THE ARAUCARIA PROJECT: NEAR-INFRARED PHOTOMETRY OF CEPHEID VARIABLES IN THE SCULPTOR GALAXY NGC 300

摘要

We have obtained deep near-infrared images in J and K filters of three fields in the Sculptor galaxy NGC 300 with the ESO VLT and ISAAC Camera. For 16 Cepheid variables in these fields, we have determined J and K magnitudes at two different epochs and have derived their mean magnitudes in these bands. The slopes of the resulting period-luminosity relations are in very good agreement with the slopes of these relations measured in the Large Magellanic Cloud (LMC) by Persson et al. Fitting the LMC slopes to our data, we have derived distance moduli in J and K. Using these values together with the values derived in the optical V and I bands in our previous work, we have determined an improved total reddening for NGC 300 of E(B — V) = 0.096 ± 0.006 mag, which yields extremely consistent values for the absorption-corrected distance modulus of the galaxy from VIJK bands. Our distance result for NGC 300 from this combined opticalear-infrared Cepheid study is (m — M)_0 = 26.37 ± 0.05 (random) ± 0.03 (systematic) mag and is tied to an adopted true LMC distance modulus of 18.50 mag. Both random and systematic uncertainties are dominated by photometric errors, while errors due to reddening, metallicity effects, and crowding are less important. Our distance determination is consistent with the earlier result from near-infrared (H-band) photometry of two Cepheids in NGC 300 by Madore et al., but far more accurate. Our distance value also agrees with the HST Key Project result of Freedman et al. and with the recent distance estimate for NGC 300 from Butler et al. from the tip of the red giant branch (TRGB) I-band magnitude when our improved reddening is used to calculate the absorption corrections. Our distance results from the different optical and near-infrared bands indicate that the reddening law in NGC 300 must be very similar to the Galactic one. With the results of this work, the distance of NGC 300 relative to the LMC now seems determined with an accuracy of approximately ±3%. The distance to this nearby Sculptor galaxy is therefore now known with higher accuracy than that of most (nearer) Local Group galaxies.