AEGIS: Enhancement of Dust-enshrouded Star Formation in Close Galaxy Pairs and Merging Galaxies up to z ~ 1 (original) (raw)
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Infrared Properties of Close Pairs of Galaxies
Astronomical Journal, 2006
We discuss spectroscopy and IR photometry for a complete sample of ~800 galaxies in close pairs objectively selected from the second Center for Astrophysics redshift survey. We use the Two Micron All Sky Survey to compare near-IR color-color diagrams for our sample with the Nearby Field Galaxy Sample and with a set of IRAS flux-limited pairs from Surace and coworkers. We construct a basic statistical model to explore the physical sources of the substantial differences among these samples. The model explains the spread of near-IR colors and is consistent with a picture in which central star formation is triggered by the galaxy-galaxy interaction before a merger occurs. For 160 galaxies we report new, deep JHK photometry within our spectroscopic aperture, and we use the combined spectroscopic and photometric data to explore the physical conditions in the central bursts. We find a set of objects with H-K>=0.45 and with a large FFIR/FH. We interpret the very red H-K colors as evidence for 600-1000 K dust within compact star-forming regions, perhaps similar to super star clusters identified in individual well-studied interacting galaxies. The galaxies in our sample are candidate ``hidden'' bursts or, possibly, ``hidden'' active galactic nuclei. Over the entire pair sample, both spectroscopic and photometric data show that the specific star formation rate decreases with the projected separation of the pair. The data suggest that the near-IR color-color diagram is also a function of the projected separation; all of the objects with central near-IR colors indicative of bursts of star formation lie at small projected separation.
Interacting galaxies are thought to be the essential building blocks of elliptical galaxies under the hierarchical galaxy formation scenario. The goal of my dissertation is to broaden our understanding of galaxy merger evolution through both observational studies and instrumentation development. Observationally, photometric studies conducted in this dissertation better constrain wet and dry merger density evolution up to z 1 using the five CFHTLS broad band photometry. I have discovered that the most massive ellipticals may not be formed via merging processes, unless the merging timescale is much longer than the expected value. Spectroscopically, kinematic study of close pair galaxies shows that red close pairs tend to live in more massive galactic haloes, which supports the gravitational star formation quenching mechanism proposed by the hot halo model. Further constraining the details of galactic color transformations requires careful analyses of 2D spectra from integral-field spe...
A Spitzer study of interacting luminous and ultra-luminous infrared galaxies
Proceedings of the International Astronomical Union, 2011
We conducted a Spitzer Space Telescope survey of 28 Luminous (11 < log (LIR/L⊙) < 12, LIRGs) and Ultra-Luminous Infrared Galaxies (log (LIR/L⊙) > 12, ULIRGs). Many of these galaxies are found in pairs or associations and are powered by either nuclear activity or star-formation (Sanders & Mirabel 1996). Our main goal is to understand the relative importance of starbursts and AGNs in interacting systems. Is the frequency of AGN and starbursts in these interacting galaxies related to their luminosities? What is the importance of the merger stage and the frequency of AGNs? We present our conclusions and diagnostic diagrams based in the observed near infrared lines and compare to studies based solely in optical data.
Galaxy and Mass Assembly (GAMA): merging galaxies and their properties
We derive the close pair fractions and volume merger rates for galaxies in the Galaxy and Mass Assembly (GAMA) survey with -23 < Mr < -17 (ΩM = 0.27, ΩΛ = 0.73, H0 = 100 km s-1 Mpc-1) at 0.01 < z < 0.22 (look-back time of <2 Gyr). The merger fraction is approximately 1.5 per cent Gyr-1 at all luminosities (assuming 50 per cent of pairs merge) and the volume merger rate is ≈3.5 × 10-4 Mpc-3 Gyr-1. We examine how the merger rate varies by luminosity and morphology. Dry mergers (between red/spheroidal galaxies) are found to be uncommon and to decrease with decreasing luminosity. Fainter mergers are wet, between blue/discy galaxies. Damp mergers (one of each type) follow the average of dry and wet mergers. In the brighter luminosity bin (-23 < Mr < -20), the merger rate evolution is flat, irrespective of colour or morphology, out to z ˜ 0.2. The makeup of the merging population does not appear to change over this redshift range. Galaxy growth by major mergers appears comparatively unimportant and dry mergers are unlikely to be significant in the buildup of the red sequence over the past 2 Gyr. We compare the colour, morphology, environmental density and degree of activity (BPT class, Baldwin, Phillips & Terlevich) of galaxies in pairs to those of more isolated objects in the same volume. Galaxies in close pairs tend to be both redder and slightly more spheroid dominated than the comparison sample. We suggest that this may be due to `harassment' in multiple previous passes prior to the current close interaction. Galaxy pairs do not appear to prefer significantly denser environments. There is no evidence of an enhancement in the AGN fraction in pairs, compared to other galaxies in the same volume.