Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982aj.....87.1106g&link_type=abstract
Astronomical Journal, vol. 87, Aug. 1982, p. 1106-1126.
Astronomy and Astrophysics
Astronomy
77
Astronomical Photometry, Galactic Bulge, Infrared Astronomy, Spiral Galaxies, Ubv Spectra, Visual Photometry, Elliptical Galaxies, Errors, Optical Correction Procedure, Seyfert Galaxies, Tables (Data)
Scientific paper
New UBVJHK multiaperture photometry is presented for 65 early-type spirals. As distinct from earlier studies, we have derived (mainly by interpolation) colors and magnitudes at a small fraction of the galaxy size (A/D1 = 0.14), so that we are sampling the bulge light in these bulge dominated galaxies. After further correcting the data for K effect and Galactic reddening, we derive the following results:
(1) For colors such as U - V, V - K, and j - K we find radial color gradients in the inner (bulge) regions of normal (class A) early-type spirals that are measurable, but smaller than those measured previously in E and SO galaxies.
(2) We find no significant dependence of colors on either inclination or absolute magnitude. Neither result is unexpected for colors that sample mainly the bulge light in spirals, and for galaxies that span only a small range in absolute magnitude.
(3) The UBVJHK colors for the inner (bulge) of normal (class A) early-type spirals are constant with type T over the range T = - 1 (late 50) to T = 3 (Sb). This result is used to argue that the integrated or large-aperture UBV colors of early-type spirals become monotonically bluer with increasing T because of star formation in the outer (disk) regions of spirals rather than because of a mean metallicity decrease with increasing T for the spirals.
(4) The UBVJHK colors for the majority of class A early-type spirals are very similar to the colors of ellipticals of similar luminosity. Thus even though there are dynamical differences between spiral bulges and ellipticals, their stellar populations are similar.
(5) In the UVK and JHK two-color diagrams, about one quarter of the class A early-type spirals have unusual colors compared to the majority of spirals or ellipticals. The unusual colors for these galaxies (many are of Sab or Sb type) are explained by the contamination of a dominant bulge by a small reddened component of gaseous emission and/or young stars, rather than by an abnormal bulge stellar population.
(6) Compared with normal (class A) galaxies without nuclear activity, emission-line (class B) and Seyfert early-type spirals generally have bluer UBV colors and redder JHK colors. The infrared colors of these galaxies may be explained in terms of a normal galaxian component plus a component of 600 K dust emission (5% to 10% of total K light), together with a small amount of nuclear reddening (0 < AV < 1).
(7) The color distributions for the inner (bulge) regions of all early-type spirals (classes A and B plus Seyferts) are normally distributed and similar to those of ellipticals at UBV wavelengths. However, in the infrared (notably V - K), the spiral colors show a skew distribution with a tail extended to the red that is populated by the class B (emission-line) galaxies.
Griersmith D.
Hyland A. R.
Jones Terry J.
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