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The outskirts of spiral galaxies as viewed by SDSS

Ignacio Trujillo & Michael Pohlen

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The outskirts, the mystery

• The presence of stars at gas densities lowest than ~10Msun/pc2 (~24 mag/arcsec2 in r-band) is not easily explained in present models of star formation.

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Truncation

NGC5923

101.4”

NGC5923

From Pohlen et al. (2002)

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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

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The outskirts, the observational challenge• We would need ~500 hundred nearby galaxies where the surface brightness

can be explored reliably down to 25-27 mag/arcsec^2

• Using SDSS to build the sample:• Excellent homogeneous sky background (27-28 mag/arcsec2 in r-band)• Hundreds of nearby galaxies in 5 bands (u, g, r, i, z)

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101.4”

UGC09837

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First results: SDSS DR2• Volume limited sample: SDSS Data Release 2

98 Sb-Sdm cz<3250 km/s (corrected for Virgo inflow; LEDA) MB<-18.5 mag and e<0.5 (low inclination) Profiles in g and r SDSS band

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First results: SDSS DR2

• Profile Type vs Hubble Type

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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

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Feasibility of the Projectz=0.76 z=0

56 h70-1 kpc

MB-21.4 mag

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Breaks in the UDF

High-z sample: UDF

z<1.1 & MB<-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)

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SDSS DR2 vs UDF• a) Observed distribution• b) Assuming only surface brightness evolution:

d<μB>/dz=-1.430.03 (Barden et al. 2005)

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