4 Notes on individual members

CG J0247+449a. The morphological analysis in all four photometric bands indicates a regular galaxy without asymmetric structures. It is well fitted by an exponential bulge ($n \sim 1$) and the B/T ratio is $\sim$0.37. No residuals are visible after model subtraction (see Fig. 3). For this object (also known as 2MASXi J0247252+445039) we suggest a morphological type Sa/Sab. The optical spectrum shows weak continuum and emission lines (Fig. 4). [O III]5007 is the brightest emission line, while Balmer hydrogen lines are partly absorbed by the underlying stellar continuum. After the subtraction of this stellar contribution by means of a template galaxy spectrum, following the prescriptions by Ho et al. (1993), we observe an H$\alpha$/H$\beta$ ratio $\sim$2.89, very close to the theoretical value of 2.86 for Case B recombination at electronic temperature $T_{\rm e} = 10^4$ K (Osterbrock 1989), indicating very low internal extinction. The logarithmic ratios [O III]5007/H $\beta = 0.95\pm 0.34$ and [N II]6583/H $\alpha = -0.30\pm 0.18$, even with large uncertainties, are typical of a Seyfert-2 nucleus (Veilleux & Osterbrock 1987).

 

 

Table 5: Radial velocities.

Obj. Id.	$\alpha$ (J2000)	$\delta$ (J2000)	$V_{\rm hel}$
	( $^{\rm h~~m~~s}$)	( $^{\circ~~\prime~~\prime\prime}$)	(km s-1)
CG J0247+449a	02 47 25.2	44 50 39	10981 $\pm$ 57
CG J0247+449b	02 47 37.6	44 51 45	11346 $\pm$ 116
CG J0247+449c	02 47 46.3	44 52 58	11386 $\pm$ 101
CG J0247+449d	02 47 49.8	44 53 26	12240 $\pm$ 32
CG J0247+449e	02 47 41.9	44 50 34	11707 $\pm$ 41
CG J0247+449f	02 47 40.4	44 50 29	11931 $\pm$ 88
2MASXi J0247387+445008	02 47 38.7	44 50 08	51000 (?)

CG J0247+449b. This galaxy (2MASXi J0247376+ 445145) shows a B/T ratio $\sim$0.57, almost constant in all bands (see Table 3). The bulge is well reproduced by a de Vaucouleurs r^1/4-law, therefore we classify this object as E/S0. The residuals show in each band a ring-like structure at a radius of $\sim$4 arcsec (better visible in the R-band in Fig. 3) and a central X-structure aligned with the major and minor photometric axes, which indicates a disky shape of the inner isophotes (Schweizer 1998). Numerical simulations (Naab & Burkert 2001) have shown that faint ellipticals with disky isophotes might be the final product of unequal mass disk galaxy mergers (mass ratio 3:1 or 4:1).

The integrated spectrum of the galaxy shows only absorption lines and a continuum typical of an early-type galaxy (Fig. 4).

CG J0247+449c. This galaxy (2MASXi J0247463+ 445258) has a B/T ratio around or even less than $\sim$0.4. Its bulge is well fitted by a de Vaucouleurs r^1/4-law like for object "b''. So we classify it as S0/Sa. The residuals in VRI bands show the presence of a nuclear source, confirmed by the analysis of the optical spectrum. Indeed, the spectrum has the continuum of an early-type spiral (see Fig. 4) with deep metal absorption lines but with H$\alpha$, [N II]6583 and [S II]6724 emissions. Since the [N II]6583 line appears more intense than H$\alpha$ and the [O III]5007 is barely detectable at noise level, we suggest that this galaxy could host a LINER. In order to avoid an underestimate of the H$\alpha$ flux due to the underlying stellar absorption, we applied a template correction, as in the case of object "a''. After this correction the two emission lines H$\alpha$ and [N II]6583 have comparable intensity. The diagnostic logarithmic emission-line ratios [N II]6583/H$\alpha$ and [S II]6724/H$\alpha$ are $0.22\pm0.10$ and $-0.16\pm 0.15$, respectively, confirming the classification as a LINER.

CG J0247+449d. Object "d'' is a galaxy seen almost edge-on (i $\sim$ 80$^\circ$). Although it is generally not recommended for highly inclined galaxies, we attempted a morphological analysis in this case, as well. Despite the lack of visible residuals after the subtraction of the bidimensional galaxy model in the four photometric bands (Fig. 3), the output values of the fit (Table 3) are somehow puzzling, suggesting that the bulge-disk decomposition mostly failed. Therefore we limit our comments to point out that the galaxy is significantly asymmetric and the bulge seems to follow an exponential law. We propose a Sbc classification for this object. The optical spectrum is very faint, but weak extended [S II]6724 and H$\alpha$ emission lines are measurable and their logarithmic ratio is $-0.26\pm0.21$, somewhat higher than expected for H II-like galaxies. However the non-detection of [N II]6583 and [O III]5007 indicates a low ionization degree of the gas. The H$\beta$ emission-line is detectable at noise level. We interpret this emission spectrum as an indication of a normal level of star formation for a late-type spiral galaxy.

CG J0247+449e/f. These two galaxies form a close pair known as IRAS 02443+4437. Despite the application of the maximum entropy algorithm to the far infrared (FIR) raw data extracted from the IRAS database to approach the diffraction limit of the telescope, the galaxy pair could not be resolved. A single infrared source, centered at the position of galaxy "f'', is detectable only at 60 (Fig. 5) and 100 $\mu$m with measured fluxes $0.618\pm0.005$ and $1.313\pm0.085$, respectively. The total FIR luminosity between 40 and 120 $\mu$m calculated following Helou et al. (1985) is $L_{\rm FIR} = 2.75\times10^{10}$ $L_{\odot}$, which yields a total star formation rate $SFR = 14.4~M_{\odot}$ (Hunter et al. 1986). The spectroscopic analysis reveals that the FIR emission is dominated by galaxy "e'', which shows bright emission lines typical of a starburst galaxy. Measured fluxes of the emission lines (Table 6) have been corrected for internal extinction $A_{\rm V} = 1.61$ determined assuming a theoretical H$\alpha$/H $\beta = 2.86$ and applying the CCM extinction law. The logarithmic diagnostic ratios [N II]6583/H $\alpha = -0.41\pm0.02$, [S II]6724/H $\alpha = -0.51\pm0.04$, [O I]6300/H $\alpha = -1.61\pm0.13$, and [O III]5007/H $\beta = -0.16\pm0.06$ confirm the thermal nature of the ionizing source. The reddening corrected H$\alpha$ luminosity L(H$\alpha$) = $5.1\times10^{41}$ erg s^-1 corresponds to a $SFR \simeq 4~M_{\odot}$ yr^-1 (Kennicutt 1998). This value is lower than the SFR of the galaxy pair estimated from the FIR luminosity, but it only accounts for the portion of the galaxy covered by the slit. The spectrum of object "f'' shows the typical absorption features of an early-type galaxy, without any emission line, but with a relatively blue continuum. The morphological analysis confirms the spectroscopic results. Galaxy "e'' is clearly a spiral with irregular shape, as indicated by the high value of the asymmetry index, which made less accurate the bidimensional fit. In fact strong residuals remain where star forming regions are located. These regions, brighter in the nucleus and fainter in the inner spiral arms, are likely to be responsible for the relatively high value of the obtained B/T ratio ($\sim$0.37), and for the negative B-V color (see Table 4). Since the Sérsic index of the bulge results <1, we suggest a Sbc classification for this object. Galaxy "f'' shows a mean B/T ratio of $\sim$0.7 and its bulge is well fitted by a de Vaucouleurs r^1/4-law, indicative of a morphological type E/S0. A moderate asymmetry is present (Table 3) and the residuals show in all bands an arm-like structure, which departs from the south of the nucleus winding around it, and a blob north of the nucleus. The morphological distortions observed in these galaxies together with their accordant redshifts indicate that this is a real interacting pair. As demonstrated by some authors (Rampazzo & Sulentic 1992; Hernández Toledo et al. 1999) galaxy pairs with mixed morphology exist in significant numbers and are believed to be the product of interaction phenomena. In agreement with our results about this galaxy pair, it is found that spiral + lenticular systems show an enhancement in the FIR emission with increased rate and efficiency of induced star formation (Hernández Toledo et al. 2001).

Figure 5: Contour map of the 60 $\mu$m IRAS emission of the galaxy pair IRAS 02443+4437, after application of the maximum entropy algorithm, overplotted to the Digitized Sky Survey optical image. Dashed contours are drawn at 1$\sigma$ and 2$\sigma$ level over the background; solid contours are drawn at 3, 4, 5, 6, 10, and 20$\sigma$ levels.