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We use an updated version of the halo-based galaxy group catalog of Yang et al., and take the surface brightness of the galaxy group (μlim) based on projected positions and luminosities of galaxy members as a compactness proxy to divide groups into subsystems with different compactness. By comparing various properties, including galaxy conditional luminosity function, stellar population, active galactic nuclei (AGN) activity, and X-ray luminosity of the intracluster medium of carefully controlled high (HC) and low compactness (LC) group samples, we find that group compactness plays an essential role in characterizing the detailed physical properties of the group themselves and their group members, especially for low-mass groups with Mh ≲ 1013.5 h−1 M⊙. We find that the low-mass HC groups have a systematically lower magnitude gap Δm12 and X-ray luminosity than their LC counterparts, indicating that the HC groups are probably in the early stage of group merging. On the other hand, a higher fraction of passive galaxies is found in the HC group, which however is a result of systematically smaller halo-centric distance distribution of their satellite population. After controlling for both Mh and halo-centric distance, we did not find any differences in both the quenching fraction and AGN activity of the member galaxies between the HC and LC groups. Therefore, we conclude that the halo quenching effect, which results in the halo-centric dependence of a galaxy population, is a faster process compared to the dynamical relaxed timescale of galaxy groups. [ABSTRACT FROM AUTHOR]

We use an updated version of the halo-based galaxy group catalog of Yang et al., and take the surface brightness of the galaxy group (ÎĽ lim) based on projected positions and luminosities of galaxy members as a compactness proxy to divide groups into subsystems with different compactness. By comparing various properties, including galaxy conditional luminosity function, stellar population, active galactic nuclei (AGN) activity, and X-ray luminosity of the intracluster medium of carefully controlled high (HC) and low compactness (LC) group samples, we find that group compactness plays an essential role in characterizing the detailed physical properties of the group themselves and their group members, especially for low-mass groups with M h ≲ 1013.5 h âˆ'1 M ⊙. We find that the low-mass HC groups have a systematically lower magnitude gap Î" m 12 and X-ray luminosity than their LC counterparts, indicating that the HC groups are probably in the early stage of group merging. On the other hand, a higher fraction of passive galaxies is found in the HC group, which however is a result of systematically smaller halo-centric distance distribution of their satellite population. After controlling for both M h and halo-centric distance, we did not find any differences in both the quenching fraction and AGN activity of the member galaxies between the HC and LC groups. Therefore, we conclude that the halo quenching effect, which results in the halo-centric dependence of a galaxy population, is a faster process compared to the dynamical relaxed timescale of galaxy groups. [ABSTRACT FROM AUTHOR]

Compact groups (CGs) of galaxies appear to be the densest galaxy systems containing a few luminous galaxies in close proximity to each other, which have a typical size of a few tens of kiloparsec in observation. On the other hand, in the modern hierarchical structure formation paradigm, galaxies are assembled and grouped in dark matter halos, which have a typical size of a few hundreds of kiloparsec. Few studies have explored the physical connection between the observation-based CGs and halo model-based galaxy groups to date. In this study, by matching the largest local CG catalog of Zheng & Shen to the halo-based group catalog of Yang et al., we find that CGs are physically heterogeneous systems and can be mainly separated into two categories, the isolated systems and those embedded in rich groups or clusters. By examining the dynamical features of CGs, we find that isolated CGs have systematically lower dynamical masses than noncompact ones at the same group luminosity, indicating a more evolved stage of isolated CGs. On the other hand, the embedded CGs are mixtures of chance alignments in poor clusters and recent infalling groups (substructures) of rich clusters. [ABSTRACT FROM AUTHOR]

The interaction between galaxies is believed to be the main origin of the peculiarities of galaxies. It can disturb not only the morphology but also the kinematics of galaxies. These disturbed and asymmetric features are the indicators of galaxy interaction. We study the velocity field of ionized gas in galaxy pairs based on MaNGA survey. Using the kinemetry package, we fit the velocity field and quantify the degree of kinematic asymmetry. We find that the fraction of high kinematic asymmetry is much higher for galaxy pairs with dp⩽30h−1kpc. Moreover, compared to a control sample of single galaxies, we find that the star formation rate is enhanced in paired galaxies with high kinematic asymmetry. For paired galaxies with low kinematic asymmetry, no significant SFR enhancement has been found. The galaxy pairs with high kinematic asymmetry are more likely to be real interacting galaxies rather than projected pairs. [ABSTRACT FROM AUTHOR]

Green Pea and Blueberry galaxies are well known for their compact size, low mass, strong emission lines, and analogs to high- z Ly α -emitting galaxies. In this study, 1547 strong [O iii ] λ 5007 emission-line compact galaxies with 1694 spectra are selected from LAMOST DR9 at the redshift range from 0.0 to 0.59. According to the redshift distribution, these samples can be separated into three groups: Blueberries, Green Peas, and Purple Grapes. Optical [Mg ii ] λ 2800 line feature, BPT diagram, multiwavelength spectral energy distribution (SED) fitting, mid-IR (MIR) color, and MIR variability are deployed to identify 23 active galactic nucleus candidates from these samples, which are excluded for the following star formation rate (SFR) discussions. We perform the multiwavelength SED fitting with GALEX UV and WISE MIR data. Color excess from the Balmer decrement shows that these strong [O iii ] λ 5007 emission-line compact galaxies are not highly reddened. The stellar mass of the galaxies is obtained by fitting LAMOST calibrated spectra with the emission lines masked. We find that the SFR is increasing with the increase of redshift, while for the sources within the same redshift bin the SFR increases with mass with a similar slope to the star-forming main sequence. These samples have a median metallicity of 12 + log(O/H) of 8.10. The metallicity increases with mass, and all the sources are below the massâ€"metallicity relation. The direct-derived T e -based metallicity from the [O iii ] λ 4363 line agrees with the empirical N2-based empirical gas-phase metallicity. Moreover, these compact strong [O iii ] λ 5007 lines are mostly in a less dense environment. [ABSTRACT FROM AUTHOR]

Abstract: The 395 late-type spiral galaxies brighter than 15m in r-band are selected from the Data Release 2 of Sloan Digital Sky Survey and the colormagnitude relations of these galaxies and their disks are investigated. It is found that the colors g − r, r − z and g − z of these galaxies and their disks are strongly correlated with the r-band absolute magnitudes, i.e., the more luminous galaxies (or disks) have the redder colors than the less luminous galaxies (or disks). And the correlation of galaxies is stronger than that of their disks. [Copyright &y& Elsevier]