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STATISTICS and PROPERTIES of Hii REGIONS in a SAMPLE OF AA manuscript no will b e inserted by hand later ASTRONOMY AND Your thesaurus co des are ASTROPHYSICS NGC NGC NGC NGC STATISTICS AND PROPERTIES OF H i i REGIONS IN A SAMPLE OF GRAND DESIGN GALAXIES I LUMINOSITY FUNCTIONS 1 1 2 M Rozas JE Beckman and JH Knap en Instituto de Astrofsicade Canarias E La Laguna Tenerife Canarias Spain Departement de Physique Universitede MontrealCP Succursale Centre Ville MontrealQuebec HC J Canada Received accepted July th Abstract We present new high quality continuum This is the rst of two pap ers in which we describ e an subtracted H images of the granddesign galaxies analysis of the luminosity functions LFs and geometri NGC NGC NGC and NGC We have cal distribution of H i i regions in the discs of NGC determined the p ositions angular sizes and uxes of their NGC NGC and NGC These galaxies individual H i i regions and describ e statistical prop erties were observed as part of our ongoing program to image of the H i i region samples We construct luminosity func granddesign spiral galaxies in the H emission line tions for all the H i i regions in the disc and separately for In the present pap er we will discuss exclusively late arm and interarm zones for each galaxy The slop es of the type spiral galaxies although other galaxies of other mor luminosity functions for the complete sample agree well phological types have b een studied For example for LFs with values published for other spiral galaxies of compara for Sa galaxies we refer to Caldwell et al Kenni ble morphological type For three galaxies we determined cutt Edgar Ho dge hereafter referred to as KEH the slop es of the luminosity functions for the spiral arm have studied the H i i region LFs in a sample of galaxies and interarm zones separately We nd that for NGC ranging in morphological type from Sb to Irr They found NGC and NGC these slop es are equal within that the H i i region LF can b e describ ed by a p ower law 205 the errors of determination We compare our results to function with N L / L Late type spirals p ossess those found from earlier work sp ecically for M and more H i i regions than early type galaxies and their LF NGC and discuss implications for massive star form is shallower KEH constructed arm and interarm LFs for ing pro cesses ve galaxies in their sample for which the H i i region LF for the interarm is signicantly dierent from that for the Key words ISM H i i regions galaxies individual arm astro-ph/9509060 11 Sep 1995 NGC NGC NGC NGC galaxies Cepa Beckman have studied the distribution spiral of H i i regions in the barred spiral NGC and did not nd any signicant dierence in the arm and interarm LF slop es The same authors Cepa Beckman pub 0 0 lished a catalogue of the H i i regions in the inner of NGC In that galaxy they did nd a signicant Introduction dierence b etween arm and interarm LFs a result similar to that obtained from an analysis of the H i i region LF in The distribution of H i i regions is an excellent tracer of re M by Rand hereafter referred to as R The dis cent massive star formation in spiral galaxies see eg the tribution of H i i regions in the disc of NGC Knap en review by Kennicutt Complete catalogues of these et al hereafter referred to as KACB shows that the regions provide an observational base which is increasingly slop es of the arm and interarm LFs are equal within the used in programmes aimed at determining global massive uncertainties of the ts to the slop es for that galaxy star formation parameters across galactic discs However The H image used by R and the image of high quality catalogues and detailed statistical analyses NGC as used by KACB which forms part of the are still not frequently found in the literature same program as the galaxies analysed in the present pa p er are similar in quality to the images presented now Send oprint requests to JE Beckman M Rozas et al Statistics and Prop erties of H i i regions I Table Basic prop erties of galaxies Galaxy Arm Class Type R D RA Dec 0 RC Mp c h m s 0 00 NGC SABb crs h m s 0 00 NGC Scs h m s 0 00 NGC SBb cs h m s 0 00 NGC SABb crs We can therefore compare our results directly with those is describ ed in Sec The results are presented in terms found in R KACB and more qualitatively with KEH of LFs in Sec and briey discussed in terms of star In Table we give basic prop erties of the four galaxies formation pro cesses in Sec The main conclusions are presented in this pap er NGC NGC NGC summarized in Sec and NGC Column two in the Table is the arm class as dened by Elmegreen Elmegreen where class Observations and data reduction galaxies have the b estdened spiral arms Column three is the morphological type de Vaucouleurs et al The observations of NGC NGC and NGC hereafter RC Column four is the radius at mag th th were made during the nights of September and 2 arcsec R in arcmin from the RC Column ve is 25 with the m William Herschel Telescope WHT on the distance in Mp c as determined from the redshift as La Palma We used the TAURUS instrument in imaging 1 1 suming H km s Mp c Finally columns six and 0 mo de as a reimaging camera mounted at the Cassegrain seven give the p ositions of the centres of the galaxies for fo cus of the telescop e The detector used was an EEV ep o ch from RC 00 00 CCD with pro jected pixel size Observ The galaxies were selected to give a balance b etween 00 ing conditions were very go o d with seeing FWHM barred and nonbarred ob jects with the aim of comparing as measured in the nal images and photometric sky We and contrasting their prop erties obtained two exp osures of seconds each p er galaxy NGC is an angularly small weakly barred galaxy one through a A wide lter whose central wavelength with well dened spiral arms The nuclear region is rel coincided with that of the redshifted H emission from the atively small and it is noted for several dusty regions galaxy A for NGC A for NGC and which can b e clearly recognized on a blue image not A for NGC and another through a nonred repro duced here shifted H lter A with A width for continuum NGC is a latetype spiral galaxy of type Sc It subtraction NGC was observed during the night of th shows no sign of a bar and has no obvious companion May using the same telescop e and instrumen nearby It has two main spiral arms and some smaller tation Given the angular size of this galaxy we decided to arm sections as describ ed by Bo eshaar and Ho dge take three sets of line and continuum images of s each who studied the distribution of H i i regions in comp osed of separate s images at three dierent this galaxy p ositions of the galaxy disc We used the A wide A NGC is an angularly small barred galaxy of arm lter for the line images and the equally wide A l class It has two spiral arms and very little emission ter for the continuum imaging H continuumsubtracted b etween them The brightest star forming regions are images were pro duced for these three p ositions separately at the ends of the bar The nucleus of NGC is a see b elow which were then pasted together into one nal LINER H image of the galaxy The resolution of the nal image 00 NGC is the second mixedtype weakly barred was limited to the resolution of the subimage with spiral in our sample A bright and well dened ring the p o orest resolution which also led us to rebin the nal 00 00 structure surrounds the very bright nuclear region image to a pixelsize Photometric calibration which is elongated along an axis at nearly right angles was achieved by comparison of the nal image with an to the bar axis We will not discuss this inner region in image of the inner part of the disc of NGC obtained the present pap er NGC hosts a Seyfert nucleus earlier with the WHT Bo er Schulz Standard reduction routines were used following In Fig we show grey scale representations of the closely the pro cedure used in KACB for NGC A continuumsubtracted H images of NGC NGC bias level was rst subtracted and the images were then NGC and NGC The observations and data re corrected using appropriate dawn sky atelds Next a duction pro cedures are summarized in Section and the value for the sky background was obtained by measuring H i i region selection and the construction of the catalogues the background and asso ciated noise levels in p ortions of M Rozas et al Statistics and Prop erties of H i i regions I Fig Grey scale representations of the H continuumsubtracted images of NGC a NGC b NGC c and NGC d the images where there was no emission from the galaxies Pro duction of the H i i region catalogues In order to align the two line and continuum images of each galaxy p ositions of several foreground stars were de termined making gaussian ts and the oband image was displaced to coincide with the H image using the stellar Table The rms noise in instrumental counts column p ositions The accuracy of the sup erp ositions was in all of the background subtracted H images the lower limit to the luminosity of the detected H i i regions in each galaxy col cases b etter than pixels In the case of NGC we and the approximate size of the smallest catalogued regions also used foreground star p ositions to align the three sub col images for subsequent combination into the nal galaxy image Galaxy rms log L erg s D p c H NGC Once the aligned images were cleaned of cosmic ray NGC eects see KACB for a discussion and an o ccasional bad NGC pixel
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