Lukas Labhardt

The Cepheid Distance to NGC 5236 (M83) with the ESO Very Large Telescope

Published in: Astrophys. J. 590 (2003) 256-270 citations recorded in [Science Citation Index] Abstract: Cepheids have been observed in NGC 5236 (M 83) using the ANTU (UT1) 8.2 meter telescope of the ESO VLT with FORS1. Observations over 34 epochs in V and I have been made between January 2000 and July 2001. Twelve Cepheid candidates have periods between 12 and 55 days. The true distance modulus is adopted to be (m-M)_0 = 28.25 +/- 0.15, which corresponds to a distance of 4.5 +/- 0.3 Mpc. The distance of NGC 5253 has been rediscussed. The mean distance of (m-M)_0 = 28.01 +/- 0.15 (based on SN 1972E) shows the galaxy to be a close neighbor of M 83 (separation = 0.5 +/- 0.4 Mpc), suggesting that the two galaxies may have interacted in the past and thus possibly explaining the amorphous morphology of NGC 5253. M 83 is the principal member of the nearby M 83 group containing also, besides NGC 5253, several dwarf members, for five of which TRGB distances are available (Karachentsev et al. 2002a, A&A, 385, 21). The adopted group distance of (m-M)_0 = 28.28 +/- 0.10 (4.5 +/- 0.2 Mpc) together with its mean recession velocity of v_LG = 249 +/- 42 km/s shows again the extreme quietness of the local (1 Mpc to 10 Mpc) expansion field. M 83 fits onto the local mean Hubble flow line of the velocity-distance relation (with H_0 ~ 60) with no significant deviation, supporting the earlier conclusion that the local velocity expansion field is remarkably cold on a scale of 10 Mpc, contrary to the predictions of the simplest cold dark matter model for large scale structure. The role of a cosmological constant has been invoked as a possible solution in providing a nearly uniform force field everywhere in the presence of a lumpy galaxy distribution. (abridged)Cepheids have been observed in NGC 5236 (M83) using the Antu (Unit Telescope 1) 8.2 m telescope of the ESO Very Large Telescope with the Focal Reducer/Low Dispersion Spectrograph 1. Repeated imaging observations have been made between 2000 January and 2001 July. Images were obtained in 34 epochs in the V band and in six epochs in the I band. The photometry was made with the ROMAFOT reduction package and checked independently with DoPHOT and a modified version of HSTPHOT. Twelve Cepheid candidates have periods ranging between 12 and 55 days. The dereddened distance modulus is adopted to be (m - M)0 = 28.25 ± 0.15, which corresponds to a distance of 4.5 ± 0.3 Mpc. The Cepheid distance of NGC 5253 has been rediscussed and strengthened by its SN 1972E. The mean distance of (m - M)0 = 28.01 ± 0.15 (based on SN 1972E) shows the galaxy to be a close neighbor of M83, suggesting that the two galaxies may have interacted in the past and thus possibly explaining the amorphous morphology of NGC 5253. The distance difference between M83 and NGC 5253 is only 0.5 ± 0.4 Mpc. The projected distance is only ~ 0.15 Mpc. M83 is the principal member of the nearby M83 group containing also, besides NGC 5253, several dwarf members, for five of which tip of the red giant branch distances are available. The adopted group distance of (m - M)0 = 28.28 ± 0.10 (4.5 ± 0.2 Mpc), together with its mean recession velocity of vLG = 249 ± 42 km s-1, shows again the extreme quietness of the local (1-10 Mpc) expansion field. M83 fits onto the local mean Hubble flow line of the velocity-distance relation (with H0~ 60) with no significant deviation, supporting the earlier conclusion that the local velocity expansion field is remarkably cold on a scale of 10 Mpc, contrary to the predictions of the simplest cold dark matter model for large-scale structure. The role of a cosmological constant has been invoked as a possible solution in providing a nearly uniform force field everywhere in the presence of a lumpy galaxy distribution.

Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. VIII. SN 1990N in NGC 4639

Repeated imaging observations have been made of NGC 3982 with the Hubble Space Telescope between 2000 March and May, over an interval of 53 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the Type Ia supernova (SN Ia) SN 1998aq. A total of 26 Cepheid candidates were identified, with periods ranging from 10 to 45 days, using photometry with the DoPHOT program. The dereddened distance to NGC 3982 is estimated from these data using various criteria to maximize signal-to-noise ratio and reliability: the values lie between 31.71 and 31.82, with uncertainties in the mean of typically ±0.14 mag for each case. A parallel analysis using photometry with HSTphot discovered 13 variables, yielding a distance modulus of 31.85 ± 0.16. The final adopted modulus is (M-m)0 = 31.72 ± 0.14 (22 ± 1.5 Mpc). Photometry of SN 1998aq that is available in the literature is used in combination with the derived distance to NGC 3982 to obtain the peak absolute magnitude of this supernova. The lower limit (no extinction within the host galaxy) for MV is -19.47 ± 0.15 mag. Corrections for decline rate and intrinsic color to carry these to the reduced system of Parodi and collaborators have been performed. The derived luminosities at hand are fully consistent with the mean of the eight normal SNe Ia previously calibrated with Cepheids. Together they yield H0 ≈ 60 ± 2(internal) km s-1 Mpc-1 based on an assumed LMC distance modulus of 18.50. We point out that correcting some of the systematic errors and including uncertainty estimates due to them leads to H0 = 58.7 ± 6.3(internal) km s-1 Mpc-1.

Discovery of Cepheids in NGC 5253: Absolute peak brightness of SN Ia 1895B and SN Ia 1972E and the value of H(sub 0)

Observations of the Hubble Space Telescope (HST) between 1993 May 31 and 1993 July 19 in 20 epochs in the F555W passband and five epochs in the F785LP passband have led to the discovery of 14 Cepheids in the Amorphous galaxy NGC 5253. The apparent V distance modulus is (m-M)(sub AV) = 28.08 +/- 0.10 determined from the 12 Cepheids with normal amplitudes. The distance modulus using the F785LP data is consistent with the V value to within the errors. Five methods used to determine the internal reddening are consistent with zero differential reddening, accurate to a level of E(B-V) less than 0.05 mag, over the region occupied by Cepheids and the two supernovae (SNe) produced by NGC 5253. The apparent magnitudes at maximum for the two SNe in NGC 5253 are adopted as B(sub max) = 8.33 +/- 0.2 mag for SN 1895B, and B(sub max) = 8.56 +/- 0.1 and V(sub max) = 8.60 +/- 0.1 for SN 1972E which is a prototype SN of Type Ia. The apparent magnitude system used by Walker (1923) for SN 1859B has been corrected to the modern B scale and zero point to determine its adopted B(sub max) value.

Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. VI. SN 1960F in NGC 4496A

Cepheid variables have been found in the SBcII galaxy NGC 4496A, parent to the Type Ia supernova 1960F. Of the 130 variables discovered with the Hubble Space Telescope (HST) over a 70 day observing internal from 1994 June to August, comprising 17 epochs in the F555W band and four epochs in the F814W band, 95 are bona fide Cepheids. The periods range from 7 days to greater than 70 days, with the mean magnitudes ranging from V = 24.4 to 26.8. The distance modulus of NGC 4496A, based on the Cepheids, is (m ? M)0 = 31.03 ? 0.14, where a formal reddening of E(V ? I) = 0.04 ? 0.06 derived from the colors of the Cepheids has been used to account for possible extinction. There is no measurable differential reddening over the field. The absolute magnitudes of SN 1960F at maximum are M(B)max = -19.43 ? 0.17 and M(V)max = ?19.52 ? 0.21. Combining these absolute magnitudes with the Hubble diagrams of Branch normal Type Ia supernovae (SNe Ia), determined earlier, gives Hubble constants, based on SN 1960F alone, of HO(B) = 56 ? 9 km s?1,? ? ?(1) and H0(V) = 55 ? 9 km s?1.? ? ?(2) Combining the calibration of SN 1960F here with six other extant calibrations set out in Paper VII gives interim mean absolute magnitude calibrations of M(B)max = ?19.45 ? 0.07 and M(V)max = ?19.47 ? 0.07, with no evidence for appreciable dependence on the light-curve decay rate. These mean interim calibrations require H0(B) = 57 ? 4 km s?1 and H0(V) = 58 ? 4 km s-1 Mpc?1.

A Forty-Year Search for the Hubble Constant

The calibration of the Hubble constant H 0 to within ~10% has been a long and painful process with many setbacks. Thanks to HST the process is coming to an end. Almost twenty Cepheid distances to nearby galaxies from HST do not themselves yield a useful value of H 0, but they provide the luminosity calibration of seven SNe Ia, put the calibration of the 21cm-line width-luminosity relation on much firmer footing, and discriminate against fallacious distance indicators. The consistent evidence of the large-scale value of the Hubble constant Ho is reviewed in the light of SNe Ia, the Virgo cluster tied into the cosmic expansion field, and field galaxies. Also the evidence from physical distance determinations is discussed. The conclusion is Ho = 55 f 8 km s−1 Mpc−1, corresponding to an expansion age of 15.2 ± 2.2 Gy (if q 0 = 0.1) and 12 ± 1.7 Gy (if q 0 = ½). Globular clusters, white dwarfs, and radioactive actinides require a time frame of ~12 Gy. This and the expansion age agree perfectly if the Universe is open; even for a critical Universe with q 0 = ½ the time agreement is as good as one can expect.

Distance Indicators and the Expansion Field of the Universe

Several distance indicators are reflected against the potential of VLT. Distances to many galaxies, reliable peculiar motions, the accuracy of Ho, and even the determination of qo will enormously benefit from higher signal-to-noise and angular resolution, using mainly — in order of increasing range — RR Lyraes, Cepheids, brightest stars, globular clusters, novae, the rotation-luminosity relation of disk galaxies, the Dn-σ relation, SNe II, SNe Ia, and gravitational lenses.

Calibration of Photometric Systems from Homogeneous Spectrophotometric Data

The atlas of stellar spectrophotometric data published by Gunn and Stryker (GS, 1983) constitutes an extremely valuable tool for the evaluation and calibration of photometric systems. The resolution of the scanner fluxes (10 or 20 A), given for a broad wavelength range (λλ 3160-10620 A) and the systematic coverage of stellar types are (almost) ideal for calculating synthetic colors for Becker’s (1946) photographic RGU system which has been extensively applied in galactic structure work (cf. Buser 1981). Since RGU photometry is tightly linked to UBV data (Steinlin 1968, Buser 1978b), the Gunn-Stryker atlas has been used in the present paper to evaluate these two systems and subsequently investigate the resulting calibration of the RGU colors in terms of MK spectral classification.