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The AMIGA sample of isolated galaxies. V. Quantification of the isolation
Context: The AMIGA project aims to build a well defined andstatistically significant reference sample of isolated galaxies in orderto estimate the environmental effects on the formation and evolution ofgalaxies. Aims: The goal of this paper is to provide a measure of theenvironment of the isolated galaxies in the AMIGA sample, quantifyingthe influence of the candidate neighbours identified in our previouswork and their potential effects on the evolution of the primarygalaxies. Here we provide a quantification of the isolation degree ofthe galaxies in this sample. Methods: Our starting sample is theCatalogue of Isolated Galaxies (CIG). We used two parameters to estimatethe influence exerted by the neighbour galaxies on the CIG galaxy: thelocal number density of neighbour galaxies and the tidal strengthaffecting the CIG galaxy. We show that both parameters together providea comprehensive picture of the environment. For comparison, thoseparameters have also been derived for galaxies in denser environmentssuch as triplets, groups and clusters. Results: The CIG galaxies show acontinuous spectrum of isolation, as quantified by the two parameters,from very isolated to interacting. The fraction of CIG galaxies whoseproperties are expected to be influenced by the environment is howeverlow (159 out of 950 galaxies). The isolated parameters derived for thecomparison samples gave higher values than for the CIG and we foundclear differences for the average values of the 4 samples considered,proving the sensitivity of these parameters. Conclusions: Theenvironment of the galaxies in the CIG has been characterised, using twocomplementary parameters quantifying the isolation degree, the localnumber density of the neighbour galaxies and the tidal forces affectingthe isolated galaxies. A final catalogue of galaxies has been producedand the most isolated of these galaxies are consequently appropriate toserve as a reference sample for the AMIGA project.Full Tables [see full text], [see full text] and [see full text]-[see full text] are available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/472/121 and fromhttp://www.iaa.es/AMIGA.html.
| The AMIGA sample of isolated galaxies. II. Morphological refinement
We present a refinement of the optical morphologies for galaxies in theCatalog of Isolated Galaxies that forms the basis of the AMIGA (Analysisof the interstellar Medium of Isolated GAlaxies) project. Uniformreclassification using the digitized POSS II data benefited from thehigh resolution and dynamic range of that sky survey. Comparison withindependent classifications made for an SDSS overlap sample of more than200 galaxies confirms the reliability of the early vs. late-typediscrimination and the accuracy of spiral subtypes within Δ T =1-2. CCD images taken at the Observatorio de Sierra Nevada were alsoused to solve ambiguities in early versus late-type classifications. Aconsiderable number of galaxies in the catalog (n = 193) are flagged forthe presence of nearby companions or signs of distortion likely due tointeraction. This most isolated sample of galaxies in the local Universeis dominated by two populations: 1) 82% are spirals (Sa-Sd) with thebulk being luminous systems with small bulges (63% between types Sb-Sc)and 2) a significant population of early-type E-S0 galaxies (14%). Mostof the types later than Sd are low luminosity galaxies concentrated inthe local supercluster where isolation is difficult to evaluate. Thelate-type spiral majority of the sample spans a luminosity rangeMB-corr = -18 to -22 mag. Few of the E/S0 population are moreluminous than -21.0 marking the absence of the often-sought superL* merger (e.g. fossil elliptical) population. The rarity ofhigh luminosity systems results in a fainter derived M* forthis population compared to the spiral optical luminosity function(OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending onhow the sample is defined. This marks the AMIGA sample as unique amongsamples that compare early and late-type OLFs separately. In othersamples, which always involve galaxies in higher density environments,M^*_E/S0 is almost always 0.3-0.5 mag brighter than M^*_S, presumablyreflecting a stronger correlation between M* andenvironmental density for early-type galaxies.
| Revised positions for CIG galaxies
We present revised positions for the 1051 galaxies belonging to theKarachentseva Catalog of Isolated Galaxies (CIG). New positions werecalculated by applying SExtractor to the Digitized Sky Survey CIG fieldswith a spatial resolution of 1 arcsper 2. We visually checked theresults and for 118 galaxies had to recompute the assigned positions dueto complex morphologies (e.g. distorted isophotes, undefined nuclei,knotty galaxies) or the presence of bright stars. We found differencesbetween older and newer positions of up to 38 arcsec with a mean valueof 2 arcsper 96 relative to SIMBAD and up to 38 arcsec and 2 arcsper 42respectively relative to UZC. Based on star positions from the APMcatalog we determined that the DSS astrometry of five CIG fields has amean offset in (alpha , delta ) of (-0 arcsper 90, 0 arcsper 93) with adispersion of 0 arcsper 4. These results have been confirmed using the2MASS All-Sky Catalog of Point Sources. The intrinsic errors of ourmethod combined with the astrometric ones are of the order of 0 arcsper5.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/391
| Spatial Analysis of the Hα Emission in the Local Star-forming UCM Galaxies
We present a photometric study of the Hα emission in theUniversidad Complutense de Madrid (UCM) Survey galaxies. This workcomplements our previously published spectroscopic data. We study thelocation of the star-forming knots, their intensity and concentration,and the relationship of these properties with those of the host galaxy.We also estimate that the amount of Hα emission that arises fromthe diffuse ionized gas is about 15%-30% of the total Hα flux fora typical UCM galaxy. This percentage seems to be independent of theHubble type. Conversely, we find that an ``average'' UCM galaxy harborsa star formation event with 30% of its Hα luminosity arising froma nuclear component. The implications of these results for higherredshift studies are discussed, including the effects of galaxy size andthe depth of the observations. A correlation between the star formationrate and the Balmer decrement is observed, but such correlation breaksdown for large values of the extinction. Finally, we recalculate theHα luminosity function and star formation rate density of thelocal universe using the new imaging data. Our results point out that,on average, spectroscopic observations detected about one-third of thetotal emission-line flux of a typical UCM galaxy. The new valuesobtained for the Hα luminosity density and the star formation ratedensity of the local universe are 1039.3+/-0.2 ergss-1 Mpc-3 andρSFR=0.016+0.007-0.004Msolar yr-1 Mpc-3 (H0=50 kms-1 Mpc-1, ΩM=1.0, Λ=0).The corresponding values for the ``concordance cosmology''(H0=70 km s-1 Mpc-1,ΩM=0.3, Λ=0.7) are 1039.5+/-0.2 ergss-1 Mpc-3 andρSFR=0.029+0.008-0.005Msolar yr-1 Mpc-3.
| Stellar populations in local star-forming galaxies - II. Recent star formation properties and stellar masses
We present the integrated properties of the stellar populations in theUniversidad Complutense de Madrid (UCM) Survey galaxies. Applying thetechniques described in the first paper of this series, we derive ages,burst masses and metallicities of the newly formed stars in our samplegalaxies. The population of young stars is responsible for the Hαemission used to detect the objects in the UCM Survey. We also infertotal stellar masses and star formation rates in a consistent way takinginto account the evolutionary history of each galaxy. We find that anaverage UCM galaxy has a total stellar mass of ~1010Msolar, of which about 5 per cent was formed in aninstantaneous burst that occurred about 5 Myr ago, and subsolarmetallicity. Less than 10 per cent of the sample shows massivestarbursts involving more than half of the total mass of the galaxy.Several correlations are found among the derived properties. The burststrength is correlated with the extinction and with the integratedoptical colours for galaxies with low obscuration. The current starformation rate is correlated with the gas content. A stellarmass-metallicity relation is also found. Our analysis indicates that theUCM Survey galaxies span a broad range in properties between those ofgalaxies completely dominated by current/recent star formation and thoseof normal quiescent spirals. We also find evidence indicating that starformation in the local Universe is dominated by galaxies considerablyless massive than L*.
| Stellar populations in local star-forming galaxies - I. Data and modelling procedure
We present an analysis of the integrated properties of the stellarpopulations in the Universidad Complutense de Madrid (UCM) Survey ofHα-selected galaxies. In this paper, the first of a series, wedescribe in detail the techniques developed to model star-forminggalaxies using a mixture of stellar populations, and taking into accountthe observational uncertainties. We assume a recent burst of starformation superimposed on a more evolved population. The effects of thenebular continuum, line emission and dust attenuation are taken intoaccount. We also test different model assumptions, including the choiceof specific evolutionary synthesis model, initial mass function, starformation scenario and the treatment of dust extinction. Quantitativetests are applied to determine how well these models fit ourmultiwavelength observations for the UCM sample. Our observations spanthe optical and near-infrared, including both photometric andspectroscopic data. Our results indicate that extinction plays a keyrole in this kind of study, revealing that low- and high-obscuredobjects may require very different extinction laws and must be treateddifferently. We also demonstrate that the UCM Survey galaxies are bestdescribed by a short burst of star formation occurring within aquiescent galaxy, rather than by continuous star formation. A detaileddiscussion on the inferred parameters, such as the age, burst strength,metallicity, star formation rate, extinction and total stellar mass forindividual objects, is presented in Paper II of this series.
| Optical photometry of the UCM lists I and II. II. B band surface photometry and morphological discussion
We present Johnson B surface photometry for the UCM Survey galaxies.One-dimensional bulge-disk decomposition is attempted, discussing onfitting functions and computational procedures. The results from thisdecomposition, jointly with concentration indices and an asymmetrycoefficient, are employed to study the morphological properties of thesegalaxies. We also compare our results with the previous morphologicalclassification established using Gunn r imaging data and with othersamples of galaxies. No major statistical differences in morphology arefound between red and blue data, although some characteristics such assize and luminosity concentration vary. We find a correlation betweenluminosity and size. Several parameters are used to segregate theobjects according to their morphological type. Tables 2 and 3 are alsoavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/365/370
| Star formation properties of Universidad Complutense de Madrid survey galaxies
We present new near-infrared J and K imaging data for 67 galaxies fromthe Universidad Complutense de Madrid (UCM) survey used in thedetermination of the SFR density of the local Universe by Gallego et al.This is a sample of local star-forming galaxies with redshift lower than0.045, and they constitute a representative subsample of the galaxies inthe complete UCM survey. From the new data, complemented with our ownGunn-r images and long-slit optical spectroscopy, we have measuredintegrated K-band luminosities, r-J and J-K colours, and Hαluminosities and equivalent widths. Using a maximum likelihood estimatorand a complete set of evolutionary synthesis models, these observationsallow us to estimate the strength of the current (or most recent) burstof star formation, its age, the star formation rate and the totalstellar mass of the galaxies. An average galaxy in the sample has astellar mass of 5×1010Msolar and isundergoing (or has recently completed) a burst of star formationinvolving about 2per cent of its total stellar mass. We identify twoseparate classes of star-forming galaxies in the UCM sample:low-luminosity, high-excitation galaxies (Hiilike) and relativelyluminous spiral galaxies (starburst disc-like). The former show higherspecific star formation rates (SFRs per unit mass) and burst strengths,and lower stellar masses than the latter. With regard to their specificstar formation rates, the UCM galaxies are intermediate objects betweennormal quiescent spirals and the most extreme Hii galaxies.
| Optical photometry of the UCM Lists I and II I. The data
We present Johnson B CCD photometry for the whole sample of galaxies ofthe Universidad Complutense de Madrid (UCM) Survey Lists I and II. Theyconstitute a well-defined and complete sample of galaxies in the LocalUniverse with active star formation. The data refer to 191 S0 to Irrgalaxies at an averaged redshift of 0.027, and complement the alreadypublished Gunn r, J and K photometries. In this paper the observationaland reduction features are discussed in detail, and the new colourinformation is combined to search for clues on the properties of thegalaxies, mainly by comparing our sample with other surveys. Tables 1and 3 are also available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html}
| Observations of a complete sample of Hα emission-line galaxies. Long-slit spectroscopy of galaxies in UCM lists 1 and 2.
Spectroscopic observations for the full sample of Hα emission-linegalaxy candidates (ELGs) from the Universidad Complutense de Madridobjective-prism survey Lists 1 and 2 have been obtained in order toinvestigate fully the properties of the survey constituents as well asthe selection characteristics and completeness limits of the surveyitself. The spectroscopic data include redshifts, line fluxes,equivalent widths, emission-line ratios, optical reddening estimates andsynthesized color indexes. We find that 74% of the objects in thissample do exhibit emission lines. We compare our observational data withparameters given in the published survey lists in order to assess theusefulness of the latter. The different emission-line galaxies have beenclassified according to their spectra in several groups. Gray-scaleimages of the CCD spectra near the main emission lines, spatial profilesat the continuum and the line for [OIII] λ5007 and Hαlines, as well as plots of the coadded spectra of selected galaxies arepresented, and a number of peculiar objects are described.
| Survey for Emission-Line Galaxies: Universidad Complutense de Madrid List 2
A low-dispersion objective-prism survey for low-redshift emission-linegalaxies (ELGs) is being carried out by the Universidad Complutense deMadrid with the Schmidt telescope at the German-Spanish Observatory ofCalar Alto (Almeria, Spain). A 4^deg^ full-aperture prism, whichprovides a dispersion of 1950 A mm^-1^, and IIIa-F emulsion combinationhas been used to search for ELGs selected by the presence of Hαemission in their spectra. A compilation of descriptions and positions,along with finding charts, is presented for 103 emission-line objects.This is the second list, which contains objects located in a region ofthe sky covering 201.4 deg^2^ in seven fields near α = 15^h^ andδ = 25^deg^.
| Photometric and morphological analysis of UCM galaxies. I. Observations and reductions. Morphological classifications.
We present the results of Thuan & Gunn r CCD imaging observations ofthe Universidad Complutense de Madrid (UCM) sample of emission-linegalaxies (ELGs), selected by the presence of Hα emission inlow-resolution objective prism spectra. In this work we characterizephotometrically and morphologically a total of 212 objects from the UCMsurvey. This Paper presents the observations and basic reductions, andlists a set of photometric parameters calculated for each UCM object. Inaddition, for the first time in a ELGs sample, we have determined themorphological classification of the objects using simultaneously fivedifferent criteria.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| Survey of emission-line galaxies: Universidad Complutense de Madrid list
A low-dispersion objective-prism survey for low-redshift emission-linegalaxies (ELGs) is being carried out by the University Complutense deMadrid with the Schmidt telescope at the German-Spanish Observatory ofCalar Alto (Almeria, Spain). A 4 deg full aperture prism, which providesa dispersion of 1950 A/mm, and IIIaF emulsion combination has been usedto search for ELGs selected by the presence of H-alpha emission in theirspectra. Our survey has proved to be able to recover objects alreadyfound by similar surveys with different techniques and, what is moreimportant, to discover new objects not previously cataloged. Acompilation of descriptions and positions, along with finding chartswhen necessary, is presented for 160 extragalactic emission-lineobjects. This is the first list, which contains objects located in aregion of the sky covering 270 sq deg in 10 fields near alpha =0h and delta = 20 deg.
| A survey of the Pisces-Perseus supercluster. VI - The declination zone +15.5 deg to 21.5 deg
New results are presented of Arecibo observations in the 21 cm line of765 galaxies with declinations between 15.5 deg and 21.5 deg, in thePisces-Perseus supercluster zone. If considered independently on theneighboring parts of sky, this region, to the South of the superclusterridge, shows significantly less evidence of structure on large scales inexcess of 30 Mpc, contrasting substantially with the characteristics ofthe declination zones immediately to the North.
| IRAS observations of H-alpha selected emission-line galaxies
We present the results of IRAS observations of the UCM (UniversidadComplutense de Madrid) sample of emission-line galaxies, which have beenselected from wide-dispersion H-alpha objective-prism plates. These dataare intended to provide a convenient summary of the relevant FIRproperties of these galaxies. Color-color diagrams, as interpreted bytheoretical models, suggest that emission from UCM galaxies is mainlydue to dust heated directly by photons emitted in active star-formingregions. Statistical analysis of some samples, including the IRASminisurvey and blue-selected objective-prism samples, have beenperformed. Comparisons, based on FIR luminosity distributions, with theIRAS minisurvey make evident the lower metallicity of the CUM galaxieswhich cannot be considered as a parent population of IRAS-detectedgalaxies.
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