DOI: 10.20350/digitalcsic/16362
title: The HI content of Hickson Compact Groups : J/A+A/670/A21

description: Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- HCG [1/100] HCG number (Cat. VII/213) 5 I1 --- Nmemb [2/8] Number of galaxies in group 7- 15 F9.5 deg RAdeg Group right ascension (J2000) 17- 25 F9.5 deg DEdeg Group declination (J2000) 27- 31 I5 km/s HRV Group heliocentric radial velocity 33- 35 I3 Mpc Dist [0/160] Group distance (1) 37- 41 A5 --- VLAConfig VLA configuration(s) the group was observed with 43- 46 F4.1 km/s DVChan Channel width of reduced VLA HI observations 48- 51 F4.2 mJy/beam rms RMS noise in reduced VLA HI cube 53- 56 F4.1 arcsec beamMaj Major axis diameter of VLA synthesized beam 58- 61 F4.1 arcsec beamMin Minor axis diameter VLA synthesized beam 63- 66 F4.1 10+19cm-2 NHI 4-sigma HI column density sensitivity (over 20km/s) -------------------------------------------------------------------------------- Note (1): group distance calculated via the Cosmicflows-3 model (Tully et al., 2016AJ....152...50T, Cat. J/AJ/152/50; Kourkchi et al.. 2020AJ....159...67K), which have uncertainties of 3Mpc, -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- HCG [2/100] HCG number (Cat. VII/213) 5 A1 --- l_logMHI-VLA [&lt;] Upper limit flag for HI mass from VLA 7- 11 F5.2 [Msun] logMHI-VLA Logarithm of total group HI mass from VLA 13- 16 F4.2 [Msun] e_logMHI-VLA ?=- Uncertainty in HI mass from VLA 18- 22 F5.2 [Msun] logMHI-GBT ?=- Logarithm of total group HI mass from GBT observations (Borthakur et al., 2010ApJ...710..385B) 24- 28 F5.2 [Msun] logMHI-pred Logarithm of predicted total group HI mass based on B-band luminosity (Jones et al., 2016MNRAS.457.4393J) 30 A1 --- l_HIdef-VLA [&gt;] Lower limit flag for HI deficiency from the VLA 32- 36 F5.2 --- HIdef-VLA HI deficiency of group from VLA HI mass 38- 42 F5.2 --- HIdef-GBT ?=- HI deficiency of group from GBT HI mass 44- 48 F5.2 [Msun] logMHI-gals ?=- Total HI mass in galaxies (VLA) 50- 53 F4.2 [Msun] logMHI-exfs ?=- Total HI mass in extended features (VLA) 55- 58 F4.2 --- fexfs ?=- Fraction of HI mass in extended features (VLA) 60- 61 A2 --- HIphase HI morphological phase (cf. Verdes-Montenegro et al., 2001A&A...377..812V) -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablec1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- HCG [2/100] HCG number (Cat. VII/213) 5- 14 A10 --- Name Galaxy name 16- 24 F9.5 deg RAdeg Galaxy right ascension (J2000) 26- 34 F9.5 deg DEdeg Galaxy declination (J2000) 36- 39 A4 --- MType Galaxy morphological type (Hickson et al., 1989ApJS...70..687H, Cat. VII/213) 41- 49 A9 --- IRclass IR activity classification (Zucker et al., 2016ApJ...821..113Z, Cat. J/ApJ/821/113) 51- 55 I5 km/s HRV Galaxy heliocentric radial velocity (Hickson et al., 1992ApJ...399..353H, Cat. VII/213) 57- 61 F5.2 mag Bmag Galaxy B-band apparent magnitude (Hickson et al., 1989ApJS...70..687H, Cat. VII/213) 63- 66 F4.2 mag e_Bmag Uncertainty in B-band apparent magnitude 68- 72 F5.2 [Msun] logMHI-pred Logarithm of predicted HI mass (Jones et al., 2018A&A...609A..17J, Cat. J/A+A/609/A17) 74- 77 F4.2 [Msun] e_logMHI-pred Uncertainty in predicted HI mass 79- 83 F5.2 [Msun] logMHI ?=- Logarithm of HI mass (VLA) 85- 89 F5.2 --- HIdef ?=- Galaxy HI deficiency (VLA) -------------------------------------------------------------------------------- Byte-by-byte Description of file: list.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- HCG [2/100] HCG number (Cat. VII/213) 5- 13 F9.5 deg RAdeg Right Ascension of center (J2000) 14- 22 F9.5 deg DEdeg Declination of center (J2000) 24- 27 I4 --- Nx Number of pixels along X-axis 29- 32 I4 --- Ny Number of pixels along Y-axis 34- 36 I3 --- Nz Number of pixels along Z-axis 38- 63 A26 "datime" Obs.date Observation date 65- 75 E11.6 m/s bVRAD Lower value of VRAD interval 77- 87 E11.6 m/s BVRAD Upper value of VRAD interval 89- 96 F8.2 m/s dVRAD VRAD resolution 98-103 I6 Kibyte size Size of FITS file 105-124 A20 --- FileName Name of FITS file, in subdirectory fits 126-149 A24 --- Title Title of the FITS file --------------------------------------------------------------------------------
description: Hickson compact groups (HCGs) are dense configurations of four to ten galaxies, whose HI morphology appears to follow an evolutionary sequence of three phases, with gas initially confined to galaxies, then significant amounts spread throughout the intra-group medium, and finally with almost no gas remaining in the galaxies themselves. It has also been suggested that several groups may harbour a diffuse HI component that is resolved out by interferometric observations. The HI deficiency of HCGs is expected to increase as the HI morphological phase progresses along the evolutionary sequence. If this is the case, HI deficiency would be a rough proxy for the age and evolutionary state of a HCG. We aim to test this hypothesis for the first time using a large sample of HCGs and to investigate the evidence for diffuse HI in HCGs. We performed a uniform reduction of all publicly available VLA HI observations (38 HCGs) with a purpose-built pipeline that also maximises the reproducibility of this study. The resulting HI data cubes were then analysed with the latest software tools to perform a manual separation of emission features into those belonging to galaxies and those extending into the intra-group medium. We thereby classified the HI morphological phase of each group as well as quantified their HI deficiency compared to galaxies in isolation. We find little evidence that HI deficiency can be used as a proxy for the evolutionary phase of a compact group in either of the first two phases, with the distribution of HI deficiency being consistent in both. However, for the final phase, the distribution clearly shifts to high HI deficiencies, with more than 90% of the expected HI content typically missing. Across all HCGs studied, we identify a few cases where there is strong evidence for a diffuse gas component in the intra-group medium, which might be detectable with improved observations. We also classify a new sub-phase where groups contain a lone HI-bearing galaxy, but are otherwise devoid of gas. The new morphological phase we have identified is likely the result of an evolved, gas-poor group acquiring a new, gas-rich member. The large spread of HI deficiencies in the first two morphological phases suggests that there is a broad range of initial HI content in HCGs, which is perhaps influenced by large-scale environment, and that the timescale for morphological changes is, in general, considerably shorter than the timescale for the destruction or consumption of neutral gas in these systems.