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The Evolution of Galaxy Mergers and Morphology at z<1.2 in the Extended Groth Strip
Astrophysics · Submitted 3 Feb 2006
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We conclude (1) the galaxy merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star-formation rate density since z ~ 1 is a result of declining star-formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ~ 1.2.
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The abstract, sentence by sentence
We present the quantitative rest-frame B morphological evolution and galaxy merger fractions at 0.2 < z < 1.2 as observed by the All-wavelength Extended Groth Strip International Survey (AEGIS). We use the Gini coefficent and M_20 to identify major mergers and classify galaxy morphology for a volume-limited sample of 3009 galaxies brighter than 0.4 L_B^*, assuming pure luminosity evolution of 1.3 M_B per unit redshift. We find that the merger fraction remains roughly constant at 10 +/- 2% for 0.2 < z < 1.2. The fraction of E/S0/Sa increases from 21+/- 3% at z ~ 1.1 to 44 +/- 9% at z ~ 0.3, while the fraction of Sb-Ir decreases from 64 +/- 6% at z ~ 1.1 to 47 +/- 9% at z ~ 0.3. The majority of z < 1.2 Spitzer MIPS 24 micron sources with L(IR) > 10^11 L_sun are disk galaxies, and only ~ 15% are classified as major merger candidates. Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence at z ~ 1.1, while E/S0/Sa makeup over 90% of the red sequence at z ~ 0.3. Approximately 2% of our full sample are red mergers. We conclude (1) the galaxy merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star-formation rate density since z ~ 1 is a result of declining star-formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ~ 1.2.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We present the quantitative rest-frame B morphological evolution and galaxy merger fractions at 0.2 < z < 1.2 as observed by the All-wavelength Extended Groth Strip International Survey (AEGIS). | contribution 1.00 | 0.95 | 0.03 | asserted 0.94 |
| s1 | We use the Gini coefficent and M_20 to identify major mergers and classify galaxy morphology for a volume-limited sample of 3009 galaxies brighter than 0.4 L_B^*, assuming pure luminosity evolution of 1.3 M_B per unit redshift. | method 1.00 | 0.95 | 0.02 | asserted 0.99 |
| s2 | We find that the merger fraction remains roughly constant at 10 +/- 2% for 0.2 < z < 1.2. | result 1.00 | 0.97 | 0.28 | asserted 1.00 |
| s3 | The fraction of E/S0/Sa increases from 21+/- 3% at z ~ 1.1 to 44 +/- 9% at z ~ 0.3, while the fraction of Sb-Ir decreases from 64 +/- 6% at z ~ 1.1 to 47 +/- 9% at z ~ 0.3. | result 1.00 | 0.95 | 0.09 | asserted 1.00 |
| s4 | The majority of z < 1.2 Spitzer MIPS 24 micron sources with L(IR) > 10^11 L_sun are disk galaxies, and only ~ 15% are classified as major merger candidates. | result 1.00 | 0.90 | 0.03 | asserted 1.00 |
| s5 | Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence at z ~ 1.1, while E/S0/Sa makeup over 90% of the red sequence at z ~ 0.3. | result 1.00 | 0.91 | 0.04 | asserted 1.00 |
| s6 | Approximately 2% of our full sample are red mergers. | result 1.00 | 0.94 | 0.03 | asserted 1.00 |
| s7 | We conclude (1) the galaxy merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star-formation rate density since z ~ 1 is a result of declining star-formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ~ 1.2. | interpretation 1.00 | 0.88 | 0.96 | asserted 0.87 |
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The paper
Original abstract
We present the quantitative rest-frame B morphological evolution and galaxy merger fractions at 0.2 < z < 1.2 as observed by the All-wavelength Extended Groth Strip International Survey (AEGIS). We use the Gini coefficent and M_20 to identify major mergers and classify galaxy morphology for a volume-limited sample of 3009 galaxies brighter than 0.4 L_B^*, assuming pure luminosity evolution of 1.3 M_B per unit redshift. We find that the merger fraction remains roughly constant at 10 +/- 2% for 0.2 < z < 1.2. The fraction of E/S0/Sa increases from 21+/- 3% at z ~ 1.1 to 44 +/- 9% at z ~ 0.3, while the fraction of Sb-Ir decreases from 64 +/- 6% at z ~ 1.1 to 47 +/- 9% at z ~ 0.3. The majority of z < 1.2 Spitzer MIPS 24 micron sources with L(IR) > 10^11 L_sun are disk galaxies, and only ~ 15% are classified as major merger candidates. Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence at z ~ 1.1, while E/S0/Sa makeup over 90% of the red sequence at z ~ 0.3. Approximately 2% of our full sample are red mergers. We conclude (1) the galaxy merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star-formation rate density since z ~ 1 is a result of declining star-formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ~ 1.2.
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References
How later papers used it
99 later papers cite it
9 later papers by other authors are listed below: 7 used its method or tool and 2 compared their own results with it. 1 more paper by the same authors is listed: 1 used its method or tool.
Uses its method or tool 8 of 23 papers with this label · 1 by the same authors
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Adopted this paper's G-M20 classifications, which place galaxies with G > -0.14 M20 + 0.33 as merger-like and those below that line with G > 0.14 M20 + 0.80 as bulge-dominated.
On the Nature of AGN and Star Formation Enhancement in the $z = 3.1$ SSA22 Protocluster: The HST WFC3 IR View (2021) · 0.95 · paraphrased: the licence does not allow quoting
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Here, we include dividing lines between the regions of mergers, Sb/Sc/Irr and E/S0/Sa galaxy types taken from [ref] , according to the following definitions, Mergers: G $>$ $-$0.14$×$M20 + 0.33; Early(E/S0/Sa): G $≤$ $-$0.14$×$M20 + 0.33, and G $>$ 0.14$×$M20 + 0.80; Late(Sb/Ir): G $≤$ $-$0.14$×$M20 + 0.33, and G $≤$ 0.14$×$M20 + 0.80.
Host galaxy and nuclear properties of IR-selected AGNs with and without outflow signatures (2023) · Non-parametric morphology · 0.81
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The bulge statistic $F(G, M_20)$: defined as [ref] [equation] which means the line intersects at $(G_0, M_20,0)=(0.533, -1.75)$ and is also perpendicular to the line separating merging and non-merging galaxies. here selects $G>0.14M_20+0.80$ as the function of $F(G, M_20)$ and $G>-0.14M_20+0.33$ [ref] as the function of $S(G, M_20)$, and if $F(G, M_20)>0$ means the galaxy is ETG, otherwise, the galaxy is LTG and also is closely related to Concentration index (C) and Sérsic index.
A Morphological Study on AGN-host Dwarf Galaxies (2025) · Non-parametric Measurements · 0.98
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The lines denote the boundary between mergers, disk galaxies, and ellipticals/S0s following [ref] .
z~2 dual AGN host galaxies are disky: stellar kinematics in the ASTRID Simulation (2023) · Morphology measures of mock observations · 0.88
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The division lines are obtained from [ref] with the following definitions for Extended Groth Strip (EGS) galaxies at $0.2<z<1.2$: $Mergers: G > -0.14 M_20+0.33$, $E/S0/Sa: G≤-0.14 M_20+0.33 & G > 0.14M_20+0.80$, and $Sb/Sc/Irr: G ≤-0.14M_20+0.33 & G ≤0.14M_20+0.80$.
A Morphological Study on Galaxies Hosting Optical Variability-Selected AGNs in the COSMOS Field (2021) · Non-parametric Parameter Diagnostics · 0.94
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The Gini-M20 statistics [ref] classify z19863 as a merger based on the stellar emission (F182M) but a non-merger based on the gas emission (F210M-F182M).
MOSEL survey: Spatially offset Lyman-continuum emission in a new emitter at z=3.088 (2024) · Merger activity · 0.99
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We refer to [ref] for demarcating the galaxy population into spirals/ irregular, elliptical/ lenticular, and merger candidates on $G$ vs. $M20$ plane.
Exploring filament galaxies using {\em AstroSat}/ UVIT (2024) · Morphological classification using non-parametric methods · 1.00
By the same authors
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Visually identified galaxy pairs and galaxies with distorted morphologies using the criteria in this paper.
A Complete 16 $\mu$m selected Galaxy Sample at $z \sim 1$. II: Morphological Analysis (2024) (same authors) · 1.00 · paraphrased: the licence does not allow quoting
Compares with it 2 of 9 papers with this label
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Found its synthetic morphologies tend to lie along this paper's dividing line between mergers and non-mergers and exhibit a shallower slope than the corresponding locus of CANDELS galaxies.
The Connection between Mergers and AGN Activity in Simulated and Observed Massive Galaxies (2021) · 0.96 · paraphrased: the licence does not allow quoting
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Found its Gini-M20 results consistent with its visual classification, with nearly all its E galaxies in the region of this paper's E/S0/Sa galaxies and most of its D galaxies where their disk galaxies would populate.
Morphological Evolution of the Hosts of Far-Infrared/Submillimeter Galaxies (2021) · 1.00 · paraphrased: the licence does not allow quoting
How the literature uses it
4 arXiv papers cite this in 6 sentences
Papers whose main result relates to this one's
States a conflicting result 1 paper
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We conclude that (1) the optical galaxy merger fraction does evolve with redshift, (2) the merger fraction depends mildly on stellar mass, with lower mass galaxies having higher merger fractions at z<1, and (3) star formation is triggered at all phases of a merger, with larger enhancements at later stages, consistent with N-body simulations.
The CFHTLS Deep Catalog of Interacting Galaxies I. Merger Rate Evolution to z=1.2 · 0.96
Papers citing it · 5 sentences without a confident label
Cites it as background 1 paper
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Typically merger candidates are identified from photometric catalogues through either pair selection [ref] or morphology [ref] .
Galaxy pairs as a probe for mergers at z ~ 2 · Introduction · 0.82
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