We use the Galaxy And Mass Assembly (GAMA) survey to measure the local Universe mass-dependent merger fraction and merger rate using galaxy pairs and the CAS (concentration, asymmetry, and ...smoothness) structural method, which identifies highly asymmetric merger candidate galaxies. Our goals are to determine which types of mergers produce highly asymmetrical galaxies and to provide a new measurement of the local galaxy major merger rate. We examine galaxy pairs at stellar mass limits down to M* = 10... M... with mass ratios of <100:1 and line-of-sight velocity differences of ... < 500 km s... We find a significant increase in mean asymmetries for projected separations less than the sum of the individual galaxy's Petrosian 90 radii. For systems in major merger pairs with mass ratios of <4:1, both galaxies in the pair show a strong increase in asymmetry, while in minor merger systems (with mass ratios of >4:1) the lower mass companion becomes highly asymmetric, whereas the larger galaxy is much less affected. The fraction of highly asymmetric paired galaxies which have a major merger companion is highest for the most massive galaxies and drops progressively with decreasing mass. We calculate that the mass-dependent major merger fraction is fairly constant at ~1.3-2 per cent within 109.5 < M* < 10... M..., and increases to ~4 per cent at lower masses. When the observability time-scales are taken into consideration, the major merger rate is found to approximately triple over the mass range we consider. The total comoving volume major merger rate over the range 108.0 < M* < 10... M... is (1.2 plus or minus 0.5) x 10... h... Mpc-3 Gyr... (ProQuest: ... denotes formulae/symbols omitted.)
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 investigate the relationship between colour and structure within galaxies using a large, volume-limited sample of bright, low-redshift galaxies with optical–near-infrared imaging from the Galaxy ...And Mass Assembly survey. We fit single-component, wavelength-dependent, elliptical Sérsic models to all passbands simultaneously, using software developed by the MegaMorph project. Dividing our sample by n and colour, the recovered wavelength variations in effective radius (R
e) and Sérsic index (n) reveal the internal structure, and hence formation history, of different types of galaxies. All these trends depend on n; some have an additional dependence on galaxy colour. Late-type galaxies (n
r
< 2.5) show a dramatic increase in Sérsic index with wavelength. This might be a result of their two-component (bulge–disc) nature, though stellar population gradients within each component and dust attenuation are likely to play a role. All galaxies show a substantial decrease in R
e with wavelength. This is strongest for early types (n
r
> 2.5), even though they maintain constant n with wavelength, revealing that ellipticals are a superimposition of different stellar populations associated with multiple collapse and merging events. Processes leading to structures with larger R
e must be associated with lower metallicity or younger stellar populations. This appears to rule out the formation of young cores through dissipative gas accretion as an important mechanism in the recent lives of luminous elliptical galaxies.
We investigate the relationship between colour and structure within galaxies using a large, volume-limited sample of bright, low-redshift galaxies with optical to near-infrared imaging from the GAMA ...survey. We fit single-component, wavelength-dependent, elliptical Sersic models to all passbands simultaneously, using software developed by the MegaMorph project. Dividing our sample by Sersic index and colour, the recovered wavelength variations in effective radius (R_e) and Sersic index (n) reveal the internal structure, and hence formation history, of different types of galaxies. All these trends depend on n; some have an additional dependence on galaxy colour. Late-type galaxies (n_r < 2.5) show a dramatic increase in Sersic index with wavelength. This might be a result of their two-component (bulge-disk) nature, though stellar population gradients within each component and dust attenuation are likely to play a role. All galaxies show a substantial decrease in R_e with wavelength. This is strongest for early-types (n_r > 2.5), even though they maintain constant n with wavelength, revealing that ellipticals are a superimposition of different stellar populations associated with multiple collapse and merging events. Processes leading to structures with larger R_e must be associated with lower metallicity or younger stellar populations. This appears to rule out the formation of young cores through dissipative gas accretion as an important mechanism in the recent lives of luminous elliptical galaxies.
We use the Galaxy And Mass Assembly (GAMA) survey to measure the local Universe mass dependent merger fraction and merger rate using galaxy pairs and the CAS structural method, which identifies ...highly asymmetric merger candidate galaxies. Our goals are to determine which types of mergers produce highly asymmetrical galaxies, and to provide a new measurement of the local galaxy major merger rate. We examine galaxy pairs at stellar mass limits down to \(M_{*} = 10^{8}M_{\odot}\) with mass ratios of \(<\)100:1 and line of sight velocity differences of \(\Delta V<500\) km s\(^{-1}\). We find a significant increase in mean asymmetries for projected separations less than the sum of the individual galaxy's Petrosian 90 radii. For systems in major merger pairs with mass ratios of \(<\)4:1 both galaxies in the pair show a strong increase in asymmetry, while in minor merger systems (with mass ratios of \(>\)4:1) the lower mass companion becomes highly asymmetric, while the larger galaxy is much less affected. The fraction of highly asymmetric paired galaxies which have a major merger companion is highest for the most massive galaxies and drops progressively with decreasing mass. We calculate that the mass dependent major merger fraction is fairly constant at \(\sim1.3-2\%\) between \(10^{9.5}<M_{*}<10^{11.5} M_{\odot}\), and increases to \(\sim4\%\) at lower masses. When the observability time scales are taken into consideration, the major merger rate is found to approximately triple over the mass range we consider. The total co-moving volume major merger rate over the range \(10^{8.0}<M_{*}<10^{11.5} M_{\odot}\) is \((1.2 \pm 0.5) \times 10^{-3}\) \(h^{3}_{70}\) Mpc\(^{-3}\) Gyr\(^{-1}\).
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 x 10^5 Mpc^3 ) into E, S0-Sa, ...SB0-SBa, Sab-Scd, SBab-SBcd, Sd-Irr
and little blue spheroid classes. Approximately 70% of galaxies in our sample
are disk dominated systems, with the remaining ~30% 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 disk dominated populations generate ~1.3x
as much energy as the spheroid dominated populations. On the grandest scale,
this implies that chemical evolution in the local Universe is currently
confined to mid-type spiral classes like our Milky Way.
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 x 10^5 Mpc^3 ) into E, S0-Sa, ...SB0-SBa, Sab-Scd, SBab-SBcd, Sd-Irr and little blue spheroid classes. Approximately 70% of galaxies in our sample are disk dominated systems, with the remaining ~30% 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 disk dominated populations generate ~1.3x as much energy as the spheroid dominated populations. On the grandest scale, this implies that chemical evolution in the local Universe is currently confined to mid-type spiral classes like our Milky Way.
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