The Size Evolution of Galaxies sincez∼3: Combining SDSS, GEMS, and FIRES

Abstract

We present the evolution of the luminosity-size and stellar massYsize relations of luminous (L V k 3:4 ; 10 10 h À2 70 L) and massive (M Ã k 3 ; 10 10 h À2 70 M) galaxies in the last $11 Gyr. We use very deep near-infrared images of the Hubble Deep FieldYSouth and the MS 1054-03 field in the J s , H, and K s bands from FIRES to retrieve the sizes in the optical rest frame for galaxies with z > 1. We combine our results with those from GEMS at 0:2 < z < 1 and SDSS at z $ 0:1 to achieve a comprehensive picture of the optical rest-frame size evolution from z ¼ 0 to 3. Galaxies are differentiated according to their light concentration using the Sérsic index n. For less concentrated objects, the galaxies at a given luminosity were typically $3 AE 0:5 (AE2) times smaller at z $ 2:5 than those we see today. The stellar massYsize relation has evolved less: the mean size at a given stellar mass was $2 AE 0:5 times smaller at z $ 2:5, evolving proportionally to (1 þ z) À0:40AE0:06. Simple scaling relations between dark matter halos and baryons in a hierarchical cosmogony predict a stronger (although consistent within the error bars) than observed evolution of the stellar massYsize relation. The observed luminosity-size evolution out to z $ 2:5 matches well recent infall model predictions for Milky WayYtype objects. For low-n galaxies, the evolution of the stellar massYsize relation would follow naturally if the individual galaxies grow inside out. For highly concentrated objects, the situation is as follows: at a given luminosity, these galaxies were $2:7 AE 1:1 times smaller at z $ 2:5 (or, put differently, were typically $2:2 AE 0:7 mag brighter at a given size than they are today), and at a given stellar mass the size has evolved proportionally to (1 þ z) À0:45AE0:10 .

The size evolution of star-forming and quenched galaxies in the IllustrisTNG simulation

“…Given these corrections, the simulated widths appear to be somewhat larger than the observationally-inferred intrinsic widths. Nevertheless, they are 0.2 dex, which compares favourably to the robust (model-independent) conclusion quoted by van der Wel et al (2014). In addition, we find that the distribution widths of earlytype galaxies are smaller than those of late-types, as inferred observationally as well.…”

“…For the simulation we use the age and metallicity of the stellar particles to produce mock rest-frame r-band luminosity, and do not consider the effects of dust on the apparent size of galaxies. For the measurements, there exist systematic differences depending on the exact band that is used, and we apply empirically-derived corrections to convert them uniformly to the rest-frame r-band (Kelvin et al 2012;Szomoru et al 2013;van der Wel et al 2014), as described below. (iv) In terms of the stellar mass assigned to each galaxy, we use the bound mass assigned by SUBFIND, while observationally it is determined using the aforementioned profile fits to the light profiles and a conversion to stellar mass using model massto-light (M/L) ratios.…”

“…(iii) The Shen et al (2003) and Bernardi et al (2014) measurements are based on z ∼ 0.1 galaxies from the SDSS survey, while the ones from van der Wel et al (2014) are based on the CANDELS survey at z ∼ 0.25, which we extrapolate to z = 0.1 using R ∝ H(z) β H with the mass-dependent βH values provided in their Table 2, where H(z) is the Hubble rate 6 . (iv) The Shen et al (2003) and Bernardi et al (2014) measurements are made directly in the SDSS r-band, while the ones from van der Wel et al (2014) are made in the Hubble Space Telescope Wide Field Camera 3 (WFC3) F125W filter, centered on an observedframe wavelength of 1.25 µm. van der Wel et al (2014) report these sizes after their conversion to rest-frame 500 nm using the gradient ∆ logR/∆ logλ they directly measure between the F814W (814 nm) and F125W filters, and we further convert them using their Equation 1 back to a somewhat longer wavelength, namely to the center of the r-band at rest-frame 623 nm, in order to match the SDSS-based studies.…”

“…(iv) The Shen et al (2003) and Bernardi et al (2014) measurements are made directly in the SDSS r-band, while the ones from van der Wel et al (2014) are made in the Hubble Space Telescope Wide Field Camera 3 (WFC3) F125W filter, centered on an observedframe wavelength of 1.25 µm. van der Wel et al (2014) report these sizes after their conversion to rest-frame 500 nm using the gradient ∆ logR/∆ logλ they directly measure between the F814W (814 nm) and F125W filters, and we further convert them using their Equation 1 back to a somewhat longer wavelength, namely to the center of the r-band at rest-frame 623 nm, in order to match the SDSS-based studies. (v) Most probably the principal reason for the systematic difference between Shen et al (2003) and Bernardi et al (2014) versus van der Wel et al (2014, besides possible systematics on the stellar mass, is that Shen et al (2003) and Bernardi et al (2014) For each of these two size definitions, relations using two mass definitions are shown: full mass and mass within 2R * ,3D (colored curves).…”

“…Galaxy size is a basic observational property that is found to significantly vary with galaxy mass, color or star-formation activity, and redshift (Shen et al 2003;Ferguson et al 2004;Trujillo et al 2006;Elmegreen et al 2007;Williams et al 2010;Mosleh et al 2012;Ono et al 2013;van der Wel et al 2014;Lange et al 2015). These dependencies encode important information on the formation processes of galaxies of different types.…”