Galaxy And Mass Assembly (GAMA): Structural Investigation of Galaxies via Model Analysis (original) (raw)
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Galaxy And Mass Assembly (GAMA): Structural Investigation of Galaxies via Model Analysis (SIGMA)
2011
We present single-Sérsic two-dimensional model fits to 167, 600 galaxies modelled independently in the ugrizY JHK bandpasses using reprocessed Sloan Digital Sky Survey Data Release Seven (SDSS DR7) and UKIRT Infrared Deep Sky Survey Large Area Survey (UKIDSS-LAS) imaging data available from the GAMA database. In order to facilitate this study we developed 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 PSF 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 10 r 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 ∆m = 0.5 magnitudes 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% from g through K. LTGs exhibit a more extreme change in Sérsic index, increasing by 52% across the same range. In addition, ETGs and LTGs exhibit a 38% and 25% 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 use data from the Galaxy And Mass Assembly (GAMA) survey in the redshift range 0.01$<$z$<$0.1 (8399 galaxies in ggg to KsK_sKs bands) to derive the stellar mass −-− half-light radius relations for various divisions of 'early' and 'late'-type samples. We find the choice of division between early and late (i.e., colour, shape, morphology) is not particularly critical, however, the adopted mass limits and sample selections (i.e., the careful rejection of outliers and use of robust fitting methods) are important. In particular we note that for samples extending to low stellar mass limits ($<10^{10}\mathcal{M_{\odot}}$) the S\'ersic index bimodality, evident for high mass systems, becomes less distinct and no-longer acts as a reliable separator of early- and late-type systems. The final set of stellar mass −-− half-light radius relations are reported for a variety of galaxy population subsets in 10 bands ($ugrizZYJHK_s$) and are intended to provide a comprehensive low-z benchmark for the many ongoing high-z studies. Exploring the variation of the stellar mass −-− half-light radius relations with wavelength we confirm earlier findings that galaxies appear more compact at longer wavelengths albeit at a smaller level than previously noted: at 1010mathcalModot10^{10}\mathcal{M_{\odot}}1010mathcalModot both spiral systems and ellipticals show a decrease in size of 13% from ggg to KsK_sKs (which is near linear in log wavelength). Finally we note that the sizes used in this work are derived from 2D S\'ersic light profile fitting (using GALFIT3), i.e., elliptical semi-major half light radii, improving on earlier low-z benchmarks based on circular apertures.
Galaxy and Mass Assembly (GAMA): ugriz galaxy luminosity functions
2011
Galaxy and Mass Assembly (GAMA) is a project to study galaxy formation and evolution, combining imaging data from ultraviolet to radio with spectroscopic data from the AAOmega spectrograph on the Anglo-Australian Telescope. Using data from phase 1 of GAMA, taken over three observing seasons, and correcting for various minor sources of incompleteness, we calculate galaxy luminosity functions (LFs) and their evolution in the ugriz passbands.
Monthly Notices of the Royal Astronomical Society, 2022
In Galaxy And Mass Assembly Data Release 4 (GAMA DR4), we make available our full spectroscopic redshift sample. This includes 248 682 galaxy spectra, and, in combination with earlier surveys, results in 330 542 redshifts across five sky regions covering ∼250 deg2. The redshift density, is the highest available over such a sustained area, has exceptionally high completeness (95 per cent to rKiDS = 19.65 mag), and is well-suited for the study of galaxy mergers, galaxy groups, and the low redshift (z < 0.25) galaxy population. DR4 includes 32 value-added tables or Data Management Units (DMUs) that provide a number of measured and derived data products including GALEX, ESO KiDS, ESO VIKING, WISE, and HerschelSpace Observatory imaging. Within this release, we provide visual morphologies for 15 330 galaxies to z < 0.08, photometric redshift estimates for all 18 million objects to rKiDS ∼ 25 mag, and stellar velocity dispersions for 111 830 galaxies. We conclude by deriving the tota...
The SLUGGS survey: exploring the metallicity gradients of nearby early-type galaxies to large radii
Monthly Notices of the Royal Astronomical Society, 2014
Stellar metallicity gradients in the outer regions of galaxies are a critical tool for disentangling the contributions of in-situ and ex-situ formed stars. In the two-phase galaxy formation scenario, the initial gas collapse creates steep metallicity gradients, while the accretion of stars formed in satellites tends to flatten these gradients in the outskirts, particularly for massive galaxies. This work presents the first compilation of extended metallicity profiles over a wide range of galaxy mass. We use the DEIMOS spectrograph on the Keck telescope in multi-slit mode to obtain radial stellar metallicity profiles for 22 nearby early-type galaxies. From the calcium triplet lines in the near-infrared we measure the metallicity of the starlight up to 3 effective radii. We find a relation between the outer metallicity gradient and galaxy mass, in the sense that lower mass systems show steeper metallicity gradients than more massive galaxies. This result is consistent with a picture in which the ratio of ex-situ to in-situ formed stars is lower in less massive galaxies as a consequence of the smaller contribution by accretion. In addition, we infer a correlation between the strength of the calcium triplet feature in the near-infrared and the stellar initial mass function slope that is consistent with recent models in the literature.
Arxiv preprint astro-ph/ …, 2004
By providing homogeneous photometric and spectroscopic data of high quality for very large and objectively selected samples of galaxies, the Sloan Digital Sky Survey allows statistical studies of the physical properties of galaxies and AGN to be carried out at an unprecedented level of precision and detail. Here we publicly release catalogues of derived physical properties for 211,894 galaxies, including 33,589 narrow-line AGN. These are complete samples with well understood selection criteria drawn from the normal galaxy spectroscopic sample in the second SDSS public data release (DR2). We list properties obtained from the SDSS spectroscopy and photometry using modelling techniques presented in papers already published by our group. These properties include: stellar masses; stellar mass-to-light ratios; attenuation of the starlight by dust; indicators of recent major starbursts; current total and specific star-formation rates, both for the regions with spectroscopy and for the galaxies as a whole; gas-phase metallicities; AGN classifications based on the standard emission line ratio diagnostic diagrams and AGN [OIII] emission line luminosities. We also list our own measurements of absorption line indices and emission line fluxes from which these quantities were derived, together with a few quantities from the standard SDSS pipelines which play an important role in our work. Many other observed properties of these galaxies can be obtained from the SDSS DR2 catalogues themselves. We will add further physical properties to this release site as the relevant papers are accepted for publication. Catalogues containing these parameters may be accessed at
Galaxy And Mass Assembly (GAMA): Spectroscopic analysis
2013
The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric and spectroscopic survey, using the AAOmega spectrograph on the Anglo-Australian Telescope to obtain spectra for up to ∼ 300 000 galaxies over 280 square degrees, to a limiting magnitude of r pet < 19.8 mag. The target galaxies are distributed over 0 < z 0.5 with a median redshift of z ≈ 0.2, although the redshift distribution includes a small number of systems, primarily quasars, at higher redshifts, up to and beyond z = 1. The redshift accuracy ranges from σ v ≈ 50 km s −1 to σ v ≈ 100 km s −1 depending on the signal-to-noise of the spectrum. Here we describe the GAMA spectroscopic reduction and analysis pipeline. We present the steps involved in taking the raw two-dimensional spectroscopic images through to flux-calibrated one-dimensional spectra. The resulting GAMA spectra cover an observed wavelength range of 3750 λ 8850Å at a resolution of R ≈ 1300. The final flux calibration is typically accurate to 10 − 20%, although the reliability is worse at the extreme wavelength ends, and poorer in the blue than the red. We present details of the measurement of emission and absorption features in the GAMA spectra. These measurements are characterised through a variety of quality control analyses detailing the robustness and reliability of the measurements. We illustrate the quality of the measurements with a brief exploration of elementary emission line properties of the galaxies in the GAMA sample. We demonstrate the luminosity dependence of the Balmer decrement, consistent with previously published results, and explore further how Balmer decrement varies with galaxy mass and redshift. We also investigate the mass and redshift dependencies of the [NII]/Hα vs [OIII]/Hβ spectral diagnostic diagram, commonly used to discriminate between star forming and nuclear activity in galaxies.
Monthly Notices of the Royal Astronomical Society, 2017
We derive the low redshift galaxy stellar mass function (GSMF), inclusive of dust corrections, for the equatorial Galaxy And Mass Assembly (GAMA) dataset covering 180 deg 2. We construct the mass function using a density-corrected maximum volume method, using masses corrected for the impact of optically thick and thin dust. We explore the galactic bivariate brightness plane (M − µ), demonstrating that surface brightness effects do not systematically bias our mass function measurement above 10 7.5 M. The galaxy distribution in the M −µ-plane appears well bounded, indicating that no substantial population of massive but diffuse or highly compact galaxies are systematically missed due to the GAMA selection criteria. The GSMF is fit with a double Schechter function, with M = 10 10.78±0.01±0.20 M , φ 1 = (2.93 ± 0.40) × 10 −3 h 3 70 Mpc −3 , α 1 = −0.62 ± 0.03 ± 0.15, φ 2 = (0.63 ± 0.10) × 10 −3 h 3 70 Mpc −3 , and α 2 = −1.50±0.01±0.15. We find the equivalent faint end slope as previously estimated using the GAMA-I sample, although we find a higher value of M. Using the full GAMA-II sample, we are able to fit the mass function to masses as low as 10 7.5 M , and assess limits to 10 6.5 M. Combining GAMA-II with data from G10-COSMOS we are able to comment qualitatively on the shape of the GSMF down to masses as low as 10 6 M. Beyond the well known upturn seen in the GSMF at 10 9.5 the distribution appears to maintain a single power-law slope from 10 9 to 10 6.5. We calculate the stellar mass density parameter given our best-estimate GSMF, finding Ω = 1.66 +0.24 −0.23 ± 0.97h −1 70 × 10 −3 , inclusive of random and systematic uncertainties.
Stellar mass-to-light ratio gradients in galaxies: correlations with mass
Monthly Notices of the Royal Astronomical Society, 2011
We analyze the stellar mass-to-light ratio (M/L) gradients in a large sample of local galaxies taken from the Sloan Digital Sky Survey, spanning a wide range of stellar masses and morphological types. As suggested by the well known relationship between mass-to-light (M/L) ratios and colors, we show that M/L gradients are strongly correlated with colour gradients, which we trace to the effects of age variations. Stellar M/L gradients generally follow patterns of variation with stellar mass and galaxy type that were previous found for colour and metallicty gradients. In late-type galaxies M/L gradients are negative, steepening with increasing mass. In early-type galaxies M/L gradients are shallower while presenting a two-fold trend: they decrease with mass up to a characteristic mass of M * ∼ 10 10.3 M ⊙ and increase at larger masses. We compare our findings with other analyses and discuss some implications for galaxy formation and for dark matter estimates.
The Luminosity Function of Galaxies from SDSS Commissioning Data
2000
In the course of its commissioning observations, the Sloan Digital Sky Survey (SDSS) has produced one of the largest redshift samples of galaxies selected from CCD images. Using 11,275 galaxies complete to r * = 17.6 over 140 square degrees, we compute the luminosity function of galaxies in the r * band over a range −23 < M r * < −16 (for h = 1). The result is well-described by a Schechter function with parameters φ * = (1.46±0.12)×10 −2 h 3 Mpc −3 , M * = −20.83±0.03, and α = −1.20 ± 0.03. The implied luminosity density in r * is j ≈ (2.6 ± 0.3) × 10 8 hL ⊙ Mpc −3. We find that the surface brightness selection threshold has a negligible impact for M r * < −18. Using subsets of the data, we measure the luminosity function in the u * , g * , i * , and z * bands as well; the slope at low luminosities ranges from α = −1.35 to α = −1.2. We measure the bivariate distribution of r * luminosity with half-light surface brightness, intrinsic g * − r * color, and morphology. In agreement with previous studies, we find that high surface brightness, red, highly concentrated galaxies are on average more luminous than low surface brightness, blue, less concentrated galaxies. An important feature of the SDSS luminosity function is the use of Petrosian magnitudes, which measure a constant fraction of a galaxy's total light regardless of the amplitude of its surface brightness profile. If we synthesize results for R GKC-band or b j-band using these Petrosian magnitudes, we obtain luminosity densities 2 times that found by the Las Campanas Redshift Survey in R GKC and 1.4 times that found by the Two-degree Field Galaxy Redshift Survey in b j. However, we are able to reproduce the luminosity functions obtained by these surveys if we also mimic their isophotal limits for defining galaxy magnitudes, which are shallower and more redshift dependent than the Petrosian magnitudes used by the SDSS.