The properties of stellar disk truncations in a sample of nearby spiral galaxies

I. Martín, J. Bakos, I. Trujillo & J. Knapen Instituto de Astrofísica de Canarias

ABSTRACT

The origin of the edge of galaxy disks remains a mystery. Several hypothesis have been suggested to explain the truncations in the outer regions of the galaxy disks. With the aim of exploring this phenomena, we have collected a sample of 19 edge-on galaxies present both in the Sloan Sky Digital Survey (SDSS) and in the Spitzer Survey of Stellar Structure in Galaxies (S4G). We have obtained their radial surface brightness profiles in the 5 SDSS optical bands as well as in the 3.6 μm Spitzer band. We have probed whether the truncation phenomena is related to the observed wavelength in order to explore the effect of dust. We find that the characteristic truncation radius remains constant independently of the observed band. Using radial color profiles we have obtained the stellar mass distribution of those galaxies, as well as the radial dust extinction, age and metallicity. We conclude that the truncation is more likely a feature associated to the galactic angular momentum.

RESULTS

CONCLUSIONS

For each of the galaxies, the surface brightness profiles, the color profiles and the surface mass density profile were calculated.

BRIEF HISTORY

Nowadays, the presence of breaks in the surface brightness profiles of spiral galaxies is well known. We can distinguish three basic types: single exponential (TI), downbending profile (TII) and upbending profile (TIII).

Despite of the theoretical efforts, there is not a consensus about the mechanism acting at the break radius, with apparently inconsistent observational results between edge-on (EO) and face-on galaxies (FO) (see Pohlen & Trujillo 2006; Bakos et al. 2008 ).

THE DATA

Our sample contains 19 edge-on galaxies contained in the SDSS and in the S4G surveys. The surface brightness profiles were measured by placing a rectangular slit over the galactic plane, with the final profile representing the average of the two sides of the galaxy.

NGC4244 viewed by the S4G survey (3.6 μm band)

NGC4244 viewed by the SDSS survey (r' band)

NOTE: an accurate sky subtraction is needed to reach the break radius. The 3.6 μm band background was polynomially fitted to obtain a flatter sky.

We found two differentiated features: breaks (black dashed line) and truncations (red one).

rbreak

= 8.4 ± 1.2 kpc

rtrunc

= 13.2 ± 1.4 kpc

rtrunc

/ r

break = 1.57 ± 0.46

Ignacio Martín  e­mail: imartin@iac.es

- Breaks and truncations might be caused by distinct mechanisms at different radius.

- Truncations are phenomena apparently connected to a real drop of the stellar mass density.

- Break features are related to stellar population changes along the galaxies.

The 6 bands can be used to create radial SEDs and derive the dust extinction among our sample of edge-on galaxies.

Judit Bakos  e­mail: jbakos@iac.es Ignacio Trujillo  e­mail: trujillo@iac.es Johan Knapen  e­mail: jhk@iac.es

ORIGINAL MASK FINALBakos, J., Trujillo, I. & Pohlen, M. 2008, ApJL, 683, L103Pohlen, M. & Trujillo, I. 2006, A&A, 454, 759