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A Digital Archive of H I 21 Centimeter Line Spectra of Optically Targeted Galaxies
We present a homogeneous compilation of H I spectral parametersextracted from global 21 cm line spectra for some 9000 galaxies in thelocal universe (heliocentric velocity-200
| New Reference Galaxy Standards for H I Emission Observations
We have taken advantage of the improved baselines and higher sensitivityavailable with the upgraded Arecibo 305 m telescope to create a new H Ispectral line catalog of disk galaxies that can be used as a referencecatalog for anyone interested in 21 cm spectral line work. In all 108galaxies were observed, covering 24 hr of the sky at declinationsbetween 0° and 36° and velocities between 0 and 25,000 kms-1. The majority of the galaxies were observed at least twotimes on different nights to avoid problems with radio frequencyinterference, baseline fluctuations, etc. Comparing our measured valueswith all those available in the literature shows that although largeindividual variations may exist, the average difference between themeasurements is zero. In all we have considerable confidence in ourmeasurements, and the resulting catalog should be extremely useful as awell-defined reference catalog for anyone interested in 21 cm spectralline work.
| Dwarf and Normal Spiral Galaxies: are they Self-Similar?
The investigation presented here was focused on clarifying the existenceof dwarf spiral galaxies as a separate group from classical spirals.First, a list of spiral galaxies with small sizes was obtained.Information on colors, luminosities, morphologies and chemical contentwas searched for in the literature for these galaxies. Using thisinformation, it can be concluded that dwarf spirals are not likely to bethe tail of the distribution of classical galaxies. On the contrary,significant differences in some of the most important properties ofspiral galaxies, such as the metallicity gradient and the bar frecuency,were found. In any case, further and more accurate observations areneeded for a definitive answer.
| Are interactions the primary triggers of star formation in dwarf galaxies?
We investigate the assumption that the trigger of star formation indwarf galaxies is interactions with other galaxies, in the context of asearch for a `primary' trigger of a first generation of stars. This iscosmologically relevant because the galaxy formation process consistsnot only of the accumulation of gas in a gravitational potential wellbut also of the triggering of star formation in this gas mass, and alsobecause some high-z potentially primeval galaxy blocks look like nearbystar-forming dwarf galaxies. We review theoretical ideas proposed toaccount for the tidal interaction triggering mechanism and present aseries of observational tests of this assumption using published data.We also show results of a search in the vicinity of a composite sampleof 96 dwarf late-type galaxies for interaction candidates showing starformation. The small number of possible perturbing galaxies identifiedin the neighbourhood of our sample galaxies, along with similar findingsfrom other studies, supports the view that tidal interactions may not berelevant as primary triggers of star formation. We conclude thatinteractions between galaxies may explain some forms of star formationtriggering, perhaps in central regions of large galaxies, but they donot seem to be significant for dwarf galaxies and, by inference, forfirst-time galaxies forming at high redshifts. Intuitive reasoning,based on an analogy with stellar dynamics, shows that conditions forprimary star formation triggering may occur in gas masses oscillating ina dark-matter gravitational potential. We propose this mechanism as aplausible primary trigger scenario, which would be worth investigatingtheoretically.
| The Westerbork HI survey of spiral and irregular galaxies. II. R-band surface photometry of late-type dwarf galaxies
R-band surface photometry is presented for 171 late-type dwarf andirregular galaxies. For a subsample of 46 galaxies B-band photometry ispresented as well. We present surface brightness profiles as well asisophotal and photometric parameters including magnitudes, diameters andcentral surface brightnesses. Absolute photometry is accurate to 0.1 magor better for 77% of the sample. For over 85% of the galaxies the radialsurface brightness profiles are consistent with published data withinthe measured photometric uncertainty. For most of the galaxies in thesample H I data have been obtained with the Westerbork Synthesis RadioTelescope. The galaxies in our sample are part of the WHISP project(Westerbork H I Survey of Spiral and Irregular Galaxies), which aims atmapping about 500 nearby spiral and irregular galaxies in H I. Theavailability of H I data makes this data set useful for a wide range ofstudies of the structure, dark matter content and kinematics oflate-type dwarf galaxies. Based on observations made with INT operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias. The tables in Appendix A are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/863. Thefigures in Appendix B are only available in electronic formhttp://www.edpsciences.org
| H I observations of emission-line galaxies
We present single-dish Lovell telescope H i observations of a sample of67 emission-line and UV-excess galaxies, of which 52 are taken from theUniversity of Michigan (UM) catalogue. In addition, H i observations of24 gas-rich irregular galaxies are presented. We find that emission-linegalaxies are H i-rich with a median H i mass to blue luminosity ratioMHI/LB of ~ 0.45 Msun/Lsun.Within the UM galaxy sample the MHI/LB ratio tendsto increase with decreasing luminosity. Finally, it is found that themost H i-rich UM galaxies are the most metal deficient, implying thatthese objects are less evolved.
| Lopsidedness in dwarf irregular galaxies
We quantify the amplitude of the lopsidedness, the azimuthal angularasymmetry index and the concentration of star-forming regions, asrepresented by the distribution of the Hα emission, in a sample of78 late-type irregular galaxies. We bin the observed galaxies into twogroups representing blue compact galaxies (BCDs) andlow-surface-brightness dwarf galaxies (LSBs). The light distribution isanalysed with a novel algorithm, which allows detection of details inthe light distribution pattern. We find that while the asymmetry of theunderlying continuum light, representing the older stellar generations,is relatively small, the Hα emission is very asymmetric and iscorrelated in position angle with the continuum light. We show that theconcentration of continuum light is correlated with the Hαconcentration; this implies that the young star formation has the samespatial properties as the older stellar populations, but that theseproperties are more strongly expressed by the young stars. We test amodel of random star formation over the extent of a galaxy by simulatingHii regions in artificial dwarf galaxies. A galaxy is traced by assumingred star clusters distributed on an underlying exponential disc ofradius twice the scalelength. The disc is allowed to change in apparentmagnitude, scaleradius, position angle and ellipticity. We compare theasymmetry-concentration distribution predicted by the simulations withthe real observed distribution; we find that only LSBs match thedistribution predicted by the model. The reason is that, independentlyof the number of Hii regions, LSBs show no particular location of Hiiregions, whereas BCDs show current star formation activity restrictedvery much to the central parts of the galaxies. A consideration of theproperties of the continuum light leads to the conclusion that most ofLSBs can be approximated by exponential discs of radius twice theirscalelength; BCDs call, however, for much more concentrated underlyingsystems, with smaller scalelengths than assumed in the simulations. Theimplication is that random star formation over the full extent of agalaxy may be generated in LSB dwarf irregular galaxies but not in BCDgalaxies.
| On the star formation history of IZw 18
It has been suggested that a continuous low star formation rate has beenthe dominant regime in IZw 18 and in dwarf galaxies for the lifetime ofthese objects \citep{LKRMHW99}. Here, we discuss and model variousstar-forming histories for IZw 18. Particularly, we show that if themetallicity observed in IZw 18 results from starburst events only, theobserved colors constrain the fraction of the metals ejected from thegalaxy to be less than 50-70%. We demonstrate that the continuous starformation scenario reproduces the observed parameters of IZw 18. Acontinuous star formation rate (SFR) of about 10-4\Msun yr-1 during 14 Gyr reproduces precisely theobserved abundances. This SFR is comparable with the lowest SFR observedin low surface brightness galaxies \citep{VZHSB97}. Generalized to allgalaxies, the low continuous SFR scenario accounts for various facts:the presence of star formation in quiescent dwarfs and LSBG, themetallicity increase with time in the most underabundant DLA systems,and the metal content extrapolations to the outskirts of spiralgalaxies. Also the apparent absence of galaxies with a metallicity lowerthan IZw 18, the apparent absence of HI clouds without opticalcounterparts, and the homogeneity of abundances in dwarfs galaxies arenatural outcomes of the scenario. This implies that, even if starburstsare strong and important events in the life of galaxies, their moresubdued but continuous star formation regime cannot be ignored whenaccounting for their chemical evolution. This research has made use ofNASA's Astrophysics Data System Abstract Service.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| B and R CCD surface photometry of late-type galaxies
We present B and R CCD observations of 16 late-type galaxies, mainlyMagellanic irregulars and blue compact galaxies, at a limiting surfacebrightness of mu_ {B} ~ 26-27 mag arcsec(-2) . The sample is derivedfrom a H I-rich subset of an H I survey of late-type dwarfs and consistsof objects with -19.5<=MB<=-14.4, nine galaxies beingfainter than MB=-17 (H0=75 km s(-1) Mpc(-1) ).Radial luminosity distributions for all the sample objects arepresented. We find that the blue compacts become redder in (B-R) withincreasing distances from their centres confirming other studiesindicating that recent star formation in these galaxies may be centrallyconcentrated. The Im and Sm galaxies show flatter (B-R) colour profilesindicating less centrally concentrated recent star formation. Themajority of the galaxies have an identifiable exponential disk whilehalf also have a central bulge.
| Morphology of star formation regions in irregular galaxies
The location of HII regions, which indicates the locus of present starformation in galaxies, is analysed for a large collection of 110irregular galaxies (Irr) imaged in Hα and nearby continuum. Theanalysis is primarily by visual inspection, although a two-dimensionalquantitative measure is also employed. The two different analyses yieldessentially identical results. HII regions appear preferentially at theedges of the light distribution, predominantly on one side of thegalaxy, contrary to what is expected from stochastic self-propagatingstar formation scenarios. This peculiar distribution of star-formingregions cannot be explained by a scenario of star formation triggered byan interaction with extragalactic gas, or by a strong one-armed spiralpattern.
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Element Enrichment and Stellar Populations O Gas-Rich Low Surface Brightness Dwarf Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2497V&db_key=AST
| Optical Colors and the Metallicities of Gas-Rich Quiescent Dwarf Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2479V&db_key=AST
| Obtaining High Precision HI Fluxes for Galaxies
We present a method to obtain well-calibrated HI fluxes using standardcontinuum sources as absolute line flux calibrators. The method isapplied to observations of 44 gas-rich dwarf galaxies with the GreenBank 43m telescope. The absolute flux calibration of the observations isaccurate to 2%; our final error budget of 5% on the derived HI fluxes isconservative and predominately due to errors in baseline removal. Theobservations indicate that despite relatively small optical sizes ( ~2\arcmin), these systems have a large diffuse gas component. For 20galaxies previously mapped at Arecibo, the median correction between acentral Arecibo pointing and the observed flux density with the GreenBank 43m is 1.6. For 24 systems without known extended HI, the observedline fluxes reported here may be used in the future to search for thepresence of a diffuse gas component through beam-matching experiments.
| 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.
| H I envelopes around low luminosity galaxies
H I mapping observations of a sample of isolated low luminosity galaxieswere undertaken with the Arecibo 305 m telescope in order to determinethe extent of their H I distribution. The sample included both compactemission-line galaxies (BCDs) and galaxies with hydrogen mass to-blueluminosity ratios, MH/LB, greater than five. Of 78targeted galaxies, 49 were found to have extended H I envelopes. Whereasmost (25 of 41) of the BCDs are compact in both optical light and in HI, 29 of the 33 high MH/LB galaxies has someevidence of extended hydrogen. As a class, the highMH/LB galaxies are low luminosity, low opticalsurface brightness, gas-rich dwarfs. Their extreme values ofMH/LB and large H I extent make them similar to HI 1225+01 and I Zw 18, but the possibility that the highMH/LB galaxies are BCDs in a quiescent phase isstill unresolved.
| Uncertainties in 21 centimeter redshifts. I - Data
High-precision data on the 21-cm redshifts, profile widths, and shapesfor 625 galaxies are presented. Each galaxy is listed in across-identification and morphology table. High-resolution spectra arealso given for each galaxy. Internal redshift consistency is roughly 1km/s for galaxies for which the S/N is above 15. No systematic effectshave been found which might influence the observed redshift quantizationat 72.5 km/s or its submultiples.
| A Study of the Largescale Structure in the Distribution of Galaxies in a Region Centered about the Cancer Cluster - Part Two - Further Observational Results
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986AJ.....91..732B&db_key=AST
| A redshift survey of low-surface-brightness galaxies. I - The basic data
Initial results from a 21 cm redshift survey of 375 very low surfacebrightness galaxies contained in the Uppsala General Catalog of Galaxiesare presented. The selection criteria and detection statistics as afunction of the sample optical properties are fully discussed. Theredshift distribution for the sample exhibits a pronounced peak at 5000km/s, corresponding to the well-studied Perseus-Pisces supercluster. Theoverall detection rate was 65 percent, and the bulk of the detectionsare genuine low surface brightness spiral galaxies, may with linewidthsin excess of 300 km/s, as opposed to true dwarf galaxies. It is arguedthat most of the nondetections are unlikely to be gas-poor dwarfs, butinstead are galaxies with velocities beyond 10,000 km/s. Taken as awhole, the sample demonstrates that optical surface brightness is notnecessarily a reliable indicator of intrinsic luminosity or mass.
| High signal-to-noise ratio observations of H I in 243 galaxies
The 21 cm spectral-line system of the Arecibo Observatory was used tomeasure neutral hydrogen emission from 243 faint galaxies. Most lie nearthe plane of the Local Supercluster. All observations reach anunsmoothed signal-to-noise ratio of at least 7.0; the average for theset is 23. The resulting data are used to estimate H I masses, systemicvelocities, and accurate profile widths at 20 percent, 25 percent, 50percent, and 80 percent of peak intensity levels. The widths are used tocalibrate directly the bias introduced by popular data-smoothingoperation. The data include observations of 65 objects with previouslyunknown redshifts.
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