2.2 The data
2.2.2 Far-Infrared Data
2.2.1.3 Molecular gas mass
We calculate the molecular gas mass,MH2 using the following equation:
MH2=75×D2ICO(1−0)Ω (2.3)
whereΩis the area covered by the observations in arcsec2(i.e.Ω=1.13θ2for a single pointing with a gaussian beam whereθ is the HPBW). The former equation assumes a ratio X=NH2/ICO
=2×1020cm−2(K km s−1)−1(e.g. Dickman et al. 1986). TheMH2 calculated for the 86 galaxies are listed in Table 2.2.
In both the observations we carried out and the data obtained from the literature, a single position at the center of the galaxy was observed. Because of this and the different beams used by us and in the literature we need to correct for possible emission outside the beam. To correct the observed CO intensities we need to know the distribution and extension of the CO emission.
Different authors (Nishiyama et al. 2001; Regan et al. 2001; Leroy et al. 2008) have found that the integrated CO intensity in spiral galaxies follows an exponential distribution as a function of radius with a scale lenghtre:
ICO(r) =I0∝e(r/re) (2.4)
We adopt a scale length ofre =0.2×r25, wherer25is the isophotal radius at an optical sufrace brightness of 25 mag arcsec−1isophotal radius, following Lisenfeld et al. (in prep.), who derived this scale length from studies of the above mentioned authors and from their own CO data.
We have used this distribution to calculate the expected CO emission from the entire disk, tak- ing into account the galaxy inclination. The expected emission has been compared with the observed emission in the central pointing to calculate a correction factor.
The correction factor to the CO(1-0) intensities is shown in Figure 2.1. The ratio between the corrected and uncorrected intensities is below 2 in most of the galaxies (66 out of 86, or 77 %), with an average value of 1.78. To check the consistency of the correction, we have also performed the analysis presented in this paper for a sample restricted to the galaxies with cor- rections lower than 1.6 (45 galaxies), finding no significant differences with respect to the full sample, so we can conclude that the aperture correction does not introduce a bias in the results.
The values for the extraoplated molecular gas mass are shown in Table 2.2. Here, and in the following, we always use the extrapolated molecular gas mass and denote itMH2 for simplicity.
TheMH2 distribution is shown in Fig. 2.2. The average value for the full sample and the spiral galaxies is shown in Table 2.3. The distribution and average values ofMH2, as well as the sta- tistical distributions and average values throughout this work, have been calculated using the Kaplan-Meier estimator implemented in ASURV4, to take into account the upper limits in the data.
2.2 The data 21
Figure 2.1:MH2aperture correction factor distribution.
Table 2.3: Average values forLB,MH2, MH2 deficiency,LFIR, LFIR deficiency andMHI deficiency for HCGs galaxies and AMIGA isolated galaxies.
HCGs AMIGA
All nU L/n T>0 nU L/n All nU L/n T>0 nU L/n LB 9.91±0.04 0/86 9.95±0.06 0/46 9.72±0.03 0/173 9.75±0.04 0/150 MH2 8.71±0.07 41/86 9.02±0.09 11/46 8.24±0.09 84/173 8.32±0.09 69/150 Def(MH2) 0.10±0.09 41/86 -0.22±0.09 11/46 0.05±0.04 84/173 0.02±0.04 69/150 LFIR 8.96±0.12 50/85 9.53±0.09 15/45 9.11±0.05 75/172 9.16±0.05 58/150 Def(LFIR) 0.32±0.09 50/85 -0.11±0.08 15/45 -0.05±0.05 75/172 -0.09±0.04 58/150 Def(HI) 1.34±0.10 34/68 0.93±0.13 9/37
In the case of the isolated galaxies, we have calculated the average LB, MH2, MH2 deficiency, LFIR and LFIR
deficiency for the subsample of galaxies withMH2data. For each subsample,nis the number of galaxies andnU L
is the number of upper limits.LFIRof the AMIGA galaxies are calculated form the new release (see Sec. 2.3) of the AMIGA sample, while theMH2values are calculated form the data in Lisenfeld et al. (in prep.)
produces a scan profile along the average scan direction. It is 3-5 times more sensitive than IRAS PSC since it combines all survey data and it is therefore more suitable for detection of the total flux from slightly extended objects.
We have compiled from Verdes-Montenegro et al. (1998) (Table 2.4) the FIR data (also de- rived using ADDSCAN/SCANPI) for 63 galaxies in our sample. In the case of the remaining 23 galaxies, we derived FIR fluxes directly using ADDSCAN/SCANPI. To choose the best flux esti- mator we have followed the guidelines given in the IPAC website6, which are also detailed in Lisenfeld et al. (2007).
This procedure was also followed for 14 galaxies in the list of Verdes-Montenegro et al.
(1998) to check for consistency. We found no significant differences, with an average difference of 15% between our reprocessed fluxes and those in Verdes-Montenegro et al. (1998).
6http://irsa.ipac.caltech.edu/IRASdocs/scanpi_interp.html
Figure 2.2:MH2andLFIRdistribution ratios of the HCG galaxies. The (red) filled bins show the distribution of the detected galaxies, t the dashed line gives the distribution of upper limits and the full line shows the combined distribution given by ASURV.
From the fluxes at 60 and 100µm,LFIRis computed as
log(LFIR/L⊙) =log(FIR) +2logD+19.495 (2.5)
where FIR is defined as (Helou et al. 1988):
FIR=1.26×10−14(2.58F60+F100)Wm−2. (2.6)
The computed LFIR, together with the 60 and 100 µm fluxes compiled from ADDSCAN/SCANPI are detailed in Table 2.4. In this table we also show the values of the Star Formation Rate (SFR), the Star Formation Efficiency (SFE) and the specific Star Formation Rate (sSFR) (see Sec. 2.3.2). The distribution ofLFIRis shown in Fig. 2.2. The average value of LFIRfor the full sample and the spiral galaxies is shown in Table 2.3.
For galaxies HCG31aandcFIR fluxes can not be separated. Therefore, we use the sum of both. When comparingLFIRto other magnitudes (LB,MH2orMH I), we also use the sum of these magnitudes.
Table 2.4: FIR, SFR, SFE and sSFR
Galaxy Ref(1) I60 I100 log(LFIR) SFR log(SFE)(2) log(sSFR) (Jy) (Jy) (L⊙) (M⊙yr−1) log(yr−1) (M⊙yr−1)
7a 2 3.32 6.61 10.23 5.96 -8.93 -10.43
7b 2 <0.18 <0.32 <8.95 <0.31 <-11.40
7c 2 0.61 2.35 9.65 1.57 -8.97 -10.72
7d 2 <0.15 <0.39 <8.95 <0.31 <-10.73
10a 2 0.50 1.81 9.72 1.84 -9.24 -11.12
10b 2 <0.11 0.47 <9.10 <0.44 <-11.79
10c 2 0.78 2.06 9.84 2.43 -9.15 -10.49
10d 2 <0.12 <0.28 <9.00 <0.35 <-10.93 15a 1 <0.17 0.50 <9.48 <1.06 <-11.23 15b 1 <0.22 <0.70 <9.61 <1.43 <-10.87 15c 1 <0.24 <0.80 <9.65 <1.57 <-10.80
2.2 The data 23 Galaxy Ref(1) I60 I100 log(LFIR) SFR log(SFE)(2) log(sSFR)
(Jy) (Jy) (L⊙) (M⊙yr−1) log(yr−1) (M⊙yr−1)
15d 1 <0.24 0.53 <9.56 <1.27 <-8.45 <-10.70
15e 1 <0.13 0.28 <9.29 <0.68 <-10.88 15f 1 <0.24 0.79 <9.65 <1.57 <-9.78
16a 2 5.73 12.83 10.47 10.36 -8.98 -10.29
16b 2 <0.12 <0.33 <8.84 <0.24 <-9.73 <-11.71
16c 2 12.20 19.99 10.74 19.29 -8.44 -9.70
16d 2 11.80 12.00 10.66 16.04 -8.75 -9.75
23a 1 <0.30 <1.93 <9.57 <1.30 <-8.27 <-10.95
23b 1 <1.50 <4.02 <10.03 <3.76 <-9.10 <-10.41
23c 1 <0.14 <0.80 <9.21 <0.57 <-11.02
23d 1 0.63 1.23 9.59 1.37 -8.62 -10.20
25a 1 0.55 1.16 9.84 2.43 -8.85 -10.32
25b 1 <0.15 <0.71 <9.46 <1.01 <-9.05 <-11.12
25d 1 <0.25 <0.63 <9.53 <1.19 <-10.26 25f 1 <0.13 <0.70 <9.44 <0.97 <-10.38 30a 2 <0.09 0.55 <9.00 <0.35 <-11.56 30b 2 0.10 <0.44 <8.95 <0.31 <-11.50
30c 2 0.17 0.75 9.19 0.54 >-9.09 -10.15
30d 2 <0.10 <0.30 <8.85 <0.25 <-10.55 31ac(3) 2 4.98 6.69 10.35 7.86 >-7.92 <-9.29
31b 2 0.08 0.38 8.84 0.24 >-9.39 -10.15
31g 2 0.50 0.40 9.29 0.68 >-8.89 -10.20
37a 2 0.56 2.30 10.06 4.03 -7.80 -11.01
37b 2 0.66 2.13 10.07 4.12 -9.18 -10.50
37c 2 <0.09 <0.26 <9.19 <0.54 <-8.57
37d 2 <0.08 <0.12 <9.01 <0.36 <-8.71 <-10.34
37e 2 <0.11 <0.17 <9.13 <0.47 <-10.55 40a 2 <0.10 <0.30 <9.18 <0.53 <-11.78
40b 2 <0.08 <0.25 <9.11 <0.45 <-9.04 <-11.43
40c 2 0.85 2.00 10.06 4.03 -9.23 -10.64
40d 2 1.03 2.30 10.13 4.73 -8.76 -10.35
40e 2 <0.10 <0.24 <9.13 <0.47 <-9.20 <-10.75
44a 2 3.40 10.72 9.43 0.94 -8.89 -11.04
44b 2 <0.12 <0.39 <7.99 <0.03 <-12.27
44c 2 1.55 3.71 9.03 0.38 -9.12 -10.77
44d 2 1.30 3.12 8.96 0.32 -8.49 -10.15
58a 1 3.06 6.64 10.59 13.66 -9.09 -10.32
58b 1 0.41 1.88 9.90 2.79 -8.95 -10.89
58c 1 <0.21 <0.60 <9.49 <1.08 <-11.18 58d 1 <0.19 <0.94 <9.59 <1.37 <-10.93
58e 2 0.29 0.88 9.64 1.53 -8.89 -10.46
67a 2 <0.19 <0.74 <9.64 <1.53 <-11.63
67b 2 1.01 2.59 10.26 6.39 -8.96 -10.50
67c 2 <0.21 0.90 <9.71 <1.80 <-10.29
68a 2 0.42 1.70 8.90 0.28 >-8.58 -11.81
Galaxy Ref(1) I60 I100 log(LFIR) SFR log(SFE)(2) log(sSFR) (Jy) (Jy) (L⊙) (M⊙yr−1) log(yr−1) (M⊙yr−1) 68b 2 <0.12 <0.31 <8.25 <0.06
68c 2 2.34 8.45 9.62 1.46 -8.94 -10.70
68d 2 <0.16 <0.26 <8.28 <0.07 <-11.30 68e 2 <0.18 <0.29 <8.34 <0.08 <-11.07
79a 2 1.28 2.82 9.90 2.79 >-8.61 -10.31
79b 2 <0.13 <0.45 <9.01 <0.36 <-9.00 <-11.18
79c 2 <0.10 <0.40 <8.94 <0.31 <-8.64
79d 2 <0.09 <0.40 <8.92 <0.29
88a 2 0.47 2.44 9.96 3.20 -9.04 -10.85
88b 2 0.14 <0.50 <9.34 <0.77 <-9.41 <-11.36
88c 2 0.36 2.03 9.87 2.60 -9.18 -10.08
88d 2 0.18 0.77 9.49 1.08 -8.60 -10.38
92b 2 0.85 2.78 10.16 5.07 >-8.46 -10.90
92c 2 0.85 2.60 10.14 4.85 -8.50 -10.61
92d 2 <0.85 <0.75 <9.93 <2.99 <-11.13 92e 2 <0.09 <0.92 <9.52 <1.16 <-11.01
93a 1 <0.40 <1.04 <9.50 <1.11 <-8.78 <-11.43
93b 1 1.82 4.90 10.16 5.07 -8.94 -10.22
93c 1 <0.18 <1.14 <9.39 <0.86 <-9.07 <-11.11
93d 1 <0.20 <1.14 <9.40 <0.88 <-10.68 97a 2 <0.13 <0.38 <9.29 <0.68 <-11.51
97b 2 0.15 0.86 9.53 1.19 -9.17 -10.65
97c 2 <0.12 <0.36 <9.26 <0.64 <-11.14 97d 2 <0.20 <0.36 <9.38 <0.84 <-11.20 97e 2 <0.12 <0.43 <9.31 <0.72 <-10.38
100a 2 2.13 4.02 10.28 6.69 -8.28 -10.39
100b 2 <0.09 <0.44 <9.13 <0.47 <-8.69 <-10.58
100c 2 0.30 0.45 9.39 0.86 -8.52 -10.24
100d 2 <0.12 <0.77 <9.34 <0.77 <-9.61
(1)Reference code (see 2.2.2): 1: Our data analysis. 2:Verdes-Montenegro et al. (1998).
(2)The value of the SFE is not displayed for the galaxies with upper limits in bothLFIRandMH2.
(3)The SFE of 31ac has been calculated using the sum of their respectiveMH2.