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Up: Near-infrared observations of galaxies

5 Summary  

We have presented the results of a programme of NIR imaging of disk galaxies in the Pisces-Perseus supercluster area, $22^{\rm h}<{\rm RA}<4^{\rm h}$ and $0^\circ<\delta<45^\circ$.This programme constitutes the first large NIR imaging survey of the supercluster and complements previous similar surveys in the Coma and Virgo areas. The present paper is the first of a series and contains images in the H passband of a composite sample of 174 galaxies.

The sample galaxies, a subset of the PP supercluster galaxies, are mainly late spirals with a median $T\sim 5$.The sample starts lacking completeness at $B_{\rm T} = 14.0$,and extends up to $B_{\rm T} = 16.5$.

For each galaxy we present a grey-scale image reaching an isophote of $\sim 21.0\, H$-mag arcsec-2. For each image we supply the elliptically-averaged radial profile of the surface brightness, the ellipticity, and the position angle of the isophotes.

We derive a total magnitude $H_{\rm T}$, an isophotal magnitude H21.5, an effective diameter $D_{\rm e}$, an isophotal one D21.5, the concentration index C31, and estimate the ellipticity $\epsilon$ and the position angle PA of the outer disk. These data, together with basic information regarding the sample objects and their observation, are collected in a single table which is available in electronic form at the CDS. Radial profiles in tabular form and images FITS files are also available upon request.

The trends of $(H_{21.5}-H_{\rm T})$ with H21.5 and $\langle\mu_{21.5}\rangle$ imply that the average outer disk has an isophotal radius $D_{21.5}/2 \simeq 3.5 r_{\rm d}$ and a central surface brightness $\mu(0) \simeq 17.5$ H-mag arcsec-2.

The empirical relation in our sample, D21.5 = 0.89 D25, implies that the B-H color of the outer disk is bluer, on average, than 3.5, in agreement with de Jong (1996). The ratio D21.5/D25 depends, although weakly, on the total galaxy B-H, and consequently on its absolute magnitude.

We confirm the dependence of the (model independent) concentration index C31 on luminosity and, to a lesser degree, on morphological type. Large values for C31, that is values in excess of what is expected for pure disks ($\log C_{31}\mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil
 ...ffinterlineskip\halign{\hfil$\scriptscriptstyle ... ), are preferentially observed in galaxies brighter than $M_{\rm H}\simeq -23$ and $T\mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil
$\displaystyle ... .

Even in the NIR, objective estimates of outer ellipticities and position angles can often be contaminated by the geometry of bars and spiral patterns; the effect is strongest for shallow images, and for low inclinations. Their impact on the measurement of global photometric properties is, in any case, not dramatic. It virtually affects only D21.5, with discrepancies exceeding 10% only in the two worst cases.


G.M. warmly acknowledges the hospitality of the Astronomy Dept. of Cornell University, where part of the data reduction was done. We acknowledge the partial support of the Italian Space Agency (ASI) through the grant ARS-98-116/22.

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