Stellar Disk Truncations Research Articles

Probing the stellar populations in the outskirts of spiral galaxies

We present our results on the stellar population properties of the outskirts of disk galaxies. In particular, we focus on spiral galaxies with stellar disk truncations in their radial surface brightness profiles. Using SDSS data we show color gradients. We find that the color radial profile exhibits a "U'-shape", showing a minimum at the position of the break of the surface brightness profile. We obtain stellar surface mass density profiles of truncated galaxies as well, these show a peculiar behaviour: they follow very closely an exponential decrement. This suggests the idea that the observed properties of truncated galaxies are not caused by a drop in the mass distribution but by a different stellar population in the outer regions of the disks. Confronting this with current theoretical scenarios we find that this is likely to be a result of secular evolution, in which scenario stars are being formed inside the break and then being motioned outwards which would result in an inverted age gradient corresponding to the observed color profiles. Having maintained this idea, using multiwave-length data from GALEX, SDSS, UKIDSS and SPITZER we showed a dependence of the inner-outer scale-length ratio of truncated disks. Our results suggest that there is an existing general trend of the scale-length ratio: from bluer to redder bands the scale-length ratio decreases, which is in accordance with the stellar disk being dominated by an older stellar population in the outer disk.

Cosmic Evolution of Stellar Disk Truncations: Fromz ∼ 1 to the Local Universe

We have conducted the largest systematic search so far for stellar disk truncations in disk-like galaxies at intermediate redshift (z<1.1), using the Great Observatories Origins Deep Survey South (GOODS-S) data from the Hubble Space Telescope - ACS. Focusing on Type II galaxies (i.e. downbending profiles) we explore whether the position of the break in the rest-frame B-band radial surface brightness profile (a direct estimator of the extent of the disk where most of the massive star formation is taking place), evolves with time. The number of galaxies under analysis (238 of a total of 505) is an order of magnitude larger than in previous studies. For the first time, we probe the evolution of the break radius for a given stellar mass (a parameter well suited to address evolutionary studies). Our results suggest that, for a given stellar mass, the radial position of the break has increased with cosmic time by a factor 1.3+/-0.1 between z~1 and z~0. This is in agreement with a moderate inside-out growth of the disk galaxies in the last ~8 Gyr. In the same period of time, the surface brightness level in the rest-frame B-band at which the break takes place has increased by 3.3+/-0.2 mag/arcsec^2 (a decrease in brightness by a factor of 20.9+/-4.2). We have explored the distribution of the scale lengths of the disks in the region inside the break, and how this parameter relates to the break radius. We also present results of the statistical analysis of profiles of artificial galaxies, to assess the reliability of our results.

Cosmic evolution of stellar disk truncations: from z = 1 to the Local Universe

AbstractWe present our recent results on the cosmic evolution of the outskirts of disk galaxies. In particular we focus on disk–like galaxies with stellar disk truncations. Using UDF, GOODS and SDSS data we show how the position of the break (i.e. a direct estimator of the size of the stellar disk) evolves with time since z~1. Our findings agree with an evolution on the radial position of the break by a factor of 1.3 ± 0.1 in the last 8 Gyr for galaxies with similar stellar masses. We also present radial color gradients and how they evolve with time. At all redshifts we find a radial inside-out bluing reaching a minimum at the position of the break radius, this minimum is followed by a reddening outwards. Our results constraint several galaxy disk formation models and favour a scenario where stars are formed inside the break radius and are relocated in the outskirts of galaxies through secular processes.

Stellar Disk Truncations at High z : Probing Inside-Out Galaxy Formation

We have conducted a systematic search for stellar disk truncations in disk-like galaxies at intermediate redshift (z<1.1) using the Hubble Ultra Deep Field (UDF) data. We use the position of the truncation as a direct estimator of the size of the stellar disk. After accounting for the surface brightness evolution of the galaxies, our results suggest that the radial position of the truncations has increased with cosmic time by ~1-3 kpc in the last ~8 Gyr. This result indicates a small to moderate (~25%) inside-out growth of the disk galaxies since z~1.

Truncation of stellar disks in galaxies at z ≈ 1

We report here the first evidence for stellar disk truncation at high redshift, based on surface photometry of a sample of 16 high redshift (0.6 < z < 1.0) disk galaxies from the GOODS HST/ACS data. The radial profiles are best fit by a double exponential profile. This result agrees with the profile of disks in local galaxies. The cosmological surface brightness dimming at this redshift range only allows us to detect galaxies with spatially early truncation, Rbr/hin 3.5. Six galaxies show the radial double exponential structure, with an average value of Rbr/hin ≈ 1.8. Such early truncated galaxies are missing in local samples so far. This result opens the ground for observing directly disk evolution through the study of the truncation radius as a function of redshift.

Flattening and truncation of stellar discs in edge-on spiral galaxies

We analyse the global structure of the old stellar discs in 34 edge-on spiral galaxies. The radial and vertical exponential scale parameters of the discs are obtained by applying an improved two-dimensional decomposition technique to our I-band photometry. We find a clear increase in the disc scaleheight with maximum rotational velocity, in accordance with observations of the stellar velocity dispersions in galaxy discs. The range and maximum of the intrinsic flattening of the disc light seem to increase with both maximum rotational velocity and total HI mass. We use the disc flattening to estimate the disc contribution to the maximum rotational velocity, resulting in an average of 57+-22 percent. The disc light distributions are further investigated for the presence of radial truncations. We find that the radial light distributions of at least 20 spirals are truncated, corresponding to 60 percent of the sample. For small scalelength spirals, which are the most numerous in the local Universe, the results suggest that the average ratio of disc truncation radius to disc scalelength is at least four.

The truncation of stellar discs: The magnetic hypothesis

We propose a hypothesis of the truncation of stellar discs based on the magnetic model of the rotation curve of spiral galaxies. Once the disc had formed and acquired its present structure, approximately, three balanced forces were acting on the initial gas: gravity and magnetic forces, inwards, and centrifugal force. When stars are formed from this gas, the magnetic force is suddenly suppressed. Gravitation alone cannot retain the newly-formed stars and at birth places beyond a certain galactocentric radius they escape to intergalactic space. This radius is the so-called ``truncation radius'', which is predicted to be at about 4-5 disc radial scale lengths, in promising agreement with observations.

Near infrared observations of the truncation of stellar disks

We present a first study of of the stellar disks of spiral galaxies in the near infrared. Observations of NGC 4013, NGC 4217, NGC 6504 and NGC 5981 were made with the CAIN NIR camera on the CST in Tenerife. This wavelength range provides the best description of the phenomenon, not only because extinction effects are minimized, but also because the distribution of the old stellar population is directly obtained. The four galaxies are edge-on and an inversion method was developed to obtain the deprojected profiles. We did not assume any model of the different galactic components. The truncation curve, i.e. T(R) =mu (R) mu (D)(R), where mu is the actual surface brightness in mag/arcsec(2) and muD the exponential disk surface brightness, has been obtained with unprecedented precision. It is suggested that T(R) is proportional to (R(t)-R)(-1), where R(t) is the radius, i.e. the radius beyond which no star is observed.