Galaxy interactions II: High density environments (original) (raw)

Galaxy interactions in different environments: An analysis of galaxy pairs from the SDSS

2021

We analyze the galaxy pairs in a volume limited sample (Mr ≤ −21) from the SDSS to study the effects of galaxy interactions on the star formation rate and colour of galaxies in different environments. We study the star formation rate and colour of the paired galaxies as a function of projected separation and compare the results with their control samples matched in stellar mass, redshift and local density. We find that the major interactions significantly enhance the star formation rate in paired galaxies and turn them bluer with decreasing pair separation within 30 kpc. The impact of tidal interactions on star formation rate and colour are more significant in the heavier members of the major pairs. The star formation enhancement in major pairs is significantly higher at the low-density environments, where the influence can extend up to ∼ 100 kpc. Contrarily, the major pairs at high-density environments show suppression in their star formation. Depending on the embedding environment...

Galaxy ecology: groups and low-density environments in the SDSS and 2dFGRS

Monthly Notices of The Royal Astronomical Society, 2003

We analyse the observed correlation between galaxy environment and H-alpha emission line strength, using volume-limited samples and group catalogues of 24968 galaxies drawn from the 2dF Galaxy Redshift Survey (Mb<-19.5) and the Sloan Digital Sky Survey (Mr<-20.6). We characterise the environment by 1) Sigma_5, the surface number density of galaxies determined by the projected distance to the 5th nearest neighbour; and 2) rho1.1 and rho5.5, three-dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 Mpc and 5.5 Mpc, respectively. We find that star-forming and quiescent galaxies form two distinct populations, as characterised by their H-alpha equivalent width, EW(Ha). The relative numbers of star-forming and quiescent galaxies varies strongly and continuously with local density. However, the distribution of EW(Ha) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, rho5.5, which is likely independent of the trend with local density, rho1.1. We use two differently-selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for sigma=200-1000 km/s. Even in the lowest density environments, no more than ~70 per cent of galaxies show significant H-alpha emission. Based on these results, we conclude that the present-day correlation between star formation rate and environment is a result of short-timescale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy-galaxy interactions.

The Evolution and Growth of Nearby Galaxy Groups

Proceedings of the Wisconsin Space Conference, 2020

To determine how galaxy groups grow and individual galaxies evolve in the local universe, this project used 19 high-richness, high-mass galaxy groups at z < 0.1 from the Berlind et al. 2006 paper to study the nearby group environment through its optical properties. Using position, g-r color, and r-band absolute magnitude data, the shapes, luminosities, and colors of each member galaxy was mapped in group combination plots and an inter-group color-magnitude diagram of all 477 sample galaxies. These figures show that members of the high-mass group environment trend towards redness where the most luminous members of each galaxy group are found to be red. Both findings are consistent with previous predictions of the group environment’s bias towards red elliptical galaxies. Future work using optical properties and the galaxy sequence will be crucial to identify galaxies in groups undergoing evolutionary change as potential indicators of a changing group environment.

Physical Galaxy Pairs and Their Effects on Star Formation

We present 776 truly physical galaxy pairs, 569 of them are close pairs and 208 false pairs from Karachentsev (1972) and Reduzzi & Rampazzo (1995) catalogues, which contains 1012 galaxy pairs. Also we carried out star formation activity through the far-infrared emission (FIR) in physical (truly) interacting galaxies in some galaxy pairs and compared them with projection (optical) interacting galaxy pairs. We focused on the triggering of star formation by interactions and analyzed the enhancement of star formation activity in terms of truly physical galaxy pairs. The large fraction of star formation activity is probably due to the activity in the exchange of matter between the truly companions. The star formation rate (SFR) of galaxies in truly galaxy pairs is found to be more enhanced than the apparent pairs.