Abstract
We use the energy-balance code magphys to determine stellar and dust masses, and dust corrected star formation rates for over 200 000 GAMA galaxies, 170 000 G10-COSMOS galaxies, and 200 000 ...3D-HST galaxies. Our values agree well with previously reported measurements and constitute a representative and homogeneous data set spanning a broad range in stellar-mass (108–1012 M⊙), dust-mass (106–109 M⊙), and star formation rates (0.01–100 M⊙yr−1), and over a broad redshift range (0.0 < z < 5.0). We combine these data to measure the cosmic star formation history (CSFH), the stellar-mass density (SMD), and the dust-mass density (DMD) over a 12 Gyr timeline. The data mostly agree with previous estimates, where they exist, and provide a quasi-homogeneous data set using consistent mass and star formation estimators with consistent underlying assumptions over the full time range. As a consequence our formal errors are significantly reduced when compared to the historic literature. Integrating our CSFH we precisely reproduce the SMD
with an interstellar medium replenishment factor of 0.50 ± 0.07, consistent with our choice of Chabrier initial mass function plus some modest amount of stripped stellar mass. Exploring the cosmic dust density evolution, we find a gradual increase in dust density with lookback time. We build a simple phenomenological model from the CSFH to account for the dust-mass evolution, and infer two key conclusions: (1) For every unit of stellar mass which is formed 0.0065–0.004 units of dust mass is also formed. (2) Over the history of the Universe approximately 90–95 per cent of all dust formed has been destroyed and/or ejected.
We present single-Sérsic two-dimensional (2D) model fits to 167 600 galaxies modelled independently in the ugrizYJHK bandpasses using reprocessed Sloan Digital Sky Survey Data Release Seven (SDSS ...DR7) and UKIRT Infrared Deep Sky Survey Large Area Survey imaging data available from the Galaxy And Mass Assembly (GAMA) data base. In order to facilitate this study we developed Structural Investigation of Galaxies via Model Analysis (sigma), an r wrapper around several contemporary astronomy software packages including source extractor, psf extractor and galfit 3. sigma produces realistic 2D model fits to galaxies, employing automatic adaptive background subtraction and empirical point spread function measurements on the fly for each galaxy in GAMA. Using these results, we define a common coverage area across the three GAMA regions containing 138 269 galaxies. We provide Sérsic magnitudes truncated at 10r
e which show good agreement with SDSS Petrosian and GAMA photometry for low Sérsic index systems (n < 4), and much improved photometry for high Sérsic index systems (n > 4), recovering as much as Δm= 0.5 mag in the r band. We employ a K-band Sérsic index/u−r colour relation to delineate the massive (n > ∼2) early-type galaxies (ETGs) from the late-type galaxies (LTGs). The mean Sérsic index of these ETGs shows a smooth variation with wavelength, increasing by 30 per cent from g through K. LTGs exhibit a more extreme change in Sérsic index, increasing by 52 per cent across the same range. In addition, ETGs and LTGs exhibit a 38 and 25 per cent decrease, respectively, in half-light radius from g through K. These trends are shown to arise due to the effects of dust attenuation and stellar population/metallicity gradients within galaxy populations.
We measure the mass functions for generically red and blue galaxies, using a z < 0.12 sample of log M* > 8.7 field galaxies from the Galaxy And Mass Assembly (GAMA) survey. Our motivation is that, as ...we show, the dominant uncertainty in existing measurements stems from how 'red' and 'blue' galaxies have been selected/defined. Accordingly, we model our data as two naturally overlapping populations, each with their own mass function and colour-mass relation, which enables us characterize the two populations without having to specify a priori which galaxies are 'red' and 'blue'. Our results then provide the means to derive objective operational definitions for the terms 'red' and 'blue', which are based on the phenomenology of the colour-mass diagrams. Informed by this descriptive modelling, we show that (1) after accounting for dust, the stellar colours of 'blue' galaxies do not depend strongly on mass; (2) the tight, flat 'dead sequence' does not extend much below log M* ~ 10.5; instead, (3) the stellar colours of 'red' galaxies vary rather strongly with mass, such that lower mass 'red' galaxies have bluer stellar populations; (4) below log M* ~ 9.3, the 'red' population dissolves into obscurity, and it becomes problematic to talk about two distinct populations; as a consequence, (5) it is hard to meaningfully constrain the shape, including the existence of an upturn, of the 'red' galaxy mass function below log M* ~ 9.3. Points 1-4 provide meaningful targets for models of galaxy formation and evolution to aim for.
In this paper, we demonstrate a new method for fitting galaxy profiles which makes use of the full multiwavelength data provided by modern large optical-near-infrared imaging surveys. We present a ...new version of galapagos, which utilizes a recently developed multiwavelength version of galfit, and enables the automated measurement of wavelength-dependent Sérsic profile parameters for very large samples of galaxies. Our new technique is extensively tested to assess the reliability of both pieces of software, galfit and galapagos on both real ugrizY JHK imaging data from the Galaxy And Mass Assembly survey and simulated data made to the same specifications. We find that fitting galaxy light profiles with multiwavelength data increases the stability and accuracy of the measured parameters, and hence produces more complete and meaningful multiwavelength photometry than has been available previously. The improvement is particularly significant for magnitudes in low-S/N bands and for structural parameters like half-light radius r
e and Sérsic index n for which a prior is used by constraining these parameters to a polynomial as a function of wavelength. This allows the fitting routines to push the magnitude of galaxies for which sensible values can be derived to fainter limits. The technique utilizes a smooth transition of galaxy parameters with wavelength, creating more physically meaningful transitions than single-band fitting and allows accurate interpolation between passbands, perfect for derivation of rest-frame values.
We present a maximum-likelihood weak-lensing analysis of the mass distribution in optically selected spectroscopic Galaxy Groups (...) in the Galaxy And Mass Assembly (GAMA) survey, using background ...Sloan Digital Sky Survey (SDSS) photometric galaxies. The scaling of halo mass, ..., with various group observables is investigated. Our main results are as follows. (1) The measured relations of halo mass with group luminosity, virial volume and central galaxy stellar mass, M*, agree very well with predictions from mock group catalogues constructed from a GALFORM semi-analytical galaxy formation model implemented in the Millennium ...CDM N-body simulation. (2) The measured relations of halo mass with velocity dispersion and projected half-abundance radius show weak tension with mock predictions, hinting at problems in the mock galaxy dynamics and their small-scale distribution. (3) The median ... measured from weak lensing depends more sensitively on the lognormal dispersion in M* at fixed ... than it does on the median ... Our measurements suggest an intrinsic dispersion of ... Comparing our mass estimates with those in the catalogue, we find that the ... mass can give biased results when used to select subsets of the group sample. Of the various new halo-mass estimators that we calibrate using our weak-lensing measurements, group luminosity is the best single-proxy estimator of group mass. (ProQuest: ... denotes formulae/symbols omitted.)
From a volume-limited sample of 45 542 galaxies and 6000 groups with z ≤ 0.213, we use an adapted minimal spanning tree algorithm to identify and classify large-scale structures within the Galaxy And ...Mass Assembly (GAMA) survey. Using galaxy groups, we identify 643 filaments across the three equatorial GAMA fields that span up to 200 h
−1 Mpc in length, each with an average of eight groups within them. By analysing galaxies not belonging to groups, we identify a secondary population of smaller coherent structures composed entirely of galaxies, dubbed 'tendrils' that appear to link filaments together, or penetrate into voids, generally measuring around 10 h
−1 Mpc in length and containing on average six galaxies. Finally, we are also able to identify a population of isolated void galaxies. By running this algorithm on GAMA mock galaxy catalogues, we compare the characteristics of large-scale structure between observed and mock data, finding that mock filaments reproduce observed ones extremely well. This provides a probe of higher order distribution statistics not captured by the popularly used two-point correlation function.
Dust lanes bisect the plane of a typical edge-on spiral galaxy as a dark optical absorption feature. Their appearance is linked to the gravitational stability of spiral disks; the fraction of edge-on ...galaxies that displays a dust lane is a direct indicator of the typical vertical balance between gravity and turbulence: a balance struck between the energy input from star formation and the gravitational pull into the plane of the disk. Based on morphological classifications by the Galaxy Zoo project on the Kilo Degree Survey (KiDS) imaging data in the Galaxy and Mass Assembly (GAMA) fields, we explore the relation of dust lanes to the galaxy characteristics, most of which were determined using the Magphys spectral energy distribution fitting tool: stellar mass, total and specific star formation rates, and several parameters describing the cold dust component. We find that the fraction of dust lanes does depend on the stellar mass of the galaxy; they start to appear at M* ∼ 109 M . A dust lane also strongly implies a dust mass of at least 105 M , but otherwise does not correlate with cold dust mass parameters of the Magphys spectral energy distribution analysis, nor is there a link with the star formation rate, specific or total. Dust lane identification does not depend on disk ellipticity (disk thickness) or Sérsic profile but correlates with bulge morphology; a round bulge favors dust lane votes. The central component along the line of sight that produces the dust lane is not associated with either one of the components fit by Magphys, the cold diffuse component or the localized, heated component in H ii regions, but a mix of these two.
We report the morphological classification of 3727 galaxies from the Galaxy and Mass Assembly survey with M
r
< −17.4 mag and in the redshift range 0.025 < z < 0.06 (2.1 × 105 Mpc3) into E, S0-Sa, ...SB0-SBa, Sab-Scd, SBab-SBcd, Sd-Irr and little blue spheroid classes. Approximately 70 per cent of galaxies in our sample are disc-dominated systems, with the remaining ∼30 per cent spheroid dominated. We establish the robustness of our classifications, and use them to derive morphological-type luminosity functions and luminosity densities in the ugrizYJHK passbands, improving on prior studies that split by global colour or light profile shape alone. We find that the total galaxy luminosity function is best described by a double-Schechter function while the constituent morphological-type luminosity functions are well described by a single-Schechter function. These data are also used to derive the star formation rate densities for each Hubble class, and the attenuated and unattenuated (corrected for dust) cosmic spectral energy distributions, i.e. the instantaneous energy production budget. While the observed optical/near-IR energy budget is dominated 58:42 by galaxies with a significant spheroidal component, the actual energy production rate is reversed, i.e. the combined disc-dominated populations generate ∼1.3 times as much energy as the spheroid-dominated populations. On the grandest scale, this implies that chemical evolution in the local Universe is currently largely confined to mid-type spiral classes like our Milky Way.
We present evidence for stochastic star formation histories in low-mass (M
* < 1010 M) galaxies from observations within the Galaxy And Mass Assembly (GAMA) survey. For ∼73 000 galaxies between 0.05 ...< z < 0.32, we calculate star formation rates (SFR) and specific star formation rates (SSFR = SFR/M
*) from spectroscopic Hα measurements and apply dust corrections derived from Balmer decrements. We find a dependence of SSFR on stellar mass, such that SSFRs decrease with increasing stellar mass for star-forming galaxies, and for the full sample, SSFRs decrease as a stronger function of stellar mass. We use simple parametrizations of exponentially declining star formation histories to investigate the dependence on stellar mass of the star formation time-scale and the formation redshift. We find that parametrizations previously fit to samples of z ∼ 1 galaxies cannot recover the distributions of SSFRs and stellar masses observed in the GAMA sample between 0.05 < z < 0.32. In particular, a large number of low-mass (M
* < 1010 M) galaxies are observed to have much higher SSFRs than can be explained by these simple models over the redshift range of 0.05 < z < 0.32, even when invoking mass-dependent staged evolution. For such a large number of galaxies to maintain low stellar masses, yet harbour such high SSFRs, requires the late onset of a weak underlying exponentially declining star formation history with stochastic bursts of star formation superimposed.
Abstract
There are many proposed mechanisms driving the morphological transformation of disc galaxies to elliptical galaxies. In this paper, we determine if the observed transformation in low-mass ...groups can be explained by the merger histories of galaxies. We measured the group mass–morphology relation for groups from the Galaxy and Mass Assembly group catalogue with masses from 1011 to 1015 M⊙. Contrary to previous studies, the fraction of elliptical galaxies in our more complete group sample increases significantly with group mass across the full range of group mass. The elliptical fraction increases at a rate of 0.163 ± 0.012 per dex of group mass for groups more massive than 1012.5 M⊙. If we allow for uncertainties in the observed group masses, our results are consistent with a continuous increase in elliptical fraction from group masses as low as 1011 M⊙. We tested if this observed relation is consistent with the merger activity using a gadget-2 dark matter simulation of the galaxy groups. We specified that a simulated galaxy would be transformed to an elliptical morphology either if it experienced a major merger or if its cumulative mass gained from minor mergers exceeded 30 per cent of its final mass. We then calculated a group mass–morphology relation for the simulations. The position and slope of the simulated relation were consistent with the observational relation, with a gradient of 0.184 ± 0.010 per dex of group mass. These results demonstrate a strong correlation between the frequency of merger events and disc-to-elliptical galaxy transformation in galaxy group environments.
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