Small Magellanic Cloud: Reaching The Outer Edge? Noelia E. D. Noël Noël & Gallart 2007, ApJL, 665, 23 Breaking News, IAC, 18 de diciembre 2007

Small Magellanic Cloud: Reaching The Outer Edge?

Noelia E. D. Noël

Noël & Gallart 2007, ApJL, 665, 23

Breaking News, IAC, 18 de diciembre 2007

Introduction

• Data

• The SMC Outskirts

• Surface Brightness Profile

• Discussion



• Host clues about the galaxy assembly processes.

• Sandage (1962) first discovered faint red stars extended beyond IC1613’s center.

• Controversy: some authors affirm the outer faint stellar envelopes evidence oldstellar halos, others suggest they are tidal debris, while others find a range ofages.

• SMC studies of outer parts began with Gardiner & Hatzidimitriou (1992) withCMDs reaching R~20 up to ~6 kpc in the LMC direction

• Carbon stars were detected in outer regions of the SMC (e.g. Kunkel 2000)

• Recent bursts of star formation were found in the Wing area (Demers &Battinelli 1998)

• Harris (2007) analyzed the MCs Bridge region and found intermediate-age and old population at ~5.5 kpc from the SMC center but only young stars at ~7 kpc

Faint Outskirts of Galaxies

•

Faint Outskirts of Galaxies (cont.)

Recently, Noël et al. (2007) presented the age distribution of 12 SMC fields through unprecedented deep CMDs:


But… how is the actual stellar content in the outer parts?....

Two differentiated stellar components?i.e. do dIrr have stellar halos? (MW-like ones: old, metal poor, devoid of gas, kinematically hot)

Smooth gradient of stellar ages?e.g. star formation shrinking with time?


• Introduction

Data



• Discussion


Small Magellanic Cloud

Location

smc

lmc

Milky Way


B, R images2.2m at La SillaMosaic 2048x4096 CCDs34’ x 33’ (0.64 x 0.615 kpc)

-78º

-76º


Fields from Noël et al. (2007)

• Introduction

• Data

The SMC Outskirts


• Discussion


CMDs of the SMC WFI fields

4.7 kpc 5.6 kpc

6.5 kpc

Mosaic field: 34’ x 33’


Foreground stars’ contamination was

simulatedusing the TRILEGAL code (Girardi et al.

2005)

CMDs of the SMC WFI fields with BaSTI isochrones (Pietrinferni et al. 2004)

4.7 kpc 5.6 kpc

6.5 kpc4.7 kpc

Z=0.002: 1, 2, 3 Gyr Z=0.001: 6, 7, 10, 13 Gyr

• Presence stars as young as ~3 Gyr old at 5.6 kpc • There is still galaxy at 6.5 kpc from the SMC center• Lack of blue extended Horizontal Branch


CMDs of the SMC WFI fields

4.7 kpc 5.6 kpc

6.5 kpc

Mosaic field: 34’ x 33’


Foreground stars’ contamination was

simulatedusing the TRILEGAL code (Girardi et al.

2005)

• Introduction

• Data


Surface Brightness Profile

• Discussion


r (arcmin)

B (

mag

/arc

sec2

)Surface Brightness in the B band Simulation of foreground stars

• Eastern fields • Western fields• Southern fields•WFI fields analyzed here

• Dot-dashed boxes: portion of CMD devoided of SMC stars• Solid lines: area where SMC stars are expected


• Introduction

• Data



Discussion


If intermediate-age and old stars were formed at their current position, the SMC is more extended and more massive than previously thought

Stars unlikely represent tidal debris torn off through interactions MW-LMC-SMC since the falling surface profile is well fit by exponential disk

SMC disk is dominating over a possible old MW-like halo (if it does exist!) in agreement with the results for the LMC (Gallart et al. 2004), pointing out the importance of reaching the old MS turnoffs

More studies farther away from the SMC center and with larger spatial coverage are needed to confirm the actual extent of the SMC


FIN… GRACIAS!!!!


Documents

Small Magellanic Cloud: Reaching The Outer Edge? Noelia E. D. Noël Noël & Gallart 2007, ApJL, 665, 23 Breaking News, IAC, 18 de diciembre 2007