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Register a new userDistances to PHANGS Galaxies: New Tip of the Red Giant Branch Measurements and Adopted Distances
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PHANGS-HST is an ultraviolet-optical imaging survey of 38 spiral galaxies within ~20 Mpc. Combined with the PHANGS-ALMA, PHANGS-MUSE surveys and other multiwavelength data, the dataset will provide an unprecedented look into the connections between young stars, HII regions, and cold molecular gas in these nearby star-forming galaxies. Accurate distances are needed to transform measured observables into physical parameters (e.g., brightness to luminosity, angular to physical sizes of molecular clouds, star clusters and associations). PHANGS-HST has obtained parallel ACS imaging of the galaxy halos in the F606W and F814W bands. Where possible, we use these parallel fields to derive tip of the red giant branch (TRGB) distances to these galaxies. In this paper, we present TRGB distances for 11 galaxies from ~4 to ~15 Mpc, based on the first year of PHANGS-HST observations. Five of these represent the first published TRGB distance measurements (IC 5332, NGC 2835, NGC 4298, NGC 4321, and NGC 4328), and eight of which are the best available distances to these targets. We also provide a compilation of distances for the 118 galaxies in the full PHANGS sample, which have been adopted for the first PHANGS-ALMA public data release.
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(Abridged) We have investigated the reliability of the widely used I-band Tip of the RGB relative distances for a sample of Local Group galaxies with complex Star Formation Histories (SFR) and Age Metallicity Relationships (AMR) namely the LMC, SMC and LGS3. The use of the K-band is also discussed. By employing theoretical stellar population synthesis techniques, we find that using actual determinations of SFR and AMR of the LMC and SMC, their RGB is populated by stars much younger (by 9 Gyr) than the Galactic globular cluster counterparts, on which the I-band (and K-band) TRGB absolute magnitude is calibrated. This age difference induces a bias in both the photometric metallicity estimates based on the comparison of RGB colours with globular cluster ones, and the TRGB distances. The extent of the distance bias is strongly dependent on the specific TRGB technique applied, and on the assumed I-band BC scale adopted; the correction to apply to the SMC-LMC distance modulus ranges from 0 up to +0.10 mag. LGS3 is an example of galaxy populated mainly by old stars, so that photometric metallicity and distance estimates using globular cluster calibrations are reliable. However, the relative distance moduli between Magellanic Clouds and LGS3 are affected by the population effects discussed for the LMC and SMC. The corrections to apply to the K-band TRGB distances are larger than the I-band case. Our results clearly show that the presence of a well developed RGB in the CMD of a stellar system with a complex SFR does not guarantee that it is populated by globular cluster-like red giants, and therefore the TRGB method for distance determination has to be applied with caution.
The Carnegie-Chicago Hubble Program (CCHP) is re-calibrating the extragalactic SN Ia distance scale using exclusively Population II stars. This effort focuses on the Tip of the Red Giant Branch (TRGB) method, whose systematics are entirely independent of the Population I Cepheid-based determinations that have long served as calibrators for the SN Ia distance scale. We present deep Hubble Space Telescope imaging of the low surface-density and low line-of-sight reddening halos of two galaxies, NGC 1448 and NGC 1316, each of which have been hosts to recent SN Ia events. Provisionally anchoring the TRGB zero-point to the geometric distance to the Large Magellanic Cloud derived from detached eclipsing binaries, we measure extinction-corrected distance moduli of 31.23 +/-0.04 (stat) +/- 0.06 (sys) mag for NGC 1448 and 31.37 +/- 0.04 (stat) and +/- 0.06 (sys) mag for NGC 1316, respectively, giving metric distances of 17.7 +/- 0.3 (stat) +/- 0.5 (sys) Mpc, and 18.8 +/- 0.3 (stat) +/- 0.5 (sys) Mpc. We find agreement between our result and the available Cepheid distance for NGC 1448; for NGC 1316, where there are relatively few published distances based on direct measurements, we find that our result is consistent with the published SN Ia distances whose absolute scales are set from other locally-determined methods such as Cepheids. For NGC 1448 and NGC 1316, our distances are some of the most precise (and systematically accurate) measurements with errors at 1.7 (2.8) % and 1.6 (2.7) % levels, respectively.
The primary goal of the Carnegie Chicago Hubble Program (CCHP) is to calibrate the zero-point of the Type Ia supernova (SN Ia) Hubble Diagram through the use of Population II standard candles. So far, the CCHP has measured direct distances to 11 SNe Ia, and here we increase that number to 15 with two new TRGB distances measured to NGC 5643 and NGC 1404, for a total of 20 SN Ia calibrators. We present resolved, point-source photometry from new Hubble Space Telescope (HST) imaging of these two galaxies in the F814W and F606W bandpasses. From each galaxys stellar halo, we construct an F814W-band luminosity function in which we detect an unambiguous edge feature identified as the Tip of the Red Giant Branch (TRGB). For NGC 5643, we find $mu_0 = 30.48pm0.03(stat)pm0.07(sys) $ mag, and for NGC 1404 we find $ mu_0=31.36pm 0.04(stat)pm 0.05(sys)$ mag. From a preliminary consideration of the SNe Ia in these galaxies, we find increased confidence in the results presented in Paper VIII (Freedman et al. 2019). The high precision of our TRGB distances enables a significant measurement of the 3D displacement between the Fornax Cluster galaxies NGC 1404 and NGC 1316 (Fornax A) equal to $1.50^{+0.25}_{-0.39}$ Mpc, which we show is in agreement with independent literature constraints.
We have used WFPC2 VRI observations to calculate the distances to three nearby galaxies, NGC 4214, UGC 685, and UGC 5456 using the tip of the red giant branch method. Our values for NGC 4214 (2.94 +/- 0.18 Mpc) and UGC 685 (4.79 +/- 0.30 Mpc) are the most precise measurementes of the distances to these objects ever made. For UGC 5456 the data do not allow us to reach a decisive conclusion since there are two possible solutions, one leading towards a short distance around 3.8 Mpc and another one towards a long distance of 5.6 Mpc or more.
We have obtained accurate near-infrared photometry of the Tip of the Red Giant Branches in the Local Group galaxies Sculptor, NGC 6822, NGC 3109, IC 1613 and WLM. We have used the derived TRGB magnitudes together with the absolute magnitude calibration of the near-infrared TRGB magnitude of Valenti, Ferraro and Origlia to determine the distances of these five galaxies. The statis- tical errors in the distance moduli are typically 4%. The systematic uncertain- ties are dominated by the knowledge of the mean metallicities of the red giant branches, and are in the range of 5-8%. We observe a slight (2%) systematic difference between the distances derived from the J and K bands, respectively, which is within the 1 {sigma} errors of the distances. We compare the new distances derived in this paper with other recent distance determinations for our target galaxies and find excellent agreement. In particular, the near-infrared TRGB distances to the four dwarf irregular galaxies in the sample agree to better than 5% in each case with their Cepheid distances obtained from infrared photome- try, indicating that there is no appreciable systematic offset between these two fundamental techniques using old and young stellar populations, respectively.
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