW & McQuinn, KBW 2017, 'Blue diffuse dwarf galaxies: A clearer picture', Monthly Notices of the Royal Astronomical Society, vol. 465, no. 4, pp. 3977-4015. https://doi.org/10.1093/mnras/stw2962
James, Bethan L. ; Koposov, Sergey E. ; Stark, Daniel P ; Belokurov, Vasily ; Pettini, Max ; Olszewski, Edward W ; McQuinn, Kristen B.W. / Blue diffuse dwarf galaxies : A clearer picture. In: Monthly Notices of the Royal Astronomical Society. 2017 ; Vol. 465, No. 4. pp. 3977-4015.
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