J/A+A/570/A24 CO in HCG galaxies with enhanced warm H2 (Lisenfeld+, 2014)
CO in Hickson Compact Group galaxies with enhanced warm H2 emission:
Evidence for galaxy evolution?
Lisenfeld U., Appleton P.N., Cluver M.E., Guillard P., Alatalo K, Ogle P.
<Astron. Astrophys. 570, A24 (2014)>
=2014A&A...570A..24L 2014A&A...570A..24L
ADC_Keywords: Clusters, galaxy ; Galaxies, IR ; Carbon monoxide ; Spectroscopy
Keywords: galaxies: evolution - galaxies: groups: general -
galaxies: ISM - galaxies: interactions - infrared: galaxies -
intergalactic medium
Abstract:
Galaxies in Hickson Compact Groups (HCGs) are believed to experience
morphological transformations from blue, star-forming galaxies to red,
early-type galaxies. Galaxies with a high ratio between the
luminosities of the warm H2 to the 7.7micron PAH emission (so-called
Molecular Hydrogen Emission Galaxies, MOHEGs) are predominantly in an
intermediate phase, the green valley. Their enhanced H2 emission
suggests that the molecular gas is affected in the transition.
We study the properties of the molecular gas traced by CO in galaxies
in HCGs with measured warm H2 emission in order to look for evidence
of the perturbations affecting the warm H2 in the kinematics,
morphology and mass of the molecular gas.
We observed the CO(1-0) emission of 20 galaxies in HCGs and
complemented our sample with 11 CO(1-0) spectra from the literature.
Most of the galaxies have measured warm H2 emission, and 14 of them
are classified as MOHEGs. We mapped some of these galaxies in order to
search for extra-galactic CO emission. We analyzed the molecular gas
mass derived from CO(1-0), MH2, and its kinematics, and then compared
it to the mass of the warm molecular gas, the stellar mass and star
formation rate (SFR).
Our results are the following.
(i) The mass ratio between the CO-derived and the warm H2 molecular
gas is in the same range as found for field galaxies.
(ii) Some of the galaxies, mostly MOHEGs, have very broad CO
linewidths of up to 1000km/s in the central pointing. The line shapes
are irregular and show various components.
(iii) In the mapped objects we found asymmetric distributions of the
cold molecular gas.
(iv) The star formation efficiency (=SFR/MH2) of galaxies in HCGs is
very similar to isolated galaxies. No significant difference between
MOHEGs and non-MOHEGs or between early-type and spiral galaxies has
been found. In a few objects the SFE is significantly lower,
indicating the presence of molecular gas that is not actively forming
stars.
(v) The molecular gas masses, MH2, and ratios MH2/Lk are lower in
MOHEGs (predominantly early-types) than in non-MOHEGs (predominantly
spirals). This trend remains when comparing MOHEGs and non-MOHEGs of
the same morphological type.
We found differences in the molecular gas properties of MOHEGs that
support the view that they have suffered (or are presently suffering)
perturbations of the molecular gas, as well as a decrease in the
molecular gas content and associated SFR. Higher resolution
observations of the molecular gas are needed to shed light on the
nature of these perturbations and their cause.
Description:
The files name hcgxxco10offx_offy.fits are the fits files of the
spectra in Fig. A1 (CO(1-0) spectra).
The files name hcgxxco21offx_offy.fits are the fits files of the
spectra in Fig. A2 (CO(2-1) spectra). Here, xx stands for the HCG
number of the galaxy and offx, offy are the offsets with respect to
the central pointing.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 41 31 Basic data of the sample galaxies
list.dat 148 66 List of FITS spectra
fits/* . 66 Individual FITS spectra
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See also:
VII/213 : Hickson's Compact groups of Galaxies (Hickson+ 1982-1994)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Galaxy Galaxy name
9- 14 F6.2 Mpc Dist [18/217] Distance (1)
16- 17 I2 --- TT [-3/9] Morphological T-type, from LEDA (2)
19- 22 F4.2 arcmin D25 Optical major diameter at the
25mag/arcsec2 isophote (from LEDA)
24- 25 I2 deg i Inclination angle (from LEDA)
27- 31 F5.2 [Lsun] logLK ?=- luminosity in the K-band (3)
33- 36 A4 --- CO10 Indicates CO(1-0) spectra
38- 41 A4 --- CO21 Indicates CO(2-1) spectra
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Note (1): Distance, based on redshifts from the NASA/IPAC Extragalactic
Database (NED) listed in Cluver et al. (2013ApJ...765...93C 2013ApJ...765...93C) and adopting
a Hubble constant of 73km/s/Mpc.
Note (2): Morphological type taken from the LEDA database, following the RC3
classification (de Vaucouleurs et al., 1991, Cat. VII/155)
Note (3): Decimal logarithm of the luminosity in the K-band in units of
the solar luminosity in the Ks-band (LK,☉=5.0735x1032erg/s). We
calculated the Ks luminosity LK from the total (extrapolated) Ks flux,
fK, as LK=ν*fK(ν) (where ν is the frequency of the K-band,
1.38x1014Hz). The fluxes in the Ks (2.17um) band were taken from Bitsakis
et al. (2011A&A...533A.142B 2011A&A...533A.142B, Cat. J/A+A/533/A142) who obtained them partly
from their own observations and partly from the 2MASX (Jarrett et al.
2000AJ....119.2498J 2000AJ....119.2498J, Cat. VII/233).
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Galaxy Galaxy name
9- 17 F9.5 deg RAdeg Right ascension (J2000)
18- 26 F9.5 deg DEdeg Declination (J2000)
28- 30 I3 --- Nx Number of spectrum elements
32- 41 A10 "date" ObsDate Observation date
43- 47 F5.2 km/s dV [15/17] Velocity spacing
49- 56 F8.4 GHz nu0 [109/230] Rest frequency ν0
58- 64 F7.1 km/s Vmin Lower limit of (relative) velocity scan
66- 72 F7.1 km/s Vmax Upper limit of (relative) velocity scan
75 I1 Kibyte size [8] Size of FITS file
77-100 A24 --- FileName Name of the FITS file in subdirectory fits
102-148 A47 --- Title Title of the file
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Acknowledgements:
Ute Lisenfeld, ute(at)ugr.es
(End) Ute Lisenfeld [UGR], Patricia Vannier [CDS] 28-Jul-2014