The Faintest Dwarf Galaxies in Groups and Poor Clusters R. Marzke & A. Danielson (SFSU) M. Hudson (U. Waterloo) R. Windhorst (ASU) 1

Benson et al Galaxy luminosity function from semi-analytic models of galaxy formation K-band LFs from Cole et al. 2001, Kochanek et al. 2001, Huang et al Cooling time > t H Supernova feedback, photoionization 2

Dekel & Silk 1986 Feedback 3

Dekel & Silk 1986 Luminosity-metallicity relation for spheroidal galaxies Chemical Enrichment 4

The field galaxy luminosity function Norberg et al dF Galaxy Redshift Survey 5

Beijersbergen et al Rich cluster LFs measured by statistical background subtraction 6

Christlein & Zabludoff 2003 Spectroscopic measurement of the rich cluster LF 7

Armandroff, Jacoby & Davies 1999 The luminosity function in a more representative environment Little is known about the faintest dwarfs beyond the Local Group 8

At 100 Mpc, the faintest Local Group dwarfs would have apparent magnitudes B~26 Needles in a haystack 9

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Drinkwater et al Not all dwarfs are diffuse Ultra-compact dwarfs in the Fornax cluster 11

Drinkwater et al

Crude redshifts improve background rejection dramatically Multislit spectroscopy can be efficient after preliminary photometric redshift filtering 13

Photometric redshifts S/N=20 S/N=10 S/N=5 UBVRIBATC At low redshift, UV filters are critical but expensive 14

Measuring the LF down to globular cluster luminosities: Uncertainty in Statistical Background Subtraction Simulated observations of rich clusters No redshift information Photometric redshift filtering (UBVRI) Coma cluster, density decreased by 2,5,10 15

BATC filter set Wavelength Xia et al

Photometric redshifts S/N=20 S/N=10 S/N=5 UBVRIBATC For the faintest LSB dwarfs, spectroscopic redshifts will be out of reach 17

The Survey MKW/AWM clusters: CTIO 4m (BTC pilot survey) –Lower density environment than rich clusters –Higher merger probability –How do galaxy interactions affect the LF? CfA/SSRS2 groups: MMT Megacam –Most common galaxy environment –Local-Group counterparts –Is the faint end of the Local-Group LF representative? Photometric calibration: WIYN 0.9m + Mosaic Spectroscopy: Magellan/IMACS 18