1 The outskirts of spiral galaxies as viewed by SDSS Ignacio Trujillo & Michael Pohlen

2 The outskirts, the mystery The presence of stars at gas densities lowest than ~10M sun /pc 2 (~24 mag/arcsec 2 in r-band) is not easily explained in present models of star formation. 2 Truncation NGC ” NGC5923 From Pohlen et al. (2002)

3 The outskirts, the mystery The presence of stars at outermost regions of galactic disks must be related to the galaxy formation and evolution We lack understanding about the surface brightness distribution at faintest regions versus  luminosity  mass  morphological type  wavelength 3

4 The outskirts, the observational challenge We would need ~500 hundred nearby galaxies where the surface brightness can be explored reliably down to mag/arcsec^2 Using SDSS to build the sample : Excellent homogeneous sky background (27-28 mag/arcsec 2 in r-band) Hundreds of nearby galaxies in 5 bands (u, g, r, i, z) ” UGC09837

5 First results: SDSS DR2 Volume limited sample: SDSS Data Release 2  98 Sb-Sdm  cz<3250 km/s (corrected for Virgo inflow; LEDA)  M B <-18.5 mag and e<0.5 (low inclination)  Profiles in g and r SDSS band 5

6 First results: SDSS DR2 Profile Type vs Hubble Type 6

7 Exploring evolution at high-z We need:  1. Deep exposures due to the cosmological surface brightness dimming: (1+z) 4  2. High resolution images to avoid the seeing effects on the shape of the profiles This implies to use the Hubble Space Telescope deepest observations:  1. Hubble Ultra Deep Field  2. Hubble Deep Field North and South  3. GOODs and (probably also) COSMOS 7

8 Feasibility of the Project z=0.76 z=0 56 h kpc M B  mag 8

9 Breaks in the UDF High-z sample: UDF  z<1.1 & M B <-18.6 mag (from COMBO-17; Wolf et al. 2004)  Sérsic index n<2.5 (late-types) & e<0.5 (from GEMS; Barden et al. 2005)  36 objects (21 show truncation)  Profiles in B band-restframe: 0<z<0.5 (V-band); 0.5<z<0.8 (i- band); 0.8<z<1.1 (z-band) (Trujillo & Pohlen, 2005, ApJ Letters) 9

10 SDSS DR2 vs UDF a) Observed distribution b) Assuming only surface brightness evolution: d /dz=-1.43  0.03 (Barden et al. 2005) 10