- ID:
- ivo://CDS.VizieR/J/ApJ/881/42
- Title:
- HST phot. & GMOS spectra of Lynx E & W clusters
- Short Name:
- J/ApJ/881/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Few detailed investigations of stellar populations in passive galaxies beyond z~1 are based on deep spectroscopic observations, due to the difficulty in obtaining such data. We present a study of stellar populations, structure, and mass-to-light ratios (M/L) of a large sample of bulge-dominated galaxies in the two z=1.27 clusters Lynx E and Lynx W, based on deep ground-based optical spectroscopy combined with imaging from the Hubble Space Telescope. We find that Lynx E has a well-defined core of red passive galaxies, while Lynx W lacks such a core. If all the sample galaxies evolve similarly in size from z=1.27 to the present, the data would allow only 0.1dex size growth at a fixed dynamical mass. However, to link the Lynx central galaxies to brightest cluster galaxies similar to those of low-redshift clusters, the Lynx galaxies would have to grow by at least a factor 5, possibly through major merging. The M/L ratios and the Balmer absorption lines of the Lynx galaxies are consistent with passive evolution of the stellar populations from z=1.27 to the present and support ages of 1-3Gyr. The galaxies in the outskirts of the clusters contain younger stellar populations than found in the cluster cores. However, when evolved passively to z~0 both populations are consistent with the observed populations in the Coma cluster galaxies. The bulge-dominated emission line galaxies in the clusters are dominated by stellar populations with subsolar metallicities. Thus, additional enrichment of these is required to produce Coma-like stellar populations by z~0.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/143/74
- Title:
- HST photometry in 6 dwarf galaxies
- Short Name:
- J/AJ/143/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive study of young stellar populations in six dwarf galaxies in or near the Local Group: Phoenix, Pegasus, Sextans A, Sextans B, WLM, and NGC 6822. Their star-forming regions, selected from GALEX wide-field far-UV imaging, were imaged (at sub-pc resolution) with the WFPC2 camera on board the Hubble Space Telescope (HST) in six bandpasses from far-UV to IR to detect and characterize their hot massive star content. This study is part of HST treasury survey program HST-GO-11079; the general data characteristics and reduction procedures are detailed in this paper and results are presented for the first six galaxies. From a total of 180 HST images, we provide catalogs of the multi-band stellar photometry and derive the physical parameters of massive stars by analyzing it with model-atmosphere colors. We use the results to infer ages, number of massive stars, extinction, and spatial characteristics of the young stellar populations. The hot massive star content varies largely across our galaxy sample, from an inconspicuous presence in Phoenix and Pegasus to the highest relative abundance of young massive stars in Sextans A and WLM. Albeit to a largely varying extent, most galaxies show a very young population (a few Myrs, except for Phoenix), and older ones (a few 10^7^ years in Sextans A, Sextans B, NGC 6822, and WLM, ~10^8^yr in Phoenix and Pegasus), suggesting discrete bursts of recent star formation in the mapped regions. The hot massive star content (indicative of the young populations) broadly correlates with the total galaxy stellar mass represented by the integrated optical magnitude, although it varies by a factor of ~3 between Sextans A, WLM, and Sextans B, which have similar M_V_. Extinction properties are also derived.
- ID:
- ivo://CDS.VizieR/J/A+A/532/A147
- Title:
- HST photometry in extragalactic star clusters
- Short Name:
- J/A+A/532/A147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present colour-magnitude diagrams (CMDs) for a sample of seven young massive clusters in the galaxies NGC 1313, NGC 1569, NGC 1705 and NGC 5236. The clusters have ages in the range 5-50 million years and masses of 10^5^-10^6^M_{sun}_. Although crowding prevents us from obtaining photometry in the inner regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters, along with the brighter main sequence stars. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergiants from the main sequence complicates this comparison. In several cases we observe a large spread (1-2mag) in the luminosities of the supergiant stars that cannot be accounted for by observational errors. This spread can be reproduced by including an age spread of 10-30 million years in the models. However, age spreads cannot fully account for the observed morphology of the CMDs and other processes, such as the evolution of interacting binary stars, may also play a role.
- ID:
- ivo://CDS.VizieR/J/ApJ/672/914
- Title:
- HST photometry in NGC 346
- Short Name:
- J/ApJ/672/914
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the third part of our photometric study of the star-forming region NGC 346/N66 and its surrounding field in the Small Magellanic Cloud (SMC), we focus on the large number of low-mass pre-main-sequence (PMS) stars revealed by the Hubble Space Telescope observations with the Advanced Camera for Surveys. We investigate the origin of the observed broadening of the PMS population in the V-I,V color-magnitude diagram. The most likely explanations are either the presence of differential reddening or an age spread among the young stars.
- 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.
- 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/ApJ/603/503
- Title:
- HST photometry in NGC 5253 and NGC 3077
- Short Name:
- J/ApJ/603/503
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present multicolor photometry of bright star cluster candidates in the nearby starburst galaxies NGC 3077 and NGC 5253, observed with the Hubble Space Telescope Wide Field Planetary Camera 2 in both broadband (F300W, F547M, and F814W) and narrowband (F487N and F656N) filters on three visits between 1996 and 2001. By comparing the photometry with theoretical population synthesis models, we estimate the age and mass of each star cluster, which provides constraints on the recent star formation histories of the host galaxies. We compare the star cluster populations in these dwarf starburst galaxies with those of the nuclear starburst in the barred spiral M83 and discuss the implications for our understanding of the nature and evolution of starburst events.
2728. HST photometry in R136
- ID:
- ivo://CDS.VizieR/J/ApJ/448/179
- Title:
- HST photometry in R136
- Short Name:
- J/ApJ/448/179
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed Hubble Space Telescope (HST) images of the compact, luminous star cluster R136 in the LMC that were taken with the refurbished HST and new Wide Field/Planetary Camera. These images allow us to examine the stellar population in a region of unusually intense star formation at a scale of 0.01pc. We have detected stars to 23.5 in F555W and have quantified the stellar population to an M_555.0 of 0.9 or a mass of 2.8M_{sun}_. Comparisons of HR diagrams with isochrones that were constructed for the HST flight filter system from theoretical stellar evolutionary tracks reveal massive stars, a main sequence to at least 2.8M_{sun}_, and stars with M_555.0>=0.5 still on pre-main sequence tracks. The average stellar population is fit with a 3-4Myr isochrone. Contrary to expectations from star formation models, however, the formation period for the massive stars and lower mass stars appear to largely overlap. We have measured the IMF for stars 2.8-15M_{sun}_ in three annuli from 0.5-4.7pc from the center of the cluster. The slopes of the IMF in all three annuli are the same within the uncertainties, thus, showing no evidence for mass segregation beyond 0.5pc. Furthermore, the combined IMF slope, -1.22+/-0.06, is close to a normal Salpeter IMF. The lower mass limit must be lower than the limits of our measurements: <=2.8M_{sun}_ beyond 0.5pc and <=7M_{sun}_ within 0.1pc. This is contrary to some predictions that the lower mass limit could be as high as 10M_{sun}_ in regions of intense massive star formation. Integrated properties of R136 are consistent with its being comparable to a rather small globular cluster when such clusters were the same age as R136. From the surface brightness profile, an upper limit for core radius of 0.02pc is set. Within a radius of 0.4pc we estimate that there have been roughly 20 crossing times and relaxation should be well along. Within 0.5pc crowding prevents us from detecting the intermediate mass population, but there is a hint of an excess of stars brighter than M_555.0=-5 and of a deficit in the highest mass stars between 0.6pc and 1.2pc. This would be consistent with dynamical segregation.
- 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/AJ/130/1083
- Title:
- HST photometry in the wing of the SMC
- Short Name:
- J/AJ/130/1083
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope to image a star field in the wing of the Small Magellanic Cloud (SMC), near the HII region N81. The images were taken in the F336W, F547M, F675W, and F814W filters. From photometry of stars in this field, we construct color-magnitude diagrams (CMDs) for about 4200 stars and compare them with theoretical isochrones.
