NOAO >   Observing Info >   Approved Programs >   2016A-0294

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Program Information for 2016A-0294


PI: Marla Geha, Yale U., marla.geha@yale.edu
Address: Astronomy Department, New Haven, CT 06520 U.S.

CoI: Risa Wechsler, Stanford U.
CoI: Erik Tollerud, STScI
CoI: Ben Hoyle, Universitaets-Sternwarte Munchen
CoI: Benjamin Weiner, U. of Arizona

Title: The SAGA Project: A Machine Learning Search for Dwarf Galaxy Satellites Around Milky Way Analogs

Abstract: The Milky Way (MW) galaxy is host to four dwarf galaxy satellites brighter than $M_r=-11.5$. These bright satellites and their properties do not fully agree with predictions from galaxy formation models. Understanding these discrepancies requires measuring satellite luminosity functions around a statistical sample of MW analogs. In the past two years, we have taken 15,000 redshifts around 10 MW analogs, revealing a dozen new satellites down to $M_r=-11.5$ ($m_r =21$ at 30,Mpc). We are just approaching sufficient spectroscopic completeness to state with confidence that there is a significant spread in satellite number per host (from 1 to 9 satellites). The large number of redshifts required is because satellite galaxies are difficult to distinguish from the thousands of higher redshift background galaxies via photometry alone, and spectroscopic training sets to this depth were not available. Based on past allocations, we have developed a machine learning method to drastically reduce the typical number of candidate satellites within the virial radius (300 kpc, $1^{circ}$ at 30,Mpc). We request 3 AAT 2dF nights to complete our characterization of 7 hosts and apply this method to search for satellites around an additional 10 MW analogs. These will represent the only MW analogs with complete satellite luminosity functions down to $M_r < -11.5$ ($M_r = 21$) beyond our own MW.

Program Type: Standard/Extragalactic

Scheduled Nights:
Run 1 (2016A):  AAT/AAOmega -- 3n on Jul 28 - Jul 31 2016


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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