Galactic Extinction Research Articles

The galactic extinction towards Maffei 1

The extinction of Maffei 1 has been measured by two new techniques. First, BV aperture photometry has been performed to obtain the colour excess from standard aperture–colour relations for early-type galaxies. Secondly, millimetre and radio observations of galactic CO and H I have been used to calculate the total hydrogen column density along the line-of-sight, and thereby estimate the colour excess from the local dust-to-gas ratio. After consideration of all extinction measurements to date, it is concluded that Av= 5.1 ± 0.2 mag. The isophotal diameter and the corrected apparent visual magnitude are estimated to be ∼ 15 arcmin and ∼ 6.3 respectively (assuming type E), making Maffei 1 one of the biggest and brightest galaxies in the sky. The distance is found to be |$2.1^{+1.3}_{-0.8}$| Mpc, indicating that Maffei 1 is probably associated with the Ursa Major–Camelopardalis cloud, not the Local Group. The primary source of error in the distance is now the uncertainty in the central velocity dispersion.

The galactic extinction of extragalactic objects. I - The csc B law and the extinction coefficient

view Abstract Citations (75) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The galactic extinction of extragalactic objects. I - The csc B law and the extinction coefficient. de Vaucouleurs, G. ; Buta, R. Abstract Data on galaxies are used to determine the effects of galactic extinction on extragalactic objects. Counts of faint galaxies and of galactic clusters are used to establish the presence of extinction in the polar caps and the statistical validity of the csc b law right up to the poles. The mean surface brightness of bright galaxies and the hydrogen index, measuring the neutral hydrogen to luminosity ratio, are used to evaluate the total B-band extinction coefficient. The color excesses of bright galaxies in B-V and U-B are applied to evaluate the reddening coefficient which provides a third, independent estimate of the polar extinction. It is shown that all these indicators are in much better agreement with the extinction model proposed by de Vaucouleurs, de Vaucouleurs, and Corwin (1976) than with the one proposed by McClure and Crawford (1971). Publication: The Astronomical Journal Pub Date: July 1983 DOI: 10.1086/113380 Bibcode: 1983AJ.....88..939D Keywords: Astrometry; Galactic Clusters; Galaxies; Interstellar Extinction; Milky Way Galaxy; Brightness; Coefficients; Color; Distance; Luminosity; Astrophysics full text sources ADS | data products SIMBAD (1)

LMC and galactic extinction

LMC and galactic extinction

Systematics of Bulge-to-Disk Ratios

The main results of a new analysis of the spheroidal (I) and disk (II) components of 98 lenticular and spiral galaxies are : (i)on the average, the magnitude difference between spheroid and total luminosity, ΔmI = BT(I) - BT, varies smoothly along the Hubble sequence from early lenticulars to late-type spirals (Fig. 1);(ii)the trend of ΔmI confirms the concept of the lenticular class as intermediate between E and S classes, not as a parallel sequence;(iii)the large scatter at any given type, σ(ΔmI) ≃ 0.7 mag, is still dominated by measuring and decomposition errors.(iv)The effective surface brightness of the spheroid, μce(I), corrected for galactic extinction AB, decreases by ~2 mag from early to late types, but with a large range (~ 3 mag) at T = const. (Fig. 2a).(v)The effective surface brightness of the disks, corrected for galactic extinction and inclination, μce(II) = μe(II)- AB + 3 log R2s, is almost independent of type, with <μce(II)> ≃ 23.5 for spirals. This implies a corrected central surface brightness μc(0) = μce −1.82 ≃ 21.7, in good agreement with the Freeman rule, but with a large scatter. However, the disks of lenticulars (T< 0) tend to be ~ 0.5 mag fainter than the disks of spirals (Fig. 2b).(vi)The linear effective radii of the spheroidal components are largest, <re (I)> ≳ 1 kpc, among the early type spirals, in agreement with the Hubble classification criterion. The spheroid of lenticulars and late-type spirals tend to be smaller, <re(I)> ≃ 0.5 kpc, but with a large scatter (Fig. 3a). There is no indication of systematic difference between ordinary (SA) and barred (SB) spirals.(vii)The linear effective radii of the disk components are largest <re (I)> ≳ 5 kpc, among intermediate type spirals. The disks of lenticular and late type spirals tend to be smaller (Fig. 3b).(viii)The mean absolute magnitudes of the disk and spheroidal components depend on type (Fig. 4). On the average the disks are brighter (MII ≃ −19.5) among types Sb-Sbc, spheroids (MI ⋍ −19) among types L+ to Sa, but, again, with a large scatter. Disks and spheroids are about equally bright (MI ⋍ MII ⋍ − 19) at stage SO/a (T = 0).

Integrated magnitudes and mean colors of the DDO dwarf galaxies in the UBV system. I - Observations and catalog

view Abstract Citations (80) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Integrated magnitudes and mean colors of the DDO dwarf galaxies in the UBV system. I - Observations and catalog de Vaucouleurs, G. ; de Vaucouleurs, A. ; Buta, R. Abstract The integrated magnitudes and colors of 163 DDO "dwarf" galaxies in the UBV system are derived from 542 photoelectric observations with four telescopes between 1976 and 1980. Total (asymptotic) magnitude BT, mean color indices , , effective aperture diameter Ae, and mean effective surface brightness m'e are derived for 150 objects, all but two late-type (T≥6) systems. The total magnitudes are in the range 11.1 ≤ BT ≤ 15.8. The mean surface brightness m'e is in the range 22.3 ≤ m'e ≤ 25.9 mag arcsec-2; it is in all cases fainter than the night sky (22.2) and, in the mean, fainter than in the (non-DDO) late-type galaxies in the Second Reference Catalogue of Bright Galaxies (RC2), for which 20 < m'e < 24. The accidental errors in the photometry, discussed in Appendix B, are correspondingly larger. The luminosity distributions follow closely the standard magnitude-aperture curves for the appropriate types and are characteristic of exponential disks with vanishingly small spheroidal components. The color-aperture relations indicate a slight bluing with increasing aperture, contrary to earlier findings for the brighter (non-DDO) late-type systems in RC2. There is no clear indication of a dependence of color on axis ratio (i.e., inclination) or surface brightness. Mean colors corrected to the standard effective aperture and for galactic extinction are calculated. The magnitude estimates of Fisher and Tully are reduced to the BT system. Their systematic errors depend on mean surface brightness, diameter, and axis ratio. The corrected magnitudes so derived for 244 objects have mean errors of ∼0.5 mag and may be used as first approximations for the 79 objects not yet measured by us. The physical properties of the DDO sample will be discussed in Paper II. Publication: The Astronomical Journal Pub Date: October 1981 DOI: 10.1086/113028 Bibcode: 1981AJ.....86.1429D Keywords: Astronomical Catalogs; Galactic Radiation; Galaxies; Photoelectric Emission; Ubv Spectra; Brightness; Error Analysis; Luminosity; Magnitude; Spectrum Analysis; Surface Properties; Tables (Data); Astronomy full text sources ADS | data products NED (230)

Nebulosities around QSOs

In this paper independent evidence in favour of the hypothesis proposed by Thakur and Sapre (1979) that a QSO consists of a bright central object embedded in an extended nebulosity has been presented. αU−B and αB−V, the spectral indices in (U-B) and (B-V) colours, have been calculated for a sample of 80 QSOs with redshiftz≧0.76. In Figure 1 Δα = (αB−V − αU−V) has been plotted against 〈α〉 = (αB−V + αU−B)/2. In this figure the QSOs in which detectability of neubulosities has been predicted by Thakur and Sapre (1979) occupy a separate but adjacent part of the diagram as compared to those for which such a prediction has not been made. In Figure 2 (U-B)0 has been plotted against (B-V)0 for the same sample of 80 QSOs, where (U-B)0 and (B-V)0 are the (U-B) and (B-V) colours corrected for galactic extinction. In this plot also, a similar separation of the two classes of objects is discernible. Another empirical criterion—namely, (B-V)0≧0.32 for the detectability of nebulosities around QSOs—has been suggested.

ON THE DISTANCE MODULUS OF THE LARGE MAGELLANIC CLOUD

ABSTRACT The corrected modulus <μ0> = 18.31 ± 0.15 (external m.e.) previously derived from five independent primary distance indicators is confirmed by nine different secondary and tertiary indicators which give <μ0> = 18.20 ± 0.10 (internal mean error) on the same system of zero points and extinction corrections. Several recent, independent determinations from M supergiants, cepheids, and RR Lyrae variables are in poor agreement but jointly give <μ0> = 18.29 ± 0.24 (external m.e.). The total galactic and internal extinction in the LMC field derived by six independent methods is E(B - V) = 0.13 ± 0.012 and AV = 0.41 ± 0.04 (m.e.) of which ̃0m.3 is galactic and is internal. irrespective of extinction corrections the best current estimate of the apparent V-band modulus is μV = 18.6 ± 0.1.An apparent correlation between extinction corrections and absolute magnitudes of M supergiants in the LMC, recently presented by Humphreys, is discussed in Appendix A. The low extinction value derived from cepheids by Martin, White, and Feast is discussed in Appendix B. The zero point of the cepheid P-L-C relation is discussed in Appendix C.

ON THE INCLINATION OF THE LARGE MAGELLANIC CLOUD

ABSTRACT The inclination of the Large Magellanic Cloud recently derived from residuals of the Cepheid period-luminosity relation is shown to be in good agreement with the previous determinations by this and other methods. The weighted mean value of four different methods, i = 27.2 plus or minus 2.4 deg, confirms the previously adopted value. The near side of the Cloud is the east side and there is no evidence for a large-scale gradient of galactic extinction across the central 10 deg field.

A photometric and kinematic study of the barred spiral galaxy NGC 253. I - Detailed surface photometry

view Abstract Citations (83) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A photometric and kinematic study of the barred spiral galaxy NGC 253. I - Detailed surface photometry. Pence, W. D. Abstract Detailed isophotometry of NGC 253 in the Sculptor Group in blue light to a limiting surface brightness of 29 mag arcsec-2 has been obtained from a combination of photographic and photoelectric photometry. The standard photometric parameters have been derived; in particular, the total magnitude is BT = 8.05, and the maximum detected dimensions are 60' × 26', or 44 x 19 kpc at the assumed distance of 2.5 Mpc. The absolute luminosity of NGC 253, corrected for galactic and internal extinction is LT = 2.65 × 1010 Lsun. A three component luminosity model of NGC 253 is derived consisting of a r1/4 spheroid, an exponential disk, and the spiral arms, which contribute, respectively, 15, 59, and 26% of the total B luminosity. Publication: The Astrophysical Journal Pub Date: July 1980 DOI: 10.1086/158088 Bibcode: 1980ApJ...239...54P Keywords: Astronomical Photometry; Barred Galaxies; Galactic Structure; Kinematics; Surface Properties; Astronomical Maps; Astronomical Models; Astronomical Photography; Distance; Electrophotometry; Isophotes; Luminosity; Photographic Plates; Spectrophotometry; Astrophysics full text sources ADS | data products NED (2) SIMBAD (1)

Interstellar extinction in the Large Magellanic Cloud

Recent UV observations together with complementary visible data of several reddened and comparison stars of similar spectral types in the Large Magellanic Cloud have been used to study the interstellar extinction in that galaxy. Most of the reddened stars studied here are located within 2° of 30 Doradus and show remarkably high extinction in the far UV, suggesting a large abundance of small particles. From the optical wavelength to 2,600 A the normalised extinction curves of the LMC stars are similar to the mean galactic extinction law.

The brightest superassociations in spiral and irregular galaxies as extragalactic distance indicators

view Abstract Citations (59) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The brightest superassociations in spiral and irregular galaxies as extragalactic distance indicators Wray, J. D. ; de Vaucouleurs, G. Abstract The brightest blue knots (superassociations) detected by composite U,B,V color photography in spiral and irregular galaxies have absolute magnitudes B1 ranging from -10 to -15, which are from 3 to 5 magnitudes brighter than the brightest single stars. The absolute magnitude of the brightest blue knot M10 (corrected for galactic extinction) depends on the corrected color index (B-V)T0 and luminosity index Λc of the galaxy, being brighter in the bluer and most luminous galaxies. In a first approximation a two-parameter solution gives M10 = M1C + 2(Λc -1)+2.5 [(B-V)T0-0.5] where 1C> = -13.4 ± 0.2 from a sample of 78 galaxies having known distance moduli 18.3 < μ0 < 32.0. In a second approximation allowing for internal extinction a three parameter solution gives M10 = M1* +2(Λc -0.8)+2.8 [(B-V)T0 -0.5] +0.7 (log R25 -0.2) where R25 is the isophotal axis ratio of the galaxy and 1*> > = -13.0 ± 0.2. Distances derived from B1 and M1C or M1* are in good systematic agreement with distances derived from primary, secondary and tertiary indicators, but with a rather large dispersion (σ ≅ 0.55 mag) due in part to errors in the preliminary photometry (σ ≅ 0.4 mag). With some refinements and better photometry this new distance indicator appears capable of providing distance moduli with mean errors ≲0.5 mag out to distances in excess of 100 megaparsecs. Publication: The Astronomical Journal Pub Date: January 1980 DOI: 10.1086/112625 Bibcode: 1980AJ.....85....1W Keywords: Astrometry; Galactic Structure; Luminous Intensity; Spiral Galaxies; Stellar Luminosity; Hydrogen Clouds; Magnitude; Star Clusters; Stellar Spectrophotometry; Astrophysics full text sources ADS | data products NED (81)

The extragalactic distance scale. V - Tertiary distance indicators

view Abstract Citations (109) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The extragalactic distance scale. V. Tertiary distance indicators. de Vaucouleurs, G. Abstract A sample of 28 nearby galaxies whose distances were previously derived from five primary and four secondary distance indicators is used to calibrate the two main tertiary indicators: the isophotal diameters and the total magnitudes of the galaxies themselves, both fully corrected for galactic and internal extinction as well as redshift. The luminosity class of the DDO system and the morphological type of the revised Hubble system are combined into a composite luminosity index that is more closely correlated with absolute magnitude (or diameter) than either morphological type or luminosity class alone. This luminosity index is corrected for inclination effects and given for the calibrating galaxies, along with corrected isophotal diameters. The total magnitudes are reduced to face-on and corrected for galactic extinction and redshift. The zero points and their mean errors are determined, and the corresponding distance moduli are obtained. An error analysis shows that total magnitudes are better distance indicators than isophotal diameters. Publication: The Astrophysical Journal Pub Date: January 1979 DOI: 10.1086/156742 Bibcode: 1979ApJ...227..380D Keywords: Astrometry; Galactic Clusters; Interstellar Extinction; Luminous Intensity; Astronomical Photometry; Calibrating; Error Analysis; Red Shift; Astrophysics; Diameters:Galaxies; Distance Scale:Universe; Distances:Galaxies; Galaxies:Luminosities full text sources ADS | Related Materials (9) Part 1: 1978ApJ...223..351D Part 2: 1978ApJ...223..730D Part 3: 1978ApJ...224...14D Part 4: 1978ApJ...224..710D Part 6: 1979ApJ...227..729D Part 7: 1979ApJ...233..433D Part 8: 1982Obs...102..178D Part 9: 1983MNRAS.202..367D Part 10: 1993ApJ...415...10D

Galactic dust and extinction

The ratio R between visual extinction and colour excess, is slightly larger than 3 and does not vary much throughout our part of the Galaxy. The distribution of dust in the galactic plane shows, on the large scale, a gradient with higher colour excesses towards 1=50° than towards 1=230°. On the smaller scale, much of the dust responsible for extinction is situated in clouds which tend to group together. The correlation between positions of interstellar dust clouds and positions of spiral tracers seems rather poor in our Galaxy. However, concentrated dark clouds as well as extended regions of dust show an inclined distribution similar to the Gould belt of bright stars.

Integrated masses of galaxies

view Abstract Citations (136) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Integrated masses of galaxies. Dickel, J. R. ; Rood, H. J. Abstract Twenty-one centimeter hydrogen line velocities, half-widths, and fluxes are presented for 112 spiral and irregular galaxies, the majority in groups. Comparison of the velocities with values listed in the de Vaucouleurs (1976) Second Reference Catalog (RC2) suggests that the mean errors of RC2 velocities may be underestimated typically by a factor of 1.5. Integrated Brandt (1960) masses are derived from the half-widths, taking into account the increased knowledge of the properties of galactic rotation curves obtained by Huchtmeier (1975). Masses derived by the present technique are, on the average, within a factor of 1.4 of those determined by detailed analysis of individual rotation curves. Holmberg luminosities corrected for internal and Galactic extinction are determined. The sample of galaxies has an average integrated mass-to-light ratio of 11 + or - 1 solar units (when H = 50 km/s per Mpc), and the average integrated mass-to-light ratio is independent of morphological type. The mass-to-light ratio of the region within a Holmberg radius, however, tends to decrease toward later Hubble types. Publication: The Astrophysical Journal Pub Date: July 1978 DOI: 10.1086/156274 Bibcode: 1978ApJ...223..391D Keywords: Galactic Clusters; Galactic Structure; Radio Sources (Astronomy); Astronomical Catalogs; Brightness Temperature; Centimeter Waves; Hydrogen; Spectral Line Width; Spiral Galaxies; Astrophysics; Galaxies:Line Profiles; Galaxies:Masses; Galaxies: 21 cm Radiation full text sources ADS | data products NED (113)

The luminosity function of galaxies in cluster A2670

view Abstract Citations (17) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The luminosity function of galaxies in cluster A 2670. Mottmann, J. ; Abell, G. O. Abstract Photovisual magnitudes are obtained for galaxies in the rich, compact cluster A2670, and also for galaxies in the surrounding field, on the system of extrafocal photographic photometry defined by Abell and Mihalas. The luminosity function, corrected for the field, is in good agreement with that found by Oemler with a different technique and in a different spectral bandpass, and matches that found by Abell for galaxies in the Coma cluster. Comparison of the luminosity functions of Coma and of A2670 suggests relative distances for those clusters that are in the same ratio as their redshifts, within the uncertainties of the corrections for galactic extinction. The total luminosity of cluster A2670 is estimated to be 7 x 1012 L0. Subject headings: galaxies: clusters of - luminosity function Publication: The Astrophysical Journal Pub Date: November 1977 DOI: 10.1086/155656 Bibcode: 1977ApJ...218...53M Keywords: Astronomical Photometry; Galactic Clusters; Galactic Radiation; Luminous Intensity; Distribution Functions; Optical Correction Procedure; Red Shift; Tables (Data); Astrophysics full text sources ADS | data products SIMBAD (1)

Distances of nearby Groups and Clusters, and the Local Value of the Hubble Ratio

AbstractThe correct approach to build up the extragalactic distance scale is to use all available primary (novae, cepheids, RR Lyrae) and secondary indicators (brightest stars, globular clusters, largest HII rings) to calibrate without arbitrary extrapolation all reliable tertiary indicators (magnitudes and diameters of galaxies), precisely corrected for all known effects of type, luminosity class, orientation, internal and galactic extinction and redshift. Such data are now available for over 1000 galaxies in the Second Reference Catalogue.Revised distances to members of the Local Group from primary indicators and new estimates of distances to the nearest groups from primary and secondary indicators are used to calibrate the tertiary indicators via a new, composite luminosity index.The distances derived from globular clusters for 3 galaxy clusters dominated by ellipticals (Vir I, For I, Hya I) with mean corrected velocities 1000 ≤ Vo ≤ 3650 km s-1 give a mean Hubble ratio &lt;H&gt; = 88 (1 ± 0.15) km s-1 Mpc-1. This value rests entirely on the calibration of the globular clusters luminosity function in the Galaxy as a gaussian of dispersion σ = 1.1 mag. and mean &lt;MB&gt;(⊕) = -6.55, with &lt;(B-V)o &gt; = 0.75, based on the adopted RR Lyrae zero point &lt;Mv&gt; (RR) = + 0.86 ± 0.15.The distances derived from tertiary indicators to 19 field spirals and 28 nearby groups dominated by spirals with corrected velocities Vo &lt; 1800 km s-1 give &lt;H&gt; = 82 (1 ± 0.15) km s-1 Mpc-1. This value rests on the relations between luminosity index and fully corrected absolute magnitudes or linear diameters of galaxies derived without extrapolation and calibrated in ~20 nearby galaxies by seven secondary indicators. The zero points were derived from the 3 primary indicators, including 15 galactic novae with &lt;M15&gt; = -5.5 ± 0.15, and 13 cepheids in 8 galactic clusters with &lt;MB&gt; (logPo = 0.8) = -2.92 ± 0.15 (for an adopted Hyades modulus of 3.16 ± 0.05).The low values of Ho≃50 to 55 can be explained by an accumulation of complex systematic errors arising from a multiplicity of sources. These errors, all but one acting in the same sense, have been identified and evaluated; a full report will appear elsewhere.

Motion of the Galaxy and the local group determined from the velocity anisotropy of distant SC I galaxies. I - The data

view Abstract Citations (210) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Motion of the Galaxy and the Local Group determined from the velocity anisotropy of distant Sc I galaxies. I. The data. Rubin, V. C. ; Ford, W. K., Jr. ; Thonnard, N. ; Roberts, M. S. ; Graham, J. A. Abstract For a homogeneous all-sky sample of faint Sc I-Sc II galaxies, we present velocities, magnitudes, and diameters. The 96 galaxies, 3500 <V< 6500 kml sec, are used to evaluate the coefficients describing the change in apparent magnitude with path length through the Galaxy, with path length through each galaxy, with luminosity class, and with linear diameter. The sample is also used to evaluate the coefficients describing the decrease in apparent diameter with path length through the Galaxy and through the atmosphere. Such corrections must be applied to remove all systematic effects as a function of position on the sky before a study of the Hubble flow can be properly undertaken. The results indicate a low value for the galactic extinction, A B = 0.15+0.03, and a smaller dependence of magnitude and diameter on inclination than is generally adopted, A = 0.12+0.08 and D = 0. A major conclusion from the analysis is that a well-defined relation between linear diameter and luminosity makes the linear diameter of a high-luminosity Sc galaxy a valuable luminosity discriminant. Assigning to each galaxy an absolute magnitude dependent upon its linear diameter produces a significant decrease in the scatter in the sample; the dispersion in absolute magnitude is oM o<0" 33 near that of brightest ellipticals in clusters. Hence, high-luminosity Sc galaxies are a useful tool for mapping the velocity field, r < 100 Mpc, where cluster ellipticals are few, and not well distributed on the sky. Publication: The Astronomical Journal Pub Date: September 1976 DOI: 10.1086/111942 Bibcode: 1976AJ.....81..687R Keywords: Galactic Clusters; Local Group (Astronomy); Luminous Intensity; Milky Way Galaxy; Spatial Distribution; Astronomical Models; Hubble Diagram; Interstellar Extinction; Spiral Galaxies; Astrophysics full text sources ADS | data products NED (182)

Supergalactic studies. III - The supergalactic distribution of nearby groups of galaxies. IV - Systematic orientation of galaxy clouds relative to the supergalactic plane

The probability that the observed concentration of nearby groups of galaxies within 10degree, 20degree or 30degree from the same great circle (supergalactic equator SGE) in both galactic hemispheres could arise by chance in a random (Poisson) distribution of cluster centers is less than 2x10$sup -2$ for the 17 nearer groups ($delta$ 12 and at all longitudes for m> or =12. It is clear that the ''super cluster effect'' cannotmore » be explained by the combined effects of galactic extinction, small-scale clustering and a hypothetical ''large'' Virgo cluster. (AIP)« less

Properties of Galaxies: color-magnitude diagram

view Abstract Citations (33) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Properties of Galaxies: color-magnitude diagram Chester, Craig ; Roberts, Morton S. Abstract Color-magnitude diagrams for field galaxies and for the Virgo Cluster are presented. The necessary photo- metric data, on a homogeneous system, are derived exclusively from Holmberg's catalogue. All colors and magnitudes have been corrected for galactic extinction and, when possible, for the effects due to the inclina- tion of the individual galaxies. The field diagram shows a well-defined C-M relation for intermediate and late-type spirals not only from one type to another but within each of these structural types; the sense of the required inclination correction for Irr I galaxies would locate them on the blue and faint end of the spiral C-M relation. The existence of such a correlation implies a systematic variation in both the relative and absolute spectrum-luminosity functions for these galaxy types. The C-M diagram for the Virgo Cluster is more poorly defined than that for field galaxies; this may in part be due to contamination by noncluster objects. In addition, there are a number of late-type faint galaxies in Virgo which appear too red when com- pared to the field diagram. These galaxies are of low surface brightness and if true members of the Cluster have relatively small linear diameters. Publication: The Astronomical Journal Pub Date: October 1964 DOI: 10.1086/109339 Bibcode: 1964AJ.....69..635C full text sources ADS | data products NED (180)