Connecting galaxies with their descendants (or progenitors) at different redshifts can yield strong constraints on galaxy evolution. Observational studies have historically selected samples of ...galaxies using a physical quantity, such as stellar mass, either above a constant limit or at a constant cumulative number density. Investigation into the efficacy of these selection methods has not been fully explored. Using a set of four semi-analytical models based on the output of the Millennium Simulation, we find that selecting galaxies at a constant number density (in the range −4.3 < log n Mpc−3 h
3 < −3.0) is superior to a constant stellar mass selected sample, although it still has significant limitations. Recovery of the average stellar mass, stellar mass density and average star formation rate is highly dependent on the choice of number density but can all be recovered to within <50 per cent at the commonly employed choice of log n Mpc−3 h
3 = −4.0, corresponding to log M⊙ h
−1 ∼ 11.2 at z = 0, but this increases at lower mass limits. We show that there is a large scatter between the location of a given galaxy in a rank ordering based on stellar mass between different redshifts. We find that the inferred velocity dispersion may be a better tracer of galaxy properties, although further investigation is warranted into simulating this property. Finally, we find that over large redshift ranges selection at a constant number density is more effective in tracing the progenitors of modern galaxies than vice versa.
We present a study on the stellar mass growth of the progenitors of local massive galaxies with a variety of number density selections with n ≤ 1 × 10−4 Mpc−3 (corresponding to M
* = 1011.24 M⊙ at ...z = 0.3) in the redshift range 0.3 < z < 3.0. We select the progenitors of massive galaxies using a constant number density selection, and one which is adjusted to account for major mergers. We find that the progenitors of massive galaxies grow by a factor of 4 in total stellar mass over this redshift range. On average the stellar mass added via the processes of star formation, major and minor mergers account for 24 ± 8, 17 ± 15 and 34 ± 14 per cent, respectively, of the total galaxy stellar mass at z = 0.3. Therefore 51 ± 20 per cent of the total stellar mass in massive galaxies at z = 0.3 is created externally to their z = 3 progenitors. We explore the implication of these results on the cold gas accretion rate and size evolution of the progenitors of most massive galaxies over the same redshift range. We find an average gas accretion rate of ∼66 ± 32 M⊙ yr−1 over the redshift range of 1.5 < z < 3.0. We find that the size evolution of a galaxy sample selected this way is on average lower than the findings of other investigations.
In this paper we present a detailed study of the structures and morphologies of a sample of 1188 massive galaxies with M
* ≥ 1010 M between redshifts z = 1 and 3 within the Ultra Deep Survey (UDS) ...region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Using this sample we determine how galaxy structure and morphology evolve with time, and investigate the nature of galaxy structure at high redshift. We visually classify our sample into discs, ellipticals and peculiar systems and correct for redshift effects on these classifications through simulations. We find significant evolution in the fractions of galaxies at a given visual classification as a function of redshift. The peculiar population is dominant at z > 2 with a substantial spheroid population, and a negligible disc population. We compute the transition redshift, z
trans, where the combined fraction of spheroidal and disc galaxies is equal to that of the peculiar population, as z
trans = 1.86 ± 0.62 for galaxies in our stellar mass range. We find that this transition changes as a function of stellar mass, with Hubble-type galaxies becoming dominant at higher redshifts for higher mass galaxies (z
trans = 2.22 ± 0.82), than for the lower mass galaxies (z
trans = 1.73 ± 0.57). Higher mass galaxies become morphologically settled before their lower mass counterparts, a form of morphological downsizing. We furthermore compare our visual classifications with the Sérsic index, the concentration, asymmetry and clumpiness (CAS) parameters, star formation rate and rest-frame U − B colour. We find links between the colour of a galaxy, its star formation rate and how extended or peculiar it appears. Finally, we discuss the negligible z > 2 disc fraction based on visual morphologies and speculate that this is an effect of forming disc appearing peculiar through processes such as violent disc instabilities or mergers. We conclude that to properly define and measure high-redshift morphology and structure a new and more exact classification scheme is needed.
We combine photometry from the Ultra Deep Survey (UDS), Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) UDS and CANDELS the Great Observatories Origins Deep Survey-South ...(GOODS-S) surveys to construct the galaxy stellar mass function probing both the low- and high-mass end accurately in the redshift range 0.3 < z < 3. The advantages of using a homogeneous concatenation of these data sets include meaningful measures of environment in the UDS, due to its large area (0.88 deg2), and the high-resolution deep imaging in CANDELS (H
160 > 26.0), affording us robust measures of structural parameters. We construct stellar mass functions for the entire sample as parametrized by the Schechter function, and find that there is a decline in the values of ϕ and of α with higher redshifts, and a nearly constant M* up to z ∼ 3. We divide the galaxy stellar mass function by colour, structure, and environment and explore the links between environmental overdensity, morphology, and the quenching of star formation. We find that a double Schechter function describes galaxies with high Sérsic index (n > 2.5), similar to galaxies which are red or passive. The low-mass end of the n > 2.5 stellar mass function is dominated by blue galaxies, whereas the high-mass end is dominated by red galaxies. This shows that there is a possible link between morphological evolution and star formation quenching in high mass galaxies, which is not seen in lower mass systems. This in turn suggests that there are strong mass-dependent quenching mechanisms. In addition, we find that the number density of high-mass systems is elevated in dense environments, suggesting that an environmental process is building up massive galaxies quicker in over densities than in lower densities.
Due to significant galaxy contamination and impurity in stellar mass selected samples (up to 95 per cent from z = 0-3), we examine the star formation history, quenching time-scales, and structural ...evolution of galaxies using a constant number density selection with data from the United Kingdom Infra-Red Deep Sky Survey Ultra-Deep Survey field. Using this methodology, we investigate the evolution of galaxies at a variety of number densities from z = 0-3. We find that samples chosen at number densities ranging from 3 x 10 super( -4) to 10 super( -5) galaxies Mpc-3 (corresponding to z ~ 0.5 stellar masses of M* = 10 super( 10.95-11.6) M0) have a star-forming blue fraction of ~50 per cent at z ~ 2.5, which evolves to a nearly 100 per cent quenched red and dead population by z ~ 1. We also see evidence for number density downsizing, such that the galaxies selected at the lowest densities (highest masses) become a homogeneous red population before those at higher number densities. Examining the evolution of the colours for these systems furthermore shows that the formation redshift of galaxies selected at these number densities is zform > 3. The structural evolution through size and Sersic index fits reveal that while there remains evolution in terms of galaxies becoming larger and more concentrated in stellar mass at lower redshifts, the magnitude of the change is significantly smaller than for a mass-selected sample. We also find that changes in size and structure continues at z < 1, and is coupled strongly to passivity evolution. We conclude that galaxy structure is driving the quenching of galaxies, such that galaxies become concentrated before they become passive.
Abstract
We present a study of the resolved star-forming properties of a sample of distant massive (M > 1011 M⊙) galaxies in the GOODS NICMOS Survey (GNS), based on deep Hubble Space Telescope ...imaging from the GOODS North and South fields. We derive dust corrected ultraviolet star formation rates (SFRs) as a function of radius for 45 massive galaxies within the redshift range of 1.5 < z < 3 in order to measure the spatial location of ongoing star formation in massive galaxies. We find that the SFRs present in different regions of a galaxy reflect the already existent stellar mass density, i.e. high-density regions have higher SFRs than lower density regions, on average. This observed star formation is extrapolated in several ways to the present day, and we measure the amount of new stellar mass that is created in individual portions of each galaxy to determine how the stellar mass added via star formation changes the observed stellar mass profile, the Sérsic index and effective radius over time. We find that these massive galaxies fall into three broad classifications of star formation distribution: (1) total stellar mass added via star formation is insignificant compared to the stellar mass that is already in place at high redshift. (2) Stellar mass added via star formation is only significant in the outer regions (R > 1 kpc) of the galaxy. (3) Stellar mass added via star formation is significant in both the inner (R < 1 kpc) and outer regions of the galaxy. These different star formation distributions increase the effective radii over time, which are on average a factor of ∼16 ± 5 per cent larger, with little change in the Sérsic index (average Δn = −0.9 ± 0.9) after evolution. We also implement a range of simple stellar migration models into the simulated evolutionary path of these galaxies in order to gauge its effect on the properties of our sample. This yields a larger increase in the evolved effective radii than the pure static star formation model, with a maximum average increase of ΔR
e ∼ 54 ± 19 per cent, but with little change in the Sérsic index, Δn ∼ −1.1 ± 1.3. These results are not in agreement with the observed change in the effective radius and Sérsic index between z ∼ 2.5 and z ∼ 0 obtained via various observational studies. We conclude that star formation and stellar migration alone cannot account for the observed change in structural parameters for this galaxy population, implying that other mechanisms must additionally be at work to produce the evolution, such as merging.
We present quantified visual morphologies of approximately 48 000 galaxies observed in three Hubble Space Telescope legacy fields by the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey ...(CANDELS) and classified by participants in the Galaxy Zoo project. 90 per cent of galaxies have z less than or equal to 3 and are observed in rest-frame optical wavelengths by CANDELS. Each galaxy received an average of 40 independent classifications, which we combine into detailed morphological information on galaxy features such as clumpiness, bar instabilities, spiral structure, and merger and tidal signatures. We apply a consensus-based classifier weighting method that preserves classifier independence while effectively down-weighting significantly outlying classifications. After analysing the effect of varying image depth on reported classifications, we also provide depth-corrected classifications which both preserve the information in the deepest observations and also enable the use of classifications at comparable depths across the full survey. Comparing the Galaxy Zoo classifications to previous classifications of the same galaxies shows very good agreement; for some applications, the high number of independent classifications provided by Galaxy Zoo provides an advantage in selecting galaxies with a particular morphological profile, while in others the combination of Galaxy Zoo with other classifications is a more promising approach than using any one method alone. We combine the Galaxy Zoo classifications of 'smooth' galaxies with parametric morphologies to select a sample of featureless discs at 1 less than or equal to z less than or equal to 3, which may represent a dynamically warmer progenitor population to the settled disc galaxies seen at later epochs.
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