A mass-dependent slope of the galaxy size-mass relation out to z~3: further evidence for a direct relation between median galaxy size and median halo mass

We reassess the galaxy size-mass relation out to z~3 using a new definition of size and a sample of >29,000 galaxies from the 3D-HST, CANDELS, and COSMOS-DASH surveys. Instead of the half-light radius r_50 we use r_80, the radius containing 80% of the stellar light. We find that the r_80 -- M_star relation has the form of a broken power law, with a clear change of slope at a pivot mass M_p. Below the pivot mass the relation is shallow (r_80 \propto M_star^0.15) and above it it is steep (r_80\propto M_star^0.6). The pivot mass increases with redshift, from log(M_p/M_sun)~ 10.2 at z=0.4 to log(M_p/M_sun)~ 10.9 at z=1.7-3. We compare these r_80-M_star relations to the M_halo-M_star relations derived from galaxy-galaxy lensing, clustering analyses, and abundance matching techniques. Remarkably, the pivot stellar masses of both relations are consistent with each other at all redshifts, and the slopes are very similar both above and below the pivot when assuming M_halo \propto r_80^3. The implied scaling factor to relate galaxy size to halo size is r_80 / R_vir = 0.047, independent of stellar mass and redshift.From redshift 0 to 1.5, the pivot mass also coincides with the mass where the fraction of star-forming galaxies is 50%, suggesting that the pivot mass reflects a transition from dissipational to dissipationless galaxy growth. Finally, our results imply that the scatter in the stellar-to-halo mass ratio is relatively small for massive halos (~0.2 dex for M_halo>10^12.5 M_sun).Comment: Accepted in ApJL. Please also see complementary paper Miller et al. 201

A mass-dependent slope of the galaxy size-mass relation out to z ∼ 3 : further evidence for a direct relation between median galaxy size and median halo mass

We reassess the galaxy size-mass relation out to z similar to 3 using a new definition of size and a sample of >29,000 galaxies from the 3D-HST, CANDELS, and COSMOS-DASH surveys. Instead of the half-light radius r(50) we use r(80), the radius containing 80% of the stellar light. We find that the r(80)M(*) relation has the form of a broken power law, with a clear change of slope at a pivot mass M-p. Below the pivot mass the relation is shallow (r(80) proportional to M-*(0.)15); above it, it is steep (r(80) proportional to M-*(0.)6). The pivot mass increases with redshift, from log(M-p/M-circle dot) approximate to 10.2 at z = 0.4 to log(M-p/M-circle dot) approximate to 10.9 at z = 1.7-3. We compare these r(80)-M-* relations to the M-helo-M-* relations derived from galaxy-galaxy lensing, clustering analyses, and abundance matching techniques. Remarkably, the pivot stellar masses of both relations are consistent with each other at all redshifts, and the slopes are very similar both above and below the pivot when assuming M-halo proportional to r(8)(0)(3). The implied scaling factor to relate galaxy size to halo size is r(80)/R-vir = 0.047, independent of stellar mass and redshift. From redshift 0 to 1.5, the pivot mass also coincides with the mass where the fraction of star-forming galaxies is 50%, suggesting that the pivot mass reflects a transition from dissipational to dissipationless galaxy growth. Finally, our results imply that the scatter in the stellar-to-halo mass is relatively small for massive halos (similar to 0.2 dex for M-halo > 10(1)(2.)(5) M-circle dot)

The Relation between Galaxy Structure and Spectral Type: Implications for the Buildup of the Quiescent Galaxy Population at 0.5<z<2.0

We present the relation between galaxy structure and spectral type, using a K-selected galaxy sample at 0.5<z<2.0. Based on similarities between the UV-to-NIR spectral energy distributions, we classify galaxies into 32 spectral types. The different types span a wide range in evolutionary phases, and thus -- in combination with available CANDELS/F160W imaging -- are ideal to study the structural evolution of galaxies. Effective radii (R_e) and Sersic parameters (n) have been measured for 572 individual galaxies, and for each type, we determine R_e at fixed stellar mass by correcting for the mass-size relation. We use the rest-frame U-V vs. V-J diagram to investigate evolutionary trends. When moving into the direction perpendicular to the star-forming sequence, in which we see the Halpha equivalent width and the specific star formation rate (sSFR) decrease, we find a decrease in R_e and an increase in n. On the quiescent sequence we find an opposite trend, with older redder galaxies being larger. When splitting the sample into redshift bins, we find that young post-starburst galaxies are most prevalent at z>1.5 and significantly smaller than all other galaxy types at the same redshift. This result suggests that the suppression of star formation may be associated with significant structural evolution at z>1.5. At z<1, galaxy types with intermediate sSFRs (10^{-11.5}-10^{-10.5} yr^-1) do not have post-starburst SED shapes. These galaxies have similar sizes as older quiescent galaxies, implying that they can passively evolve onto the quiescent sequence, without increasing the average size of the quiescent galaxy population.Comment: 7 pages, 5 figures; Accepted for publication in ApJ

A New View of the Size-Mass Distribution of Galaxies: Using r20r_{20} and r80r_{80} instead of r50r_{50}

When investigating the sizes of galaxies it is standard practice to use the half-light radius, $r_{50}$. Here we explore the effects of the size definition on the distribution of galaxies in the size -- stellar mass plane. Specifically, we consider $r_{20}$ and $r_{80}$, the radii that contain 20% and 80% of a galaxy's total luminosity, as determined from a Sersic profile fit, for galaxies in the 3D-HST/CANDELS and COSMOS-DASH surveys. These radii are calculated from size catalogs based on a simple calculation assuming a Sersic profile. We find that the size-mass distributions for $r_{20}$ and $r_{80}$ are markedly different from each other and also from the canonical $r_{50}$ distribution. The most striking difference is in the relative sizes of star forming and quiescent galaxies at fixed stellar mass. Whereas quiescent galaxies are smaller than star forming galaxies in $r_{50}$, this difference nearly vanishes for $r_{80}$. By contrast, the distance between the two populations increases for $r_{20}$. Considering all galaxies in a given stellar mass and redshift bin we detect a significant bimodality in the distribution of $r_{20}$, with one peak corresponding to star forming galaxies and the other to quiescent galaxies. We suggest that different measures of the size are tracing different physical processes within galaxies; $r_{20}$ is closely related to processes controlling the star formation rate of galaxies and $r_{80}$ may be sensitive to accretion processes and the relation of galaxies with their halos.Comment: Resubmitted to ApJL after responding to referee's comments. Please also see Mowla et al. submitted today as wel

Deprojecting Sersic Profiles for Arbitrary Triaxial Shapes: Robust Measures of Intrinsic and Projected Galaxy Sizes

We present the analytical framework for converting projected light distributions with a S\'ersic profile into three-dimensional light distributions for stellar systems of arbitrary triaxial shape. The main practical result is the definition of a simple yet robust measure of intrinsic galaxy size: the median radius $r_\mathrm{med}$, defined as the radius of a sphere that contains 50% of the total luminosity or mass, that is, the median distance of a star to the galaxy center. We examine how $r_\mathrm{med}$ depends on projected size measurements as a function of S\'ersic index and intrinsic axis ratios, and demonstrate its relative independence of these parameters. As an application we show that the projected semi-major axis length of the ellipse enclosing 50% of the light is an unbiased proxy for $r_\mathrm{med}$, with small galaxy-to-galaxy scatter of $\sim$10% (1$\sigma$), under the condition that the variation in triaxiality within the population is small. For galaxy populations with unknown or a large range in triaxiality an unbiased proxy for $r_\mathrm{med}$ is $1.3\times R_{e}$, where $R_{e}$ is the circularized half-light radius, with galaxy-to-galaxy scatter of 20-30% (1$\sigma$). We also describe how inclinations can be estimated for individual galaxies based on the measured projected shape and prior knowledge of the intrinsic shape distribution of the corresponding galaxy population. We make the numerical implementation of our calculations available.Comment: 7 pages, 4 figures; accepted for publication in Ap

A constant limiting mass scale for flat early-type galaxies from z=1 to z=0: density evolves but shapes do not

We measure the evolution in the intrinsic shape distribution of early-type galaxies from z~1 to z~0 by analyzing their projected axis-ratio distributions. We extract a low-redshift sample (0.04 < z < 0.08) of early-type galaxies with very low star-formation rates from the SDSS, based on a color-color selection scheme and verified through the absence of emission lines in the spectra. The inferred intrinsic shape distribution of these early-type galaxies is strongly mass dependent: the typical short-to-long intrinsic axis-ratio of high-mass early-type galaxies (>1e11 M_sun) is 2:3, where as at masses below 1e11 M_sun this ratio narrows to 1:3, or more flattened galaxies. In an entirely analogous manner we select a high-redshift sample (0.6 < z < 0.8) from two deep-field surveys: GEMS and COSMOS. We find a seemingly universal mass of ~1e11 M_sun for highly flatted early-type systems at all redshifts. This implies that the process that grows an early-type galaxy above this ceiling mass involves forming round systems. Using both parametric and non-parametric tests, we find no evolution in the projected axis-ratio distribution for galaxies with masses >3e10 M_sun with redshift. At the same time, our samples imply an increase of 2-3x in co-moving number density for early-type galaxies at masses >3e10 M_sun, in agreement with previous studies. Given the direct connection between the axis-ratio distribution and the underlying bulge-to-disk ratio distribution, our findings imply that the number density evolution of early-type galaxies is not exclusively driven by the emergence of either bulge- or disk-dominated galaxies, but rather by a balanced mix that depends only on the stellar mass of the galaxy. The challenge for galaxy formation models is to reproduce this overall non-evolving ratio of flattened to round early-type galaxies in the context of a continually growing population.Comment: 14 pages in emulate ApJ format, 8 color figures, submitted to ApJ, comments welcome, fixed missing reference

The Dependence of Galaxy Morphology and Structure on Environment and Stellar Mass

From the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5), we extract a sample of 4594 galaxies at redshifts 0.02<z<0.03, complete down to a stellar mass of M=10^10 Msol. We quantify their structure (Sersic index), morphology (Sersic index + ``Bumpiness''), and local environment. We show that morphology and structure are intrinsically different galaxy properties, and we demonstrate that this is a physically relevant distinction by showing that these properties depend differently on galaxy mass and environment. Structure mainly depends on galaxy mass whereas morphology mainly depends on environment. This is driven by variations in star formation activity, as traced by color, which only weakly affects the structure of a galaxy but strongly affects its morphological appearance. The implication of our results is that the existence of the morphology-density relation is intrinsic and not just due to a combination of more fundamental, underlying relations. Our findings have consequences for high-redshift studies, which often use some measure of structure as a proxy for morphology. A direct comparison with local samples selected through visually classified morphologies may lead to biases in the inferred evolution of the morphological mix of the galaxy population, and misinterpretations in terms of how galaxy evolution depends on mass and environment.Comment: Accepted for publication in ApJ Letters, 5 pages, 5 figures. Minor changes made to match published versio

MaNGA integral-field stellar kinematics of LoTSS radio galaxies: Luminous radio galaxies tend to be slow rotators

The radio jets of an active galactic nucleus (AGN) can heat up the gas around a host galaxy and quench star formation activity. The presence of a radio jet could be related to the evolutionary path of the host galaxy and may be imprinted in the morphology and kinematics of the galaxy. In this work, we use data from the Sloan Digital Sky Survey's Mapping Nearby Galaxies at Apache Point Observatory survey and the Low Frequency Array (LOFAR) Two-Metre Sky Survey as well as the National Radio Astronomy Observatory (NRAO) the Karl G. Jansky Very Large Array (VLA) Sky Survey and the Faint Images of the Radio Sky at Twenty Centimeter survey. We combine these integral field spectroscopic data and radio data to study the link between stellar kinematics and radio AGNs. We find that the luminosity-weighted stellar angular momentum $\lambda_{Re}$ is tightly related to the range of radio luminosity and the fraction of radio AGNs F radio present in galaxies, as high-luminosity radio AGNs are only in galaxies with a small $\lambda_{Re}$, and the $F_{radio}$ at a fixed stellar mass decreases with $\lambda_{Re}$. These results indicate that galaxies with stronger random stellar motions with respect to the ordered motions might be better breeding grounds for powerful radio AGNs. This would also imply that the merger events of galaxies are important in the triggering of powerful radio jets in our sample.Comment: 10 pages,7 figures. Accepted in A&

Spatially Resolved Stellar Kinematics of Field Early-Type Galaxies at z=1: Evolution of the Rotation Rate

We use the spatial information of our previously published VLT/FORS2 absorption line spectroscopy to measure mean stellar velocity and velocity dispersion profiles of 25 field early-type galaxies at a median redshift z=0.97 (full range 0.6<z<1.2). This provides the first detailed study of early-type galaxy rotation at these redshifts. From surface brightness profiles from HST imaging we calculate two-integral oblate axisymmetric Jeans equation models for the observed kinematics. Fits to the data yield for each galaxy the degree of rotational support and the mass-to-light ratio M/L_Jeans. S0 and Sa galaxies are generally rotationally supported, whereas elliptical galaxies rotate less rapidly or not at all. Down to M(B)=-19.5 (corrected for luminosity evolution), we find no evidence for evolution in the fraction of rotating early-type (E+S0) galaxies between z=1 (63+/-11%) and the present (61+/-5%). We interpret this as evidence for little or no change in the field S0 fraction with redshift. We compare M/L_Jeans with M/L_vir inferred from the virial theorem and globally averaged quantities and assuming homologous evolution. There is good agreement for non-rotating (mostly E) galaxies. However, for rotationally supported galaxies (mostly S0) M/L_Jeans is on average ~40% higher than M/L_vir. We discuss possible explanations and the implications for the evolution of M/L between z=1 and the present and its dependence on mass.Comment: To appear in ApJ 683 (9 pages, 7 figures). Minor changes included to match published versio

Major Merging: The Way to Make a Massive, Passive Galaxy

We analyze the projected axial ratio distribution, p(b/a), of galaxies that were spectroscopically selected from the Sloan Digital Sky Survey (DR6) to have low star-formation rates. For these quiescent galaxies we find a rather abrupt change in p(b/a) at a stellar mass of ~10^{11} M_sol: at higher masses there are hardly any galaxies with b/a<0.6, implying that essentially none of them have disk-like intrinsic shapes and must be spheroidal. This transition mass is ~3-4 times higher than the threshold mass above which quiescent galaxies dominate in number over star-forming galaxies, which suggests these mass scales are unrelated. At masses lower than ~10^{11} M_sol, quiescent galaxies show a large range in axial ratios, implying a mix of bulge- and disk-dominated galaxies. Our result strongly suggests that major merging is the most important, and perhaps only relevant, evolutionary channel to produce massive (>10^{11} M_sol), quiescent galaxies, as it inevitably results in spheroids.Comment: Minor changes to match published version in ApJ Letter