The SAGA Survey

Exploring Satellites Around Galactic Analogs

Survey Paper

SAGA Science Goals

Put our Milky Way in Context

Our Milky Way Galaxy is the most well-studied galaxy in the Universe. A particularly informative component of the Milky Way is its system of satellite dwarf galaxies. To interpret the Milky Way satellite system in a cosmological context, it is critical to study a representative sample of systems analogous to the Milky Way. The goal of the SAGA Survey is to find and characterize satellite systems around 100 Milky Way analog galaxies.

Discover Dwarf Galaxies

The SAGA Survey aims to determine dwarf galaxy satellite systems around 100 Milky Way analogs down to the brightness of the Leo I galaxy (Mr < −12.3). We have complete spectroscopic coverage within 300 kpc of 8 Milky Way analogs so far. We have discovered 16 satellite galaxies, in addition to 13 satellites already known in the Sloan Digital Sky Survey, for a total of 29 satellites (images below). Unlike the Milky Way, the majority of our satellites are actively forming stars. This surprising result already challenges many current models of galaxy formation.

Learn about the Galaxy-Halo Connection

Dwarf galaxies provide a key test of cosmological models on small scales. At present most of our information comes only from the satellite dwarf galaxies around the Milky Way and Andromeda galaxies. The SAGA Survey will measure satellite luminosity functions around a representative sample of Milky Way-like galaxies. Follow-up observations of the SAGA dwarfs will further determine mass functions and HI gas fractions. This will provide new information about the connection between galaxies and their dark matter halos on the smallest scales.

SAGA Hosts and Satellites

Gilgamesh satellite (NSA)
RA = 234.132926177
Dec = 16.4404552908 Gilgamesh satellite (MMT)
RA = 233.787037531
Dec = 16.8704375988 Odyssey satellite (NSA)
RA = 247.84002995
Dec = 20.1840758135 Odyssey satellite (AAT)
RA = 248.393225697
Dec = 19.9461400824 Odyssey satellite (AAT)
RA = 248.051339587
Dec = 19.6957396993 Odyssey satellite (AAT)
RA = 247.825892241
Dec = 20.2108787761 Odyssey satellite (MMT)
RA = 247.877387573
Dec = 20.0936248407 Odyssey satellite (MMT)
RA = 248.152079686
Dec = 19.8102591366 Odyssey satellite (AAT)
RA = 248.580638518
Dec = 19.7208013394 Odyssey satellite (MMT)
RA = 248.195368592
Dec = 19.8670126788 Odyssey satellite (MMT)
RA = 248.16342684
Dec = 19.792207594 Dune satellite (AAT)
RA = 221.316115836
Dec = -0.159937082521 AnaK satellite (NSA)
RA = 354.350599991
Dec = 0.390802769345 AnaK satellite (MMT)
RA = 354.195229736
Dec = 0.62342377148 AnaK satellite (MMT)
RA = 353.778805283
Dec = 0.301058523211 Narnia satellite (MMT)
RA = 39.9254642529
Dec = -1.41874190874 Narnia satellite (AAT)
RA = 39.5361613388
Dec = -1.39669557972 OBrother satellite (NSA)
RA = 336.048161241
Dec = -3.48293869003 OBrother satellite (NSA)
RA = 335.836305444
Dec = -3.65980264084 OBrother satellite (AAT)
RA = 335.97997618
Dec = -3.27054858631 OBrother satellite (AAT)
RA = 335.953849494
Dec = -3.70119481833 StarTrek satellite (NSA)
RA = 123.243173206
Dec = 36.198359966 StarTrek satellite (NSA)
RA = 123.649897556
Dec = 36.4343553979 Catch22 satellite (NSA)
RA = 348.643816258
Dec = 4.4984434911 Catch22 satellite (MMT)
RA = 348.696648891
Dec = 4.63995487019 Catch22 satellite (MMT)
RA = 348.776907636
Dec = 4.373197012 Catch22 satellite (AAT)
RA = 348.621488524
Dec = 4.50717078054 Catch22 satellite (MMT)
RA = 348.874199097
Dec = 4.61326147472 Catch22 satellite (MMT)
RA = 348.554591739
Dec = 4.91500326962

SAGA Team Members

Marla Geha (Yale)
Risa Wechsler (Stanford/SLAC)
Rebecca Bernstein (Carnegie)
Ben Hoyle (U Sternwarte/MPE)
Yu Lu (Carnegie)
Yao-Yuan Mao (U Pittsburgh)
Sebastian Marchi (U Chile)
Phil Marshall (SLAC)
Ricardo Muñoz (U Chile)
Erik Tollerud (STScI)
Benjamin Weiner (U Arizona)

More Information

Data Release

The SAGA Survey measured spectroscopic redshifts for 17,344 unique objects, including 15,734 galaxies and 1,610 stars. We will make these spectra available upon publication of the SAGA Survey paper. In addition, we have identified a catalog of about 2,000 galaxies that is as complete as possible for galaxies with MK < −19.6 within 40 Mpc. From this, we selected a sample of 202 Milky Way analogs that SAGA will consider for spectroscopic follow up. 71 of these have nearly complete imaging within the Sloan Digital Sky Survey footprint. Our current spectroscopic sample is based on follow up around 16 of these hosts.

For questions and early access to these data, please contact us at saga@sagasurvey.org.

Acknowledgements

The SAGA Survey is supported by the National Science Foundation (NSF) Collaborative Grant No. AST-1517148 awarded to MG and RW.

We thank Emily Sandford for suggesting the acronym "SAGA".

The banner background and the SAGA satellite images are taken from the Sloan Digital Sky Survey layer in the DECam Legacy Survey Viewer. We thank Dustin Lang for building the DECaLS Viewer.

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