The Infrared Properties of Hickson Compact Groups

Abstract

Compact groups of galaxies provide a unique environment to study the mechanisms by which star formation occurs amid continuous gravitational encounters. We present 2MASS (JHK), Spitzer IRAC (3.5-8 micron) and MIPS (24 micron) observations of a sample of twelve Hickson Compact Groups (HCGs 2, 7, 16, 19, 22, 31, 42, 48, 59, 61, 62, and 90) that includes a total of 45 galaxies. The near-infrared colors of the sample galaxies are largely consistent with being dominated by slightly reddened normal stellar populations. Galaxies that have the most significant PAH and/or hot dust emission (as inferred from excess 8 micron flux) also tend to have larger amounts of extinction and/or K-band excess and stronger 24 micron emission, all of which suggest ongoing star formation activity. We separate the twelve HCGs in our sample into three types based on the ratio of the group HI mass to dynamical mass. We find evidence that galaxies in the most gas-rich groups tend to be the most actively star forming. Galaxies in the most gas-poor groups tend to be tightly clustered around a narrow range in colors consistent with the integrated light from a normal stellar population. We interpret these trends as indicating that galaxies in gas-rich groups experience star formation and/or nuclear actively until their neutral gas consumed, stripped, or ionized. The galaxies in this sample exhibit a ``gap'' between gas-rich and gas-poor groups in infrared color space that is sparsely populated and not seen in the Spitzer First Look Survey sample. This gap may suggest a rapid evolution of galaxy properties in response to dynamical effects. These results suggest that the global properties of the groups and the local properties of the galaxies are connected.Comment: 34 pages, 26 figures, accepted for publication in AJ, higher quality images available in publicatio

Probing the dust properties of galaxies up to submillimetre wavelengths

“…IRAC fluxes are uncertain at the ∼10% level due to systematic effects. The data we obtained were compared and verified with those published in Johnson et al (2007) for Mrk 1089 andCannon et al (2006) for NCG 1705. Images are presented in Fig.…”

“…2c) clearly shows the interaction between the galaxies NGC 1741 (East) and Mrk 1089 (West). A Spitzer color composition image of the complete Hickson group observed with Spitzer is described in Johnson et al (2007). The merging center of Mrk 1089 dominates the emission at MIR, FIR and 870 μm.…”

“…The two galaxies present similar kinematics suggesting a single entity (Richer et al 2003). At the location of their interaction is a very strong 24 μm source and high levels of infrared emission can be found throughout the whole group (Johnson et al 2007). Mrk 1089 and NGC 1741 are referred to collectively as NGC 1741 in the catalog of WR galaxies of Conti (1991).…”

“…MIPS flux uncertainties were estimated to be 10% in the MIPS 24 μm band and 20% in the MIPS 70 and 160 μm bands. The fluxes calculated compared to those published in Johnson et al (2007) for Mrk 1089 andCannon et al (2006) for NCG 1705.…”

Exploring X-Ray Binary Populations in Compact Group Galaxies With Chandra

“…This in turn likely leads to fast consumption of the available gas and abrupt quenching. The observational signatures of this are "gaps" both in mid-infrared colors (Johnson et al 2007;Walker et al 2010Walker et al , 2012 as well as massnormalized star formation rates (specific SFRs, sSFRs, Tzanavaris et al 2010;L. Lenkic et al 2015, in preparation).…”