Eight ultra-faint galaxy candidates discovered in year two of the Dark Energy Survey

Journal Article · Wed Nov 04 00:00:00 EST 2015 · The Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/813/2/109· OSTI ID:1221344

Drlica-Wagner, A. ^[1]

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1. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States). et al.

Here, we report the discovery of eight new ultra-faint dwarf galaxy candidates in the second year of optical imaging data from the Dark Energy Survey (DES). Six of these candidates are detected at high confidence, while two lower-confidence candidates are identified in regions of non-uniform survey coverage. The new stellar systems are found by three independent automated search techniques and are identified as overdensities of stars, consistent with the isochrone and luminosity function of an old and metal-poor simple stellar population. The new systems are faint (M_V > –4.7 $$\mathrm{mag}$$) and span a range of physical sizes (17 _{$$\mathrm{pc}$$} < r_1/2 < 181 _{$$\mathrm{pc}$$}) and heliocentric distances (25 kpc < D_⊙ < 214 kpc). All of the new systems have central surface brightnesses consistent with known ultra-faint dwarf galaxies (μ ≳ 27.5 _{$$\mathrm{mag}$$ $$\mathrm{arcsec}$$}^–2). Roughly half of the DES candidates are more distant, less luminous, and/or have lower surface brightnesses than previously known Milky Way satellite galaxies. Most of the candidates are found in the southern part of the DES footprint close to the Magellanic Clouds. We find that the DES data alone exclude (p < 10^–3) a spatially isotropic distribution of Milky Way satellites and that the observed distribution can be well, though not uniquely, described by an association between several of the DES satellites and the Magellanic system. Our model predicts that the full sky may hold ~100 ultra-faint galaxies with physical properties comparable to the DES satellites and that 20%–30% of these would be spatially associated with the Magellanic Clouds.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Contributing Organization: DES Collaboration; The DES Collaboration
• Grant/Contract Number: AC02-07CH11359; AC02-76SF00515
• OSTI ID: 1221344
• Alternate ID(s): OSTI ID: 1263407
• Report Number(s): FERMILAB-PUB-15-351-AE; SLAC-PUB-16631; arXiv eprint number arXiv:1508.03622
• Journal Information: The Astrophysical Journal (Online), Vol. 813, Issue 2; ISSN 1538-4357
• Publisher: Institute of Physics (IOP)
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
galaxies: dwarf
local group
astrophysics
phenomenology-HEP
ASTRO