THE IMPACT OF BARS ON DISK BREAKS AS PROBED BY S⁴G IMAGING

Abstract

We have analyzed the radial distribution of old stars in a sample of 218 nearby face-on disks, using deep 3.6 µm images from the Spitzer Survey of Stellar Structure in Galaxies (S 4 G). In particular, we have studied the structural properties of those disks with a broken or down-bending profile. We find that, on average, disks with a genuine single exponential profile have a scale-length and a central surface brightness which are intermediate to those of the inner and outer components of a downbending disk with the same total stellar mass. In the particular case of barred galaxies, the ratio between the break and the bar radii (R br /R bar ) depends strongly on the total stellar mass of the galaxy. For galaxies more massive than 10 10 M ⊙ , the distribution is bimodal, peaking at R br /R bar ∼ 2 and ∼ 3.5. The first peak, which is the most populated one, is linked to the Outer Lindblad Resonance of the bar, whereas the second one is consistent with a dynamical coupling between the bar and the spiral pattern. For galaxies below 10 10 M ⊙ , breaks are found up to ∼ 10R bar , but we show that they could still be caused by resonances given the rising nature of rotation curves in these low-mass disks. While not ruling out star formation thresholds, our results imply that radial stellar migration induced by non-axysymmetric features can be responsible not only for those breaks at ∼ 2R bar , but also for many of those found at larger radii.

HERschelObservations of Edge-on Spirals (HEROES)

“…However, analysis of surface brightness profiles of galaxies has shown that not all galactic discs can be described accurately by Eq. (2), since they typically show truncations and anti-truncations (Erwin et al 2005(Erwin et al , 2008Muñoz-Mateos et al 2013). A modified profile can be presented as (Erwin et al 2008;Erwin 2015)…”

Testing MOND gravity in the shell galaxy NGC 3923

“…First, we manually masked bright foreground stars and also the brightest shells that could influence the surface photometry. The surface brightness analysis was done following Muñoz-Mateos et al (2013, see also Gil de Paz & Madore 2005and Muñoz-Mateos et al 2009). Galaxy isophotes were fitted using the IRAF (Tody 1993) task ellipse.…”

Outer-disk reddening and gas-phase metallicities: The CALIFA connection

“…The observational results obtained at high redshift (Pérez 2004;Azzollini et al 2008) also suggest that breaks are present in distant galaxies and that, once formed, are long lived (Governato et al 2007;Martínez-Serrano et al 2009). This variety of radial morphologies have been tentatively explained by different mechanisms: outer Lindblad resonances (OLR; Martín-Navarro et al 2012;Muñoz-Mateos et al 2013), the presence of a bar (Debattista et al 2006) or longlived spiral arms (Scarano et al 2011), a shrinking of the starforming disk (Sánchez-Blázquez et al 2009;Zheng et al 2015, Z15 hereafter), changes in star-formation triggering mechanisms (Elmegreen & Parravano 1994), satellite accretion or the existence of a star formation (SF) threshold radius beyond which only stellar migration would populate the outer disk (Roškar et al 2008, R08 hereafter). The recent findings of a reddening in the optical broadband colors for 39 Tii profiles (Bakos et al 2008, B08 hereafter) have provided a fundamental piece of evidence to the actual scenario for the formation of galaxy disks and posed a challenge to these mechanisms.…”