- ID:
- ivo://CDS.VizieR/J/A+A/548/A129
- Title:
- HST photometry in NGC 6822
- Short Name:
- J/A+A/548/A129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On the basis of a new photometric analysis of the Local Group dwarf irregular galaxy NCG 6822 based on observations obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope, we have obtained a new estimate of the extinction of two fields located in the southeast region of the galaxy. Because of significant differences in the distance estimates to NGC 6822 available in literature, we decided to provide an independent determination of the distance to this galaxy based on an updated and self-consistent theoretical calibration of the tip of the red giant branch brightness. As a result we newly determined the distance to NGC 6822 to be equal to (m-M)_0_=23.54+/-0.05, and compared our measurement with the most recent determinations of this distance.
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- ID:
- ivo://CDS.VizieR/J/A+A/572/A26
- Title:
- HST photometry in NGC 6822
- Short Name:
- J/A+A/572/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed photometric study of the dwarf irregular galaxy NGC 6822 aimed at investigating the properties of its stellar populations, and in particular, the presence of stellar radial gradients. Our goal is to analyze the stellar populations in six fields, which cover the whole bar of this dwarf galaxy. We derived the quantitative star formation history (SFH) of the six fields using the IAC method, involving IAC-pop/MinnIAC codes. The solutions we derived show an enhanced star formation rate (SFR) in fields 1 and 3 during the last 500Myr. The SFRs of the other fields almost extinguish at very recent epochs. We study the radial gradients of the SFR. We consider the total mass converted into stars in two time intervals (between 0 and 0.5Gyr ago and between 0.5 and 13.5Gyr ago). We find that the scale lengths of the young and intermediate-old populations are perfectly compatible, with the exception of the young populations in fields 1 and 3. The recent SF in these two fields is larger than in the other ones. This might be an indication that in these two fields we are sampling incipient spiral arms. Further evidence and new observations are required to prove this hypothesis. In addition, we derived the age-metallicity relations. As expected, for all of the fields the metallicity increases with time. We do not observe any radial gradient in the metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A155
- Title:
- HST photometry in six M31 globular clusters
- Short Name:
- J/A+A/531/A155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep (V~28.0) BV photometry obtained with the wide field channel of the Advanced Camera for Surveys on board HST for four M31 globular clusters that were identified as candidate intermediate-age (age~1-9Gyr) by various authors, based on their integrated spectra and/or broad/intermediate-band colors. Two of them (B292 and B350) display an obvious blue horizontal branch, indicating that they are as old as the oldest Galactic globulars. On the other hand, for the other two (B058 and B337), which display red horizontal branches, it was not possible either to confirm or disconfirm the age estimate from integrated spectra. The analysis of the distribution in the spectral indices Mg2 and H{beta} of the M31 and Milky Way clusters whose horizontal branch can be classified as red or blue based on existing CMDs, strongly suggests that classical age diagnostics from integrated spectra may be significantly influenced by the HB morphology of the clusters and can lead to erroneous age-classifications. We also provide the CMD for another two clusters that fall into the field of the main targets, B336, an old and metal-poor globular with a significant population of RR-Lyrae variables, and the newly discovered B531, a cluster with a very red red giant branch.
- ID:
- ivo://CDS.VizieR/J/A+A/426/399
- Title:
- HST photometry of brightest stars of NGC 588
- Short Name:
- J/A+A/426/399
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a double analysis of the ionizing cluster in NGC 588, a giant HII region (GHR) in the outskirts of the nearby galaxy M33. For this purpose, we obtained ground based long-slit spectroscopy and combined it with archival ground based and space borne imaging and spectroscopy, in the wavelength range 1100-9800{AA}. A first modeling of the cluster was performed using integrated properties, such as the spectral energy distribution (SED), broad band colors, nebular emission H{beta} equivalent width, the main ultraviolet resonance lines, and the presence of Wolf-Rayet star features. By applying standard assumptions about the initial mass function (IMF), we were unable to fit satisfactorily these observational data. This contradictory result led us to carry out a second modeling, based on a resolved photometric analysis of individual stars in Hubble Space Telescope (HST) images, by means of finding the best fit isochrone in color-magnitude diagrams (CMD), and assigning a theoretical SED to each individual star. The overall SED of the cluster, obtained by integrating the individual stellar SEDs, is found to fit better the observed SED than the best solution found through the integrated first analysis, but at a significantly later stage of evolution of the cluster of 4.2Myr, as obtained from the best fit to the CMD. A comparative analysis of both methods traces the different results to the effects of statistical fluctuations in the upper end of the IMF, which are significant in NGC 588, with a computed cluster mass of 5600M_{sun}_, as predicted by Cervino et al. (2002A&A...381...51C). We discuss the results in terms of the strong influence of the few most massive stars, six in the case of NGC 588, that dominate the overall SED and, in particular, the ionizing far ultraviolet range beyond the Lyman limit.
- ID:
- ivo://CDS.VizieR/J/ApJ/777/79
- Title:
- HST photometry of Cepheid candidates in M101
- Short Name:
- J/ApJ/777/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The impact of metallicity on the Cepheid period-luminosity (P-L) relation is investigated using Hubble Space Telescope Advanced Camera for Surveys V and I images of M101. Variations in the reddening-free Wesenheit parameter (W), which is employed as a proxy for luminosity, are examined as a function of the radial distance from the center of M101 (and thus metallicity). We determine that there is no dependence of the slope on metallicity. However, the intercept is found to depend on metallicity by {gamma}_VI_=-0.33+/-0.12mag.dex^-1^ and {gamma}_VI_=-0.71+/-0.17mag.dex^-1^ using 2{sigma} and 3{sigma} rejection criteria, respectively. Sigma-clipping impacts the derived metallicity dependence, and the 2{sigma} criterion applied likely mitigates blending, particularly in the crowded inner regions of M101. A metallicity-corrected distance for M101 is obtained from 619 Cepheids ({mu}=28.96+/-0.11), a result that agrees with the recently determined SN Ia distance. The metallicity effects described can be bypassed by working at near and mid-infrared wavelengths (e.g., the Carnegie Hubble Program).
- ID:
- ivo://CDS.VizieR/J/AJ/147/4
- Title:
- HST photometry of 5 globular clusters
- Short Name:
- J/AJ/147/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We quantified and calibrated the metallicity and temperature sensitivities of colors derived from nine Wide-Field Camera 3 filters on board the Hubble Space Telescope using Dartmouth isochrones and Kurucz atmosphere models. The theoretical isochrone colors were tested and calibrated against observations of five well studied galactic clusters, M92, NGC 6752, NGC 104, NGC 5927, and NGC 6791, all of which have spectroscopically determined metallicities spanning -2.30<[Fe/H]<+0.4. We found empirical corrections to the Dartmouth isochrone grid for each of the following color-magnitude diagrams (CMDs): (F555W-F814W, F814W), (F336W-F555W, F814W), (F390M-F555W, F814W), and (F390W-F555W, F814W). Using empirical corrections, we tested the accuracy and spread of the photometric metallicities assigned from CMDs and color-color diagrams (which are necessary to break the age-metallicity degeneracy). Testing three color-color diagrams [(F336W-F555W),(F390M-F555W),(F390W-F555W), versus (F555W-F814W)], we found the colors (F390M-F555W) and (F390W-F555W) to be the best suited to measure photometric metallicities. The color (F390W-F555W) requires much less integration time, but generally produces wider metallicity distributions and, at very low metallicity, the metallicity distribution function (MDF) from (F390W-F555W) is ~60% wider than that from (F390M-F555W). Using the calibrated isochrones, we recovered the overall cluster metallicity to within ~0.1dex in [Fe/H] when using CMDs (i.e., when the distance, reddening, and ages are approximately known). The measured MDF from color-color diagrams shows that this method measures metallicities of stellar clusters of unknown age and metallicity with an accuracy of ~0.2-0.5dex using F336W-F555W, ~0.15-0.25dex using F390M-F555W, and ~0.2-0.4dex with F390W-F555W, with the larger uncertainty pertaining to the lowest metallicity range.
- ID:
- ivo://CDS.VizieR/J/AJ/142/183
- Title:
- HST photometry of globulars in M81 (NGC 3031)
- Short Name:
- J/AJ/142/183
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform aperture photometry and profile fitting on 419 globular cluster (GC) candidates with m_V_<=23mag identified in Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) BVI imaging, and estimate the effective radii of the clusters. We identify 85 previously known spectroscopically confirmed clusters, and newly identify 136 objects as good cluster candidates within the 3{sigma} color and size ranges defined by the spectroscopically confirmed clusters, yielding a total of 221 probable GCs. The luminosity function peak for the 221 probable GCs with estimated total dereddening applied is V~(20.26+/-0.13)mag, corresponding to a distance of ~3.7+/-0.3Mpc. The blue and red GC candidates, and the metal-rich and metal-poor spectroscopically confirmed clusters, respectively, are similar in half-light radius. Red confirmed clusters are about 6% larger in median half-light radius than blue confirmed clusters, and red and blue good GC candidates are nearly identical in half-light radius. The total population of confirmed and "good" candidates shows an increase in half-light radius as a function of galactocentric distance.
- ID:
- ivo://CDS.VizieR/J/AJ/143/16
- Title:
- HST photometry of IC 883 star clusters
- Short Name:
- J/AJ/143/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New optical Hubble Space Telescope (HST), Spitzer Space Telescope, Galaxy Evolution Explorer, and Chandra observations of the single-nucleus, Luminous InfraRed Galaxy (LIRG) merger IC 883 are presented. The galaxy is a member of the Great Observatories All-sky LIRG Survey (GOALS) and is of particular interest for a detailed examination of a luminous late-stage merger due to the richness of the optically visible star clusters and the extended nature of the nuclear X-ray, mid-IR, CO, and radio emission. In the HST Advanced Camera for Surveys images, the galaxy is shown to contain 156 optically visible star clusters distributed throughout the nuclear regions and tidal tails of the merger, with a majority of visible clusters residing in an arc ~3-7kpc from the position of the mid-infrared core of the galaxy. The luminosity functions of the clusters have an {alpha}_F435W_~-2.17 +/-0.22 and {alpha}_F814W_~-2.01+/-0.21, compared with V-band-derived values measured for the well-studied LIRG NGC 34 and the Antennae Galaxy of {alpha}~-1.7+/-0.1 and -2.13+/-0.07, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/648/1026
- Title:
- HST photometry of M5 blue stragglers
- Short Name:
- J/ApJ/648/1026
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have surveyed the blue straggler star population of the Galactic globular cluster M5 using high-resolution images of the core along with wide-field ground-based images reaching to more than 19 core radii. To gauge M5's relative efficiency of producing stragglers, we compared our sample to five studies of other globular clusters. Using a bright sample selected in the same way as that of Ferraro and coworkers (Ferraro et al., 1993AJ....106.2324F, 1997, Cat. <J/A+A/320/757>, Cat. <J/A+A/324/915>) we found a bimodal radial distribution similar to those found in three other luminous clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/42
- Title:
- HST photometry of M87 globular clusters
- Short Name:
- J/ApJ/703/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the M87 GC system using deep, archival HST/ACS imaging with the F606W and F814W filters, in which we find a significant color-magnitude relation for the metal-poor globular clusters (GCs). The slope of this relation in the I versus V-I color-magnitude diagram ({gamma}_I_=-0.024+/-0.006) is perfectly consistent with expectations based on previously published results using data from the ACS Virgo Cluster Survey. We show that previously measured half-light radii of M87 GCs from best-fit PSF-convolved King models are consistent with the more accurate measurements in this study, and we also explain how the color-magnitude relation for metal-poor GCs is real and cannot be an artifact of the photometry. We fit Gaussian and evolved Schechter functions to the luminosity distribution of GCs across all colors, as well as divided into blue and red subpopulations, finding that the blue GCs have a brighter mean luminosity and a narrower distribution than the red GCs. Finally, we present a catalog of astrometry and photometry for 2250 M87 GCs.
