NGC 4314. I - Visible and short-wavelength infrared surface photometry of the nucleus and bar

Abstract

We present BVI (TI CCD) and JHK (University of Texas IR Camera) surface photometry of NGC 4314, an SB (rs) ap anemic spiral with a nuclear ring containing recent star formation. The shortwave IR (SWIR) frames reveal a nuclear bar of length 2 arcsec at P.A. = 0^deg^. The nuclear ring and associated dust have been detected in all SWIR color indices. We have detected a nuclear spiral in the visible and SWIR just exterior to the ring. We find extremely low amplitude spiral-shaped deficits in the stellar distribution in the SWIR in this same region. We attribute these to dust, since CO is detectable at or near these locations. Average minor-axis profiles show this galaxy to have a nuclear bulge obeying the de Vaucouleurs r^1/4^ law for values of 2 < r < 7 arcsec. Away from the dust lanes and patches, the bar is shown to have an exponential cross section. We find that the extinction characteristics of a dusty region in the bar are similar to those of dust in our Galaxy. We have determined extinction and scattering characteristics of dust near the sites of recent star formation in the nuclear ring. Because of scattering, the I - J color index best maps dust near the nuclear ring. Unsharp masking techniques reveal structure all along the bar. The dust lanes associated with the bar terminate well before the ends of the bar and appear to turn back toward the galaxy center. We argue that some of the structure in the bar can be explained as resonance phenomena. We also interpret multiple peaks within previously published CO spectra as gas streaming along the dust lanes in the bar. Shocks at the intersection points of the gas in the bar dust lanes and the gas in the rotating inner ring are a likely explanation for the ring of star formation. We discuss several mechanisms capable of forming and maintaining the nuclear spiral found just outside the nuclear ring. No one mechanism compellingly explains this spiral.